I just run 120v extension cords from my EV during power outages (it has 2 15A capable outlets). I added a manual transfer switch to my furnace so it can be plugged into an extension cord, and I can power my furnace, blower, refrigerator and freezer, wifi and internet for a couple of days.
I really wanted to set up an automatic transfer switch for the whole house from my car in v2h mode, but I found it impossible to spend any amount of money and be confident that the system would actually work with my current EV (the wallbox quasar _sounds_ promising but I couldn't find any reports that it actually _works_)
Is that the transfer switch just for the furnace or the whole house? I was staring at my furnace yesterday, trying to figure out what to do if power stops and temperature drops below freezing. Doing the whole house transfer switch is too much, esp given o don’t have a 30amp power source, but it never occurred to me to do just the furnace.
Don't do this. Install a transfer switch. A simple plug and another power source feeds power back into the grid. It's absolutely against code. If you remember to flip the furnace breaker off before you do this, then it's not going to backfeed, but this isn't something you should rely on remembering to do. It doesn't cost much more to do it right.
Here’s how you’d set up just your furnace to allow a generator to power it in a permanent way.
For the transfer switch, you can use either a single-pole double throw motor rated switch for a 120V like a Leviton 1285, or a double-pole double throw motor rated switch like a Leviton 1288 for 240V. It must be motor rated.
You’ll also need a power inlet and a cord that connects between your generator and the inlet. Please buy a premade cable and the proper inlet, do not hack together a cord with two male ends aka a suicide cable that you plug into a standard outlet. Example of a safe setup: https://www.vevor.com/power-outlet-box-c_12116/vevor-30-amp-...
Wire the generator inlet to one side of the switch and connect the other side of switch to the utility fed circuit.
Label the switch positions so you don’t forget.
When the power goes out, flip your switch to the generator side, connect your generator to the inlet and turn it on. When the power comes back, flip the switch back to utility and turn off the generator. The center position of the switch is off and it’s impossible to backfeed the utility under normal conditions.
This entire area is a mess, I spent a year or so trying to get bidirectional charging set up at home in the UK. I even went to several of the vendors mentioned in that post and said "I've got basically a blank cheque and permission to do whatever you want however you want, even use it all as a case study to make this work" and nowhere could/would do it.
The most frustrating thing is it looks like V2G is easier and more accessible than V2H[1]: it's easier to give control of your battery to your energy provider and bypass your house to help the energy companies than it is just to power your own home with your own car battery.
Technically, this is ridiculous. You don't bypass your house when you do V2G.
My tinfoil hat is clearly making me too cynical when I say this, but I think it's this way because of the relationship between energy providers and law makers. These are the same energy providers that use "changes in wholesale pricing" to justify increasing how much they sell me electricity for, whilst reducing the amount they pay me for the solar electricity I sell them.
You're definitely right on the tinfoil hat angle. Vehicle to home is inevitable, but the rollout is intentionally slow / designed to fail, so the utilities can keep milking folks and justify their natural gas peaker plant investments. Also, once it works, vehicle to home will immediately tank the grid-storage and home-storage battery industry.
Some company is going to create a gray-market "high voltage -> top N home battery systems" dongle that you can just wire into the battery pack on your car. That company will make a fortune (but only if they're able to dodge liability).
I've heard of people doing similar with old prius beaters. You wire the 500V (or whatever) DC battery into an inverter, and then plug your fridge, etc into it. Leave the car ignition on, and it runs the gas engine for a few minutes an hour indefinitely because it sees the drain and thinks you are driving it.
Most modern EV's support this sort of thing officially, but they're hardwired to one brand of house battery. So, when you buy a new car, I guess they think you will throw out your house solar panels and backup battery. If you want two cars, then I guess you get a divorce?
Thanks, I really appreciated this comment, a lot to think about!
> Some company is going to create a gray-market "high voltage -> top N home battery systems" dongle that you can just wire into the battery pack on your car.
I agree. I've been thinking of trying to build a similar but more generically, a "240v in dongle" which would just be a bench PSU with phase synching and islanding config (e.g. allow power if islanding is handled at home level, or operate grid tied and cut off if not). This would allow any device with a standard 240v AC output to safely power a home, so this would include basically any EV (as most have V2L) as well as a lot of other generators, UPS batteries etc. I thought the phase synching/grid tying stuff was really hard or complex or expensive to do, but the recent boom in balcony solar shows it's totally feasible to make and distribute hardware that apparently safely does this for less than a couple hundered.
This issue is regs. Tbf, I think in the UK, it just needs someone with money and confidence to do it fast and safe enough that the obvious immediate benefits force a law change. The balcony solar regs changes this year really showed how needlessly behind our grid regs are. Now is the time to do it too, with big scares around energy costs and WW3, this would gel well with the push for EVs.
> Leave the car ignition on, and it runs the gas engine for a few minutes an hour indefinitely because it sees the drain and thinks you are driving it.
Oh wow, I hadn't even thought of that! I'd only ever considered pure EVs. Feels like hybrids have a lot to go wrong, but this is a really interesting use case that I could justify a hybrid to entertain.
> Most modern EV's support this sort of thing officially, but they're hardwired to one brand of house battery.
I haven't seen this much though - most cars I've seen that mention v2g or v2h mention the generic standards around it, rather than any specific manufacturers. The "hardwired to one brand" tend to be hardwired to the brands that have said they support the standards (OCPP, ISO 15118 etc.), at least in the UK.
With widespread solar and batteries, energy is becoming less and less of a "natural monopoly", the state should stop granting legal monopolies to energy companies under the outdated assumption that it's more efficient.
My biggest problem with batteries for grid outages is that the only outages I am actually concerned with would drain them to zero before the outage is resolved. For short term, smaller/portable batteries are fantastic at bridging a few hours. Plug the wifi & fridge in and you can sometimes go for 2-3 days.
I am not aware of any economically feasible way to run my 5+ ton HVAC system full-time on batteries after a hurricane just reset all the infrastructure, and you do need to run it full time because of the insane humidity and latent heat that follows a tropical system. Doing the math, I'd need something approaching 800kWh of storage to ride through this kind of event (7+ days). This is approaching half a million dollars in batteries. I can install an extremely nice 1800 RPM generator for ~15% of this cost, which would also include a year's worth of propane buried on the property.
I think a simple generator on an ATS remains undefeated from an engineering perspective. If you have an air cooled unit, the maintenance is not much more complicated than with a lawnmower. You just have one extra spark plug to deal with, and sometimes the oil pressure sensor needs replacing. I can get my stubborn Honda generator to start with all kinds of weird tricks. If my Ecoflow battery starts to act weird, I have very little recourse by comparison.
Batteries alone are not suitable for long duration outages, but solar+batteries, designed correctly, can not only supply enough power during long outages, it can get you to be off-grid entirely in the first place at a dramatically more cost effective number than your $500k quoted - perhaps 1/5 or less for a system suitable for your needs of 115kWh per day. So while the system might be more expensive than a generator alone, it can still beat on value because it provides power all year round.
You also do an unfair comparison here - you are OK with portable batteries providing only fridge & WiFi for a couple hours, but expect whole-hole batteries to last a week. Many people use whole-home batteries to bridge typical outages that last <24 hours, and do so without ever having to notice any change of use of their home - powering their full heating/cooling etc.
Batteries and generators are also not mutually exclusive. You can install a solar+battery system because it makes economic sense and pays for itself while providing zero-downtime backup for most outages, while also backing that up with a generator for longer term edge case outages eg long extended outages during the winter or where there is an unusually long “solar drought” - it really depends on how much resilience you are designing for.
We have frequent power cuts and follow this same philosophy.
Our first line of defence is the solar system's battery. When power goes out, that will keep things running for some time with the big optional loads switched off - e.g. hot tub, hot water cylinder and pool.
If the sun's shining we can run like this for a long time.
In a solar drought, when the solar battery runs low, the next step is to plug the EV in via V2L and use it as a generator to charge the solar battery. EVs have comparatively huge batteries, so at the cost of losing mobility, which may be important in an emergency, this will keep things going for even longer.
One great feature of using an EV is you can drive to a fast charger, charge up in an hour, and transport all that energy back home.
The final fallback is to plug the 2KW petrol generator in to charge the solar battery. This is enough to keep things going forever assuming a petrol supply. A petrol generator is nicely portable and can be loaned to less prepared neighbours who likely have their own petrol.
The key to it all is the solar battery. That gives you uninterrupted power while mucking around with the alternate sources. It doesn't even have to be all that large if you have an EV.
In the scenario mentioned in the GP post where a giant tropical storm hit resetting the grid for 7+ days, how big is the chance that your solar panels installation has survived? Also, if the grid is gone, won’t the fast chargers also be out of service?
Don’t get me wrong, I think you’re right for most cases but I also think for some more end of the world type of scenarios there is little that beats a generator and stored fuel.
If you can stay there (no evacuation for building doesn't seal enough to make it habitable), most of the solar should have survived. Moving a broken panel out of the way and swapping one from the end of the array in to make the cables fit, or even having a spare jumper cable to swap in place of a broken panel, is quite easy to do. Mostly just make sure there's no load current at all on the string when you disconnect the MC4 connector with the special tool that keeps uneducated people from unplugging them under load and getting greeted with a persistent low current (not "arc flash", we're in the region of "high powered welder used with just normal welding PPE") DC arc (that may supply several hundred volts for a long drawn out burn). As long as it's around substantially below 500 mA you're not gonna sustain an arc.
Indeed, that's why I mentioned petrol generator as the last level of backup.
Though the most recent big tropical storm we had a few years ago, the power was out for 3 days, it was dark and cloudy obviously so no solar, the local petrol pumps had no power and the roads were blocked with fallen trees so we couldn't even drive anywhere. In that situation it really is candles and cooking on wood fires once the petrol runs dry.
The comparison is unfair for many reasons, actually. A real install would have solar inputs charging the batteries and offsetting loads during the day.
It also wouldn’t run a 5-ton HVAC system 24/7 for 7 straight days, which is how the post got to the extremely high number.
Highly dependent on where you are, what your electricity costs, and what your backfeeding compensation scheme is (eg net metering). In California solar alone is no longer economically viable with NEM 3.0 but solar+batteries to maximize self consumption is still in that sticky ~7 year layback range - and those calculations tend to assume today’s power prices, that are in reality going up quite quickly.
If you have free night charging plan you can recoup quite faster. My system paid off for itself in 3 years - although I designed and set it up myself, so it was about 3x cheaper than through contractors (and yes I'm in US and I pulled permits to do this).
It's nice to do this for more than just the direct economic costs. The generator doesn't have to run 24/7 since the batteries absorb the excess power produced by the generator. This means less fuel wasted as well as less noise produced. I used to have two small generators that I could run (and team, if needed) but adding a battery component meant being able to sleep at night without a combustion engine burning fuel all night long.
Yup, even better if you power a separate battery charger with the generator, but let loads be handled by the battery+inverter. You don’t need to provision the generator for peak loads (which can be quite high), or even worry about high harmonic distortion from a cheap generator screwing with your electronics. It basically turns your system into a fully ‘online’ UPS.
Also, really handy for diesel gens which will ‘wet stack’ if you only run them for short periods or with light loads.
Provision a generator size which you expect to run say 6-10 hours at a time (at say 70-80% rated load) to fully charge your batteries, and a battery bank sized for 3-4 days of load.
Keeps your total gen hours much lower, much more efficient fuel wise (you can set the ideal load using your charger, and it will keep it that way regardless of increasing/decreasing loads), doesn’t require as big a generator if you have things like AC compressors, heat pumps, etc. with high start loads, and gives you a lot of redundancy and flexibility. It even gives you time to fix your gen or find/beg/borrow another if yours breaks, and you won’t need to keep the gen running overnight if you plan appropriately, so your neighbors will like you more.
Best of all worlds. Especially if you have natural gas, or get a tri-fuel generator and keep propane handy. Propane doesn’t go bad like gas or diesel can.
I think for most people it would be if they can they afford a 20 year advance on electricity costs all at once. That is a lot of money if you have more pressing needs, but if you got that money sitting around then yea of course it is a good investment.
You don’t need to run your 5+ ton HVAC full time. Get an EV and run the AC there (no more than 3kW). Sleep in the EV. A typical 80kWh EV battery will last several days. And this is not just theoretical; plenty of people have done this.
For Christ’s sake a natural disaster just struck and you want to live like nothing happened? The entitlement is unbelievable.
I think you’re better off getting a good sleeping bag and sleeping in the house in relative comfort. You can camp down to very cold temps, and your house is both better insulated than a tent wall and is a better wind break, even if it was bad enough that you got well below freezing. If we’re at the stage of “sleeping in the car”, indoor camping is reasonable to me.
They were talking about loss of power during heat stress and needing cooling not heating, more specifically dealing with latent heat & needing dehumidification, mainly in a post-hurricane context, whereas you are talking about a cold stress event.
I’ve been torn about this. On one hand, I could spend $2k on a small portable generator, get a window unit, lots of extension cords, and survive a few days without power with cords strung all through the house.
I’d still have to deal with wheeling it out, and doing periodic oil changes. Not sure how/where I’d want to deal with a 200lb unit… A natural gas unit would be more practical - I don't have gasoline yard tools.
I could get a transfer switch installed and use my house’s main AC unit. The cost of the larger generator isn’t that much more and I wouldn’t need a window unit and lots of cords.
Of course, then I could skip the portable unit and get a whole house generator with automatic transfer switch.
It’s hard to put a finger on it. The “cheap” solution doesn’t seem worthwhile while the others start making me wonder “how often does the power really go out”? It all seems silly for 3 days outage once every 5-10 years.
> others start making me wonder “how often does the power really go out”? It all seems silly for 3 days outage once every 5-10 years.
I think very little is worth it for three days every few years. Instead, I see the benefit of batteries + solar or a serious generator as reducing tail risk from rare serious disasters that leave the grid down for months or longer. These are not likely, but if they happen I'd want to have something in place.
I figured refrigerator uses about 1KWh per day. Just 2 days would require 200Ah of 12V batteries. Lithium looks attractive for weight and other factors but is more expensive than lead acid.
Have a large overhang that could temporarily be used to lay panels on too.
For portable AC unit, seems like would need another 10KWh per day or so of capacity. At that point, generator becomes more financially practical…
I don't think it's entitlement if it's actually doable. They're not saying they expect the world to give this to them on a silver platter. They're saying that they can actually do it. And if that's what they want to spend their money on, who are we to say that it's not a good use of their resources?
i am regularly shocked by the assumptions that the techbro crowd makes. I should not be, but i still am.
The desire to operate a massive AC just after a natural disaster is just unhinged. Similarly, this idea that your life should be able to continue as before, your neighbours be damned, is also psychotic.
People like me push for the better solution (against great opposition) - neighbourhood-level improvements so the rich don't hoard all the resources while the rest are left to die.
> The desire to operate a massive AC just after a natural disaster is just unhinged
The humidity after a hurricane is a great way to get mold problems in your walls. It is a major health hazard, and once it sets in you have a very disruptive and expensive remediation effort. Keeping the AC and central dehumidifier (assuming newer construction) running is pretty much the only way to prevent it.
The biggest issue is any wind damage to the roof. If it's leaking even a little bit, it's going to be leaking hard for hours.
With a consumer dehumidifier you might get 5-6 gallons per day. A 5-ton HVAC system will pull over 50 no problem. You might have hundreds of gallons of water soaked throughout the framing, drywall, insulation, etc. It can take a really long time to remediate without a powerful HVAC system.
when a natural disaster happens, especially one that disrupts electricity for weeks, your likely first priority is being alive, safe and being able to eat, not mould or your air conditioning.
Assuming you have enough solar, how about running your 5+ ton HVAC system only when there is enough production? And properly insulating your home, of course, using it as a thermal battery of sorts.
If there is a grid outage, surely one can shift consumption to solar production hours while using the battery for the always-on systems (fridge, lights, some computing...).
Insulation won’t help post-hurricane when they are trying to fight humidity/latent heat. Your thermal battery comment makes it sound like you are viewing this from a cold stress perspective (in which case a tight, highly insulated home is indeed a great way to slow heat loss and keep the home warm), but they are talking about dehumidification post-hurricane, which is really a separate story.
Yes this is what I do with power outage with solar and battery and 5 ton, I have to modify my behavior and conserve, increase ac some from say 73 to 77, shower during the day when there is excess power etc.
If there are clouds lowering solar output the ac isnt running as much either or at night.
If I wanted to run as though the grid was up would probably need double the size solar and battery.
>I think a simple generator on an ATS remains undefeated from an engineering perspective.
Let me just inject a bit of nuance here to avoid what I think is an unintentional sleight if hand...
For the small sliver of the population that lives under threat of a large area week long blackout in a hot humid climate, I think a simple generator on an ATS remains undefeated from an engineering perspective.
For the vast majority of the population, it's incredibly rare to lose power for that long, and need AC 24/7 afterwards. It basically only happens in the gulf.
Homes in cold climates using heat pumps for heat have a similar issue. No grid power means no heat, no heat means frozen pipes and mortal risk to vulnerable people. There is a decision cycle to it too. Central air dies, you replace with a modern heat pump. Then the boiler dies and it becomes difficult to justify replacing it, except the boiler is more practical to run off a battery in a power outage.
In the spirit of nuance, the vast majority of the population of Florida is at risk. Something like 10% of the US population in total could be impacted directly. You don't actually have to live on the coast to get rocked by a hurricane. Ike took out power for millions in Ohio.
Correct, but you don't need 24/7 AC in ohio during hurricane season. Your reference storm was in September, when Ohio basically needs no heat or AC at all. The nuance is the extreme emergency energy demands (mandatory constant AC) are pretty rare.
These replies and the down votes are just reinforcing why I made my comment. People are unable to grasp nuance, apparently even when it is spelled out.
> For the small sliver of the population that lives under threat of a large area week long blackout [...]
I've lost power for weeks from snow, wind, storms, and ice, living in the central midwest and mid south. We lose power almost every time it rains in the spring and summer for many hours.
To be fair, losing power in a winter storm can be equally dangerous because while the gas might still work your central HVAC system requires electricity to run its blower, power the thermostat, etc.
That said, you are still absolutely correct about the proportion of the population that's really at risk of extended blackouts being incredibly small.
In the US 80% of the population lives in urban or suburban areas, where for the most part power outages are measured in either seconds or hours and while extreme weather or bad drivers might sometimes cause enough damage that it takes a few days to get power back on to a specific neighborhood it's rare outside of large-scale natural disasters for the power to be out over more than a couple of neighborhoods.
I live in an older suburban neighborhood in Ohio and the one time we had power out for more than 12 hours the literal next street over still had power. Even if my whole neighborhood was out for a week, the nearest fast chargers to me in either direction are both technically in another city and on an entirely different section of the grid. If power is out for all of them for days on end stuff is really messed up to a point that FEMA and/or the National Guard would likely be involved, and that's beyond the level of disaster I'm really worried about.
Obviously those who live in low-lying coastal regions like Florida and the Gulf Coast where a disaster is pretty much a given or those living in extremely rural areas where restoring service is going to be deprioritized have different risk assessments and if I were in their position I'd be looking in to trying to be as grid-independent as possible, have enough battery power and solar generation to support living comfortably without requiring grid input under normal conditions and to support "emergency mode" operation with half your system or more destroyed in case of a major disaster.
A bunch of it has to do with humidity levels that impair our natural ability to sweat. If the wet-bulb temperature [0] is high enough, a place may be unlivable without artificial cooling.
I cut it off because it's not relevant in the context of why the power is out other than being a force of nature.
Just about every place in the US, with some minor exceptions, has extreme heat (120F+) extreme cold (-10F), high winds, tropical storms, ice storms, blizzards, tornados, or even earthquakes regularly that take down poles and lines, damage substations, etc.
> am not aware of any economically feasible way to run my 5+ ton HVAC system full-time on batteries after a hurricane just reset all the infrastructure, and you do need to run it full time because of the insane humidity and latent heat that follows a tropical system.
Which region is this?
Are hurricanes that reset all the infrastructure a recent phenomena in this region? How did people manage in the 60s, 70s, 80s, 90s etc before these rather large (5+ ton HVAC) were even an option?
>Doing the math, I'd need something approaching 800kWh of storage to ride through this kind of event (7+ days)
How airtight is your House? You may be better off with a tighter house to reduce the infiltration load from the outdoor air and possibly section out the house so that post hurricane the primary living spaces are the only spaces that are constantly getting fresh air and there fore humidity load and for the non primary spaces, you dehumidify once and hold it there.
>I think a simple generator on an ATS remains undefeated from an engineering perspective. If you have an air cooled unit
Yes, if your outages are under lets say 10 days a year a generator + fuel will be orders of magnitude cheaper wrt TCO, unless your grid is super expensive.
What’s 5 ton in new money, 5kW power draw max? Are you planning to run that full power for a week?
Yes, that much in batteries would cost a lot but uk prices right now would be ~87.5k for the batteries themselves (so a shade over $100k I guess). £7k for 64kWh
Batteries are for load shifting between day and night and for short term backups. Yes, 7+ days of outages do require means of replenishing the battery, whether it's from a diesel unit or a solar. That's not a battery cost problem.
Yeah it's hard for batteries alone to compete with generators, unless we put a lot of weight on things like noise, or are just focused on small loads like fridges.
I think the more interesting comparison is generators vs solar, though it depends on the local weather etc.
This is exactly what the post is trying to address: during a serious long-term outage, batteries on their own will run empty. What you need is the ability to recharge batteries from solar during an extended outage, while also flexibly drawing from the batteries when solar isn't enough.
I’ve been looking into a smaller scale option to run limited items medium term on part time hours…
Best option so far involves a mix of batteries that are charged from the mains when available and topped up from a mix of solar and a LPG/multi-fuel generator.
But unless you want to go very large on the solar and generator size it’s unlikely to cover everything full time.
I have 18kw of solar and 30kwh of batteries with a 5ton ac it will run it will run indefinitely assuming the sun comes out, if it doesn’t I have a chargeverter that can keep the batteries charged off my RV’s diesel generator or gas portable.
My solar system generates excess power daily and has zero maintenance, the generators are pure money sinks for backup power and require regular maintenance.
Options are nice.
Also heat pump water heater and dryer help reduce load along with efficient variable speed hvac and good insulation.
Fuel is a problem during a storm too and a buried large propane tank is a good way to go but very expensive on top of installation.
An electric car with bi directional charging would add to flexibility either charging from home system or being able to go find power and bring it home.
Ideally I would like a gasoline hybrid with power out like a F150 power boost and a fully electric with large battery and V2L any Tesla would do now as they all have 2400w out I believe Cybertruck can do more. My chargeverter can take 120v or 240v
How about reducing energy use? In general, but then especially after a grid-destroying event that keeps you offline for a week? You surely don't need to have everything HVAC running on full blast in the whole house during that time. And your laundry and next oven long cook can probably also wait until the grid power is back.
If you then add some solar into the mix, it doesn't sound as dramatic anymore.
There is something in between flashlights and a grid scale battery that van power your full electric home.
I just have a plugin battery that I can run the lights, fridges, phone chargers off of for 24 hrs. That is good enough for me, and I think most people. Anything shorter, and it's not necessary to run the rest, much longer, there also isn't because apparently shit hit the fan and we're not necessarily assuming the power comes back on in the next weeks or ever.
For me where I am, things are different. We don't get hurricanes here.
Our longest power outages tend to follow ice storms. We need heat because these things happen in the winter time when it's cold outside, and that's dangerous for various human and infrastructure reasons (pipes freezing and breaking).
But I use natural gas for heat and I don't recall ever having a weather-related natural gas outage. So that's helpful. And ice storms tend to happen when it's cold, but not damn cold -- that helps, too.
My furnace uses about 600W of electricity while running. It does not run all the time. According to my charts on a random day/night cycle last February with a high of -8C and a low of -16C, it was running with an average duty cycle of about 30% over that period.
600 Watts × 30% × 24 hours = around 4.3kWh for that 24-hour period, just for heat.
I'll also need to keep the fridge cold, and some lights running, and will surely be getting some use out of a laptop and some network stuff.
A common-enough home battery size is 48v, 100Ah, or 4.8kWh. They cost around $1,000 right now (some more, some less) in DIY-friendly shapes.
As a spitball effort: If I live more-conservatively and dial back the thermostat (it is a power outage, after all), I can probably get enough power to live a productive, comfortable-enough life on one such 4.8kWh battery, per day. Ish. If I'm careful.
So for batteries, alone, I'm at $1,000 per day. I'll need an inverter as well. That can be either minimal or extensively integrated, grid-tied or not, solar-accepting or not, and etc. Let's just pin that at $3000, with the wiring and accoutrements, and assume I'm doing the labor for free.
I'm now at ~$10k to survive a week of power outage at home in the winter on batteries alone. That's expensive[1], yes, but a whole lot less than half a million bucks. A whole lot less than a very nice, installed, low-RPM generator, too. :)
...except, realistically: It's more like $13k for a week, because future-me will surely not be as careful with energy use as present-me suggests that I should be and 3 more batteries adds some safety capacity. :)
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And that can be supplemented. Solar input can obviously be used (if available), but may be limited by winter sunlight conditions and storm accumulation.
Gas-fired generators can also be used. An inexpensive-ish portable inverter generator does the trick well when combined with, say, an EG4-6000XP do-all inverter.
That particular inverter wants to see at least 2 of these batteries connected, so let's play with that minimum: 2 batteries, 1 inverter, 1 generator. ~1.4 batteries worth of load every 24 hours, as with the safe $13k figure above.
The generator can be run pretty hard (it has a continuous max rating for a reason), and it can be run intermittently. The EG4 allows programming of generator input power.
So let's pick a generator: Champion 201509. It can do 7kW continuous, and we'll load it to 75% of that, or 5,250 W. From this 5,250W, it provides for the house's present consumption while it runs, and it restores the charge of the two batteries to 100% SoC[2].
If it is run once per day, it can do this job in about 2 hours and then be switched off until tomorrow.
If it runs like this once per day for a week, I guesstimate that it uses about 11 gallons of gas over this week. That's a very manageable quantity of fuel.
So we're at $2k for batteries, $3k for inverter+stuff, and $2k for an appropriate generator. That's $7k to run ~indefinitely, or as long as I can keep bringing in fuel, with enough power to survive a blackout (with heat, lights, refrigeration, some entertainment) long-enough on batteries alone for the roads to become passable and then decide if I'm making a run to fill up the gas cans with fresh fuel.
Not so bad for a relatively quiet time of living in a temporary blackout, and the house gains a gains a big UPS for some stuff (which is nice). (The installed gear also offers an easy entry into solar power.)
But I'm not in hurricane country. And while I do love me some aircon, our summers are pretty survivable, usually. My needs are not the same as your needs are. :)
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[1]: Except, for the price of this kind of self-sufficiency: Draining/blowing out the plumbing and staying at a hotel or with friends/family for a few days in an unaffected area might be a better option. The cheap portable air compressor I have doesn't leak down at all, so it's always got a full tank of air while just sitting there unplugged. I'll figure something out: Power outages are very quiet, creative times.
[2]: 100% SoC? Yep. It's a temporary blackout where the batteries are operating as a UPS, not a long-term operation where the typical 20%-80% SoC goals are important for longevity. They won't stay at 100% for very long, anyway.
Oil generators have an “artificially” low price because there’s a lot of demand for oil for other things. If the other sources of demand go away, the price may become unfavorable even if gas generators make a lot more sense from a redundancy perspective.
In this application, at this scale, on the timeline of an individual human: It doesn't matter much.
It's just a bit of temporary[1] redundant local infrastructure that is hopefully never used at all, and when it is used it won't be used for very long. The fuel will remain available for as long as any of us reading this are alive.
The price of the fuel may go up (it probably will go up), but it doesn't really matter much at this scale whether it costs $25 per day to run or $100 instead -- the power grid will come back online soon enough.
[1]: It's a backup generator, not an heirloom. In 50 years, people will look at that old thing and laugh at how interesting its archaic nature is. They might tinker with it. They might give up and have Jeb haul it off as scrap. And that's all fine, too.
Recovered biodiesel (fryer oil) is always gonna be a thing to some degree. Either chemical synthesis or just plain devoting some agricultural output in the future doesn't sound completely insane.
Hate to break it to you but fossil fuels comes from acient plant and microbial material, not dinosaurs. Coal comes from the Carboniferous period from massive land plants that accumulated in oxygen-poor water. Oil and natural gas mainly comes from plankton, algae, and bacteria that settled on the ocean floor and mixed with sediment.
Dinosaurs contributed an infinitesimal fraction of the biomass that is needed for the fossil fuel reserves.
A fundamental problem here is that V2H during an outage requires a disconnection device (in the NEC this is a “microgrid interconnect device”), and the manufacturers of such things have made no effort whatsoever to standardize the control protocol. This means that you cannot build an islanded-V2H-ready house and just plug in a car. So the whole concept is kind of dead in the water.
At least Tesla is vertically integrated enough to pull it off within their own product portfolio, but this has approximately no value if you want to use a non-Tesla car.
You can't do just V2H, but Enphase and others have moved to simpler meter collars and grid disconnect for exactly this reason.
The main question for this thread remains who the Enphase / ISO standards friendly OEMs will be. With Tesla saying they'll allow it now, maybe others will get onboard, but the risk is that they wall themselves off.
What Enphase/ISO standard is this? I’ve never heard of it, and my attempt to search came up with nothing useful. There’s ISO 15518-20 bidirectional, which seems like it barely solves the problem.
It should be possible for a vehicle’s built-in inverter/charger, the EVSE, and the MID to all cooperate even if all three are from different vendors, but this is not a thing.
I think the standard is called "V2H". It's unobtanium from what I can tell.
If you have a Ford EV and a SunRun house, then it supposedly has worked for a few years now. (But that's just vehicle to home charging, not the "V2H" standard.)
It’s unfortunate and inconvenient. However A transfer switch requires <3 minutes to engage. If a car was able to supply 30-50 amp via compatible plug it would work reasonably well even absent unified v2h standard.
Most recent teslas support 20amp at 120v output via official $100 cable adapter. Some other cars support about 20amps too, eg RivianR2. While it falls short of desirable amperage the car manufactures can bridge the gap if they wanted to. Even now I can run the bare minimum of workloads - a full size fridge, a small AC or Microwave, LED lights, and phone chargers.
It solves my problem just fine - power critical loads for a few days by spending $100 upfront fir the cable and 5 minutes to manually switch the load. It’s a difference between moving to a hotel for indefinite time and staying put.
Sure you can set a loftier goal and spend tens of thousands of dollars and countless hours solving it. Most people won’t though.
Sorry, what device are you using to supply power once you've flipped the switch? Sure, you can get a (legal, even) manual transfer switch and plug in a little portable generator, but if we're talking about using your car as a power source, this is not going to work.
I previously used a portable propane generator for a 30amp inlet to transfer switch. In my test runs it didn’t go that high.
Today I could plug in a car that gives off 20amp into the same inlet, it would limit how much load it can carry, but I could stay below 2.4 kw if needed. Why wouldn’t that work?
A lot of houses won’t run off 120V/20A. You’ll also need to kludge around the fact that your house wants 120V/240V.
In any case, serious V2H should support much more than 2kW. An EV with a charger with less than 6kW capacity is almost unheard of. Two EVs should be able to supply twice the current. All that’s technically needed is an charger that is physically capable of operating as an inverter (which I believe adds little cost), some way to derive a neutral (the usual solution is a relay and an autotransformer, again not particularly expensive), and the control logic to convince all of the above to actually operate in this mode.
Tesla just brought this functionality to new Model 3 and Model Y cars as of Oct 1. It requires at least one Powerwall 3 to enable bidirectional V2H - what they call Powershare. But those cars can now power the home and charge from solar while the grid is offline.
> By default, all Cybertruck trims ever produced and all Model 3 and Model Y vehicles ordered in the U.S. and Puerto Rico after October 1, 2026 are capable of Powershare. Some, but not all, Model 3 and Model Y vehicles produced before October 1, 2026 are also capable of Powershare. [0]
I presume it is a hardware revision, like how Tesla removed radar.
Yes. Typically V2G works by connecting an external inverter to the high-voltage bus.
It just needs to start a charging session, and then siphon energy _off_ instead of supplying it. People tried that before, but the firmware on Model 3/Y monitors the flow and terminates the session if the flow is negative.
Not an issue on my system (or rarely) as it generates enough to not need grid at the moment even with EV charging. So simply don't charge the EV and avoid washing machine, dryer etc. until grid comes back will probably do it. Another tactic is run some stuff off the car to reduce load on house battery
In case of V2H it therefore doesn’t matter what supported EV you are using, rather what charger you are using.
In general for changeover during a black out, V2L is probably better, because with V2H the charger itself needs POWER to boot up and request V2G whereas V2L you can start from the EV itself.
Also, generally speaking V2H is designed to be grid-following and certified to half a dozen standards whereas V2L forms an isolated microgrid, and a lot of the rules are tossed out, which is what you want.
For V2L you just need a generator changeover to isolate your house from the grid (most commonly just a manual switch), and a reverse plug to connect EV output to switchboard input.
V2H can charge home battery systems, but V2L "cannot". There's obviously a market for "plug the 240V outlet on my EV into my house battery. Use the car to charge the house battery while the house is running off the house battery".
The other problem with purely EV based home backup is that if you have to drive somewhere you house no longer has power.
IMO such a system should be additive to a home based battery backup system with solar, which should be sized for a day of emergency (minimal) home usage.
Such a system could top up from the EV when the EV is plugged in - assuming the PVs aren't producing.
Most Tesla models don't support bidirectional because they had free Supercharging, and also probably because having your car not full at all times is not always the best experience. Other brands like Nissan had always supported V2H and in fact it has always been a selling point of OG leaf that it could double as the Powerwall equivalent since back in 2012.
Most V2H systems don't support zero-interrupt automatic transition because it has no means to know if the perceived grid outage is accidental or intentional, and if intentional, trying to back it up could injure/kill electrician who commanded it. But if the system is operating off-grid, I think those can be configured to be always uninterruptible.
I don't think either of those are real concerns. The free supercharging did not overlap with homes that could be charged by cars.
Also, safe islanding devices have been very standard for at least 5-10 years. Policy 1: House watches incoming voltage, and turns off the breaker if the grid is down. House electricity + solar stay on; line to power company stays at 0V. Policy 2: Panels see that the house voltage is low, so they turn themselves off.
Policy 1 requires an electrician, but mostly just for permitting. I'd guess a good fraction of the people reading this could safely do it themselves after reading a manual. Policy 2 does not require an electrician or understanding electricity at all. It's how DIY balcony solar usually works.
As far as I can tell, the Leaf never had this in the US. The 1st and 2nd gen hard the hardware, but the chargers weren't there. And the 3rd gen has only announced V2L.
From my perspective, "zero-interrupt automatic transition" is not that important, but being able to have the system smoothly move between having the solar recharge the car and the car power the house during an extended grid outage is critical.
You can do it with an F150 lightning if you have the 10kW inverter. Rather than use the charge port and the official charger, you use the 30A 240V plug in the bed to power your panel. You can charge the truck while using this too.
The F-150 can do this, but by charging the batteries you don't have.
It could also probably run the house off the 240V outlet in the bed, but only if you knife switched the solar + grid off and just ran the house off the truck.
When the sun came out, you could knife-switch the house back, and charge the truck.
Alternatively, you could rip out your solar and put in the one brand that Ford works with (SunRun, I think), and then the truck would be able to bi-directional charge with the house batteries using the solar, or something like that.
(Yes, this is all dumb, especially since there are standards that should allow a dongle to be made to make this work transparently, and to just automatically do the right thing".)
I can go most of a week on the Lightning's battery, and it will shut down the 240V 30A outlet well before leaving me stranded. Thankfully the longest outage we've had in my lifetime (and I'm not a young man) is 3 days, for an extremely rare severe ice storm.
I really wonder if part of the reason this isn’t more widespread is that utilities with variable rate electricity pricing would get burnt on it. Imagine charging during cheap time then dumping 5-20kWh back onto the grid during expensive time. You could have a positive ROI on a vehicle you regularly drive (timing permitting)
No, the main barrier is concern over warranties for the vehicles.
In California, the law requires that vehicles still hold up to 70% of their original charge after 8 years and 75% in the future [1]:
> and d., to deteriorate to less than 70% for a warranty period of eight years or 100,000 miles, whichever first occurs, for 2026 through 2030 model years, and 75% for a warranty period of eight years or 100,000 miles, whichever first occurs, for 2031 and subsequent model years.
The law is unclear on bidirectional charging and whether this would give manufacturers an out. So they're cautious.
In TX, the power producers, distributors, and retail electric utilities are (most commonly) different parties, so the latter two are very much interested in the type of decentralized time-shifting you mention since it smooths wholesale costs somewhat and reduces grid buildout and maintenance.
For EV owners in TX, its not uncommon to have fairly free charging overnight (just paying the distribution costs of 5-6 cents/kWh).
For homes with residential solar and batteries in addition to the EV, you can have essentially free power and EV charging due to time-shifting and incentives.
Residential batteries are still quite expensive, though, so it would be amazing to recruit those in the above EV to time-shift using V2H.
Why? That's the entire point of moving towards dynamic tariffs. In the systems I'm familiar with the utility company makes money through a fee charged on top of the market purchase/sale price, much like an investment broker.
V2H was popular among Japanese Nissan Leaf owners and there were tons of Leafs on cinderblocks with dead batteries used to milk incentives sold on used market for like $1k with 10 mi on the meter. Tiny household sellers are credited for sales for generosity, but apparently often just a noise that needs to be compensated by increasing power output at power plants to then just burn off. Great idea on paper, often not so much in practice.
Maybe. I did the math and in our area a Powerwall would roughly pay for itself over the speced lifespan of the device, IIRC that was just the cost of the device not the cost of installation. I did that calculation ~4 years ago, so maybe it has changed, but definitely do the math, I was surprised.
Why shouldn't utilities pay for this? You're provide grid load balancing. Theoretically their pricing should be considering this? It's not actually free to you since charging and discharging your battery costs money.
But naturally the situation is they want to be the ones paid the big bucks for such services.
One of the problems with companies like GM is that they still see this as a premium feature and require their hardware (not just a charger). Tesla requires not only their chargers but also their inverters and cars.
What is missing is a spec that inverters and cars and chargers can all follow, then we will see mass adoption.
CHAdeMO had that spec, but of course is obsoleted now.
If I understand things correctly tho many of the V2L solutions just work with pretty much any car that does CCS, regardless of whether the manufacturer officially supports this or not. My Polestar2 for example doesn't official have any kind of V2H/V2L option but I've heard of many success stories.
SAE-J2847 includes "how to convert your building side to supporting BPT grid works, and pairs well - it looks - with ISO 15118-20 BPT. (and reasonably well with ISO-15118-2 and the BPT extensions in SAE-J2847). Anyway, supporting AC grids requires some additional electronics both in battery systems and in the local hookups.
I haven't explored the actual space much, as I work on ISO 15118-20 for busses, and a bus as a local grid backup scales pretty well. (and even then, I work protocol level, not electrical).
> The only way I can see to do this today is with Tesla Powershare + Cybertruck, which says "If the system includes a UL 1741-listed solar system
Since this was posted Tesla rolled out PowerShare to recent ModelY and some other cars. Not sure about solar recharge though. Where I live storms come in winter and I have natgas so most of the power will go to fridges and electronics, which will hopefully last long enough.
When I was living in the PNW and had a 5 day power outage due to a windstorm, my PowerShare/cybertruck made life so much better. Nat gas water heater, furnace, and stovetop definitely helped. Had options to top up the charge too, took the kids to a play date at a house that let us charge, and I had a nat gas generator that worked well to charge the truck too.
New builds in WA state don’t get nat gas anymore though, so people will have to be a lot more careful about using appliances during an outage.
I'm not sure what the laws are like in the USA I assume they are similar to elsewhere.
However I think there are two problems here that have to be solved:
1) you need to island your house, that is, physically disconnect your house from the grid
2) once you have disconnected the grid, you then need to provide some sort of pilot sine wave to allow the plug to function.
I have an islanding system for my (house) battery and solar, so in theory, I could have a bidirectional charger whilst being off grid. However both my car and charger don't support that (my charger is also deeply shit, and has no local API access.)
The bigger problem, which is tangentially touched on, is that vanishingly few chargers can actually support islanding. It makes the installation harder, and drives up the compliance and installation cost[1]. this means that you are taping together two disparate systems together (or going all in on enphase, which also has a limited local API)
There isn't a spec for a household systems to talk together to do energy management. currently I use homeassistant to monitor the variable electricity prices, car plug status and how happy the fucking powerwall is, so that I can make sure the car charges from solar, without draining the house battery to 0, or only charge at night when the price us uber cheap (and also not drain the house battery).
The amount of sysadminig to make that work reliably means that no normal person is able to achieve it. The problem for consumers is that there isn't any motivation for manufactures to work together on this. because they want to vertically integrate.
[1] The installation cost for what is effectively a very thin software wrapper around a local contactor is egregious.
> I have an islanding system for my (house) battery and solar, so in theory, I could have a bidirectional charger whilst being off grid. However both my car and charger don't support that (my charger is also deeply shit, and has no local API access
...
> The amount of sysadminig to make that work reliably means that no normal person is able to achieve it. The problem for consumers is that there isn't any motivation for manufactures to work together on this. because they want to vertically integrate.
We are in a very similar position. The issue is every company in this area is like you say: deeply shit with limited local API access. Setting up bidirectional charging in the UK is technically, really not that hard, especially with islanding handled at the household level.
Good luck trying to get someone willing to put their career and certifications on the line to actually do it though.
Part of the challenge is finding an electrician willing to work like a sysadmin and do things because they know how they work, rather than only doing things they've explicitly been taught as in line with (dated) regulations.
Wouldn't the charge / discharge cycles reduce the life of the car battery? I presume the same is true of in-home batteries, but although an in-home battery is an extra capital expense, I imagine the replacement cost of in-home batteries is quite a bit lower, isn't it? Would be interested to know more about the medium-to-long term economics of this.
> Wouldn't the charge / discharge cycles reduce the life of the car battery?
While I'd presume the answer here is "yes", I'd also presume we're talking like a fraction of the vehicle's lifetime charge cycles. Like, (generously/conservatively) 20 to 40 cycles total over the life of the vehicle, no? How often would you estimate your power going out?
Even if you aggressively used the vehicle for this, you're talking about wearing out a ~ $5-10K battery over many years. For reference, a generator that can do this costs $10K, and would be burning way more than that in propane before the car battery wore out.
The point wouldn't be just for backup during outages. It would be growing your kWh of storage and doing daily TOU optimization. That increases the charge / discharge profile by a lot.
Though for an 80 kWh or larger battery, you're only likely to store up and discharge 10-ish per day maybe this way? (Assuming you have actual dedicated BESS, and this is supplementing that). Still that's ~30 cycles per year, which is nothing in the grand scheme of a vehicle battery.
I don't think that wear would be worse than driving around. Unless you go out, recharge, and come back, by definition you only have a single charge single cycle to give.
My thinking is that driving has a typical burn rate (eg 1 kWh/mile or whatever), so the battery will be designed around this load pattern. Using it as a battery backup may be pulling a lot faster than optimal and cause additional wear.
It is probably only a minor impact, but I could believe it is outside the design constraints.
Yeah. A big EV, yeah, can pull 20 kW (29HP) continuous at 60mph (close to 100km/h ish). And much much much more accelerating! It's not continuous at all but just to say it, a 500HP engine translates to a 370kW demand!
They also have to endure enormously strong charge cycles, and in many ways that is even more difficult time for the battery. Charging at >1C (better than a one hour charge cycle), at 100kW or whatever (and many cars charge far faster)? That strongly implies a very competent discharge. Charge performance almost always trails discharge performance in batteries, signficisntly, and yet we expect huge charge capacity from EVs, thus their discharge should be even more hard to imagine huge.
These batteries in EV are all built with chemistries for huge power dense. Not tuned for energy density (storage) but tuned for power density (instantaneous output). The load here, by compare, is tiny.
GM Energy PowerShift is one of the biggest inverters you can get factory for a vehicle and will do 20kW. For reference. Perhaps we could put on a 50kW v2h inverter, power the whole mcmansion. Ignore the fact that the battery is going to last 2 hours. I think even that would be perfectly fine, no worse than a day about the town.
For something you (hopefully) don't have to do that often, it seems negligible. But if you're charging and discharging the car daily to do arbitrage you might eventually notice the degradation
Likewise, there are plenty of plug-in hybrid cars which ought to be great home emergency backup generators (ie. they have a 40+ kilowatt generator and 7+ kilowatt inverter), but very few have this functionality even if the hardware in most cases supports it and would simply require a firmware update.
I had good luck with telling claude to rewrite my laptop bios to enable various power modes which were theoretically possible but disabled by firmware, like powering a fullsize screen from the laptop battery over usbc.
Maybe I'll tell claude to rewrite the car firmware too...
I know someone that did this with an old Prius. No software hacking required. Just leave the ignition on, and wire into the high-voltage system (not at the same time, of course!). The engine auto-starts when the battery gets too low.
The more interesting approach is to do it with a used EV. You can get a 100-133 kWh car used for $20-30K. The last time I checked, that was below the price of a house backup battery with a quarter the capacity.
I live rural and I'm hoping the next decade will bring a wave of cheaper safer sodium ion battery options. Something I'd feel a lot more comfortable with putting in or around my home since they don't have thermal runaway issues, their materials are theoretically cheaper, and they can withstand colder temperatures.
While I'd like to use my EV as backup, the cost and integration issues right now are just not sensible. The utilities and manufacturers have made it too cost prohibitive.
LiFePO4 are much more robust against thermal runaway, omit a lot of the expensive materials that are in typical Li-NMC batteries, and have a better cycle life. They still can't be charged below 0°C, they have worse specific energy, and they generally can't handle the same peak power output, but they're a better choice for fixed storage applications IMO.
GP is referring to sodium ion batteries. They’re even cheaper materials wise (no lithium) and have even more favorable outcomes for freezing conditions.
Worse energy density and similar or potentially worse number of cycles, but that’s being worked on.
But an important difference is that LFP is available today. Expecting a dramatic shift to sodium ion anytime soon is wishful thinking. Battery tech evolves steadily but slowly.
CATL is already producing sodium ion at competitive prices. Expect 5-10 years to end up with a flood of stationary battery products based on them, at prices less than LFP.
Do you have a link to a good brief on these from an engineering point of view? Where can I buy cells, in what packaging, with what specific energy & power, peak draw, charge rate, etc etc? I do some tinkering around with batteries for various purposes and I'd love to learn more.
I have a Tesla 3. There’s no good way to get a lot of power out of the car as an end user except via the wheels. You can get like ~1kW of 12VDC via the dc-to-dc computer/accessory system but even that is pushing it.
I am saddened by this. I’d like to be able to access the large amount of power in it in a pinch.
There is also no good way to charge it as an end user from a DC source like my large 48VDC solar battery system. I end up having to invert the DC to 220VAC which then charges it normally (involving rectifying it back to DC for the onboard batteries) - an unnecessary and inefficient double conversion.
there are several devices that allow for 4kw+ to be pulled out of the NACS port, it tricks the car into thinking its CCS charging. Google "tesla v2h" or "tesla discharge device"
I just run 120v extension cords from my EV during power outages (it has 2 15A capable outlets). I added a manual transfer switch to my furnace so it can be plugged into an extension cord, and I can power my furnace, blower, refrigerator and freezer, wifi and internet for a couple of days.
I really wanted to set up an automatic transfer switch for the whole house from my car in v2h mode, but I found it impossible to spend any amount of money and be confident that the system would actually work with my current EV (the wallbox quasar _sounds_ promising but I couldn't find any reports that it actually _works_)
Is that the transfer switch just for the furnace or the whole house? I was staring at my furnace yesterday, trying to figure out what to do if power stops and temperature drops below freezing. Doing the whole house transfer switch is too much, esp given o don’t have a 30amp power source, but it never occurred to me to do just the furnace.
I had a transfer switch installed just for the furnace.
https://www.reliancecontrols.com/products/reliance-controls-...
Hacky way is to install a plug on your furnace that you can connect directly to a generator or power station. Takes maybe 5$ in parts and is DIYable.
Lots of tutorials on YouTube.
Don't do this. Install a transfer switch. A simple plug and another power source feeds power back into the grid. It's absolutely against code. If you remember to flip the furnace breaker off before you do this, then it's not going to backfeed, but this isn't something you should rely on remembering to do. It doesn't cost much more to do it right.
Sounds not-up-to-code and potentially dangerous
Because it is both.
Makes sense. My mind went into a less safe direction, I’m glad I asked before following it.
Here’s how you’d set up just your furnace to allow a generator to power it in a permanent way.
For the transfer switch, you can use either a single-pole double throw motor rated switch for a 120V like a Leviton 1285, or a double-pole double throw motor rated switch like a Leviton 1288 for 240V. It must be motor rated.
You’ll also need a power inlet and a cord that connects between your generator and the inlet. Please buy a premade cable and the proper inlet, do not hack together a cord with two male ends aka a suicide cable that you plug into a standard outlet. Example of a safe setup: https://www.vevor.com/power-outlet-box-c_12116/vevor-30-amp-...
Wire the generator inlet to one side of the switch and connect the other side of switch to the utility fed circuit.
Label the switch positions so you don’t forget.
When the power goes out, flip your switch to the generator side, connect your generator to the inlet and turn it on. When the power comes back, flip the switch back to utility and turn off the generator. The center position of the switch is off and it’s impossible to backfeed the utility under normal conditions.
This entire area is a mess, I spent a year or so trying to get bidirectional charging set up at home in the UK. I even went to several of the vendors mentioned in that post and said "I've got basically a blank cheque and permission to do whatever you want however you want, even use it all as a case study to make this work" and nowhere could/would do it.
The most frustrating thing is it looks like V2G is easier and more accessible than V2H[1]: it's easier to give control of your battery to your energy provider and bypass your house to help the energy companies than it is just to power your own home with your own car battery.
Technically, this is ridiculous. You don't bypass your house when you do V2G.
My tinfoil hat is clearly making me too cynical when I say this, but I think it's this way because of the relationship between energy providers and law makers. These are the same energy providers that use "changes in wholesale pricing" to justify increasing how much they sell me electricity for, whilst reducing the amount they pay me for the solar electricity I sell them.
[1] https://octopus.energy/power-pack/
You're definitely right on the tinfoil hat angle. Vehicle to home is inevitable, but the rollout is intentionally slow / designed to fail, so the utilities can keep milking folks and justify their natural gas peaker plant investments. Also, once it works, vehicle to home will immediately tank the grid-storage and home-storage battery industry.
Some company is going to create a gray-market "high voltage -> top N home battery systems" dongle that you can just wire into the battery pack on your car. That company will make a fortune (but only if they're able to dodge liability).
I've heard of people doing similar with old prius beaters. You wire the 500V (or whatever) DC battery into an inverter, and then plug your fridge, etc into it. Leave the car ignition on, and it runs the gas engine for a few minutes an hour indefinitely because it sees the drain and thinks you are driving it.
Most modern EV's support this sort of thing officially, but they're hardwired to one brand of house battery. So, when you buy a new car, I guess they think you will throw out your house solar panels and backup battery. If you want two cars, then I guess you get a divorce?
Thanks, I really appreciated this comment, a lot to think about!
> Some company is going to create a gray-market "high voltage -> top N home battery systems" dongle that you can just wire into the battery pack on your car.
I agree. I've been thinking of trying to build a similar but more generically, a "240v in dongle" which would just be a bench PSU with phase synching and islanding config (e.g. allow power if islanding is handled at home level, or operate grid tied and cut off if not). This would allow any device with a standard 240v AC output to safely power a home, so this would include basically any EV (as most have V2L) as well as a lot of other generators, UPS batteries etc. I thought the phase synching/grid tying stuff was really hard or complex or expensive to do, but the recent boom in balcony solar shows it's totally feasible to make and distribute hardware that apparently safely does this for less than a couple hundered.
This issue is regs. Tbf, I think in the UK, it just needs someone with money and confidence to do it fast and safe enough that the obvious immediate benefits force a law change. The balcony solar regs changes this year really showed how needlessly behind our grid regs are. Now is the time to do it too, with big scares around energy costs and WW3, this would gel well with the push for EVs.
> Leave the car ignition on, and it runs the gas engine for a few minutes an hour indefinitely because it sees the drain and thinks you are driving it.
Oh wow, I hadn't even thought of that! I'd only ever considered pure EVs. Feels like hybrids have a lot to go wrong, but this is a really interesting use case that I could justify a hybrid to entertain.
> Most modern EV's support this sort of thing officially, but they're hardwired to one brand of house battery.
I haven't seen this much though - most cars I've seen that mention v2g or v2h mention the generic standards around it, rather than any specific manufacturers. The "hardwired to one brand" tend to be hardwired to the brands that have said they support the standards (OCPP, ISO 15118 etc.), at least in the UK.
> My tinfoil hat [...] the relationship between energy providers and law makers
My local establishment's energy czar is also on the board of the electric company (itself a natural monopoly of course).
No tinfoil hat required. They have re-elected her several times as well.
>itself a natural monopoly
With widespread solar and batteries, energy is becoming less and less of a "natural monopoly", the state should stop granting legal monopolies to energy companies under the outdated assumption that it's more efficient.
My biggest problem with batteries for grid outages is that the only outages I am actually concerned with would drain them to zero before the outage is resolved. For short term, smaller/portable batteries are fantastic at bridging a few hours. Plug the wifi & fridge in and you can sometimes go for 2-3 days.
I am not aware of any economically feasible way to run my 5+ ton HVAC system full-time on batteries after a hurricane just reset all the infrastructure, and you do need to run it full time because of the insane humidity and latent heat that follows a tropical system. Doing the math, I'd need something approaching 800kWh of storage to ride through this kind of event (7+ days). This is approaching half a million dollars in batteries. I can install an extremely nice 1800 RPM generator for ~15% of this cost, which would also include a year's worth of propane buried on the property.
I think a simple generator on an ATS remains undefeated from an engineering perspective. If you have an air cooled unit, the maintenance is not much more complicated than with a lawnmower. You just have one extra spark plug to deal with, and sometimes the oil pressure sensor needs replacing. I can get my stubborn Honda generator to start with all kinds of weird tricks. If my Ecoflow battery starts to act weird, I have very little recourse by comparison.
Batteries alone are not suitable for long duration outages, but solar+batteries, designed correctly, can not only supply enough power during long outages, it can get you to be off-grid entirely in the first place at a dramatically more cost effective number than your $500k quoted - perhaps 1/5 or less for a system suitable for your needs of 115kWh per day. So while the system might be more expensive than a generator alone, it can still beat on value because it provides power all year round.
You also do an unfair comparison here - you are OK with portable batteries providing only fridge & WiFi for a couple hours, but expect whole-hole batteries to last a week. Many people use whole-home batteries to bridge typical outages that last <24 hours, and do so without ever having to notice any change of use of their home - powering their full heating/cooling etc.
Batteries and generators are also not mutually exclusive. You can install a solar+battery system because it makes economic sense and pays for itself while providing zero-downtime backup for most outages, while also backing that up with a generator for longer term edge case outages eg long extended outages during the winter or where there is an unusually long “solar drought” - it really depends on how much resilience you are designing for.
We have frequent power cuts and follow this same philosophy.
Our first line of defence is the solar system's battery. When power goes out, that will keep things running for some time with the big optional loads switched off - e.g. hot tub, hot water cylinder and pool.
If the sun's shining we can run like this for a long time.
In a solar drought, when the solar battery runs low, the next step is to plug the EV in via V2L and use it as a generator to charge the solar battery. EVs have comparatively huge batteries, so at the cost of losing mobility, which may be important in an emergency, this will keep things going for even longer.
One great feature of using an EV is you can drive to a fast charger, charge up in an hour, and transport all that energy back home.
The final fallback is to plug the 2KW petrol generator in to charge the solar battery. This is enough to keep things going forever assuming a petrol supply. A petrol generator is nicely portable and can be loaned to less prepared neighbours who likely have their own petrol.
The key to it all is the solar battery. That gives you uninterrupted power while mucking around with the alternate sources. It doesn't even have to be all that large if you have an EV.
In the scenario mentioned in the GP post where a giant tropical storm hit resetting the grid for 7+ days, how big is the chance that your solar panels installation has survived? Also, if the grid is gone, won’t the fast chargers also be out of service?
Don’t get me wrong, I think you’re right for most cases but I also think for some more end of the world type of scenarios there is little that beats a generator and stored fuel.
If you can stay there (no evacuation for building doesn't seal enough to make it habitable), most of the solar should have survived. Moving a broken panel out of the way and swapping one from the end of the array in to make the cables fit, or even having a spare jumper cable to swap in place of a broken panel, is quite easy to do. Mostly just make sure there's no load current at all on the string when you disconnect the MC4 connector with the special tool that keeps uneducated people from unplugging them under load and getting greeted with a persistent low current (not "arc flash", we're in the region of "high powered welder used with just normal welding PPE") DC arc (that may supply several hundred volts for a long drawn out burn). As long as it's around substantially below 500 mA you're not gonna sustain an arc.
Indeed, that's why I mentioned petrol generator as the last level of backup.
Though the most recent big tropical storm we had a few years ago, the power was out for 3 days, it was dark and cloudy obviously so no solar, the local petrol pumps had no power and the roads were blocked with fallen trees so we couldn't even drive anywhere. In that situation it really is candles and cooking on wood fires once the petrol runs dry.
> You also do an unfair comparison here
The comparison is unfair for many reasons, actually. A real install would have solar inputs charging the batteries and offsetting loads during the day.
It also wouldn’t run a 5-ton HVAC system 24/7 for 7 straight days, which is how the post got to the extremely high number.
It’s about as bad faith as the argument can get.
Add wind and I think you are onto something. Where I live it can rain for weeks on end so having another source of renewable is great.
> You can install a solar+battery system because it makes economic sense and pays for itself
Would take longer than 20yr at current power rates in many US locales.
Highly dependent on where you are, what your electricity costs, and what your backfeeding compensation scheme is (eg net metering). In California solar alone is no longer economically viable with NEM 3.0 but solar+batteries to maximize self consumption is still in that sticky ~7 year layback range - and those calculations tend to assume today’s power prices, that are in reality going up quite quickly.
If you have free night charging plan you can recoup quite faster. My system paid off for itself in 3 years - although I designed and set it up myself, so it was about 3x cheaper than through contractors (and yes I'm in US and I pulled permits to do this).
It's nice to do this for more than just the direct economic costs. The generator doesn't have to run 24/7 since the batteries absorb the excess power produced by the generator. This means less fuel wasted as well as less noise produced. I used to have two small generators that I could run (and team, if needed) but adding a battery component meant being able to sleep at night without a combustion engine burning fuel all night long.
Yup, even better if you power a separate battery charger with the generator, but let loads be handled by the battery+inverter. You don’t need to provision the generator for peak loads (which can be quite high), or even worry about high harmonic distortion from a cheap generator screwing with your electronics. It basically turns your system into a fully ‘online’ UPS.
Also, really handy for diesel gens which will ‘wet stack’ if you only run them for short periods or with light loads.
Provision a generator size which you expect to run say 6-10 hours at a time (at say 70-80% rated load) to fully charge your batteries, and a battery bank sized for 3-4 days of load.
Keeps your total gen hours much lower, much more efficient fuel wise (you can set the ideal load using your charger, and it will keep it that way regardless of increasing/decreasing loads), doesn’t require as big a generator if you have things like AC compressors, heat pumps, etc. with high start loads, and gives you a lot of redundancy and flexibility. It even gives you time to fix your gen or find/beg/borrow another if yours breaks, and you won’t need to keep the gen running overnight if you plan appropriately, so your neighbors will like you more.
Best of all worlds. Especially if you have natural gas, or get a tri-fuel generator and keep propane handy. Propane doesn’t go bad like gas or diesel can.
Will you not own your home for more than 20yr?
I think for most people it would be if they can they afford a 20 year advance on electricity costs all at once. That is a lot of money if you have more pressing needs, but if you got that money sitting around then yea of course it is a good investment.
And in some, like ours, it takes 5.
You don’t need to run your 5+ ton HVAC full time. Get an EV and run the AC there (no more than 3kW). Sleep in the EV. A typical 80kWh EV battery will last several days. And this is not just theoretical; plenty of people have done this.
For Christ’s sake a natural disaster just struck and you want to live like nothing happened? The entitlement is unbelievable.
I think you’re better off getting a good sleeping bag and sleeping in the house in relative comfort. You can camp down to very cold temps, and your house is both better insulated than a tent wall and is a better wind break, even if it was bad enough that you got well below freezing. If we’re at the stage of “sleeping in the car”, indoor camping is reasonable to me.
They were talking about loss of power during heat stress and needing cooling not heating, more specifically dealing with latent heat & needing dehumidification, mainly in a post-hurricane context, whereas you are talking about a cold stress event.
Oh that’s a good catch, internal environmental bias there.
I’ve been torn about this. On one hand, I could spend $2k on a small portable generator, get a window unit, lots of extension cords, and survive a few days without power with cords strung all through the house.
I’d still have to deal with wheeling it out, and doing periodic oil changes. Not sure how/where I’d want to deal with a 200lb unit… A natural gas unit would be more practical - I don't have gasoline yard tools.
I could get a transfer switch installed and use my house’s main AC unit. The cost of the larger generator isn’t that much more and I wouldn’t need a window unit and lots of cords.
Of course, then I could skip the portable unit and get a whole house generator with automatic transfer switch.
It’s hard to put a finger on it. The “cheap” solution doesn’t seem worthwhile while the others start making me wonder “how often does the power really go out”? It all seems silly for 3 days outage once every 5-10 years.
> others start making me wonder “how often does the power really go out”? It all seems silly for 3 days outage once every 5-10 years.
I think very little is worth it for three days every few years. Instead, I see the benefit of batteries + solar or a serious generator as reducing tail risk from rare serious disasters that leave the grid down for months or longer. These are not likely, but if they happen I'd want to have something in place.
I’ve also thought about that.
I figured refrigerator uses about 1KWh per day. Just 2 days would require 200Ah of 12V batteries. Lithium looks attractive for weight and other factors but is more expensive than lead acid.
Have a large overhang that could temporarily be used to lay panels on too.
For portable AC unit, seems like would need another 10KWh per day or so of capacity. At that point, generator becomes more financially practical…
Also wrestle with how much I can depend on solar.
If only 100KWh of battery capacity was practical…
I didn’t hear this person expecting anyone else to do this for them
I don't think it's entitlement if it's actually doable. They're not saying they expect the world to give this to them on a silver platter. They're saying that they can actually do it. And if that's what they want to spend their money on, who are we to say that it's not a good use of their resources?
i am regularly shocked by the assumptions that the techbro crowd makes. I should not be, but i still am.
The desire to operate a massive AC just after a natural disaster is just unhinged. Similarly, this idea that your life should be able to continue as before, your neighbours be damned, is also psychotic.
People like me push for the better solution (against great opposition) - neighbourhood-level improvements so the rich don't hoard all the resources while the rest are left to die.
> The desire to operate a massive AC just after a natural disaster is just unhinged
The humidity after a hurricane is a great way to get mold problems in your walls. It is a major health hazard, and once it sets in you have a very disruptive and expensive remediation effort. Keeping the AC and central dehumidifier (assuming newer construction) running is pretty much the only way to prevent it.
The only thing unhinged here is your response.
The biggest issue is any wind damage to the roof. If it's leaking even a little bit, it's going to be leaking hard for hours.
With a consumer dehumidifier you might get 5-6 gallons per day. A 5-ton HVAC system will pull over 50 no problem. You might have hundreds of gallons of water soaked throughout the framing, drywall, insulation, etc. It can take a really long time to remediate without a powerful HVAC system.
when a natural disaster happens, especially one that disrupts electricity for weeks, your likely first priority is being alive, safe and being able to eat, not mould or your air conditioning.
Assuming you have enough solar, how about running your 5+ ton HVAC system only when there is enough production? And properly insulating your home, of course, using it as a thermal battery of sorts.
If there is a grid outage, surely one can shift consumption to solar production hours while using the battery for the always-on systems (fridge, lights, some computing...).
Insulation won’t help post-hurricane when they are trying to fight humidity/latent heat. Your thermal battery comment makes it sound like you are viewing this from a cold stress perspective (in which case a tight, highly insulated home is indeed a great way to slow heat loss and keep the home warm), but they are talking about dehumidification post-hurricane, which is really a separate story.
Yes this is what I do with power outage with solar and battery and 5 ton, I have to modify my behavior and conserve, increase ac some from say 73 to 77, shower during the day when there is excess power etc.
If there are clouds lowering solar output the ac isnt running as much either or at night.
If I wanted to run as though the grid was up would probably need double the size solar and battery.
>I think a simple generator on an ATS remains undefeated from an engineering perspective.
Let me just inject a bit of nuance here to avoid what I think is an unintentional sleight if hand...
For the small sliver of the population that lives under threat of a large area week long blackout in a hot humid climate, I think a simple generator on an ATS remains undefeated from an engineering perspective.
For the vast majority of the population, it's incredibly rare to lose power for that long, and need AC 24/7 afterwards. It basically only happens in the gulf.
Homes in cold climates using heat pumps for heat have a similar issue. No grid power means no heat, no heat means frozen pipes and mortal risk to vulnerable people. There is a decision cycle to it too. Central air dies, you replace with a modern heat pump. Then the boiler dies and it becomes difficult to justify replacing it, except the boiler is more practical to run off a battery in a power outage.
> For the vast majority of the population
In the spirit of nuance, the vast majority of the population of Florida is at risk. Something like 10% of the US population in total could be impacted directly. You don't actually have to live on the coast to get rocked by a hurricane. Ike took out power for millions in Ohio.
https://www.facebook.com/100044470387919/posts/ohio-remember...
Correct, but you don't need 24/7 AC in ohio during hurricane season. Your reference storm was in September, when Ohio basically needs no heat or AC at all. The nuance is the extreme emergency energy demands (mandatory constant AC) are pretty rare.
These replies and the down votes are just reinforcing why I made my comment. People are unable to grasp nuance, apparently even when it is spelled out.
Eastern Canada and New England see multi-day power outages every 5-10 years. I've had power outages when my solar panels were mostly covered in snow.
I have an EV which supports V2L (20A/120V). Even if it supported V2H, I'd want to save the battery for driving.
Our backup power is a 9kW gasoline generator, with a manual transfer switch.
> For the small sliver of the population that lives under threat of a large area week long blackout [...]
I've lost power for weeks from snow, wind, storms, and ice, living in the central midwest and mid south. We lose power almost every time it rains in the spring and summer for many hours.
>in a hot humid climate
It seems you cut off part of the quote. I know it can get hot in the midwest, but places like Florida are borderline "humans shouldn't live here" hot.
To be fair, losing power in a winter storm can be equally dangerous because while the gas might still work your central HVAC system requires electricity to run its blower, power the thermostat, etc.
That said, you are still absolutely correct about the proportion of the population that's really at risk of extended blackouts being incredibly small.
In the US 80% of the population lives in urban or suburban areas, where for the most part power outages are measured in either seconds or hours and while extreme weather or bad drivers might sometimes cause enough damage that it takes a few days to get power back on to a specific neighborhood it's rare outside of large-scale natural disasters for the power to be out over more than a couple of neighborhoods.
I live in an older suburban neighborhood in Ohio and the one time we had power out for more than 12 hours the literal next street over still had power. Even if my whole neighborhood was out for a week, the nearest fast chargers to me in either direction are both technically in another city and on an entirely different section of the grid. If power is out for all of them for days on end stuff is really messed up to a point that FEMA and/or the National Guard would likely be involved, and that's beyond the level of disaster I'm really worried about.
Obviously those who live in low-lying coastal regions like Florida and the Gulf Coast where a disaster is pretty much a given or those living in extremely rural areas where restoring service is going to be deprioritized have different risk assessments and if I were in their position I'd be looking in to trying to be as grid-independent as possible, have enough battery power and solar generation to support living comfortably without requiring grid input under normal conditions and to support "emergency mode" operation with half your system or more destroyed in case of a major disaster.
Your central HVAC system, heating, can run on a very small generator though, since the heat is provided by burning propane/NG/fuel oil.
AC needs electricity for the cooling itself too - lots and lots.
Unless you have electric heat.
> "humans shouldn't live here" hot.
A bunch of it has to do with humidity levels that impair our natural ability to sweat. If the wet-bulb temperature [0] is high enough, a place may be unlivable without artificial cooling.
[0] https://en.wikipedia.org/wiki/Wet-bulb_temperature
I cut it off because it's not relevant in the context of why the power is out other than being a force of nature.
Just about every place in the US, with some minor exceptions, has extreme heat (120F+) extreme cold (-10F), high winds, tropical storms, ice storms, blizzards, tornados, or even earthquakes regularly that take down poles and lines, damage substations, etc.
Heating is a different problem.
> am not aware of any economically feasible way to run my 5+ ton HVAC system full-time on batteries after a hurricane just reset all the infrastructure, and you do need to run it full time because of the insane humidity and latent heat that follows a tropical system.
Which region is this?
Are hurricanes that reset all the infrastructure a recent phenomena in this region? How did people manage in the 60s, 70s, 80s, 90s etc before these rather large (5+ ton HVAC) were even an option?
>Doing the math, I'd need something approaching 800kWh of storage to ride through this kind of event (7+ days)
How airtight is your House? You may be better off with a tighter house to reduce the infiltration load from the outdoor air and possibly section out the house so that post hurricane the primary living spaces are the only spaces that are constantly getting fresh air and there fore humidity load and for the non primary spaces, you dehumidify once and hold it there.
>I think a simple generator on an ATS remains undefeated from an engineering perspective. If you have an air cooled unit
Yes, if your outages are under lets say 10 days a year a generator + fuel will be orders of magnitude cheaper wrt TCO, unless your grid is super expensive.
You average 100kWh of use per day?
What’s 5 ton in new money, 5kW power draw max? Are you planning to run that full power for a week?
Yes, that much in batteries would cost a lot but uk prices right now would be ~87.5k for the batteries themselves (so a shade over $100k I guess). £7k for 64kWh
You’re not going to run HVAC, but I’m more than happy to have the freezer running, the light on the TV etc
Batteries are for load shifting between day and night and for short term backups. Yes, 7+ days of outages do require means of replenishing the battery, whether it's from a diesel unit or a solar. That's not a battery cost problem.
Yeah it's hard for batteries alone to compete with generators, unless we put a lot of weight on things like noise, or are just focused on small loads like fridges.
I think the more interesting comparison is generators vs solar, though it depends on the local weather etc.
This is exactly what the post is trying to address: during a serious long-term outage, batteries on their own will run empty. What you need is the ability to recharge batteries from solar during an extended outage, while also flexibly drawing from the batteries when solar isn't enough.
I have a 100kwh battery (my car, Zeekr 7x, in Australia). That can run quite a few days or even a week with careful usage.
I’ve been looking into a smaller scale option to run limited items medium term on part time hours…
Best option so far involves a mix of batteries that are charged from the mains when available and topped up from a mix of solar and a LPG/multi-fuel generator.
But unless you want to go very large on the solar and generator size it’s unlikely to cover everything full time.
You can run a fridge, natural gas furnace and some lights for a few days on 5kWh (I've done it a few times).
EVs have 60kWh+, which should get you through a week (if not two) easily.
You can run your hvac fan and an oversized dehumidifier for a while off batteries. You don't need the whole hvac system.
I have 18kw of solar and 30kwh of batteries with a 5ton ac it will run it will run indefinitely assuming the sun comes out, if it doesn’t I have a chargeverter that can keep the batteries charged off my RV’s diesel generator or gas portable.
My solar system generates excess power daily and has zero maintenance, the generators are pure money sinks for backup power and require regular maintenance.
Options are nice.
Also heat pump water heater and dryer help reduce load along with efficient variable speed hvac and good insulation.
Fuel is a problem during a storm too and a buried large propane tank is a good way to go but very expensive on top of installation.
An electric car with bi directional charging would add to flexibility either charging from home system or being able to go find power and bring it home.
Ideally I would like a gasoline hybrid with power out like a F150 power boost and a fully electric with large battery and V2L any Tesla would do now as they all have 2400w out I believe Cybertruck can do more. My chargeverter can take 120v or 240v
How about reducing energy use? In general, but then especially after a grid-destroying event that keeps you offline for a week? You surely don't need to have everything HVAC running on full blast in the whole house during that time. And your laundry and next oven long cook can probably also wait until the grid power is back.
If you then add some solar into the mix, it doesn't sound as dramatic anymore.
There is something in between flashlights and a grid scale battery that van power your full electric home.
I just have a plugin battery that I can run the lights, fridges, phone chargers off of for 24 hrs. That is good enough for me, and I think most people. Anything shorter, and it's not necessary to run the rest, much longer, there also isn't because apparently shit hit the fan and we're not necessarily assuming the power comes back on in the next weeks or ever.
> and you do need to run it full time
Or what? Are you made of salt or sugar?
Mold is the issue. Once it starts growing in the walls, remediation is extremely disruptive and expensive. Not fixing it is a massive health hazard.
Not if you build it properly instead of building a cardboard home with 10gw of AC to keep it nice
Maybe a signal that you shouldn’t be building there?
That's a valid concern for you where you are.
For me where I am, things are different. We don't get hurricanes here.
Our longest power outages tend to follow ice storms. We need heat because these things happen in the winter time when it's cold outside, and that's dangerous for various human and infrastructure reasons (pipes freezing and breaking).
But I use natural gas for heat and I don't recall ever having a weather-related natural gas outage. So that's helpful. And ice storms tend to happen when it's cold, but not damn cold -- that helps, too.
My furnace uses about 600W of electricity while running. It does not run all the time. According to my charts on a random day/night cycle last February with a high of -8C and a low of -16C, it was running with an average duty cycle of about 30% over that period.
600 Watts × 30% × 24 hours = around 4.3kWh for that 24-hour period, just for heat.
I'll also need to keep the fridge cold, and some lights running, and will surely be getting some use out of a laptop and some network stuff.
A common-enough home battery size is 48v, 100Ah, or 4.8kWh. They cost around $1,000 right now (some more, some less) in DIY-friendly shapes.
As a spitball effort: If I live more-conservatively and dial back the thermostat (it is a power outage, after all), I can probably get enough power to live a productive, comfortable-enough life on one such 4.8kWh battery, per day. Ish. If I'm careful.
So for batteries, alone, I'm at $1,000 per day. I'll need an inverter as well. That can be either minimal or extensively integrated, grid-tied or not, solar-accepting or not, and etc. Let's just pin that at $3000, with the wiring and accoutrements, and assume I'm doing the labor for free.
I'm now at ~$10k to survive a week of power outage at home in the winter on batteries alone. That's expensive[1], yes, but a whole lot less than half a million bucks. A whole lot less than a very nice, installed, low-RPM generator, too. :)
...except, realistically: It's more like $13k for a week, because future-me will surely not be as careful with energy use as present-me suggests that I should be and 3 more batteries adds some safety capacity. :)
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And that can be supplemented. Solar input can obviously be used (if available), but may be limited by winter sunlight conditions and storm accumulation.
Gas-fired generators can also be used. An inexpensive-ish portable inverter generator does the trick well when combined with, say, an EG4-6000XP do-all inverter.
That particular inverter wants to see at least 2 of these batteries connected, so let's play with that minimum: 2 batteries, 1 inverter, 1 generator. ~1.4 batteries worth of load every 24 hours, as with the safe $13k figure above.
The generator can be run pretty hard (it has a continuous max rating for a reason), and it can be run intermittently. The EG4 allows programming of generator input power.
So let's pick a generator: Champion 201509. It can do 7kW continuous, and we'll load it to 75% of that, or 5,250 W. From this 5,250W, it provides for the house's present consumption while it runs, and it restores the charge of the two batteries to 100% SoC[2].
If it is run once per day, it can do this job in about 2 hours and then be switched off until tomorrow.
If it runs like this once per day for a week, I guesstimate that it uses about 11 gallons of gas over this week. That's a very manageable quantity of fuel.
So we're at $2k for batteries, $3k for inverter+stuff, and $2k for an appropriate generator. That's $7k to run ~indefinitely, or as long as I can keep bringing in fuel, with enough power to survive a blackout (with heat, lights, refrigeration, some entertainment) long-enough on batteries alone for the roads to become passable and then decide if I'm making a run to fill up the gas cans with fresh fuel.
Not so bad for a relatively quiet time of living in a temporary blackout, and the house gains a gains a big UPS for some stuff (which is nice). (The installed gear also offers an easy entry into solar power.)
But I'm not in hurricane country. And while I do love me some aircon, our summers are pretty survivable, usually. My needs are not the same as your needs are. :)
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[1]: Except, for the price of this kind of self-sufficiency: Draining/blowing out the plumbing and staying at a hotel or with friends/family for a few days in an unaffected area might be a better option. The cheap portable air compressor I have doesn't leak down at all, so it's always got a full tank of air while just sitting there unplugged. I'll figure something out: Power outages are very quiet, creative times.
[2]: 100% SoC? Yep. It's a temporary blackout where the batteries are operating as a UPS, not a long-term operation where the typical 20%-80% SoC goals are important for longevity. They won't stay at 100% for very long, anyway.
Oil generators have an “artificially” low price because there’s a lot of demand for oil for other things. If the other sources of demand go away, the price may become unfavorable even if gas generators make a lot more sense from a redundancy perspective.
In this application, at this scale, on the timeline of an individual human: It doesn't matter much.
It's just a bit of temporary[1] redundant local infrastructure that is hopefully never used at all, and when it is used it won't be used for very long. The fuel will remain available for as long as any of us reading this are alive.
The price of the fuel may go up (it probably will go up), but it doesn't really matter much at this scale whether it costs $25 per day to run or $100 instead -- the power grid will come back online soon enough.
[1]: It's a backup generator, not an heirloom. In 50 years, people will look at that old thing and laugh at how interesting its archaic nature is. They might tinker with it. They might give up and have Jeb haul it off as scrap. And that's all fine, too.
The future cost would likely be based on chemical synthesis.
Recovered biodiesel (fryer oil) is always gonna be a thing to some degree. Either chemical synthesis or just plain devoting some agricultural output in the future doesn't sound completely insane.
Power density of dino juice is virtually undefeated
Hate to break it to you but fossil fuels comes from acient plant and microbial material, not dinosaurs. Coal comes from the Carboniferous period from massive land plants that accumulated in oxygen-poor water. Oil and natural gas mainly comes from plankton, algae, and bacteria that settled on the ocean floor and mixed with sediment.
Dinosaurs contributed an infinitesimal fraction of the biomass that is needed for the fossil fuel reserves.
A fundamental problem here is that V2H during an outage requires a disconnection device (in the NEC this is a “microgrid interconnect device”), and the manufacturers of such things have made no effort whatsoever to standardize the control protocol. This means that you cannot build an islanded-V2H-ready house and just plug in a car. So the whole concept is kind of dead in the water.
At least Tesla is vertically integrated enough to pull it off within their own product portfolio, but this has approximately no value if you want to use a non-Tesla car.
You can't do just V2H, but Enphase and others have moved to simpler meter collars and grid disconnect for exactly this reason.
The main question for this thread remains who the Enphase / ISO standards friendly OEMs will be. With Tesla saying they'll allow it now, maybe others will get onboard, but the risk is that they wall themselves off.
What Enphase/ISO standard is this? I’ve never heard of it, and my attempt to search came up with nothing useful. There’s ISO 15518-20 bidirectional, which seems like it barely solves the problem.
It should be possible for a vehicle’s built-in inverter/charger, the EVSE, and the MID to all cooperate even if all three are from different vendors, but this is not a thing.
I think the standard is called "V2H". It's unobtanium from what I can tell.
If you have a Ford EV and a SunRun house, then it supposedly has worked for a few years now. (But that's just vehicle to home charging, not the "V2H" standard.)
It’s unfortunate and inconvenient. However A transfer switch requires <3 minutes to engage. If a car was able to supply 30-50 amp via compatible plug it would work reasonably well even absent unified v2h standard.
Most recent teslas support 20amp at 120v output via official $100 cable adapter. Some other cars support about 20amps too, eg RivianR2. While it falls short of desirable amperage the car manufactures can bridge the gap if they wanted to. Even now I can run the bare minimum of workloads - a full size fridge, a small AC or Microwave, LED lights, and phone chargers.
A manual switch doesn’t solve the problem: there still needs to be a way to inform the inverter that the switch is open.
It solves my problem just fine - power critical loads for a few days by spending $100 upfront fir the cable and 5 minutes to manually switch the load. It’s a difference between moving to a hotel for indefinite time and staying put.
Sure you can set a loftier goal and spend tens of thousands of dollars and countless hours solving it. Most people won’t though.
Sorry, what device are you using to supply power once you've flipped the switch? Sure, you can get a (legal, even) manual transfer switch and plug in a little portable generator, but if we're talking about using your car as a power source, this is not going to work.
I previously used a portable propane generator for a 30amp inlet to transfer switch. In my test runs it didn’t go that high.
Today I could plug in a car that gives off 20amp into the same inlet, it would limit how much load it can carry, but I could stay below 2.4 kw if needed. Why wouldn’t that work?
A lot of houses won’t run off 120V/20A. You’ll also need to kludge around the fact that your house wants 120V/240V.
In any case, serious V2H should support much more than 2kW. An EV with a charger with less than 6kW capacity is almost unheard of. Two EVs should be able to supply twice the current. All that’s technically needed is an charger that is physically capable of operating as an inverter (which I believe adds little cost), some way to derive a neutral (the usual solution is a relay and an autotransformer, again not particularly expensive), and the control logic to convince all of the above to actually operate in this mode.
What about using a step up transformer to send 240V to your panel from the 120V output from some EVs?
Tesla just brought this functionality to new Model 3 and Model Y cars as of Oct 1. It requires at least one Powerwall 3 to enable bidirectional V2H - what they call Powershare. But those cars can now power the home and charge from solar while the grid is offline.
So they always had it, just disabled in software?
> By default, all Cybertruck trims ever produced and all Model 3 and Model Y vehicles ordered in the U.S. and Puerto Rico after October 1, 2026 are capable of Powershare. Some, but not all, Model 3 and Model Y vehicles produced before October 1, 2026 are also capable of Powershare. [0]
I presume it is a hardware revision, like how Tesla removed radar.
[0]: https://www.tesla.com/support/powershare
Or you can deploy the hardware while software is not ready...and allow it when software is built, tested and updated.
That's why Tesla gets cool features like door open pedestrian/car alert, child left behind detection, smooth stop etc over the life of the car.
Yes. Typically V2G works by connecting an external inverter to the high-voltage bus.
It just needs to start a charging session, and then siphon energy _off_ instead of supplying it. People tried that before, but the firmware on Model 3/Y monitors the flow and terminates the session if the flow is negative.
Not an issue on my system (or rarely) as it generates enough to not need grid at the moment even with EV charging. So simply don't charge the EV and avoid washing machine, dryer etc. until grid comes back will probably do it. Another tactic is run some stuff off the car to reduce load on house battery
—- Types of V2G ——
V2H - charger inverts DC to grid AC
V2L - EV inverts DC to grid AC
In case of V2H it therefore doesn’t matter what supported EV you are using, rather what charger you are using.
In general for changeover during a black out, V2L is probably better, because with V2H the charger itself needs POWER to boot up and request V2G whereas V2L you can start from the EV itself.
Also, generally speaking V2H is designed to be grid-following and certified to half a dozen standards whereas V2L forms an isolated microgrid, and a lot of the rules are tossed out, which is what you want.
For V2L you just need a generator changeover to isolate your house from the grid (most commonly just a manual switch), and a reverse plug to connect EV output to switchboard input.
V2H can charge home battery systems, but V2L "cannot". There's obviously a market for "plug the 240V outlet on my EV into my house battery. Use the car to charge the house battery while the house is running off the house battery".
Someone will make it work.
The other problem with purely EV based home backup is that if you have to drive somewhere you house no longer has power.
IMO such a system should be additive to a home based battery backup system with solar, which should be sized for a day of emergency (minimal) home usage.
Such a system could top up from the EV when the EV is plugged in - assuming the PVs aren't producing.
Most Tesla models don't support bidirectional because they had free Supercharging, and also probably because having your car not full at all times is not always the best experience. Other brands like Nissan had always supported V2H and in fact it has always been a selling point of OG leaf that it could double as the Powerwall equivalent since back in 2012.
Most V2H systems don't support zero-interrupt automatic transition because it has no means to know if the perceived grid outage is accidental or intentional, and if intentional, trying to back it up could injure/kill electrician who commanded it. But if the system is operating off-grid, I think those can be configured to be always uninterruptible.
I don't think either of those are real concerns. The free supercharging did not overlap with homes that could be charged by cars.
Also, safe islanding devices have been very standard for at least 5-10 years. Policy 1: House watches incoming voltage, and turns off the breaker if the grid is down. House electricity + solar stay on; line to power company stays at 0V. Policy 2: Panels see that the house voltage is low, so they turn themselves off.
Policy 1 requires an electrician, but mostly just for permitting. I'd guess a good fraction of the people reading this could safely do it themselves after reading a manual. Policy 2 does not require an electrician or understanding electricity at all. It's how DIY balcony solar usually works.
As far as I can tell, the Leaf never had this in the US. The 1st and 2nd gen hard the hardware, but the chargers weren't there. And the 3rd gen has only announced V2L.
From my perspective, "zero-interrupt automatic transition" is not that important, but being able to have the system smoothly move between having the solar recharge the car and the car power the house during an extended grid outage is critical.
You can do it with an F150 lightning if you have the 10kW inverter. Rather than use the charge port and the official charger, you use the 30A 240V plug in the bed to power your panel. You can charge the truck while using this too.
How does solar recharge your F150 with this setup?
120V or 240V through the charge port.
Reading more about this, it doesn't look like it does what I want. I'm looking for:
1. House has solar.
2. House does not have batteries.
3. Grid is down.
4. When solar production exceeds house consumption, the extra goes to the electric vehicle.
5. When house consumption exceeds solar production, the extra comes from the electric vehicle.
This really doesn't look like something the F150 can do.
The F-150 can do this, but by charging the batteries you don't have.
It could also probably run the house off the 240V outlet in the bed, but only if you knife switched the solar + grid off and just ran the house off the truck.
When the sun came out, you could knife-switch the house back, and charge the truck.
Alternatively, you could rip out your solar and put in the one brand that Ford works with (SunRun, I think), and then the truck would be able to bi-directional charge with the house batteries using the solar, or something like that.
(Yes, this is all dumb, especially since there are standards that should allow a dongle to be made to make this work transparently, and to just automatically do the right thing".)
And then after a little while you can be without power AND stranded!
I can go most of a week on the Lightning's battery, and it will shut down the 240V 30A outlet well before leaving me stranded. Thankfully the longest outage we've had in my lifetime (and I'm not a young man) is 3 days, for an extremely rare severe ice storm.
I really wonder if part of the reason this isn’t more widespread is that utilities with variable rate electricity pricing would get burnt on it. Imagine charging during cheap time then dumping 5-20kWh back onto the grid during expensive time. You could have a positive ROI on a vehicle you regularly drive (timing permitting)
No, the main barrier is concern over warranties for the vehicles.
In California, the law requires that vehicles still hold up to 70% of their original charge after 8 years and 75% in the future [1]:
> and d., to deteriorate to less than 70% for a warranty period of eight years or 100,000 miles, whichever first occurs, for 2026 through 2030 model years, and 75% for a warranty period of eight years or 100,000 miles, whichever first occurs, for 2031 and subsequent model years.
The law is unclear on bidirectional charging and whether this would give manufacturers an out. So they're cautious.
[1] https://www.law.cornell.edu/regulations/california/13-CCR-19...
In TX, the power producers, distributors, and retail electric utilities are (most commonly) different parties, so the latter two are very much interested in the type of decentralized time-shifting you mention since it smooths wholesale costs somewhat and reduces grid buildout and maintenance.
For EV owners in TX, its not uncommon to have fairly free charging overnight (just paying the distribution costs of 5-6 cents/kWh).
For homes with residential solar and batteries in addition to the EV, you can have essentially free power and EV charging due to time-shifting and incentives.
Residential batteries are still quite expensive, though, so it would be amazing to recruit those in the above EV to time-shift using V2H.
Why? That's the entire point of moving towards dynamic tariffs. In the systems I'm familiar with the utility company makes money through a fee charged on top of the market purchase/sale price, much like an investment broker.
V2H was popular among Japanese Nissan Leaf owners and there were tons of Leafs on cinderblocks with dead batteries used to milk incentives sold on used market for like $1k with 10 mi on the meter. Tiny household sellers are credited for sales for generosity, but apparently often just a noise that needs to be compensated by increasing power output at power plants to then just burn off. Great idea on paper, often not so much in practice.
Maybe. I did the math and in our area a Powerwall would roughly pay for itself over the speced lifespan of the device, IIRC that was just the cost of the device not the cost of installation. I did that calculation ~4 years ago, so maybe it has changed, but definitely do the math, I was surprised.
Why shouldn't utilities pay for this? You're provide grid load balancing. Theoretically their pricing should be considering this? It's not actually free to you since charging and discharging your battery costs money.
But naturally the situation is they want to be the ones paid the big bucks for such services.
One of the problems with companies like GM is that they still see this as a premium feature and require their hardware (not just a charger). Tesla requires not only their chargers but also their inverters and cars.
What is missing is a spec that inverters and cars and chargers can all follow, then we will see mass adoption.
CHAdeMO had that spec, but of course is obsoleted now.
If I understand things correctly tho many of the V2L solutions just work with pretty much any car that does CCS, regardless of whether the manufacturer officially supports this or not. My Polestar2 for example doesn't official have any kind of V2H/V2L option but I've heard of many success stories.
SAE-J2847 includes "how to convert your building side to supporting BPT grid works, and pairs well - it looks - with ISO 15118-20 BPT. (and reasonably well with ISO-15118-2 and the BPT extensions in SAE-J2847). Anyway, supporting AC grids requires some additional electronics both in battery systems and in the local hookups.
I haven't explored the actual space much, as I work on ISO 15118-20 for busses, and a bus as a local grid backup scales pretty well. (and even then, I work protocol level, not electrical).
> The only way I can see to do this today is with Tesla Powershare + Cybertruck, which says "If the system includes a UL 1741-listed solar system
Since this was posted Tesla rolled out PowerShare to recent ModelY and some other cars. Not sure about solar recharge though. Where I live storms come in winter and I have natgas so most of the power will go to fridges and electronics, which will hopefully last long enough.
When I was living in the PNW and had a 5 day power outage due to a windstorm, my PowerShare/cybertruck made life so much better. Nat gas water heater, furnace, and stovetop definitely helped. Had options to top up the charge too, took the kids to a play date at a house that let us charge, and I had a nat gas generator that worked well to charge the truck too.
New builds in WA state don’t get nat gas anymore though, so people will have to be a lot more careful about using appliances during an outage.
I'm not sure what the laws are like in the USA I assume they are similar to elsewhere.
However I think there are two problems here that have to be solved:
1) you need to island your house, that is, physically disconnect your house from the grid
2) once you have disconnected the grid, you then need to provide some sort of pilot sine wave to allow the plug to function.
I have an islanding system for my (house) battery and solar, so in theory, I could have a bidirectional charger whilst being off grid. However both my car and charger don't support that (my charger is also deeply shit, and has no local API access.)
The bigger problem, which is tangentially touched on, is that vanishingly few chargers can actually support islanding. It makes the installation harder, and drives up the compliance and installation cost[1]. this means that you are taping together two disparate systems together (or going all in on enphase, which also has a limited local API)
There isn't a spec for a household systems to talk together to do energy management. currently I use homeassistant to monitor the variable electricity prices, car plug status and how happy the fucking powerwall is, so that I can make sure the car charges from solar, without draining the house battery to 0, or only charge at night when the price us uber cheap (and also not drain the house battery).
The amount of sysadminig to make that work reliably means that no normal person is able to achieve it. The problem for consumers is that there isn't any motivation for manufactures to work together on this. because they want to vertically integrate.
[1] The installation cost for what is effectively a very thin software wrapper around a local contactor is egregious.
> I have an islanding system for my (house) battery and solar, so in theory, I could have a bidirectional charger whilst being off grid. However both my car and charger don't support that (my charger is also deeply shit, and has no local API access
...
> The amount of sysadminig to make that work reliably means that no normal person is able to achieve it. The problem for consumers is that there isn't any motivation for manufactures to work together on this. because they want to vertically integrate.
We are in a very similar position. The issue is every company in this area is like you say: deeply shit with limited local API access. Setting up bidirectional charging in the UK is technically, really not that hard, especially with islanding handled at the household level.
Good luck trying to get someone willing to put their career and certifications on the line to actually do it though.
Part of the challenge is finding an electrician willing to work like a sysadmin and do things because they know how they work, rather than only doing things they've explicitly been taught as in line with (dated) regulations.
Wouldn't the charge / discharge cycles reduce the life of the car battery? I presume the same is true of in-home batteries, but although an in-home battery is an extra capital expense, I imagine the replacement cost of in-home batteries is quite a bit lower, isn't it? Would be interested to know more about the medium-to-long term economics of this.
> Wouldn't the charge / discharge cycles reduce the life of the car battery?
While I'd presume the answer here is "yes", I'd also presume we're talking like a fraction of the vehicle's lifetime charge cycles. Like, (generously/conservatively) 20 to 40 cycles total over the life of the vehicle, no? How often would you estimate your power going out?
Even if you aggressively used the vehicle for this, you're talking about wearing out a ~ $5-10K battery over many years. For reference, a generator that can do this costs $10K, and would be burning way more than that in propane before the car battery wore out.
The point wouldn't be just for backup during outages. It would be growing your kWh of storage and doing daily TOU optimization. That increases the charge / discharge profile by a lot.
Though for an 80 kWh or larger battery, you're only likely to store up and discharge 10-ish per day maybe this way? (Assuming you have actual dedicated BESS, and this is supplementing that). Still that's ~30 cycles per year, which is nothing in the grand scheme of a vehicle battery.
Duh, yes, slow brain day.
I don't think that wear would be worse than driving around. Unless you go out, recharge, and come back, by definition you only have a single charge single cycle to give.
My thinking is that driving has a typical burn rate (eg 1 kWh/mile or whatever), so the battery will be designed around this load pattern. Using it as a battery backup may be pulling a lot faster than optimal and cause additional wear.
It is probably only a minor impact, but I could believe it is outside the design constraints.
driving an obese, modern EV at highway speeds of around 100 km/h uses about 20 kW.
The average house in the US and Canada uses between 2 - 5 kW around 98% of the time.
Yeah. A big EV, yeah, can pull 20 kW (29HP) continuous at 60mph (close to 100km/h ish). And much much much more accelerating! It's not continuous at all but just to say it, a 500HP engine translates to a 370kW demand!
They also have to endure enormously strong charge cycles, and in many ways that is even more difficult time for the battery. Charging at >1C (better than a one hour charge cycle), at 100kW or whatever (and many cars charge far faster)? That strongly implies a very competent discharge. Charge performance almost always trails discharge performance in batteries, signficisntly, and yet we expect huge charge capacity from EVs, thus their discharge should be even more hard to imagine huge.
These batteries in EV are all built with chemistries for huge power dense. Not tuned for energy density (storage) but tuned for power density (instantaneous output). The load here, by compare, is tiny.
GM Energy PowerShift is one of the biggest inverters you can get factory for a vehicle and will do 20kW. For reference. Perhaps we could put on a 50kW v2h inverter, power the whole mcmansion. Ignore the fact that the battery is going to last 2 hours. I think even that would be perfectly fine, no worse than a day about the town.
For something you (hopefully) don't have to do that often, it seems negligible. But if you're charging and discharging the car daily to do arbitrage you might eventually notice the degradation
Likewise, there are plenty of plug-in hybrid cars which ought to be great home emergency backup generators (ie. they have a 40+ kilowatt generator and 7+ kilowatt inverter), but very few have this functionality even if the hardware in most cases supports it and would simply require a firmware update.
I had good luck with telling claude to rewrite my laptop bios to enable various power modes which were theoretically possible but disabled by firmware, like powering a fullsize screen from the laptop battery over usbc.
Maybe I'll tell claude to rewrite the car firmware too...
I know someone that did this with an old Prius. No software hacking required. Just leave the ignition on, and wire into the high-voltage system (not at the same time, of course!). The engine auto-starts when the battery gets too low.
The more interesting approach is to do it with a used EV. You can get a 100-133 kWh car used for $20-30K. The last time I checked, that was below the price of a house backup battery with a quarter the capacity.
Be sure to alert the fire department ahead of time.
I live rural and I'm hoping the next decade will bring a wave of cheaper safer sodium ion battery options. Something I'd feel a lot more comfortable with putting in or around my home since they don't have thermal runaway issues, their materials are theoretically cheaper, and they can withstand colder temperatures.
While I'd like to use my EV as backup, the cost and integration issues right now are just not sensible. The utilities and manufacturers have made it too cost prohibitive.
LiFePO4 are much more robust against thermal runaway, omit a lot of the expensive materials that are in typical Li-NMC batteries, and have a better cycle life. They still can't be charged below 0°C, they have worse specific energy, and they generally can't handle the same peak power output, but they're a better choice for fixed storage applications IMO.
GP is referring to sodium ion batteries. They’re even cheaper materials wise (no lithium) and have even more favorable outcomes for freezing conditions.
Worse energy density and similar or potentially worse number of cycles, but that’s being worked on.
But an important difference is that LFP is available today. Expecting a dramatic shift to sodium ion anytime soon is wishful thinking. Battery tech evolves steadily but slowly.
CATL is already producing sodium ion at competitive prices. Expect 5-10 years to end up with a flood of stationary battery products based on them, at prices less than LFP.
Do you have a link to a good brief on these from an engineering point of view? Where can I buy cells, in what packaging, with what specific energy & power, peak draw, charge rate, etc etc? I do some tinkering around with batteries for various purposes and I'd love to learn more.
They'd have to beat used car battery pricing and I suspect used car batteries are going to be worth ~ $0 until recycling becomes better.
Apparently, it's almost impossible for wrecker yards to get rid of EV car batteries, even if the battery pack is still fine (but the car was totaled).
One of the biggest misses in NACS (J3400) is bi-directional power in the spec. SAE J3400/2 will fix it.
I have a Tesla 3. There’s no good way to get a lot of power out of the car as an end user except via the wheels. You can get like ~1kW of 12VDC via the dc-to-dc computer/accessory system but even that is pushing it.
I am saddened by this. I’d like to be able to access the large amount of power in it in a pinch.
There is also no good way to charge it as an end user from a DC source like my large 48VDC solar battery system. I end up having to invert the DC to 220VAC which then charges it normally (involving rectifying it back to DC for the onboard batteries) - an unnecessary and inefficient double conversion.
there are several devices that allow for 4kw+ to be pulled out of the NACS port, it tricks the car into thinking its CCS charging. Google "tesla v2h" or "tesla discharge device"
There are also older devices (for Priuses) that just tap into the high-voltage terminals of the battery pack.