Bidirectional charging during grid outages
jefftk.com
jefftk.com
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_)
Lots of tutorials on YouTube.
https://www.reliancecontrols.com/products/reliance-controls-...
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.
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.
Dinosaurs contributed an infinitesimal fraction of the biomass that is needed for the fossil fuel reserves.
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.
I think the more interesting comparison is generators vs solar, though it depends on the local weather etc.
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.
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.
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...
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.
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.
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.
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.
AC needs electricity for the cooling itself too - lots and lots.
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.
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.
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.
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...).
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.
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.
Would take longer than 20yr at current power rates in many US locales.
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.
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.
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.
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.
It’s about as bad faith as the argument can get.
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.
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
If you then add some solar into the mix, it doesn't sound as dramatic anymore.
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.
For Christ’s sake a natural disaster just struck and you want to live like nothing happened? The entitlement is unbelievable.
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 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.
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.
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.
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…
Also wrestle with how much I can depend on solar.
If only 100KWh of battery capacity was practical…
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
Or what? Are you made of salt or sugar?
EVs have 60kWh+, which should get you through a week (if not two) easily.
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?
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.
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.
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.
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?
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.
Someone will make it work.
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.
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.
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.
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.)
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.
Sure you can set a loftier goal and spend tens of thousands of dollars and countless hours solving it. Most people won’t though.
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?
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.
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.
I presume it is a hardware revision, like how Tesla removed radar.
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.
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.
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.
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".)
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.
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.
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.
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).
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.
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.
But naturally the situation is they want to be the ones paid the big bucks for such services.
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...
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.
What is missing is a spec that inverters and cars and chargers can all follow, then we will see mass adoption.
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.
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.
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> 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.
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?
It is probably only a minor impact, but I could believe it is outside the design constraints.
The average house in the US and Canada uses between 2 - 5 kW around 98% of the time.
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.
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 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...
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.
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.
Worse energy density and similar or potentially worse number of cycles, but that’s being worked on.
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).
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.