alt Hacker NewsBidirectional charging during grid outages
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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.
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.
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
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.
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.
—- 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.
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.
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.
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)
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.
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.
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.
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.
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 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.
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.
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_)