Vehicle-to-Grid Made Easy

As electric cars continue to see increased adoption, one associated technology that was touted long ago that still hasn’t seen widespread adoption is vehicle-to-grid or vehicle-to-home. Since most cars are parked most of the time, this would allow the cars to perform load-levelling for the grid or even act as emergency generators on an individual basis when needed. While this hasn’t panned out for a variety of reasons, it is still possible to use an EV battery for use off-grid or as part of a grid tie solar system, and now you can do it without needing to disassemble the battery packs at all.

Normally when attempting to use a scrapped EV battery for another use, the cells would be removed from the OEM pack and reorganized to a specific voltage. This build, however, eliminates the need to modify the packs at all. A LilyGO ESP32 is used to convert the CAN bus messages from the battery pack to the Modbus communications protocol used by the inverters, in this case a Fronius Gen24, so the inverter and battery can coordinate energy delivery from one to the other automatically. With the hard part out of the way, the only other requirements are to connect a high voltage DC cable from the battery pack to the inverter.

[Dala], the creator of this project, has taken other steps to ensure safety as well that we’d recommend anyone attempting to recreate this build pays close attention to, as these battery packs contain an extremely large amount of energy. The system itself supports battery packs from Nissan Leafs as well as the Tesla Model 3, which can usually be found for comparably low prices. Building battery energy storage systems to make up for the lack of commercially-available vehicle-to-home systems isn’t the only use for an old EV battery, though. For example, it’s possible to use Leaf batteries to triple the range of other EVs like [Muxsan] did with this Nissan van.

37 thoughts on “Vehicle-to-Grid Made Easy

  1. I wouldn’t have thought of doing that!
    That is some out of the box[y car] thinking.
    Even though it is already weather proof, I think it should have additional protection.
    (Though that might be my OCD talking)

        1. Or at utility scale, stacked on pallet racking in a 40′ shipping container. Look up the battery that Tesla built in Austrailia. Since you have to move it, space and weight matter for over the road use. Stationary use, not so much. If it just going to sit in your crawl space, the fact that that used batteries were 1/4 the price of new, more than compensates for needing 25% more cells.

  2. “these battery packs contain an extremely large amount of energy”
    Yes, about as much as a whole liter of gasoline!

    But seriously, great project, but what are the economics of this? That $3k battery can do a few thousand partial-discharge cycles, so say (generously) a total of 30,000 kWh, or $0.10/kWh. Maintenance and cost of money on the inverters and other hardware might double that.

    If you’re in the business of buying and selling the electricity, you’d need a $0.20/kWh differential to make this pay.

    But it would be great as a storage solution to NOT sell your solar-generated electricity to the grid (and so not to need to buy it back later), which is what the intent appears to be.

    1. These batteries have shown that they can do far more cycles than that. And they don’t just reach a point and stop working, they just slowly get worse. Still very useful. Despite electric cars being in common use for well over a decade, you don’t see hundreds of thousands of battery packs in scrap yards. There’s a reason for that – they’re still in the cars and the cars are still working.

      The trick is with maximising life is keeping the battery within a safe temperature range, which will be a challenge in some climates

      1. You’re right. Hopefully, keep safe working temperatures is much more easy in a building in the shadow than in a car in the sun or in the winter. Leaf batteries pack have water cooling pipes for heat exchange, so you can probably reuse a (scraped) pump and a (scraped) car sized radiator to spread it outside the building without any worry.

        1. I happen to know that at least one Tesla model also uses water cooling; however, they treat the entire pack as a single field replaceable unit, so if you have a 75 cent connector on the pack’s water cooling system break, they’ll want upwards of 15-18 grand to replace the entire pack, but isn’t very green. :(

          1. That is 100% false statement. They all use liquid cooling, and if you have a 75 cent part fail, they replace that part. If you have one of the banks fail, they replace only those banks if you are paying. If its warranty, they swap entire pack.

      2. > they don’t just reach a point and stop working, they just slowly get worse.

        That’s true, but misleading.

        They get worse slowly, until they hit the point where the SEI layer of the electrodes gets clogged up and then they get worse a lot faster. The end life of batteries that have already degraded by 20-30% is a nose dive towards zero capacity.

        1. That paper seems compelling yet there are batteries in the wild that have done more than 250 cycles. Their test procedure states a lower cutoff voltage but not an upper one. The pessimist in me wonders if they overvolted and cooked their batteries on the charge cycle by trying to cram 0.9Ah into a battery with 0.8Ah capacity.

          Got any other battery degradation papers?

        2. Their charge/discharge methods must have had some flaw. Our giant Lithium battery has done the equivalent of 391 full cycles and still retains 93% of rated capacity. In fact, most of that capacity loss occurred in the first 100 cycles. Since then the loss has tapered off.

          Not following the proper dis/charge will definitely roach your battery.

    2. I mostly agree with bootstrap, the car battery pack should last relatively well – when there are EV makers out there still offering huge mile counts and many years of warranty before the capacity drops usually more than 10% from new it is a very safe bet that battery and its BMS will not fail in a hurry from this use.

      Most EV seem to get 100,000 miles of warrenty for the battery capacity – which at around 3kWh a mile – a fairly common ballpark for most EV means that total of yours is about the ballpark before the battery may be considered out of warranty for failure, but odds are very good its still at a very high max capacity – just perhaps getting close to dropping down to that lower threshold on the warrenty for battery capacity. As they don’t want to bankrupt themselves with lots of failures and the tech is relatively new those numbers are probably very very conservative form the EV makers…

      Also remember electric isn’t dirt cheap in the EU etc…

      1. You have the consumption backwards. Most sedan sized EV can manage 4-5 miles/kWh. A 25 kw battery wouldn’t get very far at 3kw/mile. (That would mean a sub 10mpg equivalent, compared to the 100-130 mpg equivalent they are actually rated for)

        1. Opps. Right you are, did the math correctly but the units are indeed reversed in the text should have been 3 miles per… So the 1/3rd of 100,000 mile warranty to get the manufacturers warranty on battery capacity loss lifespan is in the ballpark of the OP’s entire ‘lifespan’ in energy throughput.

          I was being deliberately on the harder side on EV efficiency as many an EV or PHEV are not built for ultimate economy – they are still the larger boxy SUV type vehicles – its about right for the commonly on the road average still. But the point still stands.

        1. Looking across the many brands I can see here most warranty the battery capacity to some extent usually 10% drop from rated capacity it seems. And most have both a calendar and mileage limit for the warranty, which is usually 8-10 years or 100,000 miles. So its a good ‘universal’ guess for the many brands out there, but they are far from all the same warranty terms though! There are unlimited miles and only 5 years out there.

  3. In the aftermath of Fukushima, a variant of this was used to power some neighborhoods until wires could be restored. This was done in places where there was accessible power ~15 km or less away.

    An inverter that could plug directly into the high speed charging port was installed by a small cluster of residences. An ordinary Leaf drove up, and connected to the inverter, providing power. When it’s battery started to get low, a driver in a freshly charged leaf pulled up, and moved the cable. They drove the now depleted car to the charging station to refill. Lather, rinse, repeat.

    Oh yea, a liter of gasoline contains 9 kWh of energy.

    In fact, battery packs from scrapped EV are very popular with the off grid power crowd. A lithium pack is a whole lot lighter than the prior standard of deep cycle golf cart or forklift batteries, and don’t require regular visits with watering can full of distilled water to top the cells back up.

        1. Then you would have to listen to the generator all night. This solution is effectively silent by comparison.

          And while that liter of diesel may contain 10 kwh of energy, when the generator finishes dumping most of it as heat out the radiator and tailpipe, you wind up with about 2.2-2.5 kwh of actual usuable power. A current generation leaf would have about 55 kwh available for this scheme so 25-30 equivalent liters of diesel per trip. Still a fair number of trips, but not as bad as first imagined.

        2. In emergency situations you probably don’t have 1000 litre of fuel to spare anyway. As those big digger etc that tend to be required in the recovery operations eat fuel at a huge rate. But some folks with no currently more important job and a spare EV fleet to cycle around is easy to find (at least for them at that time) and keeps the lights on. Not even bad efficiency wise as that generator almost certainly sucks massively compared to the much much bigger grid powerstations.

  4. Hi! Very nice job.
    How did you find the CAN protocol and the switch sequence?
    Did you use a CAN spy? Or you have the good contact in Nissan? :)
    Because it doesn’t look standard yet and complicated.

      1. Wonderful project! You’ve illuminated several things I didn’t even know that I didn’t know, so thanks for that. On your HV diagram, you drew a fuse on the black wire instead of the red. Is that on purpose or a small mistake? I normally think of black as an uninterrupted ground path, and red as positive with all the switches and fuses. Thanks for sharing your talent!


  5. Is this really vehicle to grid??? Can I hook up my bolt and it works the same? If not, this is just another backup battery that you have to charge from the grid or solar.

  6. I saw what my power company pays for electricity returned to the grid, and after that I’d say you are a right idiot if you return power to the grid, and double so if it also degrades you batteries in the process.

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