![Maker [Dala] showing powerwall statistics](https://hackaday.com/wp-content/uploads/2024/08/diy-batteries-800.jpg?w=800)
As battery-to-grid and vehicle-to-home technologies become increasingly mainstream, the potential for repurposing electric vehicle (EV) batteries has grown significantly. No longer just a niche pursuit, using retired EV batteries for home energy storage has become more accessible and appealing, especially as advancements in DIY solutions continue to emerge. Last year, this project by [Dala] showcased how to repurpose Nissan Leaf and Tesla Model 3 battery packs for home energy storage using a LilyGO ESP32, simplifying the process by eliminating the need for battery disassembly.
In the past few months, this project has seen remarkable progress. It now supports over 20 different solar inverter brands and more than 25 EV battery models. The most exciting development, however, is the newly developed method for chaining two EV packs together to create a single large super-battery. This breakthrough enables the combination of, for example, two 100kWh Tesla packs into a massive 200kWh storage system. This new capability offers an accessible and affordable way to build large-scale DIY home powerwalls, providing performance that rivals commercial systems at a fraction of the cost.
With these advancements, the possibilities for creating powerful, cost-effective energy storage solutions have expanded significantly. We do however stress to put safety first at all times.
Hungry for more home powerbanks? We’ve been there before.
How the battery packs are obtained? Are they discarded? Brought at auction? I am curious how those 2 100kWh Tesla packs came from. Thanks
They may be obtained on eBay, about $4,000 per 60KWh. They seem like a good deal, but significantly larger and heavier than standard 48V 5KWh rack mounts.
eBay, Ok. But how the batteries turn up in eBay?
More than zero, obviously.
4 tweakers with angle grinders while you’re parked in a public garage;)
1) tweakers, angle grinders and a big NMC battery in a garage are a very bad combo
2) simply unbolting it would be faster
3) at around 400kg, 4 tweakers are not lifting it
You greatly underestimate the drive of tweakers when they’re…. tweaking. lol.
Packs come from crashed/totaled cars and are sold by scrapyards who disassemble cars.
When there are battery issues, the EV manufacturers only seem to do replacement as a whole module. This is also why people get upset about $30k for a new pack, out of warranty. Often it is only a few degraded cells that need to be replaced, so there is a recycling/salvage market for the “bad” EV packs. I’m not sure the exact business exchange, but we (hobbyists/hackers) can buy as-is packs and used cells from these specialty businesses. For example, jag35.com (US, west coast) and batteryhookup.com (US, east coast). I have no association, other than being a customer of both.
Fascinating project and a really effective way to kill two birds with one stone – waste batteries from EV and reducing cost of home-harvested solar.
Any electrical engineers or electricians able to chime in on the safety risks / level of expertise needed for the average joe to dive into this?
Here in Australia, this would be a regulatory nightmare to undertake being that practically all work above ELV levels is prohibited without an electrical license.
It’s not really worth it. You don’t know if it came from a vehicle involved in a high-speed accident and is hanging on by a thread on the insides.
You can check the State-of-health and individual cells and cell balance before deciding to purchase a battery. But if you buy one sight unseen, it is always a bit of a gamble. But oh so worth it!
It is moderately dangerous. 400VDC is far more dangerous than 240VAC, the highest voltage most DIYers deal with. You need different breakers, different fuses and different levels of insulation. (Standard SOOJW for example will not work.)
It is also moderately difficult. You will need to be familiar with basic wiring and soldering, and must be able to set up the Arduino environment for the somewhat unusual ESP32 board they use. And the wiring needed for the CAN breakout board is not straightforward, and may require some additional soldering depending on how you do it.
Finally the system is somewhat sensitive to ground loops, so you have to understand them before working on this.
It’s one of those things where if you have to ask, it’s probably not a good idea to try it.
“It is moderately dangerous. 400VDC is far more dangerous than 240VAC,”
The electrical risk is a lot less than the fire risk. I mean, OK, the electrical risk is bad, but you can learn about it and there are simple steps you can take to protect yourself (work one-handed, for instance).
The fire risk is just there. Big battery farms manage it via a lot of different ways, but the fact that one of them is “isolate them so a fire can’t spread once it starts” should tell you something.
This isn’t necessarily a fundamental thing – eventually you’d hope that battery tech can get to the point where they fail-safe, and it’s definitely being worked on. But it’s not there yet.
Questionable battery packs in ones garage, basement or attached to the house.
What could go wrong?
Yes, there’s a reason big battery parks are built from steel containers and have a lot of separation between banks. And yet, fires happen there as well.
The risk of a fire is probably not significantly more than the many other sources of fire in a house, but the bigger issue is putting it out (and its contribution if another fire starts). I wouldn’t be surprised at all if this voids a home insurance policy.
200kWh seems really massive for a regular house (with say ~20kWh per day energy usage).
That said, in the winter for a couple of weeks my solar array doesn’t cover all my daily usage (not enough hours of sun), having a 200kWh battery would likely help cover most of that deficit.
I wish my energy usage was 20kWh. My hottest and coldest months average to 80kWh per day for a ~1200 sq ft space, although spring and fall are lower. It’s partly because the summer heat is intense and cooking adds to the heat that must be removed, and partly because the oven, water heater, hvac heater, and dryer are all resistive electric and the pipes even require portable heaters when it freezes.
Past-their-sell-by-date car batteries bolted to the wall of your garage?
I would think that if you have room for a garage you have room to build a detached enclosure for them.
Yup. Spend the extra couple thousand to trench to a battery shed at least a couple dozen feet from any structures.
I have a garage, but the yard itself is not large enough for “a couple of dozen feet” from all other structures.
Not everywhere has the space that you have in the USA or Australia.
I live in Germany. The entire plot for the house is smaller than the backyard of most houses I lived in as a kid in the USA.
You probably should not be playing with big battery packs in your case. Just like people in the city should not fill 55 gallon drums with gas and keep them around the house.
I owned a house on a small quiet street, another small quiet street led into it, and had a stop sign turning onto my street. I owned the second house from the corner.
Our city had a truck with a guy that had a side post car battery in the back, some jumper cables and a can or two of starting fluid and a couple metal 10 gallon gas cans. If one of the city mowing crews got disabled, the mower would not start or what not, they would call him out. I think he also may have topped off the gas in them.
One fateful day, he came down the side street next to my street and stopped at the stop sign and turned the corner. He saw flames in the back by the time he got in front of my house, and jumped out of the truck. By the time I got there the fire department had the whole street and much of the front of my house covered in foam and there were flames so high the power company was a bit concerned they may have taken the wires to my house down. In the end there was nothing left of the truck that could not be burnt. Not a trace of a tire, not a trace of a seat, not a trace of any plastic at all. When it was burning it was sending out flaming pieces of the paint as it bubbled off. Black clumps of crap all over the road and the house.
As you may have guessed, the guy came to a stop at the stop sign and either the battery slid into the gas or the gas slid into the battery, with enough force for the side posts to just scratch through the paint and into the metal. That instantly welded the tank to the battery, melted a hole in the side of the tank and boom. And it all happened within a few seconds. He probably went out like that thousands of times before but this time…
I’m not “playing” with big battery packs.
I have a professionally installed, commercially produced 7kWh lithium-iron battery in my garage connected to my professionally installed solar power system.
I’m as much for DIY as anybody, but I also know my limits and the limits of the law and my homeowner’s insurance. If my professionally installed system goes “bang,” I’m covered.
Anything I might have cobbled together would cause the insurance company to deny the claim, and might even get me hauled before the court for endangering my neighbors.
Saving a few thousand Euros is not worth the risk of losing my entire house.
“I’m as much for DIY as anybody, but I also know my limits and the limits of the law and my homeowner’s insurance.”
It’s not just the legal and risk limits. If you do electrical work in your house, obviously there’s significant risk there, but you can mitigate it by learning the proper way to do things, researching, finding help, etc. It’s manageable.
You could extend this to, say, doing DIY work on a car with junkyard parts. Even though you don’t know the entire history there, you can do research, inspect, and test parts again and reinforce. Again – it’s a solvable problem.
The problem with salvaged battery packs is that the safety issue is not solvable. Go ahead. Research it. They do not know how to detect overstress conditions (lithium plating, dendrite formation, etc.) without destructively tearing down the packs.
These vehicle-to-grid ideas are incredibly short sighted.
Batteries have a limited number of charge cycles.
Vehicle batteries already die well before the rest of the car, even when treated optimally.
See the problem here?
This isn’t a “Oh hey! Look at these free batteries! I could get free energy storage!” situation.
Those charge cycles aren’t free.
If we estimate 4 charge cycles a week from driving, being careful to stay within the optimal 25-80% charge range, we get 6-10 years of use in a good climate (above freezing).
If a vehicle-to-grid situation uses even HALF those charge cycles, which would be so little storage that it wouldn’t be useful, your battery is only going to last 66% as long before replacing.
As another source of power in an emergency? Absolutely. If it could replace the 16-24h a year I run a generator to keep vital systems running during a power outage, it would be worth me installing the hardware.
But for daily use?
Absolutely not.
I don’t know what you are talking about, but your are wrong in your computation. First, the battery used aren’t End Of Life vehicle’s battery. They are battery saved from destruction because the mechanics don’t want to pay for the (required) certification to work on EV vehicle, so the only few who do charge so much that the vehicle is discarded instead of being repaired. The battery are often very new or close to new.
The vehicle battery are WAY safer than the battery used in home storage. The constraint on a vehicle battery are a lot higher than in a garage or attic. Thus they are certified to work on automotive temperature range (-15°C / 65°C), while the one you buy at your solar shop only support (0/40°C) range. They can handle a shock and are usually mounted in a very rigid and solid metallic enclosure (unlike the plastic case for consumer’s solar battery).
The number of cycle of a Li-Ion is so high that the electronic will simply fails earlier than you’ll have exhausted your battery. It not unusual to have 3000 cycles on such technology, so for a 60kWh, it’s
180MWh of energy you can draw from the battery. If you draw 20kWh from your battery every day, you’ll be able to do so for 9000 days, or 24 years.
And even then, the number of cycle is computed as when you can only draw 80% of the nominal charge, so even after 24 years, you’ll still be able to draw for a lot more cycles (and hopefully, since the appliance in your home will become more energy efficient by that time, you can expect not to need 20kWh per day, but on 16kWh per day).
If you can draw 20kWh from your battery anyway, it means that your solar source can fill that up usually. So you’ll likely draw a lot from your solar current when it’s available anyway.
” If you draw 20kWh from your battery every day, you’ll be able to do so for 9000 days, or 24 years.”
Battery life isn’t actually purely cycles. Batteries have multiple aging mechanisms, and one of them is calendar aging. They just get old, period – and worse, with lithium-ions, they tend to age faster at high SoC – so if you’re imagining oh, this car wasn’t used a lot, the battery will be great: nope.
“so even after 24 years, you’ll still be able to draw for a lot more cycles”
Wait, you think a battery that’s severely internally degraded is perfectly OK, just a smaller battery?
It’s not like an SSD or something that just says “ok I won’t use this part.” It’s physically changing. The electrodes are degrading, completely – cracks form, bits break off, etc. And you have no way of knowing how safe the battery is at that point – you could be lucky and everything’s aging nice and safely, or the next time you discharge it, a cell goes into thermal runaway and the whole thing collapses.
It’s not fearmongering. It will fail, and the deeper into aging you go, the more risk you accumulate.
Please produce proper documentation of your fearmongering claims, because they currently aren’t worth the electrons they’re printed on.
I’m not sure why this is even in question? My proof is…every car on the road?
The body and drivetrain of a car/truck is good for 20+ years.
If you want to know how long the vehicle manufacturers think their batteries will last,go look at their warranties. Most guarantee 70% capacity at 100k miles or ~8 years, which ever comes first, under ideal conditions.
That’s not 20+ years.
Even if you want to use the average number of years a car stays on the road in the USA, which includes vehicles “retired” early due to crashes, that is still ~12.5 years. Which is 50% more than ~8.
Anecdotaly, I have 7 friends/acquaintances who have been driving plug-in hybrids or fully electric vehicles for over a decade. All but one have had to replace a battery, or the vehicle (due to a battery replacement costing the same $$) within that time. Climates range from “it rains every day at 11am” Florida to “your pee will freeze before it hits the ground” North Dakota.
My current vehicles are both over 20 years old (1998 and 2004), but I drive less than 1k miles a year between the two. Bad gas mileage doesn’t mean much when you use ~4 tanks of gas a year(~50 gallons/200 liters).
I’m not against electric vehicles at all. We NEED to be transitioning away from ICE in addition to driving less in general.
My next vehicle will almost certainly be an electric, likely a used one with the plan to replace the battery. It just makes no sense to switch now. Maybe Sodium cells will be mature enough by the time I need to replace them.
“If you want to know how long the vehicle manufacturers think their batteries will last,go look at their warranties. Most guarantee 70% capacity at 100k miles or ~8 years, which ever comes first, under ideal conditions.”
Most vehicles have a similar warranty for the mechanicals. This doesn’t mean the vehicle is expected to die, it means the accountants figured out it would be too expensive to provide a warranty after this point.
I will agree that the battery will generally expire before the vehicle itself. However, some vehicles like the Prius have a robust aftermarket community that can provide reconditioned batteries at a nominal cost (at least in the SF Bay Area).
“Most vehicles have a similar warranty for the mechanicals.”
No, that’s what’s given out when you buy the car. You can buy extended warranties on vehicles that will last longer: it just costs money. Tesla doesn’t offer any way to extend out a battery’s warranty, and I don’t know of any third-party that will, either.
And the reason for that’s just economic – not only is the battery replacement cost high, there’s no guarantee it will be possible in a factory-spec way (see older Leafs).
“However, some vehicles like the Prius have a robust aftermarket community”
This… kindof proves the point that the battery outlasts the vehicle. It also stresses the difference between an easily-replaceable battery and a virtually impossible to replace one, like the frame-integrated ones many EVs are planning.
And in addition while there’s definitely aftermarket batteries available, you can just… buy an OEM one, because Toyota still provides them.
But your own argument fails when you consider the length of warranty given on ICE vehicles; Mercedes give 5yrs now I think but many are still just 3 years and some of those are expensive vehicles.
Are you trying to say that Mercedes think their engines will only last 5yrs then?
Most literature that I’ve read, that HASN’T been in the scaremongering press, says that the motors and probably batteries too, will outlive the bodywork etc of the car.
Yes there will be some exceptions, just like ICE engines that have problems (I’d rather have my EV than any Ford with the Ecoboom ICE engine!)
It seems that your understanding in this area is very limited, based on rumors and myths. Batteries in electric cars with battery heating/cooling are able to last over 10 years, losing less than a third of their original capacity. And that’s when working in harsh environmental conditions (e.g. 2C charging, 4C discharging). Even a Nissan Leaf with neither heating nor cooling manages to last 10 years as long as it has not been operated in very hot or very cold climates. Even after its capacity is no longer enough for an EV, working with a solar inverter will be a very easy task for such a battery. Nobody forces you to buy a dead one, suitable only for recycling. Those with a bit knowledge can check the condition of the batteries before buying and have 5-10 times more capacity than Tesla Wall or rack-type units for the same price. But again, it’s great that there are people like you, because it allows people like me to get batteries at a very attractive price :)
Using expended EV batteries for grid-scale storage is fine. They’ll die randomly over time, but you design the system so that the risk is physically contained. Even if it goes into thermal runaway, whatever, you just let it burn out and replace it.
Using them at home is entirely different.
“Those with a bit knowledge can check the condition of the batteries”
Yeah, that’s fooling yourself. Batteries don’t just lose SoC: they’re physically internally changing, and you can’t tell what they’re doing. There are people out there doing serious studies to figure out if there are any other indicators you can pick up from the battery over time. It’s not just someone sticking an Android app and saying “no it’s good!”
This isn’t fearmongering – even if you’re willing to take the risk, the issue is that the company that insures your home might not be! I mean, c’mon, a lot of these companies have clauses that if you disable the latch security on a self-cleaning oven it freaking voids – you think they’re going to be OK with you sticking a battery you bought on eBay in your basement?
Read my argument. I specifically call out Vehicle-to-grid.
Buying a dedicated battery, used or new, has nothing to do with my argument.
Reuse is important. If a battery which is too degraded can be safely reused before being recycled, go for it.
Though, the highlighted project isn’t what I would consider “safe”…
The biggest hurdle the uptake of this idea would have in my area is the lack of available EV packs on the used market. Why? Because those batteries are still in the cars, still working and yet to enter the “waste stream”.
EV batteries are far more durable than you describe, and the use case for a powewall battery is light duties compared to being in an EV
The article and source material specifically call out Vehicle-to-grid. Not simply a “power wall”.
That is not “light use”.
The idea of Vehicle-to-grid is to use many vehicles to store excess energy during peak grid generation with low loads, then feed that energy back into the grid later. Basically, a city with solar/wind uses 10k cars to store energy INSTEAD (or in addition to) a grid scale battery.
“Batteries have a limited number of charge cycles.”
I don’t know why people constantly focus on charge cycle count and capacity fade (SoC drops). Maybe it’s because you can measure both of them, and any time there’s something you can monitor some people obsess over it?
It’s physical degradation. The solid electrolyte interface (SEI) layer is thickening, there are dendrites growing, and bits of the electrolyte fracturing off (particle fracture), etc. Capacity fade is actually probably the least concerning age mechanism. The people who study batteries do crazy stuff to monitor things – they build batteries with windows, gas chromatography, and teardown the batteries over time studying them with AFM/SEM. There’s a ton of active research on this.
Eventually you might get to the point where you only have to worry about capacity fade, but right now, with older batteries… yeah, no.
You’ve repeated yourself three times in the comments, so I’ll paraphrase what @pelrun asked of @Ian: if you’re going to make the statement of physical battery degradation, an actual link to a study would be helpful. Otherwise, it looks a bit handwavy.
Sure: there’s an open-access review of study of safety issues for aged batteries here:
https://iopscience.iop.org/article/10.1149/1945-7111/ab89bf
This is only from about 4 years ago, and they specifically highlight the fact that it’s a difficult topic because age acceleration is typically done.
“I don’t know why people constantly focus on charge cycle count and capacity fade (SoC drops). Maybe it’s because you can measure both of them, and any time there’s something you can monitor some people obsess over it?”
Well yes, you are right that physical degradation is the problem. This degradation can be considerably accelerated however by usage (including charge/discharge) pattern according to everything I researched before I bought my LiFePO batteries several years ago. I think what most people miss is that charge cycle count is not just charging it then using / discharging it. It is based on a curve of charging at x Amps and x Volts over y time and discharging at x Amps over y time down to “0” volts (somewhere actually around 10V for a “12” V pack for example, ignoring environmental conditions). Simplified example is using your laptop on battery or a cell phone battery every day that says “200 cycles” for a small fraction of its rated Ah capacity and charging it every night will not result in it being bricked in 200 days. Shallower charge/discharge will lessen the degradation from use. There is a whole family of curves related to the lifetime of a li battery. If you want to kill it (cause excessive degradation) faster, charge it at higher than the rate recommended and discharge it to zero faster than recommended, as often as possible, or leave it on a charger where nothing turns off the high charging voltage after it is charged (float charge).
While driving an EV recklessly, or bad battery pack construction could abuse a battery I suppose, I would think getting a 100kW pack with 50kW left and discharging a small fraction of it every day would last a long time especially if rates of charge and discharge were lower that spec. I searched all over the place for info but I only remember a couple like “battery university” and “dakota lithium” I think were a couple that showed fairly good info.
” I would think getting a 100kW pack with 50kW left and discharging a small fraction of it every day would last a long time”
No, I disagree. This is what I was trying to stress: first, batteries also age just by, well, aging, and capacity fade (so here 50 kW/100 kW = 50% loss) is not a proxy for “how close the battery is to total failure.”
A lot of capacity fade is driven by SEI layer growth at the anode just due to electrochemical interactions with the electrolyte. But the most dangerous ‘aging’ on a battery is either lithium plating or physical damage to the electrodes, which can cause growth which can puncture the separator and short-circuit the cell.
And that you can’t really get from just capacity fade/state of health. In some sense you can’t get it at all since the critical safety aging stuff isn’t well understood at all.
So what? When it’s finished just buy another for $3000 in twenty years time! So many arguments over nothing! Cheap battery, use till finished, replace with cheap battery!
Your computation of how many cycles a battery can last when going 25-80% doesn’t seem reasonable. If the cars these batteries came from had consumed an amount of energy equivalent to your 4 complete cycles per week when driving, the product of 200 by 4 is 800, so that should be somewhere in the realm of 3000 miles per week split between the cars you pulled them from, which appears to be two. So these people must have been driving a lot more than average, because the average is more like 300 miles not 1500.
If you always limit yourself to between 25% and 80% when using whatever batteries you get, then if you only do it once a day you consume a total of 7*55% = 385% after a week, not 400%, but it’s close enough I guess. And even then, by staying within 25 and 80, you magnify the total number of cycles it will survive because that’s gentler than the rating is determined by. And you consume the energy equivalent of 55% of a cycle per day, not a full cycle. So if they’re a shorter life originally, say 2000 cycles, and you get them when there’s about a thousand left, but you treat them gently enough to get two thousand out of them and then you only need about half a cycle a day, that’s still enough cycles left to get years of use out of it until there’s a better replacement.
Decades ago I read an article in an Australian Alternative Lifestyle magazine (‘Grass Roots’ I think it was) about some bloke who put together his own off-grid battery.
It was made from dozens of old discarded lead-acid car batteries hooked together in series and parallel. He obtained The batteries free from car repair garages, where they had been replaced due to lack of starting grunt.
The batteries were spaced on shelves in a small purpose-built well-ventilated shed well away from the main dwelling on his property. When the batteries were run down even for his application he took them back and exchanged then for more “new” ones.