Used EV Vehicle Battery as Solar Storage

[HedgePig]

Hello forum!

Inputting a search for 'EV battery solar storage' brings up plenty results for people using their EV car batteries to store excess solar power, but they are still using their car as an EV car.

I am in the UK and am in the late stages of fitting a solar panel array and since I have space, I can add as many panels as is appropriate. However, since the government feed in tariff is insultingly low, for the moment I am only putting in a straight solar only system with no storage, to meet my daytime needs (home office) and not much more. I have excellent south facing space.
However, with a few additional panels I can generate a decent excess and divert that to a battery/storage.
A little investigating has left me understanding there are 2 clear options, but I am interested in a 3rd.
1) Buy an assembled off the shelf battery storage solution. I am rounding off here but a 5kw battery costs about £3,000 in the UK. To me this is crazy! My whole array is costing less.
2) Buy individual LiPo cells as I did with the panels from legitimate sources in China for a lot less and build my own. In round numbers I can expect to build about twice the commercial capacity (so 10kw) for about £2,000. Twice the size for about 2/3 the price. Better, but still not compelling.

Enter option 3.
It's hard to ignore the value in 2nd hand/used EV (electric vehicle) batteries. A few examples:
A really neat, nearly new 1.3kw VW eGolf/BMW i3 battery is only £125. Buy 4 of those and I would be spending about £500 on the batteries for a 5kw 'set'.
A full 13kw Mitsubishi Outlander EV battery, I can pick up for about £1,400.

I am in a technical field as a career and I am not so naive as to believe its a simple interface between the battery and the inverter, but a quick google seems to indicate that there are compatible BMS (battery management systems) like SIMP which are capable of communicating effectively with a large number of EV batteries by BMW and VW and even Tesla. Right down to individual cell management with temperature and charge state etc.

All the usual caveats in place, I have no desire to turn myself into a crisp but I am genuinely interested to know if anyone has done anything like this or even if it is possible?
Can I use a second hand EV battery to store my excess solar power and how do I find out more?

 

[400bird]

Enter option 3.
It's hard to ignore the value in 2nd hand/used EV (electric vehicle) batteries. A few examples:
A really neat, nearly new 1.3kw VW eGolf/BMW i3 battery is only £125. Buy 4 of those and I would be spending about £500 on the batteries for a 5kw 'set'.
A full 13kw Mitsubishi Outlander EV battery, I can pick up for about £1,400.

It's been done. Plenty have used Chevy Volt batteries, I think that's the Opal Ampera over there.
I'm using Chevy Bolt batteries.
Nissan Leaf cells were very common for a long time.

When I was doing the shopping and planning for my build, I spent a long time looking at things like an i3 or 530e/740e (or whatever, BMW hybrid from the 2015 era)

The issue I ran into was they are typically not in a configuration well suited to match a storage inverter. The common options are 12s and 16s
With these lipo/nmc cells 12s the low SOC voltage is below the min threshold for many inverters. At 16s, the high SOC voltage is above the max voltage for most storage inverters.
From memory, both left something like 30% of capacity unusable.

It's a great idea, just be aware of the voltage ranges when selecting components.

I was able to purchase a complete pack and tear it down. That saved some money and also meant that I had all the electrical connectors. It worked out well.

 

[Hedges]

Most EV batteries are a serious fire hazard. To the extent LG is spending $2,000,000,000 to replace the once they sold Chevy for use in the Bolt. And recalling (at least some) of the LG branded RESU powerwalls.

BMS is a key protection against over-charging the batteries, but defects have also resulted in fire.

LiFePO4 is much safer but not completely. If using any other lithium chemistry, suggest keeping it where a major fire wouldn't cause any harm. By the way, they can't be charged while below freezing, either.

Some people here do have repurposed EV batteries in their home or vehicle.
Some brands have degraded rapidly, because manufacturer didn't manage cell temperature as well. Others have extremely long life.
Many surplus sellers will praise the brand they have in stock. Get other opinions elsewhere.

New reject LiFePO4 batteries are available from China, didn't make the cut for electric busses. There are shady and good resellers of those. We have some trusted vendors with stock in U.S. warehouses. Those, and "server rack batteries", may provide power for $0.05/kWh of cycle life. Server Rack could be 48V (nominall) 100 Ah claimed 6000 cycles, $1600. Loose cells 280 Ah 3.4V, use 16s + BMS for around $2000, 13 kWh. You can read about both approaches on this forum.

 

[HedgePig]

It's been done. Plenty have used Chevy Volt batteries, I think that's the Opal Ampera over there.
I'm using Chevy Bolt batteries.
Nissan Leaf cells were very common for a long time.

When I was doing the shopping and planning for my build, I spent a long time looking at things like an i3 or 530e/740e (or whatever, BMW hybrid from the 2015 era)

The issue I ran into was they are typically not in a configuration well suited to match a storage inverter. The common options are 12s and 16s
With these lipo/nmc cells 12s the low SOC voltage is below the min threshold for many inverters. At 16s, the high SOC voltage is above the max voltage for most storage inverters.
From memory, both left something like 30% of capacity unusable.

It's a great idea, just be aware of the voltage ranges when selecting components.

I was able to purchase a complete pack and tear it down. That saved some money and also meant that I had all the electrical connectors. It worked out well.

@400bird Thank you for the quick reply!
Forgive more obvious questions but where would I start?
You say I need to ensure I match the voltage ranges, how do I do this and what are some specific examples I should look out for? There are a huge range of EV batteries for sale online, many with guaranteed states of charge.
One thing I was thinking about last night as I lay in bed, was a car EV battery that is only producing 75% of its new output would be considered 'broken'. Of course if thats something like the Volt (Ampera) battery thats still as pretty impressive 14Kw or so! I would be delighted with that sort of capacity. I'd be happy with 40% of that!

Where do I start? And again I apologise for asking what are very rudimentary questions. HP.

 

[HedgePig]

Most EV batteries are a serious fire hazard. To the extent LG is spending $2,000,000,000 to replace the once they sold Chevy for use in the Bolt. And recalling (at least some) of the LG branded RESU powerwalls.

BMS is a key protection against over-charging the batteries, but defects have also resulted in fire.

LiFePO4 is much safer but not completely. If using any other lithium chemistry, suggest keeping it where a major fire wouldn't cause any harm. By the way, they can't be charged while below freezing, either.

Some people here do have repurposed EV batteries in their home or vehicle.
Some brands have degraded rapidly, because manufacturer didn't manage cell temperature as well. Others have extremely long life.
Many surplus sellers will praise the brand they have in stock. Get other opinions elsewhere.

New reject LiFePO4 batteries are available from China, didn't make the cut for electric busses. There are shady and good resellers of those. We have some trusted vendors with stock in U.S. warehouses. Those, and "server rack batteries", may provide power for $0.05/kWh of cycle life. Server Rack could be 48V (nominall) 100 Ah claimed 6000 cycles, $1600. Loose cells 280 Ah 3.4V, use 16s + BMS for around $2000, 13 kWh. You can read about both approaches on this forum.

Hi @Hedges I'm HedgePig! We could be related!

Thanks for the reply. So it is your position that there is perhaps too much risk you are taking on by looking at EV batteries and as long as you are buying LiFePO4 batteries from reputable sources it should work out cheaper?

 

[PlaneBatteries]

Most EV batteries are a serious fire hazard. To the extent LG is spending $2,000,000,000 to replace the once they sold Chevy for use in the Bolt. And recalling (at least some) of the LG branded RESU powerwalls.

BMS is a key protection against over-charging the batteries, but defects have also resulted in fire.

LiFePO4 is much safer but not completely. If using any other lithium chemistry, suggest keeping it where a major fire wouldn't cause any harm. By the way, they can't be charged while below freezing, either.

Some people here do have repurposed EV batteries in their home or vehicle.
Some brands have degraded rapidly, because manufacturer didn't manage cell temperature as well. Others have extremely long life.
Many surplus sellers will praise the brand they have in stock. Get other opinions elsewhere.

New reject LiFePO4 batteries are available from China, didn't make the cut for electric busses. There are shady and good resellers of those. We have some trusted vendors with stock in U.S. warehouses. Those, and "server rack batteries", may provide power for $0.05/kWh of cycle life. Server Rack could be 48V (nominall) 100 Ah claimed 6000 cycles, $1600. Loose cells 280 Ah 3.4V, use 16s + BMS for around $2000, 13 kWh. You can read about both approaches on this forum.

Think the Bolt is the 2000's version of the Ford Pinto lol

 

[Hedges]

It can be done, and people here do.
We've also seen photos of incinerated cabins and vans. Sometimes, root cause (design mistake) may have been visible in the wreckage, other times not as clear.
Consider value of what you're installing it in, insurance/denial, human safety, early warning and escape routes.

Both LiFePO4 and more "explody" chemistries are used in vehicles and houses, both commercially and DIY.
You have to make your choice and trade-offs.

I went with AGM 2 years ago, because the lithium I was aware of was 5x the cost for 5x the cycle life, and my application is infrequent grid failure. I only expect to use 20% of my battery's cycle life, will have spent $2.50/kWh for what I do cycle through them. Or, the home-made cappuccinos I made during grid failures in 2020 cost me $1000 each. But most of the power I make and use, e.g. running A/C during grid outage, is PV direct to AC, with batteries just supplying starting surge (and night time smaller loads.)

LiFePO4 is looking attractive for stationary applications that deep cycle every day.

Various other lithium polymer etc. could be more attractive for mobile, higher energy/weight ratio. But even Tesla reportedly will use LiFePO4 in some new models.

Over expected cycle life (which could be as short as 1 year or a long as 16 years deep cycling, 20 years or more have been reported for shallow cycled FLA), I put AGM at $0.50/kWh, FLA at $0.25/kWh. Used to be the lithium I saw as $0.50/kWh but some LiFePO4 now $0.05/kWh. Maybe some repurposed EV batteries can be even cheaper, of course more labor, less off-the shelf BMS setups for them.

 

[chess-equality]

Hi @Hedges I'm HedgePig! We could be related!

 

[PlaneBatteries]

Or, the home-made cappuccinos I made during grid failures in 2020 cost me $1000 each.

That will be coming again very soon- sans the grid failures.
Courtesy of the US Federal Reserve

 

[Hedges]

Hi @Hedges I'm HedgePig! We could be related!

I'm hedging my bets.
Or have put up a hedge to protect me.
Or, maybe I'm heir to a cigarette fortune, and that's how I can afford the toys I play with.

Welcome, ? (or is that ?)?

I was looking for "Fuz" nightclub, and Apple iPhone showed me where to find police stations.
So I searched for "pig". Apple only showed me barbeques, not police stations.

 

[Bluedog225]

@400bird Thank you for the quick reply!
Forgive more obvious questions but where would I start?
You say I need to ensure I match the voltage ranges, how do I do this and what are some specific examples I should look out for? There are a huge range of EV batteries for sale online, many with guaranteed states of charge.
One thing I was thinking about last night as I lay in bed, was a car EV battery that is only producing 75% of its new output would be considered 'broken'. Of course if thats something like the Volt (Ampera) battery thats still as pretty impressive 14Kw or so! I would be delighted with that sort of capacity. I'd be happy with 40% of that!

Where do I start? And again I apologise for asking what are very rudimentary questions. HP.

In general, there are hundreds of diy build threads here with ali express cells. Find by searching bms or eve cells or diy.

And the will prowse videos are a great source of info.

And welcome!

 

[chess-equality]

I'm from the Philippines and our LiFePO4 market here is 90% Chinese used cells (also goes for our inverters). Most here (in the forum) say that they are used EV cells or those that didn't make the EV cut.

They are cheap but most are wary that they are finicky and doesn't live up to the advertised capacity (in Ah). There are quite a handful of videos and testimonies about this, mostly about sub-par BMSes.

I myself have a particular battery (or its BMS) that doesn't like my computer when I turn it on.

In my experience, I went for stacking up capacity since they are quite cheap. And for the problematic battery above, I connect my computer to another battery bank that is more welcoming to the surge when I power the computer on.

Given this, I follow the general consensus ("do not put them in series" -- something like this, although I am about to challenge this one ? ) and I do not stress them in terms of power draw, but yet I carefully size (=oversize) my wires and also use decent safely precaution (or so I have learned here). I use DC MCCBs instead of T-class fuses -- both have high AIC ratings.

So far it's been good; although I haven't tested the full capacity yet, a handful of times that I have used my battery banks I am quite satisfied with them.

Also I haven't heard of anyone here of getting a fire from their solar systems, which is a good sign. Well, this may also be partly due to the fact that we are not an RV-ing culture. Most of our systems here are stationary. But most likely this will change since EV public transport here is growing, and malls are putting up more and more EV charging stations.

 

[A.Justice]

You say I need to ensure I match the voltage ranges, how do I do this and what are some specific examples I should look out for?

I'll use lower voltages because they are easier to write out, but the same concept applies to the higher voltage packs.

My (and most) 12 volt inverters will run between ~9v-16v. Four LiFePO4's in series (3.6v X 4 cells), fully charged are 14.6v, and they are around 10v fully discharged. That's perfect for the inverter, and can be used from zero to 100% SOC (state of charge), no problem.

If you used four "Li-Po" (what most EV manufacturers use) cells in series (4s), you get a full charge of 16.8v (4.2v X 4), and a full discharge of about 11v, which would put the top charge of your battery above the inverters maximum voltage range, and your inverter would either release the magic smoke, or not power up. You also might find that there's not a lot of solar charge controllers, chargers, converters, and fuses available for higher voltage EV packs. They exist, but your options will be limited.

A lot of EV batteries come in strange voltage configurations that are hard to split apart because of the pack design. Cutting off a row of cells from a welded, and plastic molded battery frame can be difficult, wasteful, and / or dangerous.

I would be delighted with that sort of capacity. I'd be happy with 40% of that!

If you are aware of the limitations of using an EV battery going into it, you'll probably be happy with the result. Make sure you get a pack that didn't have a safety recall, and don't charge or discharge it near it's upper and lower limits and you should be fine. I've seen some EV packs for sale locally from wrecked vehicles that even if I only got 30% of the capacity, it would still be a good deal. Plus, I always advocate for recycling, especially when it doesn't require re-manufacturing.

 

[Bluedog225]

I'm from the Philippines and our LiFePO4 market here is 90% Chinese used cells (also goes for our inverters). Most here (in the forum) say that they are used EV cells or those that didn't make the EV cut.

They are cheap but most are wary that they are finicky and doesn't live up to the advertised capacity (in Ah). There are quite a handful of videos and testimonies about this, mostly about sub-par BMSes.

I myself have a particular battery (or its BMS) that doesn't like my computer when I turn it on.

In my experience, I went for stacking up capacity since they are quite cheap. And for the problematic battery above, I connect my computer in another battery bank that is more welcoming to the surge when I power the computer on.

Given this, I follow the general consensus ("do not put them in series" -- something like this, although I am about to challenge this one ? ) and I do not stress them in terms of power draw, but yet I carefully size (=oversize) my wires and also use decent safely precaution (or so I have learned here). I use DC MCCBs instead of T-class fuses -- both have high AIC ratings.

So far it's been good; although I haven't tested the full capacity yet, a handful of times that I have used my battery banks I am quite satisfied with them.

Also I haven't heard of anyone here of getting a fire from their solar systems, which is a good sign. Well, this may also be partly due to the fact that we are not an RV-ing culture. Most of our systems here are stationary. But most likely this will change since EV public transport here is growing, and malls are putting up more and more EV charging stations.

Kamusta! Great to hear from new places.

 

[Bvillebob]

A couple of thoughts that haven't been brought out.

The main issue is that EV batteries are configured for high voltage, much higher than we can use, so they have to be broken up and reassembled into packs that work with 48 volt inverters. That means the internal cooling systems and possibly the BMS systems are no longer useable.

The second issue is that if the battery is only holding, for example, 50 percent of its original capacity it means it's WAY down the degradation curve, and the capacity drop will be ongoing and will be faster and faster is time goes by. Is it really a good deal to pay half as much for a battery that's only going to last for another 500-1000 cycles versus a new one that's good for 5-6,000 cycles?

 

[PhiPhi]

With a sample of 1, myself, take this for what it's worth. I think the BMW/I3 batteries will be composed of 4 x 93ah Samsung SDI NMC cells which I've had fantastic results with. According to the specs they are very safe and have an excellent lifecycle, I brought 14 secondhand cells and a 100amp ANT smart BMS at the beginning of the year, until yesterday I had only been charging them to 80% and discharged to 20% however unbelievably I charged to 99% of specified capacity yesterday due to several days of bad weather and needing to go on battery earlier in the afternoon. I'm kicking myself on not buying more as in my neck of the wood they are no longer easy to find and what ones are available are pre-configured into 7s, with welded busbars and 30% more expensive than my original ones.

 

[MattiFin]

With a sample of 1, myself, take this for what it's worth. I think the BMW/I3 batteries will be composed of 4 x 93ah Samsung SDI NMC cells which I've had fantastic results with. According to the specs they are very safe and have an excellent lifecycle, I brought 14 secondhand cells and a 100amp ANT smart BMS at the beginning of the year, until yesterday I had only been charging them to 80% and discharged to 20% however unbelievably I charged to 99% of specified capacity yesterday due to several days of bad weather and needing to go on battery earlier in the afternoon. I'm kicking myself on not buying more as in my neck of the wood they are no longer easy to find and what ones are available are pre-configured into 7s, with welded busbars and 30% more expensive than my original ones.

VW ID3/ID4 batteries also look like really neat package:

VW ID Module 12S - 6.85kWh / 156Ah / 44V

VW ID Modules for EV Project VW ID 6.85kwh. 44.4V VW ID3 Module Lithium-ion Battery Has come from a 2020

www.secondlife-evbatteries.com

Pretty neat package that looks like easy to repurpose. 40v to 50v voltage range should work nicely with most 48V equipment.

On negative side the package is welded closed and vw MEB platform is still kind of new so not too many crash vehicles available as battery donors.

IIRC balancing wires are also really thin and might cause issues with some BMS modules. On the other hand the true automotive grade li-ion needs minimal balancing compared to china-quality LiFePo

 

[PhiPhi]

VW ID3/ID4 batteries also look like really neat package:

VW ID Module 12S - 6.85kWh / 156Ah / 44V

VW ID Modules for EV Project VW ID 6.85kwh. 44.4V VW ID3 Module Lithium-ion Battery Has come from a 2020

www.secondlife-evbatteries.com

Pretty neat package that looks like easy to repurpose. 40v to 50v voltage range should work nicely with most 48V equipment.

On negative side the package is welded closed and vw MEB platform is still kind of new so not too many crash vehicles available as battery donors.

IIRC balancing wires are also really thin and might cause issues with some BMS modules. On the other hand the true automotive grade li-ion needs minimal balancing compared to china-quality LiFePo

The OP stated a 1.3kWh package so I'd imagine the original module had already been disassemble and reconfigured into 4s 14.4v batteries.

 

[Delmar]

I would leave the EV as-is and get a high-voltage inverter. Will need to modify the main contactor to pull-in while parked. I see this as becoming a trend when used EV’s start becoming affordable, and a manufacturer steps-up and adds the required power cord.

Example high-voltage inverter with communication to the vehicle controller: Bel Power Solutions 350INV60-120-240-9G

I am doing the same thing, albeit at much lower speed and lower voltage. EV's make a dandy self-propelled storage system.

 

[MattiFin]

I would leave the EV as-is and get a high-voltage inverter. Will need to modify the main contactor to pull-in while parked. I see this as becoming a trend when used EV’s start becoming affordable, and a manufacturer steps-up and adds the required power cord.

Example high-voltage inverter with communication to the vehicle controller: Bel Power Solutions 350INV60-120-240-9G

I am doing the same thing, albeit at much lower speed and lower voltage. EV's make a dandy self-propelled storage system.

Fine, if you have the entire EV to start with..and space to keep it and so on.

Some of the new EV’s make this really easy with V2L (vehicle to load) functionality.
I’m on a waiting list for a Kia EV6 and it has onboard 3.7kW inverter.

vehicle to grid functionality would be even better but I’m not aware of any car models coming out anytime soon with V2G functionality.