Used EV Batteries for storing solar energy

[janan]

I am newbie to the forum and need some help in clarifying certain concerns related to the titled topic.

1. I plan to have have a 10KW solar setup. How much battery storage is required to run 2-3 air conditioners plus running other household appliances.
2. Nissan Leaf or Tesla? Pros and cons of these two batteries.
3. How do I check if EV batteries salvaged from a certain car model is compatible with the solar inverter that will be a part of my setup. Any key consideration or pitfalls I should be aware of?

[organic farmer]

I am newbie to the forum and need some help in clarifying certain concerns related to the titled topic.

1. I plan to have have a 10KW solar setup. How much battery storage is required to run 2-3 air conditioners plus running other household appliances.

How many days of solar production do you plan for each hour of running these A/C units?

... 2. Nissan Leaf or Tesla? Pros and cons of these two batteries.

That is taking the long way around the barn.

In a field where thousands of people have been on off-grid power for decades. A few corporations have duct-taped together battery banks with issues and you want to choose one of them?

... 3. How do I check if EV batteries salvaged from a certain car model is compatible with the solar inverter that will be a part of my setup. Any key consideration or pitfalls I should be aware of?

As with every battery-bank, you need to go back to the manufacturer and get the details of charging voltage/amperage, float voltage/amperage, and equalize voltage/amperage. In your case, Nissan and Tesla should hold the data you seek.

[peakbagger]

There are plenty of hobbyists and several You Tubers making a living off of selling info on reconfiguring automotive battery packs into storage. In all the cases I have seen, they keep the batteries cell but fit third party BMS systems. Some of the "experts" have incidentally had serious fires from battery fires. Viewing some of the videos, I see a lot of homebrew in the background which does not inspire confidence.

If you do elect to go into that world, I think the key is to locate the equipment somewhere that if there is a failure that it can be contained. Many folks seem to have standardized on 1/4 length shipping containers located outdoors and separated from any other structures so if there is a fire it will be contained. Dont even try to insure it.

IMHO For home use, Lmnc type batteries are just not worth the risk. Even Tesla is switching to Lithium Polymer chemistry for the Megapacks and at some point the Powerwalls. There are multiple firms selling Lithium polymer batteries out there with integrated BMSs that are far more plug and play and far less to prone to burn the house down.

[Ampster]

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IMHO For home use, Lmnc type batteries are just not worth the risk. Even Tesla is switching to Lithium Polymer chemistry for the Megapacks and at some point the Powerwalls. There are multiple firms selling Lithium polymer batteries out there with integrated BMSs that are far more plug and play and far less to prone to burn the house down.

Are you sure about Lithium Polymer being more safe than LMNC? I am pretty sure Lithium Polymer is the most volatile and LFP the least. I have heard Tesla is putting LFP in some Model 3s. I am using LFP for my home storage. LFP is also know as LiFePO4 and maybe there is some confusion about the chemistries.

[janan]

Thank you all for your valuable comments. From the above discussion/ comments, I infer that DIY is not a viable option. I am not really well aware about LFP or LIfePO4 batteries. I have a superficial understanding of the topic. Would you guys recommend to buy such batteries from China? Will it be a safe bet? Any complications/ issues? Is there any literature available to learn more about the LifePo4 batteries. My home country prices of a Lithium batteries are astronomical and can cost your more that the whole solar system itself. I am planning to do a 10KW Hybrid system with backup storage for the night (at least 5-6 hours )

[Ampster]

I had luck buying new LFP batteries from specific vendors in China. My cost delivered was $125 per kWh which compared favorably to Tesla or Nissan modules. I researched vendors on diysolarforum dot com. I use the same handle on that site.

[peakbagger]

My bad Lithium Iron Phosphate is the safer battery, lower energy density but safer and no "conflict" materials.

As for your battery source, folks report mixed success in buying batteries from China. Most batteries on the market are "seconds" from major battery manufacturers. They sell the best to the car manufacturers and the rest go on the secondary market. There are so called B cells but I do not think there is 3rd party agency with standards on what constitutes a B battery so the rating may not be worth much. The general recommendation is buy from a firm that does volume and its likely that their product will be better than a place that is buying on a tertiary market.. Shipping and the associated paperwork can be a real hassle especially during Covid where the shipping channels got clogged up. Ideally you buy from a middleman that has stock of bulk shipments of product and let them have the hassle.

With respect to BMS systems, it sure looks like there is lot of crap out there and the BMS is vital to long term operation of the cells that make up a battery. I have read that the secondary market cells tend not to be matched cells so the BMS has to work harder to get all the cells to store a charge.

BTW with respect to Tesla, I have heard, but not seen documented, from electrical engineers that the cells used in Powerwalls are the B spec cells from Tesla's battery factory. If they do not make the grade to go in car battery they get shunted to the Powerwall line. It makes sense but not sure that Tesla would admit it. I do know that Tesla's grid batteries have made a lot of fire departments wary if not hostile to grid batteries. I think their transition to Lithium Iron Phosphate for the Megapacks is partially cost plus ability to compete with safer chemistries.

[Ampster]

Yes, what peakbagger says about Grade B cells or automotive seconds is true. I only use 80 percent or less of my pack for that reason. My settings are designed to keep the cells out of the knees. Those cells are still a good value for a stationary pack. I do use an expensive Orion BMS and a 2 Amp active balancer. I turn off the balancing function on the Orion because it is too weak for my pack and I do not want a conflict between it and the active balancer.