I was topping up the water in my giant lead-acid batteries and got to musing about temperature. Have you ever really thought about batteries and temperature? We had a warm summer. I’m wondering if winter will ever get here. (The batteries only took 6 gallons of distilled water.)
I don’t think this last summer was as hot as the previous one, but one day my flooded lead-acid (FLA) outdoor batteries got overheated and went into thermal runaway and the inverter shut down. The batteries are too big to go inside, so they normally sit outside with an insulating plastic cover over the top. Regardless of that, with 100 degrees outside, the sun beating down on uncovered batteries and 200 amps of charge, they got to boiling. It is a rare thing, but it can get scary. I ran the hose over it to cool it down and then added another layer of insulation. No more trouble. Keep your lead batteries out of the sun and make sure you don’t exceed the published charge rate.
Had this been a lithium ion (LI) battery, there would have been a spectacular fire. Don’t use LI batteries at home. Don’t leave your phone or laptop on the dash of your car on a hot day. They have LI batteries. Some cars, which use LI batteries, come with a specific recommendation to not charge them in your garage…so you won’t burn the house down.
Most solar house batteries, these days, are lithium iron phosphate (LFP or LiFePO4). They don’t burn.
Hot isn’t the only concern with batteries. In the cold, FLA batteries get sluggish. You already know that because your car grinds a little on a cold morning. My big FLAs weigh over a ton, each, and we have wide swinging daily winter temperatures, so the thermal mass keeps cold from being a big deal. My smaller sealed (AGM) batteries are indoors in an unheated area and they do ok, but our winters are mild, here in NW Florida. Folks in colder climates find it best to insulate. Duct tape and builders’ foam sheets work. Many folks use an insulated wooden box. Oh, consider the inevitable acid spills and the production of explosive hydrogen gas with FLA. They need ventilation.
LFP just won’t charge when it gets below freezing. Some batteries come with built in heaters, but they consume some of the power you are trying to store. I just dipped my toe into LFP last week, 80kwh worth, and was sweating getting the things into a climate-controlled area. My battery room is probably warm enough, but the humidity is high, with a good possibility of cat pee. The steel cabinet and the battery management system (BMS) electronics would be in jeopardy in there. In the end, I did manage to get the units into the Solar Shed’s control room, stuffed behind the sofa. Wall to wall power and climate control.
You don’t have to put LFP indoors, if you get a unit made to mount on an outdoor wall. My neighbor, Brad, has 3 Tesla Powerwalls on the side of his house. Indoor units don’t have to be in climate control, but the brochures for the big batteries often depict them in a living room. Whatever works, but bringing batteries indoors, think about how strong your floor is. The Man Cave has a wooden floor and the batteries weigh around 1700 lbs.! I built the floor so I knew it was plenty strong. Still, I was having second thoughts for a while, there. A concrete slab would be even better. An insulated wooden box in the unheated garage will work, just fine in cold areas.
Generally speaking batteries are comfortable if you are.
I’ll be talking about the LFP install in an upcoming post.
—Neal