MarkSolar
Solar Enthusiast
We have solar powered batteries on the automatic gate openers on our farm in Illinois. Temps typically get well below 0F and have gone as low as -30F in the past few years. I've experimented with a variety of ways to keep the batteries from freezing in the winter. Here is a typical example of a gate in the summer, that's a deep cycle marine battery:
The biggest complication I encountered trying to make an insulated box was condensation inside whatever I built because of the moisture in the air and the wide temperature swings from day to night inside the box. The best solution I found is an insulated ice chest like you use at the beach in the summer. Here's one of my experiments as an example, I took the lid off the ice chest and put it upside down on the ground, then used a heating pad made for a car battery. I put a piece of ceramic tile on top of a piece of wood, then the heating pad, then a ceramic tile, then put the battery on top of the tile and covered it with the ice chest. The short version is I set that piece of wood on fire in the middle of the night and it's lucky I didn't melt the battery and start our trees on fire. I didn't think about how high the energy density is in that kind of heater and how hot it gets when it's well insulated.
So I eliminated the heater and just set the battery on top of the upside down lid then covered it with the big part of the chest and put a remote temperature sensor inside the chest and set the whole thing on the ground on a piece of insulated foam board. That has proven to be adequate without any supplemental heat, it is generally 10-20F hotter in the chest than outside which is enough to help the battery keep from freezing. It helps that the box is in the sun all day. I also had to vent the chest since this is a lead acid battery, so I drilled a small hole in the top of the chest and put a piece of aquarium tubing in the hole as a vent.
If I had to do this for a large bank of solar batteries I would build some kind of box insulated with pink foam and make it as airtight as I could since you don't need to vent LiFePo batteries. That should help reduce the air exchange in the box that feeds the condensing moisture. I'd put a temp sensor inside so I could monitor how large the temperature swings were, and whether it was getting close to the dew point. I don't think condensing moisture can hurt a battery, but I think it provides an environment for small current drains and for mold to grow. All this depends on your climate, we can see 40F on a sunny winter day and it frequently gets well below 0F at night, we've had stretches of -30F that lasted 3 days. If this was near my house I'd probably hang some fire suppression balls above the enclosure just so I could sleep at night.
The biggest complication I encountered trying to make an insulated box was condensation inside whatever I built because of the moisture in the air and the wide temperature swings from day to night inside the box. The best solution I found is an insulated ice chest like you use at the beach in the summer. Here's one of my experiments as an example, I took the lid off the ice chest and put it upside down on the ground, then used a heating pad made for a car battery. I put a piece of ceramic tile on top of a piece of wood, then the heating pad, then a ceramic tile, then put the battery on top of the tile and covered it with the ice chest. The short version is I set that piece of wood on fire in the middle of the night and it's lucky I didn't melt the battery and start our trees on fire. I didn't think about how high the energy density is in that kind of heater and how hot it gets when it's well insulated.
So I eliminated the heater and just set the battery on top of the upside down lid then covered it with the big part of the chest and put a remote temperature sensor inside the chest and set the whole thing on the ground on a piece of insulated foam board. That has proven to be adequate without any supplemental heat, it is generally 10-20F hotter in the chest than outside which is enough to help the battery keep from freezing. It helps that the box is in the sun all day. I also had to vent the chest since this is a lead acid battery, so I drilled a small hole in the top of the chest and put a piece of aquarium tubing in the hole as a vent.
If I had to do this for a large bank of solar batteries I would build some kind of box insulated with pink foam and make it as airtight as I could since you don't need to vent LiFePo batteries. That should help reduce the air exchange in the box that feeds the condensing moisture. I'd put a temp sensor inside so I could monitor how large the temperature swings were, and whether it was getting close to the dew point. I don't think condensing moisture can hurt a battery, but I think it provides an environment for small current drains and for mold to grow. All this depends on your climate, we can see 40F on a sunny winter day and it frequently gets well below 0F at night, we've had stretches of -30F that lasted 3 days. If this was near my house I'd probably hang some fire suppression balls above the enclosure just so I could sleep at night.
