Solar Batteries And Heat

pabloesguapo

I have read some discussions about how to protect a bank of batteries from extreme cold, but I think I'm facing the opposite problem.

I'd like to build my off-grid system on and inside a shed. Panels on the roof, batteries and other equip. inside, run the AC cable to the house.

Where we're building, Kirkland AZ has the following temperature extremes:

http://climate-fizber.com/arizona-city-kirkland-climate.html

Avg high (July): 90.3
Avg. low (Jan.): 19.7
Extreme max (July): 103
Extreme low (Jan): 6

It's been my experience, at least with car batteries, that batteries dislike heat more than cold.


What steps should I take to protect the batteries from the aforementioned temperature averages and extremes, especially the heat, if I had them inside the shed instead of the house?

niel

Re: Solar Batteries And Heat

short of putting an air conditioner on them, you can't protect them from the heat. eventually the ambient air temp will cause a rise to the battery temp no matter the measures taken. add to that even if you stopped the heat of the day from reaching them through insulation, or whatever, that using and charging batteries creates heat too and will build up with nowhere to go. be very sure to have a battery temperature sensor no matter what.

peakbagger

Re: Solar Batteries And Heat

Any chance you could put them in a pit in the shade. With conditions like that evaporative cooling could help.

Zome works sells these http://zomeworks.com/products/cool-cell/introduction.

stephendv

Re: Solar Batteries And Heat

Earth-bermed construction of the shed. Or put the shed underground if you can.

niel

Re: Solar Batteries And Heat

having them underground may help, but the batteries are still a source of heat themselves so it will build up until it hits the ambient and then some. i think peakbagger has an idea using a small swamp cooler to help cool them. if placed into the shed as originally planned then insulate that shed very well and use the swamp cooler.

pabloesguapo

Re: Solar Batteries And Heat

A swamp cooler is probably the most practical solution for me.

Based on the temps provided, what kind of performance and longevity issues could I be facing? I saw on a thread dealing with cold how a battery's efficiency drops along with temperature, but what about heat?

BB.

Re: Solar Batteries And Heat

From the Battery FAQ:



You will get ~10% more capacity at high temperatures (call it 45C) and 1/4 the life... That would be assuming your battery bank is at 45C (113F) 24 hours day for years on end)...

Cycling also affects life too (generic Lead Acid graph--Number of cycles on left, % discharge on bottom):



-Bill

pabloesguapo

Re: Solar Batteries And Heat

That first graph was the one I saw. Once we get the mid-80's (f), we get into the dotted red line, +100% territory. What does that mean?

BB.

Re: Solar Batteries And Heat

The numbers on the left of the first graph are % of apparent capacity... Around 77F is 100% capacity. Colder batteries appear to have less AH capacity. Higher than 77F, and the battery appears to have more usable capacity. The bottom/X axis is temperature C/(F) as in 0C/(32F).

The Dashed line just means the battery is above the standard rated temperature of ~77F (as far as I know).

Hot batteries tend to age much faster than cool batteries (need replacement sooner).

-Bill

pabloesguapo

Re: Solar Batteries And Heat

Got it. In the summer and the winter, in the shed, my efficiency should be ok, but I'll shorten the batts' life a bit

But, if I store them in the house, how much voltage drop will I have running a dc line 50+ feet each way?

If I store them and invert in the shed, what's the voltage drop of an AC run that long... Then, I'd still ned to run a line back to the shed in order to run the well pumps.

Hmm... Battery life vs. voltage drop.

BB.

Re: Solar Batteries And Heat

Need to know your power needs.... Watts, volts, AC or DC, etc... The higher the voltage, the less you have to worry about voltage drop.

Here is a very simple voltage drop calculator. Note this drop calculator uses 1-way wire run... Some you have to do the two way wire run (i.e., 50 feet of 10 AWG wire pair, vs 100 feet of round trip 10 AWG wire carrying XX amps).

http://www.csgnetwork.com/voltagedropcalc.html

-Bill

pabloesguapo

Re: Solar Batteries And Heat

Sorry, BB, I was kinda thinking out loud. I was at work and couldn't dig up an old thread on this I made a few months ago. You answered the question with a lot of math then too. Thanks for your patience. I used that one and THIS ONE and THIS OTHER ONE to figure out that with 4 AWG wire on a 100ft run, I can keep my voltage drop below 2% with the right panels. (I found some @ 205w, 27.9v, 7.36IMP, 4 lines at 6 apiece)

But it's all a moot point. My wife and I decided it would be safer if we left the batts in the shed instead of the house. Sure, we lose a little lifespan from them this way, but if they happen to catch fire, we at least won't lose the house, especially since the water pumps are run on electricity generated by the batteries... which would no longer be working because they'd be on fire. I'd rather lose a shed full of equipment than my entire house.

Now, I just have to calculate a 120/240 run to the house. BAH!! Tomorrow.

Volvo Farmer

Re: Solar Batteries And Heat

Looks like the average low in the summer is in the high 50's? I wouldn't worry about cooling them at all. My experience is that that batteries in a shed will settle somewhere around the center of the diurnal temperature swing. So if you have a high of 90 and a low of 60, all that lead is going to settle somewhere around 75F. They might be a little warmer than that because of self-heating on use, but since battery powered loads are generally higher after the sun goes down, they are more willing to give their heat to the ambient air when it is cooler at night.

Vic

Re: Solar Batteries And Heat

Believe that almost all of the heat generated within the batteries is from the last portion of Asorb, and during EQ, where the batt efficiency is lowest. It is possible that under very heavy discharges that appreciable heat may be generated.

Some form of cooling of the power shed would help a lot, or at least forced air fan cooling 2-3 hours before sunrise should help a lot. High heat IS death for batts. If you can spare the H20, Swanp coolers work very well in low humidity (obvious) Vic

solar_dave

Re: Solar Batteries And Heat

Volvo Farmer wrote: »

Looks like the average low in the summer is in the high 50's? I wouldn't worry about cooling them at all. My experience is that that batteries in a shed will settle somewhere around the center of the diurnal temperature swing. So if you have a high of 90 and a low of 60, all that lead is going to settle somewhere around 75F. They might be a little warmer than that because of self-heating on use, but since battery powered loads are generally higher after the sun goes down, they are more willing to give their heat to the ambient air when it is cooler at night.

I don't know about that, I am about 40 miles south of there and I have seen 100F at midnight. He may be at elevation however and that does have an impact. Earth Berm might be a good solution.