Keeping LiFePO4 Battery Banks cool in Australia

[ArthurEld]

I put a small window air conditioner thru the wall of my shed. I plan to put four full size solar panels on the roof. I spent more than a year thinking of ways to deal with the batteries.
It's an expensive battery enclosure but I sleep better not worrying about fires. It is cheaper and safer than the commercial battery solutions I have seen.

 

[mcart117]

It is cheaper and safer than the commercial battery solutions I have seen.

I agree with you there

 

[curiouscarbon]

Do everyone overthink this? Why not simply let the cells at 35-40°C?
From specs, those cells are rated to be discharge at up to 55° or even 65°C, so why bother?
Do anyone have visual/technical proof that cycling LFP cells part of the year at high temperature will drastically reduce their life?

without any first hand experience...

it seems that 40C might reduce the calendar life of the cells by more than a few months.

here is one resource that goes into some detail

Why temperature of lithium cells is important

Temperature is an important parameter that influences the aging of a lithium battery. At 35°C a lithium cell ages twice as fast as it does at 15°C. So if the battery’s useful life is 15 years at 15°C, it will be 7.5 years at 35°C. I summarize...

diysolarforum.com

 

[Robbert]

I live on Bonaire (Dutch Caribbean) and in the garage where my inverters are, temperures go over 35 Celsius. Also the humidity here is very high.

Since I am upgrading to lifepo4 and have plenty of solar, I'll install a mini split next week to keep everything stable at 25 celcius and keep humidity low.

 

[yabert]

here is one resource that goes into some detail

Interesting, thanks to share.
Based on this, It's clear that I would never spend money, time and effort to try to save a bit of life over a long period of time.
Imagine, if you use your cells wisely and discharge them at an average of 75% you could save around 4% of capacity over 10 years. It's nothing and a cheap BMS will probably destroy it before 10 years.
Take a look at the cells available 10 years ago (price, energy density, cycle life) and try to imagine the cells available in 10 years (price↓, energy density↑, cycle life↑). You will certainly be tempted to add or replace it with a low cost/high cycle life new battery in 10 years.

And please don't tell me you are living in a place where it's temperature is always 35°C. Some place are hot, like on the edge of the Great Sandy Desert, but most of the year (night, winter), the temperature is lower. So, really, add all this stuff to save ridiculous amount of life out of the cells is way more about interesting experiments than real needs.

I'm all to extend life of things to reduce waste and be gentle on new resources extraction, but it's clearly not the case here as those mini split/evaporative cooler have their own impact (resources, energy, garbage).

 

[wopachop]

Sounds like a fun project. I mess around with DIY evaporative coolers. Theyre fun to build but never work that great.

There are smaller 12v mini split systems designed for trucker cabs. Maybe you could score a really good deal on those. Then build an enclosure from foam board.

Like others said i would be worried about moisture. You could use your existing cooler but build a different enclosure. Pretend you had 2 enclosures. The batteries and inverter on the inside. Then you cool the outer enclosure around it. The batteries would have a barrier of cooled air around them. While not getting hit with moisture.

Another cheap option is shade. If its not too ugly. Hanging a shade fabric over the shed would keep the overall temp down. Especially that morning sun. Longer you can block it the better.

 

[toms]

Interesting, thanks to share.
Based on this, It's clear that I would never spend money, time and effort to try to save a bit of life over a long period of time.
Imagine, if you use your cells wisely and discharge them at an average of 75% you could save around 4% of capacity over 10 years. It's nothing and a cheap BMS will probably destroy it before 10 years.
Take a look at the cells available 10 years ago (price, energy density, cycle life) and try to imagine the cells available in 10 years (price↓, energy density↑, cycle life↑). You will certainly be tempted to add or replace it with a low cost/high cycle life new battery in 10 years.

And please don't tell me you are living in a place where it's temperature is always 35°C. Some place are hot, like on the edge of the Great Sandy Desert, but most of the year (night, winter), the temperature is lower. So, really, add all this stuff to save ridiculous amount of life out of the cells is way more about interesting experiments than real needs.

I'm all to extend life of things to reduce waste and be gentle on new resources extraction, but it's clearly not the case here as those mini split/evaporative cooler have their own impact (resources, energy, garbage).

View attachment 140814

That’s if you believe what you read. My personal experience is that heat is a major contributor to cell degradation. I’ve seen the same installations where temp controlled cells are still going after close to a decade where neighbouring non-temp controlled cells are finished inside 5 years.

 

[curiouscarbon]

Cell degradation speed increases as temperature increases. To what degree, I cannot personally attest.
Degradation speed slows as temperature decreases. However, past a certain point, the cell can't deliver nominal capacity until warmed back up.

Each person's situation and goals/priorities are different, and engineering thermal management systems is a real extra effort.
Having the cells last a very long time is one of my goals personally. Even if new chemistries come out, I want my system to still work.

HVAC or peliter are my two preferred ways to keep LFP cells in an optimal range to reduce degradation (both calendar aging and cycle aging).

With an insulated pack, the inefficiency of peltier units does not matter as much as without insulation.

Below is one way to do it. Still designing hope this info is of some use.

 

[octal_ip]

Cell degradation speed increases as temperature increases. To what degree, I cannot personally attest.
Degradation speed slows as temperature decreases. However, past a certain point, the cell can't deliver nominal capacity until warmed back up.

Each person's situation and goals/priorities are different, and engineering thermal management systems is a real extra effort.
Having the cells last a very long time is one of my goals personally. Even if new chemistries come out, I want my system to still work.

HVAC or peliter are my two preferred ways to keep LFP cells in an optimal range to reduce degradation (both calendar aging and cycle aging).

With an insulated pack, the inefficiency of peltier units does not matter as much as without insulation.

Below is one way to do it. Still designing hope this info is of some use.

I'd be interested to hear how your experiments with peltiers go. My initial work with a small phase change refrigeration system didn't produce enough cooling to be worthwhile. I estimate that it was able to move about 100W of heat, however this wasn't enough to keep an insulated container much below ambient temperature, let alone remove the heat produced by charging/discharging batteries and the BMS.

 

[littleharbor2]

This is on a smaller scale than the other units discussed here but thought I'd mention it anyway.
I built my own cooling unit for my LiFePo4 enclosure using this 12 volt mini refer unit and digital thermostat. It gets, and stays HOT for 3 solid months here on the Baja peninsula and this thing works pretty well keeping my battery bank cool.

 

[octal_ip]

This is on a smaller scale than the other units discussed here but thought I'd mention it anyway.
I built my own cooling unit for my LiFePo4 enclosure using this 12 volt mini refer unit and digital thermostat. It gets, and stays HOT for 3 solid months here on the Baja peninsula and this thing works pretty well keeping my battery bank cool.
View attachment 140903
View attachment 140904

Do you have a photo or any more details about your setup?

These pre-built coolers usually have a peltier in the range of 60 - 70W attached. Based on the datasheets, the best case scenario is that they can move about 30W of heat with a delta temperature of 40°C if the hot side is kept below 50°C, which would be a real challenge as the peltier alone is producing about 90W of waste heat at this load. I can't see the hot side heat sink keeping the peltier at 50°C when it needs to remove 120W of heat, with ambient temperature already being very high. The figures only get worse as the hot side temperature increases.

This is all based on theory, of course. With these numbers alone I've always hesitated to spend any money on a peltier setup, however I'm happy to be proven wrong as there are probably other factors at play.

 

[littleharbor2]

I have a separate dedicated 12 volt panel and battery running this unit. The small end goes into the battery box, the large end hangs outside the box. It actually starts frosting up when the humidity is high. The frost ends up turning to water and I have cut a small chute under the unit which slopes downhill, causing the water to run out the back of the box onto the concrete floor.
This thing won't ever freeze up the batteries (thermostat would prevent that ) but it will keep the batteries in the high 70's Fahrenheit, when it's over 100 degrees all summer long.

 

[curiouscarbon]

I have a separate dedicated 12 volt panel and battery running this unit. The small end goes into the battery box, the large end hangs outside the box. It actually starts frosting up when the humidity is high. The frost ends up turning to water and I have cut a small chute under the unit which slopes downhill, causing the water to run out the back of the box onto the concrete floor.
This thing won't ever freeze up the batteries (thermostat would prevent that ) but it will keep the batteries in the high 70's Fahrenheit, when it's over 100 degrees all summer long.

delightful! nice numbers

happy to check out any photos you might be comfortable to share of the setup with the battery.

thanks for mentioning your temperature management solution! that's so neat.

 

[littleharbor2]

delightful! nice numbers

happy to check out any photos you might be comfortable to share of the setup with the battery.

thanks for mentioning your temperature management solution! that's so neat.

The digital thermostat mounted on top of the enclosure. You can see the warm side of the cooling unit hanging off the back of the box. Interior showing the cold side of the unit.

 

[Robbert]

That’s if you believe what you read. My personal experience is that heat is a major contributor to cell degradation. I’ve seen the same installations where temp controlled cells are still going after close to a decade where neighbouring non-temp controlled cells are finished inside 5 years.

Cooling is not only beneficial for batteries, but also for the other equipment (inverters etc).
I installed a cheap mini split in my garage last week and set it to 27 celcius. Good for the batteries and the inverter stays cool as well.

 

[Bluedog225]

Cell degradation speed increases as temperature increases. To what degree, I cannot personally attest.
Degradation speed slows as temperature decreases. However, past a certain point, the cell can't deliver nominal capacity until warmed back up.

Each person's situation and goals/priorities are different, and engineering thermal management systems is a real extra effort.
Having the cells last a very long time is one of my goals personally. Even if new chemistries come out, I want my system to still work.

HVAC or peliter are my two preferred ways to keep LFP cells in an optimal range to reduce degradation (both calendar aging and cycle aging).

With an insulated pack, the inefficiency of peltier units does not matter as much as without insulation.

Below is one way to do it. Still designing hope this info is of some use.

This is very cool. Do you have any consumption numbers? I was wondering how this would do if the battery were placed in a styrofoam cooler. The goal would be to have a couple of panels running a peltier and overcoming both the ambient air temp of 110 eff and the internal heat generated by the charge current.

 

[RCinFLA]

Peltier coolers are very inefficient. They take a lot of input power and generate a lot of their own heating losses.

Better if you can use a small compressor base A/C and keep condenser outside.

 

[TomC4306]