High Ambient temperature

[asder]

Greetings, just wanted your opinion on high ambient temperature and whether that would be an issue to keeping LFO batteries, or should I look for cooling solutions?

These days where my solar inverter is set up, the ambient temperature is around 45 degrees celcius to 50 degrees celcius. I am guessing during the afternoons it climbs up a bit more. Would using a few computer cooling fans do the trick of keeping the cells happy? Or should I start wondering about cooling solutions and insulation?

I have a 48V solar set up, professionally installed and inspected for net metering. Still in the process of getting the cells sourced from Alibaba, shipping to Pakistan is no joke apparently, no one is willing to touch my order.

 

[zaps]

I'm not familiar with LFO (Lithium Iron Oxide) batteries. Did you perhaps mean Lithium Iron Phosphate (LiFePo4 / LFP)?

 

[gnubie]

Assuming lifepo4, 45c ambient is getting up there, you really want the batteries to be less than that to ensure the cells don't go over temperature during high loads. Fans wouldn't help much since they will just blow hot air around, unless its an enclosure and you are talking about venting it to get cooler air in. Can you shade where they kept or are we talking about the air temp in the shade?

 

[asder]

My bad, typo there. I meant LFP, LifePo4. Sorry about that. That is 45 degrees in the inside in shade. Didn't know about the 1hr edit rule.

 

[zaps]

From https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/, about premature LiFePo4 battery aging:

Go over 45 Centigrade and things speed up considerably! Public enemy no. 1 for lithium-ion batteries, by far, is heat!

There is more to calendar life and how quickly a LiFePO4 battery will age: State-Of-Charge has something to do with it as well. While high temperatures are bad, these batteries really, really do not like to sit at 0% SOC and very high temperatures! Also bad, though not quite as bad as 0% SOC, is for them to sit at 100% SOC and high temperatures.

 

[asder]

Thank you zaps. I read that article and a few more like that. While others have low temperature issues, I have the other end. Other than using a wooden box and using insulation, anyone have any ideas on how to cool down batteries? Night time the weather remains hot for a few months. With a break every 3~8 days for a day or two. I was thinking a DIY CPU cooling setup kind of thing, if anyone has better, more efficient, less power consuming ideas, I would love to hear those.

 

[BiduleOhm]

Use some peltiers elements; super cheap on ebay/aliexpress and plenty good enough if you use an insulated battery box to keep the cold inside.

Also, run them at half their rated power to have better efficiency

 

[asder]

Use some peltiers elements; super cheap on ebay/aliexpress and plenty good enough if you use an insulated battery box to keep the cold inside.

Also, run them at half their rated power to have better efficiency

Thank you BiduleOhm, I will look into that. Would I put the cold side in a small square cutout in the box? Or would I use an aluminum/copper sheet that is attached to the cold side? The hot side will have a heatsink and fans blowing the air out? All this would work on a 12V system?

Or do I just expose the hot side to the elements with a heat sink on it but no fans?

Longevity doesn't seem to be an issue, especially if running them at half the power. How tricky would it be for a beginner to set up a temperature sensor for it, so that it automatically turns on and off at specific temperatures? Wouldn't want this to keep on running during winter times or bringing the temperature down during cool autumn days.

I am still in the planning stage with LifePo4. No batteries, no equipment, just lots and lots of questions. Still trying to get the shipping sorted, I have to get everything sorted out at my end for shipping as they don't ship here sadly.

 

[BiduleOhm]

The best for the cold side would be to attach it to a 4-6 mm thick aluminium (or copper but it's expensive for not much more perfs, so unless you have one taking dust on a shelf use aluminum) plate the size of the side (or bottom) of the battery box so it spreads the power the best it can to all the cells.

For the hot side you need a decent heatsink with fans or a big heatsink without fans. That's because you need to get rid of the power you removed from inside the battery box + the power the peltier use.

Yes, pretty much all peltiers device are made for 12 V. The simplest thing to do to run them at a fraction of their max power is to put two in series (so each gets 6 V), that way they'll not work too hard and the efficiency will be a lot better, like 2 or even 3 times better, the downside is that delta T will be less but you don't need a lot of delta T anyway, 20-25 °C will be plenty good. For more info you can read: https://www.meerstetter.ch/customer-center/compendium/71-peltier-element-efficiency

Given your usage and with an isolated box you'll not need to remove more than a dozen W max once the steady state is reached so two TEC1-12706 (or 12705) should be plenty enough.

I recommend a simple thermostat with a nice 8 or 10 A relay so it has a long life. You can go with something like that https://www.ebay.fr/itm/20A-W3230-L...754077?hash=item286d9ddcdd:g:pDgAAOSworhb6i5a for example. Make sure it works in 12 VDC (and not 120 or 240 V) and that it can be used in cooling mode (most thermostats are used to control heating so some of them can do only that). Place the sensor on the opposite side of the battery from the peltier plate so it doesn't spend its life short cycling.

NB: do not put the BMS inside the cooled box unless you want to triple or quadruple the power you need to extract with the peltiers...

NB²: if you want to run all the maths: https://www.meerstetter.ch/customer-center/compendium/32-tec-peltier-element-design-guide

 

[sremick]

One big thing to watch out w/ peltiers: condensation or frost on the cold side. If you have any humidity, you might need to devise a means to deal with the accumulated water and make sure it stays away from the electronics.

 

[nosys70]

peltier element sucks because conversion rate is VERY low. So it would work only with very good insulation and lot of extra energy.
you have the choice to either use passive cooling (that in your case should be easy) or active cooling (but the energy bill is high).
passive can be otbained by evaporating water on a clay surface for example, if you got some wind is is even more efficient.
active cooling can be obtained by recycling a small fridge (top loading/chest type).
getting the enclosure air tight is important because cooling significantly air will cause condensation, that will put water everywhere.
i let you imagine the result when mixed with electricity.

Peltier is ok when you have a small insulated enclosure and want to cool a bootle for example.
When the bottle is cold, it requires very small energy to keep it cool if insulation is good.
but if the thing you want to cool is continuously releasing heat, it will not work.
I think your battery will be on the large type, so peltier cooling seems not a good idea.

 

[BiduleOhm]

Based on what I recommend the COP will be at least 0.6 and the average should be around 1 so that means one watt of heat removed for each watt eaten on the electrical side.

It's true peltiers have a pretty bad COP (usually less than 0.5 so you need 2 W or more for each watt of heat moved) but here we are talking moving a dozen of watts released by the battery when charging/discharging + the losses through the isolation which should be a few watts max; and we can have a pretty nice COP thanks to the low delta T needed, but even with a COP of 0.5 it wouldn't be a big problem.

You're right about condensation. It all depends on the % RH and the delta T, we need more info (country?) as if it's in the middle of a desert condensation will not be a problem, but if it's a tropical island it will definitely be a problem.

 

[asder]

Communication is key. I can't always speak to the voices in my head and expect others to listen . Should have given all this info in the first post.

Country: Pakistan
Temperature ranges according to months with humidity (in Celsius)
April to July: Temperature starts around 30 degrees and quickly climbs to 40 degrees range by May. June and July it starts touching 45~49 and coming back. Humidity before the monsoon is around 50% to 75%.
July-September: Temperature stays between 35~45 degrees. When it is raining, it cools down, other times....Humidity is close to 100%, depending on the monsoon.
September to November: Temperature slowly comes back down to 25~29
November to January: Depending on winter severity, the temperature drops to about 3~5 degrees, day time is about 12~19 on different days. There is significant fog.
January to April: Around mid February we see a rise back to the 20's range and crossing the 30's range closer to April.

Night time temperature from May to September is only about 4~8 degrees cooler than the day.

Just to give you an idea of the ambient heat. By mid May usually, the cold water pipes stop giving cold water. Water tanks are usually located on the roof, pipes are exposed and on the outside of the house on the sides (that is how they construct stuff here, don't ask why) until they run in to the bathrooms, kitchen etc.

Monsoon season has the worst humidity, followed by winters and foggy nights. Climate is changing, so some times a season is long and other times it is very short.

There is lots of dust and sand in the air as well. Dust storms are frequent. Can't really go and build windows or holes. Could create vents and cover those to allow hot air to vent out on the roof structure. We have flat rooves here.

This roof is cramped in this picture, but the structure in the middle is where the access point is for the roof, with the windows on it. The other one is probably the water tank. Most Inverters and batteries will be found at that access point, including mine, on the inside. The main distribution box where all the ac circuit breakers is located at the ground floor usually, right underneath this roof access point. I am contemplating on getting that access point insulated better. Currently it is a single layer brick structure.

We use 220V ac here. Have a solar set up of about 5.5Kwh on a 5.2Kwh inverter. Aerox, Inverex. The name has changed here, but most of the inverters usually have a Chinese parent company supplying the world under different brands.

I want to add a 48V 280ah LifePo4 backup. 16S only for now.

I want to create as low tech solutions as possible because the higher tech you go, more chances are something will go wrong and parents will call at all hours to fix the issues.

I like nosy70's idea of using clay pots (easy to buy those here), fill them up with water and let them do their magic. Use a few 12V dc computer fans to move the air around. I was thinking of using a wooden box with a few insulation layers to keep the heat out. I question that sometimes because after 9 months, the heat is bound to creep in at some point? That is why I like peltiers but the condensation will be an issue. Even regular fridges in the houses have trouble running and keeping up with the heat and humidity. Another idea I was playing around was using cpu/gpu "water" cooling solution to keep the batteries cooler.

Hopefully this gives you guys a little idea of what I am trying to do, and why the high ambient temperature is a concern for me.

 

[nosys70]

i plan to install my system in cuba where the problems are pretty the same (even worse)
at first a planned to put the batteries into a water/air tight box with very few water or oil (soya oil is very cheap) (half inch maximum)
the box would be isolated with with polysteren.
then put a little pump that push the cooling liquid in a aluminium heat exchanger with peltier and air cooling.

but a peltier module eats a lot of amps (about 8-12 on 12V) so it means that you need to run it almost permanently and use over 100w of power.
i planned to dedicate a solar panel to peltier, so you do not even need to convert electricity. (else you go onto the problem of using battery to cool the same battery)
Peltier are small then cooling is slow. to cool a few liter of oil, it would takes hours. so you can not expect to put a thermostat and cool the oil when needed, because the inertia will be too high.
the problem is if the air you use to cool the peltier is already at 45 deg C, it will be hard to go around 20.
Another solution is just to use liquid to absob the eventual temperature spike, but it requires more liquid.
Basically it would be the same setup without the peltier and use passive dissipation.
the problem of evaporating water to get cool is it works fine if you can evaporate water.
but with 75% of humidity in air, this would not work.
you can also think about using solar heating to create cold.

 

[DThames]

About 2 meters deep in the ground, the ground should be a lot cooler than the air (25C). You could make a liquid cooling loop and dump the heat into the ground. This is how a geothermal cooled air conditioner works. Pumps cool water in a pipe, the water It cools the Freon, and then circulates the warm water under ground to cool the water off, (closed loop water cooling). Or if you have an endless supply of well water, you can pump from the well and circulate that water to carry away the heat. Dump that warmed water or use it to water plants.

 

[BiduleOhm]

Communication is key. I can't always speak to the voices in my head and expect others to listen . Should have given all this info in the first post.

Country: Pakistan
Temperature ranges according to months with humidity (in Celsius)
April to July: Temperature starts around 30 degrees and quickly climbs to 40 degrees range by May. June and July it starts touching 45~49 and coming back. Humidity before the monsoon is around 50% to 75%.
July-September: Temperature stays between 35~45 degrees. When it is raining, it cools down, other times....Humidity is close to 100%, depending on the monsoon.
September to November: Temperature slowly comes back down to 25~29
November to January: Depending on winter severity, the temperature drops to about 3~5 degrees, day time is about 12~19 on different days. There is significant fog.
January to April: Around mid February we see a rise back to the 20's range and crossing the 30's range closer to April.

Night time temperature from May to September is only about 4~8 degrees cooler than the day.

Just to give you an idea of the ambient heat. By mid May usually, the cold water pipes stop giving cold water. Water tanks are usually located on the roof, pipes are exposed and on the outside of the house on the sides (that is how they construct stuff here, don't ask why) until they run in to the bathrooms, kitchen etc.

Monsoon season has the worst humidity, followed by winters and foggy nights. Climate is changing, so some times a season is long and other times it is very short.

There is lots of dust and sand in the air as well. Dust storms are frequent. Can't really go and build windows or holes. Could create vents and cover those to allow hot air to vent out on the roof structure. We have flat rooves here.

This roof is cramped in this picture, but the structure in the middle is where the access point is for the roof, with the windows on it. The other one is probably the water tank. Most Inverters and batteries will be found at that access point, including mine, on the inside. The main distribution box where all the ac circuit breakers is located at the ground floor usually, right underneath this roof access point. I am contemplating on getting that access point insulated better. Currently it is a single layer brick structure.

We use 220V ac here. Have a solar set up of about 5.5Kwh on a 5.2Kwh inverter. Aerox, Inverex. The name has changed here, but most of the inverters usually have a Chinese parent company supplying the world under different brands.

I want to add a 48V 280ah LifePo4 backup. 16S only for now.

I want to create as low tech solutions as possible because the higher tech you go, more chances are something will go wrong and parents will call at all hours to fix the issues.

I like nosy70's idea of using clay pots (easy to buy those here), fill them up with water and let them do their magic. Use a few 12V dc computer fans to move the air around. I was thinking of using a wooden box with a few insulation layers to keep the heat out. I question that sometimes because after 9 months, the heat is bound to creep in at some point? That is why I like peltiers but the condensation will be an issue. Even regular fridges in the houses have trouble running and keeping up with the heat and humidity. Another idea I was playing around was using cpu/gpu "water" cooling solution to keep the batteries cooler.

Hopefully this gives you guys a little idea of what I am trying to do, and why the high ambient temperature is a concern for me.

Ok so humidity can by very high. If you go that path I recommend to have the cold plate on the side (instead of on the bottom) with a few small holes below it to drain any condensation.

Also with high % RH you can forget about using evaporative cooling (clay pots, etc...) unfortunately.

but a peltier module eats a lot of amps (about 8-12 on 12V) so it means that you need to run it almost permanently and use over 100w of power.

It all depends on the module and how you power it. Here I recommended 5 or 6 A ones running at half the current only so around 30 W total. And it'll not run all the time, only when the temp goes too high.

About 2 meters deep in the ground, the ground should be a lot cooler than the air (25C). You could make a liquid cooling loop and dump the heat into the ground. This is how a geothermal cooled air conditioner works. Pumps cool water in a pipe, the water It cools the Freon, and then circulates the warm water under ground to cool the water off, (closed loop water cooling). Or if you have an endless supply of well water, you can pump from the well and circulate that water to carry away the heat. Dump that warmed water or use it to water plants.

I like this idea

 

[asder]

i plan to install my system in cuba where the problems are pretty the same (even worse)
at first a planned to put the batteries into a water/air tight box with very few water or oil (soya oil is very cheap) (half inch maximum)
the box would be isolated with with polysteren.
then put a little pump that push the cooling liquid in a aluminium heat exchanger with peltier and air cooling.

but a peltier module eats a lot of amps (about 8-12 on 12V) so it means that you need to run it almost permanently and use over 100w of power.
i planned to dedicate a solar panel to peltier, so you do not even need to convert electricity. (else you go onto the problem of using battery to cool the same battery)
Peltier are small then cooling is slow. to cool a few liter of oil, it would takes hours. so you can not expect to put a thermostat and cool the oil when needed, because the inertia will be too high.
the problem is if the air you use to cool the peltier is already at 45 deg C, it will be hard to go around 20.
Another solution is just to use liquid to absob the eventual temperature spike, but it requires more liquid.
Basically it would be the same setup without the peltier and use passive dissipation.
the problem of evaporating water to get cool is it works fine if you can evaporate water.
but with 75% of humidity in air, this would not work.
you can also think about using solar heating to create cold.

Best of luck with your oil set up. That idea never came to me, nor would I have the expertise to ensure that it would work for me. My batteries would probably get a tan. My brother went with liquid cooling for his pc. I just saved up more money and got an AC installed in the room. DIY is amazing in my head, but practically just starting to get into it to solve things to make life easier.

About 2 meters deep in the ground, the ground should be a lot cooler than the air (25C). You could make a liquid cooling loop and dump the heat into the ground. This is how a geothermal cooled air conditioner works. Pumps cool water in a pipe, the water It cools the Freon, and then circulates the warm water under ground to cool the water off, (closed loop water cooling). Or if you have an endless supply of well water, you can pump from the well and circulate that water to carry away the heat. Dump that warmed water or use it to water plants.

This is a fascinating idea. Right now I would have to dig through lots of concrete and ruin a few tiles to make this work. Parents would definitely kill me. I will definitely keep this idea for the house we build next time. Just have a pvc pipe within a pvc pipe. Dig a hole 2 meters underground, create a small water tank. I am guessing a water pump would be required at the ground level to pump the water up? An ac kind of unit at the top to regulate the air. This would be a very efficient solution indeed. I emailed a few companies, let's see if any of them check their emails or just send new emails to trash (companies in Montreal had that setup, weird). Beside the cost issue and to see if anyone has the expertise here, this is a simpler solution. I will definitely keep this in mind for future construction projects.

Ok so humidity can by very high. If you go that path I recommend to have the cold plate on the side (instead of on the bottom) with a few small holes below it to drain any condensation.

Also with high % RH you can forget about using evaporative cooling (clay pots, etc...) unfortunately.

Would the small holes allow hot air to come in? Or that won't be a major issue? I figured, during monsoon season the sweat never evaporates from your clothes. If I put a fan on the same circuit (still learning these little things) as the peltiers, would the fan have to be in parallel, series or a totally different wire to get dc power?

I was talking with my mom. Our initial idea is to use some thick insulation foam on the outside. Put a wooden board. Cover the whole structure on each side of the wall with fiber glass so as to protect it from rain and high winds. The roof of the connection point will be similarly covered. Wooden boards would be varnished to protect against sun and rain. As long as that brings the temperature down by 4~8 degrees celcius, that would be a major step forward. Or would that kind of insulation not make such a big difference? I have never used insulation actively in projects. Homes either had it or it didn't, never bothered to wonder how much and what kinds affected temperature in what way. This should also help in winter time to keep the cold out a bit. This installation would require drill and long screws (bolts, not sure what they are called, the long threaded bolts). I would not require to call anyone to do this. The fiber glass will require a professional installation because they always make custom installation here.

 

[BiduleOhm]

No, just a few 5 or 6 mm holes won't be a problem as they all would be on the bottom, no convection possible.

The fan(s) is/are fed by the same thermostat as the peltiers to be turned on and off at the same time

 

[asder]

No, just a few 5 or 6 mm holes won't be a problem as they all would be on the bottom, no convection possible.

The fan(s) is/are fed by the same thermostat as the peltiers to be turned on and off at the same time

What kind of material would be best for the case? I was thinking a simple wooden case with 2 layers of Styrofoam? Or are there better insulation materials available?

 

[DThames]

For a water circulation system a tiny pump is all that is needed.