Where do you keep your batteries?

So as im building a big pack, 20KwH, and its my first pack, for our new house, i was originally planning on storing the batteries in the garage. However, im not sure if the insurance will cover a fire started by an enormous battery which is home made.

Then i thought, well i will build a outside shed, big enough for batteries and inverters, but i recently learned that if the batteries gets cold, and charged at the same time, i will ruin them?

Im from denmark, so in the winter, it gets cold. Maybe minus 10, but mostly around 0 degrees. I know the batteries AND the inverters will generate heat, but im not sure if the shed will be warm enough, it depends ofcoourse on the sun.

So what do you guys think? Where do you have your batteries? Did you ask the insurance company?

Thanks, and best regards from Denmark.

Good idea to build a separate shed for the batteries. Not on for insurance coverage, but also the insurance that if something does go wrong, you aren't out of a home.

It is true that trying to charge a cold battery can do damage to them. However, you could always preheat the cells "before" charging. This is only required if the cells are lower than what the datasheet says is the lowest temps. I looked at a few random datasheets from our Cell Database and looks like most are 0*C charge temps. So, if you can get them above 0*C before charging, you increase the reliability of those cells.
You would want to check the low charge temps for all your cells and go with the highest temp so you don't damage a few cells and make them weak or become leakers.

What you could do to heat them up, is the first couple hours of sun, you divert the solar energy to creating heat in the shed.
If you run the inverter all night long, that might even be enough to keep the cells warm enough as the inverters put off a lot of heat as well. You could also just have a small space heater in there that is triggered to come on if the temps drop below 5*C, for example. It would only need to run for a few minutes as the shed is probably gonna fairly small foot print.
It would be best to also insulate the shed as best as possible to protect from the winter temps. I would suggest using foil board, thermal-ply, or what ever your area calls them. It's basically aluminum foil on one side of the board. Face the foil inside to make sure to radiate any heat back inside the shed.
You could even use regular aluminum foil glued to wood sheets as well if that's cheaper, though is more time consuming.
Also do a double wall like a home to give extra insulation barrier.
If you wanted to make the shed even more fireproof/resistant, build the walls out of concrete blocks. The passages would help keep a secondary barrier and you could even line the inside of the blocks with plastic to keep moisture/cold out.

Korishan said:

Good idea to build a separate shed for the batteries. Not on for insurance coverage, but also the insurance that if something does go wrong, you aren't out of a home.

It is true that trying to charge a cold battery can do damage to them. However, you could always preheat the cells "before" charging. This is only required if the cells are lower than what the datasheet says is the lowest temps. I looked at a few random datasheets from our Cell Database and looks like most are 0*C charge temps. So, if you can get them above 0*C before charging, you increase the reliability of those cells.
You would want to check the low charge temps for all your cells and go with the highest temp so you don't damage a few cells and make them weak or become leakers.

What you could do to heat them up, is the first couple hours of sun, you divert the solar energy to creating heat in the shed.
If you run the inverter all night long, that might even be enough to keep the cells warm enough as the inverters put off a lot of heat as well. You could also just have a small space heater in there that is triggered to come on if the temps drop below 5*C, for example. It would only need to run for a few minutes as the shed is probably gonna fairly small foot print.
It would be best to also insulate the shed as best as possible to protect from the winter temps. I would suggest using foil board, thermal-ply, or what ever your area calls them. It's basically aluminum foil on one side of the board. Face the foil inside to make sure to radiate any heat back inside the shed.
You could even use regular aluminum foil glued to wood sheets as well if that's cheaper, though is more time consuming.
Also do a double wall like a home to give extra insulation barrier.
If you wanted to make the shed even more fireproof/resistant, build the walls out of concrete blocks. The passages would help keep a secondary barrier and you could even line the inside of the blocks with plastic to keep moisture/cold out.

Click to expand...

Good info as usual Korishan! i was gonna insulate the concrete floor, as well as the walls with rockwool leftovers from the house. I think you're right, just putting a small heater out there would be enough. the shed will only be 1 square meter or similiar.


Is there an upper temperature limit that can damage the cells - In case the shed gets like 35 Degrees celcius?

Did you check with your insurance regarding your battery, or is that already outside your home?

My battery set up will be outside when done. But it's also going to be inside a metal box. Similar to server racks.

You'll have to check the datasheets for your upper temps as well. But they are usually pretty high. I think the ones I looked at quickly were around 60*C. Obviously this is super upper limit and you wouldn't want to come close to it.
A cell working in >40*C should be fine, you just don't want the cell itself to be putting off those kinds of temps during charging/discharging. I think 35*C is about what Peter (HBPowerwalls) said his shed was at in one of his vids. So you should be fine, I would think.

But again, you'd want to look at the datasheet for your cells. And then the "lowest" high temp rating is your ceiling.

I am not sure that insulating the concrete floor is a good idea. In the winter time heat from the ground will probably help keep the shed above freezing, and in the summer time when the Air Temp is alot higher than the ground temp an uninsulated concrete floor will probably help lower the temperature in the shed. I think everything else should be insulated though.

Storing and using the cells in high temperatures shortens the life too. But how my how much the life is shortened and how hot is too hot is always being studied and debated. I use the rule if it is to hot for a human to work or live comfortably, it is probably too hot for the cells to be stored at too.

Cheers,
Rip

Just insulate it with some kind of insulation. I just use 3" rockwool (roughly R13?) and tarp the outside for moisture barrier for my outhouse. I put rockwool at the base too. Depends on your idle loss and the size of your enclosure, for example my PIP generates 50W of idle loss heat. With that a -10C outside temp is nothing to my outhouse. I have a small ceramic heater that kicks in under 5C. So the temps have to drop below -10C to activate the heater.

See the temp chart.

not2bme said:

Just insulate it with some kind of insulation. I just use 3" rockwool (roughly R13?) and tarp the outside for moisture barrier for my outhouse. I put rockwool at the base too. Depends on your idle loss and the size of your enclosure, for example my PIP generates 50W of idle loss heat. With that a -10C outside temp is nothing to my outhouse. I have a small ceramic heater that kicks in under 5C. So the temps have to drop below -10C to activate the heater.

See the temp chart.

Click to expand...

Then i thought, well i will build a outside shed, big enough for batteries and inverters, but i recently learned that if the batteries gets cold, and charged at the same time, i will ruin them?

Korishan said:

What you could do to heat them up, is the first couple hours of sun, you divert the solar energy to creating heat in the shed.

Click to expand...

Great Idea Now, have You got a good idea of how to actually do this?

We need to get the power from the panels to the heater, but using the charger is not an option, so I can not seem to wrap my head around this one.

Can You help me?

ChrisD

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amcic1998 said:

not2bme said:

Just insulate it with some kind of insulation. I just use 3" rockwool (roughly R13?) and tarp the outside for moisture barrier for my outhouse. I put rockwool at the base too. Depends on your idle loss and the size of your enclosure, for example my PIP generates 50W of idle loss heat. With that a -10C outside temp is nothing to my outhouse. I have a small ceramic heater that kicks in under 5C. So the temps have to drop below -10C to activate the heater.

See the temp chart.

Click to expand...

Then i thought, well i will build a outside shed, big enough for batteries and inverters, but i recently learned that if the batteries gets cold, and charged at the same time, i will ruin them?

Click to expand...

This depends how cold. Most cells can be charged as long as the temp is above freezing, but the capacity will degrade quite a lot.

My personal experience is that You have to keep the cells above freezing to play it safe. Frost took 18 of myNCR18650PFcells.
They simply opened the CID. End of life.

ChrisD

ChrisD5710 said:

Korishan said:

What you could do to heat them up, is the first couple hours of sun, you divert the solar energy to creating heat in the shed.

Click to expand...

Great Idea Now, have You got a good idea of how to actually do this?

We need to get the power from the panels to the heater, but using the charger is not an option, so I can not seem to wrap my head around this one.

Can You help me?

Click to expand...

I'm not exactly sure of the electronics and wiring, but I think the easiest would be to use a thermocouple to detect the pack temps, a double throw relay (1-0 and 0-2 connections) that can handle full amps of the panels, and a power source (the panels)

The relay default position is to the charger. But the thermocouple with some other bits of components like a transistor and resistor, diode and such, will pull the power to trigger the relay to the heating element. The reason you want the default to go to the charger is in the event the thermocouple malfunctions or some other component and you don't end up cooking your packs. Altho, the heating element should also have it's own thermostat to shut it off if it gets to high anyways. When dealing with heat, always have plenty of safety features in place.

I know it can be done as I've seen this type of circuit used in other applications. The solar panel provides the input voltage that powers the relay, thermocouple and transistor. When it gets enough sun, everything comes alive. If the thermo is cool enough, there's enough resistance (or not enough, depending on which way it works, i'm not sure) it allows the transistor to activate and power the relay to switch to the other leg.
Once the temp comes high enough, the thermo has the proper resistance and releases the transistor, which releases the relay back to the default position.
You would also need to add in a secondary circuit to keep the thermo from triggering the relay back until the panels have gone non-powered. So you'd have a capacitor in the circuit to create a latching effect. This is so that if a cloud goes by, or the packs cool a little while not being used it doesn't trigger the heater and turn the charger off.

Or, the other option, if you want to get into programming, is to use an MCU of some sort, like an arduinio or other microcontroller. You can program it to perform exactly the way you want it when you want during the times of day you want. Also, you could even make it so that if the temps drop low enough, trigger the heater to bring the cells back up before continuing to charge.

@not2beme,
For your info: For an insulation value of an r13 you will need ~15 inch of rookwool, 3 inch will give you an extra in your construction of ~2.
Rc is your added(not total!) construction value, rd is your declared value of the material thickness (heat loss in time)

It is never a bad idea to insulate your concrete floor, but use a material that will not absorb any moisture, like:xps and not styrofoam or pir/pur sheets.
It will surely help you to get more stable temperatures in your shed.
If the temps will drop with 10c, your insulated concrete floor is still warm enough to get you thru the first nights, other way around also.
And it will give you an average temperature between night and day.
If its not insulated you will lose a lot of heat into the ground(winter) and you will not get rid of it easy in the summer.
It is also advised that you glue a pir sheet at the inside of your door(1 to 2 inch will do fine)

For use of rockwool in walls there is a rule: never let living moisture get into your construction.
So use at the inside of your shed closed plastic foil, simple cheap construction foil is the best.
At the outside of your shed use that so called: damp open foil.
Mine plan of attack would be, a dehumidifier if you live in a humid area and a small 100 watt heating element set on a min and max temperature.

https://www.aliexpress.com/item/33025927630.html?spm=a2g0s.9042311.0.0.4e874c4dlK0GLW
https://www.aliexpress.com/item/33003897649.html?spm=a2g0s.9042311.0.0.27424c4dkbR3hC

I must say for my tobacco oven/curing kiln i am very pleased, but it is very good insulated
You can always go bigger in watts.

Hope this was helpful information, my two cents.
Best.