FoxESS Community - Owners & Installers Forum

I am planning a DIY solar setup that will have a 6'X6' battery and inverter shed 30m from the house. For added anti theft security, this will be a metal shed.

My question is should I install and air conditioning unit into the shed to keep things cool in the Summer? I could buy a mobile AC unit for not a lot of money and then maintain the environment at a maximum of 20C which would keep the inverter and batteries running happily. It'd only be running on hot sunny days so the PV panels should be putting out surplus energy on our off-grid setup anyway meaning it'd only be using power that otherwise would be surplus.

Has anyone done this? Good idea or waste of space and money?

That’s a good question, for what its worth the inverter and battery are both rated to 50C after which the inverter will derate, the batteries should never be operated above 50C or they will be damaged.

So that said, it depends on location and shading if the shed is in direct sunlight (make sure it is painted white) there is a good chance that it will get close to that in summer, normally good airflow and/or cooling fans should keep the temperature in the usable range - there’s nothing wrong with using a portable air-conditioner but it will itself generate heat, make noise and require maintenance so arguably using good air-flow and cooling fans would be best.

Also just to say the battery temperature ‘sweet spot’ is 30C (not 20C) where they will give you their best performance - so a note for winter that a small tubular greenhouse type heater will keep them operational.

I'd say passive measures like insulating and ventilating your shed will be much more cost effective than air con. The insulation is arguably particularly important if you want to use the batteries in winter since their performance really drops off if they get cold.

I've had good success putting x3 12V 120mm PC fans on top of the cooling fins of my inverter to control the temperatures of that bit of kit. While the inverters can and do run at elevated temperatures, given how hot the power electronics will get when doing this (especially in a shed which itself may get warm!) a bit of extra cooling in the summer definitely doesn't hurt in my opinion, I think it will very probably extend the life of your inverter, possibly considerably.

To provide some feedback into this conundrum. My set up has now been running for 2 weeks and being new, it does get looked in on often using the Fox and TIGO cloud apps to see what is happening.

The battery/inverter shed does come with its own venting louvres. Regarding the battery operating temperatures, they aren't getting as hot as I had expected. We have seen ambient temperatures in the end July beginning of August period ranging from 12C to 24C, so it hasn't been a properly hot or cold period. It's been pretty normal temperatures for Midlands UK at this time of year. The battery temperature seems to be consistently hovering around 3C above the prevailing external ambient. So, it's looking like forced cooling isn't going to be required. Our battery shed does get tree shade cover for the second half of the daylight hours.

In Winter, the outside temperature rarely falls below 0C for any extended time period and LiPO batteries retain 90% capacity at that temperature. It seems, rather than cooling maybe heating could be desirable over the Winter. I could put into the battery shed a 3Kwh heater on a thermostat set to a little over 0C; probably 3C. This would have the obvious problem of adding power demand at night when the solar input will be zero but its use to provide heat would be infrequent. Time will tell on the practicality of this approach.

Going on my experience, if your shed is uninsulated and it's close to 0 during the winter, your batteries will cool down to the point the BMS will probably disable them due to temperature. We had our system installed November '21, and by January the system had basically stopped. I bought materials (thin OSB, battens and polystyrene sheet) and made an insulated enclosure. I have since added a couple of small 92mm PC fans to circulate the air inside the enclosure. The temperature delta between the hottest and coldest cells basically never drops below 3C, and even in winter we still see the "right" amount of battery capacity - ie performance is maintained. The batteries are self heating to a certain extent, since there are losses when power goes in or out,

If we had an extended cold snap I would probably need to add a greenhouse heater or similar to my enclosure, but thus far it hasn't been needed.

Also, your home batteries are lithium based, but it's not LiPo, it's lithium iron phosphate, so their temperature and other characteristics can be quite different

The shed is uninsulated so internal temperature, you'd assume, will be closely following the outside ambient conditions. If anyone has experience of electric greenhouse heaters which seem to range from 60W to 2Kw units then that'd be useful to share. Otherwise I'll likely elect to go for a 1Kw glass panel heater that is wi-fi app linked as they have a setting available for frost protection which kicks in at 5C and switches off at 7C.

Are there the same issues with cold temperature discharging as there is with cold battery charging? If discharging isn't as much of a cold weather issue then there would be nothing to gain from heating overnight with potentially lots of battery charge to consume over a 15 hour Winters night. Basically, would cold temperature heating be best restricted to daylight solar active hours only when the batteries will be looking to be charged; PV output permitting?

Addition - Glass panel heaters are on special at the moment so I have bought a 1500W unit that can be set to run at 750W or 1500W and has the frost protection option. Reading Fox material it recommends discharge temperatures do not fall below -10C and charging temperatures do not fall below 0C.

I would really look at insulating before you spend a small fortune on keeping a metal walled shed up to temperature in winter. You could insulate the shed, but seeing how well it works just insulating around the battery stack itself, that would be my suggestion. If you leave enough volume around the battery stack to mount a couple of small fans to circulate the air, the waste heat from the BMS and the batteries themselves does a pretty decent job of keeping the batteries at a good temperature. You just want to make sure you have the potential to remove one of the sides in case the batteries are getting too warm. My garage is on the north side of the house so it is always pretty cool, and I've not had a problem with overheating, but if it were on the south side I've no doubt it would be baking, seeing as the roof is not insulated at all.

Bear in mind your batteries will lose both capacity and current delivery capacity before they actually stop working. You want to maintain the temperatures such that the lowest temperature cells in the stack are above 15C, going on what I've seen. If your internal temps of the batteries get down to single digit degrees C, you're probably looking at losing 30-40% of the working capacity.

I've actually found keeping the batteries warm enough is the hardest thing here in the UK. This is especially the case now I have both sides of the roof covered with solar panels. I've found even in July and August, the minimum cell temperature is dropping below 20C (sometimes well below) and they haven't exceeded 31C max cell temperature.

Looking at the inverter logs, they wont charge at 48A until the minimum cell temperature is 20.9C. As Dave mentions above, 30C is actually the sweet spot for these batteries and unfortunately a temperature I can rarely get them to hit even in summer.

I would think, as long as the shed is not in direct sunshine you'll struggle to get anywhere near the 50C maximum of the batteries. You'll definitely struggle in winter to keep them warm though.

With the glass panel heater I can monitor the shed temperature over the home network and using the Fox app I can also view the battery temperature. It'll be a see how it goes with regard to heating as I'm sure there will be a couple of test ground nights in the Autumn period before we enter the deepest darkest Winter months. The heating will be run off the solar input and battery store so there will, in theory, be no money cost to heating the shed. The main question will be is the heat input sufficient to maintain the desired temperature and economical enough to not drain the batteries overnight.

Even with a 8kW array, I doubt that in December or January (or February for that matter) you'll get enough solar gain to make running a 750W heater cost neutral, especially if you're heating an uninsulated metal shed, and you want to use whatever gain you do get for ordinary household purposes. I saw in your other thread you're thinking of using a generator to top up the batteries in winter? If so you'd be running a genset using very expensive petrol or diesel, in order to power a heater that would lose most of that heat to the atmosphere because it's in a ventilated metal shed. Even if you're topping up the battery from the grid at off peak prices, that's still going to incur non-trivial cost.

Is there a reason you're reluctant to insulate the batteries? Done right, that is going to take care of this problem for you with minimal to no running costs.