Battery Insulation/heating?

[Ched]

I have 2 x hv2600 batteries in my loft and they are getting too cold to charge and discharge.
I was thinking of making an insulated box out of 50mm of polystyrene. Is this ok or is there a better way?

Cheers for any suggestions.

[Dave Foster]

The community has come up with many elaborate solutions for this (me included) - 50mm Kingspan would be better, but anything is better than nothing.

Make sure you maintain an air-gap (officially 300mm) and make it such that it can be removed when the weather warms up in June/July/August as getting too hot (>50C) is worse than too cold.

[calum]

We had our system fitted almost exactly a year ago, and the unprotected batteries stopped working several times during the cold snaps we had last winter. I built the box in mid January, and after that everything worked pretty well, although we probably weren't getting the absolute best capacity out of the batteries. I suspect a lot of that was more down to firmware than temps, though.

If I were doing it again (or advising someone else!) I would say make sure you insulate all six sides, allow for internal air circulation, and ideally allow that air circulation to become air throughput if needed - potentially allows you to duct in cooler air from outside if elevated battery temps are a concern.

I bought the 25mm sheets of EPS in a pack because a) they would fit in my car easily and b) it was the cheapest way to get the amount of insulation I needed. I cut them up to fit on the OSB panels. The back panel of the box (not visible in the photo) only has 25mm of insulation, because otherwise it doesnt fit! It maybe that is part of the reason for the variance in my case, there are individual cell temp values available in the Foxess website, and I daresay I could work out which cells are at the front or back of the banks, but we'd be well into diminishing returns at that point. But I put the box together in the garage and all the other panels got 50mm of insulation from the off, so I can't really say how much difference it would have made vs 25mm (or 50mm!) all round.

If you're going to the trouble of getting up into the loft and building an enclosure, I'd go with 50mm to begin with. How warm did your batteries get in the summer? if you expect to need to dismantle the thing to allow them to cool, I'd aim to add some hard materials to the outside, otherwise just making it out of insulation will likely fall to bits after a few seasons, especially with EPS. The Kingspan polyurethane stuff might do better but I'd still suggest you do something structural even then. I did 9mm OSB for lightness, with battens on the corners and threaded inserts and bolts so it won't mind being disassembled and reassembled.

I couldn't get a big sheet of 50mm Kingspan into the car, so I went with the EPS. It works fine, but it's quite crumbly when you cut it. The official guidance does indeed say 300mm air gap all around, my box has something like 25mm at the back and sides, more like 100mm at the front as it has to make room for the cables. I was fully prepared to dismantle it for summer but I've also been keeping an eye on the temps. It's been completely fine and overheating has never been a problem, I just prop the lid open in the summer. BUT that's in a cool shaded garage with a lot of thermal mass to regulate temperature changes.

In a loft you don't have the same thermal mass, and of course they can get really hot in the summer. Even without an insulating box, during a long spell of warm weather I could see your batteries getting uncomfortably warm. So again, if I was doing this in your situation but knowing what I know, I'd be looking at arranging to duct cool(er) air in from the outside and passing it through the battery enclosure.

During cold weather you'd still want to circulate air within the enclosure to keep temps as even as possible. Ideally you'd be able to use the same fan for this as you were using for throughflow in the summer, but this is already possibly a bit overengineered.

EDIT: I didn't explicitly mention heating, given that a 40W tube heater from the likes of Dimplex is relatively inexpensive, combining that with a fan and the built in thermostat definitely seems worthwhile. My enclosure is currently unheated, thus far the tactic of spreading the heat from charging and discharging around with fans is keeping the "Low Cell Temp" above 15C, but I can see the amount of charge it accepts starting to drop a little, so I'd not want it to get much colder than this.

All that said, these batteries are costly and resource intensive to manufacture, I think it makes good financial sense (as well as moral and practical sense) to look after things and give them as long a working life as possible.

[Ched]

Cheers everyone.
I nipped out to Wicks as they had smaller sheets that would fit in the car, the kingspan they had was either 2400 x 1200 or 1200 x 450 which would have been better it it were 1200 x 600.
I ended up buying 3 x Jablite HP+ External Wall Insulation 70 Expanded Polystyrene Insulation - 1200 x 600 x 50mm at £10 each. Just cut 2 of them in half so 600x 600mm then created a box with that and some 50mm gaffer tape. Then cut the remaining one to make a lid. Couple of slots for the cables and looks good for the winter. I will keep an eye on the cell temps over the coming days and probably remove it in spring. It's very easy to get at as we have a dormer bungalow with a small door to the loft space and the batteries and inverter.

It's not perfect but it will do till I can monitor the temps and see how we go.

Thanks again.

[Ched]

OK so it's not even been 24 hrs since I fitted my insulating box and the battery temps are so much better. After a full charge overnight the cell temp was 28.7C and at 12 midday today it's down to 21C so not too bad at all. The batteries charged at their full rate which is great. Looks like a box of 50mm of polystyrene (chipboard floor under batteries) in a loft works fine.
I will continue to monitor the battery temps as the weather warms up a bit.
Cheers

[calum]

Out of interest what are the ambient temps in your loft?

[Ched]

Out of interest what are the ambient temps in your loft?

Just had a quick check the loft is about 4 deg C, outside is about 2 deg C, batteries currently on Self Use at 25.2 deg C = BMS Cell Temp Low.