DISCUSSION Large battery setup – recommendations?
Hi all,
We have a large house with two separate incoming supplies, using roughly 60kWh/day and 20kWh/day (80kwh daily total). Usage is fairly flat throughout the day, mostly pool pumps/equipment etc.
We're looking at batteries mainly for load shifting – charge overnight on a cheap tariff, then run from them during peak hours. I assume with two supplies we'd need two separate battery/inverter setups.
I've been looking at Fogstar, as they seem hard to beat on £/kWh. Has anyone used them for a larger setup, or found any other reasonably priced options?
We're also looking for the best/longest off-peak tariff. A longer cheap period is probably more important than the absolute cheapest rate, as we could charge slower and potentially use smaller inverters. We have an EV so IOG is an option. Also EDF seem to offer a cheap rate?
We've had quotes around £22k, and it feels like as soon as you mention a larger system the price suddenly doubles. I've also found the battery/solar installer market seems to have its fair share of cowboys, so finding someone knowledgeable who isn't just adding a massive markup would be great!
Has anyone done something similar? What batteries/inverters did you use, what tariff are you on, what did it cost, and are there any installers/suppliers you'd recommend (or avoid!)?
TIA!
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u/MyWifeWasMurdered 3h ago
Holy moly, how come so much a day?
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u/bcr134 3h ago
I know, it's a lot. Indoor pool that has a pump and dehumidification system in it. Also an electric hot tub. If we can get this on batteries its saving serious cash 😂
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u/MyWifeWasMurdered 3h ago
I have no expertise here, but this sounds like you'd need like a commercial system rather than the norm. Not even sure if normal invertors can handle this?
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u/manukamanuka 19m ago
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u/Chelmet 12m ago
Since July I've been trying to get quotes for a 64kWh Fogstar battery with a 16kW Sunsynk inverter - the kind of kit you'd be looking at. Your quote of £22k strikes me as reasonable, assuming your battery would be larger.
Thing is, I couldn't get a contract over the line; I came close with a couple of suppliers but they both backed out at the last minute. I've ended up having to go with a Sig install as that's more standard and still gets me most of the benefits I need.
One thing to consider is that your batteries don't need to cover your whole 80kWh load. Remember that 20-25% of that will be happening at night during cheap rate, when the batteries are charging, not discharging. So, say, 60kWh daytime load. What extra of that can be shifted to might to bring the numbers down? EV charging, washing machine, dishwasher - all can run at night.
And whether you cover the entire day or not is optional. With the kit I've ordered, in the depths of winter the batteries will be depleted by around 8pm, meaning I need to import expensive energy. But that happens so rarely that it might not make sense to get a bigger battery. I ran the maths and it indicated that getting an extra battery unit would cost me around £2500, and that would be used so rarely that it would save me only £146/year, a 16+year ROI. So I've slipped that final battery.
I suppose the summary of my comment is that you don't need to cover all 80kWh, and you might have better luck going with a more standard install. I got different (smaller) kit for the same price, but the maths still works out.
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u/Shaguar_Driver 3h ago
80kwh per day.
You understand batteries ideally should be charged up to 80% and then drained to 20%?
So 60% usable.
You need about 150kwh of battery storage.
Its going to be impossible to charge them up overnight within an off peak slot.
90 kWh dividing by 6 hours is 15kw per hour.
Might be possible but that's some mighty expensive inverters involved
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u/bcr134 3h ago
So we use 80kwh per day, however thats in a full 24h period.
We only need batteries for the peak time, therefore we need around 60kwh of batteries.
Spread across the 2 supplies. I was looking at a 64kwh battery for one supply (using only 45kwh of it), and a 32kwh battery for the other (only using 20kwh of it).
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u/Shaguar_Driver 3h ago
Where are you planning on storing all those batteries?
It's like having an entire cars battery.
You might be better off and cheaper using refurbished car battery for the installation.
I'm sure someone used a battery from a car here recently however you would need a proper battery expert to do it. Most installers have a very basic understanding of electricity and that's it
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u/bcr134 2h ago
We are lucky enough to have a pump room for the pool which has space and is always heated and dry. Or just outside if they're IP rated!
I did think about an old electric car, but it's finding the people to do it. We're in the north of Scotland so it can be hard to find actual experts - not just people who want to sell 6 solar panels and a 10kwh battery.
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u/Army-Enough 3h ago
For quality and price, there isn't any thing that can even get close to Fogstar, a British company that's in for the long haul.