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Adding batteries to our UK solar setup
Adding batteries to our UK solar setup
We have a small (4.35 kWp) split east/west array, producing around 3,600 kWhs p.a. It was one of the last FiT installs in March 2019.
The panels are *absolutely* filthy with bird muck and lichen though, and are going to be cleaned soon. Even allowing for some panel degradation, I’m expecting that to go back up to about 3,900 kWhs p.a. (they were doing over 4,200 at install 7 years ago).
We imported 3,027 kWhs last year but Octoaid tells me 2/3rds of that was off peak (mostly EV charging and some time-shifted dishwasher). So our actual annual peak time import should only be about 1,000 kWhs. In terms of winter peak though it looks like about 7 kWhs peak time daily winter import is pretty normal.
On a *really* bad winter’s day the solar might only produce 0.2kWhs (so basically not worth factoring in). But more commonly around 1.5 kWhs per day minimum.
We have a non-hybrid Solis inverter and understand we’d need a new AC coupled one as part of the battery install (given the FiT).
We don’t have an attached garage or outbuilding and so the forthcoming, outdoor rated (and heated) 16.1 kWh Fogstar units look like really good value.
This would obviously be way bigger than we need right now but might it make sense to allow for our cooking and heating potentially being electrified over the next few years (we’re gas currently)?
Or do you reckon we’d be better getting the smallest battery we can get away with now, and then adding modules later (as and when required)?
Out of interest, does anyone know if you can set min/max DOD/SOC on the Fogstars?
If so presumably we could say remain within 30% – 80% or something for now (which would obviously be a bit of a waste but would presumably do wonders for the battery health)?
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13 Replies
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Not worth it. You can only save about £250 a yr. need cheaper batteries. Keep waiting for them to cheapen or if usage goes up with electricfication
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that’s interesting.
Would moving to metered export as part of this help improve that number? i.e. Importing at 8.5p (or whatever) and then exporting either on Outgoing Fixed or Agile?
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definitely not on outgoing. It’ll cost you more in battery degradation than you earn. Agile, maybe, occasionally
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We find our battery is well worth while not only for saving the excess solar power ( we have 4Kwp) but during the winter we charge the battery overnight and run the house on cheap rate electricity. We get paid triple for the power we export during the day as we pay overnight. The optimum battery size is approximately your average daily consumption excluding EV charging
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I agree – not worth it now, but will be worth doing if you switch to a heatpump. We don’t have solar, but do have two EVs and a heatpump. 12KWh battery saves us between £2 and £4 a day. Payback for the battery will be between 3 and 3.5 years
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IMHO the only way to get the full benefit of solar is to also have a battery suitable for the house daily usage and sell back as much of the solar as you can…
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Size battery to current daily winter use, maybe a bit more.
Add more battery when you move away from gas.
Logic : battery prices are dropping so right size now and add later.
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The battery saving are 70% from peak usage, and the standing charge is unaffected. 1000/365=2.74 average daily usage so your figures are extremely low. 2.74*0.30=0.822 cost currently 2.74*0.07=0.192 0.82-0.192=0.628 0.628*354=222.312 saving per year, the good news is 5kwh battery would do it.
I have not used the newer Octopus EV rates and the op may be paying more or less for peak energy, yes I am aware of 10% round trip efficiency. The above is to give an idea of savings.
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Battery and solar means that 95% of consumption is at the low 7p rate, worthwhile I think
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Thanks all for the useful comments. It feels like many of you are suggesting either waiting a bit, or getting quite a small battery and adding more later (when we actually do electrify more things).
I guess the other potential issue with going ahead now could be that we end up with a really over-specced inverter (even if we went with a small battery)?
As, to avoid needing to replace the inverter later, we’d need to spec the inverter for our *anticipated* usage (so it was ready for heatpump, induction hob etc.)? Which would be more kit sat there being under-utilised.
I’m wondering if we just hold off for now.
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8kWh heat pump keeping house nice and toasty. Peak in middle was legionella’s cycle for hot water.
House empty so nothing else going on. Outside temperature varying from +2 to -5oC. North of Scotland. 1979 timber frame bungalow with 2018 double glazing and extra loft insulation. EPC B but I think that wildly optimistic.
That gives you an idea of how much draw from a HP there should be. You’d time hot water and legionella for price dips so you can ignore that. Rest of the day, really drawing circa 1kWh continuous.
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Cooking will be the bigger draw. Definitely tempted by heatpump but we have some real issues with heatloss (bad insulation/thermal tenting behind plasterboard) and heating currently (poorly sited rads etc.). It will make sense to tackle all that as part of/in readiness for heatpump but it will be quite a messy and disruptive undertaking.
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If cleaned you may get around what you did in year 2 (degradation highest in first year). My 11 year old system delivers as if new, allowing for annual variability. Then get batteries…
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