What battery size for pre installed solar?

[ade73]

Looking for advice on what sized battery for pre installed solar array.

We have x13 285w panels on the roof with a Zeversolar inverter, installed in 2015. We didn't get a battery at the time as the installers said to wait as these would drop in price as the solar installs did.

Well they never did and we have looked at getting a battery a couple of times since.

Prices seem to be around £4,000 for a 5kw and inverter.

We had a leaflet through the door for switch together (North east Mayor thing for collective prices)

After submitting our details they have got back to us with a quote of £4500 but for a 15.6kw Fox battery and inverter, much bigger then the sizes we were originally looking at.

Last year we used 1,521.9 kwh and Generated 3504.1.

2 Person household, 1 work's from home Mon-Fri and 1 work's alternating days and then lates Mon-Fri site based.

No EV and no interest in one. Regular household appliances, couple of laptops, a work computer, cross trainer and home cinema set up.


Is this this battery overkill or a good idea?

T.I.A

[kambites]

The usual advice is "get a battery big enough to cover your average daytime usage". That way you never have to import from the grid at peak rate.

[Steve H]

Or, get a battery big enough to ensure you have plenty stored when the sun isn’t shining, particularly overnight.

Your usage looks pretty low, very low in fact compared to ours . We have a 30kwh battery setup which works well so I would think 15 would suit pretty well.

I wouldn’t think it’s over the top although again, with such low usage any gains are going to be smaller and any payback will be quite long.

[biggiles]

The battery itself itself isn't all that expensive - so going from 5kwh to 15kwh can be surprisingly cheap. Bear in mind you only use about half the capacity of the battery (for longevity), so if it's only £500 to upgrade to 15kwh I'd think that was good value in itself.

[OutInTheShed]

The standard voltage for solar batteries seems to be 48V nominal.
That means 16 cells.
The best value per kWh seems to be ~305Ah cells, which makes about 16kWh the 'obvious' size.

You can have a lower voltage and fewer cells, people do this on boats and camper vans. Efficiency is less I think it's generally safe to say, unless you run 12V stuff straight off the battery.
You can have smaller cells, but a 100Ah cell is often not much cheaper than a 300+Ah.

We are starting to see much cheaper units, see the balkonsolar thread.
For a low user I suspect the best course financially is to wait, unless you are really keen to have a solution for power cuts?

[Sheepshanks]

ade73 said:

Last year we used 1,521.9 kwh and Generated 3504.1.

Are you using 1500/yr (which is extremely low) or 5000 (which is pretty hefty)?

[geeks]

I'll leave you to your musings. But I will offer this. Our install was done under the solar together scheme and we got a pretty decent deal out of it. We have a Fox Inverter and 2 x 11.5kw batteries and have been impressed with the whole thing, the Fox gear is good value and since it was installed in May has given us no trouble, the App is pretty good as well.

[untakenname]

With the current low price per kwh getting more battery capacity is worth it for future proofing.

Bear in mind that new regulations for battery placement come in next month which severely curtail where they can be mounted in the house so might be worth trying to get them installed asap beforehand.

[Byker28i]

We can use 15kw a day, oven, washing machine take their toll.
I'd get the big battery

Switch Together was formally Solar together, the scheme that we got our install done with almost 2 years ago. They get agreed cheaper prices based on having a number of residents signed up wanting solar.

We had 5kw battery, invertor and 5kw of panes for £5700. I've since added more battery storage and may add more. Wih the export tariff dropping, it's better to store as much power generated as possible.