Adding a battery to existing solar.

LateStarter

So, after about 2 years of having my solar panels, I'm comfortable with the system and my usage patterns. I'm currently exporting with EoN, at 16.5p, which seems to no longer be available. So now I wonder if there's going to be a general trend of SEG payments decreasing (as more people adopt solar and sell excess power), which will of course affect payback time.

Has anyone done the maths to see if batteries now make sense? My initial calculations say not - I don't have an EV, so ultra cheap night rates aren't available, are they? But I'm hoping someone will show me I'm wrong…

—edited to change rate to 16.5p—

Screwdriva

Glad to hear the system is performing for you! Any reason you've gone with Eon when Octopus offers export at 12p per kWh and Ecotricity at 16p per kWh?

Your annual electricity import plays a massive role in the calculation for return on investment. What is your annual consumption?

Newbie_John

Battery.. so much depends on it's size, cost, your usage, export rates, import rates for top ups etc.

For some it will make financial sense for some it won't.

LateStarter

https://forums.moneysavingexpert.com/discussion/comment/81937033#Comment_81937033

Sorry, big fat typo on my part - 16.5p. was the best deal last September. Changed now.

Screwdriva

As hard as I have tried, our numbers cannot justify a battery at ~1600 kWh per year imported & ~6000 kWh exported @ 16p per kWh.

That will change when we eventually get a heat pump but I suspect that won't be for another decade. Or if export tariffs drop dramatically.

NedS

https://forums.moneysavingexpert.com/discussion/comment/81939517#Comment_81939517

Yes, with those numbers the grid is your (annual) battery, for now. Like you say, a collapse in SEG rates will completely change the economics.

Given the complete unknowns about where ToU tariffs and rates will go over the next 10 years, trying to justify purely on price is a non-starter. If you value flexibility and resilience, or you are capital rich but income poor and want to minimise outgoings in retirement (for example), then those can factor into any decision.

Screwdriva

https://forums.moneysavingexpert.com/discussion/comment/81939820#Comment_81939820

The vast majority of the 250+ people I have helped adopt Solar PV are extremely price focussed (can't say I blame them) and a return on investment is, by far, the number of criteria used to evaluate all system quotes.

After experiencing our first 60+ second blackout a few weeks ago, I have to say I agree with your sentiment more with each passing day in this crazy world we find ourselves living in.

NedS

https://forums.moneysavingexpert.com/discussion/comment/81939894#Comment_81939894

I agree the primary focus is undoubtedly price for most people. I was just trying to highlight that there are also other factors to consider, and try to evaluate what price you may place upon them. I know at least one Tesla Powerwall owner for whom power cuts and having full home backup was a major factor in their purchasing decision.

Screwdriva

https://forums.moneysavingexpert.com/discussion/comment/81939993#Comment_81939993

Absolutely. I would rate the 2nd highest (albeit a very distant second) reason is ecological concern, followed by the desire whole house backup, which the PW3 does better than any other system on sale in the UK.

Newbie_John

https://forums.moneysavingexpert.com/discussion/comment/81939894#Comment_81939894

A lot of people just follow hype in their calculations - my main issues with them are:

• Relying on 27p/kWh price for the next 10 years, rather than exploring some ToU tarrifs
• Relying on 15/kWh export rate for 10 years
• Using average UK electricity usage, or if they use theirs not taking into consideration summer, winter, day, night consumption patterns
• Risk with battery breaking down early or assuming it will last as long as solar
• Using amount they paid to calculate pay back rather than using 150% (£10k in 10 year gilt will be worth £15k in 10 years)

Also looking back in time doesn't help, it was a good Idea years back, but I believe it's peaking now - and I have more pessimistic outlook for the next 10 years.

My calculations estimate me 20+ years payback, every sales person on the door promised 5-7 years max - and many would believe in that 😞

QrizB

Using amount they paid to calculate pay back rather than using 150% (£10k in 10 year gilt will be worth £15k in 10 years)

150% is an overcompensation, though. It assumes you won't get any of the payback until the end of the period.

A more reasonable figure would be 128%, based on today's cost of ~£10k to return £1280 a year for the next ten years in a gilt ladder.

https://lategenxer.streamlit.app/Gilt_Ladder

(£1275 a year is a closer match to the £10k cost.)

Obviously you need to match the duration of the ladder to your estimated payback time, so it might take a bit of iteration.