Cost analysis for batteries (ROI)

[marshman]

Sorry. I am grid negative (annually), however I do still shower on foggy days so I import. But I am going to check my numbers again.

I agree some things you do just for fun & nurdery.
But the wind & solar for me was an interesting and enjoyable investment. But I struggle to make batteries add-up. Some of the battery bank retailers make some wild claims. Wondered if it's was me.

Batteries in cars are a brilliant idea to microgrid, apart from the cars don't work fur me either physically or financially.

In my opinion ROI is so, so dependent on individual circumstances, i.e. work patterns, house occupancy, energy use patterns, how you heat and cook (gas, electric, oil etc.) how much on site generation you have (wind helps fill the "dips" of solar and most significantly generates in the dark.

With your 10kW solar and 13kW of wind I am not surprised that the ROI doesn't seem to work for you.

Also worth bearing in mind (won't help with your figures mind!) that you need to factor "round trip efficiency" if charging on cheap rate to discharge at peak times. I would put it at around 85 to 90% based on the observations of my system (units in vs units out).

[nowty]

Nowty Towers back of fag packet calculation, rounded some figures to make the maths easier.

Practically an all electric house with 2 EVs.
Annual usage 20,000 kWh
Solar 10,000 kWh (practically all used because of batteries)
Import 10,000 kWh @ cheap rate 10p kWh, therefore cost = £1000

Without batteries I would self use roughly half the solar so import would be 15,000 kWh @ 35p kWh, therefore cost = £5,250
So over £4k saving for having batteries.

Savings are probably over the top because of current high energy prices, could get some income exporting the solar, going back to using some gas or still using cheap rate to charge car, hot water and storage heaters.

But lets say I only save £2k per year, over 10 years would more than pay for my batteries and battery inverter. My batteries are a mixture of 1/3 expensive Pylontech and 2/3 cheaper repurposed lithium based batteries.

[Windbag]

Interestingly there have been many people recently installing batteries without the solar because the payoff from batteries was better than solar!

Presumably charging cheap rate and using an Ev tarrif? Or have I misunderstood?

[Stinsy]

Interestingly there have been many people recently installing batteries without the solar because the payoff from batteries was better than solar!

Presumably charging cheap rate and using an Ev tarrif? Or have I misunderstood?

Exactly!

[Windbag]

Which leads to.. ..

Do you have to have an EV to get an EV tariff, and perhaps its a tinsley winsey bit illegal to hot wire it to a (stationary) battery store.

Bleddy good idea though