Justifying adding batteries ????????

[Murdoch]

So we have have had PV for nearly 4 years and a immersion divertor - all works well.

So I've been pondering about adding battery storage - which will mean changing the inverter and adding the batteries - approx cost £3000

Current lecky cost is about £0.30 per kwh

If I do this and work the calculations on ONLY charging from the spare PV and setting the priority to the batteries it'll be about 10k kwh hours to break even. Realistically I don't think there is enough sun in the winter to charge the batteries unless there is a really sunny day or 2!

Our imported consumption is about 3000 kwh per year

So even if I could "assume" I'd get enough battery charge for 1/2 the year it would take about 7 years to break even if I don't take into account the "loss" of the free hot water we are currently getting.

So why are so many people rushing to install this kit ? and a lot of them using off peak lecky to charge their batteries?


Are my assumptions way off or am I missing something?

 

[binky]

say off peak is 10p per kwh, then thats £300 for 3000 kwh you import, saving 20p per kwh or around £600. At £3k for the batteries, that's a 5 year payback, but not forgetting energy is still rising at at least 5% per annum, so potential payback is shorter than that. Now if you charge the battery half the year from the panels then that's actually a 10 year payback, but you could avoid losing the hot water savings by charging up off peak to reduce that figure to less than 10 years. Plus you could also potentially sell some leccy back to Octopuss during peak demands, although that would require a smart meter, which I know you are a huge fan of!

 

[Oldman22]

You could have a play around with this utility and see what would happen, its set for Octopus flux tariffs but you can add your own. https://garydoessolar.com/utilities/dailymodellingutility/

 

[Murdoch]

You could have a play around with this utility and see what would happen, its set for Octopus flux tariffs but you can add your own. https://garydoessolar.com/utilities/dailymodellingutility/

That's a useful tool. We live in a small dip so our production "hours" is less than most

 

[johnb2713]

I did a very simple calculation for my DIY battery and only considered charging from the grid, it does of course charge from solar too but thats a bonus.
Octopus Intelligent tariff gives me 7.5p off peak and 29.2p peak. I have 14 kWh of usable battery storage in my DIY unit.
Savings per kWh = 29.2 - 7.5 = 21.7p kWh
Per charge 21.7 x 14 = £3.03
Battery and inverter cost = £4200 / £3.03 = 1386 days or 3.8 years.

There are some small losses in conversion AC to DC and DC to AC and there are also gains in Solar PV charging. There is a massive earning potential during the grid balancing sessions that are done during winter. My actual payback using the realtime data is just over 2.4 years.

 

[binky]

say off peak is 10p per kwh, then thats £300 for 3000 kwh you import, saving 20p per kwh or around £600. At £3k for the batteries, that's a 5 year payback, but not forgetting energy is still rising at at least 5% per annum, so potential payback is shorter than that. Now if you charge the battery half the year from the panels then that's actually a 10 year payback, but you could avoid losing the hot water savings by charging up off peak to reduce that figure to less than 10 years. Plus you could also potentially sell some leccy back to Octopuss during peak demands, although that would require a smart meter, which I know you are a huge fan of!

forgot to add, whilst charging from soalr you are saving the off peak, so say 1500 kwh at 10p is another £150 saving.