// BATTERY SIZING
Sizing is a best fit.
Too small, and you spill into expensive peak-rate power. Too big, and you've paid for capacity you won't use. The right size stores just enough cheap off-peak energy to carry your home through the day.
1
Find your size
Match your home to a battery on the chart.
Size the battery by referencing your annual consumption. If you are unsure of this value, you can approximate by referencing your typical annual electricity bill.
2
The sizes
Four standard systems, with what each one typically saves.
Low use
5 kWh
Best fit1,825 kWh/yr
Typical bill£685/yr
Saving / year£329
Breakeven9.3 yrs
From (£750/kWh)£3,749
Average home
10 kWh
Best fit3,650 kWh/yr
Typical bill£1,160/yr
Saving / year£657
Breakeven6.6 yrs
From (£500/kWh)£4,999
Most popular
15 kWh
Best fit5,475 kWh/yr
Typical bill£1,640/yr
Saving / year£986
Breakeven5.6 yrs
From (£417/kWh)£6,249
20 kWh
Best fit7,300 kWh/yr
Typical bill£2,115/yr
Saving / year£1,314
Breakeven5.1 yrs
From (£375/kWh)£7,499
25 kWh
Best fit9,125 kWh/yr
Typical bill£2,590/yr
Saving / year£1,643
Breakeven6.0 yrs
From (£450/kWh)£11,248
30 kWh
Best fit10,950 kWh/yr
Typical bill£3,070/yr
Saving / year£1,971
Breakeven5.6 yrs
From (£417/kWh)£12,498
35 kWh
Best fit12,775 kWh/yr
Typical bill£3,545/yr
Saving / year£2,300
Breakeven5.4 yrs
From (£393/kWh)£13,748
40 kWh
Best fit14,600 kWh/yr
Typical bill£4,020/yr
Saving / year£2,628
Breakeven5.1 yrs
From (£375/kWh)£14,998
Larger systems are available if required.
Why size matters.Unless you've specific off-peak loads, around 90% of your daily use falls outside the cheap overnight window. The battery is sized to cover this demand. A well-sized battery stores enough cheap energy overnight to run your home through the expensive peak hours.
Savings are illustrative.Your actual saving depends on your tariff, how you use power, and how fully the battery cycles each day. Every figure here is an Estimate. The right battery size and install cost is confirmed after survey, before contract, with a formal Quotation.
3
How you save
Charge cheap, run the day on it, and bank the difference.
1
Charge cheap, overnight
The battery fills on cheap off-peak power, typically between midnight and 6am, while you sleep.
2
Run the day on it
Through the day your home runs on stored power, not peak-rate grid energy.
3
Bank the difference
You keep the gap between the cheap rate you paid and the peak rate you'd have paid. Every day.
BIGGER BATTERIES COST LESS PER KWH
Beyond 20 kWh a second battery module is added, which resets the curve before it falls again.
£750
per kWh at 5 kWh
£375
per kWh at 20 kWh
£450
per kWh at 25 kWh
£375
per kWh at 40 kWh
How we work it out.Annual saving = capacity × 365 cycles × 90% round-trip efficiency × the £0.20/kWh (gap between peak and off-peak rates), about £65.70 a year per kWh of capacity. Typical bills assume the unit rate of 26.11p/kWh plus the £0.5719/day standing charge (Ofgem cap, 1 July 2026). Best fit pairs a battery with a home whose average daily use roughly matches its capacity, so it completes one full cycle per day. Breakeven is the price divided by the annual saving, with that saving assumed to grow at 5% a year as energy prices rise. We do not factor in battery degradation; it is gradual and non-linear, so it has little effect within the breakeven period. This is an Estimate. Your size, price and saving are confirmed at survey. Savings are illustrative. Actual savings will depend on your chosen tariff and system usage.