A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 813 kWh per year on a south-facing roof. We value self-used electricity at 25.8p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.
Browse the scenarios below. Each battery size has its own expand — open the one that matches your plan (or just explore). For each system size (2–8 kW) we show annual output, how much you use directly, what gets exported, annual benefit, upfront cost, break-even, and a 20-year net. Negative numbers are possible — that’s the honest trade-off when adding more battery than your usage profile justifies.
No battery 5 kW example → Annual benefit: £664, Upfront: £10,173, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1626 kWh | 650 kWh | 975 kWh | £168 | £98 | £266 | £4,069 | 15.3 yrs | £1,242 |
| 3 kW | 2438 kWh | 975 kWh | 1463 kWh | £252 | £146 | £398 | £6,104 | 15.3 yrs | £1,863 |
| 4 kW | 3251 kWh | 1300 kWh | 1951 kWh | £336 | £195 | £531 | £8,138 | 15.3 yrs | £2,484 |
| 5 kW | 4064 kWh | 1626 kWh | 2438 kWh | £420 | £244 | £664 | £10,173 | 15.3 yrs | £3,105 |
| 6 kW | 4877 kWh | 1951 kWh | 2926 kWh | £504 | £293 | £797 | £12,207 | 15.3 yrs | £3,726 |
| 7 kW | 5690 kWh | 2276 kWh | 3414 kWh | £588 | £341 | £929 | £14,242 | 15.3 yrs | £4,347 |
| 8 kW | 6502 kWh | 2601 kWh | 3901 kWh | £672 | £390 | £1,062 | £16,276 | 15.3 yrs | £4,968 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
3 kWh battery 5 kW example → Annual benefit: £793, Upfront: £12,273, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1626 kWh | 975 kWh | 650 kWh | £252 | £65 | £317 | £6,169 | 19.5 yrs | £172 |
| 3 kW | 2438 kWh | 1463 kWh | 975 kWh | £378 | £98 | £476 | £8,204 | 17.2 yrs | £1,308 |
| 4 kW | 3251 kWh | 1951 kWh | 1300 kWh | £504 | £130 | £634 | £10,238 | 16.1 yrs | £2,444 |
| 5 kW | 4064 kWh | 2438 kWh | 1626 kWh | £630 | £163 | £793 | £12,273 | 15.5 yrs | £3,580 |
| 6 kW | 4877 kWh | 2926 kWh | 1951 kWh | £756 | £195 | £951 | £14,307 | 15.0 yrs | £4,716 |
| 7 kW | 5690 kWh | 3414 kWh | 2276 kWh | £882 | £228 | £1,110 | £16,342 | 14.7 yrs | £5,852 |
| 8 kW | 6502 kWh | 3901 kWh | 2601 kWh | £1,008 | £260 | £1,268 | £18,376 | 14.5 yrs | £6,988 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
5 kWh battery 5 kW example → Annual benefit: £857, Upfront: £13,673, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1626 kWh | 1138 kWh | 488 kWh | £294 | £49 | £343 | £7,569 | 22.1 yrs | £-713 |
| 3 kW | 2438 kWh | 1707 kWh | 732 kWh | £441 | £73 | £514 | £9,604 | 18.7 yrs | £681 |
| 4 kW | 3251 kWh | 2276 kWh | 975 kWh | £588 | £98 | £686 | £11,638 | 17.0 yrs | £2,074 |
| 5 kW | 4064 kWh | 2845 kWh | 1219 kWh | £735 | £122 | £857 | £13,673 | 16.0 yrs | £3,468 |
| 6 kW | 4877 kWh | 3414 kWh | 1463 kWh | £882 | £146 | £1,028 | £15,707 | 15.3 yrs | £4,861 |
| 7 kW | 5690 kWh | 3983 kWh | 1707 kWh | £1,029 | £171 | £1,200 | £17,742 | 14.8 yrs | £6,255 |
| 8 kW | 6502 kWh | 4552 kWh | 1951 kWh | £1,176 | £195 | £1,371 | £19,776 | 14.4 yrs | £7,648 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
7.5 kWh battery 5 kW example → Annual benefit: £876, Upfront: £15,423, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1626 kWh | 1187 kWh | 439 kWh | £307 | £44 | £351 | £9,319 | 26.6 yrs | £-2,308 |
| 3 kW | 2438 kWh | 1780 kWh | 658 kWh | £460 | £66 | £526 | £11,354 | 21.6 yrs | £-838 |
| 4 kW | 3251 kWh | 2373 kWh | 878 kWh | £613 | £88 | £701 | £13,388 | 19.1 yrs | £633 |
| 5 kW | 4064 kWh | 2967 kWh | 1097 kWh | £767 | £110 | £876 | £15,423 | 17.6 yrs | £2,104 |
| 6 kW | 4877 kWh | 3560 kWh | 1317 kWh | £920 | £132 | £1,052 | £17,457 | 16.6 yrs | £3,575 |
| 7 kW | 5690 kWh | 4153 kWh | 1536 kWh | £1,073 | £154 | £1,227 | £19,492 | 15.9 yrs | £5,045 |
| 8 kW | 6502 kWh | 4747 kWh | 1756 kWh | £1,227 | £176 | £1,402 | £21,526 | 15.4 yrs | £6,516 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
10 kWh battery 5 kW example → Annual benefit: £889, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1626 kWh | 1219 kWh | 406 kWh | £315 | £41 | £356 | £11,069 | 31.1 yrs | £-3,955 |
| 3 kW | 2438 kWh | 1829 kWh | 610 kWh | £473 | £61 | £534 | £13,104 | 24.6 yrs | £-2,433 |
| 4 kW | 3251 kWh | 2438 kWh | 813 kWh | £630 | £81 | £711 | £15,138 | 21.3 yrs | £-911 |
| 5 kW | 4064 kWh | 3048 kWh | 1016 kWh | £788 | £102 | £889 | £17,173 | 19.3 yrs | £611 |
| 6 kW | 4877 kWh | 3658 kWh | 1219 kWh | £945 | £122 | £1,067 | £19,207 | 18.0 yrs | £2,134 |
| 7 kW | 5690 kWh | 4267 kWh | 1422 kWh | £1,103 | £142 | £1,245 | £21,242 | 17.1 yrs | £3,656 |
| 8 kW | 6502 kWh | 4877 kWh | 1626 kWh | £1,260 | £163 | £1,423 | £23,276 | 16.4 yrs | £5,178 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
13.5 kWh battery 5 kW example → Annual benefit: £902, Upfront: £19,623, Break-even: 21.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1626 kWh | 1252 kWh | 374 kWh | £323 | £37 | £361 | £13,519 | 37.5 yrs | £-6,302 |
| 3 kW | 2438 kWh | 1878 kWh | 561 kWh | £485 | £56 | £541 | £15,554 | 28.7 yrs | £-4,729 |
| 4 kW | 3251 kWh | 2503 kWh | 748 kWh | £647 | £75 | £722 | £17,588 | 24.4 yrs | £-3,155 |
| 5 kW | 4064 kWh | 3129 kWh | 935 kWh | £809 | £93 | £902 | £19,623 | 21.8 yrs | £-1,581 |
| 6 kW | 4877 kWh | 3755 kWh | 1122 kWh | £970 | £112 | £1,082 | £21,657 | 20.0 yrs | £-7 |
| 7 kW | 5690 kWh | 4381 kWh | 1309 kWh | £1,132 | £131 | £1,263 | £23,692 | 18.8 yrs | £1,566 |
| 8 kW | 6502 kWh | 5007 kWh | 1496 kWh | £1,294 | £150 | £1,443 | £25,726 | 17.8 yrs | £3,140 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
Figures are illustrative and use the same method as the calculator above. For exact results, adjust your roof direction, tariff, and usage in the calculator.