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 969 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £786, Upfront: £10,173, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 776 kWh | 1163 kWh | £198 | £116 | £314 | £4,069 | 12.9 yrs | £2,221 |
| 3 kW | 2908 kWh | 1163 kWh | 1745 kWh | £297 | £174 | £472 | £6,104 | 12.9 yrs | £3,331 |
| 4 kW | 3878 kWh | 1551 kWh | 2327 kWh | £396 | £233 | £629 | £8,138 | 12.9 yrs | £4,441 |
| 5 kW | 4847 kWh | 1939 kWh | 2908 kWh | £495 | £291 | £786 | £10,173 | 12.9 yrs | £5,551 |
| 6 kW | 5817 kWh | 2327 kWh | 3490 kWh | £594 | £349 | £943 | £12,207 | 12.9 yrs | £6,662 |
| 7 kW | 6786 kWh | 2714 kWh | 4072 kWh | £694 | £407 | £1,101 | £14,242 | 12.9 yrs | £7,772 |
| 8 kW | 7755 kWh | 3102 kWh | 4653 kWh | £793 | £465 | £1,258 | £16,276 | 12.9 yrs | £8,882 |
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: £937, Upfront: £12,273, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1163 kWh | 776 kWh | £297 | £78 | £375 | £6,169 | 16.5 yrs | £1,327 |
| 3 kW | 2908 kWh | 1745 kWh | 1163 kWh | £446 | £116 | £562 | £8,204 | 14.6 yrs | £3,040 |
| 4 kW | 3878 kWh | 2327 kWh | 1551 kWh | £594 | £155 | £750 | £10,238 | 13.7 yrs | £4,753 |
| 5 kW | 4847 kWh | 2908 kWh | 1939 kWh | £743 | £194 | £937 | £12,273 | 13.1 yrs | £6,466 |
| 6 kW | 5817 kWh | 3490 kWh | 2327 kWh | £892 | £233 | £1,124 | £14,307 | 12.7 yrs | £8,180 |
| 7 kW | 6786 kWh | 4072 kWh | 2714 kWh | £1,040 | £271 | £1,312 | £16,342 | 12.5 yrs | £9,893 |
| 8 kW | 7755 kWh | 4653 kWh | 3102 kWh | £1,189 | £310 | £1,499 | £18,376 | 12.3 yrs | £11,606 |
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: £1,012, Upfront: £13,673, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1357 kWh | 582 kWh | £347 | £58 | £405 | £7,569 | 18.7 yrs | £530 |
| 3 kW | 2908 kWh | 2036 kWh | 872 kWh | £520 | £87 | £607 | £9,604 | 15.8 yrs | £2,544 |
| 4 kW | 3878 kWh | 2714 kWh | 1163 kWh | £694 | £116 | £810 | £11,638 | 14.4 yrs | £4,559 |
| 5 kW | 4847 kWh | 3393 kWh | 1454 kWh | £867 | £145 | £1,012 | £13,673 | 13.5 yrs | £6,574 |
| 6 kW | 5817 kWh | 4072 kWh | 1745 kWh | £1,040 | £174 | £1,215 | £15,707 | 12.9 yrs | £8,589 |
| 7 kW | 6786 kWh | 4750 kWh | 2036 kWh | £1,214 | £204 | £1,417 | £17,742 | 12.5 yrs | £10,603 |
| 8 kW | 7755 kWh | 5429 kWh | 2327 kWh | £1,387 | £233 | £1,620 | £19,776 | 12.2 yrs | £12,618 |
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: £1,035, Upfront: £15,423, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1415 kWh | 523 kWh | £362 | £52 | £414 | £9,319 | 22.5 yrs | £-1,040 |
| 3 kW | 2908 kWh | 2123 kWh | 785 kWh | £542 | £79 | £621 | £11,354 | 18.3 yrs | £1,066 |
| 4 kW | 3878 kWh | 2831 kWh | 1047 kWh | £723 | £105 | £828 | £13,388 | 16.2 yrs | £3,171 |
| 5 kW | 4847 kWh | 3538 kWh | 1309 kWh | £904 | £131 | £1,035 | £15,423 | 14.9 yrs | £5,276 |
| 6 kW | 5817 kWh | 4246 kWh | 1570 kWh | £1,085 | £157 | £1,242 | £17,457 | 14.1 yrs | £7,381 |
| 7 kW | 6786 kWh | 4954 kWh | 1832 kWh | £1,266 | £183 | £1,449 | £19,492 | 13.5 yrs | £9,486 |
| 8 kW | 7755 kWh | 5661 kWh | 2094 kWh | £1,446 | £209 | £1,656 | £21,526 | 13.0 yrs | £11,592 |
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: £1,050, Upfront: £17,173, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1454 kWh | 485 kWh | £372 | £48 | £420 | £11,069 | 26.4 yrs | £-2,669 |
| 3 kW | 2908 kWh | 2181 kWh | 727 kWh | £557 | £73 | £630 | £13,104 | 20.8 yrs | £-503 |
| 4 kW | 3878 kWh | 2908 kWh | 969 kWh | £743 | £97 | £840 | £15,138 | 18.0 yrs | £1,662 |
| 5 kW | 4847 kWh | 3635 kWh | 1212 kWh | £929 | £121 | £1,050 | £17,173 | 16.4 yrs | £3,828 |
| 6 kW | 5817 kWh | 4362 kWh | 1454 kWh | £1,115 | £145 | £1,260 | £19,207 | 15.2 yrs | £5,993 |
| 7 kW | 6786 kWh | 5089 kWh | 1696 kWh | £1,300 | £170 | £1,470 | £21,242 | 14.5 yrs | £8,159 |
| 8 kW | 7755 kWh | 5817 kWh | 1939 kWh | £1,486 | £194 | £1,680 | £23,276 | 13.9 yrs | £10,324 |
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: £1,065, Upfront: £19,623, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1939 kWh | 1493 kWh | 446 kWh | £381 | £45 | £426 | £13,519 | 31.7 yrs | £-4,998 |
| 3 kW | 2908 kWh | 2239 kWh | 669 kWh | £572 | £67 | £639 | £15,554 | 24.3 yrs | £-2,773 |
| 4 kW | 3878 kWh | 2986 kWh | 892 kWh | £763 | £89 | £852 | £17,588 | 20.6 yrs | £-547 |
| 5 kW | 4847 kWh | 3732 kWh | 1115 kWh | £954 | £111 | £1,065 | £19,623 | 18.4 yrs | £1,679 |
| 6 kW | 5817 kWh | 4479 kWh | 1338 kWh | £1,144 | £134 | £1,278 | £21,657 | 16.9 yrs | £3,905 |
| 7 kW | 6786 kWh | 5225 kWh | 1561 kWh | £1,335 | £156 | £1,491 | £23,692 | 15.9 yrs | £6,131 |
| 8 kW | 7755 kWh | 5972 kWh | 1784 kWh | £1,526 | £178 | £1,704 | £25,726 | 15.1 yrs | £8,356 |
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.