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 904 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £731, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1808 kWh | 723 kWh | 1085 kWh | £184 | £108 | £292 | £4,069 | 13.9 yrs | £1,778 |
| 3 kW | 2711 kWh | 1085 kWh | 1627 kWh | £276 | £163 | £439 | £6,104 | 13.9 yrs | £2,667 |
| 4 kW | 3615 kWh | 1446 kWh | 2169 kWh | £368 | £217 | £585 | £8,138 | 13.9 yrs | £3,555 |
| 5 kW | 4519 kWh | 1808 kWh | 2711 kWh | £460 | £271 | £731 | £10,173 | 13.9 yrs | £4,444 |
| 6 kW | 5423 kWh | 2169 kWh | 3254 kWh | £552 | £325 | £877 | £12,207 | 13.9 yrs | £5,333 |
| 7 kW | 6327 kWh | 2531 kWh | 3796 kWh | £644 | £380 | £1,023 | £14,242 | 13.9 yrs | £6,222 |
| 8 kW | 7231 kWh | 2892 kWh | 4338 kWh | £736 | £434 | £1,169 | £16,276 | 13.9 yrs | £7,111 |
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: £870, Upfront: £12,273, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1808 kWh | 1085 kWh | 723 kWh | £276 | £72 | £348 | £6,169 | 17.7 yrs | £793 |
| 3 kW | 2711 kWh | 1627 kWh | 1085 kWh | £414 | £108 | £522 | £8,204 | 15.7 yrs | £2,240 |
| 4 kW | 3615 kWh | 2169 kWh | 1446 kWh | £552 | £145 | £696 | £10,238 | 14.7 yrs | £3,687 |
| 5 kW | 4519 kWh | 2711 kWh | 1808 kWh | £690 | £181 | £870 | £12,273 | 14.1 yrs | £5,133 |
| 6 kW | 5423 kWh | 3254 kWh | 2169 kWh | £827 | £217 | £1,044 | £14,307 | 13.7 yrs | £6,580 |
| 7 kW | 6327 kWh | 3796 kWh | 2531 kWh | £965 | £253 | £1,218 | £16,342 | 13.4 yrs | £8,027 |
| 8 kW | 7231 kWh | 4338 kWh | 2892 kWh | £1,103 | £289 | £1,392 | £18,376 | 13.2 yrs | £9,473 |
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: £940, Upfront: £13,673, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1808 kWh | 1265 kWh | 542 kWh | £322 | £54 | £376 | £7,569 | 20.1 yrs | £-49 |
| 3 kW | 2711 kWh | 1898 kWh | 813 kWh | £483 | £81 | £564 | £9,604 | 17.0 yrs | £1,677 |
| 4 kW | 3615 kWh | 2531 kWh | 1085 kWh | £644 | £108 | £752 | £11,638 | 15.5 yrs | £3,402 |
| 5 kW | 4519 kWh | 3163 kWh | 1356 kWh | £804 | £136 | £940 | £13,673 | 14.5 yrs | £5,128 |
| 6 kW | 5423 kWh | 3796 kWh | 1627 kWh | £965 | £163 | £1,128 | £15,707 | 13.9 yrs | £6,854 |
| 7 kW | 6327 kWh | 4429 kWh | 1898 kWh | £1,126 | £190 | £1,316 | £17,742 | 13.5 yrs | £8,579 |
| 8 kW | 7231 kWh | 5061 kWh | 2169 kWh | £1,287 | £217 | £1,504 | £19,776 | 13.1 yrs | £10,305 |
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: £961, Upfront: £15,423, 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 | 1808 kWh | 1320 kWh | 488 kWh | £336 | £49 | £384 | £9,319 | 24.2 yrs | £-1,631 |
| 3 kW | 2711 kWh | 1979 kWh | 732 kWh | £503 | £73 | £577 | £11,354 | 19.7 yrs | £178 |
| 4 kW | 3615 kWh | 2639 kWh | 976 kWh | £671 | £98 | £769 | £13,388 | 17.4 yrs | £1,987 |
| 5 kW | 4519 kWh | 3299 kWh | 1220 kWh | £839 | £122 | £961 | £15,423 | 16.0 yrs | £3,796 |
| 6 kW | 5423 kWh | 3959 kWh | 1464 kWh | £1,007 | £146 | £1,153 | £17,457 | 15.1 yrs | £5,606 |
| 7 kW | 6327 kWh | 4619 kWh | 1708 kWh | £1,175 | £171 | £1,345 | £19,492 | 14.5 yrs | £7,415 |
| 8 kW | 7231 kWh | 5278 kWh | 1952 kWh | £1,342 | £195 | £1,538 | £21,526 | 14.0 yrs | £9,224 |
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: £975, Upfront: £17,173, 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 | 1808 kWh | 1356 kWh | 452 kWh | £345 | £45 | £390 | £11,069 | 28.4 yrs | £-3,270 |
| 3 kW | 2711 kWh | 2034 kWh | 678 kWh | £517 | £68 | £585 | £13,104 | 22.4 yrs | £-1,405 |
| 4 kW | 3615 kWh | 2711 kWh | 904 kWh | £690 | £90 | £780 | £15,138 | 19.4 yrs | £460 |
| 5 kW | 4519 kWh | 3389 kWh | 1130 kWh | £862 | £113 | £975 | £17,173 | 17.6 yrs | £2,325 |
| 6 kW | 5423 kWh | 4067 kWh | 1356 kWh | £1,034 | £136 | £1,170 | £19,207 | 16.4 yrs | £4,190 |
| 7 kW | 6327 kWh | 4745 kWh | 1582 kWh | £1,207 | £158 | £1,365 | £21,242 | 15.6 yrs | £6,055 |
| 8 kW | 7231 kWh | 5423 kWh | 1808 kWh | £1,379 | £181 | £1,560 | £23,276 | 14.9 yrs | £7,921 |
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: £989, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1808 kWh | 1392 kWh | 416 kWh | £354 | £42 | £396 | £13,519 | 34.2 yrs | £-5,608 |
| 3 kW | 2711 kWh | 2088 kWh | 624 kWh | £531 | £62 | £593 | £15,554 | 26.2 yrs | £-3,687 |
| 4 kW | 3615 kWh | 2784 kWh | 832 kWh | £708 | £83 | £791 | £17,588 | 22.2 yrs | £-1,767 |
| 5 kW | 4519 kWh | 3480 kWh | 1039 kWh | £885 | £104 | £989 | £19,623 | 19.8 yrs | £154 |
| 6 kW | 5423 kWh | 4176 kWh | 1247 kWh | £1,062 | £125 | £1,187 | £21,657 | 18.3 yrs | £2,075 |
| 7 kW | 6327 kWh | 4872 kWh | 1455 kWh | £1,239 | £146 | £1,384 | £23,692 | 17.1 yrs | £3,996 |
| 8 kW | 7231 kWh | 5568 kWh | 1663 kWh | £1,416 | £166 | £1,582 | £25,726 | 16.3 yrs | £5,917 |
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.