A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 1034 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £867, Upfront: £10,173, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2068 kWh | 827 kWh | 1241 kWh | £223 | £124 | £347 | £4,069 | 11.7 yrs | £2,867 |
| 3 kW | 3102 kWh | 1241 kWh | 1861 kWh | £334 | £186 | £520 | £6,104 | 11.7 yrs | £4,300 |
| 4 kW | 4136 kWh | 1655 kWh | 2482 kWh | £445 | £248 | £694 | £8,138 | 11.7 yrs | £5,734 |
| 5 kW | 5171 kWh | 2068 kWh | 3102 kWh | £557 | £310 | £867 | £10,173 | 11.7 yrs | £7,167 |
| 6 kW | 6205 kWh | 2482 kWh | 3723 kWh | £668 | £372 | £1,040 | £12,207 | 11.7 yrs | £8,601 |
| 7 kW | 7239 kWh | 2896 kWh | 4343 kWh | £779 | £434 | £1,214 | £14,242 | 11.7 yrs | £10,034 |
| 8 kW | 8273 kWh | 3309 kWh | 4964 kWh | £891 | £496 | £1,387 | £16,276 | 11.7 yrs | £11,468 |
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: £1,042, Upfront: £12,273, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2068 kWh | 1241 kWh | 827 kWh | £334 | £83 | £417 | £6,169 | 14.8 yrs | £2,167 |
| 3 kW | 3102 kWh | 1861 kWh | 1241 kWh | £501 | £124 | £625 | £8,204 | 13.1 yrs | £4,300 |
| 4 kW | 4136 kWh | 2482 kWh | 1655 kWh | £668 | £165 | £834 | £10,238 | 12.3 yrs | £6,433 |
| 5 kW | 5171 kWh | 3102 kWh | 2068 kWh | £835 | £207 | £1,042 | £12,273 | 11.8 yrs | £8,567 |
| 6 kW | 6205 kWh | 3723 kWh | 2482 kWh | £1,002 | £248 | £1,250 | £14,307 | 11.4 yrs | £10,700 |
| 7 kW | 7239 kWh | 4343 kWh | 2896 kWh | £1,169 | £290 | £1,459 | £16,342 | 11.2 yrs | £12,834 |
| 8 kW | 8273 kWh | 4964 kWh | 3309 kWh | £1,336 | £331 | £1,667 | £18,376 | 11.0 yrs | £14,967 |
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: £1,129, Upfront: £13,673, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2068 kWh | 1448 kWh | 620 kWh | £390 | £62 | £452 | £7,569 | 16.8 yrs | £1,467 |
| 3 kW | 3102 kWh | 2172 kWh | 931 kWh | £585 | £93 | £678 | £9,604 | 14.2 yrs | £3,950 |
| 4 kW | 4136 kWh | 2896 kWh | 1241 kWh | £779 | £124 | £904 | £11,638 | 12.9 yrs | £6,433 |
| 5 kW | 5171 kWh | 3619 kWh | 1551 kWh | £974 | £155 | £1,129 | £13,673 | 12.1 yrs | £8,917 |
| 6 kW | 6205 kWh | 4343 kWh | 1861 kWh | £1,169 | £186 | £1,355 | £15,707 | 11.6 yrs | £11,400 |
| 7 kW | 7239 kWh | 5067 kWh | 2172 kWh | £1,364 | £217 | £1,581 | £17,742 | 11.2 yrs | £13,883 |
| 8 kW | 8273 kWh | 5791 kWh | 2482 kWh | £1,559 | £248 | £1,807 | £19,776 | 10.9 yrs | £16,366 |
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: £1,156, Upfront: £15,423, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2068 kWh | 1510 kWh | 558 kWh | £406 | £56 | £462 | £9,319 | 20.2 yrs | £-73 |
| 3 kW | 3102 kWh | 2265 kWh | 838 kWh | £610 | £84 | £693 | £11,354 | 16.4 yrs | £2,515 |
| 4 kW | 4136 kWh | 3020 kWh | 1117 kWh | £813 | £112 | £925 | £13,388 | 14.5 yrs | £5,103 |
| 5 kW | 5171 kWh | 3775 kWh | 1396 kWh | £1,016 | £140 | £1,156 | £15,423 | 13.3 yrs | £7,691 |
| 6 kW | 6205 kWh | 4529 kWh | 1675 kWh | £1,219 | £168 | £1,387 | £17,457 | 12.6 yrs | £10,280 |
| 7 kW | 7239 kWh | 5284 kWh | 1954 kWh | £1,423 | £195 | £1,618 | £19,492 | 12.0 yrs | £12,868 |
| 8 kW | 8273 kWh | 6039 kWh | 2234 kWh | £1,626 | £223 | £1,849 | £21,526 | 11.6 yrs | £15,456 |
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: £1,173, Upfront: £17,173, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2068 kWh | 1551 kWh | 517 kWh | £418 | £52 | £469 | £11,069 | 23.6 yrs | £-1,683 |
| 3 kW | 3102 kWh | 2327 kWh | 776 kWh | £626 | £78 | £704 | £13,104 | 18.6 yrs | £975 |
| 4 kW | 4136 kWh | 3102 kWh | 1034 kWh | £835 | £103 | £939 | £15,138 | 16.1 yrs | £3,633 |
| 5 kW | 5171 kWh | 3878 kWh | 1293 kWh | £1,044 | £129 | £1,173 | £17,173 | 14.6 yrs | £6,291 |
| 6 kW | 6205 kWh | 4653 kWh | 1551 kWh | £1,253 | £155 | £1,408 | £19,207 | 13.6 yrs | £8,950 |
| 7 kW | 7239 kWh | 5429 kWh | 1810 kWh | £1,462 | £181 | £1,642 | £21,242 | 12.9 yrs | £11,608 |
| 8 kW | 8273 kWh | 6205 kWh | 2068 kWh | £1,670 | £207 | £1,877 | £23,276 | 12.4 yrs | £14,266 |
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: £1,191, Upfront: £19,623, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2068 kWh | 1593 kWh | 476 kWh | £429 | £48 | £476 | £13,519 | 28.4 yrs | £-3,993 |
| 3 kW | 3102 kWh | 2389 kWh | 714 kWh | £643 | £71 | £714 | £15,554 | 21.8 yrs | £-1,265 |
| 4 kW | 4136 kWh | 3185 kWh | 951 kWh | £857 | £95 | £953 | £17,588 | 18.5 yrs | £1,463 |
| 5 kW | 5171 kWh | 3981 kWh | 1189 kWh | £1,072 | £119 | £1,191 | £19,623 | 16.5 yrs | £4,191 |
| 6 kW | 6205 kWh | 4778 kWh | 1427 kWh | £1,286 | £143 | £1,429 | £21,657 | 15.2 yrs | £6,920 |
| 7 kW | 7239 kWh | 5574 kWh | 1665 kWh | £1,500 | £166 | £1,667 | £23,692 | 14.2 yrs | £9,648 |
| 8 kW | 8273 kWh | 6370 kWh | 1903 kWh | £1,715 | £190 | £1,905 | £25,726 | 13.5 yrs | £12,376 |
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.