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 884 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £745, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1769 kWh | 708 kWh | 1061 kWh | £192 | £106 | £298 | £4,069 | 13.7 yrs | £1,890 |
| 3 kW | 2654 kWh | 1061 kWh | 1592 kWh | £288 | £159 | £447 | £6,104 | 13.7 yrs | £2,836 |
| 4 kW | 3538 kWh | 1415 kWh | 2123 kWh | £384 | £212 | £596 | £8,138 | 13.7 yrs | £3,781 |
| 5 kW | 4422 kWh | 1769 kWh | 2654 kWh | £480 | £265 | £745 | £10,173 | 13.7 yrs | £4,726 |
| 6 kW | 5307 kWh | 2123 kWh | 3184 kWh | £575 | £318 | £894 | £12,207 | 13.7 yrs | £5,671 |
| 7 kW | 6192 kWh | 2477 kWh | 3715 kWh | £671 | £371 | £1,043 | £14,242 | 13.7 yrs | £6,616 |
| 8 kW | 7076 kWh | 2830 kWh | 4246 kWh | £767 | £425 | £1,192 | £16,276 | 13.7 yrs | £7,562 |
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: £896, Upfront: £12,273, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1769 kWh | 1061 kWh | 708 kWh | £288 | £71 | £359 | £6,169 | 17.2 yrs | £1,001 |
| 3 kW | 2654 kWh | 1592 kWh | 1061 kWh | £432 | £106 | £538 | £8,204 | 15.3 yrs | £2,552 |
| 4 kW | 3538 kWh | 2123 kWh | 1415 kWh | £575 | £142 | £717 | £10,238 | 14.3 yrs | £4,102 |
| 5 kW | 4422 kWh | 2654 kWh | 1769 kWh | £719 | £177 | £896 | £12,273 | 13.7 yrs | £5,653 |
| 6 kW | 5307 kWh | 3184 kWh | 2123 kWh | £863 | £212 | £1,076 | £14,307 | 13.3 yrs | £7,203 |
| 7 kW | 6192 kWh | 3715 kWh | 2477 kWh | £1,007 | £248 | £1,255 | £16,342 | 13.0 yrs | £8,754 |
| 8 kW | 7076 kWh | 4246 kWh | 2830 kWh | £1,151 | £283 | £1,434 | £18,376 | 12.8 yrs | £10,304 |
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: £972, Upfront: £13,673, 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 | 1769 kWh | 1238 kWh | 531 kWh | £336 | £53 | £389 | £7,569 | 19.5 yrs | £206 |
| 3 kW | 2654 kWh | 1857 kWh | 796 kWh | £504 | £80 | £583 | £9,604 | 16.5 yrs | £2,060 |
| 4 kW | 3538 kWh | 2477 kWh | 1061 kWh | £671 | £106 | £778 | £11,638 | 15.0 yrs | £3,913 |
| 5 kW | 4422 kWh | 3096 kWh | 1327 kWh | £839 | £133 | £972 | £13,673 | 14.1 yrs | £5,766 |
| 6 kW | 5307 kWh | 3715 kWh | 1592 kWh | £1,007 | £159 | £1,166 | £15,707 | 13.5 yrs | £7,619 |
| 7 kW | 6192 kWh | 4334 kWh | 1857 kWh | £1,175 | £186 | £1,361 | £17,742 | 13.0 yrs | £9,473 |
| 8 kW | 7076 kWh | 4953 kWh | 2123 kWh | £1,343 | £212 | £1,555 | £19,776 | 12.7 yrs | £11,326 |
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: £995, Upfront: £15,423, 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 | 1769 kWh | 1291 kWh | 478 kWh | £350 | £48 | £398 | £9,319 | 23.4 yrs | £-1,362 |
| 3 kW | 2654 kWh | 1937 kWh | 716 kWh | £525 | £72 | £597 | £11,354 | 19.0 yrs | £582 |
| 4 kW | 3538 kWh | 2583 kWh | 955 kWh | £700 | £96 | £796 | £13,388 | 16.8 yrs | £2,526 |
| 5 kW | 4422 kWh | 3228 kWh | 1194 kWh | £875 | £119 | £995 | £15,423 | 15.5 yrs | £4,470 |
| 6 kW | 5307 kWh | 3874 kWh | 1433 kWh | £1,050 | £143 | £1,194 | £17,457 | 14.6 yrs | £6,414 |
| 7 kW | 6192 kWh | 4520 kWh | 1672 kWh | £1,225 | £167 | £1,392 | £19,492 | 14.0 yrs | £8,358 |
| 8 kW | 7076 kWh | 5165 kWh | 1911 kWh | £1,400 | £191 | £1,591 | £21,526 | 13.5 yrs | £10,302 |
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: £1,010, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1769 kWh | 1327 kWh | 442 kWh | £360 | £44 | £404 | £11,069 | 27.4 yrs | £-2,991 |
| 3 kW | 2654 kWh | 1990 kWh | 663 kWh | £540 | £66 | £606 | £13,104 | 21.6 yrs | £-986 |
| 4 kW | 3538 kWh | 2654 kWh | 884 kWh | £719 | £88 | £808 | £15,138 | 18.7 yrs | £1,018 |
| 5 kW | 4422 kWh | 3317 kWh | 1106 kWh | £899 | £111 | £1,010 | £17,173 | 17.0 yrs | £3,023 |
| 6 kW | 5307 kWh | 3980 kWh | 1327 kWh | £1,079 | £133 | £1,212 | £19,207 | 15.9 yrs | £5,027 |
| 7 kW | 6192 kWh | 4644 kWh | 1548 kWh | £1,259 | £155 | £1,414 | £21,242 | 15.0 yrs | £7,032 |
| 8 kW | 7076 kWh | 5307 kWh | 1769 kWh | £1,439 | £177 | £1,616 | £23,276 | 14.4 yrs | £9,036 |
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: £1,025, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1769 kWh | 1362 kWh | 407 kWh | £369 | £41 | £410 | £13,519 | 33.0 yrs | £-5,320 |
| 3 kW | 2654 kWh | 2043 kWh | 610 kWh | £554 | £61 | £615 | £15,554 | 25.3 yrs | £-3,255 |
| 4 kW | 3538 kWh | 2724 kWh | 814 kWh | £739 | £81 | £820 | £17,588 | 21.5 yrs | £-1,190 |
| 5 kW | 4422 kWh | 3405 kWh | 1017 kWh | £923 | £102 | £1,025 | £19,623 | 19.1 yrs | £875 |
| 6 kW | 5307 kWh | 4086 kWh | 1221 kWh | £1,108 | £122 | £1,230 | £21,657 | 17.6 yrs | £2,941 |
| 7 kW | 6192 kWh | 4767 kWh | 1424 kWh | £1,292 | £142 | £1,435 | £23,692 | 16.5 yrs | £5,006 |
| 8 kW | 7076 kWh | 5449 kWh | 1627 kWh | £1,477 | £163 | £1,640 | £25,726 | 15.7 yrs | £7,071 |
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.