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 851 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: £695, Upfront: £10,173, 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 | 1701 kWh | 680 kWh | 1021 kWh | £176 | £102 | £278 | £4,069 | 14.6 yrs | £1,489 |
| 3 kW | 2552 kWh | 1021 kWh | 1531 kWh | £264 | £153 | £417 | £6,104 | 14.6 yrs | £2,234 |
| 4 kW | 3402 kWh | 1361 kWh | 2041 kWh | £352 | £204 | £556 | £8,138 | 14.6 yrs | £2,978 |
| 5 kW | 4253 kWh | 1701 kWh | 2552 kWh | £440 | £255 | £695 | £10,173 | 14.6 yrs | £3,723 |
| 6 kW | 5103 kWh | 2041 kWh | 3062 kWh | £527 | £306 | £834 | £12,207 | 14.6 yrs | £4,467 |
| 7 kW | 5954 kWh | 2382 kWh | 3572 kWh | £615 | £357 | £973 | £14,242 | 14.6 yrs | £5,212 |
| 8 kW | 6805 kWh | 2722 kWh | 4083 kWh | £703 | £408 | £1,112 | £16,276 | 14.6 yrs | £5,956 |
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: £829, Upfront: £12,273, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1701 kWh | 1021 kWh | 680 kWh | £264 | £68 | £332 | £6,169 | 18.6 yrs | £467 |
| 3 kW | 2552 kWh | 1531 kWh | 1021 kWh | £396 | £102 | £498 | £8,204 | 16.5 yrs | £1,750 |
| 4 kW | 3402 kWh | 2041 kWh | 1361 kWh | £527 | £136 | £664 | £10,238 | 15.4 yrs | £3,034 |
| 5 kW | 4253 kWh | 2552 kWh | 1701 kWh | £659 | £170 | £829 | £12,273 | 14.8 yrs | £4,317 |
| 6 kW | 5103 kWh | 3062 kWh | 2041 kWh | £791 | £204 | £995 | £14,307 | 14.4 yrs | £5,601 |
| 7 kW | 5954 kWh | 3572 kWh | 2382 kWh | £923 | £238 | £1,161 | £16,342 | 14.1 yrs | £6,884 |
| 8 kW | 6805 kWh | 4083 kWh | 2722 kWh | £1,055 | £272 | £1,327 | £18,376 | 13.8 yrs | £8,167 |
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: £897, Upfront: £13,673, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1701 kWh | 1191 kWh | 510 kWh | £308 | £51 | £359 | £7,569 | 21.1 yrs | £-394 |
| 3 kW | 2552 kWh | 1786 kWh | 766 kWh | £462 | £77 | £538 | £9,604 | 17.8 yrs | £1,159 |
| 4 kW | 3402 kWh | 2382 kWh | 1021 kWh | £615 | £102 | £717 | £11,638 | 16.2 yrs | £2,712 |
| 5 kW | 4253 kWh | 2977 kWh | 1276 kWh | £769 | £128 | £897 | £13,673 | 15.2 yrs | £4,264 |
| 6 kW | 5103 kWh | 3572 kWh | 1531 kWh | £923 | £153 | £1,076 | £15,707 | 14.6 yrs | £5,817 |
| 7 kW | 5954 kWh | 4168 kWh | 1786 kWh | £1,077 | £179 | £1,256 | £17,742 | 14.1 yrs | £7,370 |
| 8 kW | 6805 kWh | 4763 kWh | 2041 kWh | £1,231 | £204 | £1,435 | £19,776 | 13.8 yrs | £8,923 |
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: £917, Upfront: £15,423, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1701 kWh | 1242 kWh | 459 kWh | £321 | £46 | £367 | £9,319 | 25.4 yrs | £-1,983 |
| 3 kW | 2552 kWh | 1863 kWh | 689 kWh | £481 | £69 | £550 | £11,354 | 20.6 yrs | £-349 |
| 4 kW | 3402 kWh | 2484 kWh | 919 kWh | £642 | £92 | £734 | £13,388 | 18.2 yrs | £1,285 |
| 5 kW | 4253 kWh | 3105 kWh | 1148 kWh | £802 | £115 | £917 | £15,423 | 16.8 yrs | £2,919 |
| 6 kW | 5103 kWh | 3726 kWh | 1378 kWh | £963 | £138 | £1,100 | £17,457 | 15.9 yrs | £4,552 |
| 7 kW | 5954 kWh | 4346 kWh | 1608 kWh | £1,123 | £161 | £1,284 | £19,492 | 15.2 yrs | £6,186 |
| 8 kW | 6805 kWh | 4967 kWh | 1837 kWh | £1,284 | £184 | £1,467 | £21,526 | 14.7 yrs | £7,820 |
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: £931, Upfront: £17,173, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1701 kWh | 1276 kWh | 425 kWh | £330 | £43 | £372 | £11,069 | 29.7 yrs | £-3,625 |
| 3 kW | 2552 kWh | 1914 kWh | 638 kWh | £495 | £64 | £558 | £13,104 | 23.5 yrs | £-1,937 |
| 4 kW | 3402 kWh | 2552 kWh | 851 kWh | £659 | £85 | £744 | £15,138 | 20.3 yrs | £-249 |
| 5 kW | 4253 kWh | 3190 kWh | 1063 kWh | £824 | £106 | £931 | £17,173 | 18.5 yrs | £1,438 |
| 6 kW | 5103 kWh | 3828 kWh | 1276 kWh | £989 | £128 | £1,117 | £19,207 | 17.2 yrs | £3,126 |
| 7 kW | 5954 kWh | 4466 kWh | 1489 kWh | £1,154 | £149 | £1,303 | £21,242 | 16.3 yrs | £4,813 |
| 8 kW | 6805 kWh | 5103 kWh | 1701 kWh | £1,319 | £170 | £1,489 | £23,276 | 15.6 yrs | £6,501 |
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: £944, Upfront: £19,623, Break-even: 20.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1701 kWh | 1310 kWh | 391 kWh | £338 | £39 | £378 | £13,519 | 35.8 yrs | £-5,967 |
| 3 kW | 2552 kWh | 1965 kWh | 587 kWh | £508 | £59 | £566 | £15,554 | 27.5 yrs | £-4,225 |
| 4 kW | 3402 kWh | 2620 kWh | 783 kWh | £677 | £78 | £755 | £17,588 | 23.3 yrs | £-2,484 |
| 5 kW | 4253 kWh | 3275 kWh | 978 kWh | £846 | £98 | £944 | £19,623 | 20.8 yrs | £-742 |
| 6 kW | 5103 kWh | 3930 kWh | 1174 kWh | £1,015 | £117 | £1,133 | £21,657 | 19.1 yrs | £999 |
| 7 kW | 5954 kWh | 4585 kWh | 1369 kWh | £1,185 | £137 | £1,322 | £23,692 | 17.9 yrs | £2,741 |
| 8 kW | 6805 kWh | 5240 kWh | 1565 kWh | £1,354 | £157 | £1,510 | £25,726 | 17.0 yrs | £4,482 |
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.