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 941 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £759, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 753 kWh | 1129 kWh | £191 | £113 | £304 | £4,069 | 13.4 yrs | £2,002 |
| 3 kW | 2823 kWh | 1129 kWh | 1694 kWh | £286 | £169 | £455 | £6,104 | 13.4 yrs | £3,003 |
| 4 kW | 3763 kWh | 1505 kWh | 2258 kWh | £381 | £226 | £607 | £8,138 | 13.4 yrs | £4,004 |
| 5 kW | 4704 kWh | 1882 kWh | 2823 kWh | £477 | £282 | £759 | £10,173 | 13.4 yrs | £5,006 |
| 6 kW | 5645 kWh | 2258 kWh | 3387 kWh | £572 | £339 | £911 | £12,207 | 13.4 yrs | £6,007 |
| 7 kW | 6586 kWh | 2634 kWh | 3952 kWh | £667 | £395 | £1,062 | £14,242 | 13.4 yrs | £7,008 |
| 8 kW | 7527 kWh | 3011 kWh | 4516 kWh | £763 | £452 | £1,214 | £16,276 | 13.4 yrs | £8,009 |
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: £903, Upfront: £12,273, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 1129 kWh | 753 kWh | £286 | £75 | £361 | £6,169 | 17.1 yrs | £1,056 |
| 3 kW | 2823 kWh | 1694 kWh | 1129 kWh | £429 | £113 | £542 | £8,204 | 15.1 yrs | £2,634 |
| 4 kW | 3763 kWh | 2258 kWh | 1505 kWh | £572 | £151 | £723 | £10,238 | 14.2 yrs | £4,212 |
| 5 kW | 4704 kWh | 2823 kWh | 1882 kWh | £715 | £188 | £903 | £12,273 | 13.6 yrs | £5,790 |
| 6 kW | 5645 kWh | 3387 kWh | 2258 kWh | £858 | £226 | £1,084 | £14,307 | 13.2 yrs | £7,368 |
| 7 kW | 6586 kWh | 3952 kWh | 2634 kWh | £1,001 | £263 | £1,264 | £16,342 | 12.9 yrs | £8,946 |
| 8 kW | 7527 kWh | 4516 kWh | 3011 kWh | £1,144 | £301 | £1,445 | £18,376 | 12.7 yrs | £10,524 |
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: £975, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 1317 kWh | 565 kWh | £334 | £56 | £390 | £7,569 | 19.4 yrs | £233 |
| 3 kW | 2823 kWh | 1976 kWh | 847 kWh | £500 | £85 | £585 | £9,604 | 16.4 yrs | £2,100 |
| 4 kW | 3763 kWh | 2634 kWh | 1129 kWh | £667 | £113 | £780 | £11,638 | 14.9 yrs | £3,966 |
| 5 kW | 4704 kWh | 3293 kWh | 1411 kWh | £834 | £141 | £975 | £13,673 | 14.0 yrs | £5,833 |
| 6 kW | 5645 kWh | 3952 kWh | 1694 kWh | £1,001 | £169 | £1,170 | £15,707 | 13.4 yrs | £7,699 |
| 7 kW | 6586 kWh | 4610 kWh | 1976 kWh | £1,168 | £198 | £1,365 | £17,742 | 13.0 yrs | £9,566 |
| 8 kW | 7527 kWh | 5269 kWh | 2258 kWh | £1,335 | £226 | £1,560 | £19,776 | 12.7 yrs | £11,432 |
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: £997, 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 | 1882 kWh | 1374 kWh | 508 kWh | £348 | £51 | £399 | £9,319 | 23.4 yrs | £-1,344 |
| 3 kW | 2823 kWh | 2061 kWh | 762 kWh | £522 | £76 | £598 | £11,354 | 19.0 yrs | £609 |
| 4 kW | 3763 kWh | 2747 kWh | 1016 kWh | £696 | £102 | £798 | £13,388 | 16.8 yrs | £2,562 |
| 5 kW | 4704 kWh | 3434 kWh | 1270 kWh | £870 | £127 | £997 | £15,423 | 15.5 yrs | £4,515 |
| 6 kW | 5645 kWh | 4121 kWh | 1524 kWh | £1,044 | £152 | £1,196 | £17,457 | 14.6 yrs | £6,468 |
| 7 kW | 6586 kWh | 4808 kWh | 1778 kWh | £1,218 | £178 | £1,396 | £19,492 | 14.0 yrs | £8,421 |
| 8 kW | 7527 kWh | 5495 kWh | 2032 kWh | £1,392 | £203 | £1,595 | £21,526 | 13.5 yrs | £10,375 |
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: £1,011, 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 | 1882 kWh | 1411 kWh | 470 kWh | £357 | £47 | £405 | £11,069 | 27.4 yrs | £-2,978 |
| 3 kW | 2823 kWh | 2117 kWh | 706 kWh | £536 | £71 | £607 | £13,104 | 21.6 yrs | £-968 |
| 4 kW | 3763 kWh | 2823 kWh | 941 kWh | £715 | £94 | £809 | £15,138 | 18.7 yrs | £1,043 |
| 5 kW | 4704 kWh | 3528 kWh | 1176 kWh | £894 | £118 | £1,011 | £17,173 | 17.0 yrs | £3,054 |
| 6 kW | 5645 kWh | 4234 kWh | 1411 kWh | £1,072 | £141 | £1,214 | £19,207 | 15.8 yrs | £5,065 |
| 7 kW | 6586 kWh | 4940 kWh | 1647 kWh | £1,251 | £165 | £1,416 | £21,242 | 15.0 yrs | £7,075 |
| 8 kW | 7527 kWh | 5645 kWh | 1882 kWh | £1,430 | £188 | £1,618 | £23,276 | 14.4 yrs | £9,086 |
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: £1,026, 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 | 1882 kWh | 1449 kWh | 433 kWh | £367 | £43 | £410 | £13,519 | 32.9 yrs | £-5,313 |
| 3 kW | 2823 kWh | 2173 kWh | 649 kWh | £551 | £65 | £615 | £15,554 | 25.3 yrs | £-3,245 |
| 4 kW | 3763 kWh | 2898 kWh | 866 kWh | £734 | £87 | £821 | £17,588 | 21.4 yrs | £-1,176 |
| 5 kW | 4704 kWh | 3622 kWh | 1082 kWh | £918 | £108 | £1,026 | £19,623 | 19.1 yrs | £892 |
| 6 kW | 5645 kWh | 4347 kWh | 1298 kWh | £1,101 | £130 | £1,231 | £21,657 | 17.6 yrs | £2,961 |
| 7 kW | 6586 kWh | 5071 kWh | 1515 kWh | £1,285 | £151 | £1,436 | £23,692 | 16.5 yrs | £5,029 |
| 8 kW | 7527 kWh | 5796 kWh | 1731 kWh | £1,468 | £173 | £1,641 | £25,726 | 15.7 yrs | £7,098 |
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.