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 873 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: £734, 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 | 1746 kWh | 698 kWh | 1047 kWh | £189 | £105 | £294 | £4,069 | 13.9 yrs | £1,805 |
| 3 kW | 2619 kWh | 1047 kWh | 1571 kWh | £283 | £157 | £441 | £6,104 | 13.9 yrs | £2,707 |
| 4 kW | 3491 kWh | 1397 kWh | 2095 kWh | £378 | £209 | £587 | £8,138 | 13.9 yrs | £3,610 |
| 5 kW | 4364 kWh | 1746 kWh | 2619 kWh | £472 | £262 | £734 | £10,173 | 13.9 yrs | £4,512 |
| 6 kW | 5237 kWh | 2095 kWh | 3142 kWh | £567 | £314 | £881 | £12,207 | 13.9 yrs | £5,415 |
| 7 kW | 6110 kWh | 2444 kWh | 3666 kWh | £661 | £367 | £1,028 | £14,242 | 13.9 yrs | £6,317 |
| 8 kW | 6983 kWh | 2793 kWh | 4190 kWh | £756 | £419 | £1,175 | £16,276 | 13.9 yrs | £7,219 |
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: £883, Upfront: £12,273, 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 | 1746 kWh | 1047 kWh | 698 kWh | £283 | £70 | £353 | £6,169 | 17.5 yrs | £896 |
| 3 kW | 2619 kWh | 1571 kWh | 1047 kWh | £425 | £105 | £530 | £8,204 | 15.5 yrs | £2,394 |
| 4 kW | 3491 kWh | 2095 kWh | 1397 kWh | £567 | £140 | £707 | £10,238 | 14.5 yrs | £3,892 |
| 5 kW | 4364 kWh | 2619 kWh | 1746 kWh | £709 | £175 | £883 | £12,273 | 13.9 yrs | £5,390 |
| 6 kW | 5237 kWh | 3142 kWh | 2095 kWh | £850 | £209 | £1,060 | £14,307 | 13.5 yrs | £6,888 |
| 7 kW | 6110 kWh | 3666 kWh | 2444 kWh | £992 | £244 | £1,236 | £16,342 | 13.2 yrs | £8,386 |
| 8 kW | 6983 kWh | 4190 kWh | 2793 kWh | £1,134 | £279 | £1,413 | £18,376 | 13.0 yrs | £9,884 |
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: £958, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1746 kWh | 1222 kWh | 524 kWh | £331 | £52 | £383 | £7,569 | 19.8 yrs | £92 |
| 3 kW | 2619 kWh | 1833 kWh | 786 kWh | £496 | £79 | £575 | £9,604 | 16.7 yrs | £1,888 |
| 4 kW | 3491 kWh | 2444 kWh | 1047 kWh | £661 | £105 | £766 | £11,638 | 15.2 yrs | £3,683 |
| 5 kW | 4364 kWh | 3055 kWh | 1309 kWh | £827 | £131 | £958 | £13,673 | 14.3 yrs | £5,479 |
| 6 kW | 5237 kWh | 3666 kWh | 1571 kWh | £992 | £157 | £1,149 | £15,707 | 13.7 yrs | £7,275 |
| 7 kW | 6110 kWh | 4277 kWh | 1833 kWh | £1,157 | £183 | £1,341 | £17,742 | 13.2 yrs | £9,071 |
| 8 kW | 6983 kWh | 4888 kWh | 2095 kWh | £1,323 | £209 | £1,532 | £19,776 | 12.9 yrs | £10,867 |
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: £980, Upfront: £15,423, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1746 kWh | 1274 kWh | 471 kWh | £345 | £47 | £392 | £9,319 | 23.8 yrs | £-1,480 |
| 3 kW | 2619 kWh | 1912 kWh | 707 kWh | £517 | £71 | £588 | £11,354 | 19.3 yrs | £406 |
| 4 kW | 3491 kWh | 2549 kWh | 943 kWh | £690 | £94 | £784 | £13,388 | 17.1 yrs | £2,291 |
| 5 kW | 4364 kWh | 3186 kWh | 1178 kWh | £862 | £118 | £980 | £15,423 | 15.7 yrs | £4,176 |
| 6 kW | 5237 kWh | 3823 kWh | 1414 kWh | £1,035 | £141 | £1,176 | £17,457 | 14.8 yrs | £6,061 |
| 7 kW | 6110 kWh | 4460 kWh | 1650 kWh | £1,207 | £165 | £1,372 | £19,492 | 14.2 yrs | £7,946 |
| 8 kW | 6983 kWh | 5097 kWh | 1885 kWh | £1,379 | £189 | £1,568 | £21,526 | 13.7 yrs | £9,832 |
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: £995, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1746 kWh | 1309 kWh | 436 kWh | £354 | £44 | £398 | £11,069 | 27.8 yrs | £-3,110 |
| 3 kW | 2619 kWh | 1964 kWh | 655 kWh | £531 | £65 | £597 | £13,104 | 22.0 yrs | £-1,166 |
| 4 kW | 3491 kWh | 2619 kWh | 873 kWh | £709 | £87 | £796 | £15,138 | 19.0 yrs | £779 |
| 5 kW | 4364 kWh | 3273 kWh | 1091 kWh | £886 | £109 | £995 | £17,173 | 17.3 yrs | £2,724 |
| 6 kW | 5237 kWh | 3928 kWh | 1309 kWh | £1,063 | £131 | £1,194 | £19,207 | 16.1 yrs | £4,669 |
| 7 kW | 6110 kWh | 4582 kWh | 1527 kWh | £1,240 | £153 | £1,393 | £21,242 | 15.3 yrs | £6,613 |
| 8 kW | 6983 kWh | 5237 kWh | 1746 kWh | £1,417 | £175 | £1,592 | £23,276 | 14.6 yrs | £8,558 |
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: £1,010, Upfront: £19,623, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1746 kWh | 1344 kWh | 402 kWh | £364 | £40 | £404 | £13,519 | 33.5 yrs | £-5,441 |
| 3 kW | 2619 kWh | 2016 kWh | 602 kWh | £546 | £60 | £606 | £15,554 | 25.7 yrs | £-3,437 |
| 4 kW | 3491 kWh | 2688 kWh | 803 kWh | £727 | £80 | £808 | £17,588 | 21.8 yrs | £-1,433 |
| 5 kW | 4364 kWh | 3360 kWh | 1004 kWh | £909 | £100 | £1,010 | £19,623 | 19.4 yrs | £572 |
| 6 kW | 5237 kWh | 4033 kWh | 1205 kWh | £1,091 | £120 | £1,212 | £21,657 | 17.9 yrs | £2,576 |
| 7 kW | 6110 kWh | 4705 kWh | 1405 kWh | £1,273 | £141 | £1,414 | £23,692 | 16.8 yrs | £4,580 |
| 8 kW | 6983 kWh | 5377 kWh | 1606 kWh | £1,455 | £161 | £1,616 | £25,726 | 15.9 yrs | £6,585 |
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.