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 922 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1843 kWh | 737 kWh | 1106 kWh | £188 | £111 | £298 | £4,069 | 13.6 yrs | £1,893 |
| 3 kW | 2765 kWh | 1106 kWh | 1659 kWh | £281 | £166 | £447 | £6,104 | 13.6 yrs | £2,839 |
| 4 kW | 3687 kWh | 1475 kWh | 2212 kWh | £375 | £221 | £596 | £8,138 | 13.6 yrs | £3,786 |
| 5 kW | 4608 kWh | 1843 kWh | 2765 kWh | £469 | £276 | £745 | £10,173 | 13.6 yrs | £4,732 |
| 6 kW | 5530 kWh | 2212 kWh | 3318 kWh | £563 | £332 | £894 | £12,207 | 13.6 yrs | £5,679 |
| 7 kW | 6452 kWh | 2581 kWh | 3871 kWh | £656 | £387 | £1,043 | £14,242 | 13.6 yrs | £6,625 |
| 8 kW | 7373 kWh | 2949 kWh | 4424 kWh | £750 | £442 | £1,192 | £16,276 | 13.6 yrs | £7,572 |
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: £887, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1843 kWh | 1106 kWh | 737 kWh | £281 | £74 | £355 | £6,169 | 17.4 yrs | £931 |
| 3 kW | 2765 kWh | 1659 kWh | 1106 kWh | £422 | £111 | £532 | £8,204 | 15.4 yrs | £2,446 |
| 4 kW | 3687 kWh | 2212 kWh | 1475 kWh | £563 | £147 | £710 | £10,238 | 14.4 yrs | £3,961 |
| 5 kW | 4608 kWh | 2765 kWh | 1843 kWh | £703 | £184 | £887 | £12,273 | 13.8 yrs | £5,477 |
| 6 kW | 5530 kWh | 3318 kWh | 2212 kWh | £844 | £221 | £1,065 | £14,307 | 13.4 yrs | £6,992 |
| 7 kW | 6452 kWh | 3871 kWh | 2581 kWh | £984 | £258 | £1,242 | £16,342 | 13.2 yrs | £8,507 |
| 8 kW | 7373 kWh | 4424 kWh | 2949 kWh | £1,125 | £295 | £1,420 | £18,376 | 12.9 yrs | £10,023 |
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: £959, 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 | 1843 kWh | 1290 kWh | 553 kWh | £328 | £55 | £383 | £7,569 | 19.7 yrs | £99 |
| 3 kW | 2765 kWh | 1935 kWh | 829 kWh | £492 | £83 | £575 | £9,604 | 16.7 yrs | £1,899 |
| 4 kW | 3687 kWh | 2581 kWh | 1106 kWh | £656 | £111 | £767 | £11,638 | 15.2 yrs | £3,699 |
| 5 kW | 4608 kWh | 3226 kWh | 1382 kWh | £820 | £138 | £959 | £13,673 | 14.3 yrs | £5,499 |
| 6 kW | 5530 kWh | 3871 kWh | 1659 kWh | £984 | £166 | £1,150 | £15,707 | 13.7 yrs | £7,298 |
| 7 kW | 6452 kWh | 4516 kWh | 1935 kWh | £1,148 | £194 | £1,342 | £17,742 | 13.2 yrs | £9,098 |
| 8 kW | 7373 kWh | 5161 kWh | 2212 kWh | £1,313 | £221 | £1,534 | £19,776 | 12.9 yrs | £10,898 |
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 | 1843 kWh | 1346 kWh | 498 kWh | £342 | £50 | £392 | £9,319 | 23.8 yrs | £-1,480 |
| 3 kW | 2765 kWh | 2018 kWh | 747 kWh | £513 | £75 | £588 | £11,354 | 19.3 yrs | £405 |
| 4 kW | 3687 kWh | 2691 kWh | 995 kWh | £684 | £100 | £784 | £13,388 | 17.1 yrs | £2,290 |
| 5 kW | 4608 kWh | 3364 kWh | 1244 kWh | £855 | £124 | £980 | £15,423 | 15.7 yrs | £4,175 |
| 6 kW | 5530 kWh | 4037 kWh | 1493 kWh | £1,027 | £149 | £1,176 | £17,457 | 14.8 yrs | £6,060 |
| 7 kW | 6452 kWh | 4710 kWh | 1742 kWh | £1,198 | £174 | £1,372 | £19,492 | 14.2 yrs | £7,945 |
| 8 kW | 7373 kWh | 5382 kWh | 1991 kWh | £1,369 | £199 | £1,568 | £21,526 | 13.7 yrs | £9,831 |
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: £994, 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 | 1843 kWh | 1382 kWh | 461 kWh | £352 | £46 | £398 | £11,069 | 27.8 yrs | £-3,116 |
| 3 kW | 2765 kWh | 2074 kWh | 691 kWh | £527 | £69 | £596 | £13,104 | 22.0 yrs | £-1,174 |
| 4 kW | 3687 kWh | 2765 kWh | 922 kWh | £703 | £92 | £795 | £15,138 | 19.0 yrs | £768 |
| 5 kW | 4608 kWh | 3456 kWh | 1152 kWh | £879 | £115 | £994 | £17,173 | 17.3 yrs | £2,710 |
| 6 kW | 5530 kWh | 4147 kWh | 1382 kWh | £1,055 | £138 | £1,193 | £19,207 | 16.1 yrs | £4,652 |
| 7 kW | 6452 kWh | 4839 kWh | 1613 kWh | £1,230 | £161 | £1,392 | £21,242 | 15.3 yrs | £6,594 |
| 8 kW | 7373 kWh | 5530 kWh | 1843 kWh | £1,406 | £184 | £1,591 | £23,276 | 14.6 yrs | £8,536 |
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: £1,008, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1843 kWh | 1419 kWh | 424 kWh | £361 | £42 | £403 | £13,519 | 33.5 yrs | £-5,452 |
| 3 kW | 2765 kWh | 2129 kWh | 636 kWh | £541 | £64 | £605 | £15,554 | 25.7 yrs | £-3,454 |
| 4 kW | 3687 kWh | 2839 kWh | 848 kWh | £722 | £85 | £807 | £17,588 | 21.8 yrs | £-1,455 |
| 5 kW | 4608 kWh | 3548 kWh | 1060 kWh | £902 | £106 | £1,008 | £19,623 | 19.5 yrs | £544 |
| 6 kW | 5530 kWh | 4258 kWh | 1272 kWh | £1,083 | £127 | £1,210 | £21,657 | 17.9 yrs | £2,543 |
| 7 kW | 6452 kWh | 4968 kWh | 1484 kWh | £1,263 | £148 | £1,412 | £23,692 | 16.8 yrs | £4,542 |
| 8 kW | 7373 kWh | 5677 kWh | 1696 kWh | £1,444 | £170 | £1,613 | £25,726 | 15.9 yrs | £6,541 |
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.