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 949 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: £766, Upfront: £10,173, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1899 kWh | 759 kWh | 1139 kWh | £192 | £114 | £306 | £4,069 | 13.3 yrs | £2,056 |
| 3 kW | 2848 kWh | 1139 kWh | 1709 kWh | £289 | £171 | £459 | £6,104 | 13.3 yrs | £3,085 |
| 4 kW | 3797 kWh | 1519 kWh | 2278 kWh | £385 | £228 | £613 | £8,138 | 13.3 yrs | £4,113 |
| 5 kW | 4746 kWh | 1899 kWh | 2848 kWh | £481 | £285 | £766 | £10,173 | 13.3 yrs | £5,141 |
| 6 kW | 5696 kWh | 2278 kWh | 3417 kWh | £577 | £342 | £919 | £12,207 | 13.3 yrs | £6,169 |
| 7 kW | 6645 kWh | 2658 kWh | 3987 kWh | £673 | £399 | £1,072 | £14,242 | 13.3 yrs | £7,198 |
| 8 kW | 7594 kWh | 3038 kWh | 4556 kWh | £769 | £456 | £1,225 | £16,276 | 13.3 yrs | £8,226 |
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: £911, Upfront: £12,273, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1899 kWh | 1139 kWh | 759 kWh | £289 | £76 | £364 | £6,169 | 16.9 yrs | £1,121 |
| 3 kW | 2848 kWh | 1709 kWh | 1139 kWh | £433 | £114 | £547 | £8,204 | 15.0 yrs | £2,731 |
| 4 kW | 3797 kWh | 2278 kWh | 1519 kWh | £577 | £152 | £729 | £10,238 | 14.0 yrs | £4,341 |
| 5 kW | 4746 kWh | 2848 kWh | 1899 kWh | £721 | £190 | £911 | £12,273 | 13.5 yrs | £5,952 |
| 6 kW | 5696 kWh | 3417 kWh | 2278 kWh | £866 | £228 | £1,093 | £14,307 | 13.1 yrs | £7,562 |
| 7 kW | 6645 kWh | 3987 kWh | 2658 kWh | £1,010 | £266 | £1,276 | £16,342 | 12.8 yrs | £9,172 |
| 8 kW | 7594 kWh | 4556 kWh | 3038 kWh | £1,154 | £304 | £1,458 | £18,376 | 12.6 yrs | £10,782 |
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: £984, Upfront: £13,673, 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 | 1899 kWh | 1329 kWh | 570 kWh | £337 | £57 | £394 | £7,569 | 19.2 yrs | £303 |
| 3 kW | 2848 kWh | 1993 kWh | 854 kWh | £505 | £85 | £590 | £9,604 | 16.3 yrs | £2,204 |
| 4 kW | 3797 kWh | 2658 kWh | 1139 kWh | £673 | £114 | £787 | £11,638 | 14.8 yrs | £4,105 |
| 5 kW | 4746 kWh | 3322 kWh | 1424 kWh | £842 | £142 | £984 | £13,673 | 13.9 yrs | £6,007 |
| 6 kW | 5696 kWh | 3987 kWh | 1709 kWh | £1,010 | £171 | £1,181 | £15,707 | 13.3 yrs | £7,908 |
| 7 kW | 6645 kWh | 4651 kWh | 1993 kWh | £1,178 | £199 | £1,378 | £17,742 | 12.9 yrs | £9,809 |
| 8 kW | 7594 kWh | 5316 kWh | 2278 kWh | £1,347 | £228 | £1,574 | £19,776 | 12.6 yrs | £11,711 |
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: £1,006, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1899 kWh | 1386 kWh | 513 kWh | £351 | £51 | £402 | £9,319 | 23.2 yrs | £-1,273 |
| 3 kW | 2848 kWh | 2079 kWh | 769 kWh | £527 | £77 | £603 | £11,354 | 18.8 yrs | £716 |
| 4 kW | 3797 kWh | 2772 kWh | 1025 kWh | £702 | £103 | £805 | £13,388 | 16.6 yrs | £2,705 |
| 5 kW | 4746 kWh | 3465 kWh | 1282 kWh | £878 | £128 | £1,006 | £15,423 | 15.3 yrs | £4,693 |
| 6 kW | 5696 kWh | 4158 kWh | 1538 kWh | £1,053 | £154 | £1,207 | £17,457 | 14.5 yrs | £6,682 |
| 7 kW | 6645 kWh | 4851 kWh | 1794 kWh | £1,229 | £179 | £1,408 | £19,492 | 13.8 yrs | £8,671 |
| 8 kW | 7594 kWh | 5544 kWh | 2050 kWh | £1,404 | £205 | £1,609 | £21,526 | 13.4 yrs | £10,659 |
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: £1,020, Upfront: £17,173, 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 | 1899 kWh | 1424 kWh | 475 kWh | £361 | £47 | £408 | £11,069 | 27.1 yrs | £-2,906 |
| 3 kW | 2848 kWh | 2136 kWh | 712 kWh | £541 | £71 | £612 | £13,104 | 21.4 yrs | £-859 |
| 4 kW | 3797 kWh | 2848 kWh | 949 kWh | £721 | £95 | £816 | £15,138 | 18.5 yrs | £1,188 |
| 5 kW | 4746 kWh | 3560 kWh | 1187 kWh | £902 | £119 | £1,020 | £17,173 | 16.8 yrs | £3,234 |
| 6 kW | 5696 kWh | 4272 kWh | 1424 kWh | £1,082 | £142 | £1,224 | £19,207 | 15.7 yrs | £5,281 |
| 7 kW | 6645 kWh | 4984 kWh | 1661 kWh | £1,262 | £166 | £1,428 | £21,242 | 14.9 yrs | £7,328 |
| 8 kW | 7594 kWh | 5696 kWh | 1899 kWh | £1,443 | £190 | £1,633 | £23,276 | 14.3 yrs | £9,375 |
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: £1,035, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1899 kWh | 1462 kWh | 437 kWh | £370 | £44 | £414 | £13,519 | 32.7 yrs | £-5,240 |
| 3 kW | 2848 kWh | 2193 kWh | 655 kWh | £555 | £65 | £621 | £15,554 | 25.0 yrs | £-3,135 |
| 4 kW | 3797 kWh | 2924 kWh | 873 kWh | £741 | £87 | £828 | £17,588 | 21.2 yrs | £-1,030 |
| 5 kW | 4746 kWh | 3655 kWh | 1092 kWh | £926 | £109 | £1,035 | £19,623 | 19.0 yrs | £1,075 |
| 6 kW | 5696 kWh | 4386 kWh | 1310 kWh | £1,111 | £131 | £1,242 | £21,657 | 17.4 yrs | £3,181 |
| 7 kW | 6645 kWh | 5117 kWh | 1528 kWh | £1,296 | £153 | £1,449 | £23,692 | 16.4 yrs | £5,286 |
| 8 kW | 7594 kWh | 5848 kWh | 1747 kWh | £1,481 | £175 | £1,656 | £25,726 | 15.5 yrs | £7,391 |
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.