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 911 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: £736, Upfront: £10,173, 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 | 1821 kWh | 728 kWh | 1093 kWh | £185 | £109 | £295 | £4,069 | 13.8 yrs | £1,821 |
| 3 kW | 2732 kWh | 1093 kWh | 1639 kWh | £278 | £164 | £442 | £6,104 | 13.8 yrs | £2,732 |
| 4 kW | 3642 kWh | 1457 kWh | 2185 kWh | £370 | £219 | £589 | £8,138 | 13.8 yrs | £3,643 |
| 5 kW | 4553 kWh | 1821 kWh | 2732 kWh | £463 | £273 | £736 | £10,173 | 13.8 yrs | £4,553 |
| 6 kW | 5463 kWh | 2185 kWh | 3278 kWh | £556 | £328 | £884 | £12,207 | 13.8 yrs | £5,464 |
| 7 kW | 6374 kWh | 2550 kWh | 3824 kWh | £648 | £382 | £1,031 | £14,242 | 13.8 yrs | £6,375 |
| 8 kW | 7285 kWh | 2914 kWh | 4371 kWh | £741 | £437 | £1,178 | £16,276 | 13.8 yrs | £7,285 |
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: £877, Upfront: £12,273, 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 | 1821 kWh | 1093 kWh | 728 kWh | £278 | £73 | £351 | £6,169 | 17.6 yrs | £845 |
| 3 kW | 2732 kWh | 1639 kWh | 1093 kWh | £417 | £109 | £526 | £8,204 | 15.6 yrs | £2,318 |
| 4 kW | 3642 kWh | 2185 kWh | 1457 kWh | £556 | £146 | £701 | £10,238 | 14.6 yrs | £3,791 |
| 5 kW | 4553 kWh | 2732 kWh | 1821 kWh | £695 | £182 | £877 | £12,273 | 14.0 yrs | £5,263 |
| 6 kW | 5463 kWh | 3278 kWh | 2185 kWh | £834 | £219 | £1,052 | £14,307 | 13.6 yrs | £6,736 |
| 7 kW | 6374 kWh | 3824 kWh | 2550 kWh | £973 | £255 | £1,228 | £16,342 | 13.3 yrs | £8,209 |
| 8 kW | 7285 kWh | 4371 kWh | 2914 kWh | £1,111 | £291 | £1,403 | £18,376 | 13.1 yrs | £9,681 |
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: £947, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1821 kWh | 1275 kWh | 546 kWh | £324 | £55 | £379 | £7,569 | 20.0 yrs | £7 |
| 3 kW | 2732 kWh | 1912 kWh | 820 kWh | £486 | £82 | £568 | £9,604 | 16.9 yrs | £1,761 |
| 4 kW | 3642 kWh | 2550 kWh | 1093 kWh | £648 | £109 | £758 | £11,638 | 15.4 yrs | £3,515 |
| 5 kW | 4553 kWh | 3187 kWh | 1366 kWh | £810 | £137 | £947 | £13,673 | 14.4 yrs | £5,268 |
| 6 kW | 5463 kWh | 3824 kWh | 1639 kWh | £973 | £164 | £1,136 | £15,707 | 13.8 yrs | £7,022 |
| 7 kW | 6374 kWh | 4462 kWh | 1912 kWh | £1,135 | £191 | £1,326 | £17,742 | 13.4 yrs | £8,776 |
| 8 kW | 7285 kWh | 5099 kWh | 2185 kWh | £1,297 | £219 | £1,515 | £19,776 | 13.1 yrs | £10,529 |
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: £968, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1821 kWh | 1329 kWh | 492 kWh | £338 | £49 | £387 | £9,319 | 24.1 yrs | £-1,574 |
| 3 kW | 2732 kWh | 1994 kWh | 738 kWh | £507 | £74 | £581 | £11,354 | 19.5 yrs | £264 |
| 4 kW | 3642 kWh | 2659 kWh | 983 kWh | £676 | £98 | £774 | £13,388 | 17.3 yrs | £2,102 |
| 5 kW | 4553 kWh | 3324 kWh | 1229 kWh | £845 | £123 | £968 | £15,423 | 15.9 yrs | £3,940 |
| 6 kW | 5463 kWh | 3988 kWh | 1475 kWh | £1,014 | £148 | £1,162 | £17,457 | 15.0 yrs | £5,778 |
| 7 kW | 6374 kWh | 4653 kWh | 1721 kWh | £1,183 | £172 | £1,355 | £19,492 | 14.4 yrs | £7,616 |
| 8 kW | 7285 kWh | 5318 kWh | 1967 kWh | £1,352 | £197 | £1,549 | £21,526 | 13.9 yrs | £9,454 |
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: £982, Upfront: £17,173, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1821 kWh | 1366 kWh | 455 kWh | £347 | £46 | £393 | £11,069 | 28.2 yrs | £-3,212 |
| 3 kW | 2732 kWh | 2049 kWh | 683 kWh | £521 | £68 | £589 | £13,104 | 22.2 yrs | £-1,317 |
| 4 kW | 3642 kWh | 2732 kWh | 911 kWh | £695 | £91 | £786 | £15,138 | 19.3 yrs | £577 |
| 5 kW | 4553 kWh | 3415 kWh | 1138 kWh | £868 | £114 | £982 | £17,173 | 17.5 yrs | £2,471 |
| 6 kW | 5463 kWh | 4098 kWh | 1366 kWh | £1,042 | £137 | £1,179 | £19,207 | 16.3 yrs | £4,365 |
| 7 kW | 6374 kWh | 4781 kWh | 1594 kWh | £1,216 | £159 | £1,375 | £21,242 | 15.4 yrs | £6,259 |
| 8 kW | 7285 kWh | 5463 kWh | 1821 kWh | £1,389 | £182 | £1,571 | £23,276 | 14.8 yrs | £8,153 |
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: £996, Upfront: £19,623, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1821 kWh | 1402 kWh | 419 kWh | £357 | £42 | £398 | £13,519 | 33.9 yrs | £-5,549 |
| 3 kW | 2732 kWh | 2103 kWh | 628 kWh | £535 | £63 | £598 | £15,554 | 26.0 yrs | £-3,599 |
| 4 kW | 3642 kWh | 2805 kWh | 838 kWh | £713 | £84 | £797 | £17,588 | 22.1 yrs | £-1,648 |
| 5 kW | 4553 kWh | 3506 kWh | 1047 kWh | £892 | £105 | £996 | £19,623 | 19.7 yrs | £302 |
| 6 kW | 5463 kWh | 4207 kWh | 1257 kWh | £1,070 | £126 | £1,195 | £21,657 | 18.1 yrs | £2,252 |
| 7 kW | 6374 kWh | 4908 kWh | 1466 kWh | £1,248 | £147 | £1,395 | £23,692 | 17.0 yrs | £4,203 |
| 8 kW | 7285 kWh | 5609 kWh | 1675 kWh | £1,426 | £168 | £1,594 | £25,726 | 16.1 yrs | £6,153 |
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.