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 848 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: £714, Upfront: £10,173, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1696 kWh | 678 kWh | 1017 kWh | £184 | £102 | £286 | £4,069 | 14.2 yrs | £1,643 |
| 3 kW | 2543 kWh | 1017 kWh | 1526 kWh | £276 | £153 | £428 | £6,104 | 14.2 yrs | £2,465 |
| 4 kW | 3391 kWh | 1356 kWh | 2035 kWh | £368 | £203 | £571 | £8,138 | 14.2 yrs | £3,286 |
| 5 kW | 4239 kWh | 1696 kWh | 2543 kWh | £460 | £254 | £714 | £10,173 | 14.2 yrs | £4,108 |
| 6 kW | 5087 kWh | 2035 kWh | 3052 kWh | £552 | £305 | £857 | £12,207 | 14.2 yrs | £4,930 |
| 7 kW | 5935 kWh | 2374 kWh | 3561 kWh | £644 | £356 | £1,000 | £14,242 | 14.2 yrs | £5,751 |
| 8 kW | 6782 kWh | 2713 kWh | 4069 kWh | £735 | £407 | £1,142 | £16,276 | 14.2 yrs | £6,573 |
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: £859, Upfront: £12,273, 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 | 1696 kWh | 1017 kWh | 678 kWh | £276 | £68 | £344 | £6,169 | 18.0 yrs | £704 |
| 3 kW | 2543 kWh | 1526 kWh | 1017 kWh | £414 | £102 | £515 | £8,204 | 15.9 yrs | £2,106 |
| 4 kW | 3391 kWh | 2035 kWh | 1356 kWh | £552 | £136 | £687 | £10,238 | 14.9 yrs | £3,507 |
| 5 kW | 4239 kWh | 2543 kWh | 1696 kWh | £690 | £170 | £859 | £12,273 | 14.3 yrs | £4,909 |
| 6 kW | 5087 kWh | 3052 kWh | 2035 kWh | £827 | £203 | £1,031 | £14,307 | 13.9 yrs | £6,311 |
| 7 kW | 5935 kWh | 3561 kWh | 2374 kWh | £965 | £237 | £1,203 | £16,342 | 13.6 yrs | £7,713 |
| 8 kW | 6782 kWh | 4069 kWh | 2713 kWh | £1,103 | £271 | £1,375 | £18,376 | 13.4 yrs | £9,115 |
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: £932, Upfront: £13,673, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1696 kWh | 1187 kWh | 509 kWh | £322 | £51 | £373 | £7,569 | 20.3 yrs | £-116 |
| 3 kW | 2543 kWh | 1780 kWh | 763 kWh | £483 | £76 | £559 | £9,604 | 17.2 yrs | £1,576 |
| 4 kW | 3391 kWh | 2374 kWh | 1017 kWh | £644 | £102 | £745 | £11,638 | 15.6 yrs | £3,268 |
| 5 kW | 4239 kWh | 2967 kWh | 1272 kWh | £804 | £127 | £932 | £13,673 | 14.7 yrs | £4,960 |
| 6 kW | 5087 kWh | 3561 kWh | 1526 kWh | £965 | £153 | £1,118 | £15,707 | 14.1 yrs | £6,652 |
| 7 kW | 5935 kWh | 4154 kWh | 1780 kWh | £1,126 | £178 | £1,304 | £17,742 | 13.6 yrs | £8,344 |
| 8 kW | 6782 kWh | 4748 kWh | 2035 kWh | £1,287 | £203 | £1,491 | £19,776 | 13.3 yrs | £10,036 |
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: £953, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1696 kWh | 1238 kWh | 458 kWh | £336 | £46 | £381 | £9,319 | 24.4 yrs | £-1,692 |
| 3 kW | 2543 kWh | 1857 kWh | 687 kWh | £503 | £69 | £572 | £11,354 | 19.8 yrs | £87 |
| 4 kW | 3391 kWh | 2476 kWh | 916 kWh | £671 | £92 | £763 | £13,388 | 17.6 yrs | £1,866 |
| 5 kW | 4239 kWh | 3095 kWh | 1145 kWh | £839 | £114 | £953 | £15,423 | 16.2 yrs | £3,645 |
| 6 kW | 5087 kWh | 3713 kWh | 1373 kWh | £1,007 | £137 | £1,144 | £17,457 | 15.3 yrs | £5,424 |
| 7 kW | 5935 kWh | 4332 kWh | 1602 kWh | £1,174 | £160 | £1,335 | £19,492 | 14.6 yrs | £7,203 |
| 8 kW | 6782 kWh | 4951 kWh | 1831 kWh | £1,342 | £183 | £1,525 | £21,526 | 14.1 yrs | £8,982 |
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: £968, Upfront: £17,173, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1696 kWh | 1272 kWh | 424 kWh | £345 | £42 | £387 | £11,069 | 28.6 yrs | £-3,326 |
| 3 kW | 2543 kWh | 1908 kWh | 636 kWh | £517 | £64 | £581 | £13,104 | 22.6 yrs | £-1,489 |
| 4 kW | 3391 kWh | 2543 kWh | 848 kWh | £690 | £85 | £774 | £15,138 | 19.6 yrs | £348 |
| 5 kW | 4239 kWh | 3179 kWh | 1060 kWh | £862 | £106 | £968 | £17,173 | 17.7 yrs | £2,185 |
| 6 kW | 5087 kWh | 3815 kWh | 1272 kWh | £1,034 | £127 | £1,161 | £19,207 | 16.5 yrs | £4,022 |
| 7 kW | 5935 kWh | 4451 kWh | 1484 kWh | £1,207 | £148 | £1,355 | £21,242 | 15.7 yrs | £5,859 |
| 8 kW | 6782 kWh | 5087 kWh | 1696 kWh | £1,379 | £170 | £1,549 | £23,276 | 15.0 yrs | £7,696 |
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: £982, Upfront: £19,623, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1696 kWh | 1306 kWh | 390 kWh | £354 | £39 | £393 | £13,519 | 34.4 yrs | £-5,660 |
| 3 kW | 2543 kWh | 1958 kWh | 585 kWh | £531 | £58 | £589 | £15,554 | 26.4 yrs | £-3,765 |
| 4 kW | 3391 kWh | 2611 kWh | 780 kWh | £708 | £78 | £786 | £17,588 | 22.4 yrs | £-1,870 |
| 5 kW | 4239 kWh | 3264 kWh | 975 kWh | £885 | £97 | £982 | £19,623 | 20.0 yrs | £25 |
| 6 kW | 5087 kWh | 3917 kWh | 1170 kWh | £1,062 | £117 | £1,179 | £21,657 | 18.4 yrs | £1,920 |
| 7 kW | 5935 kWh | 4570 kWh | 1365 kWh | £1,239 | £136 | £1,375 | £23,692 | 17.2 yrs | £3,815 |
| 8 kW | 6782 kWh | 5223 kWh | 1560 kWh | £1,416 | £156 | £1,572 | £25,726 | 16.4 yrs | £5,710 |
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.