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 920 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: £744, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1839 kWh | 736 kWh | 1103 kWh | £187 | £110 | £297 | £4,069 | 13.7 yrs | £1,879 |
| 3 kW | 2759 kWh | 1103 kWh | 1655 kWh | £281 | £166 | £446 | £6,104 | 13.7 yrs | £2,819 |
| 4 kW | 3678 kWh | 1471 kWh | 2207 kWh | £374 | £221 | £595 | £8,138 | 13.7 yrs | £3,759 |
| 5 kW | 4598 kWh | 1839 kWh | 2759 kWh | £468 | £276 | £744 | £10,173 | 13.7 yrs | £4,699 |
| 6 kW | 5517 kWh | 2207 kWh | 3310 kWh | £561 | £331 | £892 | £12,207 | 13.7 yrs | £5,638 |
| 7 kW | 6437 kWh | 2575 kWh | 3862 kWh | £655 | £386 | £1,041 | £14,242 | 13.7 yrs | £6,578 |
| 8 kW | 7356 kWh | 2943 kWh | 4414 kWh | £748 | £441 | £1,190 | £16,276 | 13.7 yrs | £7,518 |
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: £885, 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 | 1839 kWh | 1103 kWh | 736 kWh | £281 | £74 | £354 | £6,169 | 17.4 yrs | £915 |
| 3 kW | 2759 kWh | 1655 kWh | 1103 kWh | £421 | £110 | £531 | £8,204 | 15.4 yrs | £2,422 |
| 4 kW | 3678 kWh | 2207 kWh | 1471 kWh | £561 | £147 | £708 | £10,238 | 14.5 yrs | £3,929 |
| 5 kW | 4598 kWh | 2759 kWh | 1839 kWh | £702 | £184 | £885 | £12,273 | 13.9 yrs | £5,436 |
| 6 kW | 5517 kWh | 3310 kWh | 2207 kWh | £842 | £221 | £1,063 | £14,307 | 13.5 yrs | £6,944 |
| 7 kW | 6437 kWh | 3862 kWh | 2575 kWh | £982 | £257 | £1,240 | £16,342 | 13.2 yrs | £8,451 |
| 8 kW | 7356 kWh | 4414 kWh | 2943 kWh | £1,122 | £294 | £1,417 | £18,376 | 13.0 yrs | £9,958 |
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: £956, 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 | 1839 kWh | 1287 kWh | 552 kWh | £327 | £55 | £383 | £7,569 | 19.8 yrs | £82 |
| 3 kW | 2759 kWh | 1931 kWh | 828 kWh | £491 | £83 | £574 | £9,604 | 16.7 yrs | £1,873 |
| 4 kW | 3678 kWh | 2575 kWh | 1103 kWh | £655 | £110 | £765 | £11,638 | 15.2 yrs | £3,664 |
| 5 kW | 4598 kWh | 3218 kWh | 1379 kWh | £818 | £138 | £956 | £13,673 | 14.3 yrs | £5,455 |
| 6 kW | 5517 kWh | 3862 kWh | 1655 kWh | £982 | £166 | £1,148 | £15,707 | 13.7 yrs | £7,246 |
| 7 kW | 6437 kWh | 4506 kWh | 1931 kWh | £1,146 | £193 | £1,339 | £17,742 | 13.3 yrs | £9,037 |
| 8 kW | 7356 kWh | 5150 kWh | 2207 kWh | £1,310 | £221 | £1,530 | £19,776 | 12.9 yrs | £10,828 |
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: £978, Upfront: £15,423, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1839 kWh | 1343 kWh | 497 kWh | £341 | £50 | £391 | £9,319 | 23.8 yrs | £-1,498 |
| 3 kW | 2759 kWh | 2014 kWh | 745 kWh | £512 | £74 | £587 | £11,354 | 19.4 yrs | £379 |
| 4 kW | 3678 kWh | 2685 kWh | 993 kWh | £683 | £99 | £782 | £13,388 | 17.1 yrs | £2,255 |
| 5 kW | 4598 kWh | 3356 kWh | 1241 kWh | £854 | £124 | £978 | £15,423 | 15.8 yrs | £4,131 |
| 6 kW | 5517 kWh | 4028 kWh | 1490 kWh | £1,024 | £149 | £1,173 | £17,457 | 14.9 yrs | £6,007 |
| 7 kW | 6437 kWh | 4699 kWh | 1738 kWh | £1,195 | £174 | £1,369 | £19,492 | 14.2 yrs | £7,883 |
| 8 kW | 7356 kWh | 5370 kWh | 1986 kWh | £1,366 | £199 | £1,564 | £21,526 | 13.8 yrs | £9,759 |
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: £992, 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 | 1839 kWh | 1379 kWh | 460 kWh | £351 | £46 | £397 | £11,069 | 27.9 yrs | £-3,134 |
| 3 kW | 2759 kWh | 2069 kWh | 690 kWh | £526 | £69 | £595 | £13,104 | 22.0 yrs | £-1,201 |
| 4 kW | 3678 kWh | 2759 kWh | 920 kWh | £702 | £92 | £793 | £15,138 | 19.1 yrs | £732 |
| 5 kW | 4598 kWh | 3448 kWh | 1149 kWh | £877 | £115 | £992 | £17,173 | 17.3 yrs | £2,665 |
| 6 kW | 5517 kWh | 4138 kWh | 1379 kWh | £1,052 | £138 | £1,190 | £19,207 | 16.1 yrs | £4,598 |
| 7 kW | 6437 kWh | 4828 kWh | 1609 kWh | £1,228 | £161 | £1,389 | £21,242 | 15.3 yrs | £6,531 |
| 8 kW | 7356 kWh | 5517 kWh | 1839 kWh | £1,403 | £184 | £1,587 | £23,276 | 14.7 yrs | £8,463 |
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: £1,006, 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 | 1839 kWh | 1416 kWh | 423 kWh | £360 | £42 | £402 | £13,519 | 33.6 yrs | £-5,471 |
| 3 kW | 2759 kWh | 2124 kWh | 634 kWh | £540 | £63 | £604 | £15,554 | 25.8 yrs | £-3,481 |
| 4 kW | 3678 kWh | 2832 kWh | 846 kWh | £720 | £85 | £805 | £17,588 | 21.9 yrs | £-1,491 |
| 5 kW | 4598 kWh | 3540 kWh | 1057 kWh | £900 | £106 | £1,006 | £19,623 | 19.5 yrs | £498 |
| 6 kW | 5517 kWh | 4248 kWh | 1269 kWh | £1,080 | £127 | £1,207 | £21,657 | 17.9 yrs | £2,488 |
| 7 kW | 6437 kWh | 4956 kWh | 1480 kWh | £1,260 | £148 | £1,408 | £23,692 | 16.8 yrs | £4,478 |
| 8 kW | 7356 kWh | 5664 kWh | 1692 kWh | £1,440 | £169 | £1,610 | £25,726 | 16.0 yrs | £6,467 |
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.