A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 924 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: £745, 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 | 1847 kWh | 739 kWh | 1108 kWh | £187 | £111 | £298 | £4,069 | 13.7 yrs | £1,891 |
| 3 kW | 2771 kWh | 1108 kWh | 1663 kWh | £281 | £166 | £447 | £6,104 | 13.7 yrs | £2,837 |
| 4 kW | 3695 kWh | 1478 kWh | 2217 kWh | £374 | £222 | £596 | £8,138 | 13.7 yrs | £3,783 |
| 5 kW | 4618 kWh | 1847 kWh | 2771 kWh | £468 | £277 | £745 | £10,173 | 13.7 yrs | £4,729 |
| 6 kW | 5542 kWh | 2217 kWh | 3325 kWh | £562 | £333 | £894 | £12,207 | 13.7 yrs | £5,674 |
| 7 kW | 6466 kWh | 2586 kWh | 3880 kWh | £655 | £388 | £1,043 | £14,242 | 13.7 yrs | £6,620 |
| 8 kW | 7390 kWh | 2956 kWh | 4434 kWh | £749 | £443 | £1,192 | £16,276 | 13.7 yrs | £7,566 |
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 | 1847 kWh | 1108 kWh | 739 kWh | £281 | £74 | £355 | £6,169 | 17.4 yrs | £924 |
| 3 kW | 2771 kWh | 1663 kWh | 1108 kWh | £421 | £111 | £532 | £8,204 | 15.4 yrs | £2,436 |
| 4 kW | 3695 kWh | 2217 kWh | 1478 kWh | £562 | £148 | £709 | £10,238 | 14.4 yrs | £3,949 |
| 5 kW | 4618 kWh | 2771 kWh | 1847 kWh | £702 | £185 | £887 | £12,273 | 13.8 yrs | £5,461 |
| 6 kW | 5542 kWh | 3325 kWh | 2217 kWh | £842 | £222 | £1,064 | £14,307 | 13.4 yrs | £6,973 |
| 7 kW | 6466 kWh | 3880 kWh | 2586 kWh | £983 | £259 | £1,241 | £16,342 | 13.2 yrs | £8,485 |
| 8 kW | 7390 kWh | 4434 kWh | 2956 kWh | £1,123 | £296 | £1,419 | £18,376 | 13.0 yrs | £9,997 |
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: £957, 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 | 1847 kWh | 1293 kWh | 554 kWh | £328 | £55 | £383 | £7,569 | 19.8 yrs | £91 |
| 3 kW | 2771 kWh | 1940 kWh | 831 kWh | £491 | £83 | £574 | £9,604 | 16.7 yrs | £1,886 |
| 4 kW | 3695 kWh | 2586 kWh | 1108 kWh | £655 | £111 | £766 | £11,638 | 15.2 yrs | £3,681 |
| 5 kW | 4618 kWh | 3233 kWh | 1386 kWh | £819 | £139 | £957 | £13,673 | 14.3 yrs | £5,477 |
| 6 kW | 5542 kWh | 3880 kWh | 1663 kWh | £983 | £166 | £1,149 | £15,707 | 13.7 yrs | £7,272 |
| 7 kW | 6466 kWh | 4526 kWh | 1940 kWh | £1,146 | £194 | £1,340 | £17,742 | 13.2 yrs | £9,067 |
| 8 kW | 7390 kWh | 5173 kWh | 2217 kWh | £1,310 | £222 | £1,532 | £19,776 | 12.9 yrs | £10,863 |
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: £979, 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 | 1847 kWh | 1349 kWh | 499 kWh | £342 | £50 | £391 | £9,319 | 23.8 yrs | £-1,489 |
| 3 kW | 2771 kWh | 2023 kWh | 748 kWh | £512 | £75 | £587 | £11,354 | 19.3 yrs | £391 |
| 4 kW | 3695 kWh | 2697 kWh | 998 kWh | £683 | £100 | £783 | £13,388 | 17.1 yrs | £2,271 |
| 5 kW | 4618 kWh | 3372 kWh | 1247 kWh | £854 | £125 | £979 | £15,423 | 15.8 yrs | £4,151 |
| 6 kW | 5542 kWh | 4046 kWh | 1496 kWh | £1,025 | £150 | £1,174 | £17,457 | 14.9 yrs | £6,032 |
| 7 kW | 6466 kWh | 4720 kWh | 1746 kWh | £1,196 | £175 | £1,370 | £19,492 | 14.2 yrs | £7,912 |
| 8 kW | 7390 kWh | 5394 kWh | 1995 kWh | £1,366 | £200 | £1,566 | £21,526 | 13.7 yrs | £9,792 |
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: £993, 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 | 1847 kWh | 1386 kWh | 462 kWh | £351 | £46 | £397 | £11,069 | 27.9 yrs | £-3,126 |
| 3 kW | 2771 kWh | 2078 kWh | 693 kWh | £526 | £69 | £596 | £13,104 | 22.0 yrs | £-1,189 |
| 4 kW | 3695 kWh | 2771 kWh | 924 kWh | £702 | £92 | £794 | £15,138 | 19.1 yrs | £748 |
| 5 kW | 4618 kWh | 3464 kWh | 1155 kWh | £877 | £115 | £993 | £17,173 | 17.3 yrs | £2,685 |
| 6 kW | 5542 kWh | 4157 kWh | 1386 kWh | £1,053 | £139 | £1,191 | £19,207 | 16.1 yrs | £4,622 |
| 7 kW | 6466 kWh | 4849 kWh | 1616 kWh | £1,228 | £162 | £1,390 | £21,242 | 15.3 yrs | £6,559 |
| 8 kW | 7390 kWh | 5542 kWh | 1847 kWh | £1,404 | £185 | £1,589 | £23,276 | 14.7 yrs | £8,496 |
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: £1,007, 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 | 1847 kWh | 1422 kWh | 425 kWh | £360 | £42 | £403 | £13,519 | 33.6 yrs | £-5,463 |
| 3 kW | 2771 kWh | 2134 kWh | 637 kWh | £540 | £64 | £604 | £15,554 | 25.7 yrs | £-3,469 |
| 4 kW | 3695 kWh | 2845 kWh | 850 kWh | £721 | £85 | £806 | £17,588 | 21.8 yrs | £-1,476 |
| 5 kW | 4618 kWh | 3556 kWh | 1062 kWh | £901 | £106 | £1,007 | £19,623 | 19.5 yrs | £518 |
| 6 kW | 5542 kWh | 4267 kWh | 1275 kWh | £1,081 | £127 | £1,208 | £21,657 | 17.9 yrs | £2,511 |
| 7 kW | 6466 kWh | 4979 kWh | 1487 kWh | £1,261 | £149 | £1,410 | £23,692 | 16.8 yrs | £4,505 |
| 8 kW | 7390 kWh | 5690 kWh | 1700 kWh | £1,441 | £170 | £1,611 | £25,726 | 16.0 yrs | £6,499 |
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.