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 988 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £826, Upfront: £10,173, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1976 kWh | 790 kWh | 1186 kWh | £212 | £119 | £331 | £4,069 | 12.3 yrs | £2,542 |
| 3 kW | 2964 kWh | 1186 kWh | 1778 kWh | £318 | £178 | £496 | £6,104 | 12.3 yrs | £3,813 |
| 4 kW | 3952 kWh | 1581 kWh | 2371 kWh | £424 | £237 | £661 | £8,138 | 12.3 yrs | £5,084 |
| 5 kW | 4940 kWh | 1976 kWh | 2964 kWh | £530 | £296 | £826 | £10,173 | 12.3 yrs | £6,355 |
| 6 kW | 5928 kWh | 2371 kWh | 3557 kWh | £636 | £356 | £992 | £12,207 | 12.3 yrs | £7,626 |
| 7 kW | 6916 kWh | 2766 kWh | 4150 kWh | £742 | £415 | £1,157 | £14,242 | 12.3 yrs | £8,897 |
| 8 kW | 7904 kWh | 3162 kWh | 4742 kWh | £848 | £474 | £1,322 | £16,276 | 12.3 yrs | £10,168 |
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: £993, Upfront: £12,273, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1976 kWh | 1186 kWh | 790 kWh | £318 | £79 | £397 | £6,169 | 15.5 yrs | £1,771 |
| 3 kW | 2964 kWh | 1778 kWh | 1186 kWh | £477 | £119 | £596 | £8,204 | 13.8 yrs | £3,707 |
| 4 kW | 3952 kWh | 2371 kWh | 1581 kWh | £636 | £158 | £794 | £10,238 | 12.9 yrs | £5,643 |
| 5 kW | 4940 kWh | 2964 kWh | 1976 kWh | £795 | £198 | £993 | £12,273 | 12.4 yrs | £7,579 |
| 6 kW | 5928 kWh | 3557 kWh | 2371 kWh | £954 | £237 | £1,191 | £14,307 | 12.0 yrs | £9,514 |
| 7 kW | 6916 kWh | 4150 kWh | 2766 kWh | £1,113 | £277 | £1,390 | £16,342 | 11.8 yrs | £11,450 |
| 8 kW | 7904 kWh | 4742 kWh | 3162 kWh | £1,272 | £316 | £1,588 | £18,376 | 11.6 yrs | £13,386 |
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: £1,076, Upfront: £13,673, Break-even: 12.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1976 kWh | 1383 kWh | 593 kWh | £371 | £59 | £430 | £7,569 | 17.6 yrs | £1,036 |
| 3 kW | 2964 kWh | 2075 kWh | 889 kWh | £556 | £89 | £645 | £9,604 | 14.9 yrs | £3,304 |
| 4 kW | 3952 kWh | 2766 kWh | 1186 kWh | £742 | £119 | £861 | £11,638 | 13.5 yrs | £5,572 |
| 5 kW | 4940 kWh | 3458 kWh | 1482 kWh | £927 | £148 | £1,076 | £13,673 | 12.7 yrs | £7,841 |
| 6 kW | 5928 kWh | 4150 kWh | 1778 kWh | £1,113 | £178 | £1,291 | £15,707 | 12.2 yrs | £10,109 |
| 7 kW | 6916 kWh | 4841 kWh | 2075 kWh | £1,298 | £207 | £1,506 | £17,742 | 11.8 yrs | £12,377 |
| 8 kW | 7904 kWh | 5533 kWh | 2371 kWh | £1,484 | £237 | £1,721 | £19,776 | 11.5 yrs | £14,645 |
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: £1,101, Upfront: £15,423, 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 | 1976 kWh | 1443 kWh | 534 kWh | £387 | £53 | £440 | £9,319 | 21.2 yrs | £-514 |
| 3 kW | 2964 kWh | 2164 kWh | 800 kWh | £580 | £80 | £660 | £11,354 | 17.2 yrs | £1,853 |
| 4 kW | 3952 kWh | 2885 kWh | 1067 kWh | £774 | £107 | £880 | £13,388 | 15.2 yrs | £4,221 |
| 5 kW | 4940 kWh | 3606 kWh | 1334 kWh | £967 | £133 | £1,101 | £15,423 | 14.0 yrs | £6,589 |
| 6 kW | 5928 kWh | 4328 kWh | 1601 kWh | £1,161 | £160 | £1,321 | £17,457 | 13.2 yrs | £8,957 |
| 7 kW | 6916 kWh | 5049 kWh | 1867 kWh | £1,354 | £187 | £1,541 | £19,492 | 12.7 yrs | £11,325 |
| 8 kW | 7904 kWh | 5770 kWh | 2134 kWh | £1,548 | £213 | £1,761 | £21,526 | 12.2 yrs | £13,693 |
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: £1,117, Upfront: £17,173, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1976 kWh | 1482 kWh | 494 kWh | £397 | £49 | £447 | £11,069 | 24.8 yrs | £-2,131 |
| 3 kW | 2964 kWh | 2223 kWh | 741 kWh | £596 | £74 | £670 | £13,104 | 19.5 yrs | £303 |
| 4 kW | 3952 kWh | 2964 kWh | 988 kWh | £795 | £99 | £894 | £15,138 | 16.9 yrs | £2,737 |
| 5 kW | 4940 kWh | 3705 kWh | 1235 kWh | £994 | £124 | £1,117 | £17,173 | 15.4 yrs | £5,172 |
| 6 kW | 5928 kWh | 4446 kWh | 1482 kWh | £1,192 | £148 | £1,341 | £19,207 | 14.3 yrs | £7,606 |
| 7 kW | 6916 kWh | 5187 kWh | 1729 kWh | £1,391 | £173 | £1,564 | £21,242 | 13.6 yrs | £10,040 |
| 8 kW | 7904 kWh | 5928 kWh | 1976 kWh | £1,590 | £198 | £1,788 | £23,276 | 13.0 yrs | £12,474 |
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: £1,134, Upfront: £19,623, 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 | 1976 kWh | 1522 kWh | 454 kWh | £408 | £45 | £454 | £13,519 | 29.8 yrs | £-4,448 |
| 3 kW | 2964 kWh | 2282 kWh | 682 kWh | £612 | £68 | £680 | £15,554 | 22.9 yrs | £-1,948 |
| 4 kW | 3952 kWh | 3043 kWh | 909 kWh | £816 | £91 | £907 | £17,588 | 19.4 yrs | £553 |
| 5 kW | 4940 kWh | 3804 kWh | 1136 kWh | £1,020 | £114 | £1,134 | £19,623 | 17.3 yrs | £3,054 |
| 6 kW | 5928 kWh | 4565 kWh | 1363 kWh | £1,224 | £136 | £1,361 | £21,657 | 15.9 yrs | £5,555 |
| 7 kW | 6916 kWh | 5325 kWh | 1591 kWh | £1,428 | £159 | £1,587 | £23,692 | 14.9 yrs | £8,055 |
| 8 kW | 7904 kWh | 6086 kWh | 1818 kWh | £1,632 | £182 | £1,814 | £25,726 | 14.2 yrs | £10,556 |
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.