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 1020 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: £853, Upfront: £10,173, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2040 kWh | 816 kWh | 1224 kWh | £219 | £122 | £341 | £4,069 | 11.9 yrs | £2,755 |
| 3 kW | 3060 kWh | 1224 kWh | 1836 kWh | £328 | £184 | £512 | £6,104 | 11.9 yrs | £4,133 |
| 4 kW | 4080 kWh | 1632 kWh | 2448 kWh | £438 | £245 | £682 | £8,138 | 11.9 yrs | £5,511 |
| 5 kW | 5099 kWh | 2040 kWh | 3060 kWh | £547 | £306 | £853 | £10,173 | 11.9 yrs | £6,888 |
| 6 kW | 6119 kWh | 2448 kWh | 3672 kWh | £656 | £367 | £1,024 | £12,207 | 11.9 yrs | £8,266 |
| 7 kW | 7139 kWh | 2856 kWh | 4284 kWh | £766 | £428 | £1,194 | £14,242 | 11.9 yrs | £9,643 |
| 8 kW | 8159 kWh | 3264 kWh | 4895 kWh | £875 | £490 | £1,365 | £16,276 | 11.9 yrs | £11,021 |
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: £1,025, Upfront: £12,273, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2040 kWh | 1224 kWh | 816 kWh | £328 | £82 | £410 | £6,169 | 15.1 yrs | £2,028 |
| 3 kW | 3060 kWh | 1836 kWh | 1224 kWh | £492 | £122 | £615 | £8,204 | 13.3 yrs | £4,091 |
| 4 kW | 4080 kWh | 2448 kWh | 1632 kWh | £656 | £163 | £820 | £10,238 | 12.5 yrs | £6,155 |
| 5 kW | 5099 kWh | 3060 kWh | 2040 kWh | £821 | £204 | £1,025 | £12,273 | 12.0 yrs | £8,219 |
| 6 kW | 6119 kWh | 3672 kWh | 2448 kWh | £985 | £245 | £1,229 | £14,307 | 11.6 yrs | £10,283 |
| 7 kW | 7139 kWh | 4284 kWh | 2856 kWh | £1,149 | £286 | £1,434 | £16,342 | 11.4 yrs | £12,347 |
| 8 kW | 8159 kWh | 4895 kWh | 3264 kWh | £1,313 | £326 | £1,639 | £18,376 | 11.2 yrs | £14,411 |
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: £1,110, Upfront: £13,673, 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 | 2040 kWh | 1428 kWh | 612 kWh | £383 | £61 | £444 | £7,569 | 17.0 yrs | £1,314 |
| 3 kW | 3060 kWh | 2142 kWh | 918 kWh | £574 | £92 | £666 | £9,604 | 14.4 yrs | £3,721 |
| 4 kW | 4080 kWh | 2856 kWh | 1224 kWh | £766 | £122 | £888 | £11,638 | 13.1 yrs | £6,128 |
| 5 kW | 5099 kWh | 3570 kWh | 1530 kWh | £957 | £153 | £1,110 | £13,673 | 12.3 yrs | £8,535 |
| 6 kW | 6119 kWh | 4284 kWh | 1836 kWh | £1,149 | £184 | £1,332 | £15,707 | 11.8 yrs | £10,941 |
| 7 kW | 7139 kWh | 4997 kWh | 2142 kWh | £1,340 | £214 | £1,554 | £17,742 | 11.4 yrs | £13,348 |
| 8 kW | 8159 kWh | 5711 kWh | 2448 kWh | £1,532 | £245 | £1,777 | £19,776 | 11.1 yrs | £15,755 |
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: £1,136, Upfront: £15,423, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2040 kWh | 1489 kWh | 551 kWh | £399 | £55 | £454 | £9,319 | 20.5 yrs | £-230 |
| 3 kW | 3060 kWh | 2234 kWh | 826 kWh | £599 | £83 | £682 | £11,354 | 16.7 yrs | £2,280 |
| 4 kW | 4080 kWh | 2978 kWh | 1101 kWh | £799 | £110 | £909 | £13,388 | 14.7 yrs | £4,789 |
| 5 kW | 5099 kWh | 3723 kWh | 1377 kWh | £998 | £138 | £1,136 | £15,423 | 13.6 yrs | £7,299 |
| 6 kW | 6119 kWh | 4467 kWh | 1652 kWh | £1,198 | £165 | £1,363 | £17,457 | 12.8 yrs | £9,809 |
| 7 kW | 7139 kWh | 5212 kWh | 1928 kWh | £1,398 | £193 | £1,591 | £19,492 | 12.3 yrs | £12,319 |
| 8 kW | 8159 kWh | 5956 kWh | 2203 kWh | £1,597 | £220 | £1,818 | £21,526 | 11.8 yrs | £14,829 |
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: £1,153, Upfront: £17,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2040 kWh | 1530 kWh | 510 kWh | £410 | £51 | £461 | £11,069 | 24.0 yrs | £-1,843 |
| 3 kW | 3060 kWh | 2295 kWh | 765 kWh | £615 | £76 | £692 | £13,104 | 18.9 yrs | £735 |
| 4 kW | 4080 kWh | 3060 kWh | 1020 kWh | £821 | £102 | £923 | £15,138 | 16.4 yrs | £3,314 |
| 5 kW | 5099 kWh | 3825 kWh | 1275 kWh | £1,026 | £127 | £1,153 | £17,173 | 14.9 yrs | £5,892 |
| 6 kW | 6119 kWh | 4590 kWh | 1530 kWh | £1,231 | £153 | £1,384 | £19,207 | 13.9 yrs | £8,471 |
| 7 kW | 7139 kWh | 5354 kWh | 1785 kWh | £1,436 | £178 | £1,615 | £21,242 | 13.2 yrs | £11,049 |
| 8 kW | 8159 kWh | 6119 kWh | 2040 kWh | £1,641 | £204 | £1,845 | £23,276 | 12.6 yrs | £13,628 |
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: £1,170, Upfront: £19,623, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2040 kWh | 1571 kWh | 469 kWh | £421 | £47 | £468 | £13,519 | 28.9 yrs | £-4,156 |
| 3 kW | 3060 kWh | 2356 kWh | 704 kWh | £632 | £70 | £702 | £15,554 | 22.1 yrs | £-1,509 |
| 4 kW | 4080 kWh | 3141 kWh | 938 kWh | £842 | £94 | £936 | £17,588 | 18.8 yrs | £1,138 |
| 5 kW | 5099 kWh | 3927 kWh | 1173 kWh | £1,053 | £117 | £1,170 | £19,623 | 16.8 yrs | £3,785 |
| 6 kW | 6119 kWh | 4712 kWh | 1407 kWh | £1,264 | £141 | £1,404 | £21,657 | 15.4 yrs | £6,432 |
| 7 kW | 7139 kWh | 5497 kWh | 1642 kWh | £1,474 | £164 | £1,639 | £23,692 | 14.5 yrs | £9,079 |
| 8 kW | 8159 kWh | 6283 kWh | 1877 kWh | £1,685 | £188 | £1,873 | £25,726 | 13.7 yrs | £11,727 |
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.