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 765 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: £643, Upfront: £10,173, 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 | 1530 kWh | 612 kWh | 918 kWh | £166 | £92 | £257 | £4,069 | 15.8 yrs | £1,078 |
| 3 kW | 2295 kWh | 918 kWh | 1377 kWh | £248 | £138 | £386 | £6,104 | 15.8 yrs | £1,617 |
| 4 kW | 3060 kWh | 1224 kWh | 1836 kWh | £331 | £184 | £515 | £8,138 | 15.8 yrs | £2,157 |
| 5 kW | 3824 kWh | 1530 kWh | 2295 kWh | £414 | £229 | £643 | £10,173 | 15.8 yrs | £2,696 |
| 6 kW | 4589 kWh | 1836 kWh | 2754 kWh | £497 | £275 | £772 | £12,207 | 15.8 yrs | £3,235 |
| 7 kW | 5354 kWh | 2142 kWh | 3212 kWh | £580 | £321 | £901 | £14,242 | 15.8 yrs | £3,774 |
| 8 kW | 6119 kWh | 2448 kWh | 3671 kWh | £662 | £367 | £1,029 | £16,276 | 15.8 yrs | £4,313 |
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: £774, Upfront: £12,273, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 918 kWh | 612 kWh | £248 | £61 | £310 | £6,169 | 19.9 yrs | £22 |
| 3 kW | 2295 kWh | 1377 kWh | 918 kWh | £373 | £92 | £464 | £8,204 | 17.7 yrs | £1,083 |
| 4 kW | 3060 kWh | 1836 kWh | 1224 kWh | £497 | £122 | £619 | £10,238 | 16.5 yrs | £2,144 |
| 5 kW | 3824 kWh | 2295 kWh | 1530 kWh | £621 | £153 | £774 | £12,273 | 15.9 yrs | £3,206 |
| 6 kW | 4589 kWh | 2754 kWh | 1836 kWh | £745 | £184 | £929 | £14,307 | 15.4 yrs | £4,267 |
| 7 kW | 5354 kWh | 3212 kWh | 2142 kWh | £869 | £214 | £1,083 | £16,342 | 15.1 yrs | £5,328 |
| 8 kW | 6119 kWh | 3671 kWh | 2448 kWh | £993 | £245 | £1,238 | £18,376 | 14.8 yrs | £6,389 |
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: £839, Upfront: £13,673, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1071 kWh | 459 kWh | £290 | £46 | £336 | £7,569 | 22.5 yrs | £-856 |
| 3 kW | 2295 kWh | 1606 kWh | 688 kWh | £435 | £69 | £503 | £9,604 | 19.1 yrs | £466 |
| 4 kW | 3060 kWh | 2142 kWh | 918 kWh | £580 | £92 | £671 | £11,638 | 17.3 yrs | £1,788 |
| 5 kW | 3824 kWh | 2677 kWh | 1147 kWh | £724 | £115 | £839 | £13,673 | 16.3 yrs | £3,110 |
| 6 kW | 4589 kWh | 3212 kWh | 1377 kWh | £869 | £138 | £1,007 | £15,707 | 15.6 yrs | £4,433 |
| 7 kW | 5354 kWh | 3748 kWh | 1606 kWh | £1,014 | £161 | £1,175 | £17,742 | 15.1 yrs | £5,755 |
| 8 kW | 6119 kWh | 4283 kWh | 1836 kWh | £1,159 | £184 | £1,343 | £19,776 | 14.7 yrs | £7,077 |
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: £859, Upfront: £15,423, Break-even: 18.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1117 kWh | 413 kWh | £302 | £41 | £343 | £9,319 | 27.1 yrs | £-2,449 |
| 3 kW | 2295 kWh | 1675 kWh | 620 kWh | £453 | £62 | £515 | £11,354 | 22.0 yrs | £-1,049 |
| 4 kW | 3060 kWh | 2233 kWh | 826 kWh | £604 | £83 | £687 | £13,388 | 19.5 yrs | £352 |
| 5 kW | 3824 kWh | 2792 kWh | 1033 kWh | £755 | £103 | £859 | £15,423 | 18.0 yrs | £1,752 |
| 6 kW | 4589 kWh | 3350 kWh | 1239 kWh | £907 | £124 | £1,030 | £17,457 | 16.9 yrs | £3,152 |
| 7 kW | 5354 kWh | 3909 kWh | 1446 kWh | £1,058 | £145 | £1,202 | £19,492 | 16.2 yrs | £4,553 |
| 8 kW | 6119 kWh | 4467 kWh | 1652 kWh | £1,209 | £165 | £1,374 | £21,526 | 15.7 yrs | £5,953 |
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: £872, Upfront: £17,173, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1147 kWh | 382 kWh | £310 | £38 | £349 | £11,069 | 31.7 yrs | £-4,095 |
| 3 kW | 2295 kWh | 1721 kWh | 574 kWh | £466 | £57 | £523 | £13,104 | 25.1 yrs | £-2,642 |
| 4 kW | 3060 kWh | 2295 kWh | 765 kWh | £621 | £76 | £697 | £15,138 | 21.7 yrs | £-1,190 |
| 5 kW | 3824 kWh | 2868 kWh | 956 kWh | £776 | £96 | £872 | £17,173 | 19.7 yrs | £263 |
| 6 kW | 4589 kWh | 3442 kWh | 1147 kWh | £931 | £115 | £1,046 | £19,207 | 18.4 yrs | £1,715 |
| 7 kW | 5354 kWh | 4016 kWh | 1339 kWh | £1,087 | £134 | £1,220 | £21,242 | 17.4 yrs | £3,168 |
| 8 kW | 6119 kWh | 4589 kWh | 1530 kWh | £1,242 | £153 | £1,395 | £23,276 | 16.7 yrs | £4,621 |
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: £885, Upfront: £19,623, Break-even: 22.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1178 kWh | 352 kWh | £319 | £35 | £354 | £13,519 | 38.2 yrs | £-6,440 |
| 3 kW | 2295 kWh | 1767 kWh | 528 kWh | £478 | £53 | £531 | £15,554 | 29.3 yrs | £-4,936 |
| 4 kW | 3060 kWh | 2356 kWh | 704 kWh | £637 | £70 | £708 | £17,588 | 24.8 yrs | £-3,431 |
| 5 kW | 3824 kWh | 2945 kWh | 880 kWh | £797 | £88 | £885 | £19,623 | 22.2 yrs | £-1,926 |
| 6 kW | 4589 kWh | 3534 kWh | 1056 kWh | £956 | £106 | £1,062 | £21,657 | 20.4 yrs | £-421 |
| 7 kW | 5354 kWh | 4123 kWh | 1231 kWh | £1,116 | £123 | £1,239 | £23,692 | 19.1 yrs | £1,083 |
| 8 kW | 6119 kWh | 4712 kWh | 1407 kWh | £1,275 | £141 | £1,416 | £25,726 | 18.2 yrs | £2,588 |
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.