A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 981 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £814, Upfront: £10,173, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1963 kWh | 785 kWh | 1178 kWh | £208 | £118 | £326 | £4,069 | 12.5 yrs | £2,444 |
| 3 kW | 2944 kWh | 1178 kWh | 1766 kWh | £312 | £177 | £488 | £6,104 | 12.5 yrs | £3,666 |
| 4 kW | 3925 kWh | 1570 kWh | 2355 kWh | £416 | £236 | £651 | £8,138 | 12.5 yrs | £4,888 |
| 5 kW | 4907 kWh | 1963 kWh | 2944 kWh | £520 | £294 | £814 | £10,173 | 12.5 yrs | £6,110 |
| 6 kW | 5888 kWh | 2355 kWh | 3533 kWh | £624 | £353 | £977 | £12,207 | 12.5 yrs | £7,332 |
| 7 kW | 6869 kWh | 2748 kWh | 4122 kWh | £728 | £412 | £1,140 | £14,242 | 12.5 yrs | £8,554 |
| 8 kW | 7851 kWh | 3140 kWh | 4710 kWh | £832 | £471 | £1,303 | £16,276 | 12.5 yrs | £9,776 |
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: £976, Upfront: £12,273, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1963 kWh | 1178 kWh | 785 kWh | £312 | £79 | £390 | £6,169 | 15.8 yrs | £1,638 |
| 3 kW | 2944 kWh | 1766 kWh | 1178 kWh | £468 | £118 | £586 | £8,204 | 14.0 yrs | £3,507 |
| 4 kW | 3925 kWh | 2355 kWh | 1570 kWh | £624 | £157 | £781 | £10,238 | 13.1 yrs | £5,376 |
| 5 kW | 4907 kWh | 2944 kWh | 1963 kWh | £780 | £196 | £976 | £12,273 | 12.6 yrs | £7,245 |
| 6 kW | 5888 kWh | 3533 kWh | 2355 kWh | £936 | £236 | £1,171 | £14,307 | 12.2 yrs | £9,113 |
| 7 kW | 6869 kWh | 4122 kWh | 2748 kWh | £1,091 | £275 | £1,366 | £16,342 | 12.0 yrs | £10,982 |
| 8 kW | 7851 kWh | 4710 kWh | 3140 kWh | £1,247 | £314 | £1,561 | £18,376 | 11.8 yrs | £12,851 |
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: £1,057, Upfront: £13,673, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1963 kWh | 1374 kWh | 589 kWh | £364 | £59 | £423 | £7,569 | 17.9 yrs | £885 |
| 3 kW | 2944 kWh | 2061 kWh | 883 kWh | £546 | £88 | £634 | £9,604 | 15.1 yrs | £3,077 |
| 4 kW | 3925 kWh | 2748 kWh | 1178 kWh | £728 | £118 | £845 | £11,638 | 13.8 yrs | £5,269 |
| 5 kW | 4907 kWh | 3435 kWh | 1472 kWh | £910 | £147 | £1,057 | £13,673 | 12.9 yrs | £7,462 |
| 6 kW | 5888 kWh | 4122 kWh | 1766 kWh | £1,091 | £177 | £1,268 | £15,707 | 12.4 yrs | £9,654 |
| 7 kW | 6869 kWh | 4809 kWh | 2061 kWh | £1,273 | £206 | £1,479 | £17,742 | 12.0 yrs | £11,847 |
| 8 kW | 7851 kWh | 5496 kWh | 2355 kWh | £1,455 | £236 | £1,691 | £19,776 | 11.7 yrs | £14,039 |
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: £1,081, Upfront: £15,423, 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 | 1963 kWh | 1433 kWh | 530 kWh | £379 | £53 | £432 | £9,319 | 21.6 yrs | £-671 |
| 3 kW | 2944 kWh | 2149 kWh | 795 kWh | £569 | £79 | £649 | £11,354 | 17.5 yrs | £1,618 |
| 4 kW | 3925 kWh | 2866 kWh | 1060 kWh | £759 | £106 | £865 | £13,388 | 15.5 yrs | £3,908 |
| 5 kW | 4907 kWh | 3582 kWh | 1325 kWh | £948 | £132 | £1,081 | £15,423 | 14.3 yrs | £6,197 |
| 6 kW | 5888 kWh | 4298 kWh | 1590 kWh | £1,138 | £159 | £1,297 | £17,457 | 13.5 yrs | £8,486 |
| 7 kW | 6869 kWh | 5015 kWh | 1855 kWh | £1,328 | £185 | £1,513 | £19,492 | 12.9 yrs | £10,776 |
| 8 kW | 7851 kWh | 5731 kWh | 2120 kWh | £1,518 | £212 | £1,730 | £21,526 | 12.4 yrs | £13,065 |
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: £1,097, Upfront: £17,173, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1963 kWh | 1472 kWh | 491 kWh | £390 | £49 | £439 | £11,069 | 25.2 yrs | £-2,292 |
| 3 kW | 2944 kWh | 2208 kWh | 736 kWh | £585 | £74 | £658 | £13,104 | 19.9 yrs | £62 |
| 4 kW | 3925 kWh | 2944 kWh | 981 kWh | £780 | £98 | £878 | £15,138 | 17.2 yrs | £2,416 |
| 5 kW | 4907 kWh | 3680 kWh | 1227 kWh | £974 | £123 | £1,097 | £17,173 | 15.7 yrs | £4,770 |
| 6 kW | 5888 kWh | 4416 kWh | 1472 kWh | £1,169 | £147 | £1,317 | £19,207 | 14.6 yrs | £7,125 |
| 7 kW | 6869 kWh | 5152 kWh | 1717 kWh | £1,364 | £172 | £1,536 | £21,242 | 13.8 yrs | £9,479 |
| 8 kW | 7851 kWh | 5888 kWh | 1963 kWh | £1,559 | £196 | £1,755 | £23,276 | 13.3 yrs | £11,833 |
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: £1,113, Upfront: £19,623, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1963 kWh | 1511 kWh | 451 kWh | £400 | £45 | £445 | £13,519 | 30.4 yrs | £-4,612 |
| 3 kW | 2944 kWh | 2267 kWh | 677 kWh | £600 | £68 | £668 | £15,554 | 23.3 yrs | £-2,194 |
| 4 kW | 3925 kWh | 3023 kWh | 903 kWh | £800 | £90 | £891 | £17,588 | 19.7 yrs | £225 |
| 5 kW | 4907 kWh | 3778 kWh | 1129 kWh | £1,000 | £113 | £1,113 | £19,623 | 17.6 yrs | £2,644 |
| 6 kW | 5888 kWh | 4534 kWh | 1354 kWh | £1,201 | £135 | £1,336 | £21,657 | 16.2 yrs | £5,063 |
| 7 kW | 6869 kWh | 5289 kWh | 1580 kWh | £1,401 | £158 | £1,559 | £23,692 | 15.2 yrs | £7,481 |
| 8 kW | 7851 kWh | 6045 kWh | 1806 kWh | £1,601 | £181 | £1,781 | £25,726 | 14.4 yrs | £9,900 |
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.