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 999 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: £828, 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 | 1997 kWh | 799 kWh | 1198 kWh | £212 | £120 | £331 | £4,069 | 12.3 yrs | £2,558 |
| 3 kW | 2996 kWh | 1198 kWh | 1797 kWh | £317 | £180 | £497 | £6,104 | 12.3 yrs | £3,837 |
| 4 kW | 3994 kWh | 1598 kWh | 2396 kWh | £423 | £240 | £663 | £8,138 | 12.3 yrs | £5,116 |
| 5 kW | 4993 kWh | 1997 kWh | 2996 kWh | £529 | £300 | £828 | £10,173 | 12.3 yrs | £6,395 |
| 6 kW | 5991 kWh | 2396 kWh | 3595 kWh | £635 | £359 | £994 | £12,207 | 12.3 yrs | £7,674 |
| 7 kW | 6990 kWh | 2796 kWh | 4194 kWh | £740 | £419 | £1,160 | £14,242 | 12.3 yrs | £8,953 |
| 8 kW | 7988 kWh | 3195 kWh | 4793 kWh | £846 | £479 | £1,325 | £16,276 | 12.3 yrs | £10,232 |
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 | 1997 kWh | 1198 kWh | 799 kWh | £317 | £80 | £397 | £6,169 | 15.5 yrs | £1,774 |
| 3 kW | 2996 kWh | 1797 kWh | 1198 kWh | £476 | £120 | £596 | £8,204 | 13.8 yrs | £3,712 |
| 4 kW | 3994 kWh | 2396 kWh | 1598 kWh | £635 | £160 | £794 | £10,238 | 12.9 yrs | £5,649 |
| 5 kW | 4993 kWh | 2996 kWh | 1997 kWh | £793 | £200 | £993 | £12,273 | 12.4 yrs | £7,586 |
| 6 kW | 5991 kWh | 3595 kWh | 2396 kWh | £952 | £240 | £1,192 | £14,307 | 12.0 yrs | £9,523 |
| 7 kW | 6990 kWh | 4194 kWh | 2796 kWh | £1,111 | £280 | £1,390 | £16,342 | 11.8 yrs | £11,461 |
| 8 kW | 7988 kWh | 4793 kWh | 3195 kWh | £1,269 | £320 | £1,589 | £18,376 | 11.6 yrs | £13,398 |
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: £1,075, 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 | 1997 kWh | 1398 kWh | 599 kWh | £370 | £60 | £430 | £7,569 | 17.6 yrs | £1,033 |
| 3 kW | 2996 kWh | 2097 kWh | 899 kWh | £555 | £90 | £645 | £9,604 | 14.9 yrs | £3,299 |
| 4 kW | 3994 kWh | 2796 kWh | 1198 kWh | £740 | £120 | £860 | £11,638 | 13.5 yrs | £5,565 |
| 5 kW | 4993 kWh | 3495 kWh | 1498 kWh | £925 | £150 | £1,075 | £13,673 | 12.7 yrs | £7,832 |
| 6 kW | 5991 kWh | 4194 kWh | 1797 kWh | £1,111 | £180 | £1,290 | £15,707 | 12.2 yrs | £10,098 |
| 7 kW | 6990 kWh | 4893 kWh | 2097 kWh | £1,296 | £210 | £1,505 | £17,742 | 11.8 yrs | £12,365 |
| 8 kW | 7988 kWh | 5592 kWh | 2396 kWh | £1,481 | £240 | £1,720 | £19,776 | 11.5 yrs | £14,631 |
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: £1,100, 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 | 1997 kWh | 1458 kWh | 539 kWh | £386 | £54 | £440 | £9,319 | 21.2 yrs | £-520 |
| 3 kW | 2996 kWh | 2187 kWh | 809 kWh | £579 | £81 | £660 | £11,354 | 17.2 yrs | £1,845 |
| 4 kW | 3994 kWh | 2916 kWh | 1078 kWh | £772 | £108 | £880 | £13,388 | 15.2 yrs | £4,210 |
| 5 kW | 4993 kWh | 3645 kWh | 1348 kWh | £965 | £135 | £1,100 | £15,423 | 14.0 yrs | £6,575 |
| 6 kW | 5991 kWh | 4374 kWh | 1618 kWh | £1,158 | £162 | £1,320 | £17,457 | 13.2 yrs | £8,941 |
| 7 kW | 6990 kWh | 5102 kWh | 1887 kWh | £1,351 | £189 | £1,540 | £19,492 | 12.7 yrs | £11,306 |
| 8 kW | 7988 kWh | 5831 kWh | 2157 kWh | £1,544 | £216 | £1,760 | £21,526 | 12.2 yrs | £13,671 |
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: £1,116, 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 | 1997 kWh | 1498 kWh | 499 kWh | £397 | £50 | £447 | £11,069 | 24.8 yrs | £-2,138 |
| 3 kW | 2996 kWh | 2247 kWh | 749 kWh | £595 | £75 | £670 | £13,104 | 19.6 yrs | £293 |
| 4 kW | 3994 kWh | 2996 kWh | 999 kWh | £793 | £100 | £893 | £15,138 | 17.0 yrs | £2,724 |
| 5 kW | 4993 kWh | 3744 kWh | 1248 kWh | £992 | £125 | £1,116 | £17,173 | 15.4 yrs | £5,155 |
| 6 kW | 5991 kWh | 4493 kWh | 1498 kWh | £1,190 | £150 | £1,340 | £19,207 | 14.3 yrs | £7,585 |
| 7 kW | 6990 kWh | 5242 kWh | 1747 kWh | £1,388 | £175 | £1,563 | £21,242 | 13.6 yrs | £10,016 |
| 8 kW | 7988 kWh | 5991 kWh | 1997 kWh | £1,586 | £200 | £1,786 | £23,276 | 13.0 yrs | £12,447 |
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: £1,133, 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 | 1997 kWh | 1538 kWh | 459 kWh | £407 | £46 | £453 | £13,519 | 29.8 yrs | £-4,457 |
| 3 kW | 2996 kWh | 2307 kWh | 689 kWh | £611 | £69 | £680 | £15,554 | 22.9 yrs | £-1,960 |
| 4 kW | 3994 kWh | 3075 kWh | 919 kWh | £814 | £92 | £906 | £17,588 | 19.4 yrs | £537 |
| 5 kW | 4993 kWh | 3844 kWh | 1148 kWh | £1,018 | £115 | £1,133 | £19,623 | 17.3 yrs | £3,034 |
| 6 kW | 5991 kWh | 4613 kWh | 1378 kWh | £1,222 | £138 | £1,359 | £21,657 | 15.9 yrs | £5,530 |
| 7 kW | 6990 kWh | 5382 kWh | 1608 kWh | £1,425 | £161 | £1,586 | £23,692 | 14.9 yrs | £8,027 |
| 8 kW | 7988 kWh | 6151 kWh | 1837 kWh | £1,629 | £184 | £1,812 | £25,726 | 14.2 yrs | £10,524 |
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.