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 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: £830, 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 | £332 | £4,069 | 12.3 yrs | £2,567 |
| 3 kW | 2996 kWh | 1198 kWh | 1798 kWh | £318 | £180 | £498 | £6,104 | 12.3 yrs | £3,851 |
| 4 kW | 3995 kWh | 1598 kWh | 2397 kWh | £424 | £240 | £664 | £8,138 | 12.3 yrs | £5,134 |
| 5 kW | 4994 kWh | 1997 kWh | 2996 kWh | £530 | £300 | £830 | £10,173 | 12.3 yrs | £6,418 |
| 6 kW | 5992 kWh | 2397 kWh | 3595 kWh | £636 | £360 | £995 | £12,207 | 12.3 yrs | £7,702 |
| 7 kW | 6991 kWh | 2796 kWh | 4195 kWh | £742 | £419 | £1,161 | £14,242 | 12.3 yrs | £8,985 |
| 8 kW | 7990 kWh | 3196 kWh | 4794 kWh | £848 | £479 | £1,327 | £16,276 | 12.3 yrs | £10,269 |
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: £995, Upfront: £12,273, 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 | 1198 kWh | 799 kWh | £318 | £80 | £398 | £6,169 | 15.5 yrs | £1,788 |
| 3 kW | 2996 kWh | 1798 kWh | 1198 kWh | £477 | £120 | £597 | £8,204 | 13.7 yrs | £3,732 |
| 4 kW | 3995 kWh | 2397 kWh | 1598 kWh | £636 | £160 | £796 | £10,238 | 12.9 yrs | £5,676 |
| 5 kW | 4994 kWh | 2996 kWh | 1997 kWh | £795 | £200 | £995 | £12,273 | 12.3 yrs | £7,620 |
| 6 kW | 5992 kWh | 3595 kWh | 2397 kWh | £954 | £240 | £1,194 | £14,307 | 12.0 yrs | £9,564 |
| 7 kW | 6991 kWh | 4195 kWh | 2796 kWh | £1,113 | £280 | £1,392 | £16,342 | 11.7 yrs | £11,508 |
| 8 kW | 7990 kWh | 4794 kWh | 3196 kWh | £1,272 | £320 | £1,591 | £18,376 | 11.5 yrs | £13,452 |
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: £1,077, 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 | £371 | £60 | £431 | £7,569 | 17.6 yrs | £1,048 |
| 3 kW | 2996 kWh | 2097 kWh | 899 kWh | £556 | £90 | £646 | £9,604 | 14.9 yrs | £3,322 |
| 4 kW | 3995 kWh | 2796 kWh | 1198 kWh | £742 | £120 | £862 | £11,638 | 13.5 yrs | £5,596 |
| 5 kW | 4994 kWh | 3495 kWh | 1498 kWh | £927 | £150 | £1,077 | £13,673 | 12.7 yrs | £7,871 |
| 6 kW | 5992 kWh | 4195 kWh | 1798 kWh | £1,113 | £180 | £1,293 | £15,707 | 12.2 yrs | £10,145 |
| 7 kW | 6991 kWh | 4894 kWh | 2097 kWh | £1,298 | £210 | £1,508 | £17,742 | 11.8 yrs | £12,419 |
| 8 kW | 7990 kWh | 5593 kWh | 2397 kWh | £1,484 | £240 | £1,723 | £19,776 | 11.5 yrs | £14,693 |
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: £1,102, 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 | £387 | £54 | £441 | £9,319 | 21.1 yrs | £-504 |
| 3 kW | 2996 kWh | 2187 kWh | 809 kWh | £580 | £81 | £661 | £11,354 | 17.2 yrs | £1,870 |
| 4 kW | 3995 kWh | 2916 kWh | 1079 kWh | £774 | £108 | £882 | £13,388 | 15.2 yrs | £4,243 |
| 5 kW | 4994 kWh | 3645 kWh | 1348 kWh | £967 | £135 | £1,102 | £15,423 | 14.0 yrs | £6,616 |
| 6 kW | 5992 kWh | 4374 kWh | 1618 kWh | £1,161 | £162 | £1,322 | £17,457 | 13.2 yrs | £8,989 |
| 7 kW | 6991 kWh | 5103 kWh | 1888 kWh | £1,354 | £189 | £1,543 | £19,492 | 12.6 yrs | £11,362 |
| 8 kW | 7990 kWh | 5832 kWh | 2157 kWh | £1,547 | £216 | £1,763 | £21,526 | 12.2 yrs | £13,735 |
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: £1,118, 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 | 24.7 yrs | £-2,122 |
| 3 kW | 2996 kWh | 2247 kWh | 749 kWh | £596 | £75 | £671 | £13,104 | 19.5 yrs | £318 |
| 4 kW | 3995 kWh | 2996 kWh | 999 kWh | £795 | £100 | £895 | £15,138 | 16.9 yrs | £2,757 |
| 5 kW | 4994 kWh | 3745 kWh | 1248 kWh | £994 | £125 | £1,118 | £17,173 | 15.4 yrs | £5,196 |
| 6 kW | 5992 kWh | 4494 kWh | 1498 kWh | £1,192 | £150 | £1,342 | £19,207 | 14.3 yrs | £7,635 |
| 7 kW | 6991 kWh | 5243 kWh | 1748 kWh | £1,391 | £175 | £1,566 | £21,242 | 13.6 yrs | £10,074 |
| 8 kW | 7990 kWh | 5992 kWh | 1997 kWh | £1,590 | £200 | £1,789 | £23,276 | 13.0 yrs | £12,514 |
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: £1,135, 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 | £408 | £46 | £454 | £13,519 | 29.8 yrs | £-4,440 |
| 3 kW | 2996 kWh | 2307 kWh | 689 kWh | £612 | £69 | £681 | £15,554 | 22.8 yrs | £-1,934 |
| 4 kW | 3995 kWh | 3076 kWh | 919 kWh | £816 | £92 | £908 | £17,588 | 19.4 yrs | £571 |
| 5 kW | 4994 kWh | 3845 kWh | 1149 kWh | £1,020 | £115 | £1,135 | £19,623 | 17.3 yrs | £3,076 |
| 6 kW | 5992 kWh | 4614 kWh | 1378 kWh | £1,224 | £138 | £1,362 | £21,657 | 15.9 yrs | £5,581 |
| 7 kW | 6991 kWh | 5383 kWh | 1608 kWh | £1,428 | £161 | £1,589 | £23,692 | 14.9 yrs | £8,087 |
| 8 kW | 7990 kWh | 6152 kWh | 1838 kWh | £1,632 | £184 | £1,816 | £25,726 | 14.2 yrs | £10,592 |
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.