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 949 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £770, Upfront: £10,173, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1898 kWh | 759 kWh | 1139 kWh | £194 | £114 | £308 | £4,069 | 13.2 yrs | £2,088 |
| 3 kW | 2847 kWh | 1139 kWh | 1708 kWh | £291 | £171 | £462 | £6,104 | 13.2 yrs | £3,133 |
| 4 kW | 3796 kWh | 1518 kWh | 2278 kWh | £388 | £228 | £616 | £8,138 | 13.2 yrs | £4,177 |
| 5 kW | 4745 kWh | 1898 kWh | 2847 kWh | £485 | £285 | £770 | £10,173 | 13.2 yrs | £5,221 |
| 6 kW | 5694 kWh | 2278 kWh | 3417 kWh | £582 | £342 | £924 | £12,207 | 13.2 yrs | £6,265 |
| 7 kW | 6643 kWh | 2657 kWh | 3986 kWh | £679 | £399 | £1,078 | £14,242 | 13.2 yrs | £7,309 |
| 8 kW | 7592 kWh | 3037 kWh | 4555 kWh | £776 | £456 | £1,231 | £16,276 | 13.2 yrs | £8,354 |
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: £917, Upfront: £12,273, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1898 kWh | 1139 kWh | 759 kWh | £291 | £76 | £367 | £6,169 | 16.8 yrs | £1,169 |
| 3 kW | 2847 kWh | 1708 kWh | 1139 kWh | £436 | £114 | £550 | £8,204 | 14.9 yrs | £2,804 |
| 4 kW | 3796 kWh | 2278 kWh | 1518 kWh | £582 | £152 | £734 | £10,238 | 14.0 yrs | £4,438 |
| 5 kW | 4745 kWh | 2847 kWh | 1898 kWh | £727 | £190 | £917 | £12,273 | 13.4 yrs | £6,073 |
| 6 kW | 5694 kWh | 3417 kWh | 2278 kWh | £873 | £228 | £1,101 | £14,307 | 13.0 yrs | £7,707 |
| 7 kW | 6643 kWh | 3986 kWh | 2657 kWh | £1,018 | £266 | £1,284 | £16,342 | 12.7 yrs | £9,342 |
| 8 kW | 7592 kWh | 4555 kWh | 3037 kWh | £1,164 | £304 | £1,468 | £18,376 | 12.5 yrs | £10,976 |
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: £991, Upfront: £13,673, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1898 kWh | 1329 kWh | 569 kWh | £339 | £57 | £396 | £7,569 | 19.1 yrs | £359 |
| 3 kW | 2847 kWh | 1993 kWh | 854 kWh | £509 | £85 | £595 | £9,604 | 16.2 yrs | £2,289 |
| 4 kW | 3796 kWh | 2657 kWh | 1139 kWh | £679 | £114 | £793 | £11,638 | 14.7 yrs | £4,219 |
| 5 kW | 4745 kWh | 3322 kWh | 1424 kWh | £849 | £142 | £991 | £13,673 | 13.8 yrs | £6,148 |
| 6 kW | 5694 kWh | 3986 kWh | 1708 kWh | £1,018 | £171 | £1,189 | £15,707 | 13.2 yrs | £8,078 |
| 7 kW | 6643 kWh | 4650 kWh | 1993 kWh | £1,188 | £199 | £1,387 | £17,742 | 12.8 yrs | £10,008 |
| 8 kW | 7592 kWh | 5315 kWh | 2278 kWh | £1,358 | £228 | £1,586 | £19,776 | 12.5 yrs | £11,937 |
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: £1,013, Upfront: £15,423, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1898 kWh | 1386 kWh | 512 kWh | £354 | £51 | £405 | £9,319 | 23.0 yrs | £-1,214 |
| 3 kW | 2847 kWh | 2078 kWh | 769 kWh | £531 | £77 | £608 | £11,354 | 18.7 yrs | £805 |
| 4 kW | 3796 kWh | 2771 kWh | 1025 kWh | £708 | £102 | £811 | £13,388 | 16.5 yrs | £2,823 |
| 5 kW | 4745 kWh | 3464 kWh | 1281 kWh | £885 | £128 | £1,013 | £15,423 | 15.2 yrs | £4,841 |
| 6 kW | 5694 kWh | 4157 kWh | 1537 kWh | £1,062 | £154 | £1,216 | £17,457 | 14.4 yrs | £6,859 |
| 7 kW | 6643 kWh | 4850 kWh | 1794 kWh | £1,239 | £179 | £1,418 | £19,492 | 13.7 yrs | £8,878 |
| 8 kW | 7592 kWh | 5542 kWh | 2050 kWh | £1,416 | £205 | £1,621 | £21,526 | 13.3 yrs | £10,896 |
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: £1,028, Upfront: £17,173, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1898 kWh | 1424 kWh | 475 kWh | £364 | £47 | £411 | £11,069 | 26.9 yrs | £-2,846 |
| 3 kW | 2847 kWh | 2135 kWh | 712 kWh | £546 | £71 | £617 | £13,104 | 21.2 yrs | £-768 |
| 4 kW | 3796 kWh | 2847 kWh | 949 kWh | £727 | £95 | £822 | £15,138 | 18.4 yrs | £1,309 |
| 5 kW | 4745 kWh | 3559 kWh | 1186 kWh | £909 | £119 | £1,028 | £17,173 | 16.7 yrs | £3,386 |
| 6 kW | 5694 kWh | 4271 kWh | 1424 kWh | £1,091 | £142 | £1,234 | £19,207 | 15.6 yrs | £5,463 |
| 7 kW | 6643 kWh | 4983 kWh | 1661 kWh | £1,273 | £166 | £1,439 | £21,242 | 14.8 yrs | £7,541 |
| 8 kW | 7592 kWh | 5694 kWh | 1898 kWh | £1,455 | £190 | £1,645 | £23,276 | 14.2 yrs | £9,618 |
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: £1,043, Upfront: £19,623, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1898 kWh | 1462 kWh | 437 kWh | £373 | £44 | £417 | £13,519 | 32.4 yrs | £-5,177 |
| 3 kW | 2847 kWh | 2192 kWh | 655 kWh | £560 | £65 | £626 | £15,554 | 24.9 yrs | £-3,041 |
| 4 kW | 3796 kWh | 2923 kWh | 873 kWh | £747 | £87 | £834 | £17,588 | 21.1 yrs | £-905 |
| 5 kW | 4745 kWh | 3654 kWh | 1091 kWh | £934 | £109 | £1,043 | £19,623 | 18.8 yrs | £1,231 |
| 6 kW | 5694 kWh | 4385 kWh | 1310 kWh | £1,120 | £131 | £1,251 | £21,657 | 17.3 yrs | £3,368 |
| 7 kW | 6643 kWh | 5115 kWh | 1528 kWh | £1,307 | £153 | £1,460 | £23,692 | 16.2 yrs | £5,504 |
| 8 kW | 7592 kWh | 5846 kWh | 1746 kWh | £1,494 | £175 | £1,668 | £25,726 | 15.4 yrs | £7,640 |
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.