A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 849 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: £715, Upfront: £10,173, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1698 kWh | 679 kWh | 1019 kWh | £184 | £102 | £286 | £4,069 | 14.2 yrs | £1,650 |
| 3 kW | 2546 kWh | 1019 kWh | 1528 kWh | £276 | £153 | £429 | £6,104 | 14.2 yrs | £2,474 |
| 4 kW | 3395 kWh | 1358 kWh | 2037 kWh | £368 | £204 | £572 | £8,138 | 14.2 yrs | £3,299 |
| 5 kW | 4244 kWh | 1698 kWh | 2546 kWh | £460 | £255 | £715 | £10,173 | 14.2 yrs | £4,124 |
| 6 kW | 5093 kWh | 2037 kWh | 3056 kWh | £552 | £306 | £858 | £12,207 | 14.2 yrs | £4,949 |
| 7 kW | 5941 kWh | 2377 kWh | 3565 kWh | £644 | £356 | £1,001 | £14,242 | 14.2 yrs | £5,774 |
| 8 kW | 6790 kWh | 2716 kWh | 4074 kWh | £736 | £407 | £1,144 | £16,276 | 14.2 yrs | £6,598 |
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: £860, Upfront: £12,273, 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 | 1698 kWh | 1019 kWh | 679 kWh | £276 | £68 | £344 | £6,169 | 17.9 yrs | £711 |
| 3 kW | 2546 kWh | 1528 kWh | 1019 kWh | £414 | £102 | £516 | £8,204 | 15.9 yrs | £2,117 |
| 4 kW | 3395 kWh | 2037 kWh | 1358 kWh | £552 | £136 | £688 | £10,238 | 14.9 yrs | £3,523 |
| 5 kW | 4244 kWh | 2546 kWh | 1698 kWh | £690 | £170 | £860 | £12,273 | 14.3 yrs | £4,928 |
| 6 kW | 5093 kWh | 3056 kWh | 2037 kWh | £828 | £204 | £1,032 | £14,307 | 13.9 yrs | £6,334 |
| 7 kW | 5941 kWh | 3565 kWh | 2377 kWh | £966 | £238 | £1,204 | £16,342 | 13.6 yrs | £7,740 |
| 8 kW | 6790 kWh | 4074 kWh | 2716 kWh | £1,104 | £272 | £1,376 | £18,376 | 13.4 yrs | £9,145 |
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: £933, Upfront: £13,673, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1698 kWh | 1188 kWh | 509 kWh | £322 | £51 | £373 | £7,569 | 20.3 yrs | £-108 |
| 3 kW | 2546 kWh | 1782 kWh | 764 kWh | £483 | £76 | £560 | £9,604 | 17.2 yrs | £1,588 |
| 4 kW | 3395 kWh | 2377 kWh | 1019 kWh | £644 | £102 | £746 | £11,638 | 15.6 yrs | £3,285 |
| 5 kW | 4244 kWh | 2971 kWh | 1273 kWh | £805 | £127 | £933 | £13,673 | 14.7 yrs | £4,981 |
| 6 kW | 5093 kWh | 3565 kWh | 1528 kWh | £966 | £153 | £1,119 | £15,707 | 14.0 yrs | £6,677 |
| 7 kW | 5941 kWh | 4159 kWh | 1782 kWh | £1,127 | £178 | £1,306 | £17,742 | 13.6 yrs | £8,373 |
| 8 kW | 6790 kWh | 4753 kWh | 2037 kWh | £1,289 | £204 | £1,492 | £19,776 | 13.3 yrs | £10,069 |
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: £954, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1698 kWh | 1239 kWh | 458 kWh | £336 | £46 | £382 | £9,319 | 24.4 yrs | £-1,683 |
| 3 kW | 2546 kWh | 1859 kWh | 687 kWh | £504 | £69 | £573 | £11,354 | 19.8 yrs | £100 |
| 4 kW | 3395 kWh | 2478 kWh | 917 kWh | £672 | £92 | £764 | £13,388 | 17.5 yrs | £1,883 |
| 5 kW | 4244 kWh | 3098 kWh | 1146 kWh | £840 | £115 | £954 | £15,423 | 16.2 yrs | £3,666 |
| 6 kW | 5093 kWh | 3718 kWh | 1375 kWh | £1,008 | £137 | £1,145 | £17,457 | 15.2 yrs | £5,450 |
| 7 kW | 5941 kWh | 4337 kWh | 1604 kWh | £1,176 | £160 | £1,336 | £19,492 | 14.6 yrs | £7,233 |
| 8 kW | 6790 kWh | 4957 kWh | 1833 kWh | £1,344 | £183 | £1,527 | £21,526 | 14.1 yrs | £9,016 |
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: £969, Upfront: £17,173, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1698 kWh | 1273 kWh | 424 kWh | £345 | £42 | £388 | £11,069 | 28.6 yrs | £-3,317 |
| 3 kW | 2546 kWh | 1910 kWh | 637 kWh | £518 | £64 | £581 | £13,104 | 22.5 yrs | £-1,476 |
| 4 kW | 3395 kWh | 2546 kWh | 849 kWh | £690 | £85 | £775 | £15,138 | 19.5 yrs | £365 |
| 5 kW | 4244 kWh | 3183 kWh | 1061 kWh | £863 | £106 | £969 | £17,173 | 17.7 yrs | £2,207 |
| 6 kW | 5093 kWh | 3819 kWh | 1273 kWh | £1,035 | £127 | £1,163 | £19,207 | 16.5 yrs | £4,048 |
| 7 kW | 5941 kWh | 4456 kWh | 1485 kWh | £1,208 | £149 | £1,357 | £21,242 | 15.7 yrs | £5,889 |
| 8 kW | 6790 kWh | 5093 kWh | 1698 kWh | £1,381 | £170 | £1,550 | £23,276 | 15.0 yrs | £7,731 |
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: £983, Upfront: £19,623, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1698 kWh | 1307 kWh | 390 kWh | £354 | £39 | £393 | £13,519 | 34.4 yrs | £-5,651 |
| 3 kW | 2546 kWh | 1961 kWh | 586 kWh | £532 | £59 | £590 | £15,554 | 26.4 yrs | £-3,752 |
| 4 kW | 3395 kWh | 2614 kWh | 781 kWh | £709 | £78 | £787 | £17,588 | 22.4 yrs | £-1,852 |
| 5 kW | 4244 kWh | 3268 kWh | 976 kWh | £886 | £98 | £983 | £19,623 | 20.0 yrs | £47 |
| 6 kW | 5093 kWh | 3921 kWh | 1171 kWh | £1,063 | £117 | £1,180 | £21,657 | 18.4 yrs | £1,947 |
| 7 kW | 5941 kWh | 4575 kWh | 1367 kWh | £1,240 | £137 | £1,377 | £23,692 | 17.2 yrs | £3,846 |
| 8 kW | 6790 kWh | 5228 kWh | 1562 kWh | £1,417 | £156 | £1,574 | £25,726 | 16.3 yrs | £5,746 |
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.