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 808 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £660, Upfront: £10,173, 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 | 1617 kWh | 647 kWh | 970 kWh | £167 | £97 | £264 | £4,069 | 15.4 yrs | £1,214 |
| 3 kW | 2425 kWh | 970 kWh | 1455 kWh | £251 | £146 | £396 | £6,104 | 15.4 yrs | £1,821 |
| 4 kW | 3234 kWh | 1294 kWh | 1940 kWh | £334 | £194 | £528 | £8,138 | 15.4 yrs | £2,428 |
| 5 kW | 4042 kWh | 1617 kWh | 2425 kWh | £418 | £243 | £660 | £10,173 | 15.4 yrs | £3,035 |
| 6 kW | 4851 kWh | 1940 kWh | 2911 kWh | £501 | £291 | £792 | £12,207 | 15.4 yrs | £3,642 |
| 7 kW | 5659 kWh | 2264 kWh | 3396 kWh | £585 | £340 | £925 | £14,242 | 15.4 yrs | £4,249 |
| 8 kW | 6468 kWh | 2587 kWh | 3881 kWh | £669 | £388 | £1,057 | £16,276 | 15.4 yrs | £4,856 |
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: £788, Upfront: £12,273, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1617 kWh | 970 kWh | 647 kWh | £251 | £65 | £315 | £6,169 | 19.6 yrs | £138 |
| 3 kW | 2425 kWh | 1455 kWh | 970 kWh | £376 | £97 | £473 | £8,204 | 17.3 yrs | £1,258 |
| 4 kW | 3234 kWh | 1940 kWh | 1294 kWh | £501 | £129 | £631 | £10,238 | 16.2 yrs | £2,377 |
| 5 kW | 4042 kWh | 2425 kWh | 1617 kWh | £627 | £162 | £788 | £12,273 | 15.6 yrs | £3,496 |
| 6 kW | 4851 kWh | 2911 kWh | 1940 kWh | £752 | £194 | £946 | £14,307 | 15.1 yrs | £4,615 |
| 7 kW | 5659 kWh | 3396 kWh | 2264 kWh | £877 | £226 | £1,104 | £16,342 | 14.8 yrs | £5,735 |
| 8 kW | 6468 kWh | 3881 kWh | 2587 kWh | £1,003 | £259 | £1,262 | £18,376 | 14.6 yrs | £6,854 |
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: £852, Upfront: £13,673, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1617 kWh | 1132 kWh | 485 kWh | £292 | £49 | £341 | £7,569 | 22.2 yrs | £-749 |
| 3 kW | 2425 kWh | 1698 kWh | 728 kWh | £439 | £73 | £511 | £9,604 | 18.8 yrs | £626 |
| 4 kW | 3234 kWh | 2264 kWh | 970 kWh | £585 | £97 | £682 | £11,638 | 17.1 yrs | £2,002 |
| 5 kW | 4042 kWh | 2830 kWh | 1213 kWh | £731 | £121 | £852 | £13,673 | 16.0 yrs | £3,377 |
| 6 kW | 4851 kWh | 3396 kWh | 1455 kWh | £877 | £146 | £1,023 | £15,707 | 15.4 yrs | £4,752 |
| 7 kW | 5659 kWh | 3962 kWh | 1698 kWh | £1,024 | £170 | £1,193 | £17,742 | 14.9 yrs | £6,128 |
| 8 kW | 6468 kWh | 4528 kWh | 1940 kWh | £1,170 | £194 | £1,364 | £19,776 | 14.5 yrs | £7,503 |
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: £872, Upfront: £15,423, 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 | 1617 kWh | 1180 kWh | 437 kWh | £305 | £44 | £349 | £9,319 | 26.7 yrs | £-2,346 |
| 3 kW | 2425 kWh | 1771 kWh | 655 kWh | £458 | £65 | £523 | £11,354 | 21.7 yrs | £-893 |
| 4 kW | 3234 kWh | 2361 kWh | 873 kWh | £610 | £87 | £697 | £13,388 | 19.2 yrs | £559 |
| 5 kW | 4042 kWh | 2951 kWh | 1091 kWh | £763 | £109 | £872 | £15,423 | 17.7 yrs | £2,011 |
| 6 kW | 4851 kWh | 3541 kWh | 1310 kWh | £915 | £131 | £1,046 | £17,457 | 16.7 yrs | £3,463 |
| 7 kW | 5659 kWh | 4131 kWh | 1528 kWh | £1,068 | £153 | £1,220 | £19,492 | 16.0 yrs | £4,916 |
| 8 kW | 6468 kWh | 4722 kWh | 1746 kWh | £1,220 | £175 | £1,395 | £21,526 | 15.4 yrs | £6,368 |
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: £884, Upfront: £17,173, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1617 kWh | 1213 kWh | 404 kWh | £313 | £40 | £354 | £11,069 | 31.3 yrs | £-3,993 |
| 3 kW | 2425 kWh | 1819 kWh | 606 kWh | £470 | £61 | £531 | £13,104 | 24.7 yrs | £-2,490 |
| 4 kW | 3234 kWh | 2425 kWh | 808 kWh | £627 | £81 | £708 | £15,138 | 21.4 yrs | £-986 |
| 5 kW | 4042 kWh | 3032 kWh | 1011 kWh | £783 | £101 | £884 | £17,173 | 19.4 yrs | £517 |
| 6 kW | 4851 kWh | 3638 kWh | 1213 kWh | £940 | £121 | £1,061 | £19,207 | 18.1 yrs | £2,021 |
| 7 kW | 5659 kWh | 4245 kWh | 1415 kWh | £1,097 | £141 | £1,238 | £21,242 | 17.2 yrs | £3,524 |
| 8 kW | 6468 kWh | 4851 kWh | 1617 kWh | £1,253 | £162 | £1,415 | £23,276 | 16.4 yrs | £5,028 |
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: £897, Upfront: £19,623, Break-even: 21.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1617 kWh | 1245 kWh | 372 kWh | £322 | £37 | £359 | £13,519 | 37.7 yrs | £-6,341 |
| 3 kW | 2425 kWh | 1868 kWh | 558 kWh | £483 | £56 | £538 | £15,554 | 28.9 yrs | £-4,786 |
| 4 kW | 3234 kWh | 2490 kWh | 744 kWh | £643 | £74 | £718 | £17,588 | 24.5 yrs | £-3,231 |
| 5 kW | 4042 kWh | 3113 kWh | 930 kWh | £804 | £93 | £897 | £19,623 | 21.9 yrs | £-1,677 |
| 6 kW | 4851 kWh | 3735 kWh | 1116 kWh | £965 | £112 | £1,077 | £21,657 | 20.1 yrs | £-122 |
| 7 kW | 5659 kWh | 4358 kWh | 1302 kWh | £1,126 | £130 | £1,256 | £23,692 | 18.9 yrs | £1,433 |
| 8 kW | 6468 kWh | 4980 kWh | 1488 kWh | £1,287 | £149 | £1,436 | £25,726 | 17.9 yrs | £2,987 |
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.