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 765 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £619, Upfront: £10,173, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 612 kWh | 918 kWh | £156 | £92 | £247 | £4,069 | 16.4 yrs | £880 |
| 3 kW | 2295 kWh | 918 kWh | 1377 kWh | £233 | £138 | £371 | £6,104 | 16.4 yrs | £1,320 |
| 4 kW | 3060 kWh | 1224 kWh | 1836 kWh | £311 | £184 | £495 | £8,138 | 16.4 yrs | £1,760 |
| 5 kW | 3825 kWh | 1530 kWh | 2295 kWh | £389 | £230 | £619 | £10,173 | 16.4 yrs | £2,200 |
| 6 kW | 4590 kWh | 1836 kWh | 2754 kWh | £467 | £275 | £742 | £12,207 | 16.4 yrs | £2,639 |
| 7 kW | 5355 kWh | 2142 kWh | 3213 kWh | £545 | £321 | £866 | £14,242 | 16.4 yrs | £3,079 |
| 8 kW | 6120 kWh | 2448 kWh | 3672 kWh | £623 | £367 | £990 | £16,276 | 16.4 yrs | £3,519 |
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: £737, Upfront: £12,273, 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 | 1530 kWh | 918 kWh | 612 kWh | £233 | £61 | £295 | £6,169 | 20.9 yrs | £-276 |
| 3 kW | 2295 kWh | 1377 kWh | 918 kWh | £350 | £92 | £442 | £8,204 | 18.6 yrs | £636 |
| 4 kW | 3060 kWh | 1836 kWh | 1224 kWh | £467 | £122 | £589 | £10,238 | 17.4 yrs | £1,548 |
| 5 kW | 3825 kWh | 2295 kWh | 1530 kWh | £584 | £153 | £737 | £12,273 | 16.7 yrs | £2,460 |
| 6 kW | 4590 kWh | 2754 kWh | 1836 kWh | £700 | £184 | £884 | £14,307 | 16.2 yrs | £3,372 |
| 7 kW | 5355 kWh | 3213 kWh | 2142 kWh | £817 | £214 | £1,031 | £16,342 | 15.8 yrs | £4,285 |
| 8 kW | 6120 kWh | 3672 kWh | 2448 kWh | £934 | £245 | £1,179 | £18,376 | 15.6 yrs | £5,197 |
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: £796, Upfront: £13,673, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1071 kWh | 459 kWh | £272 | £46 | £318 | £7,569 | 23.8 yrs | £-1,204 |
| 3 kW | 2295 kWh | 1607 kWh | 689 kWh | £409 | £69 | £477 | £9,604 | 20.1 yrs | £-55 |
| 4 kW | 3060 kWh | 2142 kWh | 918 kWh | £545 | £92 | £637 | £11,638 | 18.3 yrs | £1,093 |
| 5 kW | 3825 kWh | 2678 kWh | 1148 kWh | £681 | £115 | £796 | £13,673 | 17.2 yrs | £2,241 |
| 6 kW | 4590 kWh | 3213 kWh | 1377 kWh | £817 | £138 | £955 | £15,707 | 16.5 yrs | £3,389 |
| 7 kW | 5355 kWh | 3749 kWh | 1607 kWh | £953 | £161 | £1,114 | £17,742 | 15.9 yrs | £4,537 |
| 8 kW | 6120 kWh | 4284 kWh | 1836 kWh | £1,089 | £184 | £1,273 | £19,776 | 15.5 yrs | £5,685 |
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: £813, Upfront: £15,423, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1117 kWh | 413 kWh | £284 | £41 | £325 | £9,319 | 28.6 yrs | £-2,812 |
| 3 kW | 2295 kWh | 1675 kWh | 620 kWh | £426 | £62 | £488 | £11,354 | 23.3 yrs | £-1,593 |
| 4 kW | 3060 kWh | 2234 kWh | 826 kWh | £568 | £83 | £651 | £13,388 | 20.6 yrs | £-374 |
| 5 kW | 3825 kWh | 2792 kWh | 1033 kWh | £710 | £103 | £813 | £15,423 | 19.0 yrs | £845 |
| 6 kW | 4590 kWh | 3351 kWh | 1239 kWh | £852 | £124 | £976 | £17,457 | 17.9 yrs | £2,064 |
| 7 kW | 5355 kWh | 3909 kWh | 1446 kWh | £994 | £145 | £1,139 | £19,492 | 17.1 yrs | £3,283 |
| 8 kW | 6120 kWh | 4468 kWh | 1652 kWh | £1,136 | £165 | £1,301 | £21,526 | 16.5 yrs | £4,502 |
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: £825, Upfront: £17,173, Break-even: 20.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1148 kWh | 383 kWh | £292 | £38 | £330 | £11,069 | 33.5 yrs | £-4,468 |
| 3 kW | 2295 kWh | 1721 kWh | 574 kWh | £438 | £57 | £495 | £13,104 | 26.5 yrs | £-3,201 |
| 4 kW | 3060 kWh | 2295 kWh | 765 kWh | £584 | £77 | £660 | £15,138 | 22.9 yrs | £-1,935 |
| 5 kW | 3825 kWh | 2869 kWh | 956 kWh | £730 | £96 | £825 | £17,173 | 20.8 yrs | £-669 |
| 6 kW | 4590 kWh | 3443 kWh | 1148 kWh | £875 | £115 | £990 | £19,207 | 19.4 yrs | £597 |
| 7 kW | 5355 kWh | 4016 kWh | 1339 kWh | £1,021 | £134 | £1,155 | £21,242 | 18.4 yrs | £1,863 |
| 8 kW | 6120 kWh | 4590 kWh | 1530 kWh | £1,167 | £153 | £1,320 | £23,276 | 17.6 yrs | £3,130 |
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: £837, Upfront: £19,623, Break-even: 23.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1530 kWh | 1178 kWh | 352 kWh | £300 | £35 | £335 | £13,519 | 40.4 yrs | £-6,823 |
| 3 kW | 2295 kWh | 1767 kWh | 528 kWh | £449 | £53 | £502 | £15,554 | 31.0 yrs | £-5,510 |
| 4 kW | 3060 kWh | 2356 kWh | 704 kWh | £599 | £70 | £670 | £17,588 | 26.3 yrs | £-4,196 |
| 5 kW | 3825 kWh | 2945 kWh | 880 kWh | £749 | £88 | £837 | £19,623 | 23.4 yrs | £-2,883 |
| 6 kW | 4590 kWh | 3534 kWh | 1056 kWh | £899 | £106 | £1,004 | £21,657 | 21.6 yrs | £-1,569 |
| 7 kW | 5355 kWh | 4124 kWh | 1232 kWh | £1,049 | £123 | £1,172 | £23,692 | 20.2 yrs | £-256 |
| 8 kW | 6120 kWh | 4713 kWh | 1408 kWh | £1,198 | £141 | £1,339 | £25,726 | 19.2 yrs | £1,057 |
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.