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 886 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: £724, Upfront: £10,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 709 kWh | 1064 kWh | £183 | £106 | £290 | £4,069 | 14.1 yrs | £1,723 |
| 3 kW | 2659 kWh | 1064 kWh | 1595 kWh | £275 | £160 | £434 | £6,104 | 14.1 yrs | £2,584 |
| 4 kW | 3546 kWh | 1418 kWh | 2127 kWh | £366 | £213 | £579 | £8,138 | 14.1 yrs | £3,446 |
| 5 kW | 4432 kWh | 1773 kWh | 2659 kWh | £458 | £266 | £724 | £10,173 | 14.1 yrs | £4,307 |
| 6 kW | 5318 kWh | 2127 kWh | 3191 kWh | £550 | £319 | £869 | £12,207 | 14.1 yrs | £5,169 |
| 7 kW | 6205 kWh | 2482 kWh | 3723 kWh | £641 | £372 | £1,014 | £14,242 | 14.1 yrs | £6,030 |
| 8 kW | 7091 kWh | 2836 kWh | 4255 kWh | £733 | £425 | £1,158 | £16,276 | 14.1 yrs | £6,892 |
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: £864, Upfront: £12,273, 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 | 1773 kWh | 1064 kWh | 709 kWh | £275 | £71 | £346 | £6,169 | 17.8 yrs | £746 |
| 3 kW | 2659 kWh | 1595 kWh | 1064 kWh | £412 | £106 | £519 | £8,204 | 15.8 yrs | £2,169 |
| 4 kW | 3546 kWh | 2127 kWh | 1418 kWh | £550 | £142 | £692 | £10,238 | 14.8 yrs | £3,592 |
| 5 kW | 4432 kWh | 2659 kWh | 1773 kWh | £687 | £177 | £864 | £12,273 | 14.2 yrs | £5,015 |
| 6 kW | 5318 kWh | 3191 kWh | 2127 kWh | £825 | £213 | £1,037 | £14,307 | 13.8 yrs | £6,438 |
| 7 kW | 6205 kWh | 3723 kWh | 2482 kWh | £962 | £248 | £1,210 | £16,342 | 13.5 yrs | £7,862 |
| 8 kW | 7091 kWh | 4255 kWh | 2836 kWh | £1,099 | £284 | £1,383 | £18,376 | 13.3 yrs | £9,285 |
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: £935, Upfront: £13,673, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 1241 kWh | 532 kWh | £321 | £53 | £374 | £7,569 | 20.2 yrs | £-92 |
| 3 kW | 2659 kWh | 1861 kWh | 798 kWh | £481 | £80 | £561 | £9,604 | 17.1 yrs | £1,612 |
| 4 kW | 3546 kWh | 2482 kWh | 1064 kWh | £641 | £106 | £748 | £11,638 | 15.6 yrs | £3,316 |
| 5 kW | 4432 kWh | 3102 kWh | 1330 kWh | £802 | £133 | £935 | £13,673 | 14.6 yrs | £5,019 |
| 6 kW | 5318 kWh | 3723 kWh | 1595 kWh | £962 | £160 | £1,122 | £15,707 | 14.0 yrs | £6,723 |
| 7 kW | 6205 kWh | 4343 kWh | 1861 kWh | £1,122 | £186 | £1,308 | £17,742 | 13.6 yrs | £8,427 |
| 8 kW | 7091 kWh | 4964 kWh | 2127 kWh | £1,283 | £213 | £1,495 | £19,776 | 13.2 yrs | £10,131 |
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: £956, Upfront: £15,423, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 1294 kWh | 479 kWh | £334 | £48 | £382 | £9,319 | 24.4 yrs | £-1,674 |
| 3 kW | 2659 kWh | 1941 kWh | 718 kWh | £502 | £72 | £573 | £11,354 | 19.8 yrs | £114 |
| 4 kW | 3546 kWh | 2588 kWh | 957 kWh | £669 | £96 | £765 | £13,388 | 17.5 yrs | £1,903 |
| 5 kW | 4432 kWh | 3235 kWh | 1197 kWh | £836 | £120 | £956 | £15,423 | 16.1 yrs | £3,691 |
| 6 kW | 5318 kWh | 3882 kWh | 1436 kWh | £1,003 | £144 | £1,147 | £17,457 | 15.2 yrs | £5,479 |
| 7 kW | 6205 kWh | 4529 kWh | 1675 kWh | £1,170 | £168 | £1,338 | £19,492 | 14.6 yrs | £7,267 |
| 8 kW | 7091 kWh | 5176 kWh | 1915 kWh | £1,338 | £191 | £1,529 | £21,526 | 14.1 yrs | £9,055 |
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: £970, 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 | 1773 kWh | 1330 kWh | 443 kWh | £344 | £44 | £388 | £11,069 | 28.5 yrs | £-3,311 |
| 3 kW | 2659 kWh | 1994 kWh | 665 kWh | £515 | £66 | £582 | £13,104 | 22.5 yrs | £-1,467 |
| 4 kW | 3546 kWh | 2659 kWh | 886 kWh | £687 | £89 | £776 | £15,138 | 19.5 yrs | £377 |
| 5 kW | 4432 kWh | 3324 kWh | 1108 kWh | £859 | £111 | £970 | £17,173 | 17.7 yrs | £2,221 |
| 6 kW | 5318 kWh | 3989 kWh | 1330 kWh | £1,031 | £133 | £1,164 | £19,207 | 16.5 yrs | £4,066 |
| 7 kW | 6205 kWh | 4653 kWh | 1551 kWh | £1,202 | £155 | £1,358 | £21,242 | 15.6 yrs | £5,910 |
| 8 kW | 7091 kWh | 5318 kWh | 1773 kWh | £1,374 | £177 | £1,552 | £23,276 | 15.0 yrs | £7,754 |
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: £984, Upfront: £19,623, Break-even: 19.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1773 kWh | 1365 kWh | 408 kWh | £353 | £41 | £393 | £13,519 | 34.4 yrs | £-5,649 |
| 3 kW | 2659 kWh | 2048 kWh | 612 kWh | £529 | £61 | £590 | £15,554 | 26.4 yrs | £-3,749 |
| 4 kW | 3546 kWh | 2730 kWh | 815 kWh | £705 | £82 | £787 | £17,588 | 22.3 yrs | £-1,848 |
| 5 kW | 4432 kWh | 3413 kWh | 1019 kWh | £882 | £102 | £984 | £19,623 | 19.9 yrs | £52 |
| 6 kW | 5318 kWh | 4095 kWh | 1223 kWh | £1,058 | £122 | £1,180 | £21,657 | 18.3 yrs | £1,953 |
| 7 kW | 6205 kWh | 4778 kWh | 1427 kWh | £1,235 | £143 | £1,377 | £23,692 | 17.2 yrs | £3,853 |
| 8 kW | 7091 kWh | 5460 kWh | 1631 kWh | £1,411 | £163 | £1,574 | £25,726 | 16.3 yrs | £5,754 |
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.