A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 907 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £732, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1814 kWh | 726 kWh | 1088 kWh | £184 | £109 | £293 | £4,069 | 13.9 yrs | £1,783 |
| 3 kW | 2721 kWh | 1088 kWh | 1632 kWh | £276 | £163 | £439 | £6,104 | 13.9 yrs | £2,675 |
| 4 kW | 3628 kWh | 1451 kWh | 2177 kWh | £368 | £218 | £585 | £8,138 | 13.9 yrs | £3,567 |
| 5 kW | 4535 kWh | 1814 kWh | 2721 kWh | £459 | £272 | £732 | £10,173 | 13.9 yrs | £4,458 |
| 6 kW | 5442 kWh | 2177 kWh | 3265 kWh | £551 | £326 | £878 | £12,207 | 13.9 yrs | £5,350 |
| 7 kW | 6349 kWh | 2539 kWh | 3809 kWh | £643 | £381 | £1,024 | £14,242 | 13.9 yrs | £6,241 |
| 8 kW | 7256 kWh | 2902 kWh | 4353 kWh | £735 | £435 | £1,170 | £16,276 | 13.9 yrs | £7,133 |
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: £871, Upfront: £12,273, 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 | 1814 kWh | 1088 kWh | 726 kWh | £276 | £73 | £348 | £6,169 | 17.7 yrs | £796 |
| 3 kW | 2721 kWh | 1632 kWh | 1088 kWh | £414 | £109 | £522 | £8,204 | 15.7 yrs | £2,243 |
| 4 kW | 3628 kWh | 2177 kWh | 1451 kWh | £551 | £145 | £696 | £10,238 | 14.7 yrs | £3,691 |
| 5 kW | 4535 kWh | 2721 kWh | 1814 kWh | £689 | £181 | £871 | £12,273 | 14.1 yrs | £5,139 |
| 6 kW | 5442 kWh | 3265 kWh | 2177 kWh | £827 | £218 | £1,045 | £14,307 | 13.7 yrs | £6,587 |
| 7 kW | 6349 kWh | 3809 kWh | 2539 kWh | £965 | £254 | £1,219 | £16,342 | 13.4 yrs | £8,034 |
| 8 kW | 7256 kWh | 4353 kWh | 2902 kWh | £1,103 | £290 | £1,393 | £18,376 | 13.2 yrs | £9,482 |
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: £940, Upfront: £13,673, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1814 kWh | 1270 kWh | 544 kWh | £322 | £54 | £376 | £7,569 | 20.1 yrs | £-48 |
| 3 kW | 2721 kWh | 1905 kWh | 816 kWh | £482 | £82 | £564 | £9,604 | 17.0 yrs | £1,678 |
| 4 kW | 3628 kWh | 2539 kWh | 1088 kWh | £643 | £109 | £752 | £11,638 | 15.5 yrs | £3,403 |
| 5 kW | 4535 kWh | 3174 kWh | 1360 kWh | £804 | £136 | £940 | £13,673 | 14.5 yrs | £5,129 |
| 6 kW | 5442 kWh | 3809 kWh | 1632 kWh | £965 | £163 | £1,128 | £15,707 | 13.9 yrs | £6,855 |
| 7 kW | 6349 kWh | 4444 kWh | 1905 kWh | £1,126 | £190 | £1,316 | £17,742 | 13.5 yrs | £8,581 |
| 8 kW | 7256 kWh | 5079 kWh | 2177 kWh | £1,286 | £218 | £1,504 | £19,776 | 13.1 yrs | £10,307 |
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: £961, Upfront: £15,423, 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 | 1814 kWh | 1324 kWh | 490 kWh | £335 | £49 | £384 | £9,319 | 24.2 yrs | £-1,631 |
| 3 kW | 2721 kWh | 1986 kWh | 735 kWh | £503 | £73 | £577 | £11,354 | 19.7 yrs | £178 |
| 4 kW | 3628 kWh | 2648 kWh | 979 kWh | £671 | £98 | £769 | £13,388 | 17.4 yrs | £1,987 |
| 5 kW | 4535 kWh | 3310 kWh | 1224 kWh | £839 | £122 | £961 | £15,423 | 16.0 yrs | £3,796 |
| 6 kW | 5442 kWh | 3972 kWh | 1469 kWh | £1,006 | £147 | £1,153 | £17,457 | 15.1 yrs | £5,606 |
| 7 kW | 6349 kWh | 4634 kWh | 1714 kWh | £1,174 | £171 | £1,345 | £19,492 | 14.5 yrs | £7,415 |
| 8 kW | 7256 kWh | 5297 kWh | 1959 kWh | £1,342 | £196 | £1,538 | £21,526 | 14.0 yrs | £9,224 |
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: £975, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1814 kWh | 1360 kWh | 453 kWh | £345 | £45 | £390 | £11,069 | 28.4 yrs | £-3,270 |
| 3 kW | 2721 kWh | 2041 kWh | 680 kWh | £517 | £68 | £585 | £13,104 | 22.4 yrs | £-1,405 |
| 4 kW | 3628 kWh | 2721 kWh | 907 kWh | £689 | £91 | £780 | £15,138 | 19.4 yrs | £460 |
| 5 kW | 4535 kWh | 3401 kWh | 1134 kWh | £861 | £113 | £975 | £17,173 | 17.6 yrs | £2,324 |
| 6 kW | 5442 kWh | 4081 kWh | 1360 kWh | £1,034 | £136 | £1,170 | £19,207 | 16.4 yrs | £4,189 |
| 7 kW | 6349 kWh | 4761 kWh | 1587 kWh | £1,206 | £159 | £1,365 | £21,242 | 15.6 yrs | £6,054 |
| 8 kW | 7256 kWh | 5442 kWh | 1814 kWh | £1,378 | £181 | £1,560 | £23,276 | 14.9 yrs | £7,919 |
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: £989, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1814 kWh | 1397 kWh | 417 kWh | £354 | £42 | £396 | £13,519 | 34.2 yrs | £-5,609 |
| 3 kW | 2721 kWh | 2095 kWh | 626 kWh | £531 | £63 | £593 | £15,554 | 26.2 yrs | £-3,689 |
| 4 kW | 3628 kWh | 2793 kWh | 834 kWh | £708 | £83 | £791 | £17,588 | 22.2 yrs | £-1,768 |
| 5 kW | 4535 kWh | 3492 kWh | 1043 kWh | £884 | £104 | £989 | £19,623 | 19.8 yrs | £152 |
| 6 kW | 5442 kWh | 4190 kWh | 1252 kWh | £1,061 | £125 | £1,187 | £21,657 | 18.3 yrs | £2,073 |
| 7 kW | 6349 kWh | 4888 kWh | 1460 kWh | £1,238 | £146 | £1,384 | £23,692 | 17.1 yrs | £3,993 |
| 8 kW | 7256 kWh | 5587 kWh | 1669 kWh | £1,415 | £167 | £1,582 | £25,726 | 16.3 yrs | £5,914 |
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.