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 1055 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £876, Upfront: £10,173, Break-even: 11.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2109 kWh | 844 kWh | 1265 kWh | £224 | £127 | £350 | £4,069 | 11.6 yrs | £2,938 |
| 3 kW | 3164 kWh | 1265 kWh | 1898 kWh | £336 | £190 | £526 | £6,104 | 11.6 yrs | £4,407 |
| 4 kW | 4218 kWh | 1687 kWh | 2531 kWh | £448 | £253 | £701 | £8,138 | 11.6 yrs | £5,876 |
| 5 kW | 5273 kWh | 2109 kWh | 3164 kWh | £560 | £316 | £876 | £10,173 | 11.6 yrs | £7,345 |
| 6 kW | 6327 kWh | 2531 kWh | 3796 kWh | £671 | £380 | £1,051 | £12,207 | 11.6 yrs | £8,815 |
| 7 kW | 7382 kWh | 2953 kWh | 4429 kWh | £783 | £443 | £1,226 | £14,242 | 11.6 yrs | £10,284 |
| 8 kW | 8436 kWh | 3375 kWh | 5062 kWh | £895 | £506 | £1,401 | £16,276 | 11.6 yrs | £11,753 |
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: £1,050, Upfront: £12,273, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2109 kWh | 1265 kWh | 844 kWh | £336 | £84 | £420 | £6,169 | 14.7 yrs | £2,233 |
| 3 kW | 3164 kWh | 1898 kWh | 1265 kWh | £504 | £127 | £630 | £8,204 | 13.0 yrs | £4,399 |
| 4 kW | 4218 kWh | 2531 kWh | 1687 kWh | £671 | £169 | £840 | £10,238 | 12.2 yrs | £6,565 |
| 5 kW | 5273 kWh | 3164 kWh | 2109 kWh | £839 | £211 | £1,050 | £12,273 | 11.7 yrs | £8,732 |
| 6 kW | 6327 kWh | 3796 kWh | 2531 kWh | £1,007 | £253 | £1,260 | £14,307 | 11.4 yrs | £10,898 |
| 7 kW | 7382 kWh | 4429 kWh | 2953 kWh | £1,175 | £295 | £1,470 | £16,342 | 11.1 yrs | £13,064 |
| 8 kW | 8436 kWh | 5062 kWh | 3375 kWh | £1,343 | £337 | £1,680 | £18,376 | 10.9 yrs | £15,231 |
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: £1,137, Upfront: £13,673, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2109 kWh | 1476 kWh | 633 kWh | £392 | £63 | £455 | £7,569 | 16.6 yrs | £1,530 |
| 3 kW | 3164 kWh | 2215 kWh | 949 kWh | £588 | £95 | £682 | £9,604 | 14.1 yrs | £4,045 |
| 4 kW | 4218 kWh | 2953 kWh | 1265 kWh | £783 | £127 | £910 | £11,638 | 12.8 yrs | £6,560 |
| 5 kW | 5273 kWh | 3691 kWh | 1582 kWh | £979 | £158 | £1,137 | £13,673 | 12.0 yrs | £9,075 |
| 6 kW | 6327 kWh | 4429 kWh | 1898 kWh | £1,175 | £190 | £1,365 | £15,707 | 11.5 yrs | £11,590 |
| 7 kW | 7382 kWh | 5167 kWh | 2215 kWh | £1,371 | £221 | £1,592 | £17,742 | 11.1 yrs | £14,105 |
| 8 kW | 8436 kWh | 5905 kWh | 2531 kWh | £1,567 | £253 | £1,820 | £19,776 | 10.9 yrs | £16,620 |
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: £1,164, Upfront: £15,423, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2109 kWh | 1540 kWh | 569 kWh | £408 | £57 | £465 | £9,319 | 20.0 yrs | £-11 |
| 3 kW | 3164 kWh | 2309 kWh | 854 kWh | £613 | £85 | £698 | £11,354 | 16.3 yrs | £2,609 |
| 4 kW | 4218 kWh | 3079 kWh | 1139 kWh | £817 | £114 | £931 | £13,388 | 14.4 yrs | £5,228 |
| 5 kW | 5273 kWh | 3849 kWh | 1424 kWh | £1,021 | £142 | £1,164 | £15,423 | 13.3 yrs | £7,848 |
| 6 kW | 6327 kWh | 4619 kWh | 1708 kWh | £1,225 | £171 | £1,396 | £17,457 | 12.5 yrs | £10,467 |
| 7 kW | 7382 kWh | 5389 kWh | 1993 kWh | £1,430 | £199 | £1,629 | £19,492 | 12.0 yrs | £13,087 |
| 8 kW | 8436 kWh | 6159 kWh | 2278 kWh | £1,634 | £228 | £1,862 | £21,526 | 11.6 yrs | £15,707 |
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: £1,181, Upfront: £17,173, 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 | 2109 kWh | 1582 kWh | 527 kWh | £420 | £53 | £472 | £11,069 | 23.4 yrs | £-1,621 |
| 3 kW | 3164 kWh | 2373 kWh | 791 kWh | £629 | £79 | £709 | £13,104 | 18.5 yrs | £1,068 |
| 4 kW | 4218 kWh | 3164 kWh | 1055 kWh | £839 | £105 | £945 | £15,138 | 16.0 yrs | £3,757 |
| 5 kW | 5273 kWh | 3955 kWh | 1318 kWh | £1,049 | £132 | £1,181 | £17,173 | 14.5 yrs | £6,447 |
| 6 kW | 6327 kWh | 4745 kWh | 1582 kWh | £1,259 | £158 | £1,417 | £19,207 | 13.6 yrs | £9,136 |
| 7 kW | 7382 kWh | 5536 kWh | 1845 kWh | £1,469 | £185 | £1,653 | £21,242 | 12.8 yrs | £11,825 |
| 8 kW | 8436 kWh | 6327 kWh | 2109 kWh | £1,679 | £211 | £1,890 | £23,276 | 12.3 yrs | £14,514 |
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: £1,198, Upfront: £19,623, 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 | 2109 kWh | 1624 kWh | 485 kWh | £431 | £49 | £479 | £13,519 | 28.2 yrs | £-3,932 |
| 3 kW | 3164 kWh | 2436 kWh | 728 kWh | £646 | £73 | £719 | £15,554 | 21.6 yrs | £-1,173 |
| 4 kW | 4218 kWh | 3248 kWh | 970 kWh | £862 | £97 | £959 | £17,588 | 18.3 yrs | £1,586 |
| 5 kW | 5273 kWh | 4060 kWh | 1213 kWh | £1,077 | £121 | £1,198 | £19,623 | 16.4 yrs | £4,345 |
| 6 kW | 6327 kWh | 4872 kWh | 1455 kWh | £1,293 | £146 | £1,438 | £21,657 | 15.1 yrs | £7,104 |
| 7 kW | 7382 kWh | 5684 kWh | 1698 kWh | £1,508 | £170 | £1,678 | £23,692 | 14.1 yrs | £9,863 |
| 8 kW | 8436 kWh | 6496 kWh | 1940 kWh | £1,723 | £194 | £1,917 | £25,726 | 13.4 yrs | £12,622 |
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.