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 948 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: £767, Upfront: £10,173, 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 | 1897 kWh | 759 kWh | 1138 kWh | £193 | £114 | £307 | £4,069 | 13.3 yrs | £2,066 |
| 3 kW | 2845 kWh | 1138 kWh | 1707 kWh | £289 | £171 | £460 | £6,104 | 13.3 yrs | £3,099 |
| 4 kW | 3794 kWh | 1517 kWh | 2276 kWh | £386 | £228 | £614 | £8,138 | 13.3 yrs | £4,132 |
| 5 kW | 4742 kWh | 1897 kWh | 2845 kWh | £482 | £285 | £767 | £10,173 | 13.3 yrs | £5,165 |
| 6 kW | 5691 kWh | 2276 kWh | 3414 kWh | £579 | £341 | £920 | £12,207 | 13.3 yrs | £6,198 |
| 7 kW | 6639 kWh | 2656 kWh | 3983 kWh | £675 | £398 | £1,074 | £14,242 | 13.3 yrs | £7,231 |
| 8 kW | 7587 kWh | 3035 kWh | 4552 kWh | £772 | £455 | £1,227 | £16,276 | 13.3 yrs | £8,264 |
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: £913, Upfront: £12,273, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1897 kWh | 1138 kWh | 759 kWh | £289 | £76 | £365 | £6,169 | 16.9 yrs | £1,137 |
| 3 kW | 2845 kWh | 1707 kWh | 1138 kWh | £434 | £114 | £548 | £8,204 | 15.0 yrs | £2,755 |
| 4 kW | 3794 kWh | 2276 kWh | 1517 kWh | £579 | £152 | £731 | £10,238 | 14.0 yrs | £4,374 |
| 5 kW | 4742 kWh | 2845 kWh | 1897 kWh | £724 | £190 | £913 | £12,273 | 13.4 yrs | £5,992 |
| 6 kW | 5691 kWh | 3414 kWh | 2276 kWh | £868 | £228 | £1,096 | £14,307 | 13.1 yrs | £7,611 |
| 7 kW | 6639 kWh | 3983 kWh | 2656 kWh | £1,013 | £266 | £1,279 | £16,342 | 12.8 yrs | £9,229 |
| 8 kW | 7587 kWh | 4552 kWh | 3035 kWh | £1,158 | £303 | £1,461 | £18,376 | 12.6 yrs | £10,847 |
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: £986, Upfront: £13,673, 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 | 1897 kWh | 1328 kWh | 569 kWh | £338 | £57 | £395 | £7,569 | 19.2 yrs | £322 |
| 3 kW | 2845 kWh | 1992 kWh | 854 kWh | £506 | £85 | £592 | £9,604 | 16.2 yrs | £2,233 |
| 4 kW | 3794 kWh | 2656 kWh | 1138 kWh | £675 | £114 | £789 | £11,638 | 14.7 yrs | £4,144 |
| 5 kW | 4742 kWh | 3319 kWh | 1423 kWh | £844 | £142 | £986 | £13,673 | 13.9 yrs | £6,056 |
| 6 kW | 5691 kWh | 3983 kWh | 1707 kWh | £1,013 | £171 | £1,184 | £15,707 | 13.3 yrs | £7,967 |
| 7 kW | 6639 kWh | 4647 kWh | 1992 kWh | £1,182 | £199 | £1,381 | £17,742 | 12.8 yrs | £9,878 |
| 8 kW | 7587 kWh | 5311 kWh | 2276 kWh | £1,351 | £228 | £1,578 | £19,776 | 12.5 yrs | £11,789 |
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: £1,008, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1897 kWh | 1385 kWh | 512 kWh | £352 | £51 | £403 | £9,319 | 23.1 yrs | £-1,252 |
| 3 kW | 2845 kWh | 2077 kWh | 768 kWh | £528 | £77 | £605 | £11,354 | 18.8 yrs | £747 |
| 4 kW | 3794 kWh | 2769 kWh | 1024 kWh | £704 | £102 | £807 | £13,388 | 16.6 yrs | £2,746 |
| 5 kW | 4742 kWh | 3462 kWh | 1280 kWh | £880 | £128 | £1,008 | £15,423 | 15.3 yrs | £4,745 |
| 6 kW | 5691 kWh | 4154 kWh | 1536 kWh | £1,056 | £154 | £1,210 | £17,457 | 14.4 yrs | £6,743 |
| 7 kW | 6639 kWh | 4846 kWh | 1793 kWh | £1,232 | £179 | £1,412 | £19,492 | 13.8 yrs | £8,742 |
| 8 kW | 7587 kWh | 5539 kWh | 2049 kWh | £1,409 | £205 | £1,613 | £21,526 | 13.3 yrs | £10,741 |
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: £1,023, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1897 kWh | 1423 kWh | 474 kWh | £362 | £47 | £409 | £11,069 | 27.1 yrs | £-2,885 |
| 3 kW | 2845 kWh | 2134 kWh | 711 kWh | £543 | £71 | £614 | £13,104 | 21.3 yrs | £-828 |
| 4 kW | 3794 kWh | 2845 kWh | 948 kWh | £724 | £95 | £818 | £15,138 | 18.5 yrs | £1,230 |
| 5 kW | 4742 kWh | 3557 kWh | 1186 kWh | £904 | £119 | £1,023 | £17,173 | 16.8 yrs | £3,287 |
| 6 kW | 5691 kWh | 4268 kWh | 1423 kWh | £1,085 | £142 | £1,228 | £19,207 | 15.6 yrs | £5,345 |
| 7 kW | 6639 kWh | 4979 kWh | 1660 kWh | £1,266 | £166 | £1,432 | £21,242 | 14.8 yrs | £7,402 |
| 8 kW | 7587 kWh | 5691 kWh | 1897 kWh | £1,447 | £190 | £1,637 | £23,276 | 14.2 yrs | £9,460 |
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: £1,038, Upfront: £19,623, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1897 kWh | 1461 kWh | 436 kWh | £371 | £44 | £415 | £13,519 | 32.6 yrs | £-5,218 |
| 3 kW | 2845 kWh | 2191 kWh | 654 kWh | £557 | £65 | £623 | £15,554 | 25.0 yrs | £-3,102 |
| 4 kW | 3794 kWh | 2921 kWh | 873 kWh | £743 | £87 | £830 | £17,588 | 21.2 yrs | £-986 |
| 5 kW | 4742 kWh | 3651 kWh | 1091 kWh | £929 | £109 | £1,038 | £19,623 | 18.9 yrs | £1,130 |
| 6 kW | 5691 kWh | 4382 kWh | 1309 kWh | £1,114 | £131 | £1,245 | £21,657 | 17.4 yrs | £3,246 |
| 7 kW | 6639 kWh | 5112 kWh | 1527 kWh | £1,300 | £153 | £1,453 | £23,692 | 16.3 yrs | £5,362 |
| 8 kW | 7587 kWh | 5842 kWh | 1745 kWh | £1,486 | £175 | £1,660 | £25,726 | 15.5 yrs | £7,478 |
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.