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 1034 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £867, Upfront: £10,173, 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 | 2069 kWh | 828 kWh | 1241 kWh | £223 | £124 | £347 | £4,069 | 11.7 yrs | £2,869 |
| 3 kW | 3103 kWh | 1241 kWh | 1862 kWh | £334 | £186 | £520 | £6,104 | 11.7 yrs | £4,303 |
| 4 kW | 4138 kWh | 1655 kWh | 2483 kWh | £446 | £248 | £694 | £8,138 | 11.7 yrs | £5,738 |
| 5 kW | 5172 kWh | 2069 kWh | 3103 kWh | £557 | £310 | £867 | £10,173 | 11.7 yrs | £7,172 |
| 6 kW | 6206 kWh | 2483 kWh | 3724 kWh | £668 | £372 | £1,041 | £12,207 | 11.7 yrs | £8,606 |
| 7 kW | 7241 kWh | 2896 kWh | 4344 kWh | £780 | £434 | £1,214 | £14,242 | 11.7 yrs | £10,041 |
| 8 kW | 8275 kWh | 3310 kWh | 4965 kWh | £891 | £497 | £1,388 | £16,276 | 11.7 yrs | £11,475 |
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: £1,042, Upfront: £12,273, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2069 kWh | 1241 kWh | 828 kWh | £334 | £83 | £417 | £6,169 | 14.8 yrs | £2,169 |
| 3 kW | 3103 kWh | 1862 kWh | 1241 kWh | £501 | £124 | £625 | £8,204 | 13.1 yrs | £4,303 |
| 4 kW | 4138 kWh | 2483 kWh | 1655 kWh | £668 | £166 | £834 | £10,238 | 12.3 yrs | £6,438 |
| 5 kW | 5172 kWh | 3103 kWh | 2069 kWh | £835 | £207 | £1,042 | £12,273 | 11.8 yrs | £8,572 |
| 6 kW | 6206 kWh | 3724 kWh | 2483 kWh | £1,002 | £248 | £1,251 | £14,307 | 11.4 yrs | £10,707 |
| 7 kW | 7241 kWh | 4344 kWh | 2896 kWh | £1,170 | £290 | £1,459 | £16,342 | 11.2 yrs | £12,841 |
| 8 kW | 8275 kWh | 4965 kWh | 3310 kWh | £1,337 | £331 | £1,668 | £18,376 | 11.0 yrs | £14,976 |
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: £1,130, Upfront: £13,673, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2069 kWh | 1448 kWh | 621 kWh | £390 | £62 | £452 | £7,569 | 16.7 yrs | £1,469 |
| 3 kW | 3103 kWh | 2172 kWh | 931 kWh | £585 | £93 | £678 | £9,604 | 14.2 yrs | £3,953 |
| 4 kW | 4138 kWh | 2896 kWh | 1241 kWh | £780 | £124 | £904 | £11,638 | 12.9 yrs | £6,438 |
| 5 kW | 5172 kWh | 3620 kWh | 1552 kWh | £975 | £155 | £1,130 | £13,673 | 12.1 yrs | £8,922 |
| 6 kW | 6206 kWh | 4344 kWh | 1862 kWh | £1,170 | £186 | £1,356 | £15,707 | 11.6 yrs | £11,407 |
| 7 kW | 7241 kWh | 5068 kWh | 2172 kWh | £1,364 | £217 | £1,582 | £17,742 | 11.2 yrs | £13,891 |
| 8 kW | 8275 kWh | 5793 kWh | 2483 kWh | £1,559 | £248 | £1,808 | £19,776 | 10.9 yrs | £16,376 |
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: £1,156, 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 | 2069 kWh | 1510 kWh | 559 kWh | £407 | £56 | £462 | £9,319 | 20.2 yrs | £-71 |
| 3 kW | 3103 kWh | 2265 kWh | 838 kWh | £610 | £84 | £694 | £11,354 | 16.4 yrs | £2,518 |
| 4 kW | 4138 kWh | 3020 kWh | 1117 kWh | £813 | £112 | £925 | £13,388 | 14.5 yrs | £5,108 |
| 5 kW | 5172 kWh | 3775 kWh | 1396 kWh | £1,016 | £140 | £1,156 | £15,423 | 13.3 yrs | £7,697 |
| 6 kW | 6206 kWh | 4531 kWh | 1676 kWh | £1,220 | £168 | £1,387 | £17,457 | 12.6 yrs | £10,287 |
| 7 kW | 7241 kWh | 5286 kWh | 1955 kWh | £1,423 | £195 | £1,618 | £19,492 | 12.0 yrs | £12,876 |
| 8 kW | 8275 kWh | 6041 kWh | 2234 kWh | £1,626 | £223 | £1,850 | £21,526 | 11.6 yrs | £15,466 |
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: £1,174, Upfront: £17,173, 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 | 2069 kWh | 1552 kWh | 517 kWh | £418 | £52 | £469 | £11,069 | 23.6 yrs | £-1,681 |
| 3 kW | 3103 kWh | 2327 kWh | 776 kWh | £627 | £78 | £704 | £13,104 | 18.6 yrs | £979 |
| 4 kW | 4138 kWh | 3103 kWh | 1034 kWh | £835 | £103 | £939 | £15,138 | 16.1 yrs | £3,638 |
| 5 kW | 5172 kWh | 3879 kWh | 1293 kWh | £1,044 | £129 | £1,174 | £17,173 | 14.6 yrs | £6,298 |
| 6 kW | 6206 kWh | 4655 kWh | 1552 kWh | £1,253 | £155 | £1,408 | £19,207 | 13.6 yrs | £8,957 |
| 7 kW | 7241 kWh | 5430 kWh | 1810 kWh | £1,462 | £181 | £1,643 | £21,242 | 12.9 yrs | £11,617 |
| 8 kW | 8275 kWh | 6206 kWh | 2069 kWh | £1,671 | £207 | £1,878 | £23,276 | 12.4 yrs | £14,276 |
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: £1,191, Upfront: £19,623, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2069 kWh | 1593 kWh | 476 kWh | £429 | £48 | £476 | £13,519 | 28.4 yrs | £-3,991 |
| 3 kW | 3103 kWh | 2389 kWh | 714 kWh | £643 | £71 | £715 | £15,554 | 21.8 yrs | £-1,261 |
| 4 kW | 4138 kWh | 3186 kWh | 952 kWh | £858 | £95 | £953 | £17,588 | 18.5 yrs | £1,468 |
| 5 kW | 5172 kWh | 3982 kWh | 1190 kWh | £1,072 | £119 | £1,191 | £19,623 | 16.5 yrs | £4,198 |
| 6 kW | 6206 kWh | 4779 kWh | 1427 kWh | £1,286 | £143 | £1,429 | £21,657 | 15.2 yrs | £6,927 |
| 7 kW | 7241 kWh | 5575 kWh | 1665 kWh | £1,501 | £167 | £1,667 | £23,692 | 14.2 yrs | £9,657 |
| 8 kW | 8275 kWh | 6372 kWh | 1903 kWh | £1,715 | £190 | £1,906 | £25,726 | 13.5 yrs | £12,386 |
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.