A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 976 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: £787, Upfront: £10,173, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1951 kWh | 780 kWh | 1171 kWh | £198 | £117 | £315 | £4,069 | 12.9 yrs | £2,226 |
| 3 kW | 2927 kWh | 1171 kWh | 1756 kWh | £297 | £176 | £472 | £6,104 | 12.9 yrs | £3,339 |
| 4 kW | 3902 kWh | 1561 kWh | 2341 kWh | £395 | £234 | £630 | £8,138 | 12.9 yrs | £4,453 |
| 5 kW | 4878 kWh | 1951 kWh | 2927 kWh | £494 | £293 | £787 | £10,173 | 12.9 yrs | £5,566 |
| 6 kW | 5854 kWh | 2341 kWh | 3512 kWh | £593 | £351 | £944 | £12,207 | 12.9 yrs | £6,679 |
| 7 kW | 6829 kWh | 2732 kWh | 4097 kWh | £692 | £410 | £1,102 | £14,242 | 12.9 yrs | £7,792 |
| 8 kW | 7805 kWh | 3122 kWh | 4683 kWh | £791 | £468 | £1,259 | £16,276 | 12.9 yrs | £8,905 |
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: £936, Upfront: £12,273, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1951 kWh | 1171 kWh | 780 kWh | £297 | £78 | £375 | £6,169 | 16.5 yrs | £1,323 |
| 3 kW | 2927 kWh | 1756 kWh | 1171 kWh | £445 | £117 | £562 | £8,204 | 14.6 yrs | £3,034 |
| 4 kW | 3902 kWh | 2341 kWh | 1561 kWh | £593 | £156 | £749 | £10,238 | 13.7 yrs | £4,745 |
| 5 kW | 4878 kWh | 2927 kWh | 1951 kWh | £741 | £195 | £936 | £12,273 | 13.1 yrs | £6,457 |
| 6 kW | 5854 kWh | 3512 kWh | 2341 kWh | £890 | £234 | £1,124 | £14,307 | 12.7 yrs | £8,168 |
| 7 kW | 6829 kWh | 4097 kWh | 2732 kWh | £1,038 | £273 | £1,311 | £16,342 | 12.5 yrs | £9,880 |
| 8 kW | 7805 kWh | 4683 kWh | 3122 kWh | £1,186 | £312 | £1,498 | £18,376 | 12.3 yrs | £11,591 |
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: £1,011, Upfront: £13,673, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1951 kWh | 1366 kWh | 585 kWh | £346 | £59 | £404 | £7,569 | 18.7 yrs | £521 |
| 3 kW | 2927 kWh | 2049 kWh | 878 kWh | £519 | £88 | £607 | £9,604 | 15.8 yrs | £2,531 |
| 4 kW | 3902 kWh | 2732 kWh | 1171 kWh | £692 | £117 | £809 | £11,638 | 14.4 yrs | £4,542 |
| 5 kW | 4878 kWh | 3415 kWh | 1463 kWh | £865 | £146 | £1,011 | £13,673 | 13.5 yrs | £6,552 |
| 6 kW | 5854 kWh | 4097 kWh | 1756 kWh | £1,038 | £176 | £1,213 | £15,707 | 12.9 yrs | £8,563 |
| 7 kW | 6829 kWh | 4780 kWh | 2049 kWh | £1,211 | £205 | £1,416 | £17,742 | 12.5 yrs | £10,573 |
| 8 kW | 7805 kWh | 5463 kWh | 2341 kWh | £1,384 | £234 | £1,618 | £19,776 | 12.2 yrs | £12,584 |
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: £1,034, Upfront: £15,423, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1951 kWh | 1424 kWh | 527 kWh | £361 | £53 | £413 | £9,319 | 22.5 yrs | £-1,050 |
| 3 kW | 2927 kWh | 2137 kWh | 790 kWh | £541 | £79 | £620 | £11,354 | 18.3 yrs | £1,051 |
| 4 kW | 3902 kWh | 2849 kWh | 1054 kWh | £722 | £105 | £827 | £13,388 | 16.2 yrs | £3,151 |
| 5 kW | 4878 kWh | 3561 kWh | 1317 kWh | £902 | £132 | £1,034 | £15,423 | 14.9 yrs | £5,251 |
| 6 kW | 5854 kWh | 4273 kWh | 1580 kWh | £1,082 | £158 | £1,240 | £17,457 | 14.1 yrs | £7,351 |
| 7 kW | 6829 kWh | 4985 kWh | 1844 kWh | £1,263 | £184 | £1,447 | £19,492 | 13.5 yrs | £9,452 |
| 8 kW | 7805 kWh | 5697 kWh | 2107 kWh | £1,443 | £211 | £1,654 | £21,526 | 13.0 yrs | £11,552 |
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: £1,049, Upfront: £17,173, 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 | 1951 kWh | 1463 kWh | 488 kWh | £371 | £49 | £419 | £11,069 | 26.4 yrs | £-2,680 |
| 3 kW | 2927 kWh | 2195 kWh | 732 kWh | £556 | £73 | £629 | £13,104 | 20.8 yrs | £-520 |
| 4 kW | 3902 kWh | 2927 kWh | 976 kWh | £741 | £98 | £839 | £15,138 | 18.0 yrs | £1,640 |
| 5 kW | 4878 kWh | 3658 kWh | 1219 kWh | £927 | £122 | £1,049 | £17,173 | 16.4 yrs | £3,800 |
| 6 kW | 5854 kWh | 4390 kWh | 1463 kWh | £1,112 | £146 | £1,258 | £19,207 | 15.3 yrs | £5,960 |
| 7 kW | 6829 kWh | 5122 kWh | 1707 kWh | £1,297 | £171 | £1,468 | £21,242 | 14.5 yrs | £8,120 |
| 8 kW | 7805 kWh | 5854 kWh | 1951 kWh | £1,483 | £195 | £1,678 | £23,276 | 13.9 yrs | £10,280 |
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: £1,064, Upfront: £19,623, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1951 kWh | 1502 kWh | 449 kWh | £381 | £45 | £425 | £13,519 | 31.8 yrs | £-5,010 |
| 3 kW | 2927 kWh | 2254 kWh | 673 kWh | £571 | £67 | £638 | £15,554 | 24.4 yrs | £-2,790 |
| 4 kW | 3902 kWh | 3005 kWh | 898 kWh | £761 | £90 | £851 | £17,588 | 20.7 yrs | £-571 |
| 5 kW | 4878 kWh | 3756 kWh | 1122 kWh | £951 | £112 | £1,064 | £19,623 | 18.4 yrs | £1,649 |
| 6 kW | 5854 kWh | 4507 kWh | 1346 kWh | £1,142 | £135 | £1,276 | £21,657 | 17.0 yrs | £3,869 |
| 7 kW | 6829 kWh | 5258 kWh | 1571 kWh | £1,332 | £157 | £1,489 | £23,692 | 15.9 yrs | £6,089 |
| 8 kW | 7805 kWh | 6010 kWh | 1795 kWh | £1,522 | £180 | £1,702 | £25,726 | 15.1 yrs | £8,309 |
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.