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 1078 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: £894, Upfront: £10,173, Break-even: 11.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2156 kWh | 862 kWh | 1294 kWh | £228 | £129 | £358 | £4,069 | 11.4 yrs | £3,086 |
| 3 kW | 3234 kWh | 1294 kWh | 1941 kWh | £343 | £194 | £537 | £6,104 | 11.4 yrs | £4,629 |
| 4 kW | 4312 kWh | 1725 kWh | 2587 kWh | £457 | £259 | £715 | £8,138 | 11.4 yrs | £6,172 |
| 5 kW | 5390 kWh | 2156 kWh | 3234 kWh | £571 | £323 | £894 | £10,173 | 11.4 yrs | £7,715 |
| 6 kW | 6468 kWh | 2587 kWh | 3881 kWh | £685 | £388 | £1,073 | £12,207 | 11.4 yrs | £9,258 |
| 7 kW | 7546 kWh | 3019 kWh | 4528 kWh | £799 | £453 | £1,252 | £14,242 | 11.4 yrs | £10,801 |
| 8 kW | 8625 kWh | 3450 kWh | 5175 kWh | £914 | £517 | £1,431 | £16,276 | 11.4 yrs | £12,344 |
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: £1,072, Upfront: £12,273, Break-even: 11.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2156 kWh | 1294 kWh | 862 kWh | £343 | £86 | £429 | £6,169 | 14.4 yrs | £2,407 |
| 3 kW | 3234 kWh | 1941 kWh | 1294 kWh | £514 | £129 | £643 | £8,204 | 12.8 yrs | £4,661 |
| 4 kW | 4312 kWh | 2587 kWh | 1725 kWh | £685 | £172 | £858 | £10,238 | 11.9 yrs | £6,914 |
| 5 kW | 5390 kWh | 3234 kWh | 2156 kWh | £856 | £216 | £1,072 | £12,273 | 11.4 yrs | £9,168 |
| 6 kW | 6468 kWh | 3881 kWh | 2587 kWh | £1,028 | £259 | £1,286 | £14,307 | 11.1 yrs | £11,422 |
| 7 kW | 7546 kWh | 4528 kWh | 3019 kWh | £1,199 | £302 | £1,501 | £16,342 | 10.9 yrs | £13,675 |
| 8 kW | 8625 kWh | 5175 kWh | 3450 kWh | £1,370 | £345 | £1,715 | £18,376 | 10.7 yrs | £15,929 |
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: £1,161, Upfront: £13,673, 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 | 2156 kWh | 1509 kWh | 647 kWh | £400 | £65 | £464 | £7,569 | 16.3 yrs | £1,718 |
| 3 kW | 3234 kWh | 2264 kWh | 970 kWh | £599 | £97 | £697 | £9,604 | 13.8 yrs | £4,327 |
| 4 kW | 4312 kWh | 3019 kWh | 1294 kWh | £799 | £129 | £929 | £11,638 | 12.5 yrs | £6,936 |
| 5 kW | 5390 kWh | 3773 kWh | 1617 kWh | £999 | £162 | £1,161 | £13,673 | 11.8 yrs | £9,545 |
| 6 kW | 6468 kWh | 4528 kWh | 1941 kWh | £1,199 | £194 | £1,393 | £15,707 | 11.3 yrs | £12,154 |
| 7 kW | 7546 kWh | 5283 kWh | 2264 kWh | £1,399 | £226 | £1,625 | £17,742 | 10.9 yrs | £14,763 |
| 8 kW | 8625 kWh | 6037 kWh | 2587 kWh | £1,599 | £259 | £1,857 | £19,776 | 10.6 yrs | £17,372 |
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: £1,188, Upfront: £15,423, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2156 kWh | 1574 kWh | 582 kWh | £417 | £58 | £475 | £9,319 | 19.6 yrs | £181 |
| 3 kW | 3234 kWh | 2361 kWh | 873 kWh | £625 | £87 | £713 | £11,354 | 15.9 yrs | £2,897 |
| 4 kW | 4312 kWh | 3148 kWh | 1164 kWh | £834 | £116 | £950 | £13,388 | 14.1 yrs | £5,612 |
| 5 kW | 5390 kWh | 3935 kWh | 1455 kWh | £1,042 | £146 | £1,188 | £15,423 | 13.0 yrs | £8,328 |
| 6 kW | 6468 kWh | 4722 kWh | 1746 kWh | £1,250 | £175 | £1,425 | £17,457 | 12.3 yrs | £11,043 |
| 7 kW | 7546 kWh | 5509 kWh | 2038 kWh | £1,459 | £204 | £1,663 | £19,492 | 11.7 yrs | £13,759 |
| 8 kW | 8625 kWh | 6296 kWh | 2329 kWh | £1,667 | £233 | £1,900 | £21,526 | 11.3 yrs | £16,474 |
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: £1,205, Upfront: £17,173, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2156 kWh | 1617 kWh | 539 kWh | £428 | £54 | £482 | £11,069 | 23.0 yrs | £-1,427 |
| 3 kW | 3234 kWh | 2426 kWh | 809 kWh | £642 | £81 | £723 | £13,104 | 18.1 yrs | £1,360 |
| 4 kW | 4312 kWh | 3234 kWh | 1078 kWh | £856 | £108 | £964 | £15,138 | 15.7 yrs | £4,146 |
| 5 kW | 5390 kWh | 4043 kWh | 1348 kWh | £1,071 | £135 | £1,205 | £17,173 | 14.2 yrs | £6,933 |
| 6 kW | 6468 kWh | 4851 kWh | 1617 kWh | £1,285 | £162 | £1,446 | £19,207 | 13.3 yrs | £9,720 |
| 7 kW | 7546 kWh | 5660 kWh | 1887 kWh | £1,499 | £189 | £1,687 | £21,242 | 12.6 yrs | £12,506 |
| 8 kW | 8625 kWh | 6468 kWh | 2156 kWh | £1,713 | £216 | £1,928 | £23,276 | 12.1 yrs | £15,293 |
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: £1,223, Upfront: £19,623, 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 | 2156 kWh | 1660 kWh | 496 kWh | £440 | £50 | £489 | £13,519 | 27.6 yrs | £-3,735 |
| 3 kW | 3234 kWh | 2490 kWh | 744 kWh | £659 | £74 | £734 | £15,554 | 21.2 yrs | £-877 |
| 4 kW | 4312 kWh | 3320 kWh | 992 kWh | £879 | £99 | £978 | £17,588 | 18.0 yrs | £1,981 |
| 5 kW | 5390 kWh | 4151 kWh | 1240 kWh | £1,099 | £124 | £1,223 | £19,623 | 16.0 yrs | £4,838 |
| 6 kW | 6468 kWh | 4981 kWh | 1488 kWh | £1,319 | £149 | £1,468 | £21,657 | 14.8 yrs | £7,696 |
| 7 kW | 7546 kWh | 5811 kWh | 1736 kWh | £1,539 | £174 | £1,712 | £23,692 | 13.8 yrs | £10,554 |
| 8 kW | 8625 kWh | 6641 kWh | 1984 kWh | £1,759 | £198 | £1,957 | £25,726 | 13.1 yrs | £13,411 |
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.