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 922 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: £746, Upfront: £10,173, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1844 kWh | 738 kWh | 1106 kWh | £188 | £111 | £298 | £4,069 | 13.6 yrs | £1,896 |
| 3 kW | 2766 kWh | 1106 kWh | 1660 kWh | £281 | £166 | £447 | £6,104 | 13.6 yrs | £2,843 |
| 4 kW | 3688 kWh | 1475 kWh | 2213 kWh | £375 | £221 | £596 | £8,138 | 13.6 yrs | £3,791 |
| 5 kW | 4610 kWh | 1844 kWh | 2766 kWh | £469 | £277 | £746 | £10,173 | 13.6 yrs | £4,739 |
| 6 kW | 5532 kWh | 2213 kWh | 3319 kWh | £563 | £332 | £895 | £12,207 | 13.6 yrs | £5,687 |
| 7 kW | 6454 kWh | 2582 kWh | 3873 kWh | £657 | £387 | £1,044 | £14,242 | 13.6 yrs | £6,635 |
| 8 kW | 7377 kWh | 2951 kWh | 4426 kWh | £750 | £443 | £1,193 | £16,276 | 13.6 yrs | £7,583 |
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: £888, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1844 kWh | 1106 kWh | 738 kWh | £281 | £74 | £355 | £6,169 | 17.4 yrs | £934 |
| 3 kW | 2766 kWh | 1660 kWh | 1106 kWh | £422 | £111 | £533 | £8,204 | 15.4 yrs | £2,451 |
| 4 kW | 3688 kWh | 2213 kWh | 1475 kWh | £563 | £148 | £710 | £10,238 | 14.4 yrs | £3,968 |
| 5 kW | 4610 kWh | 2766 kWh | 1844 kWh | £703 | £184 | £888 | £12,273 | 13.8 yrs | £5,485 |
| 6 kW | 5532 kWh | 3319 kWh | 2213 kWh | £844 | £221 | £1,065 | £14,307 | 13.4 yrs | £7,002 |
| 7 kW | 6454 kWh | 3873 kWh | 2582 kWh | £985 | £258 | £1,243 | £16,342 | 13.1 yrs | £8,519 |
| 8 kW | 7377 kWh | 4426 kWh | 2951 kWh | £1,126 | £295 | £1,421 | £18,376 | 12.9 yrs | £10,035 |
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: £959, Upfront: £13,673, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1844 kWh | 1291 kWh | 553 kWh | £328 | £55 | £384 | £7,569 | 19.7 yrs | £103 |
| 3 kW | 2766 kWh | 1936 kWh | 830 kWh | £492 | £83 | £575 | £9,604 | 16.7 yrs | £1,904 |
| 4 kW | 3688 kWh | 2582 kWh | 1106 kWh | £657 | £111 | £767 | £11,638 | 15.2 yrs | £3,706 |
| 5 kW | 4610 kWh | 3227 kWh | 1383 kWh | £821 | £138 | £959 | £13,673 | 14.3 yrs | £5,507 |
| 6 kW | 5532 kWh | 3873 kWh | 1660 kWh | £985 | £166 | £1,151 | £15,707 | 13.6 yrs | £7,309 |
| 7 kW | 6454 kWh | 4518 kWh | 1936 kWh | £1,149 | £194 | £1,343 | £17,742 | 13.2 yrs | £9,110 |
| 8 kW | 7377 kWh | 5164 kWh | 2213 kWh | £1,313 | £221 | £1,534 | £19,776 | 12.9 yrs | £10,912 |
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: £980, Upfront: £15,423, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1844 kWh | 1346 kWh | 498 kWh | £342 | £50 | £392 | £9,319 | 23.8 yrs | £-1,476 |
| 3 kW | 2766 kWh | 2019 kWh | 747 kWh | £514 | £75 | £588 | £11,354 | 19.3 yrs | £411 |
| 4 kW | 3688 kWh | 2692 kWh | 996 kWh | £685 | £100 | £784 | £13,388 | 17.1 yrs | £2,297 |
| 5 kW | 4610 kWh | 3366 kWh | 1245 kWh | £856 | £124 | £980 | £15,423 | 15.7 yrs | £4,184 |
| 6 kW | 5532 kWh | 4039 kWh | 1494 kWh | £1,027 | £149 | £1,176 | £17,457 | 14.8 yrs | £6,071 |
| 7 kW | 6454 kWh | 4712 kWh | 1743 kWh | £1,198 | £174 | £1,372 | £19,492 | 14.2 yrs | £7,958 |
| 8 kW | 7377 kWh | 5385 kWh | 1992 kWh | £1,369 | £199 | £1,569 | £21,526 | 13.7 yrs | £9,845 |
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: £995, Upfront: £17,173, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1844 kWh | 1383 kWh | 461 kWh | £352 | £46 | £398 | £11,069 | 27.8 yrs | £-3,112 |
| 3 kW | 2766 kWh | 2075 kWh | 692 kWh | £528 | £69 | £597 | £13,104 | 22.0 yrs | £-1,169 |
| 4 kW | 3688 kWh | 2766 kWh | 922 kWh | £703 | £92 | £796 | £15,138 | 19.0 yrs | £775 |
| 5 kW | 4610 kWh | 3458 kWh | 1153 kWh | £879 | £115 | £995 | £17,173 | 17.3 yrs | £2,719 |
| 6 kW | 5532 kWh | 4149 kWh | 1383 kWh | £1,055 | £138 | £1,193 | £19,207 | 16.1 yrs | £4,663 |
| 7 kW | 6454 kWh | 4841 kWh | 1614 kWh | £1,231 | £161 | £1,392 | £21,242 | 15.3 yrs | £6,606 |
| 8 kW | 7377 kWh | 5532 kWh | 1844 kWh | £1,407 | £184 | £1,591 | £23,276 | 14.6 yrs | £8,550 |
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: £1,009, Upfront: £19,623, Break-even: 19.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1844 kWh | 1420 kWh | 424 kWh | £361 | £42 | £404 | £13,519 | 33.5 yrs | £-5,449 |
| 3 kW | 2766 kWh | 2130 kWh | 636 kWh | £542 | £64 | £605 | £15,554 | 25.7 yrs | £-3,448 |
| 4 kW | 3688 kWh | 2840 kWh | 848 kWh | £722 | £85 | £807 | £17,588 | 21.8 yrs | £-1,447 |
| 5 kW | 4610 kWh | 3550 kWh | 1060 kWh | £903 | £106 | £1,009 | £19,623 | 19.5 yrs | £553 |
| 6 kW | 5532 kWh | 4260 kWh | 1272 kWh | £1,083 | £127 | £1,211 | £21,657 | 17.9 yrs | £2,554 |
| 7 kW | 6454 kWh | 4970 kWh | 1485 kWh | £1,264 | £148 | £1,412 | £23,692 | 16.8 yrs | £4,555 |
| 8 kW | 7377 kWh | 5680 kWh | 1697 kWh | £1,444 | £170 | £1,614 | £25,726 | 15.9 yrs | £6,555 |
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.