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 1138 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: £954, Upfront: £10,173, Break-even: 10.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2276 kWh | 910 kWh | 1365 kWh | £245 | £137 | £382 | £4,069 | 10.7 yrs | £3,563 |
| 3 kW | 3414 kWh | 1365 kWh | 2048 kWh | £368 | £205 | £572 | £6,104 | 10.7 yrs | £5,344 |
| 4 kW | 4551 kWh | 1821 kWh | 2731 kWh | £490 | £273 | £763 | £8,138 | 10.7 yrs | £7,126 |
| 5 kW | 5689 kWh | 2276 kWh | 3414 kWh | £613 | £341 | £954 | £10,173 | 10.7 yrs | £8,907 |
| 6 kW | 6827 kWh | 2731 kWh | 4096 kWh | £735 | £410 | £1,145 | £12,207 | 10.7 yrs | £10,688 |
| 7 kW | 7965 kWh | 3186 kWh | 4779 kWh | £858 | £478 | £1,336 | £14,242 | 10.7 yrs | £12,470 |
| 8 kW | 9103 kWh | 3641 kWh | 5462 kWh | £980 | £546 | £1,526 | £16,276 | 10.7 yrs | £14,251 |
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: £1,146, Upfront: £12,273, Break-even: 10.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2276 kWh | 1365 kWh | 910 kWh | £368 | £91 | £459 | £6,169 | 13.5 yrs | £3,003 |
| 3 kW | 3414 kWh | 2048 kWh | 1365 kWh | £551 | £137 | £688 | £8,204 | 11.9 yrs | £5,554 |
| 4 kW | 4551 kWh | 2731 kWh | 1821 kWh | £735 | £182 | £917 | £10,238 | 11.2 yrs | £8,106 |
| 5 kW | 5689 kWh | 3414 kWh | 2276 kWh | £919 | £228 | £1,146 | £12,273 | 10.7 yrs | £10,657 |
| 6 kW | 6827 kWh | 4096 kWh | 2731 kWh | £1,103 | £273 | £1,376 | £14,307 | 10.4 yrs | £13,209 |
| 7 kW | 7965 kWh | 4779 kWh | 3186 kWh | £1,286 | £319 | £1,605 | £16,342 | 10.2 yrs | £15,760 |
| 8 kW | 9103 kWh | 5462 kWh | 3641 kWh | £1,470 | £364 | £1,834 | £18,376 | 10.0 yrs | £18,312 |
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: £1,243, Upfront: £13,673, Break-even: 11.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2276 kWh | 1593 kWh | 683 kWh | £429 | £68 | £497 | £7,569 | 15.2 yrs | £2,373 |
| 3 kW | 3414 kWh | 2389 kWh | 1024 kWh | £643 | £102 | £746 | £9,604 | 12.9 yrs | £5,310 |
| 4 kW | 4551 kWh | 3186 kWh | 1365 kWh | £858 | £137 | £994 | £11,638 | 11.7 yrs | £8,246 |
| 5 kW | 5689 kWh | 3982 kWh | 1707 kWh | £1,072 | £171 | £1,243 | £13,673 | 11.0 yrs | £11,183 |
| 6 kW | 6827 kWh | 4779 kWh | 2048 kWh | £1,286 | £205 | £1,491 | £15,707 | 10.5 yrs | £14,119 |
| 7 kW | 7965 kWh | 5575 kWh | 2389 kWh | £1,501 | £239 | £1,740 | £17,742 | 10.2 yrs | £17,056 |
| 8 kW | 9103 kWh | 6372 kWh | 2731 kWh | £1,715 | £273 | £1,988 | £19,776 | 9.9 yrs | £19,992 |
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: £1,272, Upfront: £15,423, 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 | 2276 kWh | 1661 kWh | 614 kWh | £447 | £61 | £509 | £9,319 | 18.3 yrs | £854 |
| 3 kW | 3414 kWh | 2492 kWh | 922 kWh | £671 | £92 | £763 | £11,354 | 14.9 yrs | £3,906 |
| 4 kW | 4551 kWh | 3323 kWh | 1229 kWh | £894 | £123 | £1,017 | £13,388 | 13.2 yrs | £6,958 |
| 5 kW | 5689 kWh | 4153 kWh | 1536 kWh | £1,118 | £154 | £1,272 | £15,423 | 12.1 yrs | £10,010 |
| 6 kW | 6827 kWh | 4984 kWh | 1843 kWh | £1,342 | £184 | £1,526 | £17,457 | 11.4 yrs | £13,062 |
| 7 kW | 7965 kWh | 5814 kWh | 2151 kWh | £1,565 | £215 | £1,780 | £19,492 | 10.9 yrs | £16,114 |
| 8 kW | 9103 kWh | 6645 kWh | 2458 kWh | £1,789 | £246 | £2,035 | £21,526 | 10.6 yrs | £19,166 |
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: £1,291, Upfront: £17,173, 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 | 2276 kWh | 1707 kWh | 569 kWh | £459 | £57 | £516 | £11,069 | 21.4 yrs | £-742 |
| 3 kW | 3414 kWh | 2560 kWh | 853 kWh | £689 | £85 | £775 | £13,104 | 16.9 yrs | £2,387 |
| 4 kW | 4551 kWh | 3414 kWh | 1138 kWh | £919 | £114 | £1,033 | £15,138 | 14.7 yrs | £5,516 |
| 5 kW | 5689 kWh | 4267 kWh | 1422 kWh | £1,149 | £142 | £1,291 | £17,173 | 13.3 yrs | £8,645 |
| 6 kW | 6827 kWh | 5120 kWh | 1707 kWh | £1,378 | £171 | £1,549 | £19,207 | 12.4 yrs | £11,774 |
| 7 kW | 7965 kWh | 5974 kWh | 1991 kWh | £1,608 | £199 | £1,807 | £21,242 | 11.8 yrs | £14,903 |
| 8 kW | 9103 kWh | 6827 kWh | 2276 kWh | £1,838 | £228 | £2,065 | £23,276 | 11.3 yrs | £18,032 |
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: £1,310, Upfront: £19,623, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2276 kWh | 1752 kWh | 523 kWh | £472 | £52 | £524 | £13,519 | 25.8 yrs | £-3,038 |
| 3 kW | 3414 kWh | 2628 kWh | 785 kWh | £708 | £79 | £786 | £15,554 | 19.8 yrs | £168 |
| 4 kW | 4551 kWh | 3505 kWh | 1047 kWh | £943 | £105 | £1,048 | £17,588 | 16.8 yrs | £3,374 |
| 5 kW | 5689 kWh | 4381 kWh | 1309 kWh | £1,179 | £131 | £1,310 | £19,623 | 15.0 yrs | £6,580 |
| 6 kW | 6827 kWh | 5257 kWh | 1570 kWh | £1,415 | £157 | £1,572 | £21,657 | 13.8 yrs | £9,786 |
| 7 kW | 7965 kWh | 6133 kWh | 1832 kWh | £1,651 | £183 | £1,834 | £23,692 | 12.9 yrs | £12,992 |
| 8 kW | 9103 kWh | 7009 kWh | 2094 kWh | £1,887 | £209 | £2,096 | £25,726 | 12.3 yrs | £16,199 |
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.