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 1126 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: £944, Upfront: £10,173, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 901 kWh | 1351 kWh | £242 | £135 | £378 | £4,069 | 10.8 yrs | £3,482 |
| 3 kW | 3377 kWh | 1351 kWh | 2026 kWh | £364 | £203 | £566 | £6,104 | 10.8 yrs | £5,223 |
| 4 kW | 4503 kWh | 1801 kWh | 2702 kWh | £485 | £270 | £755 | £8,138 | 10.8 yrs | £6,964 |
| 5 kW | 5629 kWh | 2252 kWh | 3377 kWh | £606 | £338 | £944 | £10,173 | 10.8 yrs | £8,705 |
| 6 kW | 6755 kWh | 2702 kWh | 4053 kWh | £727 | £405 | £1,133 | £12,207 | 10.8 yrs | £10,446 |
| 7 kW | 7881 kWh | 3152 kWh | 4728 kWh | £849 | £473 | £1,321 | £14,242 | 10.8 yrs | £12,188 |
| 8 kW | 9007 kWh | 3603 kWh | 5404 kWh | £970 | £540 | £1,510 | £16,276 | 10.8 yrs | £13,929 |
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: £1,134, Upfront: £12,273, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1351 kWh | 901 kWh | £364 | £90 | £454 | £6,169 | 13.6 yrs | £2,906 |
| 3 kW | 3377 kWh | 2026 kWh | 1351 kWh | £546 | £135 | £681 | £8,204 | 12.1 yrs | £5,409 |
| 4 kW | 4503 kWh | 2702 kWh | 1801 kWh | £727 | £180 | £908 | £10,238 | 11.3 yrs | £7,912 |
| 5 kW | 5629 kWh | 3377 kWh | 2252 kWh | £909 | £225 | £1,134 | £12,273 | 10.8 yrs | £10,415 |
| 6 kW | 6755 kWh | 4053 kWh | 2702 kWh | £1,091 | £270 | £1,361 | £14,307 | 10.5 yrs | £12,918 |
| 7 kW | 7881 kWh | 4728 kWh | 3152 kWh | £1,273 | £315 | £1,588 | £16,342 | 10.3 yrs | £15,421 |
| 8 kW | 9007 kWh | 5404 kWh | 3603 kWh | £1,455 | £360 | £1,815 | £18,376 | 10.1 yrs | £17,924 |
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: £1,230, Upfront: £13,673, Break-even: 11.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1576 kWh | 675 kWh | £424 | £68 | £492 | £7,569 | 15.4 yrs | £2,268 |
| 3 kW | 3377 kWh | 2364 kWh | 1013 kWh | £636 | £101 | £738 | £9,604 | 13.0 yrs | £5,152 |
| 4 kW | 4503 kWh | 3152 kWh | 1351 kWh | £849 | £135 | £984 | £11,638 | 11.8 yrs | £8,036 |
| 5 kW | 5629 kWh | 3940 kWh | 1689 kWh | £1,061 | £169 | £1,230 | £13,673 | 11.1 yrs | £10,920 |
| 6 kW | 6755 kWh | 4728 kWh | 2026 kWh | £1,273 | £203 | £1,476 | £15,707 | 10.6 yrs | £13,804 |
| 7 kW | 7881 kWh | 5517 kWh | 2364 kWh | £1,485 | £236 | £1,721 | £17,742 | 10.3 yrs | £16,688 |
| 8 kW | 9007 kWh | 6305 kWh | 2702 kWh | £1,697 | £270 | £1,967 | £19,776 | 10.1 yrs | £19,572 |
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: £1,258, Upfront: £15,423, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1644 kWh | 608 kWh | £442 | £61 | £503 | £9,319 | 18.5 yrs | £747 |
| 3 kW | 3377 kWh | 2466 kWh | 912 kWh | £664 | £91 | £755 | £11,354 | 15.0 yrs | £3,745 |
| 4 kW | 4503 kWh | 3287 kWh | 1216 kWh | £885 | £122 | £1,007 | £13,388 | 13.3 yrs | £6,743 |
| 5 kW | 5629 kWh | 4109 kWh | 1520 kWh | £1,106 | £152 | £1,258 | £15,423 | 12.3 yrs | £9,742 |
| 6 kW | 6755 kWh | 4931 kWh | 1824 kWh | £1,327 | £182 | £1,510 | £17,457 | 11.6 yrs | £12,740 |
| 7 kW | 7881 kWh | 5753 kWh | 2128 kWh | £1,549 | £213 | £1,761 | £19,492 | 11.1 yrs | £15,738 |
| 8 kW | 9007 kWh | 6575 kWh | 2432 kWh | £1,770 | £243 | £2,013 | £21,526 | 10.7 yrs | £18,736 |
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: £1,277, Upfront: £17,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1689 kWh | 563 kWh | £455 | £56 | £511 | £11,069 | 21.7 yrs | £-851 |
| 3 kW | 3377 kWh | 2533 kWh | 844 kWh | £682 | £84 | £766 | £13,104 | 17.1 yrs | £2,224 |
| 4 kW | 4503 kWh | 3377 kWh | 1126 kWh | £909 | £113 | £1,022 | £15,138 | 14.8 yrs | £5,298 |
| 5 kW | 5629 kWh | 4222 kWh | 1407 kWh | £1,137 | £141 | £1,277 | £17,173 | 13.4 yrs | £8,373 |
| 6 kW | 6755 kWh | 5066 kWh | 1689 kWh | £1,364 | £169 | £1,533 | £19,207 | 12.5 yrs | £11,447 |
| 7 kW | 7881 kWh | 5911 kWh | 1970 kWh | £1,591 | £197 | £1,788 | £21,242 | 11.9 yrs | £14,522 |
| 8 kW | 9007 kWh | 6755 kWh | 2252 kWh | £1,818 | £225 | £2,044 | £23,276 | 11.4 yrs | £17,596 |
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: £1,296, Upfront: £19,623, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2252 kWh | 1734 kWh | 518 kWh | £467 | £52 | £519 | £13,519 | 26.1 yrs | £-3,149 |
| 3 kW | 3377 kWh | 2601 kWh | 777 kWh | £700 | £78 | £778 | £15,554 | 20.0 yrs | £2 |
| 4 kW | 4503 kWh | 3468 kWh | 1036 kWh | £933 | £104 | £1,037 | £17,588 | 17.0 yrs | £3,153 |
| 5 kW | 5629 kWh | 4334 kWh | 1295 kWh | £1,167 | £129 | £1,296 | £19,623 | 15.1 yrs | £6,304 |
| 6 kW | 6755 kWh | 5201 kWh | 1554 kWh | £1,400 | £155 | £1,556 | £21,657 | 13.9 yrs | £9,454 |
| 7 kW | 7881 kWh | 6068 kWh | 1813 kWh | £1,634 | £181 | £1,815 | £23,692 | 13.1 yrs | £12,605 |
| 8 kW | 9007 kWh | 6935 kWh | 2072 kWh | £1,867 | £207 | £2,074 | £25,726 | 12.4 yrs | £15,756 |
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.