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 1013 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: £842, Upfront: £10,173, 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 | 2027 kWh | 811 kWh | 1216 kWh | £215 | £122 | £337 | £4,069 | 12.1 yrs | £2,665 |
| 3 kW | 3040 kWh | 1216 kWh | 1824 kWh | £323 | £182 | £505 | £6,104 | 12.1 yrs | £3,998 |
| 4 kW | 4054 kWh | 1622 kWh | 2432 kWh | £430 | £243 | £673 | £8,138 | 12.1 yrs | £5,330 |
| 5 kW | 5067 kWh | 2027 kWh | 3040 kWh | £538 | £304 | £842 | £10,173 | 12.1 yrs | £6,663 |
| 6 kW | 6081 kWh | 2432 kWh | 3648 kWh | £645 | £365 | £1,010 | £12,207 | 12.1 yrs | £7,995 |
| 7 kW | 7094 kWh | 2838 kWh | 4256 kWh | £753 | £426 | £1,178 | £14,242 | 12.1 yrs | £9,328 |
| 8 kW | 8108 kWh | 3243 kWh | 4865 kWh | £860 | £486 | £1,347 | £16,276 | 12.1 yrs | £10,660 |
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: £1,009, Upfront: £12,273, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2027 kWh | 1216 kWh | 811 kWh | £323 | £81 | £404 | £6,169 | 15.3 yrs | £1,905 |
| 3 kW | 3040 kWh | 1824 kWh | 1216 kWh | £484 | £122 | £606 | £8,204 | 13.5 yrs | £3,908 |
| 4 kW | 4054 kWh | 2432 kWh | 1622 kWh | £645 | £162 | £807 | £10,238 | 12.7 yrs | £5,911 |
| 5 kW | 5067 kWh | 3040 kWh | 2027 kWh | £807 | £203 | £1,009 | £12,273 | 12.2 yrs | £7,913 |
| 6 kW | 6081 kWh | 3648 kWh | 2432 kWh | £968 | £243 | £1,211 | £14,307 | 11.8 yrs | £9,916 |
| 7 kW | 7094 kWh | 4256 kWh | 2838 kWh | £1,129 | £284 | £1,413 | £16,342 | 11.6 yrs | £11,918 |
| 8 kW | 8108 kWh | 4865 kWh | 3243 kWh | £1,291 | £324 | £1,615 | £18,376 | 11.4 yrs | £13,921 |
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: £1,093, Upfront: £13,673, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2027 kWh | 1419 kWh | 608 kWh | £376 | £61 | £437 | £7,569 | 17.3 yrs | £1,175 |
| 3 kW | 3040 kWh | 2128 kWh | 912 kWh | £565 | £91 | £656 | £9,604 | 14.6 yrs | £3,513 |
| 4 kW | 4054 kWh | 2838 kWh | 1216 kWh | £753 | £122 | £874 | £11,638 | 13.3 yrs | £5,851 |
| 5 kW | 5067 kWh | 3547 kWh | 1520 kWh | £941 | £152 | £1,093 | £13,673 | 12.5 yrs | £8,188 |
| 6 kW | 6081 kWh | 4256 kWh | 1824 kWh | £1,129 | £182 | £1,312 | £15,707 | 12.0 yrs | £10,526 |
| 7 kW | 7094 kWh | 4966 kWh | 2128 kWh | £1,317 | £213 | £1,530 | £17,742 | 11.6 yrs | £12,864 |
| 8 kW | 8108 kWh | 5675 kWh | 2432 kWh | £1,506 | £243 | £1,749 | £19,776 | 11.3 yrs | £15,201 |
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: £1,118, Upfront: £15,423, 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 | 2027 kWh | 1480 kWh | 547 kWh | £393 | £55 | £447 | £9,319 | 20.8 yrs | £-374 |
| 3 kW | 3040 kWh | 2219 kWh | 821 kWh | £589 | £82 | £671 | £11,354 | 16.9 yrs | £2,065 |
| 4 kW | 4054 kWh | 2959 kWh | 1095 kWh | £785 | £109 | £895 | £13,388 | 15.0 yrs | £4,503 |
| 5 kW | 5067 kWh | 3699 kWh | 1368 kWh | £981 | £137 | £1,118 | £15,423 | 13.8 yrs | £6,941 |
| 6 kW | 6081 kWh | 4439 kWh | 1642 kWh | £1,178 | £164 | £1,342 | £17,457 | 13.0 yrs | £9,379 |
| 7 kW | 7094 kWh | 5179 kWh | 1915 kWh | £1,374 | £192 | £1,565 | £19,492 | 12.5 yrs | £11,817 |
| 8 kW | 8108 kWh | 5918 kWh | 2189 kWh | £1,570 | £219 | £1,789 | £21,526 | 12.0 yrs | £14,255 |
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: £1,135, Upfront: £17,173, 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 | 2027 kWh | 1520 kWh | 507 kWh | £403 | £51 | £454 | £11,069 | 24.4 yrs | £-1,990 |
| 3 kW | 3040 kWh | 2280 kWh | 760 kWh | £605 | £76 | £681 | £13,104 | 19.2 yrs | £516 |
| 4 kW | 4054 kWh | 3040 kWh | 1013 kWh | £807 | £101 | £908 | £15,138 | 16.7 yrs | £3,021 |
| 5 kW | 5067 kWh | 3800 kWh | 1267 kWh | £1,008 | £127 | £1,135 | £17,173 | 15.1 yrs | £5,526 |
| 6 kW | 6081 kWh | 4560 kWh | 1520 kWh | £1,210 | £152 | £1,362 | £19,207 | 14.1 yrs | £8,031 |
| 7 kW | 7094 kWh | 5321 kWh | 1774 kWh | £1,412 | £177 | £1,589 | £21,242 | 13.4 yrs | £10,536 |
| 8 kW | 8108 kWh | 6081 kWh | 2027 kWh | £1,613 | £203 | £1,816 | £23,276 | 12.8 yrs | £13,042 |
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: £1,152, Upfront: £19,623, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2027 kWh | 1561 kWh | 466 kWh | £414 | £47 | £461 | £13,519 | 29.3 yrs | £-4,306 |
| 3 kW | 3040 kWh | 2341 kWh | 699 kWh | £621 | £70 | £691 | £15,554 | 22.5 yrs | £-1,733 |
| 4 kW | 4054 kWh | 3121 kWh | 932 kWh | £828 | £93 | £921 | £17,588 | 19.1 yrs | £839 |
| 5 kW | 5067 kWh | 3902 kWh | 1165 kWh | £1,035 | £117 | £1,152 | £19,623 | 17.0 yrs | £3,411 |
| 6 kW | 6081 kWh | 4682 kWh | 1399 kWh | £1,242 | £140 | £1,382 | £21,657 | 15.7 yrs | £5,983 |
| 7 kW | 7094 kWh | 5462 kWh | 1632 kWh | £1,449 | £163 | £1,612 | £23,692 | 14.7 yrs | £8,555 |
| 8 kW | 8108 kWh | 6243 kWh | 1865 kWh | £1,656 | £186 | £1,843 | £25,726 | 14.0 yrs | £11,128 |
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.