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 994 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: £825, Upfront: £10,173, 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 | 1989 kWh | 796 kWh | 1193 kWh | £211 | £119 | £330 | £4,069 | 12.3 yrs | £2,531 |
| 3 kW | 2983 kWh | 1193 kWh | 1790 kWh | £316 | £179 | £495 | £6,104 | 12.3 yrs | £3,796 |
| 4 kW | 3978 kWh | 1591 kWh | 2387 kWh | £421 | £239 | £660 | £8,138 | 12.3 yrs | £5,061 |
| 5 kW | 4972 kWh | 1989 kWh | 2983 kWh | £527 | £298 | £825 | £10,173 | 12.3 yrs | £6,327 |
| 6 kW | 5966 kWh | 2387 kWh | 3580 kWh | £632 | £358 | £990 | £12,207 | 12.3 yrs | £7,592 |
| 7 kW | 6961 kWh | 2784 kWh | 4177 kWh | £737 | £418 | £1,155 | £14,242 | 12.3 yrs | £8,857 |
| 8 kW | 7955 kWh | 3182 kWh | 4773 kWh | £843 | £477 | £1,320 | £16,276 | 12.3 yrs | £10,123 |
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: £989, Upfront: £12,273, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1989 kWh | 1193 kWh | 796 kWh | £316 | £80 | £396 | £6,169 | 15.6 yrs | £1,742 |
| 3 kW | 2983 kWh | 1790 kWh | 1193 kWh | £474 | £119 | £593 | £8,204 | 13.8 yrs | £3,663 |
| 4 kW | 3978 kWh | 2387 kWh | 1591 kWh | £632 | £159 | £791 | £10,238 | 12.9 yrs | £5,583 |
| 5 kW | 4972 kWh | 2983 kWh | 1989 kWh | £790 | £199 | £989 | £12,273 | 12.4 yrs | £7,504 |
| 6 kW | 5966 kWh | 3580 kWh | 2387 kWh | £948 | £239 | £1,187 | £14,307 | 12.1 yrs | £9,425 |
| 7 kW | 6961 kWh | 4177 kWh | 2784 kWh | £1,106 | £278 | £1,384 | £16,342 | 11.8 yrs | £11,346 |
| 8 kW | 7955 kWh | 4773 kWh | 3182 kWh | £1,264 | £318 | £1,582 | £18,376 | 11.6 yrs | £13,267 |
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: £1,071, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1989 kWh | 1392 kWh | 597 kWh | £369 | £60 | £428 | £7,569 | 17.7 yrs | £997 |
| 3 kW | 2983 kWh | 2088 kWh | 895 kWh | £553 | £89 | £642 | £9,604 | 14.9 yrs | £3,246 |
| 4 kW | 3978 kWh | 2784 kWh | 1193 kWh | £737 | £119 | £857 | £11,638 | 13.6 yrs | £5,494 |
| 5 kW | 4972 kWh | 3480 kWh | 1492 kWh | £922 | £149 | £1,071 | £13,673 | 12.8 yrs | £7,743 |
| 6 kW | 5966 kWh | 4177 kWh | 1790 kWh | £1,106 | £179 | £1,285 | £15,707 | 12.2 yrs | £9,992 |
| 7 kW | 6961 kWh | 4873 kWh | 2088 kWh | £1,290 | £209 | £1,499 | £17,742 | 11.8 yrs | £12,240 |
| 8 kW | 7955 kWh | 5569 kWh | 2387 kWh | £1,475 | £239 | £1,713 | £19,776 | 11.5 yrs | £14,489 |
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: £1,095, Upfront: £15,423, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1989 kWh | 1452 kWh | 537 kWh | £384 | £54 | £438 | £9,319 | 21.3 yrs | £-556 |
| 3 kW | 2983 kWh | 2178 kWh | 805 kWh | £577 | £81 | £657 | £11,354 | 17.3 yrs | £1,791 |
| 4 kW | 3978 kWh | 2904 kWh | 1074 kWh | £769 | £107 | £876 | £13,388 | 15.3 yrs | £4,138 |
| 5 kW | 4972 kWh | 3630 kWh | 1342 kWh | £961 | £134 | £1,095 | £15,423 | 14.1 yrs | £6,485 |
| 6 kW | 5966 kWh | 4356 kWh | 1611 kWh | £1,153 | £161 | £1,314 | £17,457 | 13.3 yrs | £8,832 |
| 7 kW | 6961 kWh | 5081 kWh | 1879 kWh | £1,346 | £188 | £1,534 | £19,492 | 12.7 yrs | £11,179 |
| 8 kW | 7955 kWh | 5807 kWh | 2148 kWh | £1,538 | £215 | £1,753 | £21,526 | 12.3 yrs | £13,526 |
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: £1,112, Upfront: £17,173, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1989 kWh | 1492 kWh | 497 kWh | £395 | £50 | £445 | £11,069 | 24.9 yrs | £-2,175 |
| 3 kW | 2983 kWh | 2237 kWh | 746 kWh | £592 | £75 | £667 | £13,104 | 19.6 yrs | £237 |
| 4 kW | 3978 kWh | 2983 kWh | 994 kWh | £790 | £99 | £889 | £15,138 | 17.0 yrs | £2,650 |
| 5 kW | 4972 kWh | 3729 kWh | 1243 kWh | £987 | £124 | £1,112 | £17,173 | 15.4 yrs | £5,062 |
| 6 kW | 5966 kWh | 4475 kWh | 1492 kWh | £1,185 | £149 | £1,334 | £19,207 | 14.4 yrs | £7,475 |
| 7 kW | 6961 kWh | 5221 kWh | 1740 kWh | £1,382 | £174 | £1,556 | £21,242 | 13.6 yrs | £9,887 |
| 8 kW | 7955 kWh | 5966 kWh | 1989 kWh | £1,580 | £199 | £1,779 | £23,276 | 13.1 yrs | £12,300 |
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: £1,128, Upfront: £19,623, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1989 kWh | 1531 kWh | 457 kWh | £406 | £46 | £451 | £13,519 | 30.0 yrs | £-4,494 |
| 3 kW | 2983 kWh | 2297 kWh | 686 kWh | £608 | £69 | £677 | £15,554 | 23.0 yrs | £-2,016 |
| 4 kW | 3978 kWh | 3063 kWh | 915 kWh | £811 | £91 | £903 | £17,588 | 19.5 yrs | £462 |
| 5 kW | 4972 kWh | 3828 kWh | 1144 kWh | £1,014 | £114 | £1,128 | £19,623 | 17.4 yrs | £2,940 |
| 6 kW | 5966 kWh | 4594 kWh | 1372 kWh | £1,217 | £137 | £1,354 | £21,657 | 16.0 yrs | £5,418 |
| 7 kW | 6961 kWh | 5360 kWh | 1601 kWh | £1,419 | £160 | £1,579 | £23,692 | 15.0 yrs | £7,896 |
| 8 kW | 7955 kWh | 6126 kWh | 1830 kWh | £1,622 | £183 | £1,805 | £25,726 | 14.3 yrs | £10,374 |
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.