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 | 1988 kWh | 795 kWh | 1193 kWh | £211 | £119 | £330 | £4,069 | 12.3 yrs | £2,529 |
| 3 kW | 2982 kWh | 1193 kWh | 1789 kWh | £316 | £179 | £495 | £6,104 | 12.3 yrs | £3,793 |
| 4 kW | 3976 kWh | 1591 kWh | 2386 kWh | £421 | £239 | £660 | £8,138 | 12.3 yrs | £5,057 |
| 5 kW | 4971 kWh | 1988 kWh | 2982 kWh | £526 | £298 | £825 | £10,173 | 12.3 yrs | £6,322 |
| 6 kW | 5965 kWh | 2386 kWh | 3579 kWh | £632 | £358 | £990 | £12,207 | 12.3 yrs | £7,586 |
| 7 kW | 6959 kWh | 2784 kWh | 4175 kWh | £737 | £418 | £1,155 | £14,242 | 12.3 yrs | £8,850 |
| 8 kW | 7953 kWh | 3181 kWh | 4772 kWh | £842 | £477 | £1,320 | £16,276 | 12.3 yrs | £10,115 |
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 | 1988 kWh | 1193 kWh | 795 kWh | £316 | £80 | £395 | £6,169 | 15.6 yrs | £1,739 |
| 3 kW | 2982 kWh | 1789 kWh | 1193 kWh | £474 | £119 | £593 | £8,204 | 13.8 yrs | £3,659 |
| 4 kW | 3976 kWh | 2386 kWh | 1591 kWh | £632 | £159 | £791 | £10,238 | 12.9 yrs | £5,579 |
| 5 kW | 4971 kWh | 2982 kWh | 1988 kWh | £790 | £199 | £989 | £12,273 | 12.4 yrs | £7,498 |
| 6 kW | 5965 kWh | 3579 kWh | 2386 kWh | £948 | £239 | £1,186 | £14,307 | 12.1 yrs | £9,418 |
| 7 kW | 6959 kWh | 4175 kWh | 2784 kWh | £1,106 | £278 | £1,384 | £16,342 | 11.8 yrs | £11,338 |
| 8 kW | 7953 kWh | 4772 kWh | 3181 kWh | £1,264 | £318 | £1,582 | £18,376 | 11.6 yrs | £13,257 |
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: £1,070, 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 | 1988 kWh | 1392 kWh | 596 kWh | £369 | £60 | £428 | £7,569 | 17.7 yrs | £995 |
| 3 kW | 2982 kWh | 2088 kWh | 895 kWh | £553 | £89 | £642 | £9,604 | 15.0 yrs | £3,242 |
| 4 kW | 3976 kWh | 2784 kWh | 1193 kWh | £737 | £119 | £856 | £11,638 | 13.6 yrs | £5,489 |
| 5 kW | 4971 kWh | 3479 kWh | 1491 kWh | £921 | £149 | £1,070 | £13,673 | 12.8 yrs | £7,737 |
| 6 kW | 5965 kWh | 4175 kWh | 1789 kWh | £1,106 | £179 | £1,285 | £15,707 | 12.2 yrs | £9,984 |
| 7 kW | 6959 kWh | 4871 kWh | 2088 kWh | £1,290 | £209 | £1,499 | £17,742 | 11.8 yrs | £12,231 |
| 8 kW | 7953 kWh | 5567 kWh | 2386 kWh | £1,474 | £239 | £1,713 | £19,776 | 11.5 yrs | £14,479 |
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 | 1988 kWh | 1451 kWh | 537 kWh | £384 | £54 | £438 | £9,319 | 21.3 yrs | £-559 |
| 3 kW | 2982 kWh | 2177 kWh | 805 kWh | £576 | £81 | £657 | £11,354 | 17.3 yrs | £1,787 |
| 4 kW | 3976 kWh | 2903 kWh | 1074 kWh | £769 | £107 | £876 | £13,388 | 15.3 yrs | £4,132 |
| 5 kW | 4971 kWh | 3629 kWh | 1342 kWh | £961 | £134 | £1,095 | £15,423 | 14.1 yrs | £6,478 |
| 6 kW | 5965 kWh | 4354 kWh | 1610 kWh | £1,153 | £161 | £1,314 | £17,457 | 13.3 yrs | £8,824 |
| 7 kW | 6959 kWh | 5080 kWh | 1879 kWh | £1,345 | £188 | £1,533 | £19,492 | 12.7 yrs | £11,169 |
| 8 kW | 7953 kWh | 5806 kWh | 2147 kWh | £1,537 | £215 | £1,752 | £21,526 | 12.3 yrs | £13,515 |
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: £1,111, Upfront: £17,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1988 kWh | 1491 kWh | 497 kWh | £395 | £50 | £445 | £11,069 | 24.9 yrs | £-2,178 |
| 3 kW | 2982 kWh | 2237 kWh | 746 kWh | £592 | £75 | £667 | £13,104 | 19.6 yrs | £233 |
| 4 kW | 3976 kWh | 2982 kWh | 994 kWh | £790 | £99 | £889 | £15,138 | 17.0 yrs | £2,645 |
| 5 kW | 4971 kWh | 3728 kWh | 1243 kWh | £987 | £124 | £1,111 | £17,173 | 15.5 yrs | £5,056 |
| 6 kW | 5965 kWh | 4473 kWh | 1491 kWh | £1,185 | £149 | £1,334 | £19,207 | 14.4 yrs | £7,467 |
| 7 kW | 6959 kWh | 5219 kWh | 1740 kWh | £1,382 | £174 | £1,556 | £21,242 | 13.7 yrs | £9,878 |
| 8 kW | 7953 kWh | 5965 kWh | 1988 kWh | £1,579 | £199 | £1,778 | £23,276 | 13.1 yrs | £12,289 |
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 | 1988 kWh | 1531 kWh | 457 kWh | £405 | £46 | £451 | £13,519 | 30.0 yrs | £-4,497 |
| 3 kW | 2982 kWh | 2296 kWh | 686 kWh | £608 | £69 | £677 | £15,554 | 23.0 yrs | £-2,020 |
| 4 kW | 3976 kWh | 3062 kWh | 915 kWh | £811 | £91 | £902 | £17,588 | 19.5 yrs | £457 |
| 5 kW | 4971 kWh | 3827 kWh | 1143 kWh | £1,013 | £114 | £1,128 | £19,623 | 17.4 yrs | £2,933 |
| 6 kW | 5965 kWh | 4593 kWh | 1372 kWh | £1,216 | £137 | £1,353 | £21,657 | 16.0 yrs | £5,410 |
| 7 kW | 6959 kWh | 5358 kWh | 1601 kWh | £1,419 | £160 | £1,579 | £23,692 | 15.0 yrs | £7,887 |
| 8 kW | 7953 kWh | 6124 kWh | 1829 kWh | £1,622 | £183 | £1,804 | £25,726 | 14.3 yrs | £10,363 |
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.