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 1043 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: £867, Upfront: £10,173, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2087 kWh | 835 kWh | 1252 kWh | £221 | £125 | £347 | £4,069 | 11.7 yrs | £2,864 |
| 3 kW | 3130 kWh | 1252 kWh | 1878 kWh | £332 | £188 | £520 | £6,104 | 11.7 yrs | £4,296 |
| 4 kW | 4174 kWh | 1669 kWh | 2504 kWh | £443 | £250 | £693 | £8,138 | 11.7 yrs | £5,728 |
| 5 kW | 5217 kWh | 2087 kWh | 3130 kWh | £554 | £313 | £867 | £10,173 | 11.7 yrs | £7,161 |
| 6 kW | 6260 kWh | 2504 kWh | 3756 kWh | £664 | £376 | £1,040 | £12,207 | 11.7 yrs | £8,593 |
| 7 kW | 7304 kWh | 2922 kWh | 4382 kWh | £775 | £438 | £1,213 | £14,242 | 11.7 yrs | £10,025 |
| 8 kW | 8347 kWh | 3339 kWh | 5008 kWh | £886 | £501 | £1,387 | £16,276 | 11.7 yrs | £11,457 |
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: £1,039, Upfront: £12,273, Break-even: 11.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2087 kWh | 1252 kWh | 835 kWh | £332 | £83 | £416 | £6,169 | 14.8 yrs | £2,144 |
| 3 kW | 3130 kWh | 1878 kWh | 1252 kWh | £498 | £125 | £623 | £8,204 | 13.2 yrs | £4,266 |
| 4 kW | 4174 kWh | 2504 kWh | 1669 kWh | £664 | £167 | £831 | £10,238 | 12.3 yrs | £6,388 |
| 5 kW | 5217 kWh | 3130 kWh | 2087 kWh | £830 | £209 | £1,039 | £12,273 | 11.8 yrs | £8,510 |
| 6 kW | 6260 kWh | 3756 kWh | 2504 kWh | £997 | £250 | £1,247 | £14,307 | 11.5 yrs | £10,632 |
| 7 kW | 7304 kWh | 4382 kWh | 2922 kWh | £1,163 | £292 | £1,455 | £16,342 | 11.2 yrs | £12,754 |
| 8 kW | 8347 kWh | 5008 kWh | 3339 kWh | £1,329 | £334 | £1,663 | £18,376 | 11.1 yrs | £14,876 |
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: £1,125, Upfront: £13,673, 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 | 2087 kWh | 1461 kWh | 626 kWh | £388 | £63 | £450 | £7,569 | 16.8 yrs | £1,434 |
| 3 kW | 3130 kWh | 2191 kWh | 939 kWh | £581 | £94 | £675 | £9,604 | 14.2 yrs | £3,901 |
| 4 kW | 4174 kWh | 2922 kWh | 1252 kWh | £775 | £125 | £900 | £11,638 | 12.9 yrs | £6,368 |
| 5 kW | 5217 kWh | 3652 kWh | 1565 kWh | £969 | £157 | £1,125 | £13,673 | 12.1 yrs | £8,835 |
| 6 kW | 6260 kWh | 4382 kWh | 1878 kWh | £1,163 | £188 | £1,350 | £15,707 | 11.6 yrs | £11,302 |
| 7 kW | 7304 kWh | 5113 kWh | 2191 kWh | £1,356 | £219 | £1,576 | £17,742 | 11.3 yrs | £13,769 |
| 8 kW | 8347 kWh | 5843 kWh | 2504 kWh | £1,550 | £250 | £1,801 | £19,776 | 11.0 yrs | £16,236 |
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: £1,151, Upfront: £15,423, 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 | 2087 kWh | 1523 kWh | 563 kWh | £404 | £56 | £460 | £9,319 | 20.2 yrs | £-109 |
| 3 kW | 3130 kWh | 2285 kWh | 845 kWh | £606 | £85 | £691 | £11,354 | 16.4 yrs | £2,461 |
| 4 kW | 4174 kWh | 3047 kWh | 1127 kWh | £808 | £113 | £921 | £13,388 | 14.5 yrs | £5,032 |
| 5 kW | 5217 kWh | 3808 kWh | 1409 kWh | £1,010 | £141 | £1,151 | £15,423 | 13.4 yrs | £7,602 |
| 6 kW | 6260 kWh | 4570 kWh | 1690 kWh | £1,212 | £169 | £1,381 | £17,457 | 12.6 yrs | £10,173 |
| 7 kW | 7304 kWh | 5332 kWh | 1972 kWh | £1,415 | £197 | £1,612 | £19,492 | 12.1 yrs | £12,743 |
| 8 kW | 8347 kWh | 6094 kWh | 2254 kWh | £1,617 | £225 | £1,842 | £21,526 | 11.7 yrs | £15,314 |
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: £1,168, Upfront: £17,173, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2087 kWh | 1565 kWh | 522 kWh | £415 | £52 | £467 | £11,069 | 23.7 yrs | £-1,721 |
| 3 kW | 3130 kWh | 2348 kWh | 783 kWh | £623 | £78 | £701 | £13,104 | 18.7 yrs | £918 |
| 4 kW | 4174 kWh | 3130 kWh | 1043 kWh | £830 | £104 | £935 | £15,138 | 16.2 yrs | £3,558 |
| 5 kW | 5217 kWh | 3913 kWh | 1304 kWh | £1,038 | £130 | £1,168 | £17,173 | 14.7 yrs | £6,197 |
| 6 kW | 6260 kWh | 4695 kWh | 1565 kWh | £1,246 | £157 | £1,402 | £19,207 | 13.7 yrs | £8,837 |
| 7 kW | 7304 kWh | 5478 kWh | 1826 kWh | £1,453 | £183 | £1,636 | £21,242 | 13.0 yrs | £11,476 |
| 8 kW | 8347 kWh | 6260 kWh | 2087 kWh | £1,661 | £209 | £1,870 | £23,276 | 12.4 yrs | £14,116 |
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: £1,186, Upfront: £19,623, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2087 kWh | 1607 kWh | 480 kWh | £426 | £48 | £474 | £13,519 | 28.5 yrs | £-4,033 |
| 3 kW | 3130 kWh | 2410 kWh | 720 kWh | £639 | £72 | £711 | £15,554 | 21.9 yrs | £-1,325 |
| 4 kW | 4174 kWh | 3214 kWh | 960 kWh | £853 | £96 | £949 | £17,588 | 18.5 yrs | £1,384 |
| 5 kW | 5217 kWh | 4017 kWh | 1200 kWh | £1,066 | £120 | £1,186 | £19,623 | 16.5 yrs | £4,092 |
| 6 kW | 6260 kWh | 4821 kWh | 1440 kWh | £1,279 | £144 | £1,423 | £21,657 | 15.2 yrs | £6,801 |
| 7 kW | 7304 kWh | 5624 kWh | 1680 kWh | £1,492 | £168 | £1,660 | £23,692 | 14.3 yrs | £9,509 |
| 8 kW | 8347 kWh | 6427 kWh | 1920 kWh | £1,705 | £192 | £1,897 | £25,726 | 13.6 yrs | £12,217 |
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.