A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 900 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £732, Upfront: £10,173, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1800 kWh | 720 kWh | 1080 kWh | £185 | £108 | £293 | £4,069 | 13.9 yrs | £1,785 |
| 3 kW | 2701 kWh | 1080 kWh | 1620 kWh | £277 | £162 | £439 | £6,104 | 13.9 yrs | £2,677 |
| 4 kW | 3601 kWh | 1440 kWh | 2161 kWh | £369 | £216 | £585 | £8,138 | 13.9 yrs | £3,569 |
| 5 kW | 4501 kWh | 1800 kWh | 2701 kWh | £462 | £270 | £732 | £10,173 | 13.9 yrs | £4,462 |
| 6 kW | 5401 kWh | 2161 kWh | 3241 kWh | £554 | £324 | £878 | £12,207 | 13.9 yrs | £5,354 |
| 7 kW | 6302 kWh | 2521 kWh | 3781 kWh | £646 | £378 | £1,024 | £14,242 | 13.9 yrs | £6,246 |
| 8 kW | 7202 kWh | 2881 kWh | 4321 kWh | £739 | £432 | £1,171 | £16,276 | 13.9 yrs | £7,139 |
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: £873, Upfront: £12,273, 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 | 1800 kWh | 1080 kWh | 720 kWh | £277 | £72 | £349 | £6,169 | 17.7 yrs | £811 |
| 3 kW | 2701 kWh | 1620 kWh | 1080 kWh | £415 | £108 | £524 | £8,204 | 15.7 yrs | £2,267 |
| 4 kW | 3601 kWh | 2161 kWh | 1440 kWh | £554 | £144 | £698 | £10,238 | 14.7 yrs | £3,722 |
| 5 kW | 4501 kWh | 2701 kWh | 1800 kWh | £692 | £180 | £873 | £12,273 | 14.1 yrs | £5,178 |
| 6 kW | 5401 kWh | 3241 kWh | 2161 kWh | £831 | £216 | £1,047 | £14,307 | 13.7 yrs | £6,633 |
| 7 kW | 6302 kWh | 3781 kWh | 2521 kWh | £969 | £252 | £1,222 | £16,342 | 13.4 yrs | £8,089 |
| 8 kW | 7202 kWh | 4321 kWh | 2881 kWh | £1,108 | £288 | £1,396 | £18,376 | 13.2 yrs | £9,544 |
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: £943, Upfront: £13,673, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1800 kWh | 1260 kWh | 540 kWh | £323 | £54 | £377 | £7,569 | 20.1 yrs | £-26 |
| 3 kW | 2701 kWh | 1890 kWh | 810 kWh | £485 | £81 | £566 | £9,604 | 17.0 yrs | £1,711 |
| 4 kW | 3601 kWh | 2521 kWh | 1080 kWh | £646 | £108 | £754 | £11,638 | 15.4 yrs | £3,448 |
| 5 kW | 4501 kWh | 3151 kWh | 1350 kWh | £808 | £135 | £943 | £13,673 | 14.5 yrs | £5,185 |
| 6 kW | 5401 kWh | 3781 kWh | 1620 kWh | £969 | £162 | £1,131 | £15,707 | 13.9 yrs | £6,923 |
| 7 kW | 6302 kWh | 4411 kWh | 1890 kWh | £1,131 | £189 | £1,320 | £17,742 | 13.4 yrs | £8,660 |
| 8 kW | 7202 kWh | 5041 kWh | 2161 kWh | £1,293 | £216 | £1,509 | £19,776 | 13.1 yrs | £10,397 |
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: £964, Upfront: £15,423, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1800 kWh | 1314 kWh | 486 kWh | £337 | £49 | £386 | £9,319 | 24.2 yrs | £-1,607 |
| 3 kW | 2701 kWh | 1972 kWh | 729 kWh | £505 | £73 | £578 | £11,354 | 19.6 yrs | £215 |
| 4 kW | 3601 kWh | 2629 kWh | 972 kWh | £674 | £97 | £771 | £13,388 | 17.4 yrs | £2,036 |
| 5 kW | 4501 kWh | 3286 kWh | 1215 kWh | £842 | £122 | £964 | £15,423 | 16.0 yrs | £3,858 |
| 6 kW | 5401 kWh | 3943 kWh | 1458 kWh | £1,011 | £146 | £1,157 | £17,457 | 15.1 yrs | £5,679 |
| 7 kW | 6302 kWh | 4600 kWh | 1701 kWh | £1,179 | £170 | £1,350 | £19,492 | 14.4 yrs | £7,501 |
| 8 kW | 7202 kWh | 5257 kWh | 1944 kWh | £1,348 | £194 | £1,542 | £21,526 | 14.0 yrs | £9,323 |
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: £978, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1800 kWh | 1350 kWh | 450 kWh | £346 | £45 | £391 | £11,069 | 28.3 yrs | £-3,244 |
| 3 kW | 2701 kWh | 2026 kWh | 675 kWh | £519 | £68 | £587 | £13,104 | 22.3 yrs | £-1,366 |
| 4 kW | 3601 kWh | 2701 kWh | 900 kWh | £692 | £90 | £782 | £15,138 | 19.3 yrs | £512 |
| 5 kW | 4501 kWh | 3376 kWh | 1125 kWh | £866 | £113 | £978 | £17,173 | 17.6 yrs | £2,389 |
| 6 kW | 5401 kWh | 4051 kWh | 1350 kWh | £1,039 | £135 | £1,174 | £19,207 | 16.4 yrs | £4,267 |
| 7 kW | 6302 kWh | 4726 kWh | 1575 kWh | £1,212 | £158 | £1,369 | £21,242 | 15.5 yrs | £6,145 |
| 8 kW | 7202 kWh | 5401 kWh | 1800 kWh | £1,385 | £180 | £1,565 | £23,276 | 14.9 yrs | £8,023 |
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: £992, Upfront: £19,623, Break-even: 19.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1800 kWh | 1386 kWh | 414 kWh | £355 | £41 | £397 | £13,519 | 34.1 yrs | £-5,582 |
| 3 kW | 2701 kWh | 2080 kWh | 621 kWh | £533 | £62 | £595 | £15,554 | 26.1 yrs | £-3,647 |
| 4 kW | 3601 kWh | 2773 kWh | 828 kWh | £711 | £83 | £794 | £17,588 | 22.2 yrs | £-1,713 |
| 5 kW | 4501 kWh | 3466 kWh | 1035 kWh | £889 | £104 | £992 | £19,623 | 19.8 yrs | £221 |
| 6 kW | 5401 kWh | 4159 kWh | 1242 kWh | £1,066 | £124 | £1,191 | £21,657 | 18.2 yrs | £2,155 |
| 7 kW | 6302 kWh | 4852 kWh | 1449 kWh | £1,244 | £145 | £1,389 | £23,692 | 17.1 yrs | £4,089 |
| 8 kW | 7202 kWh | 5545 kWh | 1656 kWh | £1,422 | £166 | £1,587 | £25,726 | 16.2 yrs | £6,024 |
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.