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 907 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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 | 1814 kWh | 726 kWh | 1089 kWh | £184 | £109 | £293 | £4,069 | 13.9 yrs | £1,785 |
| 3 kW | 2722 kWh | 1089 kWh | 1633 kWh | £276 | £163 | £439 | £6,104 | 13.9 yrs | £2,677 |
| 4 kW | 3629 kWh | 1451 kWh | 2177 kWh | £368 | £218 | £585 | £8,138 | 13.9 yrs | £3,570 |
| 5 kW | 4536 kWh | 1814 kWh | 2722 kWh | £460 | £272 | £732 | £10,173 | 13.9 yrs | £4,462 |
| 6 kW | 5443 kWh | 2177 kWh | 3266 kWh | £551 | £327 | £878 | £12,207 | 13.9 yrs | £5,354 |
| 7 kW | 6350 kWh | 2540 kWh | 3810 kWh | £643 | £381 | £1,024 | £14,242 | 13.9 yrs | £6,247 |
| 8 kW | 7257 kWh | 2903 kWh | 4354 kWh | £735 | £435 | £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: £871, 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 | 1814 kWh | 1089 kWh | 726 kWh | £276 | £73 | £348 | £6,169 | 17.7 yrs | £797 |
| 3 kW | 2722 kWh | 1633 kWh | 1089 kWh | £414 | £109 | £522 | £8,204 | 15.7 yrs | £2,246 |
| 4 kW | 3629 kWh | 2177 kWh | 1451 kWh | £551 | £145 | £697 | £10,238 | 14.7 yrs | £3,695 |
| 5 kW | 4536 kWh | 2722 kWh | 1814 kWh | £689 | £181 | £871 | £12,273 | 14.1 yrs | £5,143 |
| 6 kW | 5443 kWh | 3266 kWh | 2177 kWh | £827 | £218 | £1,045 | £14,307 | 13.7 yrs | £6,592 |
| 7 kW | 6350 kWh | 3810 kWh | 2540 kWh | £965 | £254 | £1,219 | £16,342 | 13.4 yrs | £8,041 |
| 8 kW | 7257 kWh | 4354 kWh | 2903 kWh | £1,103 | £290 | £1,393 | £18,376 | 13.2 yrs | £9,490 |
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: £940, 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 | 1814 kWh | 1270 kWh | 544 kWh | £322 | £54 | £376 | £7,569 | 20.1 yrs | £-46 |
| 3 kW | 2722 kWh | 1905 kWh | 816 kWh | £483 | £82 | £564 | £9,604 | 17.0 yrs | £1,681 |
| 4 kW | 3629 kWh | 2540 kWh | 1089 kWh | £643 | £109 | £752 | £11,638 | 15.5 yrs | £3,407 |
| 5 kW | 4536 kWh | 3175 kWh | 1361 kWh | £804 | £136 | £940 | £13,673 | 14.5 yrs | £5,134 |
| 6 kW | 5443 kWh | 3810 kWh | 1633 kWh | £965 | £163 | £1,128 | £15,707 | 13.9 yrs | £6,861 |
| 7 kW | 6350 kWh | 4445 kWh | 1905 kWh | £1,126 | £191 | £1,316 | £17,742 | 13.5 yrs | £8,588 |
| 8 kW | 7257 kWh | 5080 kWh | 2177 kWh | £1,287 | £218 | £1,505 | £19,776 | 13.1 yrs | £10,315 |
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: £961, 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 | 1814 kWh | 1324 kWh | 490 kWh | £335 | £49 | £384 | £9,319 | 24.2 yrs | £-1,629 |
| 3 kW | 2722 kWh | 1987 kWh | 735 kWh | £503 | £73 | £577 | £11,354 | 19.7 yrs | £181 |
| 4 kW | 3629 kWh | 2649 kWh | 980 kWh | £671 | £98 | £769 | £13,388 | 17.4 yrs | £1,991 |
| 5 kW | 4536 kWh | 3311 kWh | 1225 kWh | £839 | £122 | £961 | £15,423 | 16.0 yrs | £3,801 |
| 6 kW | 5443 kWh | 3973 kWh | 1470 kWh | £1,006 | £147 | £1,153 | £17,457 | 15.1 yrs | £5,612 |
| 7 kW | 6350 kWh | 4636 kWh | 1715 kWh | £1,174 | £171 | £1,346 | £19,492 | 14.5 yrs | £7,422 |
| 8 kW | 7257 kWh | 5298 kWh | 1960 kWh | £1,342 | £196 | £1,538 | £21,526 | 14.0 yrs | £9,232 |
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: £975, 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 | 1814 kWh | 1361 kWh | 454 kWh | £345 | £45 | £390 | £11,069 | 28.4 yrs | £-3,268 |
| 3 kW | 2722 kWh | 2041 kWh | 680 kWh | £517 | £68 | £585 | £13,104 | 22.4 yrs | £-1,402 |
| 4 kW | 3629 kWh | 2722 kWh | 907 kWh | £689 | £91 | £780 | £15,138 | 19.4 yrs | £464 |
| 5 kW | 4536 kWh | 3402 kWh | 1134 kWh | £862 | £113 | £975 | £17,173 | 17.6 yrs | £2,330 |
| 6 kW | 5443 kWh | 4082 kWh | 1361 kWh | £1,034 | £136 | £1,170 | £19,207 | 16.4 yrs | £4,195 |
| 7 kW | 6350 kWh | 4763 kWh | 1588 kWh | £1,206 | £159 | £1,365 | £21,242 | 15.6 yrs | £6,061 |
| 8 kW | 7257 kWh | 5443 kWh | 1814 kWh | £1,379 | £181 | £1,560 | £23,276 | 14.9 yrs | £7,927 |
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: £989, 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 | 1814 kWh | 1397 kWh | 417 kWh | £354 | £42 | £396 | £13,519 | 34.2 yrs | £-5,607 |
| 3 kW | 2722 kWh | 2096 kWh | 626 kWh | £531 | £63 | £593 | £15,554 | 26.2 yrs | £-3,685 |
| 4 kW | 3629 kWh | 2794 kWh | 835 kWh | £708 | £83 | £791 | £17,588 | 22.2 yrs | £-1,764 |
| 5 kW | 4536 kWh | 3493 kWh | 1043 kWh | £885 | £104 | £989 | £19,623 | 19.8 yrs | £158 |
| 6 kW | 5443 kWh | 4191 kWh | 1252 kWh | £1,062 | £125 | £1,187 | £21,657 | 18.2 yrs | £2,079 |
| 7 kW | 6350 kWh | 4890 kWh | 1461 kWh | £1,239 | £146 | £1,385 | £23,692 | 17.1 yrs | £4,001 |
| 8 kW | 7257 kWh | 5588 kWh | 1669 kWh | £1,415 | £167 | £1,582 | £25,726 | 16.3 yrs | £5,922 |
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.