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 781 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £657, Upfront: £10,173, 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 | 1562 kWh | 625 kWh | 937 kWh | £169 | £94 | £263 | £4,069 | 15.5 yrs | £1,187 |
| 3 kW | 2343 kWh | 937 kWh | 1406 kWh | £254 | £141 | £394 | £6,104 | 15.5 yrs | £1,781 |
| 4 kW | 3124 kWh | 1250 kWh | 1874 kWh | £338 | £187 | £526 | £8,138 | 15.5 yrs | £2,374 |
| 5 kW | 3905 kWh | 1562 kWh | 2343 kWh | £423 | £234 | £657 | £10,173 | 15.5 yrs | £2,968 |
| 6 kW | 4686 kWh | 1874 kWh | 2812 kWh | £507 | £281 | £788 | £12,207 | 15.5 yrs | £3,561 |
| 7 kW | 5467 kWh | 2187 kWh | 3280 kWh | £592 | £328 | £920 | £14,242 | 15.5 yrs | £4,155 |
| 8 kW | 6248 kWh | 2499 kWh | 3749 kWh | £676 | £375 | £1,051 | £16,276 | 15.5 yrs | £4,748 |
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: £790, Upfront: £12,273, 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 | 1562 kWh | 937 kWh | 625 kWh | £254 | £62 | £316 | £6,169 | 19.5 yrs | £153 |
| 3 kW | 2343 kWh | 1406 kWh | 937 kWh | £380 | £94 | £474 | £8,204 | 17.3 yrs | £1,280 |
| 4 kW | 3124 kWh | 1874 kWh | 1250 kWh | £507 | £125 | £632 | £10,238 | 16.2 yrs | £2,406 |
| 5 kW | 3905 kWh | 2343 kWh | 1562 kWh | £634 | £156 | £790 | £12,273 | 15.5 yrs | £3,533 |
| 6 kW | 4686 kWh | 2812 kWh | 1874 kWh | £761 | £187 | £948 | £14,307 | 15.1 yrs | £4,659 |
| 7 kW | 5467 kWh | 3280 kWh | 2187 kWh | £888 | £219 | £1,106 | £16,342 | 14.8 yrs | £5,786 |
| 8 kW | 6248 kWh | 3749 kWh | 2499 kWh | £1,014 | £250 | £1,264 | £18,376 | 14.5 yrs | £6,912 |
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: £857, Upfront: £13,673, 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 | 1562 kWh | 1093 kWh | 469 kWh | £296 | £47 | £343 | £7,569 | 22.1 yrs | £-714 |
| 3 kW | 2343 kWh | 1640 kWh | 703 kWh | £444 | £70 | £514 | £9,604 | 18.7 yrs | £679 |
| 4 kW | 3124 kWh | 2187 kWh | 937 kWh | £592 | £94 | £686 | £11,638 | 17.0 yrs | £2,072 |
| 5 kW | 3905 kWh | 2734 kWh | 1172 kWh | £740 | £117 | £857 | £13,673 | 16.0 yrs | £3,465 |
| 6 kW | 4686 kWh | 3280 kWh | 1406 kWh | £888 | £141 | £1,028 | £15,707 | 15.3 yrs | £4,858 |
| 7 kW | 5467 kWh | 3827 kWh | 1640 kWh | £1,036 | £164 | £1,200 | £17,742 | 14.8 yrs | £6,251 |
| 8 kW | 6248 kWh | 4374 kWh | 1874 kWh | £1,184 | £187 | £1,371 | £19,776 | 14.4 yrs | £7,644 |
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: £877, Upfront: £15,423, 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 | 1562 kWh | 1140 kWh | 422 kWh | £309 | £42 | £351 | £9,319 | 26.6 yrs | £-2,304 |
| 3 kW | 2343 kWh | 1710 kWh | 633 kWh | £463 | £63 | £526 | £11,354 | 21.6 yrs | £-831 |
| 4 kW | 3124 kWh | 2281 kWh | 844 kWh | £617 | £84 | £701 | £13,388 | 19.1 yrs | £642 |
| 5 kW | 3905 kWh | 2851 kWh | 1054 kWh | £771 | £105 | £877 | £15,423 | 17.6 yrs | £2,115 |
| 6 kW | 4686 kWh | 3421 kWh | 1265 kWh | £926 | £127 | £1,052 | £17,457 | 16.6 yrs | £3,588 |
| 7 kW | 5467 kWh | 3991 kWh | 1476 kWh | £1,080 | £148 | £1,228 | £19,492 | 15.9 yrs | £5,061 |
| 8 kW | 6248 kWh | 4561 kWh | 1687 kWh | £1,234 | £169 | £1,403 | £21,526 | 15.3 yrs | £6,534 |
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: £890, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1562 kWh | 1172 kWh | 391 kWh | £317 | £39 | £356 | £11,069 | 31.1 yrs | £-3,947 |
| 3 kW | 2343 kWh | 1757 kWh | 586 kWh | £476 | £59 | £534 | £13,104 | 24.5 yrs | £-2,421 |
| 4 kW | 3124 kWh | 2343 kWh | 781 kWh | £634 | £78 | £712 | £15,138 | 21.3 yrs | £-895 |
| 5 kW | 3905 kWh | 2929 kWh | 976 kWh | £793 | £98 | £890 | £17,173 | 19.3 yrs | £631 |
| 6 kW | 4686 kWh | 3515 kWh | 1172 kWh | £951 | £117 | £1,068 | £19,207 | 18.0 yrs | £2,158 |
| 7 kW | 5467 kWh | 4100 kWh | 1367 kWh | £1,110 | £137 | £1,246 | £21,242 | 17.0 yrs | £3,684 |
| 8 kW | 6248 kWh | 4686 kWh | 1562 kWh | £1,268 | £156 | £1,424 | £23,276 | 16.3 yrs | £5,210 |
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: £904, Upfront: £19,623, Break-even: 21.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1562 kWh | 1203 kWh | 359 kWh | £325 | £36 | £361 | £13,519 | 37.4 yrs | £-6,291 |
| 3 kW | 2343 kWh | 1804 kWh | 539 kWh | £488 | £54 | £542 | £15,554 | 28.7 yrs | £-4,711 |
| 4 kW | 3124 kWh | 2406 kWh | 719 kWh | £651 | £72 | £723 | £17,588 | 24.3 yrs | £-3,132 |
| 5 kW | 3905 kWh | 3007 kWh | 898 kWh | £814 | £90 | £904 | £19,623 | 21.7 yrs | £-1,552 |
| 6 kW | 4686 kWh | 3608 kWh | 1078 kWh | £976 | £108 | £1,084 | £21,657 | 20.0 yrs | £27 |
| 7 kW | 5467 kWh | 4210 kWh | 1257 kWh | £1,139 | £126 | £1,265 | £23,692 | 18.7 yrs | £1,607 |
| 8 kW | 6248 kWh | 4811 kWh | 1437 kWh | £1,302 | £144 | £1,446 | £25,726 | 17.8 yrs | £3,186 |
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.