A typical roof here lands around 6.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 882 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £721, Upfront: £10,173, 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 | 1764 kWh | 706 kWh | 1059 kWh | £182 | £106 | £288 | £4,069 | 14.1 yrs | £1,695 |
| 3 kW | 2646 kWh | 1059 kWh | 1588 kWh | £274 | £159 | £432 | £6,104 | 14.1 yrs | £2,543 |
| 4 kW | 3529 kWh | 1411 kWh | 2117 kWh | £365 | £212 | £576 | £8,138 | 14.1 yrs | £3,391 |
| 5 kW | 4411 kWh | 1764 kWh | 2646 kWh | £456 | £265 | £721 | £10,173 | 14.1 yrs | £4,238 |
| 6 kW | 5293 kWh | 2117 kWh | 3176 kWh | £547 | £318 | £865 | £12,207 | 14.1 yrs | £5,086 |
| 7 kW | 6175 kWh | 2470 kWh | 3705 kWh | £638 | £371 | £1,009 | £14,242 | 14.1 yrs | £5,934 |
| 8 kW | 7057 kWh | 2823 kWh | 4234 kWh | £729 | £423 | £1,153 | £16,276 | 14.1 yrs | £6,781 |
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: £860, Upfront: £12,273, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1764 kWh | 1059 kWh | 706 kWh | £274 | £71 | £344 | £6,169 | 17.9 yrs | £713 |
| 3 kW | 2646 kWh | 1588 kWh | 1059 kWh | £410 | £106 | £516 | £8,204 | 15.9 yrs | £2,120 |
| 4 kW | 3529 kWh | 2117 kWh | 1411 kWh | £547 | £141 | £688 | £10,238 | 14.9 yrs | £3,526 |
| 5 kW | 4411 kWh | 2646 kWh | 1764 kWh | £684 | £176 | £860 | £12,273 | 14.3 yrs | £4,933 |
| 6 kW | 5293 kWh | 3176 kWh | 2117 kWh | £821 | £212 | £1,032 | £14,307 | 13.9 yrs | £6,340 |
| 7 kW | 6175 kWh | 3705 kWh | 2470 kWh | £957 | £247 | £1,204 | £16,342 | 13.6 yrs | £7,746 |
| 8 kW | 7057 kWh | 4234 kWh | 2823 kWh | £1,094 | £282 | £1,376 | £18,376 | 13.4 yrs | £9,153 |
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: £930, Upfront: £13,673, 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 | 1764 kWh | 1235 kWh | 529 kWh | £319 | £53 | £372 | £7,569 | 20.3 yrs | £-128 |
| 3 kW | 2646 kWh | 1853 kWh | 794 kWh | £479 | £79 | £558 | £9,604 | 17.2 yrs | £1,558 |
| 4 kW | 3529 kWh | 2470 kWh | 1059 kWh | £638 | £106 | £744 | £11,638 | 15.6 yrs | £3,244 |
| 5 kW | 4411 kWh | 3088 kWh | 1323 kWh | £798 | £132 | £930 | £13,673 | 14.7 yrs | £4,930 |
| 6 kW | 5293 kWh | 3705 kWh | 1588 kWh | £957 | £159 | £1,116 | £15,707 | 14.1 yrs | £6,617 |
| 7 kW | 6175 kWh | 4323 kWh | 1853 kWh | £1,117 | £185 | £1,302 | £17,742 | 13.6 yrs | £8,303 |
| 8 kW | 7057 kWh | 4940 kWh | 2117 kWh | £1,277 | £212 | £1,488 | £19,776 | 13.3 yrs | £9,989 |
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: £951, Upfront: £15,423, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1764 kWh | 1288 kWh | 476 kWh | £333 | £48 | £380 | £9,319 | 24.5 yrs | £-1,710 |
| 3 kW | 2646 kWh | 1932 kWh | 715 kWh | £499 | £71 | £571 | £11,354 | 19.9 yrs | £60 |
| 4 kW | 3529 kWh | 2576 kWh | 953 kWh | £666 | £95 | £761 | £13,388 | 17.6 yrs | £1,830 |
| 5 kW | 4411 kWh | 3220 kWh | 1191 kWh | £832 | £119 | £951 | £15,423 | 16.2 yrs | £3,600 |
| 6 kW | 5293 kWh | 3864 kWh | 1429 kWh | £998 | £143 | £1,141 | £17,457 | 15.3 yrs | £5,370 |
| 7 kW | 6175 kWh | 4508 kWh | 1667 kWh | £1,165 | £167 | £1,332 | £19,492 | 14.6 yrs | £7,139 |
| 8 kW | 7057 kWh | 5152 kWh | 1905 kWh | £1,331 | £191 | £1,522 | £21,526 | 14.1 yrs | £8,909 |
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: £965, Upfront: £17,173, Break-even: 17.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1764 kWh | 1323 kWh | 441 kWh | £342 | £44 | £386 | £11,069 | 28.7 yrs | £-3,348 |
| 3 kW | 2646 kWh | 1985 kWh | 662 kWh | £513 | £66 | £579 | £13,104 | 22.6 yrs | £-1,523 |
| 4 kW | 3529 kWh | 2646 kWh | 882 kWh | £684 | £88 | £772 | £15,138 | 19.6 yrs | £303 |
| 5 kW | 4411 kWh | 3308 kWh | 1103 kWh | £855 | £110 | £965 | £17,173 | 17.8 yrs | £2,129 |
| 6 kW | 5293 kWh | 3970 kWh | 1323 kWh | £1,026 | £132 | £1,158 | £19,207 | 16.6 yrs | £3,955 |
| 7 kW | 6175 kWh | 4631 kWh | 1544 kWh | £1,197 | £154 | £1,351 | £21,242 | 15.7 yrs | £5,781 |
| 8 kW | 7057 kWh | 5293 kWh | 1764 kWh | £1,368 | £176 | £1,544 | £23,276 | 15.1 yrs | £7,607 |
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: £979, Upfront: £19,623, Break-even: 20.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1764 kWh | 1359 kWh | 406 kWh | £351 | £41 | £392 | £13,519 | 34.5 yrs | £-5,687 |
| 3 kW | 2646 kWh | 2038 kWh | 609 kWh | £527 | £61 | £587 | £15,554 | 26.5 yrs | £-3,805 |
| 4 kW | 3529 kWh | 2717 kWh | 812 kWh | £702 | £81 | £783 | £17,588 | 22.5 yrs | £-1,923 |
| 5 kW | 4411 kWh | 3396 kWh | 1014 kWh | £878 | £101 | £979 | £19,623 | 20.0 yrs | £-41 |
| 6 kW | 5293 kWh | 4076 kWh | 1217 kWh | £1,053 | £122 | £1,175 | £21,657 | 18.4 yrs | £1,840 |
| 7 kW | 6175 kWh | 4755 kWh | 1420 kWh | £1,229 | £142 | £1,371 | £23,692 | 17.3 yrs | £3,722 |
| 8 kW | 7057 kWh | 5434 kWh | 1623 kWh | £1,404 | £162 | £1,566 | £25,726 | 16.4 yrs | £5,604 |
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.