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 881 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: £742, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1761 kWh | 704 kWh | 1057 kWh | £191 | £106 | £297 | £4,069 | 13.7 yrs | £1,864 |
| 3 kW | 2642 kWh | 1057 kWh | 1585 kWh | £286 | £159 | £445 | £6,104 | 13.7 yrs | £2,796 |
| 4 kW | 3522 kWh | 1409 kWh | 2113 kWh | £382 | £211 | £593 | £8,138 | 13.7 yrs | £3,728 |
| 5 kW | 4403 kWh | 1761 kWh | 2642 kWh | £477 | £264 | £742 | £10,173 | 13.7 yrs | £4,660 |
| 6 kW | 5284 kWh | 2113 kWh | 3170 kWh | £573 | £317 | £890 | £12,207 | 13.7 yrs | £5,592 |
| 7 kW | 6164 kWh | 2466 kWh | 3698 kWh | £668 | £370 | £1,038 | £14,242 | 13.7 yrs | £6,524 |
| 8 kW | 7045 kWh | 2818 kWh | 4227 kWh | £764 | £423 | £1,187 | £16,276 | 13.7 yrs | £7,456 |
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: £892, Upfront: £12,273, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1761 kWh | 1057 kWh | 704 kWh | £286 | £70 | £357 | £6,169 | 17.3 yrs | £969 |
| 3 kW | 2642 kWh | 1585 kWh | 1057 kWh | £430 | £106 | £535 | £8,204 | 15.3 yrs | £2,504 |
| 4 kW | 3522 kWh | 2113 kWh | 1409 kWh | £573 | £141 | £714 | £10,238 | 14.3 yrs | £4,039 |
| 5 kW | 4403 kWh | 2642 kWh | 1761 kWh | £716 | £176 | £892 | £12,273 | 13.8 yrs | £5,573 |
| 6 kW | 5284 kWh | 3170 kWh | 2113 kWh | £859 | £211 | £1,071 | £14,307 | 13.4 yrs | £7,108 |
| 7 kW | 6164 kWh | 3698 kWh | 2466 kWh | £1,003 | £247 | £1,249 | £16,342 | 13.1 yrs | £8,643 |
| 8 kW | 7045 kWh | 4227 kWh | 2818 kWh | £1,146 | £282 | £1,428 | £18,376 | 12.9 yrs | £10,178 |
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: £968, Upfront: £13,673, 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 | 1761 kWh | 1233 kWh | 528 kWh | £334 | £53 | £387 | £7,569 | 19.6 yrs | £172 |
| 3 kW | 2642 kWh | 1849 kWh | 793 kWh | £501 | £79 | £581 | £9,604 | 16.5 yrs | £2,008 |
| 4 kW | 3522 kWh | 2466 kWh | 1057 kWh | £668 | £106 | £774 | £11,638 | 15.0 yrs | £3,844 |
| 5 kW | 4403 kWh | 3082 kWh | 1321 kWh | £836 | £132 | £968 | £13,673 | 14.1 yrs | £5,680 |
| 6 kW | 5284 kWh | 3698 kWh | 1585 kWh | £1,003 | £159 | £1,161 | £15,707 | 13.5 yrs | £7,516 |
| 7 kW | 6164 kWh | 4315 kWh | 1849 kWh | £1,170 | £185 | £1,355 | £17,742 | 13.1 yrs | £9,352 |
| 8 kW | 7045 kWh | 4931 kWh | 2113 kWh | £1,337 | £211 | £1,548 | £19,776 | 12.8 yrs | £11,188 |
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: £990, Upfront: £15,423, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1761 kWh | 1286 kWh | 476 kWh | £349 | £48 | £396 | £9,319 | 23.5 yrs | £-1,397 |
| 3 kW | 2642 kWh | 1928 kWh | 713 kWh | £523 | £71 | £594 | £11,354 | 19.1 yrs | £529 |
| 4 kW | 3522 kWh | 2571 kWh | 951 kWh | £697 | £95 | £792 | £13,388 | 16.9 yrs | £2,456 |
| 5 kW | 4403 kWh | 3214 kWh | 1189 kWh | £871 | £119 | £990 | £15,423 | 15.6 yrs | £4,382 |
| 6 kW | 5284 kWh | 3857 kWh | 1427 kWh | £1,046 | £143 | £1,188 | £17,457 | 14.7 yrs | £6,309 |
| 7 kW | 6164 kWh | 4500 kWh | 1664 kWh | £1,220 | £166 | £1,386 | £19,492 | 14.1 yrs | £8,235 |
| 8 kW | 7045 kWh | 5143 kWh | 1902 kWh | £1,394 | £190 | £1,584 | £21,526 | 13.6 yrs | £10,161 |
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: £1,005, Upfront: £17,173, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1761 kWh | 1321 kWh | 440 kWh | £358 | £44 | £402 | £11,069 | 27.5 yrs | £-3,027 |
| 3 kW | 2642 kWh | 1981 kWh | 660 kWh | £537 | £66 | £603 | £13,104 | 21.7 yrs | £-1,040 |
| 4 kW | 3522 kWh | 2642 kWh | 881 kWh | £716 | £88 | £804 | £15,138 | 18.8 yrs | £947 |
| 5 kW | 4403 kWh | 3302 kWh | 1101 kWh | £895 | £110 | £1,005 | £17,173 | 17.1 yrs | £2,934 |
| 6 kW | 5284 kWh | 3963 kWh | 1321 kWh | £1,074 | £132 | £1,206 | £19,207 | 15.9 yrs | £4,920 |
| 7 kW | 6164 kWh | 4623 kWh | 1541 kWh | £1,253 | £154 | £1,407 | £21,242 | 15.1 yrs | £6,907 |
| 8 kW | 7045 kWh | 5284 kWh | 1761 kWh | £1,432 | £176 | £1,608 | £23,276 | 14.5 yrs | £8,894 |
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: £1,020, Upfront: £19,623, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1761 kWh | 1356 kWh | 405 kWh | £368 | £41 | £408 | £13,519 | 33.1 yrs | £-5,356 |
| 3 kW | 2642 kWh | 2034 kWh | 608 kWh | £551 | £61 | £612 | £15,554 | 25.4 yrs | £-3,309 |
| 4 kW | 3522 kWh | 2712 kWh | 810 kWh | £735 | £81 | £816 | £17,588 | 21.5 yrs | £-1,262 |
| 5 kW | 4403 kWh | 3390 kWh | 1013 kWh | £919 | £101 | £1,020 | £19,623 | 19.2 yrs | £785 |
| 6 kW | 5284 kWh | 4068 kWh | 1215 kWh | £1,103 | £122 | £1,224 | £21,657 | 17.7 yrs | £2,832 |
| 7 kW | 6164 kWh | 4746 kWh | 1418 kWh | £1,287 | £142 | £1,429 | £23,692 | 16.6 yrs | £4,879 |
| 8 kW | 7045 kWh | 5424 kWh | 1620 kWh | £1,471 | £162 | £1,633 | £25,726 | 15.8 yrs | £6,926 |
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.