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 945 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £764, Upfront: £10,173, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1890 kWh | 756 kWh | 1134 kWh | £192 | £113 | £306 | £4,069 | 13.3 yrs | £2,044 |
| 3 kW | 2835 kWh | 1134 kWh | 1701 kWh | £288 | £170 | £458 | £6,104 | 13.3 yrs | £3,065 |
| 4 kW | 3780 kWh | 1512 kWh | 2268 kWh | £384 | £227 | £611 | £8,138 | 13.3 yrs | £4,087 |
| 5 kW | 4725 kWh | 1890 kWh | 2835 kWh | £481 | £283 | £764 | £10,173 | 13.3 yrs | £5,109 |
| 6 kW | 5670 kWh | 2268 kWh | 3402 kWh | £577 | £340 | £917 | £12,207 | 13.3 yrs | £6,131 |
| 7 kW | 6615 kWh | 2646 kWh | 3969 kWh | £673 | £397 | £1,070 | £14,242 | 13.3 yrs | £7,152 |
| 8 kW | 7559 kWh | 3024 kWh | 4536 kWh | £769 | £454 | £1,223 | £16,276 | 13.3 yrs | £8,174 |
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: £910, Upfront: £12,273, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1890 kWh | 1134 kWh | 756 kWh | £288 | £76 | £364 | £6,169 | 17.0 yrs | £1,110 |
| 3 kW | 2835 kWh | 1701 kWh | 1134 kWh | £433 | £113 | £546 | £8,204 | 15.0 yrs | £2,715 |
| 4 kW | 3780 kWh | 2268 kWh | 1512 kWh | £577 | £151 | £728 | £10,238 | 14.1 yrs | £4,320 |
| 5 kW | 4725 kWh | 2835 kWh | 1890 kWh | £721 | £189 | £910 | £12,273 | 13.5 yrs | £5,925 |
| 6 kW | 5670 kWh | 3402 kWh | 2268 kWh | £865 | £227 | £1,092 | £14,307 | 13.1 yrs | £7,530 |
| 7 kW | 6615 kWh | 3969 kWh | 2646 kWh | £1,009 | £265 | £1,274 | £16,342 | 12.8 yrs | £9,135 |
| 8 kW | 7559 kWh | 4536 kWh | 3024 kWh | £1,153 | £302 | £1,456 | £18,376 | 12.6 yrs | £10,740 |
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: £983, Upfront: £13,673, 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 | 1890 kWh | 1323 kWh | 567 kWh | £336 | £57 | £393 | £7,569 | 19.3 yrs | £293 |
| 3 kW | 2835 kWh | 1984 kWh | 850 kWh | £505 | £85 | £590 | £9,604 | 16.3 yrs | £2,190 |
| 4 kW | 3780 kWh | 2646 kWh | 1134 kWh | £673 | £113 | £786 | £11,638 | 14.8 yrs | £4,086 |
| 5 kW | 4725 kWh | 3307 kWh | 1417 kWh | £841 | £142 | £983 | £13,673 | 13.9 yrs | £5,983 |
| 6 kW | 5670 kWh | 3969 kWh | 1701 kWh | £1,009 | £170 | £1,179 | £15,707 | 13.3 yrs | £7,880 |
| 7 kW | 6615 kWh | 4630 kWh | 1984 kWh | £1,177 | £198 | £1,376 | £17,742 | 12.9 yrs | £9,776 |
| 8 kW | 7559 kWh | 5292 kWh | 2268 kWh | £1,346 | £227 | £1,572 | £19,776 | 12.6 yrs | £11,673 |
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: £1,005, Upfront: £15,423, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1890 kWh | 1380 kWh | 510 kWh | £351 | £51 | £402 | £9,319 | 23.2 yrs | £-1,282 |
| 3 kW | 2835 kWh | 2069 kWh | 765 kWh | £526 | £77 | £603 | £11,354 | 18.8 yrs | £702 |
| 4 kW | 3780 kWh | 2759 kWh | 1021 kWh | £702 | £102 | £804 | £13,388 | 16.7 yrs | £2,686 |
| 5 kW | 4725 kWh | 3449 kWh | 1276 kWh | £877 | £128 | £1,005 | £15,423 | 15.4 yrs | £4,670 |
| 6 kW | 5670 kWh | 4139 kWh | 1531 kWh | £1,052 | £153 | £1,206 | £17,457 | 14.5 yrs | £6,654 |
| 7 kW | 6615 kWh | 4829 kWh | 1786 kWh | £1,228 | £179 | £1,407 | £19,492 | 13.9 yrs | £8,638 |
| 8 kW | 7559 kWh | 5518 kWh | 2041 kWh | £1,403 | £204 | £1,607 | £21,526 | 13.4 yrs | £10,623 |
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: £1,019, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1890 kWh | 1417 kWh | 472 kWh | £360 | £47 | £408 | £11,069 | 27.2 yrs | £-2,915 |
| 3 kW | 2835 kWh | 2126 kWh | 709 kWh | £541 | £71 | £612 | £13,104 | 21.4 yrs | £-873 |
| 4 kW | 3780 kWh | 2835 kWh | 945 kWh | £721 | £94 | £815 | £15,138 | 18.6 yrs | £1,170 |
| 5 kW | 4725 kWh | 3543 kWh | 1181 kWh | £901 | £118 | £1,019 | £17,173 | 16.8 yrs | £3,212 |
| 6 kW | 5670 kWh | 4252 kWh | 1417 kWh | £1,081 | £142 | £1,223 | £19,207 | 15.7 yrs | £5,254 |
| 7 kW | 6615 kWh | 4961 kWh | 1654 kWh | £1,262 | £165 | £1,427 | £21,242 | 14.9 yrs | £7,297 |
| 8 kW | 7559 kWh | 5670 kWh | 1890 kWh | £1,442 | £189 | £1,631 | £23,276 | 14.3 yrs | £9,339 |
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: £1,034, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1890 kWh | 1455 kWh | 435 kWh | £370 | £43 | £414 | £13,519 | 32.7 yrs | £-5,249 |
| 3 kW | 2835 kWh | 2183 kWh | 652 kWh | £555 | £65 | £620 | £15,554 | 25.1 yrs | £-3,148 |
| 4 kW | 3780 kWh | 2910 kWh | 869 kWh | £740 | £87 | £827 | £17,588 | 21.3 yrs | £-1,047 |
| 5 kW | 4725 kWh | 3638 kWh | 1087 kWh | £925 | £109 | £1,034 | £19,623 | 19.0 yrs | £1,054 |
| 6 kW | 5670 kWh | 4366 kWh | 1304 kWh | £1,110 | £130 | £1,241 | £21,657 | 17.5 yrs | £3,154 |
| 7 kW | 6615 kWh | 5093 kWh | 1521 kWh | £1,295 | £152 | £1,447 | £23,692 | 16.4 yrs | £5,255 |
| 8 kW | 7559 kWh | 5821 kWh | 1739 kWh | £1,480 | £174 | £1,654 | £25,726 | 15.6 yrs | £7,356 |
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.