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 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 | £2,045 |
| 3 kW | 2836 kWh | 1134 kWh | 1701 kWh | £288 | £170 | £459 | £6,104 | 13.3 yrs | £3,068 |
| 4 kW | 3781 kWh | 1512 kWh | 2269 kWh | £385 | £227 | £611 | £8,138 | 13.3 yrs | £4,091 |
| 5 kW | 4726 kWh | 1890 kWh | 2836 kWh | £481 | £284 | £764 | £10,173 | 13.3 yrs | £5,113 |
| 6 kW | 5671 kWh | 2269 kWh | 3403 kWh | £577 | £340 | £917 | £12,207 | 13.3 yrs | £6,136 |
| 7 kW | 6616 kWh | 2647 kWh | 3970 kWh | £673 | £397 | £1,070 | £14,242 | 13.3 yrs | £7,159 |
| 8 kW | 7562 kWh | 3025 kWh | 4537 kWh | £769 | £454 | £1,223 | £16,276 | 13.3 yrs | £8,181 |
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 | 16.9 yrs | £1,112 |
| 3 kW | 2836 kWh | 1701 kWh | 1134 kWh | £433 | £113 | £546 | £8,204 | 15.0 yrs | £2,718 |
| 4 kW | 3781 kWh | 2269 kWh | 1512 kWh | £577 | £151 | £728 | £10,238 | 14.1 yrs | £4,324 |
| 5 kW | 4726 kWh | 2836 kWh | 1890 kWh | £721 | £189 | £910 | £12,273 | 13.5 yrs | £5,930 |
| 6 kW | 5671 kWh | 3403 kWh | 2269 kWh | £865 | £227 | £1,092 | £14,307 | 13.1 yrs | £7,536 |
| 7 kW | 6616 kWh | 3970 kWh | 2647 kWh | £1,010 | £265 | £1,274 | £16,342 | 12.8 yrs | £9,142 |
| 8 kW | 7562 kWh | 4537 kWh | 3025 kWh | £1,154 | £302 | £1,456 | £18,376 | 12.6 yrs | £10,748 |
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 | £337 | £57 | £393 | £7,569 | 19.2 yrs | £296 |
| 3 kW | 2836 kWh | 1985 kWh | 851 kWh | £505 | £85 | £590 | £9,604 | 16.3 yrs | £2,193 |
| 4 kW | 3781 kWh | 2647 kWh | 1134 kWh | £673 | £113 | £786 | £11,638 | 14.8 yrs | £4,091 |
| 5 kW | 4726 kWh | 3308 kWh | 1418 kWh | £841 | £142 | £983 | £13,673 | 13.9 yrs | £5,989 |
| 6 kW | 5671 kWh | 3970 kWh | 1701 kWh | £1,010 | £170 | £1,180 | £15,707 | 13.3 yrs | £7,887 |
| 7 kW | 6616 kWh | 4632 kWh | 1985 kWh | £1,178 | £198 | £1,376 | £17,742 | 12.9 yrs | £9,784 |
| 8 kW | 7562 kWh | 5293 kWh | 2269 kWh | £1,346 | £227 | £1,573 | £19,776 | 12.6 yrs | £11,682 |
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: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1890 kWh | 1380 kWh | 510 kWh | £351 | £51 | £402 | £9,319 | 23.2 yrs | £-1,279 |
| 3 kW | 2836 kWh | 2070 kWh | 766 kWh | £526 | £77 | £603 | £11,354 | 18.8 yrs | £706 |
| 4 kW | 3781 kWh | 2760 kWh | 1021 kWh | £702 | £102 | £804 | £13,388 | 16.7 yrs | £2,691 |
| 5 kW | 4726 kWh | 3450 kWh | 1276 kWh | £877 | £128 | £1,005 | £15,423 | 15.3 yrs | £4,676 |
| 6 kW | 5671 kWh | 4140 kWh | 1531 kWh | £1,053 | £153 | £1,206 | £17,457 | 14.5 yrs | £6,662 |
| 7 kW | 6616 kWh | 4830 kWh | 1786 kWh | £1,228 | £179 | £1,407 | £19,492 | 13.9 yrs | £8,647 |
| 8 kW | 7562 kWh | 5520 kWh | 2042 kWh | £1,404 | £204 | £1,608 | £21,526 | 13.4 yrs | £10,632 |
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: £1,020, 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 | 1418 kWh | 473 kWh | £361 | £47 | £408 | £11,069 | 27.1 yrs | £-2,913 |
| 3 kW | 2836 kWh | 2127 kWh | 709 kWh | £541 | £71 | £612 | £13,104 | 21.4 yrs | £-869 |
| 4 kW | 3781 kWh | 2836 kWh | 945 kWh | £721 | £95 | £816 | £15,138 | 18.6 yrs | £1,174 |
| 5 kW | 4726 kWh | 3545 kWh | 1182 kWh | £901 | £118 | £1,020 | £17,173 | 16.8 yrs | £3,218 |
| 6 kW | 5671 kWh | 4253 kWh | 1418 kWh | £1,082 | £142 | £1,223 | £19,207 | 15.7 yrs | £5,262 |
| 7 kW | 6616 kWh | 4962 kWh | 1654 kWh | £1,262 | £165 | £1,427 | £21,242 | 14.9 yrs | £7,305 |
| 8 kW | 7562 kWh | 5671 kWh | 1890 kWh | £1,442 | £189 | £1,631 | £23,276 | 14.3 yrs | £9,349 |
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 | 1456 kWh | 435 kWh | £370 | £43 | £414 | £13,519 | 32.7 yrs | £-5,246 |
| 3 kW | 2836 kWh | 2183 kWh | 652 kWh | £555 | £65 | £620 | £15,554 | 25.1 yrs | £-3,144 |
| 4 kW | 3781 kWh | 2911 kWh | 870 kWh | £740 | £87 | £827 | £17,588 | 21.3 yrs | £-1,042 |
| 5 kW | 4726 kWh | 3639 kWh | 1087 kWh | £925 | £109 | £1,034 | £19,623 | 19.0 yrs | £1,060 |
| 6 kW | 5671 kWh | 4367 kWh | 1304 kWh | £1,110 | £130 | £1,241 | £21,657 | 17.5 yrs | £3,162 |
| 7 kW | 6616 kWh | 5095 kWh | 1522 kWh | £1,296 | £152 | £1,448 | £23,692 | 16.4 yrs | £5,264 |
| 8 kW | 7562 kWh | 5822 kWh | 1739 kWh | £1,481 | £174 | £1,655 | £25,726 | 15.5 yrs | £7,365 |
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.