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 1062 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £882, Upfront: £10,173, Break-even: 11.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2124 kWh | 850 kWh | 1275 kWh | £225 | £127 | £353 | £4,069 | 11.5 yrs | £2,988 |
| 3 kW | 3186 kWh | 1275 kWh | 1912 kWh | £338 | £191 | £529 | £6,104 | 11.5 yrs | £4,483 |
| 4 kW | 4248 kWh | 1699 kWh | 2549 kWh | £451 | £255 | £706 | £8,138 | 11.5 yrs | £5,977 |
| 5 kW | 5310 kWh | 2124 kWh | 3186 kWh | £564 | £319 | £882 | £10,173 | 11.5 yrs | £7,471 |
| 6 kW | 6373 kWh | 2549 kWh | 3824 kWh | £676 | £382 | £1,059 | £12,207 | 11.5 yrs | £8,965 |
| 7 kW | 7435 kWh | 2974 kWh | 4461 kWh | £789 | £446 | £1,235 | £14,242 | 11.5 yrs | £10,459 |
| 8 kW | 8497 kWh | 3399 kWh | 5098 kWh | £902 | £510 | £1,411 | £16,276 | 11.5 yrs | £11,954 |
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: £1,058, Upfront: £12,273, Break-even: 11.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2124 kWh | 1275 kWh | 850 kWh | £338 | £85 | £423 | £6,169 | 14.6 yrs | £2,293 |
| 3 kW | 3186 kWh | 1912 kWh | 1275 kWh | £507 | £127 | £635 | £8,204 | 12.9 yrs | £4,489 |
| 4 kW | 4248 kWh | 2549 kWh | 1699 kWh | £676 | £170 | £846 | £10,238 | 12.1 yrs | £6,686 |
| 5 kW | 5310 kWh | 3186 kWh | 2124 kWh | £845 | £212 | £1,058 | £12,273 | 11.6 yrs | £8,882 |
| 6 kW | 6373 kWh | 3824 kWh | 2549 kWh | £1,014 | £255 | £1,269 | £14,307 | 11.3 yrs | £11,079 |
| 7 kW | 7435 kWh | 4461 kWh | 2974 kWh | £1,183 | £297 | £1,481 | £16,342 | 11.0 yrs | £13,275 |
| 8 kW | 8497 kWh | 5098 kWh | 3399 kWh | £1,353 | £340 | £1,692 | £18,376 | 10.9 yrs | £15,472 |
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: £1,146, Upfront: £13,673, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2124 kWh | 1487 kWh | 637 kWh | £394 | £64 | £458 | £7,569 | 16.5 yrs | £1,595 |
| 3 kW | 3186 kWh | 2230 kWh | 956 kWh | £592 | £96 | £687 | £9,604 | 14.0 yrs | £4,143 |
| 4 kW | 4248 kWh | 2974 kWh | 1275 kWh | £789 | £127 | £916 | £11,638 | 12.7 yrs | £6,690 |
| 5 kW | 5310 kWh | 3717 kWh | 1593 kWh | £986 | £159 | £1,146 | £13,673 | 11.9 yrs | £9,238 |
| 6 kW | 6373 kWh | 4461 kWh | 1912 kWh | £1,183 | £191 | £1,375 | £15,707 | 11.4 yrs | £11,786 |
| 7 kW | 7435 kWh | 5204 kWh | 2230 kWh | £1,381 | £223 | £1,604 | £17,742 | 11.1 yrs | £14,333 |
| 8 kW | 8497 kWh | 5948 kWh | 2549 kWh | £1,578 | £255 | £1,833 | £19,776 | 10.8 yrs | £16,881 |
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: £1,172, Upfront: £15,423, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2124 kWh | 1551 kWh | 574 kWh | £411 | £57 | £469 | £9,319 | 19.9 yrs | £56 |
| 3 kW | 3186 kWh | 2326 kWh | 860 kWh | £617 | £86 | £703 | £11,354 | 16.1 yrs | £2,709 |
| 4 kW | 4248 kWh | 3101 kWh | 1147 kWh | £823 | £115 | £937 | £13,388 | 14.3 yrs | £5,362 |
| 5 kW | 5310 kWh | 3877 kWh | 1434 kWh | £1,028 | £143 | £1,172 | £15,423 | 13.2 yrs | £8,015 |
| 6 kW | 6373 kWh | 4652 kWh | 1721 kWh | £1,234 | £172 | £1,406 | £17,457 | 12.4 yrs | £10,668 |
| 7 kW | 7435 kWh | 5427 kWh | 2007 kWh | £1,440 | £201 | £1,641 | £19,492 | 11.9 yrs | £13,321 |
| 8 kW | 8497 kWh | 6203 kWh | 2294 kWh | £1,646 | £229 | £1,875 | £21,526 | 11.5 yrs | £15,974 |
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: £1,189, Upfront: £17,173, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2124 kWh | 1593 kWh | 531 kWh | £423 | £53 | £476 | £11,069 | 23.3 yrs | £-1,554 |
| 3 kW | 3186 kWh | 2390 kWh | 797 kWh | £634 | £80 | £714 | £13,104 | 18.4 yrs | £1,170 |
| 4 kW | 4248 kWh | 3186 kWh | 1062 kWh | £845 | £106 | £952 | £15,138 | 15.9 yrs | £3,893 |
| 5 kW | 5310 kWh | 3983 kWh | 1328 kWh | £1,057 | £133 | £1,189 | £17,173 | 14.4 yrs | £6,616 |
| 6 kW | 6373 kWh | 4779 kWh | 1593 kWh | £1,268 | £159 | £1,427 | £19,207 | 13.5 yrs | £9,339 |
| 7 kW | 7435 kWh | 5576 kWh | 1859 kWh | £1,479 | £186 | £1,665 | £21,242 | 12.8 yrs | £12,062 |
| 8 kW | 8497 kWh | 6373 kWh | 2124 kWh | £1,691 | £212 | £1,903 | £23,276 | 12.2 yrs | £14,785 |
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: £1,207, Upfront: £19,623, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2124 kWh | 1636 kWh | 489 kWh | £434 | £49 | £483 | £13,519 | 28.0 yrs | £-3,863 |
| 3 kW | 3186 kWh | 2453 kWh | 733 kWh | £651 | £73 | £724 | £15,554 | 21.5 yrs | £-1,070 |
| 4 kW | 4248 kWh | 3271 kWh | 977 kWh | £868 | £98 | £966 | £17,588 | 18.2 yrs | £1,724 |
| 5 kW | 5310 kWh | 4089 kWh | 1221 kWh | £1,085 | £122 | £1,207 | £19,623 | 16.3 yrs | £4,517 |
| 6 kW | 6373 kWh | 4907 kWh | 1466 kWh | £1,302 | £147 | £1,448 | £21,657 | 15.0 yrs | £7,310 |
| 7 kW | 7435 kWh | 5725 kWh | 1710 kWh | £1,519 | £171 | £1,690 | £23,692 | 14.0 yrs | £10,104 |
| 8 kW | 8497 kWh | 6543 kWh | 1954 kWh | £1,736 | £195 | £1,931 | £25,726 | 13.3 yrs | £12,897 |
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.