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 984 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £823, Upfront: £10,173, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1967 kWh | 787 kWh | 1180 kWh | £211 | £118 | £329 | £4,069 | 12.4 yrs | £2,514 |
| 3 kW | 2951 kWh | 1180 kWh | 1771 kWh | £317 | £177 | £494 | £6,104 | 12.4 yrs | £3,771 |
| 4 kW | 3934 kWh | 1574 kWh | 2361 kWh | £422 | £236 | £658 | £8,138 | 12.4 yrs | £5,028 |
| 5 kW | 4918 kWh | 1967 kWh | 2951 kWh | £528 | £295 | £823 | £10,173 | 12.4 yrs | £6,285 |
| 6 kW | 5902 kWh | 2361 kWh | 3541 kWh | £633 | £354 | £987 | £12,207 | 12.4 yrs | £7,542 |
| 7 kW | 6885 kWh | 2754 kWh | 4131 kWh | £739 | £413 | £1,152 | £14,242 | 12.4 yrs | £8,800 |
| 8 kW | 7869 kWh | 3148 kWh | 4721 kWh | £844 | £472 | £1,317 | £16,276 | 12.4 yrs | £10,057 |
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: £988, Upfront: £12,273, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1967 kWh | 1180 kWh | 787 kWh | £317 | £79 | £395 | £6,169 | 15.6 yrs | £1,738 |
| 3 kW | 2951 kWh | 1771 kWh | 1180 kWh | £475 | £118 | £593 | £8,204 | 13.8 yrs | £3,658 |
| 4 kW | 3934 kWh | 2361 kWh | 1574 kWh | £633 | £157 | £791 | £10,238 | 12.9 yrs | £5,577 |
| 5 kW | 4918 kWh | 2951 kWh | 1967 kWh | £792 | £197 | £988 | £12,273 | 12.4 yrs | £7,496 |
| 6 kW | 5902 kWh | 3541 kWh | 2361 kWh | £950 | £236 | £1,186 | £14,307 | 12.1 yrs | £9,415 |
| 7 kW | 6885 kWh | 4131 kWh | 2754 kWh | £1,108 | £275 | £1,384 | £16,342 | 11.8 yrs | £11,335 |
| 8 kW | 7869 kWh | 4721 kWh | 3148 kWh | £1,267 | £315 | £1,582 | £18,376 | 11.6 yrs | £13,254 |
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: £1,071, Upfront: £13,673, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1967 kWh | 1377 kWh | 590 kWh | £369 | £59 | £428 | £7,569 | 17.7 yrs | £1,001 |
| 3 kW | 2951 kWh | 2066 kWh | 885 kWh | £554 | £89 | £643 | £9,604 | 14.9 yrs | £3,251 |
| 4 kW | 3934 kWh | 2754 kWh | 1180 kWh | £739 | £118 | £857 | £11,638 | 13.6 yrs | £5,501 |
| 5 kW | 4918 kWh | 3443 kWh | 1475 kWh | £924 | £148 | £1,071 | £13,673 | 12.8 yrs | £7,752 |
| 6 kW | 5902 kWh | 4131 kWh | 1771 kWh | £1,108 | £177 | £1,285 | £15,707 | 12.2 yrs | £10,002 |
| 7 kW | 6885 kWh | 4820 kWh | 2066 kWh | £1,293 | £207 | £1,500 | £17,742 | 11.8 yrs | £12,252 |
| 8 kW | 7869 kWh | 5508 kWh | 2361 kWh | £1,478 | £236 | £1,714 | £19,776 | 11.5 yrs | £14,503 |
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: £1,096, Upfront: £15,423, 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 | 1967 kWh | 1436 kWh | 531 kWh | £385 | £53 | £438 | £9,319 | 21.3 yrs | £-551 |
| 3 kW | 2951 kWh | 2154 kWh | 797 kWh | £578 | £80 | £658 | £11,354 | 17.3 yrs | £1,799 |
| 4 kW | 3934 kWh | 2872 kWh | 1062 kWh | £771 | £106 | £877 | £13,388 | 15.3 yrs | £4,149 |
| 5 kW | 4918 kWh | 3590 kWh | 1328 kWh | £963 | £133 | £1,096 | £15,423 | 14.1 yrs | £6,498 |
| 6 kW | 5902 kWh | 4308 kWh | 1593 kWh | £1,156 | £159 | £1,315 | £17,457 | 13.3 yrs | £8,848 |
| 7 kW | 6885 kWh | 5026 kWh | 1859 kWh | £1,349 | £186 | £1,534 | £19,492 | 12.7 yrs | £11,198 |
| 8 kW | 7869 kWh | 5744 kWh | 2125 kWh | £1,541 | £212 | £1,754 | £21,526 | 12.3 yrs | £13,547 |
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: £1,113, Upfront: £17,173, 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 | 1967 kWh | 1475 kWh | 492 kWh | £396 | £49 | £445 | £11,069 | 24.9 yrs | £-2,168 |
| 3 kW | 2951 kWh | 2213 kWh | 738 kWh | £594 | £74 | £668 | £13,104 | 19.6 yrs | £248 |
| 4 kW | 3934 kWh | 2951 kWh | 984 kWh | £792 | £98 | £890 | £15,138 | 17.0 yrs | £2,664 |
| 5 kW | 4918 kWh | 3689 kWh | 1230 kWh | £990 | £123 | £1,113 | £17,173 | 15.4 yrs | £5,079 |
| 6 kW | 5902 kWh | 4426 kWh | 1475 kWh | £1,188 | £148 | £1,335 | £19,207 | 14.4 yrs | £7,495 |
| 7 kW | 6885 kWh | 5164 kWh | 1721 kWh | £1,386 | £172 | £1,558 | £21,242 | 13.6 yrs | £9,911 |
| 8 kW | 7869 kWh | 5902 kWh | 1967 kWh | £1,583 | £197 | £1,780 | £23,276 | 13.1 yrs | £12,327 |
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: £1,129, Upfront: £19,623, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1967 kWh | 1515 kWh | 452 kWh | £406 | £45 | £452 | £13,519 | 29.9 yrs | £-4,486 |
| 3 kW | 2951 kWh | 2272 kWh | 679 kWh | £610 | £68 | £677 | £15,554 | 23.0 yrs | £-2,004 |
| 4 kW | 3934 kWh | 3030 kWh | 905 kWh | £813 | £90 | £903 | £17,588 | 19.5 yrs | £478 |
| 5 kW | 4918 kWh | 3787 kWh | 1131 kWh | £1,016 | £113 | £1,129 | £19,623 | 17.4 yrs | £2,960 |
| 6 kW | 5902 kWh | 4544 kWh | 1357 kWh | £1,219 | £136 | £1,355 | £21,657 | 16.0 yrs | £5,443 |
| 7 kW | 6885 kWh | 5302 kWh | 1584 kWh | £1,422 | £158 | £1,581 | £23,692 | 15.0 yrs | £7,925 |
| 8 kW | 7869 kWh | 6059 kWh | 1810 kWh | £1,626 | £181 | £1,807 | £25,726 | 14.2 yrs | £10,407 |
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.