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 984 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: £816, Upfront: £10,173, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1968 kWh | 787 kWh | 1180 kWh | £208 | £118 | £326 | £4,069 | 12.5 yrs | £2,460 |
| 3 kW | 2951 kWh | 1180 kWh | 1771 kWh | £313 | £177 | £490 | £6,104 | 12.5 yrs | £3,690 |
| 4 kW | 3935 kWh | 1574 kWh | 2361 kWh | £417 | £236 | £653 | £8,138 | 12.5 yrs | £4,920 |
| 5 kW | 4919 kWh | 1968 kWh | 2951 kWh | £521 | £295 | £816 | £10,173 | 12.5 yrs | £6,150 |
| 6 kW | 5902 kWh | 2361 kWh | 3542 kWh | £625 | £354 | £979 | £12,207 | 12.5 yrs | £7,380 |
| 7 kW | 6886 kWh | 2754 kWh | 4132 kWh | £729 | £413 | £1,143 | £14,242 | 12.5 yrs | £8,610 |
| 8 kW | 7870 kWh | 3148 kWh | 4722 kWh | £834 | £472 | £1,306 | £16,276 | 12.5 yrs | £9,840 |
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: £978, Upfront: £12,273, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1968 kWh | 1180 kWh | 787 kWh | £313 | £79 | £391 | £6,169 | 15.8 yrs | £1,657 |
| 3 kW | 2951 kWh | 1771 kWh | 1180 kWh | £469 | £118 | £587 | £8,204 | 14.0 yrs | £3,535 |
| 4 kW | 3935 kWh | 2361 kWh | 1574 kWh | £625 | £157 | £783 | £10,238 | 13.1 yrs | £5,414 |
| 5 kW | 4919 kWh | 2951 kWh | 1968 kWh | £781 | £197 | £978 | £12,273 | 12.5 yrs | £7,292 |
| 6 kW | 5902 kWh | 3542 kWh | 2361 kWh | £938 | £236 | £1,174 | £14,307 | 12.2 yrs | £9,171 |
| 7 kW | 6886 kWh | 4132 kWh | 2754 kWh | £1,094 | £275 | £1,370 | £16,342 | 11.9 yrs | £11,049 |
| 8 kW | 7870 kWh | 4722 kWh | 3148 kWh | £1,250 | £315 | £1,565 | £18,376 | 11.7 yrs | £12,928 |
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: £1,059, Upfront: £13,673, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1968 kWh | 1377 kWh | 590 kWh | £365 | £59 | £424 | £7,569 | 17.9 yrs | £905 |
| 3 kW | 2951 kWh | 2066 kWh | 885 kWh | £547 | £89 | £636 | £9,604 | 15.1 yrs | £3,108 |
| 4 kW | 3935 kWh | 2754 kWh | 1180 kWh | £729 | £118 | £847 | £11,638 | 13.7 yrs | £5,311 |
| 5 kW | 4919 kWh | 3443 kWh | 1476 kWh | £912 | £148 | £1,059 | £13,673 | 12.9 yrs | £7,513 |
| 6 kW | 5902 kWh | 4132 kWh | 1771 kWh | £1,094 | £177 | £1,271 | £15,707 | 12.4 yrs | £9,716 |
| 7 kW | 6886 kWh | 4820 kWh | 2066 kWh | £1,276 | £207 | £1,483 | £17,742 | 12.0 yrs | £11,919 |
| 8 kW | 7870 kWh | 5509 kWh | 2361 kWh | £1,459 | £236 | £1,695 | £19,776 | 11.7 yrs | £14,122 |
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: £1,084, Upfront: £15,423, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1968 kWh | 1436 kWh | 531 kWh | £380 | £53 | £433 | £9,319 | 21.5 yrs | £-650 |
| 3 kW | 2951 kWh | 2154 kWh | 797 kWh | £570 | £80 | £650 | £11,354 | 17.5 yrs | £1,650 |
| 4 kW | 3935 kWh | 2873 kWh | 1062 kWh | £761 | £106 | £867 | £13,388 | 15.4 yrs | £3,950 |
| 5 kW | 4919 kWh | 3591 kWh | 1328 kWh | £951 | £133 | £1,084 | £15,423 | 14.2 yrs | £6,250 |
| 6 kW | 5902 kWh | 4309 kWh | 1594 kWh | £1,141 | £159 | £1,300 | £17,457 | 13.4 yrs | £8,550 |
| 7 kW | 6886 kWh | 5027 kWh | 1859 kWh | £1,331 | £186 | £1,517 | £19,492 | 12.8 yrs | £10,850 |
| 8 kW | 7870 kWh | 5745 kWh | 2125 kWh | £1,521 | £212 | £1,734 | £21,526 | 12.4 yrs | £13,150 |
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: £1,100, Upfront: £17,173, 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 | 1968 kWh | 1476 kWh | 492 kWh | £391 | £49 | £440 | £11,069 | 25.2 yrs | £-2,270 |
| 3 kW | 2951 kWh | 2213 kWh | 738 kWh | £586 | £74 | £660 | £13,104 | 19.9 yrs | £94 |
| 4 kW | 3935 kWh | 2951 kWh | 984 kWh | £781 | £98 | £880 | £15,138 | 17.2 yrs | £2,459 |
| 5 kW | 4919 kWh | 3689 kWh | 1230 kWh | £977 | £123 | £1,100 | £17,173 | 15.6 yrs | £4,824 |
| 6 kW | 5902 kWh | 4427 kWh | 1476 kWh | £1,172 | £148 | £1,320 | £19,207 | 14.6 yrs | £7,189 |
| 7 kW | 6886 kWh | 5165 kWh | 1722 kWh | £1,368 | £172 | £1,540 | £21,242 | 13.8 yrs | £9,554 |
| 8 kW | 7870 kWh | 5902 kWh | 1968 kWh | £1,563 | £197 | £1,760 | £23,276 | 13.2 yrs | £11,919 |
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: £1,116, Upfront: £19,623, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1968 kWh | 1515 kWh | 453 kWh | £401 | £45 | £446 | £13,519 | 30.3 yrs | £-4,591 |
| 3 kW | 2951 kWh | 2272 kWh | 679 kWh | £602 | £68 | £670 | £15,554 | 23.2 yrs | £-2,161 |
| 4 kW | 3935 kWh | 3030 kWh | 905 kWh | £802 | £91 | £893 | £17,588 | 19.7 yrs | £269 |
| 5 kW | 4919 kWh | 3787 kWh | 1131 kWh | £1,003 | £113 | £1,116 | £19,623 | 17.6 yrs | £2,698 |
| 6 kW | 5902 kWh | 4545 kWh | 1358 kWh | £1,203 | £136 | £1,339 | £21,657 | 16.2 yrs | £5,128 |
| 7 kW | 6886 kWh | 5302 kWh | 1584 kWh | £1,404 | £158 | £1,562 | £23,692 | 15.2 yrs | £7,558 |
| 8 kW | 7870 kWh | 6060 kWh | 1810 kWh | £1,605 | £181 | £1,786 | £25,726 | 14.4 yrs | £9,987 |
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.