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 983 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 | 1966 kWh | 787 kWh | 1180 kWh | £208 | £118 | £326 | £4,069 | 12.5 yrs | £2,456 |
| 3 kW | 2949 kWh | 1180 kWh | 1770 kWh | £312 | £177 | £489 | £6,104 | 12.5 yrs | £3,684 |
| 4 kW | 3933 kWh | 1573 kWh | 2360 kWh | £417 | £236 | £652 | £8,138 | 12.5 yrs | £4,912 |
| 5 kW | 4916 kWh | 1966 kWh | 2949 kWh | £521 | £295 | £816 | £10,173 | 12.5 yrs | £6,140 |
| 6 kW | 5899 kWh | 2360 kWh | 3539 kWh | £625 | £354 | £979 | £12,207 | 12.5 yrs | £7,368 |
| 7 kW | 6882 kWh | 2753 kWh | 4129 kWh | £729 | £413 | £1,142 | £14,242 | 12.5 yrs | £8,596 |
| 8 kW | 7865 kWh | 3146 kWh | 4719 kWh | £833 | £472 | £1,305 | £16,276 | 12.5 yrs | £9,824 |
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: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1966 kWh | 1180 kWh | 787 kWh | £312 | £79 | £391 | £6,169 | 15.8 yrs | £1,652 |
| 3 kW | 2949 kWh | 1770 kWh | 1180 kWh | £469 | £118 | £587 | £8,204 | 14.0 yrs | £3,528 |
| 4 kW | 3933 kWh | 2360 kWh | 1573 kWh | £625 | £157 | £782 | £10,238 | 13.1 yrs | £5,404 |
| 5 kW | 4916 kWh | 2949 kWh | 1966 kWh | £781 | £197 | £978 | £12,273 | 12.6 yrs | £7,280 |
| 6 kW | 5899 kWh | 3539 kWh | 2360 kWh | £937 | £236 | £1,173 | £14,307 | 12.2 yrs | £9,156 |
| 7 kW | 6882 kWh | 4129 kWh | 2753 kWh | £1,093 | £275 | £1,369 | £16,342 | 11.9 yrs | £11,032 |
| 8 kW | 7865 kWh | 4719 kWh | 3146 kWh | £1,250 | £315 | £1,564 | £18,376 | 11.7 yrs | £12,908 |
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 | 1966 kWh | 1376 kWh | 590 kWh | £364 | £59 | £423 | £7,569 | 17.9 yrs | £900 |
| 3 kW | 2949 kWh | 2065 kWh | 885 kWh | £547 | £88 | £635 | £9,604 | 15.1 yrs | £3,100 |
| 4 kW | 3933 kWh | 2753 kWh | 1180 kWh | £729 | £118 | £847 | £11,638 | 13.7 yrs | £5,300 |
| 5 kW | 4916 kWh | 3441 kWh | 1475 kWh | £911 | £147 | £1,059 | £13,673 | 12.9 yrs | £7,500 |
| 6 kW | 5899 kWh | 4129 kWh | 1770 kWh | £1,093 | £177 | £1,270 | £15,707 | 12.4 yrs | £9,700 |
| 7 kW | 6882 kWh | 4817 kWh | 2065 kWh | £1,276 | £206 | £1,482 | £17,742 | 12.0 yrs | £11,900 |
| 8 kW | 7865 kWh | 5506 kWh | 2360 kWh | £1,458 | £236 | £1,694 | £19,776 | 11.7 yrs | £14,101 |
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: £1,083, 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 | 1966 kWh | 1435 kWh | 531 kWh | £380 | £53 | £433 | £9,319 | 21.5 yrs | £-655 |
| 3 kW | 2949 kWh | 2153 kWh | 796 kWh | £570 | £80 | £650 | £11,354 | 17.5 yrs | £1,642 |
| 4 kW | 3933 kWh | 2871 kWh | 1062 kWh | £760 | £106 | £866 | £13,388 | 15.5 yrs | £3,939 |
| 5 kW | 4916 kWh | 3588 kWh | 1327 kWh | £950 | £133 | £1,083 | £15,423 | 14.2 yrs | £6,236 |
| 6 kW | 5899 kWh | 4306 kWh | 1593 kWh | £1,140 | £159 | £1,300 | £17,457 | 13.4 yrs | £8,534 |
| 7 kW | 6882 kWh | 5024 kWh | 1858 kWh | £1,330 | £186 | £1,516 | £19,492 | 12.9 yrs | £10,831 |
| 8 kW | 7865 kWh | 5742 kWh | 2124 kWh | £1,520 | £212 | £1,733 | £21,526 | 12.4 yrs | £13,128 |
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: £1,099, 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 | 1966 kWh | 1475 kWh | 492 kWh | £391 | £49 | £440 | £11,069 | 25.2 yrs | £-2,276 |
| 3 kW | 2949 kWh | 2212 kWh | 737 kWh | £586 | £74 | £659 | £13,104 | 19.9 yrs | £86 |
| 4 kW | 3933 kWh | 2949 kWh | 983 kWh | £781 | £98 | £879 | £15,138 | 17.2 yrs | £2,448 |
| 5 kW | 4916 kWh | 3687 kWh | 1229 kWh | £976 | £123 | £1,099 | £17,173 | 15.6 yrs | £4,810 |
| 6 kW | 5899 kWh | 4424 kWh | 1475 kWh | £1,172 | £147 | £1,319 | £19,207 | 14.6 yrs | £7,173 |
| 7 kW | 6882 kWh | 5161 kWh | 1720 kWh | £1,367 | £172 | £1,539 | £21,242 | 13.8 yrs | £9,535 |
| 8 kW | 7865 kWh | 5899 kWh | 1966 kWh | £1,562 | £197 | £1,759 | £23,276 | 13.2 yrs | £11,897 |
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: £1,115, 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 | 1966 kWh | 1514 kWh | 452 kWh | £401 | £45 | £446 | £13,519 | 30.3 yrs | £-4,596 |
| 3 kW | 2949 kWh | 2271 kWh | 678 kWh | £601 | £68 | £669 | £15,554 | 23.2 yrs | £-2,169 |
| 4 kW | 3933 kWh | 3028 kWh | 904 kWh | £802 | £90 | £892 | £17,588 | 19.7 yrs | £258 |
| 5 kW | 4916 kWh | 3785 kWh | 1131 kWh | £1,002 | £113 | £1,115 | £19,623 | 17.6 yrs | £2,685 |
| 6 kW | 5899 kWh | 4542 kWh | 1357 kWh | £1,203 | £136 | £1,338 | £21,657 | 16.2 yrs | £5,111 |
| 7 kW | 6882 kWh | 5299 kWh | 1583 kWh | £1,403 | £158 | £1,561 | £23,692 | 15.2 yrs | £7,538 |
| 8 kW | 7865 kWh | 6056 kWh | 1809 kWh | £1,604 | £181 | £1,785 | £25,726 | 14.4 yrs | £9,965 |
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.