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 1016 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: £844, Upfront: £10,173, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 813 kWh | 1219 kWh | £216 | £122 | £338 | £4,069 | 12.1 yrs | £2,683 |
| 3 kW | 3048 kWh | 1219 kWh | 1829 kWh | £324 | £183 | £506 | £6,104 | 12.1 yrs | £4,025 |
| 4 kW | 4065 kWh | 1626 kWh | 2439 kWh | £431 | £244 | £675 | £8,138 | 12.1 yrs | £5,366 |
| 5 kW | 5081 kWh | 2032 kWh | 3048 kWh | £539 | £305 | £844 | £10,173 | 12.1 yrs | £6,708 |
| 6 kW | 6097 kWh | 2439 kWh | 3658 kWh | £647 | £366 | £1,013 | £12,207 | 12.1 yrs | £8,049 |
| 7 kW | 7113 kWh | 2845 kWh | 4268 kWh | £755 | £427 | £1,182 | £14,242 | 12.1 yrs | £9,391 |
| 8 kW | 8129 kWh | 3252 kWh | 4878 kWh | £863 | £488 | £1,350 | £16,276 | 12.1 yrs | £10,732 |
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: £1,012, Upfront: £12,273, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1219 kWh | 813 kWh | £324 | £81 | £405 | £6,169 | 15.2 yrs | £1,927 |
| 3 kW | 3048 kWh | 1829 kWh | 1219 kWh | £485 | £122 | £607 | £8,204 | 13.5 yrs | £3,940 |
| 4 kW | 4065 kWh | 2439 kWh | 1626 kWh | £647 | £163 | £810 | £10,238 | 12.6 yrs | £5,954 |
| 5 kW | 5081 kWh | 3048 kWh | 2032 kWh | £809 | £203 | £1,012 | £12,273 | 12.1 yrs | £7,967 |
| 6 kW | 6097 kWh | 3658 kWh | 2439 kWh | £971 | £244 | £1,214 | £14,307 | 11.8 yrs | £9,981 |
| 7 kW | 7113 kWh | 4268 kWh | 2845 kWh | £1,132 | £285 | £1,417 | £16,342 | 11.5 yrs | £11,994 |
| 8 kW | 8129 kWh | 4878 kWh | 3252 kWh | £1,294 | £325 | £1,619 | £18,376 | 11.3 yrs | £14,007 |
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: £1,096, Upfront: £13,673, 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 | 2032 kWh | 1423 kWh | 610 kWh | £377 | £61 | £438 | £7,569 | 17.3 yrs | £1,199 |
| 3 kW | 3048 kWh | 2134 kWh | 915 kWh | £566 | £91 | £658 | £9,604 | 14.6 yrs | £3,548 |
| 4 kW | 4065 kWh | 2845 kWh | 1219 kWh | £755 | £122 | £877 | £11,638 | 13.3 yrs | £5,897 |
| 5 kW | 5081 kWh | 3557 kWh | 1524 kWh | £944 | £152 | £1,096 | £13,673 | 12.5 yrs | £8,247 |
| 6 kW | 6097 kWh | 4268 kWh | 1829 kWh | £1,132 | £183 | £1,315 | £15,707 | 11.9 yrs | £10,596 |
| 7 kW | 7113 kWh | 4979 kWh | 2134 kWh | £1,321 | £213 | £1,534 | £17,742 | 11.6 yrs | £12,946 |
| 8 kW | 8129 kWh | 5690 kWh | 2439 kWh | £1,510 | £244 | £1,754 | £19,776 | 11.3 yrs | £15,295 |
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: £1,121, Upfront: £15,423, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1484 kWh | 549 kWh | £394 | £55 | £448 | £9,319 | 20.8 yrs | £-350 |
| 3 kW | 3048 kWh | 2225 kWh | 823 kWh | £590 | £82 | £673 | £11,354 | 16.9 yrs | £2,100 |
| 4 kW | 4065 kWh | 2967 kWh | 1097 kWh | £787 | £110 | £897 | £13,388 | 14.9 yrs | £4,551 |
| 5 kW | 5081 kWh | 3709 kWh | 1372 kWh | £984 | £137 | £1,121 | £15,423 | 13.8 yrs | £7,001 |
| 6 kW | 6097 kWh | 4451 kWh | 1646 kWh | £1,181 | £165 | £1,345 | £17,457 | 13.0 yrs | £9,451 |
| 7 kW | 7113 kWh | 5193 kWh | 1921 kWh | £1,378 | £192 | £1,570 | £19,492 | 12.4 yrs | £11,901 |
| 8 kW | 8129 kWh | 5934 kWh | 2195 kWh | £1,574 | £219 | £1,794 | £21,526 | 12.0 yrs | £14,351 |
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: £1,138, Upfront: £17,173, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1524 kWh | 508 kWh | £404 | £51 | £455 | £11,069 | 24.3 yrs | £-1,965 |
| 3 kW | 3048 kWh | 2286 kWh | 762 kWh | £607 | £76 | £683 | £13,104 | 19.2 yrs | £552 |
| 4 kW | 4065 kWh | 3048 kWh | 1016 kWh | £809 | £102 | £910 | £15,138 | 16.6 yrs | £3,069 |
| 5 kW | 5081 kWh | 3811 kWh | 1270 kWh | £1,011 | £127 | £1,138 | £17,173 | 15.1 yrs | £5,587 |
| 6 kW | 6097 kWh | 4573 kWh | 1524 kWh | £1,213 | £152 | £1,366 | £19,207 | 14.1 yrs | £8,104 |
| 7 kW | 7113 kWh | 5335 kWh | 1778 kWh | £1,415 | £178 | £1,593 | £21,242 | 13.3 yrs | £10,621 |
| 8 kW | 8129 kWh | 6097 kWh | 2032 kWh | £1,618 | £203 | £1,821 | £23,276 | 12.8 yrs | £13,139 |
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: £1,155, Upfront: £19,623, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2032 kWh | 1565 kWh | 467 kWh | £415 | £47 | £462 | £13,519 | 29.3 yrs | £-4,281 |
| 3 kW | 3048 kWh | 2347 kWh | 701 kWh | £623 | £70 | £693 | £15,554 | 22.4 yrs | £-1,696 |
| 4 kW | 4065 kWh | 3130 kWh | 935 kWh | £830 | £93 | £924 | £17,588 | 19.0 yrs | £888 |
| 5 kW | 5081 kWh | 3912 kWh | 1169 kWh | £1,038 | £117 | £1,155 | £19,623 | 17.0 yrs | £3,473 |
| 6 kW | 6097 kWh | 4695 kWh | 1402 kWh | £1,245 | £140 | £1,386 | £21,657 | 15.6 yrs | £6,057 |
| 7 kW | 7113 kWh | 5477 kWh | 1636 kWh | £1,453 | £164 | £1,617 | £23,692 | 14.7 yrs | £8,642 |
| 8 kW | 8129 kWh | 6259 kWh | 1870 kWh | £1,661 | £187 | £1,848 | £25,726 | 13.9 yrs | £11,226 |
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.