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 1023 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £858, Upfront: £10,173, 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 | 2047 kWh | 819 kWh | 1228 kWh | £220 | £123 | £343 | £4,069 | 11.9 yrs | £2,795 |
| 3 kW | 3070 kWh | 1228 kWh | 1842 kWh | £331 | £184 | £515 | £6,104 | 11.9 yrs | £4,193 |
| 4 kW | 4094 kWh | 1638 kWh | 2456 kWh | £441 | £246 | £686 | £8,138 | 11.9 yrs | £5,591 |
| 5 kW | 5117 kWh | 2047 kWh | 3070 kWh | £551 | £307 | £858 | £10,173 | 11.9 yrs | £6,989 |
| 6 kW | 6141 kWh | 2456 kWh | 3684 kWh | £661 | £368 | £1,030 | £12,207 | 11.9 yrs | £8,386 |
| 7 kW | 7164 kWh | 2866 kWh | 4298 kWh | £771 | £430 | £1,201 | £14,242 | 11.9 yrs | £9,784 |
| 8 kW | 8188 kWh | 3275 kWh | 4913 kWh | £882 | £491 | £1,373 | £16,276 | 11.9 yrs | £11,182 |
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: £1,031, Upfront: £12,273, 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 | 2047 kWh | 1228 kWh | 819 kWh | £331 | £82 | £412 | £6,169 | 15.0 yrs | £2,081 |
| 3 kW | 3070 kWh | 1842 kWh | 1228 kWh | £496 | £123 | £619 | £8,204 | 13.3 yrs | £4,171 |
| 4 kW | 4094 kWh | 2456 kWh | 1638 kWh | £661 | £164 | £825 | £10,238 | 12.4 yrs | £6,262 |
| 5 kW | 5117 kWh | 3070 kWh | 2047 kWh | £827 | £205 | £1,031 | £12,273 | 11.9 yrs | £8,352 |
| 6 kW | 6141 kWh | 3684 kWh | 2456 kWh | £992 | £246 | £1,237 | £14,307 | 11.6 yrs | £10,442 |
| 7 kW | 7164 kWh | 4298 kWh | 2866 kWh | £1,157 | £287 | £1,444 | £16,342 | 11.3 yrs | £12,533 |
| 8 kW | 8188 kWh | 4913 kWh | 3275 kWh | £1,322 | £328 | £1,650 | £18,376 | 11.1 yrs | £14,623 |
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: £1,118, Upfront: £13,673, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2047 kWh | 1433 kWh | 614 kWh | £386 | £61 | £447 | £7,569 | 16.9 yrs | £1,373 |
| 3 kW | 3070 kWh | 2149 kWh | 921 kWh | £579 | £92 | £671 | £9,604 | 14.3 yrs | £3,810 |
| 4 kW | 4094 kWh | 2866 kWh | 1228 kWh | £771 | £123 | £894 | £11,638 | 13.0 yrs | £6,247 |
| 5 kW | 5117 kWh | 3582 kWh | 1535 kWh | £964 | £154 | £1,118 | £13,673 | 12.2 yrs | £8,684 |
| 6 kW | 6141 kWh | 4298 kWh | 1842 kWh | £1,157 | £184 | £1,341 | £15,707 | 11.7 yrs | £11,120 |
| 7 kW | 7164 kWh | 5015 kWh | 2149 kWh | £1,350 | £215 | £1,565 | £17,742 | 11.3 yrs | £13,557 |
| 8 kW | 8188 kWh | 5731 kWh | 2456 kWh | £1,543 | £246 | £1,788 | £19,776 | 11.1 yrs | £15,994 |
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: £1,144, Upfront: £15,423, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2047 kWh | 1494 kWh | 553 kWh | £402 | £55 | £458 | £9,319 | 20.4 yrs | £-169 |
| 3 kW | 3070 kWh | 2241 kWh | 829 kWh | £603 | £83 | £686 | £11,354 | 16.5 yrs | £2,372 |
| 4 kW | 4094 kWh | 2988 kWh | 1105 kWh | £804 | £111 | £915 | £13,388 | 14.6 yrs | £4,913 |
| 5 kW | 5117 kWh | 3736 kWh | 1382 kWh | £1,006 | £138 | £1,144 | £15,423 | 13.5 yrs | £7,453 |
| 6 kW | 6141 kWh | 4483 kWh | 1658 kWh | £1,207 | £166 | £1,373 | £17,457 | 12.7 yrs | £9,994 |
| 7 kW | 7164 kWh | 5230 kWh | 1934 kWh | £1,408 | £193 | £1,601 | £19,492 | 12.2 yrs | £12,534 |
| 8 kW | 8188 kWh | 5977 kWh | 2211 kWh | £1,609 | £221 | £1,830 | £21,526 | 11.8 yrs | £15,075 |
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: £1,161, Upfront: £17,173, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2047 kWh | 1535 kWh | 512 kWh | £413 | £51 | £464 | £11,069 | 23.8 yrs | £-1,780 |
| 3 kW | 3070 kWh | 2303 kWh | 768 kWh | £620 | £77 | £697 | £13,104 | 18.8 yrs | £830 |
| 4 kW | 4094 kWh | 3070 kWh | 1023 kWh | £827 | £102 | £929 | £15,138 | 16.3 yrs | £3,440 |
| 5 kW | 5117 kWh | 3838 kWh | 1279 kWh | £1,033 | £128 | £1,161 | £17,173 | 14.8 yrs | £6,050 |
| 6 kW | 6141 kWh | 4606 kWh | 1535 kWh | £1,240 | £154 | £1,393 | £19,207 | 13.8 yrs | £8,659 |
| 7 kW | 7164 kWh | 5373 kWh | 1791 kWh | £1,446 | £179 | £1,626 | £21,242 | 13.1 yrs | £11,269 |
| 8 kW | 8188 kWh | 6141 kWh | 2047 kWh | £1,653 | £205 | £1,858 | £23,276 | 12.5 yrs | £13,879 |
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: £1,178, Upfront: £19,623, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2047 kWh | 1576 kWh | 471 kWh | £424 | £47 | £471 | £13,519 | 28.7 yrs | £-4,092 |
| 3 kW | 3070 kWh | 2364 kWh | 706 kWh | £636 | £71 | £707 | £15,554 | 22.0 yrs | £-1,412 |
| 4 kW | 4094 kWh | 3152 kWh | 942 kWh | £849 | £94 | £943 | £17,588 | 18.7 yrs | £1,267 |
| 5 kW | 5117 kWh | 3940 kWh | 1177 kWh | £1,061 | £118 | £1,178 | £19,623 | 16.7 yrs | £3,946 |
| 6 kW | 6141 kWh | 4728 kWh | 1412 kWh | £1,273 | £141 | £1,414 | £21,657 | 15.3 yrs | £6,625 |
| 7 kW | 7164 kWh | 5516 kWh | 1648 kWh | £1,485 | £165 | £1,650 | £23,692 | 14.4 yrs | £9,304 |
| 8 kW | 8188 kWh | 6304 kWh | 1883 kWh | £1,697 | £188 | £1,885 | £25,726 | 13.6 yrs | £11,983 |
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.