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 969 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £788, Upfront: £10,173, 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 | 1938 kWh | 775 kWh | 1163 kWh | £199 | £116 | £315 | £4,069 | 12.9 yrs | £2,232 |
| 3 kW | 2907 kWh | 1163 kWh | 1744 kWh | £298 | £174 | £473 | £6,104 | 12.9 yrs | £3,349 |
| 4 kW | 3876 kWh | 1551 kWh | 2326 kWh | £398 | £233 | £630 | £8,138 | 12.9 yrs | £4,465 |
| 5 kW | 4846 kWh | 1938 kWh | 2907 kWh | £497 | £291 | £788 | £10,173 | 12.9 yrs | £5,581 |
| 6 kW | 5815 kWh | 2326 kWh | 3489 kWh | £596 | £349 | £945 | £12,207 | 12.9 yrs | £6,697 |
| 7 kW | 6784 kWh | 2713 kWh | 4070 kWh | £696 | £407 | £1,103 | £14,242 | 12.9 yrs | £7,814 |
| 8 kW | 7753 kWh | 3101 kWh | 4652 kWh | £795 | £465 | £1,260 | £16,276 | 12.9 yrs | £8,930 |
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: £939, Upfront: £12,273, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1938 kWh | 1163 kWh | 775 kWh | £298 | £78 | £376 | £6,169 | 16.4 yrs | £1,345 |
| 3 kW | 2907 kWh | 1744 kWh | 1163 kWh | £447 | £116 | £564 | £8,204 | 14.6 yrs | £3,067 |
| 4 kW | 3876 kWh | 2326 kWh | 1551 kWh | £596 | £155 | £751 | £10,238 | 13.6 yrs | £4,790 |
| 5 kW | 4846 kWh | 2907 kWh | 1938 kWh | £745 | £194 | £939 | £12,273 | 13.1 yrs | £6,512 |
| 6 kW | 5815 kWh | 3489 kWh | 2326 kWh | £895 | £233 | £1,127 | £14,307 | 12.7 yrs | £8,235 |
| 7 kW | 6784 kWh | 4070 kWh | 2713 kWh | £1,044 | £271 | £1,315 | £16,342 | 12.4 yrs | £9,957 |
| 8 kW | 7753 kWh | 4652 kWh | 3101 kWh | £1,193 | £310 | £1,503 | £18,376 | 12.2 yrs | £11,680 |
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: £1,015, Upfront: £13,673, 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 | 1938 kWh | 1357 kWh | 581 kWh | £348 | £58 | £406 | £7,569 | 18.6 yrs | £551 |
| 3 kW | 2907 kWh | 2035 kWh | 872 kWh | £522 | £87 | £609 | £9,604 | 15.8 yrs | £2,577 |
| 4 kW | 3876 kWh | 2713 kWh | 1163 kWh | £696 | £116 | £812 | £11,638 | 14.3 yrs | £4,603 |
| 5 kW | 4846 kWh | 3392 kWh | 1454 kWh | £870 | £145 | £1,015 | £13,673 | 13.5 yrs | £6,628 |
| 6 kW | 5815 kWh | 4070 kWh | 1744 kWh | £1,044 | £174 | £1,218 | £15,707 | 12.9 yrs | £8,654 |
| 7 kW | 6784 kWh | 4749 kWh | 2035 kWh | £1,218 | £204 | £1,421 | £17,742 | 12.5 yrs | £10,679 |
| 8 kW | 7753 kWh | 5427 kWh | 2326 kWh | £1,391 | £233 | £1,624 | £19,776 | 12.2 yrs | £12,705 |
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: £1,038, Upfront: £15,423, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1938 kWh | 1415 kWh | 523 kWh | £363 | £52 | £415 | £9,319 | 22.4 yrs | £-1,017 |
| 3 kW | 2907 kWh | 2122 kWh | 785 kWh | £544 | £78 | £623 | £11,354 | 18.2 yrs | £1,100 |
| 4 kW | 3876 kWh | 2830 kWh | 1047 kWh | £726 | £105 | £830 | £13,388 | 16.1 yrs | £3,216 |
| 5 kW | 4846 kWh | 3537 kWh | 1308 kWh | £907 | £131 | £1,038 | £15,423 | 14.9 yrs | £5,333 |
| 6 kW | 5815 kWh | 4245 kWh | 1570 kWh | £1,088 | £157 | £1,245 | £17,457 | 14.0 yrs | £7,449 |
| 7 kW | 6784 kWh | 4952 kWh | 1832 kWh | £1,270 | £183 | £1,453 | £19,492 | 13.4 yrs | £9,566 |
| 8 kW | 7753 kWh | 5660 kWh | 2093 kWh | £1,451 | £209 | £1,660 | £21,526 | 13.0 yrs | £11,683 |
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: £1,053, Upfront: £17,173, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1938 kWh | 1454 kWh | 485 kWh | £373 | £48 | £421 | £11,069 | 26.3 yrs | £-2,646 |
| 3 kW | 2907 kWh | 2180 kWh | 727 kWh | £559 | £73 | £632 | £13,104 | 20.7 yrs | £-468 |
| 4 kW | 3876 kWh | 2907 kWh | 969 kWh | £745 | £97 | £842 | £15,138 | 18.0 yrs | £1,709 |
| 5 kW | 4846 kWh | 3634 kWh | 1211 kWh | £932 | £121 | £1,053 | £17,173 | 16.3 yrs | £3,886 |
| 6 kW | 5815 kWh | 4361 kWh | 1454 kWh | £1,118 | £145 | £1,264 | £19,207 | 15.2 yrs | £6,063 |
| 7 kW | 6784 kWh | 5088 kWh | 1696 kWh | £1,305 | £170 | £1,474 | £21,242 | 14.4 yrs | £8,240 |
| 8 kW | 7753 kWh | 5815 kWh | 1938 kWh | £1,491 | £194 | £1,685 | £23,276 | 13.8 yrs | £10,418 |
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: £1,068, Upfront: £19,623, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1938 kWh | 1492 kWh | 446 kWh | £383 | £45 | £427 | £13,519 | 31.6 yrs | £-4,974 |
| 3 kW | 2907 kWh | 2239 kWh | 669 kWh | £574 | £67 | £641 | £15,554 | 24.3 yrs | £-2,737 |
| 4 kW | 3876 kWh | 2985 kWh | 892 kWh | £765 | £89 | £854 | £17,588 | 20.6 yrs | £-499 |
| 5 kW | 4846 kWh | 3731 kWh | 1114 kWh | £957 | £111 | £1,068 | £19,623 | 18.4 yrs | £1,739 |
| 6 kW | 5815 kWh | 4477 kWh | 1337 kWh | £1,148 | £134 | £1,282 | £21,657 | 16.9 yrs | £3,977 |
| 7 kW | 6784 kWh | 5223 kWh | 1560 kWh | £1,339 | £156 | £1,495 | £23,692 | 15.8 yrs | £6,215 |
| 8 kW | 7753 kWh | 5970 kWh | 1783 kWh | £1,531 | £178 | £1,709 | £25,726 | 15.1 yrs | £8,453 |
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.