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 916 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £741, Upfront: £10,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1832 kWh | 733 kWh | 1099 kWh | £186 | £110 | £296 | £4,069 | 13.7 yrs | £1,857 |
| 3 kW | 2748 kWh | 1099 kWh | 1649 kWh | £280 | £165 | £444 | £6,104 | 13.7 yrs | £2,785 |
| 4 kW | 3664 kWh | 1466 kWh | 2198 kWh | £373 | £220 | £593 | £8,138 | 13.7 yrs | £3,713 |
| 5 kW | 4580 kWh | 1832 kWh | 2748 kWh | £466 | £275 | £741 | £10,173 | 13.7 yrs | £4,642 |
| 6 kW | 5496 kWh | 2198 kWh | 3298 kWh | £559 | £330 | £889 | £12,207 | 13.7 yrs | £5,570 |
| 7 kW | 6412 kWh | 2565 kWh | 3847 kWh | £652 | £385 | £1,037 | £14,242 | 13.7 yrs | £6,498 |
| 8 kW | 7328 kWh | 2931 kWh | 4397 kWh | £745 | £440 | £1,185 | £16,276 | 13.7 yrs | £7,427 |
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: £882, Upfront: £12,273, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1832 kWh | 1099 kWh | 733 kWh | £280 | £73 | £353 | £6,169 | 17.5 yrs | £887 |
| 3 kW | 2748 kWh | 1649 kWh | 1099 kWh | £419 | £110 | £529 | £8,204 | 15.5 yrs | £2,381 |
| 4 kW | 3664 kWh | 2198 kWh | 1466 kWh | £559 | £147 | £706 | £10,238 | 14.5 yrs | £3,875 |
| 5 kW | 4580 kWh | 2748 kWh | 1832 kWh | £699 | £183 | £882 | £12,273 | 13.9 yrs | £5,369 |
| 6 kW | 5496 kWh | 3298 kWh | 2198 kWh | £839 | £220 | £1,058 | £14,307 | 13.5 yrs | £6,862 |
| 7 kW | 6412 kWh | 3847 kWh | 2565 kWh | £978 | £256 | £1,235 | £16,342 | 13.2 yrs | £8,356 |
| 8 kW | 7328 kWh | 4397 kWh | 2931 kWh | £1,118 | £293 | £1,411 | £18,376 | 13.0 yrs | £9,850 |
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: £953, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1832 kWh | 1282 kWh | 550 kWh | £326 | £55 | £381 | £7,569 | 19.9 yrs | £53 |
| 3 kW | 2748 kWh | 1924 kWh | 824 kWh | £489 | £82 | £572 | £9,604 | 16.8 yrs | £1,829 |
| 4 kW | 3664 kWh | 2565 kWh | 1099 kWh | £652 | £110 | £762 | £11,638 | 15.3 yrs | £3,606 |
| 5 kW | 4580 kWh | 3206 kWh | 1374 kWh | £815 | £137 | £953 | £13,673 | 14.4 yrs | £5,382 |
| 6 kW | 5496 kWh | 3847 kWh | 1649 kWh | £978 | £165 | £1,143 | £15,707 | 13.7 yrs | £7,158 |
| 7 kW | 6412 kWh | 4489 kWh | 1924 kWh | £1,141 | £192 | £1,334 | £17,742 | 13.3 yrs | £8,935 |
| 8 kW | 7328 kWh | 5130 kWh | 2198 kWh | £1,305 | £220 | £1,524 | £19,776 | 13.0 yrs | £10,711 |
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: £974, Upfront: £15,423, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1832 kWh | 1337 kWh | 495 kWh | £340 | £49 | £390 | £9,319 | 23.9 yrs | £-1,528 |
| 3 kW | 2748 kWh | 2006 kWh | 742 kWh | £510 | £74 | £584 | £11,354 | 19.4 yrs | £334 |
| 4 kW | 3664 kWh | 2675 kWh | 989 kWh | £680 | £99 | £779 | £13,388 | 17.2 yrs | £2,195 |
| 5 kW | 4580 kWh | 3344 kWh | 1237 kWh | £850 | £124 | £974 | £15,423 | 15.8 yrs | £4,056 |
| 6 kW | 5496 kWh | 4012 kWh | 1484 kWh | £1,020 | £148 | £1,169 | £17,457 | 14.9 yrs | £5,917 |
| 7 kW | 6412 kWh | 4681 kWh | 1731 kWh | £1,190 | £173 | £1,364 | £19,492 | 14.3 yrs | £7,778 |
| 8 kW | 7328 kWh | 5350 kWh | 1979 kWh | £1,360 | £198 | £1,558 | £21,526 | 13.8 yrs | £9,640 |
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: £988, Upfront: £17,173, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1832 kWh | 1374 kWh | 458 kWh | £349 | £46 | £395 | £11,069 | 28.0 yrs | £-3,165 |
| 3 kW | 2748 kWh | 2061 kWh | 687 kWh | £524 | £69 | £593 | £13,104 | 22.1 yrs | £-1,247 |
| 4 kW | 3664 kWh | 2748 kWh | 916 kWh | £699 | £92 | £790 | £15,138 | 19.2 yrs | £671 |
| 5 kW | 4580 kWh | 3435 kWh | 1145 kWh | £874 | £115 | £988 | £17,173 | 17.4 yrs | £2,589 |
| 6 kW | 5496 kWh | 4122 kWh | 1374 kWh | £1,048 | £137 | £1,186 | £19,207 | 16.2 yrs | £4,506 |
| 7 kW | 6412 kWh | 4809 kWh | 1603 kWh | £1,223 | £160 | £1,383 | £21,242 | 15.4 yrs | £6,424 |
| 8 kW | 7328 kWh | 5496 kWh | 1832 kWh | £1,398 | £183 | £1,581 | £23,276 | 14.7 yrs | £8,342 |
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: £1,002, Upfront: £19,623, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1832 kWh | 1411 kWh | 421 kWh | £359 | £42 | £401 | £13,519 | 33.7 yrs | £-5,501 |
| 3 kW | 2748 kWh | 2116 kWh | 632 kWh | £538 | £63 | £601 | £15,554 | 25.9 yrs | £-3,527 |
| 4 kW | 3664 kWh | 2821 kWh | 843 kWh | £717 | £84 | £802 | £17,588 | 21.9 yrs | £-1,553 |
| 5 kW | 4580 kWh | 3527 kWh | 1053 kWh | £897 | £105 | £1,002 | £19,623 | 19.6 yrs | £421 |
| 6 kW | 5496 kWh | 4232 kWh | 1264 kWh | £1,076 | £126 | £1,203 | £21,657 | 18.0 yrs | £2,396 |
| 7 kW | 6412 kWh | 4937 kWh | 1475 kWh | £1,256 | £147 | £1,403 | £23,692 | 16.9 yrs | £4,370 |
| 8 kW | 7328 kWh | 5643 kWh | 1686 kWh | £1,435 | £169 | £1,604 | £25,726 | 16.0 yrs | £6,344 |
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.