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 827 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £695, Upfront: £10,173, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1653 kWh | 661 kWh | 992 kWh | £179 | £99 | £278 | £4,069 | 14.6 yrs | £1,494 |
| 3 kW | 2480 kWh | 992 kWh | 1488 kWh | £268 | £149 | £417 | £6,104 | 14.6 yrs | £2,240 |
| 4 kW | 3306 kWh | 1323 kWh | 1984 kWh | £358 | £198 | £556 | £8,138 | 14.6 yrs | £2,987 |
| 5 kW | 4133 kWh | 1653 kWh | 2480 kWh | £447 | £248 | £695 | £10,173 | 14.6 yrs | £3,734 |
| 6 kW | 4959 kWh | 1984 kWh | 2976 kWh | £537 | £298 | £834 | £12,207 | 14.6 yrs | £4,481 |
| 7 kW | 5786 kWh | 2314 kWh | 3472 kWh | £626 | £347 | £973 | £14,242 | 14.6 yrs | £5,227 |
| 8 kW | 6613 kWh | 2645 kWh | 3968 kWh | £716 | £397 | £1,113 | £16,276 | 14.6 yrs | £5,974 |
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: £836, Upfront: £12,273, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1653 kWh | 992 kWh | 661 kWh | £268 | £66 | £335 | £6,169 | 18.4 yrs | £522 |
| 3 kW | 2480 kWh | 1488 kWh | 992 kWh | £403 | £99 | £502 | £8,204 | 16.3 yrs | £1,832 |
| 4 kW | 3306 kWh | 1984 kWh | 1323 kWh | £537 | £132 | £669 | £10,238 | 15.3 yrs | £3,143 |
| 5 kW | 4133 kWh | 2480 kWh | 1653 kWh | £671 | £165 | £836 | £12,273 | 14.7 yrs | £4,454 |
| 6 kW | 4959 kWh | 2976 kWh | 1984 kWh | £805 | £198 | £1,004 | £14,307 | 14.3 yrs | £5,765 |
| 7 kW | 5786 kWh | 3472 kWh | 2314 kWh | £939 | £231 | £1,171 | £16,342 | 14.0 yrs | £7,076 |
| 8 kW | 6613 kWh | 3968 kWh | 2645 kWh | £1,074 | £265 | £1,338 | £18,376 | 13.7 yrs | £8,387 |
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: £907, Upfront: £13,673, 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 | 1653 kWh | 1157 kWh | 496 kWh | £313 | £50 | £363 | £7,569 | 20.9 yrs | £-314 |
| 3 kW | 2480 kWh | 1736 kWh | 744 kWh | £470 | £74 | £544 | £9,604 | 17.7 yrs | £1,279 |
| 4 kW | 3306 kWh | 2314 kWh | 992 kWh | £626 | £99 | £725 | £11,638 | 16.0 yrs | £2,871 |
| 5 kW | 4133 kWh | 2893 kWh | 1240 kWh | £783 | £124 | £907 | £13,673 | 15.1 yrs | £4,464 |
| 6 kW | 4959 kWh | 3472 kWh | 1488 kWh | £939 | £149 | £1,088 | £15,707 | 14.4 yrs | £6,057 |
| 7 kW | 5786 kWh | 4050 kWh | 1736 kWh | £1,096 | £174 | £1,270 | £17,742 | 14.0 yrs | £7,650 |
| 8 kW | 6613 kWh | 4629 kWh | 1984 kWh | £1,253 | £198 | £1,451 | £19,776 | 13.6 yrs | £9,243 |
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: £928, Upfront: £15,423, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1653 kWh | 1207 kWh | 446 kWh | £327 | £45 | £371 | £9,319 | 25.1 yrs | £-1,895 |
| 3 kW | 2480 kWh | 1810 kWh | 670 kWh | £490 | £67 | £557 | £11,354 | 20.4 yrs | £-218 |
| 4 kW | 3306 kWh | 2414 kWh | 893 kWh | £653 | £89 | £742 | £13,388 | 18.0 yrs | £1,460 |
| 5 kW | 4133 kWh | 3017 kWh | 1116 kWh | £816 | £112 | £928 | £15,423 | 16.6 yrs | £3,137 |
| 6 kW | 4959 kWh | 3620 kWh | 1339 kWh | £980 | £134 | £1,114 | £17,457 | 15.7 yrs | £4,815 |
| 7 kW | 5786 kWh | 4224 kWh | 1562 kWh | £1,143 | £156 | £1,299 | £19,492 | 15.0 yrs | £6,492 |
| 8 kW | 6613 kWh | 4827 kWh | 1785 kWh | £1,306 | £179 | £1,485 | £21,526 | 14.5 yrs | £8,170 |
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: £942, Upfront: £17,173, Break-even: 18.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1653 kWh | 1240 kWh | 413 kWh | £336 | £41 | £377 | £11,069 | 29.4 yrs | £-3,532 |
| 3 kW | 2480 kWh | 1860 kWh | 620 kWh | £503 | £62 | £565 | £13,104 | 23.2 yrs | £-1,798 |
| 4 kW | 3306 kWh | 2480 kWh | 827 kWh | £671 | £83 | £754 | £15,138 | 20.1 yrs | £-65 |
| 5 kW | 4133 kWh | 3100 kWh | 1033 kWh | £839 | £103 | £942 | £17,173 | 18.2 yrs | £1,669 |
| 6 kW | 4959 kWh | 3720 kWh | 1240 kWh | £1,007 | £124 | £1,131 | £19,207 | 17.0 yrs | £3,403 |
| 7 kW | 5786 kWh | 4340 kWh | 1447 kWh | £1,174 | £145 | £1,319 | £21,242 | 16.1 yrs | £5,137 |
| 8 kW | 6613 kWh | 4959 kWh | 1653 kWh | £1,342 | £165 | £1,507 | £23,276 | 15.4 yrs | £6,871 |
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: £956, Upfront: £19,623, Break-even: 20.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1653 kWh | 1273 kWh | 380 kWh | £344 | £38 | £382 | £13,519 | 35.3 yrs | £-5,869 |
| 3 kW | 2480 kWh | 1909 kWh | 570 kWh | £517 | £57 | £574 | £15,554 | 27.1 yrs | £-4,079 |
| 4 kW | 3306 kWh | 2546 kWh | 760 kWh | £689 | £76 | £765 | £17,588 | 23.0 yrs | £-2,289 |
| 5 kW | 4133 kWh | 3182 kWh | 951 kWh | £861 | £95 | £956 | £19,623 | 20.5 yrs | £-499 |
| 6 kW | 4959 kWh | 3819 kWh | 1141 kWh | £1,033 | £114 | £1,147 | £21,657 | 18.9 yrs | £1,292 |
| 7 kW | 5786 kWh | 4455 kWh | 1331 kWh | £1,206 | £133 | £1,339 | £23,692 | 17.7 yrs | £3,082 |
| 8 kW | 6613 kWh | 5092 kWh | 1521 kWh | £1,378 | £152 | £1,530 | £25,726 | 16.8 yrs | £4,872 |
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.