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 866 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £707, Upfront: £10,173, 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 | 1732 kWh | 693 kWh | 1039 kWh | £179 | £104 | £283 | £4,069 | 14.4 yrs | £1,589 |
| 3 kW | 2598 kWh | 1039 kWh | 1559 kWh | £268 | £156 | £424 | £6,104 | 14.4 yrs | £2,383 |
| 4 kW | 3464 kWh | 1385 kWh | 2078 kWh | £358 | £208 | £566 | £8,138 | 14.4 yrs | £3,178 |
| 5 kW | 4329 kWh | 1732 kWh | 2598 kWh | £447 | £260 | £707 | £10,173 | 14.4 yrs | £3,972 |
| 6 kW | 5195 kWh | 2078 kWh | 3117 kWh | £537 | £312 | £849 | £12,207 | 14.4 yrs | £4,767 |
| 7 kW | 6061 kWh | 2424 kWh | 3637 kWh | £626 | £364 | £990 | £14,242 | 14.4 yrs | £5,561 |
| 8 kW | 6927 kWh | 2771 kWh | 4156 kWh | £716 | £416 | £1,132 | £16,276 | 14.4 yrs | £6,356 |
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: £844, Upfront: £12,273, Break-even: 14.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1039 kWh | 693 kWh | £268 | £69 | £338 | £6,169 | 18.3 yrs | £586 |
| 3 kW | 2598 kWh | 1559 kWh | 1039 kWh | £403 | £104 | £507 | £8,204 | 16.2 yrs | £1,929 |
| 4 kW | 3464 kWh | 2078 kWh | 1385 kWh | £537 | £139 | £676 | £10,238 | 15.2 yrs | £3,272 |
| 5 kW | 4329 kWh | 2598 kWh | 1732 kWh | £671 | £173 | £844 | £12,273 | 14.5 yrs | £4,616 |
| 6 kW | 5195 kWh | 3117 kWh | 2078 kWh | £805 | £208 | £1,013 | £14,307 | 14.1 yrs | £5,959 |
| 7 kW | 6061 kWh | 3637 kWh | 2424 kWh | £940 | £242 | £1,182 | £16,342 | 13.8 yrs | £7,302 |
| 8 kW | 6927 kWh | 4156 kWh | 2771 kWh | £1,074 | £277 | £1,351 | £18,376 | 13.6 yrs | £8,645 |
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: £913, Upfront: £13,673, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1212 kWh | 520 kWh | £313 | £52 | £365 | £7,569 | 20.7 yrs | £-265 |
| 3 kW | 2598 kWh | 1818 kWh | 779 kWh | £470 | £78 | £548 | £9,604 | 17.5 yrs | £1,352 |
| 4 kW | 3464 kWh | 2424 kWh | 1039 kWh | £626 | £104 | £730 | £11,638 | 15.9 yrs | £2,970 |
| 5 kW | 4329 kWh | 3031 kWh | 1299 kWh | £783 | £130 | £913 | £13,673 | 15.0 yrs | £4,587 |
| 6 kW | 5195 kWh | 3637 kWh | 1559 kWh | £940 | £156 | £1,096 | £15,707 | 14.3 yrs | £6,205 |
| 7 kW | 6061 kWh | 4243 kWh | 1818 kWh | £1,096 | £182 | £1,278 | £17,742 | 13.9 yrs | £7,822 |
| 8 kW | 6927 kWh | 4849 kWh | 2078 kWh | £1,253 | £208 | £1,461 | £19,776 | 13.5 yrs | £9,439 |
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: £934, Upfront: £15,423, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1264 kWh | 468 kWh | £327 | £47 | £373 | £9,319 | 25.0 yrs | £-1,851 |
| 3 kW | 2598 kWh | 1896 kWh | 701 kWh | £490 | £70 | £560 | £11,354 | 20.3 yrs | £-151 |
| 4 kW | 3464 kWh | 2528 kWh | 935 kWh | £653 | £94 | £747 | £13,388 | 17.9 yrs | £1,549 |
| 5 kW | 4329 kWh | 3160 kWh | 1169 kWh | £817 | £117 | £934 | £15,423 | 16.5 yrs | £3,249 |
| 6 kW | 5195 kWh | 3793 kWh | 1403 kWh | £980 | £140 | £1,120 | £17,457 | 15.6 yrs | £4,948 |
| 7 kW | 6061 kWh | 4425 kWh | 1637 kWh | £1,143 | £164 | £1,307 | £19,492 | 14.9 yrs | £6,648 |
| 8 kW | 6927 kWh | 5057 kWh | 1870 kWh | £1,307 | £187 | £1,494 | £21,526 | 14.4 yrs | £8,348 |
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: £947, Upfront: £17,173, Break-even: 18.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1299 kWh | 433 kWh | £336 | £43 | £379 | £11,069 | 29.2 yrs | £-3,491 |
| 3 kW | 2598 kWh | 1948 kWh | 649 kWh | £503 | £65 | £568 | £13,104 | 23.1 yrs | £-1,736 |
| 4 kW | 3464 kWh | 2598 kWh | 866 kWh | £671 | £87 | £758 | £15,138 | 20.0 yrs | £18 |
| 5 kW | 4329 kWh | 3247 kWh | 1082 kWh | £839 | £108 | £947 | £17,173 | 18.1 yrs | £1,773 |
| 6 kW | 5195 kWh | 3896 kWh | 1299 kWh | £1,007 | £130 | £1,137 | £19,207 | 16.9 yrs | £3,527 |
| 7 kW | 6061 kWh | 4546 kWh | 1515 kWh | £1,175 | £152 | £1,326 | £21,242 | 16.0 yrs | £5,282 |
| 8 kW | 6927 kWh | 5195 kWh | 1732 kWh | £1,342 | £173 | £1,516 | £23,276 | 15.4 yrs | £7,037 |
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: £961, Upfront: £19,623, Break-even: 20.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1333 kWh | 398 kWh | £345 | £40 | £384 | £13,519 | 35.2 yrs | £-5,831 |
| 3 kW | 2598 kWh | 2000 kWh | 597 kWh | £517 | £60 | £577 | £15,554 | 27.0 yrs | £-4,022 |
| 4 kW | 3464 kWh | 2667 kWh | 797 kWh | £689 | £80 | £769 | £17,588 | 22.9 yrs | £-2,212 |
| 5 kW | 4329 kWh | 3334 kWh | 996 kWh | £861 | £100 | £961 | £19,623 | 20.4 yrs | £-403 |
| 6 kW | 5195 kWh | 4000 kWh | 1195 kWh | £1,034 | £119 | £1,153 | £21,657 | 18.8 yrs | £1,407 |
| 7 kW | 6061 kWh | 4667 kWh | 1394 kWh | £1,206 | £139 | £1,345 | £23,692 | 17.6 yrs | £3,216 |
| 8 kW | 6927 kWh | 5334 kWh | 1593 kWh | £1,378 | £159 | £1,538 | £25,726 | 16.7 yrs | £5,026 |
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.