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 786 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: £661, Upfront: £10,173, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1573 kWh | 629 kWh | 944 kWh | £170 | £94 | £265 | £4,069 | 15.4 yrs | £1,223 |
| 3 kW | 2359 kWh | 944 kWh | 1415 kWh | £255 | £142 | £397 | £6,104 | 15.4 yrs | £1,834 |
| 4 kW | 3145 kWh | 1258 kWh | 1887 kWh | £340 | £189 | £529 | £8,138 | 15.4 yrs | £2,446 |
| 5 kW | 3932 kWh | 1573 kWh | 2359 kWh | £426 | £236 | £661 | £10,173 | 15.4 yrs | £3,057 |
| 6 kW | 4718 kWh | 1887 kWh | 2831 kWh | £511 | £283 | £794 | £12,207 | 15.4 yrs | £3,669 |
| 7 kW | 5505 kWh | 2202 kWh | 3303 kWh | £596 | £330 | £926 | £14,242 | 15.4 yrs | £4,280 |
| 8 kW | 6291 kWh | 2516 kWh | 3775 kWh | £681 | £377 | £1,058 | £16,276 | 15.4 yrs | £4,891 |
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: £796, Upfront: £12,273, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1573 kWh | 944 kWh | 629 kWh | £255 | £63 | £318 | £6,169 | 19.4 yrs | £196 |
| 3 kW | 2359 kWh | 1415 kWh | 944 kWh | £383 | £94 | £477 | £8,204 | 17.2 yrs | £1,344 |
| 4 kW | 3145 kWh | 1887 kWh | 1258 kWh | £511 | £126 | £637 | £10,238 | 16.1 yrs | £2,492 |
| 5 kW | 3932 kWh | 2359 kWh | 1573 kWh | £638 | £157 | £796 | £12,273 | 15.4 yrs | £3,640 |
| 6 kW | 4718 kWh | 2831 kWh | 1887 kWh | £766 | £189 | £955 | £14,307 | 15.0 yrs | £4,788 |
| 7 kW | 5505 kWh | 3303 kWh | 2202 kWh | £894 | £220 | £1,114 | £16,342 | 14.7 yrs | £5,936 |
| 8 kW | 6291 kWh | 3775 kWh | 2516 kWh | £1,021 | £252 | £1,273 | £18,376 | 14.4 yrs | £7,084 |
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: £863, Upfront: £13,673, 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 | 1573 kWh | 1101 kWh | 472 kWh | £298 | £47 | £345 | £7,569 | 21.9 yrs | £-667 |
| 3 kW | 2359 kWh | 1651 kWh | 708 kWh | £447 | £71 | £518 | £9,604 | 18.6 yrs | £749 |
| 4 kW | 3145 kWh | 2202 kWh | 944 kWh | £596 | £94 | £690 | £11,638 | 16.9 yrs | £2,165 |
| 5 kW | 3932 kWh | 2752 kWh | 1180 kWh | £745 | £118 | £863 | £13,673 | 15.8 yrs | £3,582 |
| 6 kW | 4718 kWh | 3303 kWh | 1415 kWh | £894 | £142 | £1,035 | £15,707 | 15.2 yrs | £4,998 |
| 7 kW | 5505 kWh | 3853 kWh | 1651 kWh | £1,043 | £165 | £1,208 | £17,742 | 14.7 yrs | £6,414 |
| 8 kW | 6291 kWh | 4404 kWh | 1887 kWh | £1,192 | £189 | £1,380 | £19,776 | 14.3 yrs | £7,831 |
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: £883, Upfront: £15,423, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1573 kWh | 1148 kWh | 425 kWh | £311 | £42 | £353 | £9,319 | 26.4 yrs | £-2,256 |
| 3 kW | 2359 kWh | 1722 kWh | 637 kWh | £466 | £64 | £530 | £11,354 | 21.4 yrs | £-759 |
| 4 kW | 3145 kWh | 2296 kWh | 849 kWh | £621 | £85 | £706 | £13,388 | 19.0 yrs | £737 |
| 5 kW | 3932 kWh | 2870 kWh | 1062 kWh | £777 | £106 | £883 | £15,423 | 17.5 yrs | £2,234 |
| 6 kW | 4718 kWh | 3444 kWh | 1274 kWh | £932 | £127 | £1,059 | £17,457 | 16.5 yrs | £3,731 |
| 7 kW | 5505 kWh | 4018 kWh | 1486 kWh | £1,087 | £149 | £1,236 | £19,492 | 15.8 yrs | £5,228 |
| 8 kW | 6291 kWh | 4592 kWh | 1699 kWh | £1,243 | £170 | £1,413 | £21,526 | 15.2 yrs | £6,725 |
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: £896, Upfront: £17,173, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1573 kWh | 1180 kWh | 393 kWh | £319 | £39 | £359 | £11,069 | 30.9 yrs | £-3,899 |
| 3 kW | 2359 kWh | 1769 kWh | 590 kWh | £479 | £59 | £538 | £13,104 | 24.4 yrs | £-2,348 |
| 4 kW | 3145 kWh | 2359 kWh | 786 kWh | £638 | £79 | £717 | £15,138 | 21.1 yrs | £-798 |
| 5 kW | 3932 kWh | 2949 kWh | 983 kWh | £798 | £98 | £896 | £17,173 | 19.2 yrs | £753 |
| 6 kW | 4718 kWh | 3539 kWh | 1180 kWh | £958 | £118 | £1,076 | £19,207 | 17.9 yrs | £2,303 |
| 7 kW | 5505 kWh | 4128 kWh | 1376 kWh | £1,117 | £138 | £1,255 | £21,242 | 16.9 yrs | £3,854 |
| 8 kW | 6291 kWh | 4718 kWh | 1573 kWh | £1,277 | £157 | £1,434 | £23,276 | 16.2 yrs | £5,404 |
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: £910, Upfront: £19,623, Break-even: 21.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1573 kWh | 1211 kWh | 362 kWh | £328 | £36 | £364 | £13,519 | 37.2 yrs | £-6,242 |
| 3 kW | 2359 kWh | 1816 kWh | 543 kWh | £492 | £54 | £546 | £15,554 | 28.5 yrs | £-4,638 |
| 4 kW | 3145 kWh | 2422 kWh | 723 kWh | £655 | £72 | £728 | £17,588 | 24.2 yrs | £-3,033 |
| 5 kW | 3932 kWh | 3027 kWh | 904 kWh | £819 | £90 | £910 | £19,623 | 21.6 yrs | £-1,429 |
| 6 kW | 4718 kWh | 3633 kWh | 1085 kWh | £983 | £109 | £1,092 | £21,657 | 19.8 yrs | £175 |
| 7 kW | 5505 kWh | 4238 kWh | 1266 kWh | £1,147 | £127 | £1,274 | £23,692 | 18.6 yrs | £1,779 |
| 8 kW | 6291 kWh | 4844 kWh | 1447 kWh | £1,311 | £145 | £1,455 | £25,726 | 17.7 yrs | £3,383 |
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.