A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 942 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: £764, Upfront: £10,173, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1884 kWh | 754 kWh | 1130 kWh | £193 | £113 | £306 | £4,069 | 13.3 yrs | £2,043 |
| 3 kW | 2826 kWh | 1130 kWh | 1696 kWh | £289 | £170 | £458 | £6,104 | 13.3 yrs | £3,065 |
| 4 kW | 3768 kWh | 1507 kWh | 2261 kWh | £385 | £226 | £611 | £8,138 | 13.3 yrs | £4,086 |
| 5 kW | 4710 kWh | 1884 kWh | 2826 kWh | £481 | £283 | £764 | £10,173 | 13.3 yrs | £5,108 |
| 6 kW | 5652 kWh | 2261 kWh | 3391 kWh | £578 | £339 | £917 | £12,207 | 13.3 yrs | £6,129 |
| 7 kW | 6594 kWh | 2638 kWh | 3957 kWh | £674 | £396 | £1,070 | £14,242 | 13.3 yrs | £7,151 |
| 8 kW | 7536 kWh | 3015 kWh | 4522 kWh | £770 | £452 | £1,222 | £16,276 | 13.3 yrs | £8,172 |
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: £911, Upfront: £12,273, 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 | 1884 kWh | 1130 kWh | 754 kWh | £289 | £75 | £364 | £6,169 | 16.9 yrs | £1,115 |
| 3 kW | 2826 kWh | 1696 kWh | 1130 kWh | £433 | £113 | £546 | £8,204 | 15.0 yrs | £2,722 |
| 4 kW | 3768 kWh | 2261 kWh | 1507 kWh | £578 | £151 | £728 | £10,238 | 14.1 yrs | £4,330 |
| 5 kW | 4710 kWh | 2826 kWh | 1884 kWh | £722 | £188 | £911 | £12,273 | 13.5 yrs | £5,937 |
| 6 kW | 5652 kWh | 3391 kWh | 2261 kWh | £867 | £226 | £1,093 | £14,307 | 13.1 yrs | £7,545 |
| 7 kW | 6594 kWh | 3957 kWh | 2638 kWh | £1,011 | £264 | £1,275 | £16,342 | 12.8 yrs | £9,152 |
| 8 kW | 7536 kWh | 4522 kWh | 3015 kWh | £1,155 | £301 | £1,457 | £18,376 | 12.6 yrs | £10,760 |
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: £984, Upfront: £13,673, 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 | 1884 kWh | 1319 kWh | 565 kWh | £337 | £57 | £393 | £7,569 | 19.2 yrs | £301 |
| 3 kW | 2826 kWh | 1978 kWh | 848 kWh | £505 | £85 | £590 | £9,604 | 16.3 yrs | £2,201 |
| 4 kW | 3768 kWh | 2638 kWh | 1130 kWh | £674 | £113 | £787 | £11,638 | 14.8 yrs | £4,102 |
| 5 kW | 4710 kWh | 3297 kWh | 1413 kWh | £842 | £141 | £984 | £13,673 | 13.9 yrs | £6,002 |
| 6 kW | 5652 kWh | 3957 kWh | 1696 kWh | £1,011 | £170 | £1,180 | £15,707 | 13.3 yrs | £7,903 |
| 7 kW | 6594 kWh | 4616 kWh | 1978 kWh | £1,179 | £198 | £1,377 | £17,742 | 12.9 yrs | £9,803 |
| 8 kW | 7536 kWh | 5276 kWh | 2261 kWh | £1,348 | £226 | £1,574 | £19,776 | 12.6 yrs | £11,704 |
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: £1,006, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1884 kWh | 1375 kWh | 509 kWh | £351 | £51 | £402 | £9,319 | 23.2 yrs | £-1,273 |
| 3 kW | 2826 kWh | 2063 kWh | 763 kWh | £527 | £76 | £603 | £11,354 | 18.8 yrs | £715 |
| 4 kW | 3768 kWh | 2751 kWh | 1017 kWh | £703 | £102 | £805 | £13,388 | 16.6 yrs | £2,703 |
| 5 kW | 4710 kWh | 3439 kWh | 1272 kWh | £879 | £127 | £1,006 | £15,423 | 15.3 yrs | £4,692 |
| 6 kW | 5652 kWh | 4126 kWh | 1526 kWh | £1,054 | £153 | £1,207 | £17,457 | 14.5 yrs | £6,680 |
| 7 kW | 6594 kWh | 4814 kWh | 1780 kWh | £1,230 | £178 | £1,408 | £19,492 | 13.8 yrs | £8,669 |
| 8 kW | 7536 kWh | 5502 kWh | 2035 kWh | £1,406 | £203 | £1,609 | £21,526 | 13.4 yrs | £10,657 |
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: £1,020, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1884 kWh | 1413 kWh | 471 kWh | £361 | £47 | £408 | £11,069 | 27.1 yrs | £-2,906 |
| 3 kW | 2826 kWh | 2120 kWh | 707 kWh | £542 | £71 | £612 | £13,104 | 21.4 yrs | £-859 |
| 4 kW | 3768 kWh | 2826 kWh | 942 kWh | £722 | £94 | £816 | £15,138 | 18.5 yrs | £1,188 |
| 5 kW | 4710 kWh | 3533 kWh | 1178 kWh | £903 | £118 | £1,020 | £17,173 | 16.8 yrs | £3,235 |
| 6 kW | 5652 kWh | 4239 kWh | 1413 kWh | £1,083 | £141 | £1,224 | £19,207 | 15.7 yrs | £5,282 |
| 7 kW | 6594 kWh | 4946 kWh | 1649 kWh | £1,264 | £165 | £1,429 | £21,242 | 14.9 yrs | £7,329 |
| 8 kW | 7536 kWh | 5652 kWh | 1884 kWh | £1,444 | £188 | £1,633 | £23,276 | 14.3 yrs | £9,376 |
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: £1,035, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1884 kWh | 1451 kWh | 433 kWh | £371 | £43 | £414 | £13,519 | 32.7 yrs | £-5,239 |
| 3 kW | 2826 kWh | 2176 kWh | 650 kWh | £556 | £65 | £621 | £15,554 | 25.0 yrs | £-3,133 |
| 4 kW | 3768 kWh | 2902 kWh | 867 kWh | £741 | £87 | £828 | £17,588 | 21.2 yrs | £-1,028 |
| 5 kW | 4710 kWh | 3627 kWh | 1083 kWh | £927 | £108 | £1,035 | £19,623 | 19.0 yrs | £1,078 |
| 6 kW | 5652 kWh | 4352 kWh | 1300 kWh | £1,112 | £130 | £1,242 | £21,657 | 17.4 yrs | £3,183 |
| 7 kW | 6594 kWh | 5078 kWh | 1517 kWh | £1,297 | £152 | £1,449 | £23,692 | 16.4 yrs | £5,289 |
| 8 kW | 7536 kWh | 5803 kWh | 1733 kWh | £1,483 | £173 | £1,656 | £25,726 | 15.5 yrs | £7,394 |
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.