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 839 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: £705, 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 | 1677 kWh | 671 kWh | 1006 kWh | £182 | £101 | £282 | £4,069 | 14.4 yrs | £1,575 |
| 3 kW | 2516 kWh | 1006 kWh | 1510 kWh | £272 | £151 | £423 | £6,104 | 14.4 yrs | £2,362 |
| 4 kW | 3355 kWh | 1342 kWh | 2013 kWh | £363 | £201 | £564 | £8,138 | 14.4 yrs | £3,150 |
| 5 kW | 4193 kWh | 1677 kWh | 2516 kWh | £454 | £252 | £705 | £10,173 | 14.4 yrs | £3,937 |
| 6 kW | 5032 kWh | 2013 kWh | 3019 kWh | £545 | £302 | £847 | £12,207 | 14.4 yrs | £4,724 |
| 7 kW | 5871 kWh | 2348 kWh | 3522 kWh | £635 | £352 | £988 | £14,242 | 14.4 yrs | £5,512 |
| 8 kW | 6709 kWh | 2684 kWh | 4026 kWh | £726 | £403 | £1,129 | £16,276 | 14.4 yrs | £6,299 |
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: £849, 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 | 1677 kWh | 1006 kWh | 671 kWh | £272 | £67 | £339 | £6,169 | 18.2 yrs | £619 |
| 3 kW | 2516 kWh | 1510 kWh | 1006 kWh | £408 | £101 | £509 | £8,204 | 16.1 yrs | £1,979 |
| 4 kW | 3355 kWh | 2013 kWh | 1342 kWh | £545 | £134 | £679 | £10,238 | 15.1 yrs | £3,339 |
| 5 kW | 4193 kWh | 2516 kWh | 1677 kWh | £681 | £168 | £849 | £12,273 | 14.5 yrs | £4,698 |
| 6 kW | 5032 kWh | 3019 kWh | 2013 kWh | £817 | £201 | £1,018 | £14,307 | 14.1 yrs | £6,058 |
| 7 kW | 5871 kWh | 3522 kWh | 2348 kWh | £953 | £235 | £1,188 | £16,342 | 13.8 yrs | £7,418 |
| 8 kW | 6709 kWh | 4026 kWh | 2684 kWh | £1,089 | £268 | £1,358 | £18,376 | 13.5 yrs | £8,777 |
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: £920, Upfront: £13,673, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1677 kWh | 1174 kWh | 503 kWh | £318 | £50 | £368 | £7,569 | 20.6 yrs | £-208 |
| 3 kW | 2516 kWh | 1761 kWh | 755 kWh | £477 | £75 | £552 | £9,604 | 17.4 yrs | £1,437 |
| 4 kW | 3355 kWh | 2348 kWh | 1006 kWh | £635 | £101 | £736 | £11,638 | 15.8 yrs | £3,083 |
| 5 kW | 4193 kWh | 2935 kWh | 1258 kWh | £794 | £126 | £920 | £13,673 | 14.9 yrs | £4,729 |
| 6 kW | 5032 kWh | 3522 kWh | 1510 kWh | £953 | £151 | £1,104 | £15,707 | 14.2 yrs | £6,375 |
| 7 kW | 5871 kWh | 4109 kWh | 1761 kWh | £1,112 | £176 | £1,288 | £17,742 | 13.8 yrs | £8,021 |
| 8 kW | 6709 kWh | 4696 kWh | 2013 kWh | £1,271 | £201 | £1,472 | £19,776 | 13.4 yrs | £9,667 |
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: £942, Upfront: £15,423, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1677 kWh | 1224 kWh | 453 kWh | £331 | £45 | £377 | £9,319 | 24.7 yrs | £-1,787 |
| 3 kW | 2516 kWh | 1837 kWh | 679 kWh | £497 | £68 | £565 | £11,354 | 20.1 yrs | £-55 |
| 4 kW | 3355 kWh | 2449 kWh | 906 kWh | £663 | £91 | £753 | £13,388 | 17.8 yrs | £1,677 |
| 5 kW | 4193 kWh | 3061 kWh | 1132 kWh | £828 | £113 | £942 | £15,423 | 16.4 yrs | £3,408 |
| 6 kW | 5032 kWh | 3673 kWh | 1359 kWh | £994 | £136 | £1,130 | £17,457 | 15.5 yrs | £5,140 |
| 7 kW | 5871 kWh | 4286 kWh | 1585 kWh | £1,160 | £159 | £1,318 | £19,492 | 14.8 yrs | £6,872 |
| 8 kW | 6709 kWh | 4898 kWh | 1811 kWh | £1,325 | £181 | £1,506 | £21,526 | 14.3 yrs | £8,603 |
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: £956, Upfront: £17,173, Break-even: 18.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1677 kWh | 1258 kWh | 419 kWh | £340 | £42 | £382 | £11,069 | 29.0 yrs | £-3,422 |
| 3 kW | 2516 kWh | 1887 kWh | 629 kWh | £511 | £63 | £574 | £13,104 | 22.8 yrs | £-1,633 |
| 4 kW | 3355 kWh | 2516 kWh | 839 kWh | £681 | £84 | £765 | £15,138 | 19.8 yrs | £156 |
| 5 kW | 4193 kWh | 3145 kWh | 1048 kWh | £851 | £105 | £956 | £17,173 | 18.0 yrs | £1,944 |
| 6 kW | 5032 kWh | 3774 kWh | 1258 kWh | £1,021 | £126 | £1,147 | £19,207 | 16.7 yrs | £3,733 |
| 7 kW | 5871 kWh | 4403 kWh | 1468 kWh | £1,191 | £147 | £1,338 | £21,242 | 15.9 yrs | £5,522 |
| 8 kW | 6709 kWh | 5032 kWh | 1677 kWh | £1,362 | £168 | £1,529 | £23,276 | 15.2 yrs | £7,311 |
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: £970, Upfront: £19,623, Break-even: 20.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1677 kWh | 1292 kWh | 386 kWh | £349 | £39 | £388 | £13,519 | 34.8 yrs | £-5,758 |
| 3 kW | 2516 kWh | 1937 kWh | 579 kWh | £524 | £58 | £582 | £15,554 | 26.7 yrs | £-3,912 |
| 4 kW | 3355 kWh | 2583 kWh | 772 kWh | £699 | £77 | £776 | £17,588 | 22.7 yrs | £-2,066 |
| 5 kW | 4193 kWh | 3229 kWh | 964 kWh | £874 | £96 | £970 | £19,623 | 20.2 yrs | £-219 |
| 6 kW | 5032 kWh | 3875 kWh | 1157 kWh | £1,048 | £116 | £1,164 | £21,657 | 18.6 yrs | £1,627 |
| 7 kW | 5871 kWh | 4520 kWh | 1350 kWh | £1,223 | £135 | £1,358 | £23,692 | 17.4 yrs | £3,473 |
| 8 kW | 6709 kWh | 5166 kWh | 1543 kWh | £1,398 | £154 | £1,552 | £25,726 | 16.6 yrs | £5,319 |
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.