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 946 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £765, 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 | 1892 kWh | 757 kWh | 1135 kWh | £192 | £114 | £306 | £4,069 | 13.3 yrs | £2,050 |
| 3 kW | 2838 kWh | 1135 kWh | 1703 kWh | £289 | £170 | £459 | £6,104 | 13.3 yrs | £3,075 |
| 4 kW | 3784 kWh | 1514 kWh | 2270 kWh | £385 | £227 | £612 | £8,138 | 13.3 yrs | £4,100 |
| 5 kW | 4730 kWh | 1892 kWh | 2838 kWh | £481 | £284 | £765 | £10,173 | 13.3 yrs | £5,126 |
| 6 kW | 5676 kWh | 2270 kWh | 3405 kWh | £577 | £341 | £918 | £12,207 | 13.3 yrs | £6,151 |
| 7 kW | 6622 kWh | 2649 kWh | 3973 kWh | £674 | £397 | £1,071 | £14,242 | 13.3 yrs | £7,176 |
| 8 kW | 7568 kWh | 3027 kWh | 4541 kWh | £770 | £454 | £1,224 | £16,276 | 13.3 yrs | £8,201 |
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 | 1892 kWh | 1135 kWh | 757 kWh | £289 | £76 | £364 | £6,169 | 16.9 yrs | £1,118 |
| 3 kW | 2838 kWh | 1703 kWh | 1135 kWh | £433 | £114 | £547 | £8,204 | 15.0 yrs | £2,727 |
| 4 kW | 3784 kWh | 2270 kWh | 1514 kWh | £577 | £151 | £729 | £10,238 | 14.0 yrs | £4,336 |
| 5 kW | 4730 kWh | 2838 kWh | 1892 kWh | £722 | £189 | £911 | £12,273 | 13.5 yrs | £5,945 |
| 6 kW | 5676 kWh | 3405 kWh | 2270 kWh | £866 | £227 | £1,093 | £14,307 | 13.1 yrs | £7,554 |
| 7 kW | 6622 kWh | 3973 kWh | 2649 kWh | £1,010 | £265 | £1,275 | £16,342 | 12.8 yrs | £9,163 |
| 8 kW | 7568 kWh | 4541 kWh | 3027 kWh | £1,155 | £303 | £1,457 | £18,376 | 12.6 yrs | £10,772 |
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 | 1892 kWh | 1324 kWh | 568 kWh | £337 | £57 | £394 | £7,569 | 19.2 yrs | £302 |
| 3 kW | 2838 kWh | 1987 kWh | 851 kWh | £505 | £85 | £590 | £9,604 | 16.3 yrs | £2,203 |
| 4 kW | 3784 kWh | 2649 kWh | 1135 kWh | £674 | £114 | £787 | £11,638 | 14.8 yrs | £4,103 |
| 5 kW | 4730 kWh | 3311 kWh | 1419 kWh | £842 | £142 | £984 | £13,673 | 13.9 yrs | £6,004 |
| 6 kW | 5676 kWh | 3973 kWh | 1703 kWh | £1,010 | £170 | £1,181 | £15,707 | 13.3 yrs | £7,905 |
| 7 kW | 6622 kWh | 4635 kWh | 1987 kWh | £1,179 | £199 | £1,377 | £17,742 | 12.9 yrs | £9,806 |
| 8 kW | 7568 kWh | 5297 kWh | 2270 kWh | £1,347 | £227 | £1,574 | £19,776 | 12.6 yrs | £11,707 |
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 | 1892 kWh | 1381 kWh | 511 kWh | £351 | £51 | £402 | £9,319 | 23.2 yrs | £-1,273 |
| 3 kW | 2838 kWh | 2072 kWh | 766 kWh | £527 | £77 | £603 | £11,354 | 18.8 yrs | £715 |
| 4 kW | 3784 kWh | 2762 kWh | 1022 kWh | £702 | £102 | £805 | £13,388 | 16.6 yrs | £2,704 |
| 5 kW | 4730 kWh | 3453 kWh | 1277 kWh | £878 | £128 | £1,006 | £15,423 | 15.3 yrs | £4,692 |
| 6 kW | 5676 kWh | 4143 kWh | 1532 kWh | £1,054 | £153 | £1,207 | £17,457 | 14.5 yrs | £6,681 |
| 7 kW | 6622 kWh | 4834 kWh | 1788 kWh | £1,229 | £179 | £1,408 | £19,492 | 13.8 yrs | £8,669 |
| 8 kW | 7568 kWh | 5524 kWh | 2043 kWh | £1,405 | £204 | £1,609 | £21,526 | 13.4 yrs | £10,658 |
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 | 1892 kWh | 1419 kWh | 473 kWh | £361 | £47 | £408 | £11,069 | 27.1 yrs | £-2,906 |
| 3 kW | 2838 kWh | 2128 kWh | 709 kWh | £541 | £71 | £612 | £13,104 | 21.4 yrs | £-859 |
| 4 kW | 3784 kWh | 2838 kWh | 946 kWh | £722 | £95 | £816 | £15,138 | 18.5 yrs | £1,187 |
| 5 kW | 4730 kWh | 3547 kWh | 1182 kWh | £902 | £118 | £1,020 | £17,173 | 16.8 yrs | £3,234 |
| 6 kW | 5676 kWh | 4257 kWh | 1419 kWh | £1,083 | £142 | £1,224 | £19,207 | 15.7 yrs | £5,281 |
| 7 kW | 6622 kWh | 4966 kWh | 1655 kWh | £1,263 | £166 | £1,428 | £21,242 | 14.9 yrs | £7,328 |
| 8 kW | 7568 kWh | 5676 kWh | 1892 kWh | £1,443 | £189 | £1,633 | £23,276 | 14.3 yrs | £9,375 |
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 | 1892 kWh | 1457 kWh | 435 kWh | £370 | £44 | £414 | £13,519 | 32.7 yrs | £-5,240 |
| 3 kW | 2838 kWh | 2185 kWh | 653 kWh | £556 | £65 | £621 | £15,554 | 25.0 yrs | £-3,134 |
| 4 kW | 3784 kWh | 2914 kWh | 870 kWh | £741 | £87 | £828 | £17,588 | 21.2 yrs | £-1,029 |
| 5 kW | 4730 kWh | 3642 kWh | 1088 kWh | £926 | £109 | £1,035 | £19,623 | 19.0 yrs | £1,076 |
| 6 kW | 5676 kWh | 4370 kWh | 1305 kWh | £1,111 | £131 | £1,242 | £21,657 | 17.4 yrs | £3,181 |
| 7 kW | 6622 kWh | 5099 kWh | 1523 kWh | £1,297 | £152 | £1,449 | £23,692 | 16.4 yrs | £5,287 |
| 8 kW | 7568 kWh | 5827 kWh | 1741 kWh | £1,482 | £174 | £1,656 | £25,726 | 15.5 yrs | £7,392 |
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.