A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 947 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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 | 1894 kWh | 757 kWh | 1136 kWh | £192 | £114 | £305 | £4,069 | 13.3 yrs | £2,040 |
| 3 kW | 2840 kWh | 1136 kWh | 1704 kWh | £288 | £170 | £458 | £6,104 | 13.3 yrs | £3,061 |
| 4 kW | 3787 kWh | 1515 kWh | 2272 kWh | £384 | £227 | £611 | £8,138 | 13.3 yrs | £4,081 |
| 5 kW | 4734 kWh | 1894 kWh | 2840 kWh | £480 | £284 | £764 | £10,173 | 13.3 yrs | £5,101 |
| 6 kW | 5681 kWh | 2272 kWh | 3408 kWh | £576 | £341 | £916 | £12,207 | 13.3 yrs | £6,121 |
| 7 kW | 6627 kWh | 2651 kWh | 3976 kWh | £671 | £398 | £1,069 | £14,242 | 13.3 yrs | £7,141 |
| 8 kW | 7574 kWh | 3030 kWh | 4545 kWh | £767 | £454 | £1,222 | £16,276 | 13.3 yrs | £8,161 |
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: £909, 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 | 1894 kWh | 1136 kWh | 757 kWh | £288 | £76 | £364 | £6,169 | 17.0 yrs | £1,101 |
| 3 kW | 2840 kWh | 1704 kWh | 1136 kWh | £432 | £114 | £545 | £8,204 | 15.0 yrs | £2,702 |
| 4 kW | 3787 kWh | 2272 kWh | 1515 kWh | £576 | £151 | £727 | £10,238 | 14.1 yrs | £4,303 |
| 5 kW | 4734 kWh | 2840 kWh | 1894 kWh | £719 | £189 | £909 | £12,273 | 13.5 yrs | £5,904 |
| 6 kW | 5681 kWh | 3408 kWh | 2272 kWh | £863 | £227 | £1,091 | £14,307 | 13.1 yrs | £7,504 |
| 7 kW | 6627 kWh | 3976 kWh | 2651 kWh | £1,007 | £265 | £1,272 | £16,342 | 12.8 yrs | £9,105 |
| 8 kW | 7574 kWh | 4545 kWh | 3030 kWh | £1,151 | £303 | £1,454 | £18,376 | 12.6 yrs | £10,706 |
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: £981, 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 | 1894 kWh | 1325 kWh | 568 kWh | £336 | £57 | £393 | £7,569 | 19.3 yrs | £282 |
| 3 kW | 2840 kWh | 1988 kWh | 852 kWh | £504 | £85 | £589 | £9,604 | 16.3 yrs | £2,173 |
| 4 kW | 3787 kWh | 2651 kWh | 1136 kWh | £671 | £114 | £785 | £11,638 | 14.8 yrs | £4,064 |
| 5 kW | 4734 kWh | 3314 kWh | 1420 kWh | £839 | £142 | £981 | £13,673 | 13.9 yrs | £5,955 |
| 6 kW | 5681 kWh | 3976 kWh | 1704 kWh | £1,007 | £170 | £1,178 | £15,707 | 13.3 yrs | £7,846 |
| 7 kW | 6627 kWh | 4639 kWh | 1988 kWh | £1,175 | £199 | £1,374 | £17,742 | 12.9 yrs | £9,737 |
| 8 kW | 7574 kWh | 5302 kWh | 2272 kWh | £1,343 | £227 | £1,570 | £19,776 | 12.6 yrs | £11,628 |
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: £1,003, Upfront: £15,423, 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 | 1894 kWh | 1382 kWh | 511 kWh | £350 | £51 | £401 | £9,319 | 23.2 yrs | £-1,294 |
| 3 kW | 2840 kWh | 2073 kWh | 767 kWh | £525 | £77 | £602 | £11,354 | 18.9 yrs | £684 |
| 4 kW | 3787 kWh | 2765 kWh | 1023 kWh | £700 | £102 | £803 | £13,388 | 16.7 yrs | £2,662 |
| 5 kW | 4734 kWh | 3456 kWh | 1278 kWh | £875 | £128 | £1,003 | £15,423 | 15.4 yrs | £4,641 |
| 6 kW | 5681 kWh | 4147 kWh | 1534 kWh | £1,050 | £153 | £1,204 | £17,457 | 14.5 yrs | £6,619 |
| 7 kW | 6627 kWh | 4838 kWh | 1789 kWh | £1,225 | £179 | £1,404 | £19,492 | 13.9 yrs | £8,597 |
| 8 kW | 7574 kWh | 5529 kWh | 2045 kWh | £1,401 | £205 | £1,605 | £21,526 | 13.4 yrs | £10,575 |
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: £1,018, Upfront: £17,173, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1894 kWh | 1420 kWh | 473 kWh | £360 | £47 | £407 | £11,069 | 27.2 yrs | £-2,928 |
| 3 kW | 2840 kWh | 2130 kWh | 710 kWh | £540 | £71 | £611 | £13,104 | 21.5 yrs | £-891 |
| 4 kW | 3787 kWh | 2840 kWh | 947 kWh | £719 | £95 | £814 | £15,138 | 18.6 yrs | £1,145 |
| 5 kW | 4734 kWh | 3550 kWh | 1183 kWh | £899 | £118 | £1,018 | £17,173 | 16.9 yrs | £3,181 |
| 6 kW | 5681 kWh | 4261 kWh | 1420 kWh | £1,079 | £142 | £1,221 | £19,207 | 15.7 yrs | £5,217 |
| 7 kW | 6627 kWh | 4971 kWh | 1657 kWh | £1,259 | £166 | £1,425 | £21,242 | 14.9 yrs | £7,253 |
| 8 kW | 7574 kWh | 5681 kWh | 1894 kWh | £1,439 | £189 | £1,628 | £23,276 | 14.3 yrs | £9,289 |
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: £1,032, 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 | 1894 kWh | 1458 kWh | 436 kWh | £369 | £44 | £413 | £13,519 | 32.7 yrs | £-5,262 |
| 3 kW | 2840 kWh | 2187 kWh | 653 kWh | £554 | £65 | £619 | £15,554 | 25.1 yrs | £-3,167 |
| 4 kW | 3787 kWh | 2916 kWh | 871 kWh | £739 | £87 | £826 | £17,588 | 21.3 yrs | £-1,073 |
| 5 kW | 4734 kWh | 3645 kWh | 1089 kWh | £923 | £109 | £1,032 | £19,623 | 19.0 yrs | £1,021 |
| 6 kW | 5681 kWh | 4374 kWh | 1307 kWh | £1,108 | £131 | £1,239 | £21,657 | 17.5 yrs | £3,115 |
| 7 kW | 6627 kWh | 5103 kWh | 1524 kWh | £1,293 | £152 | £1,445 | £23,692 | 16.4 yrs | £5,210 |
| 8 kW | 7574 kWh | 5832 kWh | 1742 kWh | £1,477 | £174 | £1,651 | £25,726 | 15.6 yrs | £7,304 |
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.