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 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 | 1893 kWh | 757 kWh | 1136 kWh | £192 | £114 | £305 | £4,069 | 13.3 yrs | £2,039 |
| 3 kW | 2840 kWh | 1136 kWh | 1704 kWh | £288 | £170 | £458 | £6,104 | 13.3 yrs | £3,059 |
| 4 kW | 3787 kWh | 1515 kWh | 2272 kWh | £384 | £227 | £611 | £8,138 | 13.3 yrs | £4,079 |
| 5 kW | 4733 kWh | 1893 kWh | 2840 kWh | £480 | £284 | £764 | £10,173 | 13.3 yrs | £5,098 |
| 6 kW | 5680 kWh | 2272 kWh | 3408 kWh | £575 | £341 | £916 | £12,207 | 13.3 yrs | £6,118 |
| 7 kW | 6626 kWh | 2651 kWh | 3976 kWh | £671 | £398 | £1,069 | £14,242 | 13.3 yrs | £7,138 |
| 8 kW | 7573 kWh | 3029 kWh | 4544 kWh | £767 | £454 | £1,222 | £16,276 | 13.3 yrs | £8,158 |
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 | 1893 kWh | 1136 kWh | 757 kWh | £288 | £76 | £363 | £6,169 | 17.0 yrs | £1,100 |
| 3 kW | 2840 kWh | 1704 kWh | 1136 kWh | £432 | £114 | £545 | £8,204 | 15.0 yrs | £2,701 |
| 4 kW | 3787 kWh | 2272 kWh | 1515 kWh | £575 | £151 | £727 | £10,238 | 14.1 yrs | £4,301 |
| 5 kW | 4733 kWh | 2840 kWh | 1893 kWh | £719 | £189 | £909 | £12,273 | 13.5 yrs | £5,901 |
| 6 kW | 5680 kWh | 3408 kWh | 2272 kWh | £863 | £227 | £1,090 | £14,307 | 13.1 yrs | £7,501 |
| 7 kW | 6626 kWh | 3976 kWh | 2651 kWh | £1,007 | £265 | £1,272 | £16,342 | 12.8 yrs | £9,101 |
| 8 kW | 7573 kWh | 4544 kWh | 3029 kWh | £1,151 | £303 | £1,454 | £18,376 | 12.6 yrs | £10,701 |
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 | 1893 kWh | 1325 kWh | 568 kWh | £336 | £57 | £392 | £7,569 | 19.3 yrs | £281 |
| 3 kW | 2840 kWh | 1988 kWh | 852 kWh | £504 | £85 | £589 | £9,604 | 16.3 yrs | £2,171 |
| 4 kW | 3787 kWh | 2651 kWh | 1136 kWh | £671 | £114 | £785 | £11,638 | 14.8 yrs | £4,062 |
| 5 kW | 4733 kWh | 3313 kWh | 1420 kWh | £839 | £142 | £981 | £13,673 | 13.9 yrs | £5,952 |
| 6 kW | 5680 kWh | 3976 kWh | 1704 kWh | £1,007 | £170 | £1,177 | £15,707 | 13.3 yrs | £7,842 |
| 7 kW | 6626 kWh | 4638 kWh | 1988 kWh | £1,175 | £199 | £1,374 | £17,742 | 12.9 yrs | £9,733 |
| 8 kW | 7573 kWh | 5301 kWh | 2272 kWh | £1,343 | £227 | £1,570 | £19,776 | 12.6 yrs | £11,623 |
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 | 1893 kWh | 1382 kWh | 511 kWh | £350 | £51 | £401 | £9,319 | 23.2 yrs | £-1,295 |
| 3 kW | 2840 kWh | 2073 kWh | 767 kWh | £525 | £77 | £602 | £11,354 | 18.9 yrs | £682 |
| 4 kW | 3787 kWh | 2764 kWh | 1022 kWh | £700 | £102 | £802 | £13,388 | 16.7 yrs | £2,660 |
| 5 kW | 4733 kWh | 3455 kWh | 1278 kWh | £875 | £128 | £1,003 | £15,423 | 15.4 yrs | £4,637 |
| 6 kW | 5680 kWh | 4146 kWh | 1534 kWh | £1,050 | £153 | £1,204 | £17,457 | 14.5 yrs | £6,615 |
| 7 kW | 6626 kWh | 4837 kWh | 1789 kWh | £1,225 | £179 | £1,404 | £19,492 | 13.9 yrs | £8,592 |
| 8 kW | 7573 kWh | 5528 kWh | 2045 kWh | £1,400 | £204 | £1,605 | £21,526 | 13.4 yrs | £10,570 |
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 | 1893 kWh | 1420 kWh | 473 kWh | £360 | £47 | £407 | £11,069 | 27.2 yrs | £-2,929 |
| 3 kW | 2840 kWh | 2130 kWh | 710 kWh | £540 | £71 | £611 | £13,104 | 21.5 yrs | £-893 |
| 4 kW | 3787 kWh | 2840 kWh | 947 kWh | £719 | £95 | £814 | £15,138 | 18.6 yrs | £1,142 |
| 5 kW | 4733 kWh | 3550 kWh | 1183 kWh | £899 | £118 | £1,018 | £17,173 | 16.9 yrs | £3,178 |
| 6 kW | 5680 kWh | 4260 kWh | 1420 kWh | £1,079 | £142 | £1,221 | £19,207 | 15.7 yrs | £5,213 |
| 7 kW | 6626 kWh | 4970 kWh | 1657 kWh | £1,259 | £166 | £1,425 | £21,242 | 14.9 yrs | £7,249 |
| 8 kW | 7573 kWh | 5680 kWh | 1893 kWh | £1,439 | £189 | £1,628 | £23,276 | 14.3 yrs | £9,284 |
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 | 1893 kWh | 1458 kWh | 435 kWh | £369 | £44 | £413 | £13,519 | 32.7 yrs | £-5,263 |
| 3 kW | 2840 kWh | 2187 kWh | 653 kWh | £554 | £65 | £619 | £15,554 | 25.1 yrs | £-3,169 |
| 4 kW | 3787 kWh | 2916 kWh | 871 kWh | £739 | £87 | £826 | £17,588 | 21.3 yrs | £-1,076 |
| 5 kW | 4733 kWh | 3645 kWh | 1089 kWh | £923 | £109 | £1,032 | £19,623 | 19.0 yrs | £1,018 |
| 6 kW | 5680 kWh | 4373 kWh | 1306 kWh | £1,108 | £131 | £1,238 | £21,657 | 17.5 yrs | £3,111 |
| 7 kW | 6626 kWh | 5102 kWh | 1524 kWh | £1,292 | £152 | £1,445 | £23,692 | 16.4 yrs | £5,205 |
| 8 kW | 7573 kWh | 5831 kWh | 1742 kWh | £1,477 | £174 | £1,651 | £25,726 | 15.6 yrs | £7,299 |
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.