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 1004 kWh per year on a south-facing roof. We value self-used electricity at 26.8p 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: £840, Upfront: £10,173, Break-even: 12.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 803 kWh | 1205 kWh | £215 | £120 | £336 | £4,069 | 12.1 yrs | £2,647 |
| 3 kW | 3011 kWh | 1205 kWh | 1807 kWh | £323 | £181 | £504 | £6,104 | 12.1 yrs | £3,971 |
| 4 kW | 4015 kWh | 1606 kWh | 2409 kWh | £431 | £241 | £672 | £8,138 | 12.1 yrs | £5,295 |
| 5 kW | 5019 kWh | 2008 kWh | 3011 kWh | £538 | £301 | £840 | £10,173 | 12.1 yrs | £6,619 |
| 6 kW | 6023 kWh | 2409 kWh | 3614 kWh | £646 | £361 | £1,007 | £12,207 | 12.1 yrs | £7,942 |
| 7 kW | 7026 kWh | 2811 kWh | 4216 kWh | £754 | £422 | £1,175 | £14,242 | 12.1 yrs | £9,266 |
| 8 kW | 8030 kWh | 3212 kWh | 4818 kWh | £861 | £482 | £1,343 | £16,276 | 12.1 yrs | £10,590 |
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: £1,008, Upfront: £12,273, Break-even: 12.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 1205 kWh | 803 kWh | £323 | £80 | £403 | £6,169 | 15.3 yrs | £1,898 |
| 3 kW | 3011 kWh | 1807 kWh | 1205 kWh | £485 | £120 | £605 | £8,204 | 13.6 yrs | £3,897 |
| 4 kW | 4015 kWh | 2409 kWh | 1606 kWh | £646 | £161 | £807 | £10,238 | 12.7 yrs | £5,896 |
| 5 kW | 5019 kWh | 3011 kWh | 2008 kWh | £808 | £201 | £1,008 | £12,273 | 12.2 yrs | £7,895 |
| 6 kW | 6023 kWh | 3614 kWh | 2409 kWh | £969 | £241 | £1,210 | £14,307 | 11.8 yrs | £9,894 |
| 7 kW | 7026 kWh | 4216 kWh | 2811 kWh | £1,131 | £281 | £1,412 | £16,342 | 11.6 yrs | £11,893 |
| 8 kW | 8030 kWh | 4818 kWh | 3212 kWh | £1,292 | £321 | £1,613 | £18,376 | 11.4 yrs | £13,892 |
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: £1,093, Upfront: £13,673, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 1405 kWh | 602 kWh | £377 | £60 | £437 | £7,569 | 17.3 yrs | £1,173 |
| 3 kW | 3011 kWh | 2108 kWh | 903 kWh | £565 | £90 | £656 | £9,604 | 14.6 yrs | £3,510 |
| 4 kW | 4015 kWh | 2811 kWh | 1205 kWh | £754 | £120 | £874 | £11,638 | 13.3 yrs | £5,847 |
| 5 kW | 5019 kWh | 3513 kWh | 1506 kWh | £942 | £151 | £1,093 | £13,673 | 12.5 yrs | £8,184 |
| 6 kW | 6023 kWh | 4216 kWh | 1807 kWh | £1,131 | £181 | £1,311 | £15,707 | 12.0 yrs | £10,520 |
| 7 kW | 7026 kWh | 4918 kWh | 2108 kWh | £1,319 | £211 | £1,530 | £17,742 | 11.6 yrs | £12,857 |
| 8 kW | 8030 kWh | 5621 kWh | 2409 kWh | £1,508 | £241 | £1,748 | £19,776 | 11.3 yrs | £15,194 |
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: £1,118, Upfront: £15,423, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 1466 kWh | 542 kWh | £393 | £54 | £447 | £9,319 | 20.8 yrs | £-374 |
| 3 kW | 3011 kWh | 2198 kWh | 813 kWh | £590 | £81 | £671 | £11,354 | 16.9 yrs | £2,064 |
| 4 kW | 4015 kWh | 2931 kWh | 1084 kWh | £786 | £108 | £895 | £13,388 | 15.0 yrs | £4,502 |
| 5 kW | 5019 kWh | 3664 kWh | 1355 kWh | £983 | £136 | £1,118 | £15,423 | 13.8 yrs | £6,940 |
| 6 kW | 6023 kWh | 4397 kWh | 1626 kWh | £1,179 | £163 | £1,342 | £17,457 | 13.0 yrs | £9,378 |
| 7 kW | 7026 kWh | 5129 kWh | 1897 kWh | £1,376 | £190 | £1,565 | £19,492 | 12.5 yrs | £11,816 |
| 8 kW | 8030 kWh | 5862 kWh | 2168 kWh | £1,572 | £217 | £1,789 | £21,526 | 12.0 yrs | £14,254 |
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: £1,135, Upfront: £17,173, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 1506 kWh | 502 kWh | £404 | £50 | £454 | £11,069 | 24.4 yrs | £-1,989 |
| 3 kW | 3011 kWh | 2258 kWh | 753 kWh | £606 | £75 | £681 | £13,104 | 19.2 yrs | £517 |
| 4 kW | 4015 kWh | 3011 kWh | 1004 kWh | £808 | £100 | £908 | £15,138 | 16.7 yrs | £3,022 |
| 5 kW | 5019 kWh | 3764 kWh | 1255 kWh | £1,010 | £125 | £1,135 | £17,173 | 15.1 yrs | £5,528 |
| 6 kW | 6023 kWh | 4517 kWh | 1506 kWh | £1,211 | £151 | £1,362 | £19,207 | 14.1 yrs | £8,033 |
| 7 kW | 7026 kWh | 5270 kWh | 1757 kWh | £1,413 | £176 | £1,589 | £21,242 | 13.4 yrs | £10,539 |
| 8 kW | 8030 kWh | 6023 kWh | 2008 kWh | £1,615 | £201 | £1,816 | £23,276 | 12.8 yrs | £13,044 |
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: £1,152, Upfront: £19,623, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2008 kWh | 1546 kWh | 462 kWh | £415 | £46 | £461 | £13,519 | 29.3 yrs | £-4,304 |
| 3 kW | 3011 kWh | 2319 kWh | 693 kWh | £622 | £69 | £691 | £15,554 | 22.5 yrs | £-1,731 |
| 4 kW | 4015 kWh | 3092 kWh | 923 kWh | £829 | £92 | £922 | £17,588 | 19.1 yrs | £842 |
| 5 kW | 5019 kWh | 3865 kWh | 1154 kWh | £1,036 | £115 | £1,152 | £19,623 | 17.0 yrs | £3,415 |
| 6 kW | 6023 kWh | 4637 kWh | 1385 kWh | £1,244 | £139 | £1,382 | £21,657 | 15.7 yrs | £5,988 |
| 7 kW | 7026 kWh | 5410 kWh | 1616 kWh | £1,451 | £162 | £1,613 | £23,692 | 14.7 yrs | £8,562 |
| 8 kW | 8030 kWh | 6183 kWh | 1847 kWh | £1,658 | £185 | £1,843 | £25,726 | 14.0 yrs | £11,135 |
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.