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 1055 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £876, Upfront: £10,173, Break-even: 11.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2110 kWh | 844 kWh | 1266 kWh | £224 | £127 | £350 | £4,069 | 11.6 yrs | £2,940 |
| 3 kW | 3164 kWh | 1266 kWh | 1899 kWh | £336 | £190 | £526 | £6,104 | 11.6 yrs | £4,410 |
| 4 kW | 4219 kWh | 1688 kWh | 2531 kWh | £448 | £253 | £701 | £8,138 | 11.6 yrs | £5,880 |
| 5 kW | 5274 kWh | 2110 kWh | 3164 kWh | £560 | £316 | £876 | £10,173 | 11.6 yrs | £7,349 |
| 6 kW | 6329 kWh | 2531 kWh | 3797 kWh | £672 | £380 | £1,051 | £12,207 | 11.6 yrs | £8,819 |
| 7 kW | 7383 kWh | 2953 kWh | 4430 kWh | £784 | £443 | £1,227 | £14,242 | 11.6 yrs | £10,289 |
| 8 kW | 8438 kWh | 3375 kWh | 5063 kWh | £895 | £506 | £1,402 | £16,276 | 11.6 yrs | £11,759 |
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: £1,050, Upfront: £12,273, Break-even: 11.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2110 kWh | 1266 kWh | 844 kWh | £336 | £84 | £420 | £6,169 | 14.7 yrs | £2,235 |
| 3 kW | 3164 kWh | 1899 kWh | 1266 kWh | £504 | £127 | £630 | £8,204 | 13.0 yrs | £4,402 |
| 4 kW | 4219 kWh | 2531 kWh | 1688 kWh | £672 | £169 | £840 | £10,238 | 12.2 yrs | £6,569 |
| 5 kW | 5274 kWh | 3164 kWh | 2110 kWh | £839 | £211 | £1,050 | £12,273 | 11.7 yrs | £8,737 |
| 6 kW | 6329 kWh | 3797 kWh | 2531 kWh | £1,007 | £253 | £1,261 | £14,307 | 11.3 yrs | £10,904 |
| 7 kW | 7383 kWh | 4430 kWh | 2953 kWh | £1,175 | £295 | £1,471 | £16,342 | 11.1 yrs | £13,071 |
| 8 kW | 8438 kWh | 5063 kWh | 3375 kWh | £1,343 | £338 | £1,681 | £18,376 | 10.9 yrs | £15,238 |
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: £1,138, Upfront: £13,673, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2110 kWh | 1477 kWh | 633 kWh | £392 | £63 | £455 | £7,569 | 16.6 yrs | £1,532 |
| 3 kW | 3164 kWh | 2215 kWh | 949 kWh | £588 | £95 | £683 | £9,604 | 14.1 yrs | £4,048 |
| 4 kW | 4219 kWh | 2953 kWh | 1266 kWh | £784 | £127 | £910 | £11,638 | 12.8 yrs | £6,564 |
| 5 kW | 5274 kWh | 3692 kWh | 1582 kWh | £979 | £158 | £1,138 | £13,673 | 12.0 yrs | £9,080 |
| 6 kW | 6329 kWh | 4430 kWh | 1899 kWh | £1,175 | £190 | £1,365 | £15,707 | 11.5 yrs | £11,596 |
| 7 kW | 7383 kWh | 5168 kWh | 2215 kWh | £1,371 | £222 | £1,593 | £17,742 | 11.1 yrs | £14,112 |
| 8 kW | 8438 kWh | 5907 kWh | 2531 kWh | £1,567 | £253 | £1,820 | £19,776 | 10.9 yrs | £16,628 |
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: £1,164, Upfront: £15,423, 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 | 2110 kWh | 1540 kWh | 570 kWh | £409 | £57 | £466 | £9,319 | 20.0 yrs | £-9 |
| 3 kW | 3164 kWh | 2310 kWh | 854 kWh | £613 | £85 | £698 | £11,354 | 16.3 yrs | £2,612 |
| 4 kW | 4219 kWh | 3080 kWh | 1139 kWh | £817 | £114 | £931 | £13,388 | 14.4 yrs | £5,233 |
| 5 kW | 5274 kWh | 3850 kWh | 1424 kWh | £1,021 | £142 | £1,164 | £15,423 | 13.3 yrs | £7,853 |
| 6 kW | 6329 kWh | 4620 kWh | 1709 kWh | £1,226 | £171 | £1,397 | £17,457 | 12.5 yrs | £10,474 |
| 7 kW | 7383 kWh | 5390 kWh | 1994 kWh | £1,430 | £199 | £1,629 | £19,492 | 12.0 yrs | £13,094 |
| 8 kW | 8438 kWh | 6160 kWh | 2278 kWh | £1,634 | £228 | £1,862 | £21,526 | 11.6 yrs | £15,715 |
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: £1,181, Upfront: £17,173, 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 | 2110 kWh | 1582 kWh | 527 kWh | £420 | £53 | £472 | £11,069 | 23.4 yrs | £-1,619 |
| 3 kW | 3164 kWh | 2373 kWh | 791 kWh | £630 | £79 | £709 | £13,104 | 18.5 yrs | £1,071 |
| 4 kW | 4219 kWh | 3164 kWh | 1055 kWh | £839 | £105 | £945 | £15,138 | 16.0 yrs | £3,762 |
| 5 kW | 5274 kWh | 3955 kWh | 1318 kWh | £1,049 | £132 | £1,181 | £17,173 | 14.5 yrs | £6,452 |
| 6 kW | 6329 kWh | 4747 kWh | 1582 kWh | £1,259 | £158 | £1,417 | £19,207 | 13.6 yrs | £9,142 |
| 7 kW | 7383 kWh | 5538 kWh | 1846 kWh | £1,469 | £185 | £1,654 | £21,242 | 12.8 yrs | £11,833 |
| 8 kW | 8438 kWh | 6329 kWh | 2110 kWh | £1,679 | £211 | £1,890 | £23,276 | 12.3 yrs | £14,523 |
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: £1,199, Upfront: £19,623, 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 | 2110 kWh | 1624 kWh | 485 kWh | £431 | £49 | £479 | £13,519 | 28.2 yrs | £-3,930 |
| 3 kW | 3164 kWh | 2437 kWh | 728 kWh | £646 | £73 | £719 | £15,554 | 21.6 yrs | £-1,170 |
| 4 kW | 4219 kWh | 3249 kWh | 970 kWh | £862 | £97 | £959 | £17,588 | 18.3 yrs | £1,590 |
| 5 kW | 5274 kWh | 4061 kWh | 1213 kWh | £1,077 | £121 | £1,199 | £19,623 | 16.4 yrs | £4,351 |
| 6 kW | 6329 kWh | 4873 kWh | 1456 kWh | £1,293 | £146 | £1,438 | £21,657 | 15.1 yrs | £7,111 |
| 7 kW | 7383 kWh | 5685 kWh | 1698 kWh | £1,508 | £170 | £1,678 | £23,692 | 14.1 yrs | £9,871 |
| 8 kW | 8438 kWh | 6497 kWh | 1941 kWh | £1,724 | £194 | £1,918 | £25,726 | 13.4 yrs | £12,631 |
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.