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 921 kWh per year on a south-facing roof. We value self-used electricity at 27.7p 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: £787, Upfront: £10,173, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1842 kWh | 737 kWh | 1105 kWh | £204 | £111 | £315 | £4,069 | 12.9 yrs | £2,226 |
| 3 kW | 2763 kWh | 1105 kWh | 1658 kWh | £306 | £166 | £472 | £6,104 | 12.9 yrs | £3,339 |
| 4 kW | 3684 kWh | 1474 kWh | 2210 kWh | £408 | £221 | £630 | £8,138 | 12.9 yrs | £4,453 |
| 5 kW | 4605 kWh | 1842 kWh | 2763 kWh | £511 | £276 | £787 | £10,173 | 12.9 yrs | £5,566 |
| 6 kW | 5526 kWh | 2210 kWh | 3316 kWh | £613 | £332 | £944 | £12,207 | 12.9 yrs | £6,679 |
| 7 kW | 6447 kWh | 2579 kWh | 3868 kWh | £715 | £387 | £1,102 | £14,242 | 12.9 yrs | £7,792 |
| 8 kW | 7368 kWh | 2947 kWh | 4421 kWh | £817 | £442 | £1,259 | £16,276 | 12.9 yrs | £8,905 |
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: £950, Upfront: £12,273, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1842 kWh | 1105 kWh | 737 kWh | £306 | £74 | £380 | £6,169 | 16.2 yrs | £1,432 |
| 3 kW | 2763 kWh | 1658 kWh | 1105 kWh | £460 | £111 | £570 | £8,204 | 14.4 yrs | £3,198 |
| 4 kW | 3684 kWh | 2210 kWh | 1474 kWh | £613 | £147 | £760 | £10,238 | 13.5 yrs | £4,964 |
| 5 kW | 4605 kWh | 2763 kWh | 1842 kWh | £766 | £184 | £950 | £12,273 | 12.9 yrs | £6,730 |
| 6 kW | 5526 kWh | 3316 kWh | 2210 kWh | £919 | £221 | £1,140 | £14,307 | 12.5 yrs | £8,496 |
| 7 kW | 6447 kWh | 3868 kWh | 2579 kWh | £1,072 | £258 | £1,330 | £16,342 | 12.3 yrs | £10,262 |
| 8 kW | 7368 kWh | 4421 kWh | 2947 kWh | £1,225 | £295 | £1,520 | £18,376 | 12.1 yrs | £12,028 |
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: £1,032, Upfront: £13,673, 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 | 1842 kWh | 1289 kWh | 553 kWh | £357 | £55 | £413 | £7,569 | 18.3 yrs | £685 |
| 3 kW | 2763 kWh | 1934 kWh | 829 kWh | £536 | £83 | £619 | £9,604 | 15.5 yrs | £2,777 |
| 4 kW | 3684 kWh | 2579 kWh | 1105 kWh | £715 | £111 | £825 | £11,638 | 14.1 yrs | £4,869 |
| 5 kW | 4605 kWh | 3224 kWh | 1382 kWh | £894 | £138 | £1,032 | £13,673 | 13.3 yrs | £6,962 |
| 6 kW | 5526 kWh | 3868 kWh | 1658 kWh | £1,072 | £166 | £1,238 | £15,707 | 12.7 yrs | £9,054 |
| 7 kW | 6447 kWh | 4513 kWh | 1934 kWh | £1,251 | £193 | £1,444 | £17,742 | 12.3 yrs | £11,146 |
| 8 kW | 7368 kWh | 5158 kWh | 2210 kWh | £1,430 | £221 | £1,651 | £19,776 | 12.0 yrs | £13,239 |
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: £1,056, Upfront: £15,423, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1842 kWh | 1345 kWh | 497 kWh | £373 | £50 | £422 | £9,319 | 22.1 yrs | £-869 |
| 3 kW | 2763 kWh | 2017 kWh | 746 kWh | £559 | £75 | £634 | £11,354 | 17.9 yrs | £1,321 |
| 4 kW | 3684 kWh | 2689 kWh | 995 kWh | £745 | £99 | £845 | £13,388 | 15.8 yrs | £3,511 |
| 5 kW | 4605 kWh | 3362 kWh | 1243 kWh | £932 | £124 | £1,056 | £15,423 | 14.6 yrs | £5,701 |
| 6 kW | 5526 kWh | 4034 kWh | 1492 kWh | £1,118 | £149 | £1,267 | £17,457 | 13.8 yrs | £7,892 |
| 7 kW | 6447 kWh | 4706 kWh | 1741 kWh | £1,305 | £174 | £1,479 | £19,492 | 13.2 yrs | £10,082 |
| 8 kW | 7368 kWh | 5379 kWh | 1989 kWh | £1,491 | £199 | £1,690 | £21,526 | 12.7 yrs | £12,272 |
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: £1,073, Upfront: £17,173, Break-even: 16.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1842 kWh | 1382 kWh | 461 kWh | £383 | £46 | £429 | £11,069 | 25.8 yrs | £-2,489 |
| 3 kW | 2763 kWh | 2072 kWh | 691 kWh | £574 | £69 | £644 | £13,104 | 20.4 yrs | £-233 |
| 4 kW | 3684 kWh | 2763 kWh | 921 kWh | £766 | £92 | £858 | £15,138 | 17.6 yrs | £2,022 |
| 5 kW | 4605 kWh | 3454 kWh | 1151 kWh | £957 | £115 | £1,073 | £17,173 | 16.0 yrs | £4,278 |
| 6 kW | 5526 kWh | 4145 kWh | 1382 kWh | £1,149 | £138 | £1,287 | £19,207 | 14.9 yrs | £6,533 |
| 7 kW | 6447 kWh | 4835 kWh | 1612 kWh | £1,340 | £161 | £1,502 | £21,242 | 14.1 yrs | £8,789 |
| 8 kW | 7368 kWh | 5526 kWh | 1842 kWh | £1,532 | £184 | £1,716 | £23,276 | 13.6 yrs | £11,044 |
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: £1,089, Upfront: £19,623, Break-even: 18.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1842 kWh | 1418 kWh | 424 kWh | £393 | £42 | £436 | £13,519 | 31.0 yrs | £-4,808 |
| 3 kW | 2763 kWh | 2128 kWh | 635 kWh | £590 | £64 | £653 | £15,554 | 23.8 yrs | £-2,487 |
| 4 kW | 3684 kWh | 2837 kWh | 847 kWh | £786 | £85 | £871 | £17,588 | 20.2 yrs | £-167 |
| 5 kW | 4605 kWh | 3546 kWh | 1059 kWh | £983 | £106 | £1,089 | £19,623 | 18.0 yrs | £2,154 |
| 6 kW | 5526 kWh | 4255 kWh | 1271 kWh | £1,180 | £127 | £1,307 | £21,657 | 16.6 yrs | £4,475 |
| 7 kW | 6447 kWh | 4964 kWh | 1483 kWh | £1,376 | £148 | £1,524 | £23,692 | 15.5 yrs | £6,796 |
| 8 kW | 7368 kWh | 5673 kWh | 1695 kWh | £1,573 | £169 | £1,742 | £25,726 | 14.8 yrs | £9,117 |
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.