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 850 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £694, Upfront: £10,173, Break-even: 14.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1700 kWh | 680 kWh | 1020 kWh | £176 | £102 | £278 | £4,069 | 14.7 yrs | £1,484 |
| 3 kW | 2549 kWh | 1020 kWh | 1530 kWh | £263 | £153 | £416 | £6,104 | 14.7 yrs | £2,226 |
| 4 kW | 3399 kWh | 1360 kWh | 2039 kWh | £351 | £204 | £555 | £8,138 | 14.7 yrs | £2,968 |
| 5 kW | 4249 kWh | 1700 kWh | 2549 kWh | £439 | £255 | £694 | £10,173 | 14.7 yrs | £3,709 |
| 6 kW | 5099 kWh | 2039 kWh | 3059 kWh | £527 | £306 | £833 | £12,207 | 14.7 yrs | £4,451 |
| 7 kW | 5948 kWh | 2379 kWh | 3569 kWh | £615 | £357 | £972 | £14,242 | 14.7 yrs | £5,193 |
| 8 kW | 6798 kWh | 2719 kWh | 4079 kWh | £703 | £408 | £1,111 | £16,276 | 14.7 yrs | £5,935 |
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: £829, Upfront: £12,273, Break-even: 14.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1700 kWh | 1020 kWh | 680 kWh | £263 | £68 | £331 | £6,169 | 18.6 yrs | £461 |
| 3 kW | 2549 kWh | 1530 kWh | 1020 kWh | £395 | £102 | £497 | £8,204 | 16.5 yrs | £1,741 |
| 4 kW | 3399 kWh | 2039 kWh | 1360 kWh | £527 | £136 | £663 | £10,238 | 15.4 yrs | £3,021 |
| 5 kW | 4249 kWh | 2549 kWh | 1700 kWh | £659 | £170 | £829 | £12,273 | 14.8 yrs | £4,302 |
| 6 kW | 5099 kWh | 3059 kWh | 2039 kWh | £790 | £204 | £994 | £14,307 | 14.4 yrs | £5,582 |
| 7 kW | 5948 kWh | 3569 kWh | 2379 kWh | £922 | £238 | £1,160 | £16,342 | 14.1 yrs | £6,862 |
| 8 kW | 6798 kWh | 4079 kWh | 2719 kWh | £1,054 | £272 | £1,326 | £18,376 | 13.9 yrs | £8,142 |
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: £896, Upfront: £13,673, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1700 kWh | 1190 kWh | 510 kWh | £307 | £51 | £358 | £7,569 | 21.1 yrs | £-401 |
| 3 kW | 2549 kWh | 1785 kWh | 765 kWh | £461 | £76 | £538 | £9,604 | 17.9 yrs | £1,149 |
| 4 kW | 3399 kWh | 2379 kWh | 1020 kWh | £615 | £102 | £717 | £11,638 | 16.2 yrs | £2,698 |
| 5 kW | 4249 kWh | 2974 kWh | 1275 kWh | £769 | £127 | £896 | £13,673 | 15.3 yrs | £4,248 |
| 6 kW | 5099 kWh | 3569 kWh | 1530 kWh | £922 | £153 | £1,075 | £15,707 | 14.6 yrs | £5,797 |
| 7 kW | 5948 kWh | 4164 kWh | 1785 kWh | £1,076 | £178 | £1,254 | £17,742 | 14.1 yrs | £7,347 |
| 8 kW | 6798 kWh | 4759 kWh | 2039 kWh | £1,230 | £204 | £1,434 | £19,776 | 13.8 yrs | £8,896 |
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: £916, Upfront: £15,423, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1700 kWh | 1241 kWh | 459 kWh | £321 | £46 | £366 | £9,319 | 25.4 yrs | £-1,989 |
| 3 kW | 2549 kWh | 1861 kWh | 688 kWh | £481 | £69 | £550 | £11,354 | 20.7 yrs | £-359 |
| 4 kW | 3399 kWh | 2481 kWh | 918 kWh | £641 | £92 | £733 | £13,388 | 18.3 yrs | £1,271 |
| 5 kW | 4249 kWh | 3102 kWh | 1147 kWh | £801 | £115 | £916 | £15,423 | 16.8 yrs | £2,901 |
| 6 kW | 5099 kWh | 3722 kWh | 1377 kWh | £962 | £138 | £1,099 | £17,457 | 15.9 yrs | £4,532 |
| 7 kW | 5948 kWh | 4342 kWh | 1606 kWh | £1,122 | £161 | £1,283 | £19,492 | 15.2 yrs | £6,162 |
| 8 kW | 6798 kWh | 4963 kWh | 1836 kWh | £1,282 | £184 | £1,466 | £21,526 | 14.7 yrs | £7,792 |
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: £930, Upfront: £17,173, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1700 kWh | 1275 kWh | 425 kWh | £329 | £42 | £372 | £11,069 | 29.8 yrs | £-3,632 |
| 3 kW | 2549 kWh | 1912 kWh | 637 kWh | £494 | £64 | £558 | £13,104 | 23.5 yrs | £-1,948 |
| 4 kW | 3399 kWh | 2549 kWh | 850 kWh | £659 | £85 | £744 | £15,138 | 20.4 yrs | £-263 |
| 5 kW | 4249 kWh | 3187 kWh | 1062 kWh | £823 | £106 | £930 | £17,173 | 18.5 yrs | £1,421 |
| 6 kW | 5099 kWh | 3824 kWh | 1275 kWh | £988 | £127 | £1,116 | £19,207 | 17.2 yrs | £3,105 |
| 7 kW | 5948 kWh | 4461 kWh | 1487 kWh | £1,153 | £149 | £1,302 | £21,242 | 16.3 yrs | £4,789 |
| 8 kW | 6798 kWh | 5099 kWh | 1700 kWh | £1,317 | £170 | £1,487 | £23,276 | 15.6 yrs | £6,473 |
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: £943, Upfront: £19,623, Break-even: 20.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1700 kWh | 1309 kWh | 391 kWh | £338 | £39 | £377 | £13,519 | 35.8 yrs | £-5,974 |
| 3 kW | 2549 kWh | 1963 kWh | 586 kWh | £507 | £59 | £566 | £15,554 | 27.5 yrs | £-4,236 |
| 4 kW | 3399 kWh | 2617 kWh | 782 kWh | £676 | £78 | £754 | £17,588 | 23.3 yrs | £-2,498 |
| 5 kW | 4249 kWh | 3272 kWh | 977 kWh | £845 | £98 | £943 | £19,623 | 20.8 yrs | £-760 |
| 6 kW | 5099 kWh | 3926 kWh | 1173 kWh | £1,014 | £117 | £1,132 | £21,657 | 19.1 yrs | £978 |
| 7 kW | 5948 kWh | 4580 kWh | 1368 kWh | £1,184 | £137 | £1,320 | £23,692 | 17.9 yrs | £2,716 |
| 8 kW | 6798 kWh | 5235 kWh | 1564 kWh | £1,353 | £156 | £1,509 | £25,726 | 17.0 yrs | £4,454 |
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.