A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 877 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: £707, Upfront: £10,173, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 702 kWh | 1053 kWh | £178 | £105 | £283 | £4,069 | 14.4 yrs | £1,591 |
| 3 kW | 2631 kWh | 1053 kWh | 1579 kWh | £267 | £158 | £424 | £6,104 | 14.4 yrs | £2,386 |
| 4 kW | 3508 kWh | 1403 kWh | 2105 kWh | £355 | £211 | £566 | £8,138 | 14.4 yrs | £3,181 |
| 5 kW | 4385 kWh | 1754 kWh | 2631 kWh | £444 | £263 | £707 | £10,173 | 14.4 yrs | £3,977 |
| 6 kW | 5263 kWh | 2105 kWh | 3158 kWh | £533 | £316 | £849 | £12,207 | 14.4 yrs | £4,772 |
| 7 kW | 6140 kWh | 2456 kWh | 3684 kWh | £622 | £368 | £990 | £14,242 | 14.4 yrs | £5,567 |
| 8 kW | 7017 kWh | 2807 kWh | 4210 kWh | £711 | £421 | £1,132 | £16,276 | 14.4 yrs | £6,363 |
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: £842, Upfront: £12,273, 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 | 1754 kWh | 1053 kWh | 702 kWh | £267 | £70 | £337 | £6,169 | 18.3 yrs | £566 |
| 3 kW | 2631 kWh | 1579 kWh | 1053 kWh | £400 | £105 | £505 | £8,204 | 16.2 yrs | £1,899 |
| 4 kW | 3508 kWh | 2105 kWh | 1403 kWh | £533 | £140 | £674 | £10,238 | 15.2 yrs | £3,233 |
| 5 kW | 4385 kWh | 2631 kWh | 1754 kWh | £667 | £175 | £842 | £12,273 | 14.6 yrs | £4,566 |
| 6 kW | 5263 kWh | 3158 kWh | 2105 kWh | £800 | £211 | £1,010 | £14,307 | 14.2 yrs | £5,899 |
| 7 kW | 6140 kWh | 3684 kWh | 2456 kWh | £933 | £246 | £1,179 | £16,342 | 13.9 yrs | £7,232 |
| 8 kW | 7017 kWh | 4210 kWh | 2807 kWh | £1,066 | £281 | £1,347 | £18,376 | 13.6 yrs | £8,565 |
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: £909, Upfront: £13,673, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1228 kWh | 526 kWh | £311 | £53 | £364 | £7,569 | 20.8 yrs | £-296 |
| 3 kW | 2631 kWh | 1842 kWh | 789 kWh | £467 | £79 | £545 | £9,604 | 17.6 yrs | £1,306 |
| 4 kW | 3508 kWh | 2456 kWh | 1053 kWh | £622 | £105 | £727 | £11,638 | 16.0 yrs | £2,908 |
| 5 kW | 4385 kWh | 3070 kWh | 1316 kWh | £778 | £132 | £909 | £13,673 | 15.0 yrs | £4,510 |
| 6 kW | 5263 kWh | 3684 kWh | 1579 kWh | £933 | £158 | £1,091 | £15,707 | 14.4 yrs | £6,112 |
| 7 kW | 6140 kWh | 4298 kWh | 1842 kWh | £1,089 | £184 | £1,273 | £17,742 | 13.9 yrs | £7,715 |
| 8 kW | 7017 kWh | 4912 kWh | 2105 kWh | £1,244 | £211 | £1,455 | £19,776 | 13.6 yrs | £9,317 |
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: £929, Upfront: £15,423, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1281 kWh | 474 kWh | £324 | £47 | £372 | £9,319 | 25.1 yrs | £-1,884 |
| 3 kW | 2631 kWh | 1921 kWh | 710 kWh | £487 | £71 | £558 | £11,354 | 20.4 yrs | £-202 |
| 4 kW | 3508 kWh | 2561 kWh | 947 kWh | £649 | £95 | £743 | £13,388 | 18.0 yrs | £1,481 |
| 5 kW | 4385 kWh | 3201 kWh | 1184 kWh | £811 | £118 | £929 | £15,423 | 16.6 yrs | £3,164 |
| 6 kW | 5263 kWh | 3842 kWh | 1421 kWh | £973 | £142 | £1,115 | £17,457 | 15.7 yrs | £4,847 |
| 7 kW | 6140 kWh | 4482 kWh | 1658 kWh | £1,135 | £166 | £1,301 | £19,492 | 15.0 yrs | £6,529 |
| 8 kW | 7017 kWh | 5122 kWh | 1895 kWh | £1,297 | £189 | £1,487 | £21,526 | 14.5 yrs | £8,212 |
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: £943, Upfront: £17,173, Break-even: 18.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1316 kWh | 439 kWh | £333 | £44 | £377 | £11,069 | 29.4 yrs | £-3,527 |
| 3 kW | 2631 kWh | 1973 kWh | 658 kWh | £500 | £66 | £566 | £13,104 | 23.2 yrs | £-1,790 |
| 4 kW | 3508 kWh | 2631 kWh | 877 kWh | £667 | £88 | £754 | £15,138 | 20.1 yrs | £-54 |
| 5 kW | 4385 kWh | 3289 kWh | 1096 kWh | £833 | £110 | £943 | £17,173 | 18.2 yrs | £1,683 |
| 6 kW | 5263 kWh | 3947 kWh | 1316 kWh | £1,000 | £132 | £1,131 | £19,207 | 17.0 yrs | £3,419 |
| 7 kW | 6140 kWh | 4605 kWh | 1535 kWh | £1,166 | £153 | £1,320 | £21,242 | 16.1 yrs | £5,156 |
| 8 kW | 7017 kWh | 5263 kWh | 1754 kWh | £1,333 | £175 | £1,508 | £23,276 | 15.4 yrs | £6,892 |
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: £956, Upfront: £19,623, Break-even: 20.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1754 kWh | 1351 kWh | 403 kWh | £342 | £40 | £382 | £13,519 | 35.3 yrs | £-5,869 |
| 3 kW | 2631 kWh | 2026 kWh | 605 kWh | £513 | £61 | £574 | £15,554 | 27.1 yrs | £-4,079 |
| 4 kW | 3508 kWh | 2701 kWh | 807 kWh | £684 | £81 | £765 | £17,588 | 23.0 yrs | £-2,289 |
| 5 kW | 4385 kWh | 3377 kWh | 1009 kWh | £855 | £101 | £956 | £19,623 | 20.5 yrs | £-498 |
| 6 kW | 5263 kWh | 4052 kWh | 1210 kWh | £1,026 | £121 | £1,147 | £21,657 | 18.9 yrs | £1,292 |
| 7 kW | 6140 kWh | 4728 kWh | 1412 kWh | £1,197 | £141 | £1,339 | £23,692 | 17.7 yrs | £3,082 |
| 8 kW | 7017 kWh | 5403 kWh | 1614 kWh | £1,369 | £161 | £1,530 | £25,726 | 16.8 yrs | £4,873 |
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.