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 1025 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: £852, Upfront: £10,173, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2050 kWh | 820 kWh | 1230 kWh | £218 | £123 | £341 | £4,069 | 11.9 yrs | £2,743 |
| 3 kW | 3076 kWh | 1230 kWh | 1845 kWh | £326 | £185 | £511 | £6,104 | 11.9 yrs | £4,115 |
| 4 kW | 4101 kWh | 1640 kWh | 2461 kWh | £435 | £246 | £681 | £8,138 | 11.9 yrs | £5,487 |
| 5 kW | 5126 kWh | 2050 kWh | 3076 kWh | £544 | £308 | £852 | £10,173 | 11.9 yrs | £6,859 |
| 6 kW | 6151 kWh | 2461 kWh | 3691 kWh | £653 | £369 | £1,022 | £12,207 | 11.9 yrs | £8,230 |
| 7 kW | 7177 kWh | 2871 kWh | 4306 kWh | £762 | £431 | £1,192 | £14,242 | 11.9 yrs | £9,602 |
| 8 kW | 8202 kWh | 3281 kWh | 4921 kWh | £870 | £492 | £1,363 | £16,276 | 11.9 yrs | £10,974 |
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: £1,021, Upfront: £12,273, 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 | 2050 kWh | 1230 kWh | 820 kWh | £326 | £82 | £408 | £6,169 | 15.1 yrs | £1,999 |
| 3 kW | 3076 kWh | 1845 kWh | 1230 kWh | £490 | £123 | £613 | £8,204 | 13.4 yrs | £4,049 |
| 4 kW | 4101 kWh | 2461 kWh | 1640 kWh | £653 | £164 | £817 | £10,238 | 12.5 yrs | £6,099 |
| 5 kW | 5126 kWh | 3076 kWh | 2050 kWh | £816 | £205 | £1,021 | £12,273 | 12.0 yrs | £8,148 |
| 6 kW | 6151 kWh | 3691 kWh | 2461 kWh | £979 | £246 | £1,225 | £14,307 | 11.7 yrs | £10,198 |
| 7 kW | 7177 kWh | 4306 kWh | 2871 kWh | £1,142 | £287 | £1,429 | £16,342 | 11.4 yrs | £12,247 |
| 8 kW | 8202 kWh | 4921 kWh | 3281 kWh | £1,306 | £328 | £1,634 | £18,376 | 11.2 yrs | £14,297 |
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: £1,106, Upfront: £13,673, Break-even: 12.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2050 kWh | 1435 kWh | 615 kWh | £381 | £62 | £442 | £7,569 | 17.1 yrs | £1,277 |
| 3 kW | 3076 kWh | 2153 kWh | 923 kWh | £571 | £92 | £663 | £9,604 | 14.5 yrs | £3,666 |
| 4 kW | 4101 kWh | 2871 kWh | 1230 kWh | £762 | £123 | £885 | £11,638 | 13.2 yrs | £6,054 |
| 5 kW | 5126 kWh | 3588 kWh | 1538 kWh | £952 | £154 | £1,106 | £13,673 | 12.4 yrs | £8,443 |
| 6 kW | 6151 kWh | 4306 kWh | 1845 kWh | £1,142 | £185 | £1,327 | £15,707 | 11.8 yrs | £10,831 |
| 7 kW | 7177 kWh | 5024 kWh | 2153 kWh | £1,333 | £215 | £1,548 | £17,742 | 11.5 yrs | £13,220 |
| 8 kW | 8202 kWh | 5741 kWh | 2461 kWh | £1,523 | £246 | £1,769 | £19,776 | 11.2 yrs | £15,609 |
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: £1,131, Upfront: £15,423, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2050 kWh | 1497 kWh | 554 kWh | £397 | £55 | £452 | £9,319 | 20.6 yrs | £-269 |
| 3 kW | 3076 kWh | 2245 kWh | 830 kWh | £596 | £83 | £679 | £11,354 | 16.7 yrs | £2,221 |
| 4 kW | 4101 kWh | 2994 kWh | 1107 kWh | £794 | £111 | £905 | £13,388 | 14.8 yrs | £4,711 |
| 5 kW | 5126 kWh | 3742 kWh | 1384 kWh | £993 | £138 | £1,131 | £15,423 | 13.6 yrs | £7,201 |
| 6 kW | 6151 kWh | 4491 kWh | 1661 kWh | £1,191 | £166 | £1,357 | £17,457 | 12.9 yrs | £9,692 |
| 7 kW | 7177 kWh | 5239 kWh | 1938 kWh | £1,390 | £194 | £1,584 | £19,492 | 12.3 yrs | £12,182 |
| 8 kW | 8202 kWh | 5987 kWh | 2215 kWh | £1,588 | £221 | £1,810 | £21,526 | 11.9 yrs | £14,672 |
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: £1,148, Upfront: £17,173, 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 | 2050 kWh | 1538 kWh | 513 kWh | £408 | £51 | £459 | £11,069 | 24.1 yrs | £-1,884 |
| 3 kW | 3076 kWh | 2307 kWh | 769 kWh | £612 | £77 | £689 | £13,104 | 19.0 yrs | £674 |
| 4 kW | 4101 kWh | 3076 kWh | 1025 kWh | £816 | £103 | £919 | £15,138 | 16.5 yrs | £3,232 |
| 5 kW | 5126 kWh | 3845 kWh | 1282 kWh | £1,020 | £128 | £1,148 | £17,173 | 15.0 yrs | £5,790 |
| 6 kW | 6151 kWh | 4614 kWh | 1538 kWh | £1,224 | £154 | £1,378 | £19,207 | 13.9 yrs | £8,348 |
| 7 kW | 7177 kWh | 5383 kWh | 1794 kWh | £1,428 | £179 | £1,607 | £21,242 | 13.2 yrs | £10,906 |
| 8 kW | 8202 kWh | 6151 kWh | 2050 kWh | £1,632 | £205 | £1,837 | £23,276 | 12.7 yrs | £13,464 |
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: £1,165, Upfront: £19,623, 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 | 2050 kWh | 1579 kWh | 472 kWh | £419 | £47 | £466 | £13,519 | 29.0 yrs | £-4,198 |
| 3 kW | 3076 kWh | 2368 kWh | 707 kWh | £628 | £71 | £699 | £15,554 | 22.2 yrs | £-1,572 |
| 4 kW | 4101 kWh | 3158 kWh | 943 kWh | £838 | £94 | £932 | £17,588 | 18.9 yrs | £1,053 |
| 5 kW | 5126 kWh | 3947 kWh | 1179 kWh | £1,047 | £118 | £1,165 | £19,623 | 16.8 yrs | £3,679 |
| 6 kW | 6151 kWh | 4737 kWh | 1415 kWh | £1,257 | £141 | £1,398 | £21,657 | 15.5 yrs | £6,305 |
| 7 kW | 7177 kWh | 5526 kWh | 1651 kWh | £1,466 | £165 | £1,631 | £23,692 | 14.5 yrs | £8,931 |
| 8 kW | 8202 kWh | 6315 kWh | 1886 kWh | £1,675 | £189 | £1,864 | £25,726 | 13.8 yrs | £11,557 |
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.