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 782 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £658, Upfront: £10,173, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 626 kWh | 938 kWh | £169 | £94 | £263 | £4,069 | 15.5 yrs | £1,194 |
| 3 kW | 2346 kWh | 938 kWh | 1408 kWh | £254 | £141 | £395 | £6,104 | 15.5 yrs | £1,790 |
| 4 kW | 3128 kWh | 1251 kWh | 1877 kWh | £339 | £188 | £526 | £8,138 | 15.5 yrs | £2,387 |
| 5 kW | 3910 kWh | 1564 kWh | 2346 kWh | £423 | £235 | £658 | £10,173 | 15.5 yrs | £2,984 |
| 6 kW | 4692 kWh | 1877 kWh | 2815 kWh | £508 | £282 | £789 | £12,207 | 15.5 yrs | £3,581 |
| 7 kW | 5474 kWh | 2190 kWh | 3284 kWh | £593 | £328 | £921 | £14,242 | 15.5 yrs | £4,178 |
| 8 kW | 6256 kWh | 2502 kWh | 3754 kWh | £677 | £375 | £1,053 | £16,276 | 15.5 yrs | £4,775 |
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: £791, Upfront: £12,273, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 938 kWh | 626 kWh | £254 | £63 | £316 | £6,169 | 19.5 yrs | £161 |
| 3 kW | 2346 kWh | 1408 kWh | 938 kWh | £381 | £94 | £475 | £8,204 | 17.3 yrs | £1,291 |
| 4 kW | 3128 kWh | 1877 kWh | 1251 kWh | £508 | £125 | £633 | £10,238 | 16.2 yrs | £2,422 |
| 5 kW | 3910 kWh | 2346 kWh | 1564 kWh | £635 | £156 | £791 | £12,273 | 15.5 yrs | £3,552 |
| 6 kW | 4692 kWh | 2815 kWh | 1877 kWh | £762 | £188 | £949 | £14,307 | 15.1 yrs | £4,683 |
| 7 kW | 5474 kWh | 3284 kWh | 2190 kWh | £889 | £219 | £1,108 | £16,342 | 14.8 yrs | £5,813 |
| 8 kW | 6256 kWh | 3754 kWh | 2502 kWh | £1,016 | £250 | £1,266 | £18,376 | 14.5 yrs | £6,944 |
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: £858, Upfront: £13,673, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1095 kWh | 469 kWh | £296 | £47 | £343 | £7,569 | 22.1 yrs | £-705 |
| 3 kW | 2346 kWh | 1642 kWh | 704 kWh | £444 | £70 | £515 | £9,604 | 18.7 yrs | £692 |
| 4 kW | 3128 kWh | 2190 kWh | 938 kWh | £593 | £94 | £686 | £11,638 | 17.0 yrs | £2,089 |
| 5 kW | 3910 kWh | 2737 kWh | 1173 kWh | £741 | £117 | £858 | £13,673 | 15.9 yrs | £3,487 |
| 6 kW | 4692 kWh | 3284 kWh | 1408 kWh | £889 | £141 | £1,030 | £15,707 | 15.3 yrs | £4,884 |
| 7 kW | 5474 kWh | 3832 kWh | 1642 kWh | £1,037 | £164 | £1,201 | £17,742 | 14.8 yrs | £6,281 |
| 8 kW | 6256 kWh | 4379 kWh | 1877 kWh | £1,185 | £188 | £1,373 | £19,776 | 14.4 yrs | £7,678 |
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: £878, Upfront: £15,423, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1142 kWh | 422 kWh | £309 | £42 | £351 | £9,319 | 26.5 yrs | £-2,295 |
| 3 kW | 2346 kWh | 1713 kWh | 633 kWh | £463 | £63 | £527 | £11,354 | 21.6 yrs | £-818 |
| 4 kW | 3128 kWh | 2283 kWh | 845 kWh | £618 | £84 | £702 | £13,388 | 19.1 yrs | £659 |
| 5 kW | 3910 kWh | 2854 kWh | 1056 kWh | £772 | £106 | £878 | £15,423 | 17.6 yrs | £2,137 |
| 6 kW | 4692 kWh | 3425 kWh | 1267 kWh | £927 | £127 | £1,054 | £17,457 | 16.6 yrs | £3,614 |
| 7 kW | 5474 kWh | 3996 kWh | 1478 kWh | £1,081 | £148 | £1,229 | £19,492 | 15.9 yrs | £5,091 |
| 8 kW | 6256 kWh | 4567 kWh | 1689 kWh | £1,236 | £169 | £1,405 | £21,526 | 15.3 yrs | £6,569 |
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: £891, Upfront: £17,173, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1173 kWh | 391 kWh | £317 | £39 | £357 | £11,069 | 31.0 yrs | £-3,939 |
| 3 kW | 2346 kWh | 1760 kWh | 587 kWh | £476 | £59 | £535 | £13,104 | 24.5 yrs | £-2,408 |
| 4 kW | 3128 kWh | 2346 kWh | 782 kWh | £635 | £78 | £713 | £15,138 | 21.2 yrs | £-877 |
| 5 kW | 3910 kWh | 2933 kWh | 978 kWh | £794 | £98 | £891 | £17,173 | 19.3 yrs | £654 |
| 6 kW | 4692 kWh | 3519 kWh | 1173 kWh | £952 | £117 | £1,070 | £19,207 | 18.0 yrs | £2,184 |
| 7 kW | 5474 kWh | 4106 kWh | 1369 kWh | £1,111 | £137 | £1,248 | £21,242 | 17.0 yrs | £3,715 |
| 8 kW | 6256 kWh | 4692 kWh | 1564 kWh | £1,270 | £156 | £1,426 | £23,276 | 16.3 yrs | £5,246 |
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: £905, Upfront: £19,623, Break-even: 21.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1564 kWh | 1204 kWh | 360 kWh | £326 | £36 | £362 | £13,519 | 37.4 yrs | £-6,282 |
| 3 kW | 2346 kWh | 1806 kWh | 540 kWh | £489 | £54 | £543 | £15,554 | 28.7 yrs | £-4,698 |
| 4 kW | 3128 kWh | 2409 kWh | 719 kWh | £652 | £72 | £724 | £17,588 | 24.3 yrs | £-3,114 |
| 5 kW | 3910 kWh | 3011 kWh | 899 kWh | £815 | £90 | £905 | £19,623 | 21.7 yrs | £-1,530 |
| 6 kW | 4692 kWh | 3613 kWh | 1079 kWh | £978 | £108 | £1,086 | £21,657 | 19.9 yrs | £55 |
| 7 kW | 5474 kWh | 4215 kWh | 1259 kWh | £1,141 | £126 | £1,267 | £23,692 | 18.7 yrs | £1,639 |
| 8 kW | 6256 kWh | 4817 kWh | 1439 kWh | £1,304 | £144 | £1,447 | £25,726 | 17.8 yrs | £3,223 |
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.