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 785 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: £660, Upfront: £10,173, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1570 kWh | 628 kWh | 942 kWh | £170 | £94 | £264 | £4,069 | 15.4 yrs | £1,215 |
| 3 kW | 2355 kWh | 942 kWh | 1413 kWh | £255 | £141 | £396 | £6,104 | 15.4 yrs | £1,822 |
| 4 kW | 3141 kWh | 1256 kWh | 1884 kWh | £340 | £188 | £528 | £8,138 | 15.4 yrs | £2,429 |
| 5 kW | 3926 kWh | 1570 kWh | 2355 kWh | £425 | £236 | £660 | £10,173 | 15.4 yrs | £3,037 |
| 6 kW | 4711 kWh | 1884 kWh | 2827 kWh | £510 | £283 | £793 | £12,207 | 15.4 yrs | £3,644 |
| 7 kW | 5496 kWh | 2198 kWh | 3298 kWh | £595 | £330 | £925 | £14,242 | 15.4 yrs | £4,252 |
| 8 kW | 6281 kWh | 2512 kWh | 3769 kWh | £680 | £377 | £1,057 | £16,276 | 15.4 yrs | £4,859 |
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: £794, Upfront: £12,273, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1570 kWh | 942 kWh | 628 kWh | £255 | £63 | £318 | £6,169 | 19.4 yrs | £186 |
| 3 kW | 2355 kWh | 1413 kWh | 942 kWh | £382 | £94 | £477 | £8,204 | 17.2 yrs | £1,329 |
| 4 kW | 3141 kWh | 1884 kWh | 1256 kWh | £510 | £126 | £636 | £10,238 | 16.1 yrs | £2,473 |
| 5 kW | 3926 kWh | 2355 kWh | 1570 kWh | £637 | £157 | £794 | £12,273 | 15.4 yrs | £3,616 |
| 6 kW | 4711 kWh | 2827 kWh | 1884 kWh | £765 | £188 | £953 | £14,307 | 15.0 yrs | £4,759 |
| 7 kW | 5496 kWh | 3298 kWh | 2198 kWh | £892 | £220 | £1,112 | £16,342 | 14.7 yrs | £5,902 |
| 8 kW | 6281 kWh | 3769 kWh | 2512 kWh | £1,020 | £251 | £1,271 | £18,376 | 14.5 yrs | £7,045 |
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: £861, 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 | 1570 kWh | 1099 kWh | 471 kWh | £297 | £47 | £345 | £7,569 | 22.0 yrs | £-678 |
| 3 kW | 2355 kWh | 1649 kWh | 707 kWh | £446 | £71 | £517 | £9,604 | 18.6 yrs | £733 |
| 4 kW | 3141 kWh | 2198 kWh | 942 kWh | £595 | £94 | £689 | £11,638 | 16.9 yrs | £2,144 |
| 5 kW | 3926 kWh | 2748 kWh | 1178 kWh | £744 | £118 | £861 | £13,673 | 15.9 yrs | £3,555 |
| 6 kW | 4711 kWh | 3298 kWh | 1413 kWh | £892 | £141 | £1,034 | £15,707 | 15.2 yrs | £4,966 |
| 7 kW | 5496 kWh | 3847 kWh | 1649 kWh | £1,041 | £165 | £1,206 | £17,742 | 14.7 yrs | £6,377 |
| 8 kW | 6281 kWh | 4397 kWh | 1884 kWh | £1,190 | £188 | £1,378 | £19,776 | 14.3 yrs | £7,788 |
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: £881, Upfront: £15,423, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1570 kWh | 1146 kWh | 424 kWh | £310 | £42 | £353 | £9,319 | 26.4 yrs | £-2,267 |
| 3 kW | 2355 kWh | 1719 kWh | 636 kWh | £465 | £64 | £529 | £11,354 | 21.5 yrs | £-776 |
| 4 kW | 3141 kWh | 2293 kWh | 848 kWh | £620 | £85 | £705 | £13,388 | 19.0 yrs | £716 |
| 5 kW | 3926 kWh | 2866 kWh | 1060 kWh | £775 | £106 | £881 | £15,423 | 17.5 yrs | £2,207 |
| 6 kW | 4711 kWh | 3439 kWh | 1272 kWh | £931 | £127 | £1,058 | £17,457 | 16.5 yrs | £3,698 |
| 7 kW | 5496 kWh | 4012 kWh | 1484 kWh | £1,086 | £148 | £1,234 | £19,492 | 15.8 yrs | £5,190 |
| 8 kW | 6281 kWh | 4585 kWh | 1696 kWh | £1,241 | £170 | £1,410 | £21,526 | 15.3 yrs | £6,681 |
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: £895, Upfront: £17,173, Break-even: 19.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1570 kWh | 1178 kWh | 393 kWh | £319 | £39 | £358 | £11,069 | 30.9 yrs | £-3,910 |
| 3 kW | 2355 kWh | 1767 kWh | 589 kWh | £478 | £59 | £537 | £13,104 | 24.4 yrs | £-2,365 |
| 4 kW | 3141 kWh | 2355 kWh | 785 kWh | £637 | £79 | £716 | £15,138 | 21.1 yrs | £-820 |
| 5 kW | 3926 kWh | 2944 kWh | 981 kWh | £797 | £98 | £895 | £17,173 | 19.2 yrs | £725 |
| 6 kW | 4711 kWh | 3533 kWh | 1178 kWh | £956 | £118 | £1,074 | £19,207 | 17.9 yrs | £2,270 |
| 7 kW | 5496 kWh | 4122 kWh | 1374 kWh | £1,115 | £137 | £1,253 | £21,242 | 17.0 yrs | £3,815 |
| 8 kW | 6281 kWh | 4711 kWh | 1570 kWh | £1,275 | £157 | £1,432 | £23,276 | 16.3 yrs | £5,360 |
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: £908, Upfront: £19,623, Break-even: 21.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1570 kWh | 1209 kWh | 361 kWh | £327 | £36 | £363 | £13,519 | 37.2 yrs | £-6,253 |
| 3 kW | 2355 kWh | 1814 kWh | 542 kWh | £491 | £54 | £545 | £15,554 | 28.5 yrs | £-4,654 |
| 4 kW | 3141 kWh | 2418 kWh | 722 kWh | £654 | £72 | £727 | £17,588 | 24.2 yrs | £-3,056 |
| 5 kW | 3926 kWh | 3023 kWh | 903 kWh | £818 | £90 | £908 | £19,623 | 21.6 yrs | £-1,457 |
| 6 kW | 4711 kWh | 3627 kWh | 1084 kWh | £982 | £108 | £1,090 | £21,657 | 19.9 yrs | £141 |
| 7 kW | 5496 kWh | 4232 kWh | 1264 kWh | £1,145 | £126 | £1,272 | £23,692 | 18.6 yrs | £1,740 |
| 8 kW | 6281 kWh | 4837 kWh | 1445 kWh | £1,309 | £144 | £1,453 | £25,726 | 17.7 yrs | £3,339 |
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.