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 891 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: £719, Upfront: £10,173, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1783 kWh | 713 kWh | 1070 kWh | £181 | £107 | £288 | £4,069 | 14.1 yrs | £1,683 |
| 3 kW | 2674 kWh | 1070 kWh | 1605 kWh | £271 | £160 | £431 | £6,104 | 14.1 yrs | £2,525 |
| 4 kW | 3566 kWh | 1426 kWh | 2139 kWh | £361 | £214 | £575 | £8,138 | 14.1 yrs | £3,367 |
| 5 kW | 4457 kWh | 1783 kWh | 2674 kWh | £452 | £267 | £719 | £10,173 | 14.1 yrs | £4,208 |
| 6 kW | 5349 kWh | 2139 kWh | 3209 kWh | £542 | £321 | £863 | £12,207 | 14.1 yrs | £5,050 |
| 7 kW | 6240 kWh | 2496 kWh | 3744 kWh | £632 | £374 | £1,007 | £14,242 | 14.1 yrs | £5,891 |
| 8 kW | 7132 kWh | 2853 kWh | 4279 kWh | £723 | £428 | £1,150 | £16,276 | 14.1 yrs | £6,733 |
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: £856, Upfront: £12,273, Break-even: 14.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1783 kWh | 1070 kWh | 713 kWh | £271 | £71 | £342 | £6,169 | 18.0 yrs | £677 |
| 3 kW | 2674 kWh | 1605 kWh | 1070 kWh | £406 | £107 | £513 | £8,204 | 16.0 yrs | £2,065 |
| 4 kW | 3566 kWh | 2139 kWh | 1426 kWh | £542 | £143 | £685 | £10,238 | 15.0 yrs | £3,453 |
| 5 kW | 4457 kWh | 2674 kWh | 1783 kWh | £677 | £178 | £856 | £12,273 | 14.3 yrs | £4,841 |
| 6 kW | 5349 kWh | 3209 kWh | 2139 kWh | £813 | £214 | £1,027 | £14,307 | 13.9 yrs | £6,230 |
| 7 kW | 6240 kWh | 3744 kWh | 2496 kWh | £948 | £250 | £1,198 | £16,342 | 13.6 yrs | £7,618 |
| 8 kW | 7132 kWh | 4279 kWh | 2853 kWh | £1,084 | £285 | £1,369 | £18,376 | 13.4 yrs | £9,006 |
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: £924, Upfront: £13,673, 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 | 1783 kWh | 1248 kWh | 535 kWh | £316 | £53 | £370 | £7,569 | 20.5 yrs | £-177 |
| 3 kW | 2674 kWh | 1872 kWh | 802 kWh | £474 | £80 | £554 | £9,604 | 17.3 yrs | £1,485 |
| 4 kW | 3566 kWh | 2496 kWh | 1070 kWh | £632 | £107 | £739 | £11,638 | 15.7 yrs | £3,146 |
| 5 kW | 4457 kWh | 3120 kWh | 1337 kWh | £790 | £134 | £924 | £13,673 | 14.8 yrs | £4,808 |
| 6 kW | 5349 kWh | 3744 kWh | 1605 kWh | £948 | £160 | £1,109 | £15,707 | 14.2 yrs | £6,469 |
| 7 kW | 6240 kWh | 4368 kWh | 1872 kWh | £1,106 | £187 | £1,294 | £17,742 | 13.7 yrs | £8,131 |
| 8 kW | 7132 kWh | 4992 kWh | 2139 kWh | £1,264 | £214 | £1,478 | £19,776 | 13.4 yrs | £9,793 |
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: £945, Upfront: £15,423, Break-even: 16.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1783 kWh | 1302 kWh | 481 kWh | £330 | £48 | £378 | £9,319 | 24.7 yrs | £-1,763 |
| 3 kW | 2674 kWh | 1952 kWh | 722 kWh | £495 | £72 | £567 | £11,354 | 20.0 yrs | £-19 |
| 4 kW | 3566 kWh | 2603 kWh | 963 kWh | £659 | £96 | £756 | £13,388 | 17.7 yrs | £1,724 |
| 5 kW | 4457 kWh | 3254 kWh | 1203 kWh | £824 | £120 | £945 | £15,423 | 16.3 yrs | £3,468 |
| 6 kW | 5349 kWh | 3905 kWh | 1444 kWh | £989 | £144 | £1,133 | £17,457 | 15.4 yrs | £5,211 |
| 7 kW | 6240 kWh | 4555 kWh | 1685 kWh | £1,154 | £168 | £1,322 | £19,492 | 14.7 yrs | £6,955 |
| 8 kW | 7132 kWh | 5206 kWh | 1926 kWh | £1,319 | £193 | £1,511 | £21,526 | 14.2 yrs | £8,699 |
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: £958, Upfront: £17,173, Break-even: 17.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1783 kWh | 1337 kWh | 446 kWh | £339 | £45 | £383 | £11,069 | 28.9 yrs | £-3,404 |
| 3 kW | 2674 kWh | 2006 kWh | 669 kWh | £508 | £67 | £575 | £13,104 | 22.8 yrs | £-1,605 |
| 4 kW | 3566 kWh | 2674 kWh | 891 kWh | £677 | £89 | £767 | £15,138 | 19.7 yrs | £193 |
| 5 kW | 4457 kWh | 3343 kWh | 1114 kWh | £847 | £111 | £958 | £17,173 | 17.9 yrs | £1,991 |
| 6 kW | 5349 kWh | 4011 kWh | 1337 kWh | £1,016 | £134 | £1,150 | £19,207 | 16.7 yrs | £3,789 |
| 7 kW | 6240 kWh | 4680 kWh | 1560 kWh | £1,185 | £156 | £1,341 | £21,242 | 15.8 yrs | £5,588 |
| 8 kW | 7132 kWh | 5349 kWh | 1783 kWh | £1,355 | £178 | £1,533 | £23,276 | 15.2 yrs | £7,386 |
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: £972, Upfront: £19,623, Break-even: 20.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1783 kWh | 1373 kWh | 410 kWh | £348 | £41 | £389 | £13,519 | 34.8 yrs | £-5,744 |
| 3 kW | 2674 kWh | 2059 kWh | 615 kWh | £522 | £62 | £583 | £15,554 | 26.7 yrs | £-3,891 |
| 4 kW | 3566 kWh | 2746 kWh | 820 kWh | £695 | £82 | £777 | £17,588 | 22.6 yrs | £-2,038 |
| 5 kW | 4457 kWh | 3432 kWh | 1025 kWh | £869 | £103 | £972 | £19,623 | 20.2 yrs | £-186 |
| 6 kW | 5349 kWh | 4118 kWh | 1230 kWh | £1,043 | £123 | £1,166 | £21,657 | 18.6 yrs | £1,667 |
| 7 kW | 6240 kWh | 4805 kWh | 1435 kWh | £1,217 | £144 | £1,361 | £23,692 | 17.4 yrs | £3,520 |
| 8 kW | 7132 kWh | 5491 kWh | 1640 kWh | £1,391 | £164 | £1,555 | £25,726 | 16.5 yrs | £5,373 |
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.