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 745 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: £626, Upfront: £10,173, Break-even: 16.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1489 kWh | 596 kWh | 894 kWh | £161 | £89 | £251 | £4,069 | 16.2 yrs | £943 |
| 3 kW | 2234 kWh | 894 kWh | 1340 kWh | £242 | £134 | £376 | £6,104 | 16.2 yrs | £1,414 |
| 4 kW | 2979 kWh | 1192 kWh | 1787 kWh | £322 | £179 | £501 | £8,138 | 16.2 yrs | £1,885 |
| 5 kW | 3724 kWh | 1489 kWh | 2234 kWh | £403 | £223 | £626 | £10,173 | 16.2 yrs | £2,357 |
| 6 kW | 4468 kWh | 1787 kWh | 2681 kWh | £484 | £268 | £752 | £12,207 | 16.2 yrs | £2,828 |
| 7 kW | 5213 kWh | 2085 kWh | 3128 kWh | £564 | £313 | £877 | £14,242 | 16.2 yrs | £3,299 |
| 8 kW | 5958 kWh | 2383 kWh | 3575 kWh | £645 | £357 | £1,002 | £16,276 | 16.2 yrs | £3,771 |
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: £754, Upfront: £12,273, 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 | 1489 kWh | 894 kWh | 596 kWh | £242 | £60 | £301 | £6,169 | 20.5 yrs | £-141 |
| 3 kW | 2234 kWh | 1340 kWh | 894 kWh | £363 | £89 | £452 | £8,204 | 18.1 yrs | £839 |
| 4 kW | 2979 kWh | 1787 kWh | 1192 kWh | £484 | £119 | £603 | £10,238 | 17.0 yrs | £1,818 |
| 5 kW | 3724 kWh | 2234 kWh | 1489 kWh | £605 | £149 | £754 | £12,273 | 16.3 yrs | £2,798 |
| 6 kW | 4468 kWh | 2681 kWh | 1787 kWh | £725 | £179 | £904 | £14,307 | 15.8 yrs | £3,777 |
| 7 kW | 5213 kWh | 3128 kWh | 2085 kWh | £846 | £209 | £1,055 | £16,342 | 15.5 yrs | £4,757 |
| 8 kW | 5958 kWh | 3575 kWh | 2383 kWh | £967 | £238 | £1,206 | £18,376 | 15.2 yrs | £5,736 |
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: £817, Upfront: £13,673, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1489 kWh | 1043 kWh | 447 kWh | £282 | £45 | £327 | £7,569 | 23.2 yrs | £-1,033 |
| 3 kW | 2234 kWh | 1564 kWh | 670 kWh | £423 | £67 | £490 | £9,604 | 19.6 yrs | £201 |
| 4 kW | 2979 kWh | 2085 kWh | 894 kWh | £564 | £89 | £654 | £11,638 | 17.8 yrs | £1,434 |
| 5 kW | 3724 kWh | 2607 kWh | 1117 kWh | £705 | £112 | £817 | £13,673 | 16.7 yrs | £2,668 |
| 6 kW | 4468 kWh | 3128 kWh | 1340 kWh | £846 | £134 | £980 | £15,707 | 16.0 yrs | £3,902 |
| 7 kW | 5213 kWh | 3649 kWh | 1564 kWh | £987 | £156 | £1,144 | £17,742 | 15.5 yrs | £5,135 |
| 8 kW | 5958 kWh | 4170 kWh | 1787 kWh | £1,129 | £179 | £1,307 | £19,776 | 15.1 yrs | £6,369 |
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: £836, Upfront: £15,423, Break-even: 18.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1489 kWh | 1087 kWh | 402 kWh | £294 | £40 | £334 | £9,319 | 27.9 yrs | £-2,630 |
| 3 kW | 2234 kWh | 1631 kWh | 603 kWh | £441 | £60 | £502 | £11,354 | 22.6 yrs | £-1,320 |
| 4 kW | 2979 kWh | 2175 kWh | 804 kWh | £588 | £80 | £669 | £13,388 | 20.0 yrs | £-11 |
| 5 kW | 3724 kWh | 2718 kWh | 1005 kWh | £736 | £101 | £836 | £15,423 | 18.4 yrs | £1,299 |
| 6 kW | 4468 kWh | 3262 kWh | 1206 kWh | £883 | £121 | £1,003 | £17,457 | 17.4 yrs | £2,609 |
| 7 kW | 5213 kWh | 3806 kWh | 1408 kWh | £1,030 | £141 | £1,171 | £19,492 | 16.7 yrs | £3,919 |
| 8 kW | 5958 kWh | 4349 kWh | 1609 kWh | £1,177 | £161 | £1,338 | £21,526 | 16.1 yrs | £5,229 |
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: £849, Upfront: £17,173, 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 | 1489 kWh | 1117 kWh | 372 kWh | £302 | £37 | £340 | £11,069 | 32.6 yrs | £-4,279 |
| 3 kW | 2234 kWh | 1676 kWh | 559 kWh | £453 | £56 | £509 | £13,104 | 25.7 yrs | £-2,918 |
| 4 kW | 2979 kWh | 2234 kWh | 745 kWh | £605 | £74 | £679 | £15,138 | 22.3 yrs | £-1,557 |
| 5 kW | 3724 kWh | 2793 kWh | 931 kWh | £756 | £93 | £849 | £17,173 | 20.2 yrs | £-197 |
| 6 kW | 4468 kWh | 3351 kWh | 1117 kWh | £907 | £112 | £1,019 | £19,207 | 18.9 yrs | £1,164 |
| 7 kW | 5213 kWh | 3910 kWh | 1303 kWh | £1,058 | £130 | £1,188 | £21,242 | 17.9 yrs | £2,525 |
| 8 kW | 5958 kWh | 4468 kWh | 1489 kWh | £1,209 | £149 | £1,358 | £23,276 | 17.1 yrs | £3,885 |
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: £861, Upfront: £19,623, Break-even: 22.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1489 kWh | 1147 kWh | 343 kWh | £310 | £34 | £345 | £13,519 | 39.2 yrs | £-6,627 |
| 3 kW | 2234 kWh | 1720 kWh | 514 kWh | £466 | £51 | £517 | £15,554 | 30.1 yrs | £-5,216 |
| 4 kW | 2979 kWh | 2294 kWh | 685 kWh | £621 | £69 | £689 | £17,588 | 25.5 yrs | £-3,804 |
| 5 kW | 3724 kWh | 2867 kWh | 856 kWh | £776 | £86 | £861 | £19,623 | 22.8 yrs | £-2,393 |
| 6 kW | 4468 kWh | 3441 kWh | 1028 kWh | £931 | £103 | £1,034 | £21,657 | 20.9 yrs | £-981 |
| 7 kW | 5213 kWh | 4014 kWh | 1199 kWh | £1,086 | £120 | £1,206 | £23,692 | 19.6 yrs | £430 |
| 8 kW | 5958 kWh | 4587 kWh | 1370 kWh | £1,241 | £137 | £1,378 | £25,726 | 18.7 yrs | £1,842 |
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.