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 1120 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £939, Upfront: £10,173, Break-even: 10.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2240 kWh | 896 kWh | 1344 kWh | £241 | £134 | £376 | £4,069 | 10.8 yrs | £3,444 |
| 3 kW | 3360 kWh | 1344 kWh | 2016 kWh | £362 | £202 | £563 | £6,104 | 10.8 yrs | £5,166 |
| 4 kW | 4481 kWh | 1792 kWh | 2688 kWh | £482 | £269 | £751 | £8,138 | 10.8 yrs | £6,888 |
| 5 kW | 5601 kWh | 2240 kWh | 3360 kWh | £603 | £336 | £939 | £10,173 | 10.8 yrs | £8,610 |
| 6 kW | 6721 kWh | 2688 kWh | 4033 kWh | £724 | £403 | £1,127 | £12,207 | 10.8 yrs | £10,332 |
| 7 kW | 7841 kWh | 3136 kWh | 4705 kWh | £844 | £470 | £1,315 | £14,242 | 10.8 yrs | £12,054 |
| 8 kW | 8961 kWh | 3584 kWh | 5377 kWh | £965 | £538 | £1,503 | £16,276 | 10.8 yrs | £13,776 |
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: £1,129, Upfront: £12,273, Break-even: 10.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2240 kWh | 1344 kWh | 896 kWh | £362 | £90 | £451 | £6,169 | 13.7 yrs | £2,860 |
| 3 kW | 3360 kWh | 2016 kWh | 1344 kWh | £543 | £134 | £677 | £8,204 | 12.1 yrs | £5,340 |
| 4 kW | 4481 kWh | 2688 kWh | 1792 kWh | £724 | £179 | £903 | £10,238 | 11.3 yrs | £7,820 |
| 5 kW | 5601 kWh | 3360 kWh | 2240 kWh | £905 | £224 | £1,129 | £12,273 | 10.9 yrs | £10,301 |
| 6 kW | 6721 kWh | 4033 kWh | 2688 kWh | £1,086 | £269 | £1,354 | £14,307 | 10.6 yrs | £12,781 |
| 7 kW | 7841 kWh | 4705 kWh | 3136 kWh | £1,266 | £314 | £1,580 | £16,342 | 10.3 yrs | £15,261 |
| 8 kW | 8961 kWh | 5377 kWh | 3584 kWh | £1,447 | £358 | £1,806 | £18,376 | 10.2 yrs | £17,741 |
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: £1,223, Upfront: £13,673, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2240 kWh | 1568 kWh | 672 kWh | £422 | £67 | £489 | £7,569 | 15.5 yrs | £2,218 |
| 3 kW | 3360 kWh | 2352 kWh | 1008 kWh | £633 | £101 | £734 | £9,604 | 13.1 yrs | £5,077 |
| 4 kW | 4481 kWh | 3136 kWh | 1344 kWh | £844 | £134 | £979 | £11,638 | 11.9 yrs | £7,937 |
| 5 kW | 5601 kWh | 3920 kWh | 1680 kWh | £1,055 | £168 | £1,223 | £13,673 | 11.2 yrs | £10,796 |
| 6 kW | 6721 kWh | 4705 kWh | 2016 kWh | £1,266 | £202 | £1,468 | £15,707 | 10.7 yrs | £13,655 |
| 7 kW | 7841 kWh | 5489 kWh | 2352 kWh | £1,478 | £235 | £1,713 | £17,742 | 10.4 yrs | £16,514 |
| 8 kW | 8961 kWh | 6273 kWh | 2688 kWh | £1,689 | £269 | £1,957 | £19,776 | 10.1 yrs | £19,373 |
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: £1,252, Upfront: £15,423, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2240 kWh | 1635 kWh | 605 kWh | £440 | £60 | £501 | £9,319 | 18.6 yrs | £696 |
| 3 kW | 3360 kWh | 2453 kWh | 907 kWh | £660 | £91 | £751 | £11,354 | 15.1 yrs | £3,669 |
| 4 kW | 4481 kWh | 3271 kWh | 1210 kWh | £881 | £121 | £1,001 | £13,388 | 13.4 yrs | £6,641 |
| 5 kW | 5601 kWh | 4089 kWh | 1512 kWh | £1,101 | £151 | £1,252 | £15,423 | 12.3 yrs | £9,614 |
| 6 kW | 6721 kWh | 4906 kWh | 1815 kWh | £1,321 | £181 | £1,502 | £17,457 | 11.6 yrs | £12,587 |
| 7 kW | 7841 kWh | 5724 kWh | 2117 kWh | £1,541 | £212 | £1,753 | £19,492 | 11.1 yrs | £15,560 |
| 8 kW | 8961 kWh | 6542 kWh | 2420 kWh | £1,761 | £242 | £2,003 | £21,526 | 10.7 yrs | £18,533 |
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: £1,271, Upfront: £17,173, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2240 kWh | 1680 kWh | 560 kWh | £452 | £56 | £508 | £11,069 | 21.8 yrs | £-903 |
| 3 kW | 3360 kWh | 2520 kWh | 840 kWh | £678 | £84 | £762 | £13,104 | 17.2 yrs | £2,146 |
| 4 kW | 4481 kWh | 3360 kWh | 1120 kWh | £905 | £112 | £1,017 | £15,138 | 14.9 yrs | £5,195 |
| 5 kW | 5601 kWh | 4201 kWh | 1400 kWh | £1,131 | £140 | £1,271 | £17,173 | 13.5 yrs | £8,243 |
| 6 kW | 6721 kWh | 5041 kWh | 1680 kWh | £1,357 | £168 | £1,525 | £19,207 | 12.6 yrs | £11,292 |
| 7 kW | 7841 kWh | 5881 kWh | 1960 kWh | £1,583 | £196 | £1,779 | £21,242 | 11.9 yrs | £14,341 |
| 8 kW | 8961 kWh | 6721 kWh | 2240 kWh | £1,809 | £224 | £2,033 | £23,276 | 11.4 yrs | £17,389 |
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: £1,290, Upfront: £19,623, Break-even: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2240 kWh | 1725 kWh | 515 kWh | £464 | £52 | £516 | £13,519 | 26.2 yrs | £-3,201 |
| 3 kW | 3360 kWh | 2588 kWh | 773 kWh | £697 | £77 | £774 | £15,554 | 20.1 yrs | £-77 |
| 4 kW | 4481 kWh | 3450 kWh | 1031 kWh | £929 | £103 | £1,032 | £17,588 | 17.0 yrs | £3,048 |
| 5 kW | 5601 kWh | 4313 kWh | 1288 kWh | £1,161 | £129 | £1,290 | £19,623 | 15.2 yrs | £6,172 |
| 6 kW | 6721 kWh | 5175 kWh | 1546 kWh | £1,393 | £155 | £1,548 | £21,657 | 14.0 yrs | £9,297 |
| 7 kW | 7841 kWh | 6038 kWh | 1803 kWh | £1,625 | £180 | £1,806 | £23,692 | 13.1 yrs | £12,421 |
| 8 kW | 8961 kWh | 6900 kWh | 2061 kWh | £1,857 | £206 | £2,064 | £25,726 | 12.5 yrs | £15,546 |
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.