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 937 kWh per year on a south-facing roof. We value self-used electricity at 25.6p 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: £762, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1874 kWh | 750 kWh | 1125 kWh | £192 | £112 | £305 | £4,069 | 13.4 yrs | £2,025 |
| 3 kW | 2811 kWh | 1125 kWh | 1687 kWh | £288 | £169 | £457 | £6,104 | 13.4 yrs | £3,037 |
| 4 kW | 3749 kWh | 1499 kWh | 2249 kWh | £384 | £225 | £609 | £8,138 | 13.4 yrs | £4,049 |
| 5 kW | 4686 kWh | 1874 kWh | 2811 kWh | £481 | £281 | £762 | £10,173 | 13.4 yrs | £5,062 |
| 6 kW | 5623 kWh | 2249 kWh | 3374 kWh | £577 | £337 | £914 | £12,207 | 13.4 yrs | £6,074 |
| 7 kW | 6560 kWh | 2624 kWh | 3936 kWh | £673 | £394 | £1,066 | £14,242 | 13.4 yrs | £7,086 |
| 8 kW | 7497 kWh | 2999 kWh | 4498 kWh | £769 | £450 | £1,219 | £16,276 | 13.4 yrs | £8,099 |
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: £908, Upfront: £12,273, 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 | 1874 kWh | 1125 kWh | 750 kWh | £288 | £75 | £363 | £6,169 | 17.0 yrs | £1,097 |
| 3 kW | 2811 kWh | 1687 kWh | 1125 kWh | £433 | £112 | £545 | £8,204 | 15.1 yrs | £2,696 |
| 4 kW | 3749 kWh | 2249 kWh | 1499 kWh | £577 | £150 | £727 | £10,238 | 14.1 yrs | £4,295 |
| 5 kW | 4686 kWh | 2811 kWh | 1874 kWh | £721 | £187 | £908 | £12,273 | 13.5 yrs | £5,893 |
| 6 kW | 5623 kWh | 3374 kWh | 2249 kWh | £865 | £225 | £1,090 | £14,307 | 13.1 yrs | £7,492 |
| 7 kW | 6560 kWh | 3936 kWh | 2624 kWh | £1,009 | £262 | £1,272 | £16,342 | 12.9 yrs | £9,090 |
| 8 kW | 7497 kWh | 4498 kWh | 2999 kWh | £1,153 | £300 | £1,453 | £18,376 | 12.6 yrs | £10,689 |
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: £982, Upfront: £13,673, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1874 kWh | 1312 kWh | 562 kWh | £336 | £56 | £393 | £7,569 | 19.3 yrs | £284 |
| 3 kW | 2811 kWh | 1968 kWh | 843 kWh | £505 | £84 | £589 | £9,604 | 16.3 yrs | £2,175 |
| 4 kW | 3749 kWh | 2624 kWh | 1125 kWh | £673 | £112 | £785 | £11,638 | 14.8 yrs | £4,067 |
| 5 kW | 4686 kWh | 3280 kWh | 1406 kWh | £841 | £141 | £982 | £13,673 | 13.9 yrs | £5,959 |
| 6 kW | 5623 kWh | 3936 kWh | 1687 kWh | £1,009 | £169 | £1,178 | £15,707 | 13.3 yrs | £7,851 |
| 7 kW | 6560 kWh | 4592 kWh | 1968 kWh | £1,177 | £197 | £1,374 | £17,742 | 12.9 yrs | £9,742 |
| 8 kW | 7497 kWh | 5248 kWh | 2249 kWh | £1,346 | £225 | £1,571 | £19,776 | 12.6 yrs | £11,634 |
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: £1,004, Upfront: £15,423, 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 | 1874 kWh | 1368 kWh | 506 kWh | £351 | £51 | £401 | £9,319 | 23.2 yrs | £-1,291 |
| 3 kW | 2811 kWh | 2052 kWh | 759 kWh | £526 | £76 | £602 | £11,354 | 18.9 yrs | £689 |
| 4 kW | 3749 kWh | 2736 kWh | 1012 kWh | £702 | £101 | £803 | £13,388 | 16.7 yrs | £2,669 |
| 5 kW | 4686 kWh | 3421 kWh | 1265 kWh | £877 | £127 | £1,004 | £15,423 | 15.4 yrs | £4,649 |
| 6 kW | 5623 kWh | 4105 kWh | 1518 kWh | £1,052 | £152 | £1,204 | £17,457 | 14.5 yrs | £6,628 |
| 7 kW | 6560 kWh | 4789 kWh | 1771 kWh | £1,228 | £177 | £1,405 | £19,492 | 13.9 yrs | £8,608 |
| 8 kW | 7497 kWh | 5473 kWh | 2024 kWh | £1,403 | £202 | £1,606 | £21,526 | 13.4 yrs | £10,588 |
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: £1,018, Upfront: £17,173, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1874 kWh | 1406 kWh | 469 kWh | £360 | £47 | £407 | £11,069 | 27.2 yrs | £-2,923 |
| 3 kW | 2811 kWh | 2109 kWh | 703 kWh | £541 | £70 | £611 | £13,104 | 21.4 yrs | £-885 |
| 4 kW | 3749 kWh | 2811 kWh | 937 kWh | £721 | £94 | £815 | £15,138 | 18.6 yrs | £1,153 |
| 5 kW | 4686 kWh | 3514 kWh | 1171 kWh | £901 | £117 | £1,018 | £17,173 | 16.9 yrs | £3,192 |
| 6 kW | 5623 kWh | 4217 kWh | 1406 kWh | £1,081 | £141 | £1,222 | £19,207 | 15.7 yrs | £5,230 |
| 7 kW | 6560 kWh | 4920 kWh | 1640 kWh | £1,261 | £164 | £1,425 | £21,242 | 14.9 yrs | £7,268 |
| 8 kW | 7497 kWh | 5623 kWh | 1874 kWh | £1,442 | £187 | £1,629 | £23,276 | 14.3 yrs | £9,307 |
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: £1,033, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1874 kWh | 1443 kWh | 431 kWh | £370 | £43 | £413 | £13,519 | 32.7 yrs | £-5,256 |
| 3 kW | 2811 kWh | 2165 kWh | 647 kWh | £555 | £65 | £620 | £15,554 | 25.1 yrs | £-3,159 |
| 4 kW | 3749 kWh | 2886 kWh | 862 kWh | £740 | £86 | £826 | £17,588 | 21.3 yrs | £-1,062 |
| 5 kW | 4686 kWh | 3608 kWh | 1078 kWh | £925 | £108 | £1,033 | £19,623 | 19.0 yrs | £1,035 |
| 6 kW | 5623 kWh | 4330 kWh | 1293 kWh | £1,110 | £129 | £1,239 | £21,657 | 17.5 yrs | £3,132 |
| 7 kW | 6560 kWh | 5051 kWh | 1509 kWh | £1,295 | £151 | £1,446 | £23,692 | 16.4 yrs | £5,229 |
| 8 kW | 7497 kWh | 5773 kWh | 1724 kWh | £1,480 | £172 | £1,653 | £25,726 | 15.6 yrs | £7,326 |
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.