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 894 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: £753, Upfront: £10,173, 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 | 1788 kWh | 715 kWh | 1073 kWh | £194 | £107 | £301 | £4,069 | 13.5 yrs | £1,955 |
| 3 kW | 2682 kWh | 1073 kWh | 1609 kWh | £291 | £161 | £452 | £6,104 | 13.5 yrs | £2,933 |
| 4 kW | 3577 kWh | 1431 kWh | 2146 kWh | £388 | £215 | £602 | £8,138 | 13.5 yrs | £3,911 |
| 5 kW | 4471 kWh | 1788 kWh | 2682 kWh | £485 | £268 | £753 | £10,173 | 13.5 yrs | £4,888 |
| 6 kW | 5365 kWh | 2146 kWh | 3219 kWh | £582 | £322 | £904 | £12,207 | 13.5 yrs | £5,866 |
| 7 kW | 6259 kWh | 2504 kWh | 3755 kWh | £679 | £376 | £1,054 | £14,242 | 13.5 yrs | £6,844 |
| 8 kW | 7153 kWh | 2861 kWh | 4292 kWh | £776 | £429 | £1,205 | £16,276 | 13.5 yrs | £7,821 |
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: £906, 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 | 1788 kWh | 1073 kWh | 715 kWh | £291 | £72 | £362 | £6,169 | 17.0 yrs | £1,079 |
| 3 kW | 2682 kWh | 1609 kWh | 1073 kWh | £436 | £107 | £544 | £8,204 | 15.1 yrs | £2,669 |
| 4 kW | 3577 kWh | 2146 kWh | 1431 kWh | £582 | £143 | £725 | £10,238 | 14.1 yrs | £4,258 |
| 5 kW | 4471 kWh | 2682 kWh | 1788 kWh | £727 | £179 | £906 | £12,273 | 13.5 yrs | £5,848 |
| 6 kW | 5365 kWh | 3219 kWh | 2146 kWh | £873 | £215 | £1,087 | £14,307 | 13.2 yrs | £7,438 |
| 7 kW | 6259 kWh | 3755 kWh | 2504 kWh | £1,018 | £250 | £1,268 | £16,342 | 12.9 yrs | £9,027 |
| 8 kW | 7153 kWh | 4292 kWh | 2861 kWh | £1,164 | £286 | £1,450 | £18,376 | 12.7 yrs | £10,617 |
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: £983, 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 | 1788 kWh | 1252 kWh | 536 kWh | £339 | £54 | £393 | £7,569 | 19.3 yrs | £291 |
| 3 kW | 2682 kWh | 1878 kWh | 805 kWh | £509 | £80 | £590 | £9,604 | 16.3 yrs | £2,187 |
| 4 kW | 3577 kWh | 2504 kWh | 1073 kWh | £679 | £107 | £786 | £11,638 | 14.8 yrs | £4,082 |
| 5 kW | 4471 kWh | 3129 kWh | 1341 kWh | £848 | £134 | £983 | £13,673 | 13.9 yrs | £5,978 |
| 6 kW | 5365 kWh | 3755 kWh | 1609 kWh | £1,018 | £161 | £1,179 | £15,707 | 13.3 yrs | £7,874 |
| 7 kW | 6259 kWh | 4381 kWh | 1878 kWh | £1,188 | £188 | £1,376 | £17,742 | 12.9 yrs | £9,769 |
| 8 kW | 7153 kWh | 5007 kWh | 2146 kWh | £1,357 | £215 | £1,572 | £19,776 | 12.6 yrs | £11,665 |
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: £1,005, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1788 kWh | 1305 kWh | 483 kWh | £354 | £48 | £402 | £9,319 | 23.2 yrs | £-1,275 |
| 3 kW | 2682 kWh | 1958 kWh | 724 kWh | £531 | £72 | £603 | £11,354 | 18.8 yrs | £712 |
| 4 kW | 3577 kWh | 2611 kWh | 966 kWh | £708 | £97 | £804 | £13,388 | 16.6 yrs | £2,700 |
| 5 kW | 4471 kWh | 3264 kWh | 1207 kWh | £885 | £121 | £1,005 | £15,423 | 15.3 yrs | £4,687 |
| 6 kW | 5365 kWh | 3916 kWh | 1449 kWh | £1,062 | £145 | £1,207 | £17,457 | 14.5 yrs | £6,674 |
| 7 kW | 6259 kWh | 4569 kWh | 1690 kWh | £1,239 | £169 | £1,408 | £19,492 | 13.8 yrs | £8,662 |
| 8 kW | 7153 kWh | 5222 kWh | 1931 kWh | £1,416 | £193 | £1,609 | £21,526 | 13.4 yrs | £10,649 |
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: £1,021, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1788 kWh | 1341 kWh | 447 kWh | £364 | £45 | £408 | £11,069 | 27.1 yrs | £-2,903 |
| 3 kW | 2682 kWh | 2012 kWh | 671 kWh | £545 | £67 | £612 | £13,104 | 21.4 yrs | £-854 |
| 4 kW | 3577 kWh | 2682 kWh | 894 kWh | £727 | £89 | £817 | £15,138 | 18.5 yrs | £1,194 |
| 5 kW | 4471 kWh | 3353 kWh | 1118 kWh | £909 | £112 | £1,021 | £17,173 | 16.8 yrs | £3,243 |
| 6 kW | 5365 kWh | 4024 kWh | 1341 kWh | £1,091 | £134 | £1,225 | £19,207 | 15.7 yrs | £5,291 |
| 7 kW | 6259 kWh | 4694 kWh | 1565 kWh | £1,273 | £156 | £1,429 | £21,242 | 14.9 yrs | £7,340 |
| 8 kW | 7153 kWh | 5365 kWh | 1788 kWh | £1,454 | £179 | £1,633 | £23,276 | 14.3 yrs | £9,389 |
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: £1,036, Upfront: £19,623, Break-even: 18.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1788 kWh | 1377 kWh | 411 kWh | £373 | £41 | £414 | £13,519 | 32.6 yrs | £-5,230 |
| 3 kW | 2682 kWh | 2065 kWh | 617 kWh | £560 | £62 | £622 | £15,554 | 25.0 yrs | £-3,121 |
| 4 kW | 3577 kWh | 2754 kWh | 823 kWh | £747 | £82 | £829 | £17,588 | 21.2 yrs | £-1,011 |
| 5 kW | 4471 kWh | 3442 kWh | 1028 kWh | £933 | £103 | £1,036 | £19,623 | 18.9 yrs | £1,099 |
| 6 kW | 5365 kWh | 4131 kWh | 1234 kWh | £1,120 | £123 | £1,243 | £21,657 | 17.4 yrs | £3,209 |
| 7 kW | 6259 kWh | 4819 kWh | 1440 kWh | £1,307 | £144 | £1,450 | £23,692 | 16.3 yrs | £5,318 |
| 8 kW | 7153 kWh | 5508 kWh | 1645 kWh | £1,493 | £165 | £1,658 | £25,726 | 15.5 yrs | £7,428 |
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.