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 954 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: £774, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1908 kWh | 763 kWh | 1145 kWh | £195 | £114 | £309 | £4,069 | 13.1 yrs | £2,120 |
| 3 kW | 2862 kWh | 1145 kWh | 1717 kWh | £292 | £172 | £464 | £6,104 | 13.1 yrs | £3,180 |
| 4 kW | 3816 kWh | 1526 kWh | 2289 kWh | £390 | £229 | £619 | £8,138 | 13.1 yrs | £4,240 |
| 5 kW | 4770 kWh | 1908 kWh | 2862 kWh | £487 | £286 | £774 | £10,173 | 13.1 yrs | £5,300 |
| 6 kW | 5723 kWh | 2289 kWh | 3434 kWh | £585 | £343 | £928 | £12,207 | 13.1 yrs | £6,360 |
| 7 kW | 6677 kWh | 2671 kWh | 4006 kWh | £682 | £401 | £1,083 | £14,242 | 13.1 yrs | £7,420 |
| 8 kW | 7631 kWh | 3053 kWh | 4579 kWh | £780 | £458 | £1,238 | £16,276 | 13.1 yrs | £8,480 |
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: £922, Upfront: £12,273, Break-even: 13.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1908 kWh | 1145 kWh | 763 kWh | £292 | £76 | £369 | £6,169 | 16.7 yrs | £1,207 |
| 3 kW | 2862 kWh | 1717 kWh | 1145 kWh | £439 | £114 | £553 | £8,204 | 14.8 yrs | £2,860 |
| 4 kW | 3816 kWh | 2289 kWh | 1526 kWh | £585 | £153 | £738 | £10,238 | 13.9 yrs | £4,513 |
| 5 kW | 4770 kWh | 2862 kWh | 1908 kWh | £731 | £191 | £922 | £12,273 | 13.3 yrs | £6,167 |
| 6 kW | 5723 kWh | 3434 kWh | 2289 kWh | £877 | £229 | £1,106 | £14,307 | 12.9 yrs | £7,820 |
| 7 kW | 6677 kWh | 4006 kWh | 2671 kWh | £1,024 | £267 | £1,291 | £16,342 | 12.7 yrs | £9,473 |
| 8 kW | 7631 kWh | 4579 kWh | 3053 kWh | £1,170 | £305 | £1,475 | £18,376 | 12.5 yrs | £11,126 |
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: £996, Upfront: £13,673, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1908 kWh | 1335 kWh | 572 kWh | £341 | £57 | £398 | £7,569 | 19.0 yrs | £400 |
| 3 kW | 2862 kWh | 2003 kWh | 859 kWh | £512 | £86 | £598 | £9,604 | 16.1 yrs | £2,350 |
| 4 kW | 3816 kWh | 2671 kWh | 1145 kWh | £682 | £114 | £797 | £11,638 | 14.6 yrs | £4,300 |
| 5 kW | 4770 kWh | 3339 kWh | 1431 kWh | £853 | £143 | £996 | £13,673 | 13.7 yrs | £6,250 |
| 6 kW | 5723 kWh | 4006 kWh | 1717 kWh | £1,024 | £172 | £1,195 | £15,707 | 13.1 yrs | £8,200 |
| 7 kW | 6677 kWh | 4674 kWh | 2003 kWh | £1,194 | £200 | £1,395 | £17,742 | 12.7 yrs | £10,150 |
| 8 kW | 7631 kWh | 5342 kWh | 2289 kWh | £1,365 | £229 | £1,594 | £19,776 | 12.4 yrs | £12,100 |
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: £1,018, Upfront: £15,423, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1908 kWh | 1393 kWh | 515 kWh | £356 | £52 | £407 | £9,319 | 22.9 yrs | £-1,172 |
| 3 kW | 2862 kWh | 2089 kWh | 773 kWh | £534 | £77 | £611 | £11,354 | 18.6 yrs | £867 |
| 4 kW | 3816 kWh | 2785 kWh | 1030 kWh | £712 | £103 | £815 | £13,388 | 16.4 yrs | £2,906 |
| 5 kW | 4770 kWh | 3482 kWh | 1288 kWh | £890 | £129 | £1,018 | £15,423 | 15.1 yrs | £4,945 |
| 6 kW | 5723 kWh | 4178 kWh | 1545 kWh | £1,068 | £155 | £1,222 | £17,457 | 14.3 yrs | £6,984 |
| 7 kW | 6677 kWh | 4874 kWh | 1803 kWh | £1,245 | £180 | £1,426 | £19,492 | 13.7 yrs | £9,023 |
| 8 kW | 7631 kWh | 5571 kWh | 2060 kWh | £1,423 | £206 | £1,629 | £21,526 | 13.2 yrs | £11,062 |
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: £1,033, Upfront: £17,173, Break-even: 16.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1908 kWh | 1431 kWh | 477 kWh | £366 | £48 | £413 | £11,069 | 26.8 yrs | £-2,803 |
| 3 kW | 2862 kWh | 2146 kWh | 715 kWh | £548 | £72 | £620 | £13,104 | 21.1 yrs | £-705 |
| 4 kW | 3816 kWh | 2862 kWh | 954 kWh | £731 | £95 | £827 | £15,138 | 18.3 yrs | £1,393 |
| 5 kW | 4770 kWh | 3577 kWh | 1192 kWh | £914 | £119 | £1,033 | £17,173 | 16.6 yrs | £3,492 |
| 6 kW | 5723 kWh | 4293 kWh | 1431 kWh | £1,097 | £143 | £1,240 | £19,207 | 15.5 yrs | £5,590 |
| 7 kW | 6677 kWh | 5008 kWh | 1669 kWh | £1,280 | £167 | £1,446 | £21,242 | 14.7 yrs | £7,688 |
| 8 kW | 7631 kWh | 5723 kWh | 1908 kWh | £1,462 | £191 | £1,653 | £23,276 | 14.1 yrs | £9,786 |
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: £1,048, Upfront: £19,623, Break-even: 18.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1908 kWh | 1469 kWh | 439 kWh | £375 | £44 | £419 | £13,519 | 32.2 yrs | £-5,135 |
| 3 kW | 2862 kWh | 2204 kWh | 658 kWh | £563 | £66 | £629 | £15,554 | 24.7 yrs | £-2,977 |
| 4 kW | 3816 kWh | 2938 kWh | 878 kWh | £751 | £88 | £838 | £17,588 | 21.0 yrs | £-819 |
| 5 kW | 4770 kWh | 3673 kWh | 1097 kWh | £938 | £110 | £1,048 | £19,623 | 18.7 yrs | £1,338 |
| 6 kW | 5723 kWh | 4407 kWh | 1316 kWh | £1,126 | £132 | £1,258 | £21,657 | 17.2 yrs | £3,496 |
| 7 kW | 6677 kWh | 5142 kWh | 1536 kWh | £1,314 | £154 | £1,467 | £23,692 | 16.1 yrs | £5,653 |
| 8 kW | 7631 kWh | 5876 kWh | 1755 kWh | £1,501 | £176 | £1,677 | £25,726 | 15.3 yrs | £7,811 |
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.