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 930 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £752, 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 | 1859 kWh | 744 kWh | 1116 kWh | £189 | £112 | £301 | £4,069 | 13.5 yrs | £1,945 |
| 3 kW | 2789 kWh | 1116 kWh | 1674 kWh | £284 | £167 | £451 | £6,104 | 13.5 yrs | £2,918 |
| 4 kW | 3719 kWh | 1488 kWh | 2231 kWh | £378 | £223 | £601 | £8,138 | 13.5 yrs | £3,890 |
| 5 kW | 4649 kWh | 1859 kWh | 2789 kWh | £473 | £279 | £752 | £10,173 | 13.5 yrs | £4,863 |
| 6 kW | 5578 kWh | 2231 kWh | 3347 kWh | £567 | £335 | £902 | £12,207 | 13.5 yrs | £5,836 |
| 7 kW | 6508 kWh | 2603 kWh | 3905 kWh | £662 | £390 | £1,052 | £14,242 | 13.5 yrs | £6,808 |
| 8 kW | 7438 kWh | 2975 kWh | 4463 kWh | £757 | £446 | £1,203 | £16,276 | 13.5 yrs | £7,781 |
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: £895, Upfront: £12,273, 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 | 1859 kWh | 1116 kWh | 744 kWh | £284 | £74 | £358 | £6,169 | 17.2 yrs | £993 |
| 3 kW | 2789 kWh | 1674 kWh | 1116 kWh | £426 | £112 | £537 | £8,204 | 15.3 yrs | £2,539 |
| 4 kW | 3719 kWh | 2231 kWh | 1488 kWh | £567 | £149 | £716 | £10,238 | 14.3 yrs | £4,086 |
| 5 kW | 4649 kWh | 2789 kWh | 1859 kWh | £709 | £186 | £895 | £12,273 | 13.7 yrs | £5,632 |
| 6 kW | 5578 kWh | 3347 kWh | 2231 kWh | £851 | £223 | £1,074 | £14,307 | 13.3 yrs | £7,179 |
| 7 kW | 6508 kWh | 3905 kWh | 2603 kWh | £993 | £260 | £1,253 | £16,342 | 13.0 yrs | £8,725 |
| 8 kW | 7438 kWh | 4463 kWh | 2975 kWh | £1,135 | £298 | £1,432 | £18,376 | 12.8 yrs | £10,272 |
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: £967, Upfront: £13,673, Break-even: 14.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1859 kWh | 1302 kWh | 558 kWh | £331 | £56 | £387 | £7,569 | 19.6 yrs | £167 |
| 3 kW | 2789 kWh | 1952 kWh | 837 kWh | £497 | £84 | £580 | £9,604 | 16.6 yrs | £2,000 |
| 4 kW | 3719 kWh | 2603 kWh | 1116 kWh | £662 | £112 | £774 | £11,638 | 15.0 yrs | £3,833 |
| 5 kW | 4649 kWh | 3254 kWh | 1395 kWh | £828 | £139 | £967 | £13,673 | 14.1 yrs | £5,667 |
| 6 kW | 5578 kWh | 3905 kWh | 1674 kWh | £993 | £167 | £1,160 | £15,707 | 13.5 yrs | £7,500 |
| 7 kW | 6508 kWh | 4556 kWh | 1952 kWh | £1,159 | £195 | £1,354 | £17,742 | 13.1 yrs | £9,333 |
| 8 kW | 7438 kWh | 5206 kWh | 2231 kWh | £1,324 | £223 | £1,547 | £19,776 | 12.8 yrs | £11,167 |
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: £988, Upfront: £15,423, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1859 kWh | 1357 kWh | 502 kWh | £345 | £50 | £395 | £9,319 | 23.6 yrs | £-1,411 |
| 3 kW | 2789 kWh | 2036 kWh | 753 kWh | £518 | £75 | £593 | £11,354 | 19.1 yrs | £508 |
| 4 kW | 3719 kWh | 2715 kWh | 1004 kWh | £690 | £100 | £791 | £13,388 | 16.9 yrs | £2,428 |
| 5 kW | 4649 kWh | 3394 kWh | 1255 kWh | £863 | £126 | £988 | £15,423 | 15.6 yrs | £4,347 |
| 6 kW | 5578 kWh | 4072 kWh | 1506 kWh | £1,036 | £151 | £1,186 | £17,457 | 14.7 yrs | £6,267 |
| 7 kW | 6508 kWh | 4751 kWh | 1757 kWh | £1,208 | £176 | £1,384 | £19,492 | 14.1 yrs | £8,186 |
| 8 kW | 7438 kWh | 5430 kWh | 2008 kWh | £1,381 | £201 | £1,582 | £21,526 | 13.6 yrs | £10,105 |
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: £1,003, Upfront: £17,173, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1859 kWh | 1395 kWh | 465 kWh | £355 | £46 | £401 | £11,069 | 27.6 yrs | £-3,046 |
| 3 kW | 2789 kWh | 2092 kWh | 697 kWh | £532 | £70 | £602 | £13,104 | 21.8 yrs | £-1,070 |
| 4 kW | 3719 kWh | 2789 kWh | 930 kWh | £709 | £93 | £802 | £15,138 | 18.9 yrs | £907 |
| 5 kW | 4649 kWh | 3486 kWh | 1162 kWh | £887 | £116 | £1,003 | £17,173 | 17.1 yrs | £2,884 |
| 6 kW | 5578 kWh | 4184 kWh | 1395 kWh | £1,064 | £139 | £1,203 | £19,207 | 16.0 yrs | £4,861 |
| 7 kW | 6508 kWh | 4881 kWh | 1627 kWh | £1,241 | £163 | £1,404 | £21,242 | 15.1 yrs | £6,838 |
| 8 kW | 7438 kWh | 5578 kWh | 1859 kWh | £1,419 | £186 | £1,605 | £23,276 | 14.5 yrs | £8,814 |
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: £1,017, Upfront: £19,623, Break-even: 19.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1859 kWh | 1432 kWh | 428 kWh | £364 | £43 | £407 | £13,519 | 33.2 yrs | £-5,382 |
| 3 kW | 2789 kWh | 2148 kWh | 642 kWh | £546 | £64 | £610 | £15,554 | 25.5 yrs | £-3,347 |
| 4 kW | 3719 kWh | 2864 kWh | 855 kWh | £728 | £86 | £814 | £17,588 | 21.6 yrs | £-1,313 |
| 5 kW | 4649 kWh | 3579 kWh | 1069 kWh | £910 | £107 | £1,017 | £19,623 | 19.3 yrs | £721 |
| 6 kW | 5578 kWh | 4295 kWh | 1283 kWh | £1,092 | £128 | £1,221 | £21,657 | 17.7 yrs | £2,755 |
| 7 kW | 6508 kWh | 5011 kWh | 1497 kWh | £1,274 | £150 | £1,424 | £23,692 | 16.6 yrs | £4,789 |
| 8 kW | 7438 kWh | 5727 kWh | 1711 kWh | £1,456 | £171 | £1,627 | £25,726 | 15.8 yrs | £6,824 |
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.