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 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 | 1861 kWh | 744 kWh | 1116 kWh | £189 | £112 | £301 | £4,069 | 13.5 yrs | £1,949 |
| 3 kW | 2791 kWh | 1116 kWh | 1674 kWh | £284 | £167 | £451 | £6,104 | 13.5 yrs | £2,923 |
| 4 kW | 3721 kWh | 1488 kWh | 2233 kWh | £379 | £223 | £602 | £8,138 | 13.5 yrs | £3,897 |
| 5 kW | 4651 kWh | 1861 kWh | 2791 kWh | £473 | £279 | £752 | £10,173 | 13.5 yrs | £4,872 |
| 6 kW | 5582 kWh | 2233 kWh | 3349 kWh | £568 | £335 | £903 | £12,207 | 13.5 yrs | £5,846 |
| 7 kW | 6512 kWh | 2605 kWh | 3907 kWh | £662 | £391 | £1,053 | £14,242 | 13.5 yrs | £6,820 |
| 8 kW | 7442 kWh | 2977 kWh | 4465 kWh | £757 | £447 | £1,204 | £16,276 | 13.5 yrs | £7,795 |
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: £896, 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 | 1861 kWh | 1116 kWh | 744 kWh | £284 | £74 | £358 | £6,169 | 17.2 yrs | £997 |
| 3 kW | 2791 kWh | 1674 kWh | 1116 kWh | £426 | £112 | £537 | £8,204 | 15.3 yrs | £2,545 |
| 4 kW | 3721 kWh | 2233 kWh | 1488 kWh | £568 | £149 | £717 | £10,238 | 14.3 yrs | £4,094 |
| 5 kW | 4651 kWh | 2791 kWh | 1861 kWh | £710 | £186 | £896 | £12,273 | 13.7 yrs | £5,642 |
| 6 kW | 5582 kWh | 3349 kWh | 2233 kWh | £852 | £223 | £1,075 | £14,307 | 13.3 yrs | £7,191 |
| 7 kW | 6512 kWh | 3907 kWh | 2605 kWh | £994 | £260 | £1,254 | £16,342 | 13.0 yrs | £8,739 |
| 8 kW | 7442 kWh | 4465 kWh | 2977 kWh | £1,136 | £298 | £1,433 | £18,376 | 12.8 yrs | £10,288 |
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: £968, 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 | 1861 kWh | 1302 kWh | 558 kWh | £331 | £56 | £387 | £7,569 | 19.6 yrs | £171 |
| 3 kW | 2791 kWh | 1954 kWh | 837 kWh | £497 | £84 | £581 | £9,604 | 16.5 yrs | £2,007 |
| 4 kW | 3721 kWh | 2605 kWh | 1116 kWh | £662 | £112 | £774 | £11,638 | 15.0 yrs | £3,842 |
| 5 kW | 4651 kWh | 3256 kWh | 1395 kWh | £828 | £140 | £968 | £13,673 | 14.1 yrs | £5,678 |
| 6 kW | 5582 kWh | 3907 kWh | 1674 kWh | £994 | £167 | £1,161 | £15,707 | 13.5 yrs | £7,513 |
| 7 kW | 6512 kWh | 4558 kWh | 1954 kWh | £1,159 | £195 | £1,355 | £17,742 | 13.1 yrs | £9,349 |
| 8 kW | 7442 kWh | 5209 kWh | 2233 kWh | £1,325 | £223 | £1,548 | £19,776 | 12.8 yrs | £11,184 |
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: £989, 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 | 1861 kWh | 1358 kWh | 502 kWh | £345 | £50 | £396 | £9,319 | 23.6 yrs | £-1,407 |
| 3 kW | 2791 kWh | 2037 kWh | 754 kWh | £518 | £75 | £593 | £11,354 | 19.1 yrs | £515 |
| 4 kW | 3721 kWh | 2716 kWh | 1005 kWh | £691 | £100 | £791 | £13,388 | 16.9 yrs | £2,437 |
| 5 kW | 4651 kWh | 3395 kWh | 1256 kWh | £863 | £126 | £989 | £15,423 | 15.6 yrs | £4,358 |
| 6 kW | 5582 kWh | 4075 kWh | 1507 kWh | £1,036 | £151 | £1,187 | £17,457 | 14.7 yrs | £6,280 |
| 7 kW | 6512 kWh | 4754 kWh | 1758 kWh | £1,209 | £176 | £1,385 | £19,492 | 14.1 yrs | £8,202 |
| 8 kW | 7442 kWh | 5433 kWh | 2009 kWh | £1,382 | £201 | £1,582 | £21,526 | 13.6 yrs | £10,123 |
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 | 1861 kWh | 1395 kWh | 465 kWh | £355 | £47 | £401 | £11,069 | 27.6 yrs | £-3,042 |
| 3 kW | 2791 kWh | 2093 kWh | 698 kWh | £532 | £70 | £602 | £13,104 | 21.8 yrs | £-1,063 |
| 4 kW | 3721 kWh | 2791 kWh | 930 kWh | £710 | £93 | £803 | £15,138 | 18.9 yrs | £916 |
| 5 kW | 4651 kWh | 3488 kWh | 1163 kWh | £887 | £116 | £1,003 | £17,173 | 17.1 yrs | £2,895 |
| 6 kW | 5582 kWh | 4186 kWh | 1395 kWh | £1,065 | £140 | £1,204 | £19,207 | 16.0 yrs | £4,875 |
| 7 kW | 6512 kWh | 4884 kWh | 1628 kWh | £1,242 | £163 | £1,405 | £21,242 | 15.1 yrs | £6,854 |
| 8 kW | 7442 kWh | 5582 kWh | 1861 kWh | £1,419 | £186 | £1,605 | £23,276 | 14.5 yrs | £8,833 |
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: £1,018, 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 | 1861 kWh | 1433 kWh | 428 kWh | £364 | £43 | £407 | £13,519 | 33.2 yrs | £-5,377 |
| 3 kW | 2791 kWh | 2149 kWh | 642 kWh | £546 | £64 | £611 | £15,554 | 25.5 yrs | £-3,340 |
| 4 kW | 3721 kWh | 2865 kWh | 856 kWh | £729 | £86 | £814 | £17,588 | 21.6 yrs | £-1,304 |
| 5 kW | 4651 kWh | 3582 kWh | 1070 kWh | £911 | £107 | £1,018 | £19,623 | 19.3 yrs | £733 |
| 6 kW | 5582 kWh | 4298 kWh | 1284 kWh | £1,093 | £128 | £1,221 | £21,657 | 17.7 yrs | £2,769 |
| 7 kW | 6512 kWh | 5014 kWh | 1498 kWh | £1,275 | £150 | £1,425 | £23,692 | 16.6 yrs | £4,806 |
| 8 kW | 7442 kWh | 5730 kWh | 1712 kWh | £1,457 | £171 | £1,628 | £25,726 | 15.8 yrs | £6,842 |
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.