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 957 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: £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 | 1914 kWh | 766 kWh | 1148 kWh | £195 | £115 | £310 | £4,069 | 13.1 yrs | £2,122 |
| 3 kW | 2871 kWh | 1148 kWh | 1723 kWh | £292 | £172 | £464 | £6,104 | 13.1 yrs | £3,183 |
| 4 kW | 3828 kWh | 1531 kWh | 2297 kWh | £389 | £230 | £619 | £8,138 | 13.1 yrs | £4,244 |
| 5 kW | 4785 kWh | 1914 kWh | 2871 kWh | £487 | £287 | £774 | £10,173 | 13.1 yrs | £5,305 |
| 6 kW | 5742 kWh | 2297 kWh | 3445 kWh | £584 | £345 | £929 | £12,207 | 13.1 yrs | £6,365 |
| 7 kW | 6699 kWh | 2680 kWh | 4020 kWh | £681 | £402 | £1,083 | £14,242 | 13.1 yrs | £7,426 |
| 8 kW | 7656 kWh | 3062 kWh | 4594 kWh | £779 | £459 | £1,238 | £16,276 | 13.1 yrs | £8,487 |
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 | 1914 kWh | 1148 kWh | 766 kWh | £292 | £77 | £369 | £6,169 | 16.7 yrs | £1,203 |
| 3 kW | 2871 kWh | 1723 kWh | 1148 kWh | £438 | £115 | £553 | £8,204 | 14.8 yrs | £2,855 |
| 4 kW | 3828 kWh | 2297 kWh | 1531 kWh | £584 | £153 | £737 | £10,238 | 13.9 yrs | £4,506 |
| 5 kW | 4785 kWh | 2871 kWh | 1914 kWh | £730 | £191 | £922 | £12,273 | 13.3 yrs | £6,158 |
| 6 kW | 5742 kWh | 3445 kWh | 2297 kWh | £876 | £230 | £1,106 | £14,307 | 12.9 yrs | £7,810 |
| 7 kW | 6699 kWh | 4020 kWh | 2680 kWh | £1,022 | £268 | £1,290 | £16,342 | 12.7 yrs | £9,461 |
| 8 kW | 7656 kWh | 4594 kWh | 3062 kWh | £1,168 | £306 | £1,474 | £18,376 | 12.5 yrs | £11,113 |
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: £995, 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 | 1914 kWh | 1340 kWh | 574 kWh | £341 | £57 | £398 | £7,569 | 19.0 yrs | £394 |
| 3 kW | 2871 kWh | 2010 kWh | 861 kWh | £511 | £86 | £597 | £9,604 | 16.1 yrs | £2,341 |
| 4 kW | 3828 kWh | 2680 kWh | 1148 kWh | £681 | £115 | £796 | £11,638 | 14.6 yrs | £4,288 |
| 5 kW | 4785 kWh | 3350 kWh | 1436 kWh | £852 | £144 | £995 | £13,673 | 13.7 yrs | £6,235 |
| 6 kW | 5742 kWh | 4020 kWh | 1723 kWh | £1,022 | £172 | £1,194 | £15,707 | 13.2 yrs | £8,182 |
| 7 kW | 6699 kWh | 4689 kWh | 2010 kWh | £1,193 | £201 | £1,394 | £17,742 | 12.7 yrs | £10,128 |
| 8 kW | 7656 kWh | 5359 kWh | 2297 kWh | £1,363 | £230 | £1,593 | £19,776 | 12.4 yrs | £12,075 |
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: 15.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1914 kWh | 1397 kWh | 517 kWh | £355 | £52 | £407 | £9,319 | 22.9 yrs | £-1,179 |
| 3 kW | 2871 kWh | 2096 kWh | 775 kWh | £533 | £78 | £611 | £11,354 | 18.6 yrs | £857 |
| 4 kW | 3828 kWh | 2795 kWh | 1034 kWh | £711 | £103 | £814 | £13,388 | 16.4 yrs | £2,892 |
| 5 kW | 4785 kWh | 3493 kWh | 1292 kWh | £888 | £129 | £1,018 | £15,423 | 15.2 yrs | £4,928 |
| 6 kW | 5742 kWh | 4192 kWh | 1550 kWh | £1,066 | £155 | £1,221 | £17,457 | 14.3 yrs | £6,963 |
| 7 kW | 6699 kWh | 4890 kWh | 1809 kWh | £1,244 | £181 | £1,425 | £19,492 | 13.7 yrs | £8,999 |
| 8 kW | 7656 kWh | 5589 kWh | 2067 kWh | £1,421 | £207 | £1,628 | £21,526 | 13.2 yrs | £11,034 |
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: £1,032, 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 | 1914 kWh | 1436 kWh | 479 kWh | £365 | £48 | £413 | £11,069 | 26.8 yrs | £-2,811 |
| 3 kW | 2871 kWh | 2153 kWh | 718 kWh | £548 | £72 | £619 | £13,104 | 21.2 yrs | £-716 |
| 4 kW | 3828 kWh | 2871 kWh | 957 kWh | £730 | £96 | £826 | £15,138 | 18.3 yrs | £1,378 |
| 5 kW | 4785 kWh | 3589 kWh | 1196 kWh | £913 | £120 | £1,032 | £17,173 | 16.6 yrs | £3,473 |
| 6 kW | 5742 kWh | 4307 kWh | 1436 kWh | £1,095 | £144 | £1,239 | £19,207 | 15.5 yrs | £5,568 |
| 7 kW | 6699 kWh | 5024 kWh | 1675 kWh | £1,278 | £167 | £1,445 | £21,242 | 14.7 yrs | £7,662 |
| 8 kW | 7656 kWh | 5742 kWh | 1914 kWh | £1,460 | £191 | £1,652 | £23,276 | 14.1 yrs | £9,757 |
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: £1,047, 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 | 1914 kWh | 1474 kWh | 440 kWh | £375 | £44 | £419 | £13,519 | 32.3 yrs | £-5,143 |
| 3 kW | 2871 kWh | 2211 kWh | 660 kWh | £562 | £66 | £628 | £15,554 | 24.8 yrs | £-2,989 |
| 4 kW | 3828 kWh | 2948 kWh | 880 kWh | £750 | £88 | £838 | £17,588 | 21.0 yrs | £-835 |
| 5 kW | 4785 kWh | 3685 kWh | 1101 kWh | £937 | £110 | £1,047 | £19,623 | 18.7 yrs | £1,318 |
| 6 kW | 5742 kWh | 4421 kWh | 1321 kWh | £1,124 | £132 | £1,256 | £21,657 | 17.2 yrs | £3,472 |
| 7 kW | 6699 kWh | 5158 kWh | 1541 kWh | £1,312 | £154 | £1,466 | £23,692 | 16.2 yrs | £5,626 |
| 8 kW | 7656 kWh | 5895 kWh | 1761 kWh | £1,499 | £176 | £1,675 | £25,726 | 15.4 yrs | £7,779 |
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.