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 952 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: £772, Upfront: £10,173, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1904 kWh | 762 kWh | 1143 kWh | £195 | £114 | £309 | £4,069 | 13.2 yrs | £2,108 |
| 3 kW | 2856 kWh | 1143 kWh | 1714 kWh | £292 | £171 | £463 | £6,104 | 13.2 yrs | £3,163 |
| 4 kW | 3809 kWh | 1523 kWh | 2285 kWh | £389 | £229 | £618 | £8,138 | 13.2 yrs | £4,217 |
| 5 kW | 4761 kWh | 1904 kWh | 2856 kWh | £487 | £286 | £772 | £10,173 | 13.2 yrs | £5,271 |
| 6 kW | 5713 kWh | 2285 kWh | 3428 kWh | £584 | £343 | £927 | £12,207 | 13.2 yrs | £6,325 |
| 7 kW | 6665 kWh | 2666 kWh | 3999 kWh | £681 | £400 | £1,081 | £14,242 | 13.2 yrs | £7,379 |
| 8 kW | 7617 kWh | 3047 kWh | 4570 kWh | £778 | £457 | £1,235 | £16,276 | 13.2 yrs | £8,434 |
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: £920, 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 | 1904 kWh | 1143 kWh | 762 kWh | £292 | £76 | £368 | £6,169 | 16.8 yrs | £1,193 |
| 3 kW | 2856 kWh | 1714 kWh | 1143 kWh | £438 | £114 | £552 | £8,204 | 14.9 yrs | £2,839 |
| 4 kW | 3809 kWh | 2285 kWh | 1523 kWh | £584 | £152 | £736 | £10,238 | 13.9 yrs | £4,486 |
| 5 kW | 4761 kWh | 2856 kWh | 1904 kWh | £730 | £190 | £920 | £12,273 | 13.3 yrs | £6,132 |
| 6 kW | 5713 kWh | 3428 kWh | 2285 kWh | £876 | £229 | £1,104 | £14,307 | 13.0 yrs | £7,779 |
| 7 kW | 6665 kWh | 3999 kWh | 2666 kWh | £1,022 | £267 | £1,288 | £16,342 | 12.7 yrs | £9,425 |
| 8 kW | 7617 kWh | 4570 kWh | 3047 kWh | £1,168 | £305 | £1,472 | £18,376 | 12.5 yrs | £11,071 |
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: £994, Upfront: £13,673, Break-even: 13.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1904 kWh | 1333 kWh | 571 kWh | £341 | £57 | £398 | £7,569 | 19.0 yrs | £385 |
| 3 kW | 2856 kWh | 1999 kWh | 857 kWh | £511 | £86 | £597 | £9,604 | 16.1 yrs | £2,328 |
| 4 kW | 3809 kWh | 2666 kWh | 1143 kWh | £681 | £114 | £795 | £11,638 | 14.6 yrs | £4,270 |
| 5 kW | 4761 kWh | 3332 kWh | 1428 kWh | £851 | £143 | £994 | £13,673 | 13.8 yrs | £6,213 |
| 6 kW | 5713 kWh | 3999 kWh | 1714 kWh | £1,022 | £171 | £1,193 | £15,707 | 13.2 yrs | £8,155 |
| 7 kW | 6665 kWh | 4665 kWh | 1999 kWh | £1,192 | £200 | £1,392 | £17,742 | 12.7 yrs | £10,098 |
| 8 kW | 7617 kWh | 5332 kWh | 2285 kWh | £1,362 | £229 | £1,591 | £19,776 | 12.4 yrs | £12,040 |
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: £1,016, 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 | 1904 kWh | 1390 kWh | 514 kWh | £355 | £51 | £407 | £9,319 | 22.9 yrs | £-1,187 |
| 3 kW | 2856 kWh | 2085 kWh | 771 kWh | £533 | £77 | £610 | £11,354 | 18.6 yrs | £844 |
| 4 kW | 3809 kWh | 2780 kWh | 1028 kWh | £710 | £103 | £813 | £13,388 | 16.5 yrs | £2,875 |
| 5 kW | 4761 kWh | 3475 kWh | 1285 kWh | £888 | £129 | £1,016 | £15,423 | 15.2 yrs | £4,907 |
| 6 kW | 5713 kWh | 4170 kWh | 1542 kWh | £1,066 | £154 | £1,220 | £17,457 | 14.3 yrs | £6,938 |
| 7 kW | 6665 kWh | 4865 kWh | 1800 kWh | £1,243 | £180 | £1,423 | £19,492 | 13.7 yrs | £8,970 |
| 8 kW | 7617 kWh | 5560 kWh | 2057 kWh | £1,421 | £206 | £1,626 | £21,526 | 13.2 yrs | £11,001 |
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: £1,031, Upfront: £17,173, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1904 kWh | 1428 kWh | 476 kWh | £365 | £48 | £413 | £11,069 | 26.8 yrs | £-2,819 |
| 3 kW | 2856 kWh | 2142 kWh | 714 kWh | £547 | £71 | £619 | £13,104 | 21.2 yrs | £-728 |
| 4 kW | 3809 kWh | 2856 kWh | 952 kWh | £730 | £95 | £825 | £15,138 | 18.3 yrs | £1,362 |
| 5 kW | 4761 kWh | 3570 kWh | 1190 kWh | £912 | £119 | £1,031 | £17,173 | 16.7 yrs | £3,453 |
| 6 kW | 5713 kWh | 4285 kWh | 1428 kWh | £1,095 | £143 | £1,238 | £19,207 | 15.5 yrs | £5,544 |
| 7 kW | 6665 kWh | 4999 kWh | 1666 kWh | £1,277 | £167 | £1,444 | £21,242 | 14.7 yrs | £7,634 |
| 8 kW | 7617 kWh | 5713 kWh | 1904 kWh | £1,460 | £190 | £1,650 | £23,276 | 14.1 yrs | £9,725 |
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: £1,046, Upfront: £19,623, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1904 kWh | 1466 kWh | 438 kWh | £375 | £44 | £418 | £13,519 | 32.3 yrs | £-5,150 |
| 3 kW | 2856 kWh | 2199 kWh | 657 kWh | £562 | £66 | £628 | £15,554 | 24.8 yrs | £-3,001 |
| 4 kW | 3809 kWh | 2933 kWh | 876 kWh | £749 | £88 | £837 | £17,588 | 21.0 yrs | £-851 |
| 5 kW | 4761 kWh | 3666 kWh | 1095 kWh | £937 | £109 | £1,046 | £19,623 | 18.8 yrs | £1,299 |
| 6 kW | 5713 kWh | 4399 kWh | 1314 kWh | £1,124 | £131 | £1,255 | £21,657 | 17.3 yrs | £3,449 |
| 7 kW | 6665 kWh | 5132 kWh | 1533 kWh | £1,311 | £153 | £1,465 | £23,692 | 16.2 yrs | £5,599 |
| 8 kW | 7617 kWh | 5865 kWh | 1752 kWh | £1,499 | £175 | £1,674 | £25,726 | 15.4 yrs | £7,749 |
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.