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 915 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £738, Upfront: £10,173, 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 | 1829 kWh | 732 kWh | 1098 kWh | £185 | £110 | £295 | £4,069 | 13.8 yrs | £1,834 |
| 3 kW | 2744 kWh | 1098 kWh | 1647 kWh | £278 | £165 | £443 | £6,104 | 13.8 yrs | £2,750 |
| 4 kW | 3659 kWh | 1464 kWh | 2195 kWh | £371 | £220 | £590 | £8,138 | 13.8 yrs | £3,667 |
| 5 kW | 4574 kWh | 1829 kWh | 2744 kWh | £463 | £274 | £738 | £10,173 | 13.8 yrs | £4,584 |
| 6 kW | 5488 kWh | 2195 kWh | 3293 kWh | £556 | £329 | £885 | £12,207 | 13.8 yrs | £5,501 |
| 7 kW | 6403 kWh | 2561 kWh | 3842 kWh | £649 | £384 | £1,033 | £14,242 | 13.8 yrs | £6,418 |
| 8 kW | 7318 kWh | 2927 kWh | 4391 kWh | £741 | £439 | £1,181 | £16,276 | 13.8 yrs | £7,334 |
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: £878, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1098 kWh | 732 kWh | £278 | £73 | £351 | £6,169 | 17.6 yrs | £855 |
| 3 kW | 2744 kWh | 1647 kWh | 1098 kWh | £417 | £110 | £527 | £8,204 | 15.6 yrs | £2,333 |
| 4 kW | 3659 kWh | 2195 kWh | 1464 kWh | £556 | £146 | £702 | £10,238 | 14.6 yrs | £3,811 |
| 5 kW | 4574 kWh | 2744 kWh | 1829 kWh | £695 | £183 | £878 | £12,273 | 14.0 yrs | £5,289 |
| 6 kW | 5488 kWh | 3293 kWh | 2195 kWh | £834 | £220 | £1,054 | £14,307 | 13.6 yrs | £6,766 |
| 7 kW | 6403 kWh | 3842 kWh | 2561 kWh | £973 | £256 | £1,229 | £16,342 | 13.3 yrs | £8,244 |
| 8 kW | 7318 kWh | 4391 kWh | 2927 kWh | £1,112 | £293 | £1,405 | £18,376 | 13.1 yrs | £9,722 |
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: £948, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1281 kWh | 549 kWh | £324 | £55 | £379 | £7,569 | 20.0 yrs | £16 |
| 3 kW | 2744 kWh | 1921 kWh | 823 kWh | £487 | £82 | £569 | £9,604 | 16.9 yrs | £1,775 |
| 4 kW | 3659 kWh | 2561 kWh | 1098 kWh | £649 | £110 | £759 | £11,638 | 15.3 yrs | £3,533 |
| 5 kW | 4574 kWh | 3202 kWh | 1372 kWh | £811 | £137 | £948 | £13,673 | 14.4 yrs | £5,291 |
| 6 kW | 5488 kWh | 3842 kWh | 1647 kWh | £973 | £165 | £1,138 | £15,707 | 13.8 yrs | £7,049 |
| 7 kW | 6403 kWh | 4482 kWh | 1921 kWh | £1,135 | £192 | £1,327 | £17,742 | 13.4 yrs | £8,807 |
| 8 kW | 7318 kWh | 5123 kWh | 2195 kWh | £1,298 | £220 | £1,517 | £19,776 | 13.0 yrs | £10,565 |
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: £969, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1336 kWh | 494 kWh | £338 | £49 | £388 | £9,319 | 24.0 yrs | £-1,565 |
| 3 kW | 2744 kWh | 2003 kWh | 741 kWh | £507 | £74 | £582 | £11,354 | 19.5 yrs | £277 |
| 4 kW | 3659 kWh | 2671 kWh | 988 kWh | £677 | £99 | £775 | £13,388 | 17.3 yrs | £2,119 |
| 5 kW | 4574 kWh | 3339 kWh | 1235 kWh | £846 | £123 | £969 | £15,423 | 15.9 yrs | £3,962 |
| 6 kW | 5488 kWh | 4007 kWh | 1482 kWh | £1,015 | £148 | £1,163 | £17,457 | 15.0 yrs | £5,804 |
| 7 kW | 6403 kWh | 4674 kWh | 1729 kWh | £1,184 | £173 | £1,357 | £19,492 | 14.4 yrs | £7,646 |
| 8 kW | 7318 kWh | 5342 kWh | 1976 kWh | £1,353 | £198 | £1,551 | £21,526 | 13.9 yrs | £9,489 |
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: £983, Upfront: £17,173, Break-even: 17.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1372 kWh | 457 kWh | £348 | £46 | £393 | £11,069 | 28.1 yrs | £-3,203 |
| 3 kW | 2744 kWh | 2058 kWh | 686 kWh | £521 | £69 | £590 | £13,104 | 22.2 yrs | £-1,305 |
| 4 kW | 3659 kWh | 2744 kWh | 915 kWh | £695 | £91 | £787 | £15,138 | 19.2 yrs | £594 |
| 5 kW | 4574 kWh | 3430 kWh | 1143 kWh | £869 | £114 | £983 | £17,173 | 17.5 yrs | £2,492 |
| 6 kW | 5488 kWh | 4116 kWh | 1372 kWh | £1,043 | £137 | £1,180 | £19,207 | 16.3 yrs | £4,390 |
| 7 kW | 6403 kWh | 4802 kWh | 1601 kWh | £1,216 | £160 | £1,377 | £21,242 | 15.4 yrs | £6,289 |
| 8 kW | 7318 kWh | 5488 kWh | 1829 kWh | £1,390 | £183 | £1,573 | £23,276 | 14.8 yrs | £8,187 |
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: £997, Upfront: £19,623, Break-even: 19.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1829 kWh | 1409 kWh | 421 kWh | £357 | £42 | £399 | £13,519 | 33.9 yrs | £-5,541 |
| 3 kW | 2744 kWh | 2113 kWh | 631 kWh | £535 | £63 | £598 | £15,554 | 26.0 yrs | £-3,586 |
| 4 kW | 3659 kWh | 2817 kWh | 842 kWh | £714 | £84 | £798 | £17,588 | 22.0 yrs | £-1,632 |
| 5 kW | 4574 kWh | 3522 kWh | 1052 kWh | £892 | £105 | £997 | £19,623 | 19.7 yrs | £323 |
| 6 kW | 5488 kWh | 4226 kWh | 1262 kWh | £1,070 | £126 | £1,197 | £21,657 | 18.1 yrs | £2,277 |
| 7 kW | 6403 kWh | 4930 kWh | 1473 kWh | £1,249 | £147 | £1,396 | £23,692 | 17.0 yrs | £4,232 |
| 8 kW | 7318 kWh | 5635 kWh | 1683 kWh | £1,427 | £168 | £1,596 | £25,726 | 16.1 yrs | £6,186 |
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.