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 890 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £727, Upfront: £10,173, 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 | 1780 kWh | 712 kWh | 1068 kWh | £184 | £107 | £291 | £4,069 | 14.0 yrs | £1,748 |
| 3 kW | 2671 kWh | 1068 kWh | 1602 kWh | £276 | £160 | £436 | £6,104 | 14.0 yrs | £2,622 |
| 4 kW | 3561 kWh | 1424 kWh | 2137 kWh | £368 | £214 | £582 | £8,138 | 14.0 yrs | £3,496 |
| 5 kW | 4451 kWh | 1780 kWh | 2671 kWh | £460 | £267 | £727 | £10,173 | 14.0 yrs | £4,370 |
| 6 kW | 5341 kWh | 2137 kWh | 3205 kWh | £552 | £320 | £873 | £12,207 | 14.0 yrs | £5,244 |
| 7 kW | 6232 kWh | 2493 kWh | 3739 kWh | £644 | £374 | £1,018 | £14,242 | 14.0 yrs | £6,118 |
| 8 kW | 7122 kWh | 2849 kWh | 4273 kWh | £736 | £427 | £1,163 | £16,276 | 14.0 yrs | £6,992 |
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: £868, Upfront: £12,273, 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 | 1780 kWh | 1068 kWh | 712 kWh | £276 | £71 | £347 | £6,169 | 17.8 yrs | £776 |
| 3 kW | 2671 kWh | 1602 kWh | 1068 kWh | £414 | £107 | £521 | £8,204 | 15.7 yrs | £2,214 |
| 4 kW | 3561 kWh | 2137 kWh | 1424 kWh | £552 | £142 | £695 | £10,238 | 14.7 yrs | £3,652 |
| 5 kW | 4451 kWh | 2671 kWh | 1780 kWh | £690 | £178 | £868 | £12,273 | 14.1 yrs | £5,090 |
| 6 kW | 5341 kWh | 3205 kWh | 2137 kWh | £828 | £214 | £1,042 | £14,307 | 13.7 yrs | £6,529 |
| 7 kW | 6232 kWh | 3739 kWh | 2493 kWh | £966 | £249 | £1,215 | £16,342 | 13.4 yrs | £7,967 |
| 8 kW | 7122 kWh | 4273 kWh | 2849 kWh | £1,104 | £285 | £1,389 | £18,376 | 13.2 yrs | £9,405 |
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: £939, Upfront: £13,673, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1780 kWh | 1246 kWh | 534 kWh | £322 | £53 | £375 | £7,569 | 20.2 yrs | £-60 |
| 3 kW | 2671 kWh | 1869 kWh | 801 kWh | £483 | £80 | £563 | £9,604 | 17.1 yrs | £1,660 |
| 4 kW | 3561 kWh | 2493 kWh | 1068 kWh | £644 | £107 | £751 | £11,638 | 15.5 yrs | £3,380 |
| 5 kW | 4451 kWh | 3116 kWh | 1335 kWh | £805 | £134 | £939 | £13,673 | 14.6 yrs | £5,101 |
| 6 kW | 5341 kWh | 3739 kWh | 1602 kWh | £966 | £160 | £1,126 | £15,707 | 13.9 yrs | £6,821 |
| 7 kW | 6232 kWh | 4362 kWh | 1869 kWh | £1,127 | £187 | £1,314 | £17,742 | 13.5 yrs | £8,541 |
| 8 kW | 7122 kWh | 4985 kWh | 2137 kWh | £1,288 | £214 | £1,502 | £19,776 | 13.2 yrs | £10,261 |
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: £960, Upfront: £15,423, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1780 kWh | 1300 kWh | 481 kWh | £336 | £48 | £384 | £9,319 | 24.3 yrs | £-1,641 |
| 3 kW | 2671 kWh | 1950 kWh | 721 kWh | £504 | £72 | £576 | £11,354 | 19.7 yrs | £164 |
| 4 kW | 3561 kWh | 2599 kWh | 961 kWh | £672 | £96 | £768 | £13,388 | 17.4 yrs | £1,969 |
| 5 kW | 4451 kWh | 3249 kWh | 1202 kWh | £840 | £120 | £960 | £15,423 | 16.1 yrs | £3,774 |
| 6 kW | 5341 kWh | 3899 kWh | 1442 kWh | £1,008 | £144 | £1,152 | £17,457 | 15.2 yrs | £5,578 |
| 7 kW | 6232 kWh | 4549 kWh | 1683 kWh | £1,175 | £168 | £1,344 | £19,492 | 14.5 yrs | £7,383 |
| 8 kW | 7122 kWh | 5199 kWh | 1923 kWh | £1,343 | £192 | £1,536 | £21,526 | 14.0 yrs | £9,188 |
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: £974, Upfront: £17,173, Break-even: 17.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1780 kWh | 1335 kWh | 445 kWh | £345 | £45 | £390 | £11,069 | 28.4 yrs | £-3,278 |
| 3 kW | 2671 kWh | 2003 kWh | 668 kWh | £518 | £67 | £584 | £13,104 | 22.4 yrs | £-1,417 |
| 4 kW | 3561 kWh | 2671 kWh | 890 kWh | £690 | £89 | £779 | £15,138 | 19.4 yrs | £445 |
| 5 kW | 4451 kWh | 3338 kWh | 1113 kWh | £863 | £111 | £974 | £17,173 | 17.6 yrs | £2,306 |
| 6 kW | 5341 kWh | 4006 kWh | 1335 kWh | £1,035 | £134 | £1,169 | £19,207 | 16.4 yrs | £4,167 |
| 7 kW | 6232 kWh | 4674 kWh | 1558 kWh | £1,208 | £156 | £1,363 | £21,242 | 15.6 yrs | £6,028 |
| 8 kW | 7122 kWh | 5341 kWh | 1780 kWh | £1,380 | £178 | £1,558 | £23,276 | 14.9 yrs | £7,889 |
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: £988, Upfront: £19,623, Break-even: 19.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1780 kWh | 1371 kWh | 410 kWh | £354 | £41 | £395 | £13,519 | 34.2 yrs | £-5,615 |
| 3 kW | 2671 kWh | 2056 kWh | 614 kWh | £531 | £61 | £593 | £15,554 | 26.2 yrs | £-3,697 |
| 4 kW | 3561 kWh | 2742 kWh | 819 kWh | £709 | £82 | £790 | £17,588 | 22.3 yrs | £-1,780 |
| 5 kW | 4451 kWh | 3427 kWh | 1024 kWh | £886 | £102 | £988 | £19,623 | 19.9 yrs | £138 |
| 6 kW | 5341 kWh | 4113 kWh | 1229 kWh | £1,063 | £123 | £1,186 | £21,657 | 18.3 yrs | £2,055 |
| 7 kW | 6232 kWh | 4798 kWh | 1433 kWh | £1,240 | £143 | £1,383 | £23,692 | 17.1 yrs | £3,973 |
| 8 kW | 7122 kWh | 5484 kWh | 1638 kWh | £1,417 | £164 | £1,581 | £25,726 | 16.3 yrs | £5,890 |
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.