A typical roof here lands around 3.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 939 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: £763, Upfront: £10,173, 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 | 1879 kWh | 751 kWh | 1127 kWh | £193 | £113 | £305 | £4,069 | 13.3 yrs | £2,039 |
| 3 kW | 2818 kWh | 1127 kWh | 1691 kWh | £289 | £169 | £458 | £6,104 | 13.3 yrs | £3,058 |
| 4 kW | 3757 kWh | 1503 kWh | 2254 kWh | £385 | £225 | £611 | £8,138 | 13.3 yrs | £4,077 |
| 5 kW | 4696 kWh | 1879 kWh | 2818 kWh | £482 | £282 | £763 | £10,173 | 13.3 yrs | £5,097 |
| 6 kW | 5636 kWh | 2254 kWh | 3381 kWh | £578 | £338 | £916 | £12,207 | 13.3 yrs | £6,116 |
| 7 kW | 6575 kWh | 2630 kWh | 3945 kWh | £674 | £395 | £1,069 | £14,242 | 13.3 yrs | £7,135 |
| 8 kW | 7514 kWh | 3006 kWh | 4509 kWh | £771 | £451 | £1,222 | £16,276 | 13.3 yrs | £8,155 |
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: £910, Upfront: £12,273, 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 | 1879 kWh | 1127 kWh | 751 kWh | £289 | £75 | £364 | £6,169 | 16.9 yrs | £1,114 |
| 3 kW | 2818 kWh | 1691 kWh | 1127 kWh | £434 | £113 | £546 | £8,204 | 15.0 yrs | £2,721 |
| 4 kW | 3757 kWh | 2254 kWh | 1503 kWh | £578 | £150 | £728 | £10,238 | 14.1 yrs | £4,328 |
| 5 kW | 4696 kWh | 2818 kWh | 1879 kWh | £723 | £188 | £910 | £12,273 | 13.5 yrs | £5,935 |
| 6 kW | 5636 kWh | 3381 kWh | 2254 kWh | £867 | £225 | £1,092 | £14,307 | 13.1 yrs | £7,542 |
| 7 kW | 6575 kWh | 3945 kWh | 2630 kWh | £1,012 | £263 | £1,275 | £16,342 | 12.8 yrs | £9,149 |
| 8 kW | 7514 kWh | 4509 kWh | 3006 kWh | £1,156 | £301 | £1,457 | £18,376 | 12.6 yrs | £10,756 |
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: £984, Upfront: £13,673, Break-even: 13.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1879 kWh | 1315 kWh | 564 kWh | £337 | £56 | £394 | £7,569 | 19.2 yrs | £302 |
| 3 kW | 2818 kWh | 1973 kWh | 845 kWh | £506 | £85 | £590 | £9,604 | 16.3 yrs | £2,202 |
| 4 kW | 3757 kWh | 2630 kWh | 1127 kWh | £674 | £113 | £787 | £11,638 | 14.8 yrs | £4,103 |
| 5 kW | 4696 kWh | 3288 kWh | 1409 kWh | £843 | £141 | £984 | £13,673 | 13.9 yrs | £6,004 |
| 6 kW | 5636 kWh | 3945 kWh | 1691 kWh | £1,012 | £169 | £1,181 | £15,707 | 13.3 yrs | £7,905 |
| 7 kW | 6575 kWh | 4603 kWh | 1973 kWh | £1,180 | £197 | £1,377 | £17,742 | 12.9 yrs | £9,805 |
| 8 kW | 7514 kWh | 5260 kWh | 2254 kWh | £1,349 | £225 | £1,574 | £19,776 | 12.6 yrs | £11,706 |
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: £1,006, Upfront: £15,423, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1879 kWh | 1371 kWh | 507 kWh | £352 | £51 | £402 | £9,319 | 23.2 yrs | £-1,272 |
| 3 kW | 2818 kWh | 2057 kWh | 761 kWh | £527 | £76 | £604 | £11,354 | 18.8 yrs | £717 |
| 4 kW | 3757 kWh | 2743 kWh | 1014 kWh | £703 | £101 | £805 | £13,388 | 16.6 yrs | £2,706 |
| 5 kW | 4696 kWh | 3428 kWh | 1268 kWh | £879 | £127 | £1,006 | £15,423 | 15.3 yrs | £4,695 |
| 6 kW | 5636 kWh | 4114 kWh | 1522 kWh | £1,055 | £152 | £1,207 | £17,457 | 14.5 yrs | £6,684 |
| 7 kW | 6575 kWh | 4800 kWh | 1775 kWh | £1,231 | £178 | £1,408 | £19,492 | 13.8 yrs | £8,672 |
| 8 kW | 7514 kWh | 5486 kWh | 2029 kWh | £1,406 | £203 | £1,609 | £21,526 | 13.4 yrs | £10,661 |
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: £1,021, Upfront: £17,173, Break-even: 16.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1879 kWh | 1409 kWh | 470 kWh | £361 | £47 | £408 | £11,069 | 27.1 yrs | £-2,905 |
| 3 kW | 2818 kWh | 2113 kWh | 704 kWh | £542 | £70 | £612 | £13,104 | 21.4 yrs | £-857 |
| 4 kW | 3757 kWh | 2818 kWh | 939 kWh | £723 | £94 | £816 | £15,138 | 18.5 yrs | £1,191 |
| 5 kW | 4696 kWh | 3522 kWh | 1174 kWh | £903 | £117 | £1,021 | £17,173 | 16.8 yrs | £3,238 |
| 6 kW | 5636 kWh | 4227 kWh | 1409 kWh | £1,084 | £141 | £1,225 | £19,207 | 15.7 yrs | £5,286 |
| 7 kW | 6575 kWh | 4931 kWh | 1644 kWh | £1,264 | £164 | £1,429 | £21,242 | 14.9 yrs | £7,334 |
| 8 kW | 7514 kWh | 5636 kWh | 1879 kWh | £1,445 | £188 | £1,633 | £23,276 | 14.3 yrs | £9,382 |
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: £1,035, Upfront: £19,623, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1879 kWh | 1447 kWh | 432 kWh | £371 | £43 | £414 | £13,519 | 32.6 yrs | £-5,237 |
| 3 kW | 2818 kWh | 2170 kWh | 648 kWh | £556 | £65 | £621 | £15,554 | 25.0 yrs | £-3,131 |
| 4 kW | 3757 kWh | 2893 kWh | 864 kWh | £742 | £86 | £828 | £17,588 | 21.2 yrs | £-1,024 |
| 5 kW | 4696 kWh | 3616 kWh | 1080 kWh | £927 | £108 | £1,035 | £19,623 | 19.0 yrs | £1,082 |
| 6 kW | 5636 kWh | 4340 kWh | 1296 kWh | £1,113 | £130 | £1,242 | £21,657 | 17.4 yrs | £3,189 |
| 7 kW | 6575 kWh | 5063 kWh | 1512 kWh | £1,298 | £151 | £1,449 | £23,692 | 16.3 yrs | £5,295 |
| 8 kW | 7514 kWh | 5786 kWh | 1728 kWh | £1,484 | £173 | £1,656 | £25,726 | 15.5 yrs | £7,402 |
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.