A typical roof here lands around 4.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 927 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: £748, Upfront: £10,173, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1855 kWh | 742 kWh | 1113 kWh | £188 | £111 | £299 | £4,069 | 13.6 yrs | £1,916 |
| 3 kW | 2782 kWh | 1113 kWh | 1669 kWh | £282 | £167 | £449 | £6,104 | 13.6 yrs | £2,874 |
| 4 kW | 3710 kWh | 1484 kWh | 2226 kWh | £376 | £223 | £598 | £8,138 | 13.6 yrs | £3,832 |
| 5 kW | 4637 kWh | 1855 kWh | 2782 kWh | £470 | £278 | £748 | £10,173 | 13.6 yrs | £4,790 |
| 6 kW | 5565 kWh | 2226 kWh | 3339 kWh | £564 | £334 | £898 | £12,207 | 13.6 yrs | £5,748 |
| 7 kW | 6492 kWh | 2597 kWh | 3895 kWh | £658 | £390 | £1,047 | £14,242 | 13.6 yrs | £6,706 |
| 8 kW | 7420 kWh | 2968 kWh | 4452 kWh | £752 | £445 | £1,197 | £16,276 | 13.6 yrs | £7,664 |
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: £890, Upfront: £12,273, 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 | 1855 kWh | 1113 kWh | 742 kWh | £282 | £74 | £356 | £6,169 | 17.3 yrs | £953 |
| 3 kW | 2782 kWh | 1669 kWh | 1113 kWh | £423 | £111 | £534 | £8,204 | 15.4 yrs | £2,480 |
| 4 kW | 3710 kWh | 2226 kWh | 1484 kWh | £564 | £148 | £712 | £10,238 | 14.4 yrs | £4,007 |
| 5 kW | 4637 kWh | 2782 kWh | 1855 kWh | £705 | £185 | £890 | £12,273 | 13.8 yrs | £5,533 |
| 6 kW | 5565 kWh | 3339 kWh | 2226 kWh | £846 | £223 | £1,068 | £14,307 | 13.4 yrs | £7,060 |
| 7 kW | 6492 kWh | 3895 kWh | 2597 kWh | £987 | £260 | £1,246 | £16,342 | 13.1 yrs | £8,587 |
| 8 kW | 7420 kWh | 4452 kWh | 2968 kWh | £1,128 | £297 | £1,424 | £18,376 | 12.9 yrs | £10,113 |
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: £961, Upfront: £13,673, Break-even: 14.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1855 kWh | 1298 kWh | 556 kWh | £329 | £56 | £385 | £7,569 | 19.7 yrs | £122 |
| 3 kW | 2782 kWh | 1948 kWh | 835 kWh | £493 | £83 | £577 | £9,604 | 16.6 yrs | £1,933 |
| 4 kW | 3710 kWh | 2597 kWh | 1113 kWh | £658 | £111 | £769 | £11,638 | 15.1 yrs | £3,744 |
| 5 kW | 4637 kWh | 3246 kWh | 1391 kWh | £822 | £139 | £961 | £13,673 | 14.2 yrs | £5,555 |
| 6 kW | 5565 kWh | 3895 kWh | 1669 kWh | £987 | £167 | £1,154 | £15,707 | 13.6 yrs | £7,366 |
| 7 kW | 6492 kWh | 4545 kWh | 1948 kWh | £1,151 | £195 | £1,346 | £17,742 | 13.2 yrs | £9,177 |
| 8 kW | 7420 kWh | 5194 kWh | 2226 kWh | £1,316 | £223 | £1,538 | £19,776 | 12.9 yrs | £10,988 |
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: £983, Upfront: £15,423, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1855 kWh | 1354 kWh | 501 kWh | £343 | £50 | £393 | £9,319 | 23.7 yrs | £-1,457 |
| 3 kW | 2782 kWh | 2031 kWh | 751 kWh | £515 | £75 | £590 | £11,354 | 19.3 yrs | £439 |
| 4 kW | 3710 kWh | 2708 kWh | 1002 kWh | £686 | £100 | £786 | £13,388 | 17.0 yrs | £2,335 |
| 5 kW | 4637 kWh | 3385 kWh | 1252 kWh | £858 | £125 | £983 | £15,423 | 15.7 yrs | £4,232 |
| 6 kW | 5565 kWh | 4062 kWh | 1503 kWh | £1,029 | £150 | £1,179 | £17,457 | 14.8 yrs | £6,128 |
| 7 kW | 6492 kWh | 4739 kWh | 1753 kWh | £1,201 | £175 | £1,376 | £19,492 | 14.2 yrs | £8,025 |
| 8 kW | 7420 kWh | 5417 kWh | 2003 kWh | £1,372 | £200 | £1,572 | £21,526 | 13.7 yrs | £9,921 |
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: £997, Upfront: £17,173, Break-even: 17.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1855 kWh | 1391 kWh | 464 kWh | £352 | £46 | £399 | £11,069 | 27.8 yrs | £-3,094 |
| 3 kW | 2782 kWh | 2087 kWh | 696 kWh | £529 | £70 | £598 | £13,104 | 21.9 yrs | £-1,140 |
| 4 kW | 3710 kWh | 2782 kWh | 927 kWh | £705 | £93 | £798 | £15,138 | 19.0 yrs | £813 |
| 5 kW | 4637 kWh | 3478 kWh | 1159 kWh | £881 | £116 | £997 | £17,173 | 17.2 yrs | £2,766 |
| 6 kW | 5565 kWh | 4174 kWh | 1391 kWh | £1,057 | £139 | £1,196 | £19,207 | 16.1 yrs | £4,719 |
| 7 kW | 6492 kWh | 4869 kWh | 1623 kWh | £1,233 | £162 | £1,396 | £21,242 | 15.2 yrs | £6,673 |
| 8 kW | 7420 kWh | 5565 kWh | 1855 kWh | £1,410 | £185 | £1,595 | £23,276 | 14.6 yrs | £8,626 |
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: £1,011, Upfront: £19,623, Break-even: 19.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1855 kWh | 1428 kWh | 427 kWh | £362 | £43 | £404 | £13,519 | 33.4 yrs | £-5,430 |
| 3 kW | 2782 kWh | 2143 kWh | 640 kWh | £543 | £64 | £607 | £15,554 | 25.6 yrs | £-3,420 |
| 4 kW | 3710 kWh | 2857 kWh | 853 kWh | £724 | £85 | £809 | £17,588 | 21.7 yrs | £-1,410 |
| 5 kW | 4637 kWh | 3571 kWh | 1067 kWh | £904 | £107 | £1,011 | £19,623 | 19.4 yrs | £601 |
| 6 kW | 5565 kWh | 4285 kWh | 1280 kWh | £1,085 | £128 | £1,213 | £21,657 | 17.8 yrs | £2,611 |
| 7 kW | 6492 kWh | 4999 kWh | 1493 kWh | £1,266 | £149 | £1,416 | £23,692 | 16.7 yrs | £4,621 |
| 8 kW | 7420 kWh | 5713 kWh | 1707 kWh | £1,447 | £171 | £1,618 | £25,726 | 15.9 yrs | £6,631 |
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.