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 1106 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £927, Upfront: £10,173, Break-even: 11.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2212 kWh | 885 kWh | 1327 kWh | £238 | £133 | £371 | £4,069 | 11.0 yrs | £3,350 |
| 3 kW | 3318 kWh | 1327 kWh | 1991 kWh | £357 | £199 | £556 | £6,104 | 11.0 yrs | £5,025 |
| 4 kW | 4424 kWh | 1770 kWh | 2655 kWh | £476 | £265 | £742 | £8,138 | 11.0 yrs | £6,700 |
| 5 kW | 5531 kWh | 2212 kWh | 3318 kWh | £596 | £332 | £927 | £10,173 | 11.0 yrs | £8,375 |
| 6 kW | 6637 kWh | 2655 kWh | 3982 kWh | £715 | £398 | £1,113 | £12,207 | 11.0 yrs | £10,050 |
| 7 kW | 7743 kWh | 3097 kWh | 4646 kWh | £834 | £465 | £1,298 | £14,242 | 11.0 yrs | £11,725 |
| 8 kW | 8849 kWh | 3540 kWh | 5309 kWh | £953 | £531 | £1,484 | £16,276 | 11.0 yrs | £13,400 |
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: £1,115, Upfront: £12,273, Break-even: 11.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2212 kWh | 1327 kWh | 885 kWh | £357 | £88 | £446 | £6,169 | 13.8 yrs | £2,747 |
| 3 kW | 3318 kWh | 1991 kWh | 1327 kWh | £536 | £133 | £669 | £8,204 | 12.3 yrs | £5,171 |
| 4 kW | 4424 kWh | 2655 kWh | 1770 kWh | £715 | £177 | £892 | £10,238 | 11.5 yrs | £7,594 |
| 5 kW | 5531 kWh | 3318 kWh | 2212 kWh | £893 | £221 | £1,115 | £12,273 | 11.0 yrs | £10,018 |
| 6 kW | 6637 kWh | 3982 kWh | 2655 kWh | £1,072 | £265 | £1,337 | £14,307 | 10.7 yrs | £12,442 |
| 7 kW | 7743 kWh | 4646 kWh | 3097 kWh | £1,251 | £310 | £1,560 | £16,342 | 10.5 yrs | £14,865 |
| 8 kW | 8849 kWh | 5309 kWh | 3540 kWh | £1,429 | £354 | £1,783 | £18,376 | 10.3 yrs | £17,289 |
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: £1,208, Upfront: £13,673, Break-even: 11.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2212 kWh | 1549 kWh | 664 kWh | £417 | £66 | £483 | £7,569 | 15.7 yrs | £2,096 |
| 3 kW | 3318 kWh | 2323 kWh | 996 kWh | £625 | £100 | £725 | £9,604 | 13.2 yrs | £4,894 |
| 4 kW | 4424 kWh | 3097 kWh | 1327 kWh | £834 | £133 | £966 | £11,638 | 12.0 yrs | £7,692 |
| 5 kW | 5531 kWh | 3871 kWh | 1659 kWh | £1,042 | £166 | £1,208 | £13,673 | 11.3 yrs | £10,490 |
| 6 kW | 6637 kWh | 4646 kWh | 1991 kWh | £1,251 | £199 | £1,450 | £15,707 | 10.8 yrs | £13,287 |
| 7 kW | 7743 kWh | 5420 kWh | 2323 kWh | £1,459 | £232 | £1,691 | £17,742 | 10.5 yrs | £16,085 |
| 8 kW | 8849 kWh | 6194 kWh | 2655 kWh | £1,667 | £265 | £1,933 | £19,776 | 10.2 yrs | £18,883 |
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: £1,236, Upfront: £15,423, Break-even: 12.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2212 kWh | 1615 kWh | 597 kWh | £435 | £60 | £494 | £9,319 | 18.8 yrs | £570 |
| 3 kW | 3318 kWh | 2422 kWh | 896 kWh | £652 | £90 | £742 | £11,354 | 15.3 yrs | £3,481 |
| 4 kW | 4424 kWh | 3230 kWh | 1195 kWh | £869 | £119 | £989 | £13,388 | 13.5 yrs | £6,391 |
| 5 kW | 5531 kWh | 4037 kWh | 1493 kWh | £1,087 | £149 | £1,236 | £15,423 | 12.5 yrs | £9,301 |
| 6 kW | 6637 kWh | 4845 kWh | 1792 kWh | £1,304 | £179 | £1,483 | £17,457 | 11.8 yrs | £12,211 |
| 7 kW | 7743 kWh | 5652 kWh | 2091 kWh | £1,522 | £209 | £1,731 | £19,492 | 11.3 yrs | £15,121 |
| 8 kW | 8849 kWh | 6460 kWh | 2389 kWh | £1,739 | £239 | £1,978 | £21,526 | 10.9 yrs | £18,032 |
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: £1,255, Upfront: £17,173, Break-even: 13.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2212 kWh | 1659 kWh | 553 kWh | £447 | £55 | £502 | £11,069 | 22.1 yrs | £-1,030 |
| 3 kW | 3318 kWh | 2489 kWh | 830 kWh | £670 | £83 | £753 | £13,104 | 17.4 yrs | £1,955 |
| 4 kW | 4424 kWh | 3318 kWh | 1106 kWh | £893 | £111 | £1,004 | £15,138 | 15.1 yrs | £4,940 |
| 5 kW | 5531 kWh | 4148 kWh | 1383 kWh | £1,117 | £138 | £1,255 | £17,173 | 13.7 yrs | £7,925 |
| 6 kW | 6637 kWh | 4978 kWh | 1659 kWh | £1,340 | £166 | £1,506 | £19,207 | 12.8 yrs | £10,910 |
| 7 kW | 7743 kWh | 5807 kWh | 1936 kWh | £1,563 | £194 | £1,757 | £21,242 | 12.1 yrs | £13,895 |
| 8 kW | 8849 kWh | 6637 kWh | 2212 kWh | £1,787 | £221 | £2,008 | £23,276 | 11.6 yrs | £16,881 |
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: £1,274, Upfront: £19,623, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2212 kWh | 1703 kWh | 509 kWh | £459 | £51 | £509 | £13,519 | 26.5 yrs | £-3,330 |
| 3 kW | 3318 kWh | 2555 kWh | 763 kWh | £688 | £76 | £764 | £15,554 | 20.4 yrs | £-270 |
| 4 kW | 4424 kWh | 3407 kWh | 1018 kWh | £917 | £102 | £1,019 | £17,588 | 17.3 yrs | £2,790 |
| 5 kW | 5531 kWh | 4259 kWh | 1272 kWh | £1,146 | £127 | £1,274 | £19,623 | 15.4 yrs | £5,850 |
| 6 kW | 6637 kWh | 5110 kWh | 1526 kWh | £1,376 | £153 | £1,528 | £21,657 | 14.2 yrs | £8,910 |
| 7 kW | 7743 kWh | 5962 kWh | 1781 kWh | £1,605 | £178 | £1,783 | £23,692 | 13.3 yrs | £11,969 |
| 8 kW | 8849 kWh | 6814 kWh | 2035 kWh | £1,834 | £204 | £2,038 | £25,726 | 12.6 yrs | £15,029 |
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.