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 948 kWh per year on a south-facing roof. We value self-used electricity at 27.7p 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: £810, Upfront: £10,173, Break-even: 12.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1896 kWh | 758 kWh | 1138 kWh | £210 | £114 | £324 | £4,069 | 12.6 yrs | £2,411 |
| 3 kW | 2844 kWh | 1138 kWh | 1706 kWh | £315 | £171 | £486 | £6,104 | 12.6 yrs | £3,617 |
| 4 kW | 3792 kWh | 1517 kWh | 2275 kWh | £420 | £228 | £648 | £8,138 | 12.6 yrs | £4,822 |
| 5 kW | 4740 kWh | 1896 kWh | 2844 kWh | £526 | £284 | £810 | £10,173 | 12.6 yrs | £6,028 |
| 6 kW | 5688 kWh | 2275 kWh | 3413 kWh | £631 | £341 | £972 | £12,207 | 12.6 yrs | £7,233 |
| 7 kW | 6636 kWh | 2655 kWh | 3982 kWh | £736 | £398 | £1,134 | £14,242 | 12.6 yrs | £8,439 |
| 8 kW | 7584 kWh | 3034 kWh | 4551 kWh | £841 | £455 | £1,296 | £16,276 | 12.6 yrs | £9,644 |
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: £978, Upfront: £12,273, 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 | 1896 kWh | 1138 kWh | 758 kWh | £315 | £76 | £391 | £6,169 | 15.8 yrs | £1,655 |
| 3 kW | 2844 kWh | 1706 kWh | 1138 kWh | £473 | £114 | £587 | £8,204 | 14.0 yrs | £3,533 |
| 4 kW | 3792 kWh | 2275 kWh | 1517 kWh | £631 | £152 | £782 | £10,238 | 13.1 yrs | £5,410 |
| 5 kW | 4740 kWh | 2844 kWh | 1896 kWh | £788 | £190 | £978 | £12,273 | 12.5 yrs | £7,288 |
| 6 kW | 5688 kWh | 3413 kWh | 2275 kWh | £946 | £228 | £1,174 | £14,307 | 12.2 yrs | £9,165 |
| 7 kW | 6636 kWh | 3982 kWh | 2655 kWh | £1,104 | £265 | £1,369 | £16,342 | 11.9 yrs | £11,043 |
| 8 kW | 7584 kWh | 4551 kWh | 3034 kWh | £1,261 | £303 | £1,565 | £18,376 | 11.7 yrs | £12,920 |
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: £1,062, Upfront: £13,673, Break-even: 12.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1896 kWh | 1327 kWh | 569 kWh | £368 | £57 | £425 | £7,569 | 17.8 yrs | £927 |
| 3 kW | 2844 kWh | 1991 kWh | 853 kWh | £552 | £85 | £637 | £9,604 | 15.1 yrs | £3,141 |
| 4 kW | 3792 kWh | 2655 kWh | 1138 kWh | £736 | £114 | £850 | £11,638 | 13.7 yrs | £5,354 |
| 5 kW | 4740 kWh | 3318 kWh | 1422 kWh | £920 | £142 | £1,062 | £13,673 | 12.9 yrs | £7,568 |
| 6 kW | 5688 kWh | 3982 kWh | 1706 kWh | £1,104 | £171 | £1,274 | £15,707 | 12.3 yrs | £9,781 |
| 7 kW | 6636 kWh | 4645 kWh | 1991 kWh | £1,288 | £199 | £1,487 | £17,742 | 11.9 yrs | £11,995 |
| 8 kW | 7584 kWh | 5309 kWh | 2275 kWh | £1,472 | £228 | £1,699 | £19,776 | 11.6 yrs | £14,208 |
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: £1,087, Upfront: £15,423, 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 | 1896 kWh | 1384 kWh | 512 kWh | £384 | £51 | £435 | £9,319 | 21.4 yrs | £-621 |
| 3 kW | 2844 kWh | 2076 kWh | 768 kWh | £576 | £77 | £652 | £11,354 | 17.4 yrs | £1,693 |
| 4 kW | 3792 kWh | 2768 kWh | 1024 kWh | £767 | £102 | £870 | £13,388 | 15.4 yrs | £4,007 |
| 5 kW | 4740 kWh | 3460 kWh | 1280 kWh | £959 | £128 | £1,087 | £15,423 | 14.2 yrs | £6,322 |
| 6 kW | 5688 kWh | 4152 kWh | 1536 kWh | £1,151 | £154 | £1,305 | £17,457 | 13.4 yrs | £8,636 |
| 7 kW | 6636 kWh | 4845 kWh | 1792 kWh | £1,343 | £179 | £1,522 | £19,492 | 12.8 yrs | £10,950 |
| 8 kW | 7584 kWh | 5537 kWh | 2048 kWh | £1,535 | £205 | £1,740 | £21,526 | 12.4 yrs | £13,264 |
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: £1,104, Upfront: £17,173, Break-even: 15.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1896 kWh | 1422 kWh | 474 kWh | £394 | £47 | £442 | £11,069 | 25.1 yrs | £-2,237 |
| 3 kW | 2844 kWh | 2133 kWh | 711 kWh | £591 | £71 | £662 | £13,104 | 19.8 yrs | £145 |
| 4 kW | 3792 kWh | 2844 kWh | 948 kWh | £788 | £95 | £883 | £15,138 | 17.1 yrs | £2,526 |
| 5 kW | 4740 kWh | 3555 kWh | 1185 kWh | £985 | £119 | £1,104 | £17,173 | 15.6 yrs | £4,908 |
| 6 kW | 5688 kWh | 4266 kWh | 1422 kWh | £1,183 | £142 | £1,325 | £19,207 | 14.5 yrs | £7,289 |
| 7 kW | 6636 kWh | 4977 kWh | 1659 kWh | £1,380 | £166 | £1,546 | £21,242 | 13.7 yrs | £9,671 |
| 8 kW | 7584 kWh | 5688 kWh | 1896 kWh | £1,577 | £190 | £1,766 | £23,276 | 13.2 yrs | £12,052 |
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: £1,121, Upfront: £19,623, 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 | 1896 kWh | 1460 kWh | 436 kWh | £405 | £44 | £448 | £13,519 | 30.2 yrs | £-4,553 |
| 3 kW | 2844 kWh | 2190 kWh | 654 kWh | £607 | £65 | £672 | £15,554 | 23.1 yrs | £-2,104 |
| 4 kW | 3792 kWh | 2920 kWh | 872 kWh | £809 | £87 | £897 | £17,588 | 19.6 yrs | £345 |
| 5 kW | 4740 kWh | 3650 kWh | 1090 kWh | £1,012 | £109 | £1,121 | £19,623 | 17.5 yrs | £2,794 |
| 6 kW | 5688 kWh | 4380 kWh | 1308 kWh | £1,214 | £131 | £1,345 | £21,657 | 16.1 yrs | £5,242 |
| 7 kW | 6636 kWh | 5110 kWh | 1526 kWh | £1,416 | £153 | £1,569 | £23,692 | 15.1 yrs | £7,691 |
| 8 kW | 7584 kWh | 5840 kWh | 1744 kWh | £1,619 | £174 | £1,793 | £25,726 | 14.3 yrs | £10,140 |
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.