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 1096 kWh per year on a south-facing roof. We value self-used electricity at 26.5p 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: £909, Upfront: £10,173, Break-even: 11.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 877 kWh | 1315 kWh | £232 | £132 | £364 | £4,069 | 11.2 yrs | £3,205 |
| 3 kW | 3288 kWh | 1315 kWh | 1973 kWh | £348 | £197 | £546 | £6,104 | 11.2 yrs | £4,808 |
| 4 kW | 4384 kWh | 1754 kWh | 2631 kWh | £464 | £263 | £727 | £8,138 | 11.2 yrs | £6,411 |
| 5 kW | 5480 kWh | 2192 kWh | 3288 kWh | £580 | £329 | £909 | £10,173 | 11.2 yrs | £8,014 |
| 6 kW | 6576 kWh | 2631 kWh | 3946 kWh | £697 | £395 | £1,091 | £12,207 | 11.2 yrs | £9,616 |
| 7 kW | 7673 kWh | 3069 kWh | 4604 kWh | £813 | £460 | £1,273 | £14,242 | 11.2 yrs | £11,219 |
| 8 kW | 8769 kWh | 3507 kWh | 5261 kWh | £929 | £526 | £1,455 | £16,276 | 11.2 yrs | £12,822 |
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: £1,090, Upfront: £12,273, 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 | 2192 kWh | 1315 kWh | 877 kWh | £348 | £88 | £436 | £6,169 | 14.1 yrs | £2,551 |
| 3 kW | 3288 kWh | 1973 kWh | 1315 kWh | £522 | £132 | £654 | £8,204 | 12.5 yrs | £4,876 |
| 4 kW | 4384 kWh | 2631 kWh | 1754 kWh | £697 | £175 | £872 | £10,238 | 11.7 yrs | £7,201 |
| 5 kW | 5480 kWh | 3288 kWh | 2192 kWh | £871 | £219 | £1,090 | £12,273 | 11.3 yrs | £9,526 |
| 6 kW | 6576 kWh | 3946 kWh | 2631 kWh | £1,045 | £263 | £1,308 | £14,307 | 10.9 yrs | £11,852 |
| 7 kW | 7673 kWh | 4604 kWh | 3069 kWh | £1,219 | £307 | £1,526 | £16,342 | 10.7 yrs | £14,177 |
| 8 kW | 8769 kWh | 5261 kWh | 3507 kWh | £1,393 | £351 | £1,744 | £18,376 | 10.5 yrs | £16,502 |
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: £1,180, Upfront: £13,673, Break-even: 11.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1535 kWh | 658 kWh | £406 | £66 | £472 | £7,569 | 16.0 yrs | £1,873 |
| 3 kW | 3288 kWh | 2302 kWh | 986 kWh | £610 | £99 | £708 | £9,604 | 13.6 yrs | £4,560 |
| 4 kW | 4384 kWh | 3069 kWh | 1315 kWh | £813 | £132 | £944 | £11,638 | 12.3 yrs | £7,246 |
| 5 kW | 5480 kWh | 3836 kWh | 1644 kWh | £1,016 | £164 | £1,180 | £13,673 | 11.6 yrs | £9,933 |
| 6 kW | 6576 kWh | 4604 kWh | 1973 kWh | £1,219 | £197 | £1,416 | £15,707 | 11.1 yrs | £12,619 |
| 7 kW | 7673 kWh | 5371 kWh | 2302 kWh | £1,422 | £230 | £1,652 | £17,742 | 10.7 yrs | £15,306 |
| 8 kW | 8769 kWh | 6138 kWh | 2631 kWh | £1,625 | £263 | £1,888 | £19,776 | 10.5 yrs | £17,992 |
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: £1,207, Upfront: £15,423, Break-even: 12.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1600 kWh | 592 kWh | £424 | £59 | £483 | £9,319 | 19.3 yrs | £340 |
| 3 kW | 3288 kWh | 2400 kWh | 888 kWh | £636 | £89 | £724 | £11,354 | 15.7 yrs | £3,135 |
| 4 kW | 4384 kWh | 3201 kWh | 1184 kWh | £848 | £118 | £966 | £13,388 | 13.9 yrs | £5,930 |
| 5 kW | 5480 kWh | 4001 kWh | 1480 kWh | £1,059 | £148 | £1,207 | £15,423 | 12.8 yrs | £8,725 |
| 6 kW | 6576 kWh | 4801 kWh | 1776 kWh | £1,271 | £178 | £1,449 | £17,457 | 12.0 yrs | £11,519 |
| 7 kW | 7673 kWh | 5601 kWh | 2072 kWh | £1,483 | £207 | £1,690 | £19,492 | 11.5 yrs | £14,314 |
| 8 kW | 8769 kWh | 6401 kWh | 2368 kWh | £1,695 | £237 | £1,932 | £21,526 | 11.1 yrs | £17,109 |
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: £1,225, Upfront: £17,173, 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 | 2192 kWh | 1644 kWh | 548 kWh | £435 | £55 | £490 | £11,069 | 22.6 yrs | £-1,266 |
| 3 kW | 3288 kWh | 2466 kWh | 822 kWh | £653 | £82 | £735 | £13,104 | 17.8 yrs | £1,601 |
| 4 kW | 4384 kWh | 3288 kWh | 1096 kWh | £871 | £110 | £980 | £15,138 | 15.4 yrs | £4,469 |
| 5 kW | 5480 kWh | 4110 kWh | 1370 kWh | £1,088 | £137 | £1,225 | £17,173 | 14.0 yrs | £7,336 |
| 6 kW | 6576 kWh | 4932 kWh | 1644 kWh | £1,306 | £164 | £1,471 | £19,207 | 13.1 yrs | £10,203 |
| 7 kW | 7673 kWh | 5754 kWh | 1918 kWh | £1,524 | £192 | £1,716 | £21,242 | 12.4 yrs | £13,070 |
| 8 kW | 8769 kWh | 6576 kWh | 2192 kWh | £1,741 | £219 | £1,961 | £23,276 | 11.9 yrs | £15,937 |
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: £1,243, Upfront: £19,623, Break-even: 15.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2192 kWh | 1688 kWh | 504 kWh | £447 | £50 | £497 | £13,519 | 27.2 yrs | £-3,571 |
| 3 kW | 3288 kWh | 2532 kWh | 756 kWh | £670 | £76 | £746 | £15,554 | 20.8 yrs | £-632 |
| 4 kW | 4384 kWh | 3376 kWh | 1008 kWh | £894 | £101 | £995 | £17,588 | 17.7 yrs | £2,308 |
| 5 kW | 5480 kWh | 4220 kWh | 1260 kWh | £1,117 | £126 | £1,243 | £19,623 | 15.8 yrs | £5,247 |
| 6 kW | 6576 kWh | 5064 kWh | 1513 kWh | £1,341 | £151 | £1,492 | £21,657 | 14.5 yrs | £8,186 |
| 7 kW | 7673 kWh | 5908 kWh | 1765 kWh | £1,564 | £176 | £1,741 | £23,692 | 13.6 yrs | £11,126 |
| 8 kW | 8769 kWh | 6752 kWh | 2017 kWh | £1,788 | £202 | £1,990 | £25,726 | 12.9 yrs | £14,065 |
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.