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 853 kWh per year on a south-facing roof. We value self-used electricity at 27.1p 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: £717, Upfront: £10,173, 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 | 1706 kWh | 682 kWh | 1023 kWh | £185 | £102 | £287 | £4,069 | 14.2 yrs | £1,670 |
| 3 kW | 2558 kWh | 1023 kWh | 1535 kWh | £277 | £153 | £430 | £6,104 | 14.2 yrs | £2,504 |
| 4 kW | 3411 kWh | 1364 kWh | 2047 kWh | £369 | £205 | £574 | £8,138 | 14.2 yrs | £3,339 |
| 5 kW | 4264 kWh | 1706 kWh | 2558 kWh | £462 | £256 | £717 | £10,173 | 14.2 yrs | £4,174 |
| 6 kW | 5116 kWh | 2047 kWh | 3070 kWh | £554 | £307 | £861 | £12,207 | 14.2 yrs | £5,009 |
| 7 kW | 5969 kWh | 2388 kWh | 3582 kWh | £646 | £358 | £1,004 | £14,242 | 14.2 yrs | £5,844 |
| 8 kW | 6822 kWh | 2729 kWh | 4093 kWh | £738 | £409 | £1,148 | £16,276 | 14.2 yrs | £6,679 |
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: £863, Upfront: £12,273, 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 | 1706 kWh | 1023 kWh | 682 kWh | £277 | £68 | £345 | £6,169 | 17.9 yrs | £733 |
| 3 kW | 2558 kWh | 1535 kWh | 1023 kWh | £415 | £102 | £518 | £8,204 | 15.8 yrs | £2,150 |
| 4 kW | 3411 kWh | 2047 kWh | 1364 kWh | £554 | £136 | £690 | £10,238 | 14.8 yrs | £3,567 |
| 5 kW | 4264 kWh | 2558 kWh | 1706 kWh | £692 | £171 | £863 | £12,273 | 14.2 yrs | £4,984 |
| 6 kW | 5116 kWh | 3070 kWh | 2047 kWh | £831 | £205 | £1,035 | £14,307 | 13.8 yrs | £6,400 |
| 7 kW | 5969 kWh | 3582 kWh | 2388 kWh | £969 | £239 | £1,208 | £16,342 | 13.5 yrs | £7,817 |
| 8 kW | 6822 kWh | 4093 kWh | 2729 kWh | £1,108 | £273 | £1,380 | £18,376 | 13.3 yrs | £9,234 |
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: £936, Upfront: £13,673, Break-even: 14.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1706 kWh | 1194 kWh | 512 kWh | £323 | £51 | £374 | £7,569 | 20.2 yrs | £-85 |
| 3 kW | 2558 kWh | 1791 kWh | 767 kWh | £485 | £77 | £561 | £9,604 | 17.1 yrs | £1,623 |
| 4 kW | 3411 kWh | 2388 kWh | 1023 kWh | £646 | £102 | £748 | £11,638 | 15.5 yrs | £3,331 |
| 5 kW | 4264 kWh | 2985 kWh | 1279 kWh | £808 | £128 | £936 | £13,673 | 14.6 yrs | £5,038 |
| 6 kW | 5116 kWh | 3582 kWh | 1535 kWh | £969 | £153 | £1,123 | £15,707 | 14.0 yrs | £6,746 |
| 7 kW | 5969 kWh | 4178 kWh | 1791 kWh | £1,131 | £179 | £1,310 | £17,742 | 13.5 yrs | £8,454 |
| 8 kW | 6822 kWh | 4775 kWh | 2047 kWh | £1,292 | £205 | £1,497 | £19,776 | 13.2 yrs | £10,162 |
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: £957, Upfront: £15,423, Break-even: 16.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1706 kWh | 1245 kWh | 460 kWh | £337 | £46 | £383 | £9,319 | 24.3 yrs | £-1,660 |
| 3 kW | 2558 kWh | 1868 kWh | 691 kWh | £505 | £69 | £574 | £11,354 | 19.8 yrs | £135 |
| 4 kW | 3411 kWh | 2490 kWh | 921 kWh | £674 | £92 | £766 | £13,388 | 17.5 yrs | £1,930 |
| 5 kW | 4264 kWh | 3113 kWh | 1151 kWh | £842 | £115 | £957 | £15,423 | 16.1 yrs | £3,725 |
| 6 kW | 5116 kWh | 3735 kWh | 1381 kWh | £1,011 | £138 | £1,149 | £17,457 | 15.2 yrs | £5,520 |
| 7 kW | 5969 kWh | 4358 kWh | 1612 kWh | £1,179 | £161 | £1,340 | £19,492 | 14.5 yrs | £7,315 |
| 8 kW | 6822 kWh | 4980 kWh | 1842 kWh | £1,348 | £184 | £1,532 | £21,526 | 14.1 yrs | £9,110 |
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: £972, Upfront: £17,173, Break-even: 17.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1706 kWh | 1279 kWh | 426 kWh | £346 | £43 | £389 | £11,069 | 28.5 yrs | £-3,294 |
| 3 kW | 2558 kWh | 1919 kWh | 640 kWh | £519 | £64 | £583 | £13,104 | 22.5 yrs | £-1,440 |
| 4 kW | 3411 kWh | 2558 kWh | 853 kWh | £692 | £85 | £778 | £15,138 | 19.5 yrs | £413 |
| 5 kW | 4264 kWh | 3198 kWh | 1066 kWh | £865 | £107 | £972 | £17,173 | 17.7 yrs | £2,266 |
| 6 kW | 5116 kWh | 3837 kWh | 1279 kWh | £1,038 | £128 | £1,166 | £19,207 | 16.5 yrs | £4,119 |
| 7 kW | 5969 kWh | 4477 kWh | 1492 kWh | £1,211 | £149 | £1,361 | £21,242 | 15.6 yrs | £5,972 |
| 8 kW | 6822 kWh | 5116 kWh | 1706 kWh | £1,385 | £171 | £1,555 | £23,276 | 15.0 yrs | £7,825 |
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: £986, Upfront: £19,623, Break-even: 19.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1706 kWh | 1313 kWh | 392 kWh | £355 | £39 | £395 | £13,519 | 34.3 yrs | £-5,627 |
| 3 kW | 2558 kWh | 1970 kWh | 588 kWh | £533 | £59 | £592 | £15,554 | 26.3 yrs | £-3,716 |
| 4 kW | 3411 kWh | 2626 kWh | 785 kWh | £711 | £78 | £789 | £17,588 | 22.3 yrs | £-1,805 |
| 5 kW | 4264 kWh | 3283 kWh | 981 kWh | £888 | £98 | £986 | £19,623 | 19.9 yrs | £107 |
| 6 kW | 5116 kWh | 3940 kWh | 1177 kWh | £1,066 | £118 | £1,184 | £21,657 | 18.3 yrs | £2,018 |
| 7 kW | 5969 kWh | 4596 kWh | 1373 kWh | £1,244 | £137 | £1,381 | £23,692 | 17.2 yrs | £3,930 |
| 8 kW | 6822 kWh | 5253 kWh | 1569 kWh | £1,421 | £157 | £1,578 | £25,726 | 16.3 yrs | £5,841 |
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.