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 837 kWh per year on a south-facing roof. We value self-used electricity at 25.8p 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: £684, Upfront: £10,173, Break-even: 14.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1674 kWh | 669 kWh | 1004 kWh | £173 | £100 | £273 | £4,069 | 14.9 yrs | £1,399 |
| 3 kW | 2510 kWh | 1004 kWh | 1506 kWh | £259 | £151 | £410 | £6,104 | 14.9 yrs | £2,099 |
| 4 kW | 3347 kWh | 1339 kWh | 2008 kWh | £346 | £201 | £547 | £8,138 | 14.9 yrs | £2,798 |
| 5 kW | 4184 kWh | 1674 kWh | 2510 kWh | £432 | £251 | £684 | £10,173 | 14.9 yrs | £3,498 |
| 6 kW | 5021 kWh | 2008 kWh | 3013 kWh | £519 | £301 | £820 | £12,207 | 14.9 yrs | £4,197 |
| 7 kW | 5858 kWh | 2343 kWh | 3515 kWh | £605 | £351 | £957 | £14,242 | 14.9 yrs | £4,897 |
| 8 kW | 6695 kWh | 2678 kWh | 4017 kWh | £692 | £402 | £1,094 | £16,276 | 14.9 yrs | £5,596 |
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: £816, Upfront: £12,273, Break-even: 15.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1674 kWh | 1004 kWh | 669 kWh | £259 | £67 | £326 | £6,169 | 18.9 yrs | £360 |
| 3 kW | 2510 kWh | 1506 kWh | 1004 kWh | £389 | £100 | £490 | £8,204 | 16.8 yrs | £1,589 |
| 4 kW | 3347 kWh | 2008 kWh | 1339 kWh | £519 | £134 | £653 | £10,238 | 15.7 yrs | £2,819 |
| 5 kW | 4184 kWh | 2510 kWh | 1674 kWh | £649 | £167 | £816 | £12,273 | 15.0 yrs | £4,049 |
| 6 kW | 5021 kWh | 3013 kWh | 2008 kWh | £778 | £201 | £979 | £14,307 | 14.6 yrs | £5,279 |
| 7 kW | 5858 kWh | 3515 kWh | 2343 kWh | £908 | £234 | £1,142 | £16,342 | 14.3 yrs | £6,508 |
| 8 kW | 6695 kWh | 4017 kWh | 2678 kWh | £1,038 | £268 | £1,306 | £18,376 | 14.1 yrs | £7,738 |
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: £882, Upfront: £13,673, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1674 kWh | 1172 kWh | 502 kWh | £303 | £50 | £353 | £7,569 | 21.4 yrs | £-510 |
| 3 kW | 2510 kWh | 1757 kWh | 753 kWh | £454 | £75 | £529 | £9,604 | 18.1 yrs | £985 |
| 4 kW | 3347 kWh | 2343 kWh | 1004 kWh | £605 | £100 | £706 | £11,638 | 16.5 yrs | £2,479 |
| 5 kW | 4184 kWh | 2929 kWh | 1255 kWh | £757 | £126 | £882 | £13,673 | 15.5 yrs | £3,974 |
| 6 kW | 5021 kWh | 3515 kWh | 1506 kWh | £908 | £151 | £1,059 | £15,707 | 14.8 yrs | £5,469 |
| 7 kW | 5858 kWh | 4100 kWh | 1757 kWh | £1,060 | £176 | £1,235 | £17,742 | 14.4 yrs | £6,964 |
| 8 kW | 6695 kWh | 4686 kWh | 2008 kWh | £1,211 | £201 | £1,412 | £19,776 | 14.0 yrs | £8,459 |
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: £902, Upfront: £15,423, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1674 kWh | 1222 kWh | 452 kWh | £316 | £45 | £361 | £9,319 | 25.8 yrs | £-2,101 |
| 3 kW | 2510 kWh | 1833 kWh | 678 kWh | £474 | £68 | £541 | £11,354 | 21.0 yrs | £-527 |
| 4 kW | 3347 kWh | 2444 kWh | 904 kWh | £631 | £90 | £722 | £13,388 | 18.5 yrs | £1,048 |
| 5 kW | 4184 kWh | 3054 kWh | 1130 kWh | £789 | £113 | £902 | £15,423 | 17.1 yrs | £2,622 |
| 6 kW | 5021 kWh | 3665 kWh | 1356 kWh | £947 | £136 | £1,083 | £17,457 | 16.1 yrs | £4,196 |
| 7 kW | 5858 kWh | 4276 kWh | 1582 kWh | £1,105 | £158 | £1,263 | £19,492 | 15.4 yrs | £5,771 |
| 8 kW | 6695 kWh | 4887 kWh | 1808 kWh | £1,263 | £181 | £1,444 | £21,526 | 14.9 yrs | £7,345 |
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: £915, Upfront: £17,173, Break-even: 18.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1674 kWh | 1255 kWh | 418 kWh | £324 | £42 | £366 | £11,069 | 30.2 yrs | £-3,745 |
| 3 kW | 2510 kWh | 1883 kWh | 628 kWh | £487 | £63 | £549 | £13,104 | 23.9 yrs | £-2,118 |
| 4 kW | 3347 kWh | 2510 kWh | 837 kWh | £649 | £84 | £732 | £15,138 | 20.7 yrs | £-490 |
| 5 kW | 4184 kWh | 3138 kWh | 1046 kWh | £811 | £105 | £915 | £17,173 | 18.8 yrs | £1,137 |
| 6 kW | 5021 kWh | 3766 kWh | 1255 kWh | £973 | £126 | £1,099 | £19,207 | 17.5 yrs | £2,764 |
| 7 kW | 5858 kWh | 4393 kWh | 1464 kWh | £1,135 | £146 | £1,282 | £21,242 | 16.6 yrs | £4,392 |
| 8 kW | 6695 kWh | 5021 kWh | 1674 kWh | £1,297 | £167 | £1,465 | £23,276 | 15.9 yrs | £6,019 |
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: £929, Upfront: £19,623, Break-even: 21.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1674 kWh | 1289 kWh | 385 kWh | £333 | £38 | £371 | £13,519 | 36.4 yrs | £-6,089 |
| 3 kW | 2510 kWh | 1933 kWh | 577 kWh | £500 | £58 | £557 | £15,554 | 27.9 yrs | £-4,409 |
| 4 kW | 3347 kWh | 2577 kWh | 770 kWh | £666 | £77 | £743 | £17,588 | 23.7 yrs | £-2,728 |
| 5 kW | 4184 kWh | 3222 kWh | 962 kWh | £833 | £96 | £929 | £19,623 | 21.1 yrs | £-1,048 |
| 6 kW | 5021 kWh | 3866 kWh | 1155 kWh | £999 | £115 | £1,114 | £21,657 | 19.4 yrs | £633 |
| 7 kW | 5858 kWh | 4510 kWh | 1347 kWh | £1,166 | £135 | £1,300 | £23,692 | 18.2 yrs | £2,313 |
| 8 kW | 6695 kWh | 5155 kWh | 1540 kWh | £1,332 | £154 | £1,486 | £25,726 | 17.3 yrs | £3,993 |
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.