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 966 kWh per year on a south-facing roof. We value self-used electricity at 25.3p 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: £779, Upfront: £10,173, Break-even: 13.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1933 kWh | 773 kWh | 1160 kWh | £196 | £116 | £312 | £4,069 | 13.1 yrs | £2,167 |
| 3 kW | 2899 kWh | 1160 kWh | 1739 kWh | £294 | £174 | £468 | £6,104 | 13.1 yrs | £3,250 |
| 4 kW | 3865 kWh | 1546 kWh | 2319 kWh | £392 | £232 | £624 | £8,138 | 13.1 yrs | £4,333 |
| 5 kW | 4832 kWh | 1933 kWh | 2899 kWh | £490 | £290 | £779 | £10,173 | 13.1 yrs | £5,417 |
| 6 kW | 5798 kWh | 2319 kWh | 3479 kWh | £587 | £348 | £935 | £12,207 | 13.1 yrs | £6,500 |
| 7 kW | 6764 kWh | 2706 kWh | 4059 kWh | £685 | £406 | £1,091 | £14,242 | 13.1 yrs | £7,583 |
| 8 kW | 7731 kWh | 3092 kWh | 4638 kWh | £783 | £464 | £1,247 | £16,276 | 13.1 yrs | £8,667 |
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: £928, Upfront: £12,273, Break-even: 13.2 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1933 kWh | 1160 kWh | 773 kWh | £294 | £77 | £371 | £6,169 | 16.6 yrs | £1,252 |
| 3 kW | 2899 kWh | 1739 kWh | 1160 kWh | £441 | £116 | £557 | £8,204 | 14.7 yrs | £2,928 |
| 4 kW | 3865 kWh | 2319 kWh | 1546 kWh | £587 | £155 | £742 | £10,238 | 13.8 yrs | £4,604 |
| 5 kW | 4832 kWh | 2899 kWh | 1933 kWh | £734 | £193 | £928 | £12,273 | 13.2 yrs | £6,279 |
| 6 kW | 5798 kWh | 3479 kWh | 2319 kWh | £881 | £232 | £1,113 | £14,307 | 12.9 yrs | £7,955 |
| 7 kW | 6764 kWh | 4059 kWh | 2706 kWh | £1,028 | £271 | £1,299 | £16,342 | 12.6 yrs | £9,631 |
| 8 kW | 7731 kWh | 4638 kWh | 3092 kWh | £1,175 | £309 | £1,484 | £18,376 | 12.4 yrs | £11,307 |
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: £1,002, Upfront: £13,673, Break-even: 13.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1933 kWh | 1353 kWh | 580 kWh | £343 | £58 | £401 | £7,569 | 18.9 yrs | £444 |
| 3 kW | 2899 kWh | 2029 kWh | 870 kWh | £514 | £87 | £601 | £9,604 | 16.0 yrs | £2,417 |
| 4 kW | 3865 kWh | 2706 kWh | 1160 kWh | £685 | £116 | £801 | £11,638 | 14.5 yrs | £4,389 |
| 5 kW | 4832 kWh | 3382 kWh | 1450 kWh | £857 | £145 | £1,002 | £13,673 | 13.6 yrs | £6,361 |
| 6 kW | 5798 kWh | 4059 kWh | 1739 kWh | £1,028 | £174 | £1,202 | £15,707 | 13.1 yrs | £8,333 |
| 7 kW | 6764 kWh | 4735 kWh | 2029 kWh | £1,199 | £203 | £1,402 | £17,742 | 12.7 yrs | £10,305 |
| 8 kW | 7731 kWh | 5412 kWh | 2319 kWh | £1,371 | £232 | £1,603 | £19,776 | 12.3 yrs | £12,277 |
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: £1,024, Upfront: £15,423, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1933 kWh | 1411 kWh | 522 kWh | £357 | £52 | £410 | £9,319 | 22.8 yrs | £-1,128 |
| 3 kW | 2899 kWh | 2116 kWh | 783 kWh | £536 | £78 | £614 | £11,354 | 18.5 yrs | £933 |
| 4 kW | 3865 kWh | 2822 kWh | 1044 kWh | £715 | £104 | £819 | £13,388 | 16.3 yrs | £2,994 |
| 5 kW | 4832 kWh | 3527 kWh | 1305 kWh | £893 | £130 | £1,024 | £15,423 | 15.1 yrs | £5,055 |
| 6 kW | 5798 kWh | 4233 kWh | 1565 kWh | £1,072 | £157 | £1,229 | £17,457 | 14.2 yrs | £7,116 |
| 7 kW | 6764 kWh | 4938 kWh | 1826 kWh | £1,251 | £183 | £1,433 | £19,492 | 13.6 yrs | £9,177 |
| 8 kW | 7731 kWh | 5643 kWh | 2087 kWh | £1,429 | £209 | £1,638 | £21,526 | 13.1 yrs | £11,238 |
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: £1,039, Upfront: £17,173, Break-even: 16.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1933 kWh | 1450 kWh | 483 kWh | £367 | £48 | £415 | £11,069 | 26.6 yrs | £-2,759 |
| 3 kW | 2899 kWh | 2174 kWh | 725 kWh | £551 | £72 | £623 | £13,104 | 21.0 yrs | £-639 |
| 4 kW | 3865 kWh | 2899 kWh | 966 kWh | £734 | £97 | £831 | £15,138 | 18.2 yrs | £1,481 |
| 5 kW | 4832 kWh | 3624 kWh | 1208 kWh | £918 | £121 | £1,039 | £17,173 | 16.5 yrs | £3,602 |
| 6 kW | 5798 kWh | 4349 kWh | 1450 kWh | £1,101 | £145 | £1,246 | £19,207 | 15.4 yrs | £5,722 |
| 7 kW | 6764 kWh | 5073 kWh | 1691 kWh | £1,285 | £169 | £1,454 | £21,242 | 14.6 yrs | £7,842 |
| 8 kW | 7731 kWh | 5798 kWh | 1933 kWh | £1,469 | £193 | £1,662 | £23,276 | 14.0 yrs | £9,962 |
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: £1,054, Upfront: £19,623, Break-even: 18.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1933 kWh | 1488 kWh | 445 kWh | £377 | £44 | £421 | £13,519 | 32.1 yrs | £-5,091 |
| 3 kW | 2899 kWh | 2232 kWh | 667 kWh | £565 | £67 | £632 | £15,554 | 24.6 yrs | £-2,911 |
| 4 kW | 3865 kWh | 2976 kWh | 889 kWh | £754 | £89 | £843 | £17,588 | 20.9 yrs | £-732 |
| 5 kW | 4832 kWh | 3720 kWh | 1111 kWh | £942 | £111 | £1,054 | £19,623 | 18.6 yrs | £1,448 |
| 6 kW | 5798 kWh | 4465 kWh | 1334 kWh | £1,131 | £133 | £1,264 | £21,657 | 17.1 yrs | £3,627 |
| 7 kW | 6764 kWh | 5209 kWh | 1556 kWh | £1,319 | £156 | £1,475 | £23,692 | 16.1 yrs | £5,807 |
| 8 kW | 7731 kWh | 5953 kWh | 1778 kWh | £1,508 | £178 | £1,686 | £25,726 | 15.3 yrs | £7,987 |
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.