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 25.6p 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: £784, Upfront: £10,173, Break-even: 13.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1932 kWh | 773 kWh | 1159 kWh | £197 | £116 | £313 | £4,069 | 13.0 yrs | £2,199 |
| 3 kW | 2898 kWh | 1159 kWh | 1739 kWh | £296 | £174 | £470 | £6,104 | 13.0 yrs | £3,299 |
| 4 kW | 3865 kWh | 1546 kWh | 2319 kWh | £395 | £232 | £627 | £8,138 | 13.0 yrs | £4,399 |
| 5 kW | 4831 kWh | 1932 kWh | 2898 kWh | £494 | £290 | £784 | £10,173 | 13.0 yrs | £5,498 |
| 6 kW | 5797 kWh | 2319 kWh | 3478 kWh | £592 | £348 | £940 | £12,207 | 13.0 yrs | £6,598 |
| 7 kW | 6763 kWh | 2705 kWh | 4058 kWh | £691 | £406 | £1,097 | £14,242 | 13.0 yrs | £7,698 |
| 8 kW | 7729 kWh | 3092 kWh | 4637 kWh | £790 | £464 | £1,254 | £16,276 | 13.0 yrs | £8,797 |
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: £934, Upfront: £12,273, 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 | 1932 kWh | 1159 kWh | 773 kWh | £296 | £77 | £374 | £6,169 | 16.5 yrs | £1,301 |
| 3 kW | 2898 kWh | 1739 kWh | 1159 kWh | £444 | £116 | £560 | £8,204 | 14.6 yrs | £3,002 |
| 4 kW | 3865 kWh | 2319 kWh | 1546 kWh | £592 | £155 | £747 | £10,238 | 13.7 yrs | £4,702 |
| 5 kW | 4831 kWh | 2898 kWh | 1932 kWh | £741 | £193 | £934 | £12,273 | 13.1 yrs | £6,403 |
| 6 kW | 5797 kWh | 3478 kWh | 2319 kWh | £889 | £232 | £1,121 | £14,307 | 12.8 yrs | £8,104 |
| 7 kW | 6763 kWh | 4058 kWh | 2705 kWh | £1,037 | £271 | £1,307 | £16,342 | 12.5 yrs | £9,804 |
| 8 kW | 7729 kWh | 4637 kWh | 3092 kWh | £1,185 | £309 | £1,494 | £18,376 | 12.3 yrs | £11,505 |
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: £1,009, 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 | 1932 kWh | 1353 kWh | 580 kWh | £346 | £58 | £404 | £7,569 | 18.8 yrs | £502 |
| 3 kW | 2898 kWh | 2029 kWh | 870 kWh | £518 | £87 | £605 | £9,604 | 15.9 yrs | £2,503 |
| 4 kW | 3865 kWh | 2705 kWh | 1159 kWh | £691 | £116 | £807 | £11,638 | 14.4 yrs | £4,504 |
| 5 kW | 4831 kWh | 3381 kWh | 1449 kWh | £864 | £145 | £1,009 | £13,673 | 13.6 yrs | £6,505 |
| 6 kW | 5797 kWh | 4058 kWh | 1739 kWh | £1,037 | £174 | £1,211 | £15,707 | 13.0 yrs | £8,506 |
| 7 kW | 6763 kWh | 4734 kWh | 2029 kWh | £1,210 | £203 | £1,412 | £17,742 | 12.6 yrs | £10,507 |
| 8 kW | 7729 kWh | 5410 kWh | 2319 kWh | £1,382 | £232 | £1,614 | £19,776 | 12.3 yrs | £12,508 |
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: £1,031, Upfront: £15,423, 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 | 1932 kWh | 1411 kWh | 522 kWh | £360 | £52 | £413 | £9,319 | 22.6 yrs | £-1,068 |
| 3 kW | 2898 kWh | 2116 kWh | 783 kWh | £541 | £78 | £619 | £11,354 | 18.3 yrs | £1,024 |
| 4 kW | 3865 kWh | 2821 kWh | 1043 kWh | £721 | £104 | £825 | £13,388 | 16.2 yrs | £3,115 |
| 5 kW | 4831 kWh | 3526 kWh | 1304 kWh | £901 | £130 | £1,031 | £15,423 | 15.0 yrs | £5,206 |
| 6 kW | 5797 kWh | 4232 kWh | 1565 kWh | £1,081 | £157 | £1,238 | £17,457 | 14.1 yrs | £7,297 |
| 7 kW | 6763 kWh | 4937 kWh | 1826 kWh | £1,261 | £183 | £1,444 | £19,492 | 13.5 yrs | £9,388 |
| 8 kW | 7729 kWh | 5642 kWh | 2087 kWh | £1,442 | £209 | £1,650 | £21,526 | 13.0 yrs | £11,480 |
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: £1,046, Upfront: £17,173, Break-even: 16.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1932 kWh | 1449 kWh | 483 kWh | £370 | £48 | £419 | £11,069 | 26.4 yrs | £-2,697 |
| 3 kW | 2898 kWh | 2174 kWh | 725 kWh | £555 | £72 | £628 | £13,104 | 20.9 yrs | £-546 |
| 4 kW | 3865 kWh | 2898 kWh | 966 kWh | £741 | £97 | £837 | £15,138 | 18.1 yrs | £1,605 |
| 5 kW | 4831 kWh | 3623 kWh | 1208 kWh | £926 | £121 | £1,046 | £17,173 | 16.4 yrs | £3,756 |
| 6 kW | 5797 kWh | 4348 kWh | 1449 kWh | £1,111 | £145 | £1,256 | £19,207 | 15.3 yrs | £5,908 |
| 7 kW | 6763 kWh | 5072 kWh | 1691 kWh | £1,296 | £169 | £1,465 | £21,242 | 14.5 yrs | £8,059 |
| 8 kW | 7729 kWh | 5797 kWh | 1932 kWh | £1,481 | £193 | £1,674 | £23,276 | 13.9 yrs | £10,210 |
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: £1,061, Upfront: £19,623, Break-even: 18.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1932 kWh | 1488 kWh | 444 kWh | £380 | £44 | £425 | £13,519 | 31.8 yrs | £-5,027 |
| 3 kW | 2898 kWh | 2232 kWh | 667 kWh | £570 | £67 | £637 | £15,554 | 24.4 yrs | £-2,816 |
| 4 kW | 3865 kWh | 2976 kWh | 889 kWh | £760 | £89 | £849 | £17,588 | 20.7 yrs | £-604 |
| 5 kW | 4831 kWh | 3720 kWh | 1111 kWh | £950 | £111 | £1,061 | £19,623 | 18.5 yrs | £1,607 |
| 6 kW | 5797 kWh | 4464 kWh | 1333 kWh | £1,140 | £133 | £1,274 | £21,657 | 17.0 yrs | £3,818 |
| 7 kW | 6763 kWh | 5207 kWh | 1555 kWh | £1,331 | £156 | £1,486 | £23,692 | 15.9 yrs | £6,030 |
| 8 kW | 7729 kWh | 5951 kWh | 1778 kWh | £1,521 | £178 | £1,698 | £25,726 | 15.1 yrs | £8,241 |
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.