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 814 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: £685, 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 | 1628 kWh | 651 kWh | 977 kWh | £176 | £98 | £274 | £4,069 | 14.9 yrs | £1,408 |
| 3 kW | 2442 kWh | 977 kWh | 1465 kWh | £264 | £146 | £411 | £6,104 | 14.9 yrs | £2,112 |
| 4 kW | 3255 kWh | 1302 kWh | 1953 kWh | £352 | £195 | £548 | £8,138 | 14.9 yrs | £2,816 |
| 5 kW | 4069 kWh | 1628 kWh | 2442 kWh | £440 | £244 | £685 | £10,173 | 14.9 yrs | £3,519 |
| 6 kW | 4883 kWh | 1953 kWh | 2930 kWh | £529 | £293 | £822 | £12,207 | 14.9 yrs | £4,223 |
| 7 kW | 5697 kWh | 2279 kWh | 3418 kWh | £617 | £342 | £958 | £14,242 | 14.9 yrs | £4,927 |
| 8 kW | 6511 kWh | 2604 kWh | 3906 kWh | £705 | £391 | £1,095 | £16,276 | 14.9 yrs | £5,631 |
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: £823, Upfront: £12,273, 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 | 1628 kWh | 977 kWh | 651 kWh | £264 | £65 | £329 | £6,169 | 18.7 yrs | £419 |
| 3 kW | 2442 kWh | 1465 kWh | 977 kWh | £396 | £98 | £494 | £8,204 | 16.6 yrs | £1,678 |
| 4 kW | 3255 kWh | 1953 kWh | 1302 kWh | £529 | £130 | £659 | £10,238 | 15.5 yrs | £2,937 |
| 5 kW | 4069 kWh | 2442 kWh | 1628 kWh | £661 | £163 | £823 | £12,273 | 14.9 yrs | £4,196 |
| 6 kW | 4883 kWh | 2930 kWh | 1953 kWh | £793 | £195 | £988 | £14,307 | 14.5 yrs | £5,456 |
| 7 kW | 5697 kWh | 3418 kWh | 2279 kWh | £925 | £228 | £1,153 | £16,342 | 14.2 yrs | £6,715 |
| 8 kW | 6511 kWh | 3906 kWh | 2604 kWh | £1,057 | £260 | £1,318 | £18,376 | 13.9 yrs | £7,974 |
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: £893, Upfront: £13,673, Break-even: 15.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1628 kWh | 1139 kWh | 488 kWh | £308 | £49 | £357 | £7,569 | 21.2 yrs | £-426 |
| 3 kW | 2442 kWh | 1709 kWh | 732 kWh | £462 | £73 | £536 | £9,604 | 17.9 yrs | £1,111 |
| 4 kW | 3255 kWh | 2279 kWh | 977 kWh | £617 | £98 | £714 | £11,638 | 16.3 yrs | £2,648 |
| 5 kW | 4069 kWh | 2848 kWh | 1221 kWh | £771 | £122 | £893 | £13,673 | 15.3 yrs | £4,185 |
| 6 kW | 4883 kWh | 3418 kWh | 1465 kWh | £925 | £146 | £1,071 | £15,707 | 14.7 yrs | £5,722 |
| 7 kW | 5697 kWh | 3988 kWh | 1709 kWh | £1,079 | £171 | £1,250 | £17,742 | 14.2 yrs | £7,259 |
| 8 kW | 6511 kWh | 4558 kWh | 1953 kWh | £1,233 | £195 | £1,429 | £19,776 | 13.8 yrs | £8,796 |
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: £914, Upfront: £15,423, Break-even: 16.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1628 kWh | 1188 kWh | 439 kWh | £322 | £44 | £365 | £9,319 | 25.5 yrs | £-2,009 |
| 3 kW | 2442 kWh | 1782 kWh | 659 kWh | £482 | £66 | £548 | £11,354 | 20.7 yrs | £-389 |
| 4 kW | 3255 kWh | 2376 kWh | 879 kWh | £643 | £88 | £731 | £13,388 | 18.3 yrs | £1,231 |
| 5 kW | 4069 kWh | 2971 kWh | 1099 kWh | £804 | £110 | £914 | £15,423 | 16.9 yrs | £2,851 |
| 6 kW | 4883 kWh | 3565 kWh | 1318 kWh | £965 | £132 | £1,096 | £17,457 | 15.9 yrs | £4,472 |
| 7 kW | 5697 kWh | 4159 kWh | 1538 kWh | £1,125 | £154 | £1,279 | £19,492 | 15.2 yrs | £6,092 |
| 8 kW | 6511 kWh | 4753 kWh | 1758 kWh | £1,286 | £176 | £1,462 | £21,526 | 14.7 yrs | £7,712 |
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: £928, Upfront: £17,173, 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 | 1628 kWh | 1221 kWh | 407 kWh | £330 | £41 | £371 | £11,069 | 29.8 yrs | £-3,648 |
| 3 kW | 2442 kWh | 1831 kWh | 610 kWh | £496 | £61 | £557 | £13,104 | 23.5 yrs | £-1,973 |
| 4 kW | 3255 kWh | 2442 kWh | 814 kWh | £661 | £81 | £742 | £15,138 | 20.4 yrs | £-297 |
| 5 kW | 4069 kWh | 3052 kWh | 1017 kWh | £826 | £102 | £928 | £17,173 | 18.5 yrs | £1,379 |
| 6 kW | 4883 kWh | 3662 kWh | 1221 kWh | £991 | £122 | £1,113 | £19,207 | 17.3 yrs | £3,055 |
| 7 kW | 5697 kWh | 4273 kWh | 1424 kWh | £1,156 | £142 | £1,299 | £21,242 | 16.4 yrs | £4,731 |
| 8 kW | 6511 kWh | 4883 kWh | 1628 kWh | £1,321 | £163 | £1,484 | £23,276 | 15.7 yrs | £6,406 |
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: £941, Upfront: £19,623, Break-even: 20.8 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1628 kWh | 1253 kWh | 374 kWh | £339 | £37 | £377 | £13,519 | 35.9 yrs | £-5,987 |
| 3 kW | 2442 kWh | 1880 kWh | 562 kWh | £509 | £56 | £565 | £15,554 | 27.5 yrs | £-4,256 |
| 4 kW | 3255 kWh | 2507 kWh | 749 kWh | £678 | £75 | £753 | £17,588 | 23.4 yrs | £-2,525 |
| 5 kW | 4069 kWh | 3133 kWh | 936 kWh | £848 | £94 | £941 | £19,623 | 20.8 yrs | £-793 |
| 6 kW | 4883 kWh | 3760 kWh | 1123 kWh | £1,017 | £112 | £1,130 | £21,657 | 19.2 yrs | £938 |
| 7 kW | 5697 kWh | 4387 kWh | 1310 kWh | £1,187 | £131 | £1,318 | £23,692 | 18.0 yrs | £2,669 |
| 8 kW | 6511 kWh | 5013 kWh | 1497 kWh | £1,357 | £150 | £1,506 | £25,726 | 17.1 yrs | £4,401 |
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.