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 941 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £761, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 753 kWh | 1129 kWh | £191 | £113 | £304 | £4,069 | 13.4 yrs | £2,019 |
| 3 kW | 2823 kWh | 1129 kWh | 1694 kWh | £287 | £169 | £457 | £6,104 | 13.4 yrs | £3,028 |
| 4 kW | 3764 kWh | 1506 kWh | 2259 kWh | £383 | £226 | £609 | £8,138 | 13.4 yrs | £4,038 |
| 5 kW | 4706 kWh | 1882 kWh | 2823 kWh | £479 | £282 | £761 | £10,173 | 13.4 yrs | £5,047 |
| 6 kW | 5647 kWh | 2259 kWh | 3388 kWh | £574 | £339 | £913 | £12,207 | 13.4 yrs | £6,056 |
| 7 kW | 6588 kWh | 2635 kWh | 3953 kWh | £670 | £395 | £1,065 | £14,242 | 13.4 yrs | £7,066 |
| 8 kW | 7529 kWh | 3012 kWh | 4517 kWh | £766 | £452 | £1,218 | £16,276 | 13.4 yrs | £8,075 |
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: £906, Upfront: £12,273, Break-even: 13.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 1129 kWh | 753 kWh | £287 | £75 | £362 | £6,169 | 17.0 yrs | £1,080 |
| 3 kW | 2823 kWh | 1694 kWh | 1129 kWh | £431 | £113 | £544 | £8,204 | 15.1 yrs | £2,671 |
| 4 kW | 3764 kWh | 2259 kWh | 1506 kWh | £574 | £151 | £725 | £10,238 | 14.1 yrs | £4,261 |
| 5 kW | 4706 kWh | 2823 kWh | 1882 kWh | £718 | £188 | £906 | £12,273 | 13.5 yrs | £5,851 |
| 6 kW | 5647 kWh | 3388 kWh | 2259 kWh | £862 | £226 | £1,087 | £14,307 | 13.2 yrs | £7,441 |
| 7 kW | 6588 kWh | 3953 kWh | 2635 kWh | £1,005 | £264 | £1,269 | £16,342 | 12.9 yrs | £9,032 |
| 8 kW | 7529 kWh | 4517 kWh | 3012 kWh | £1,149 | £301 | £1,450 | £18,376 | 12.7 yrs | £10,622 |
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: £979, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 1318 kWh | 565 kWh | £335 | £56 | £392 | £7,569 | 19.3 yrs | £261 |
| 3 kW | 2823 kWh | 1976 kWh | 847 kWh | £503 | £85 | £587 | £9,604 | 16.4 yrs | £2,142 |
| 4 kW | 3764 kWh | 2635 kWh | 1129 kWh | £670 | £113 | £783 | £11,638 | 14.9 yrs | £4,023 |
| 5 kW | 4706 kWh | 3294 kWh | 1412 kWh | £838 | £141 | £979 | £13,673 | 14.0 yrs | £5,903 |
| 6 kW | 5647 kWh | 3953 kWh | 1694 kWh | £1,005 | £169 | £1,175 | £15,707 | 13.4 yrs | £7,784 |
| 7 kW | 6588 kWh | 4611 kWh | 1976 kWh | £1,173 | £198 | £1,370 | £17,742 | 12.9 yrs | £9,665 |
| 8 kW | 7529 kWh | 5270 kWh | 2259 kWh | £1,340 | £226 | £1,566 | £19,776 | 12.6 yrs | £11,545 |
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: £1,001, Upfront: £15,423, Break-even: 15.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 1374 kWh | 508 kWh | £349 | £51 | £400 | £9,319 | 23.3 yrs | £-1,314 |
| 3 kW | 2823 kWh | 2061 kWh | 762 kWh | £524 | £76 | £600 | £11,354 | 18.9 yrs | £653 |
| 4 kW | 3764 kWh | 2748 kWh | 1016 kWh | £699 | £102 | £800 | £13,388 | 16.7 yrs | £2,621 |
| 5 kW | 4706 kWh | 3435 kWh | 1270 kWh | £874 | £127 | £1,001 | £15,423 | 15.4 yrs | £4,589 |
| 6 kW | 5647 kWh | 4122 kWh | 1525 kWh | £1,048 | £152 | £1,201 | £17,457 | 14.5 yrs | £6,557 |
| 7 kW | 6588 kWh | 4809 kWh | 1779 kWh | £1,223 | £178 | £1,401 | £19,492 | 13.9 yrs | £8,524 |
| 8 kW | 7529 kWh | 5496 kWh | 2033 kWh | £1,398 | £203 | £1,601 | £21,526 | 13.4 yrs | £10,492 |
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: £1,015, Upfront: £17,173, 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 | 1882 kWh | 1412 kWh | 471 kWh | £359 | £47 | £406 | £11,069 | 27.3 yrs | £-2,948 |
| 3 kW | 2823 kWh | 2117 kWh | 706 kWh | £538 | £71 | £609 | £13,104 | 21.5 yrs | £-922 |
| 4 kW | 3764 kWh | 2823 kWh | 941 kWh | £718 | £94 | £812 | £15,138 | 18.6 yrs | £1,103 |
| 5 kW | 4706 kWh | 3529 kWh | 1176 kWh | £897 | £118 | £1,015 | £17,173 | 16.9 yrs | £3,129 |
| 6 kW | 5647 kWh | 4235 kWh | 1412 kWh | £1,077 | £141 | £1,218 | £19,207 | 15.8 yrs | £5,155 |
| 7 kW | 6588 kWh | 4941 kWh | 1647 kWh | £1,256 | £165 | £1,421 | £21,242 | 14.9 yrs | £7,181 |
| 8 kW | 7529 kWh | 5647 kWh | 1882 kWh | £1,436 | £188 | £1,624 | £23,276 | 14.3 yrs | £9,207 |
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: £1,030, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1882 kWh | 1449 kWh | 433 kWh | £369 | £43 | £412 | £13,519 | 32.8 yrs | £-5,282 |
| 3 kW | 2823 kWh | 2174 kWh | 649 kWh | £553 | £65 | £618 | £15,554 | 25.2 yrs | £-3,198 |
| 4 kW | 3764 kWh | 2899 kWh | 866 kWh | £737 | £87 | £824 | £17,588 | 21.4 yrs | £-1,114 |
| 5 kW | 4706 kWh | 3623 kWh | 1082 kWh | £921 | £108 | £1,030 | £19,623 | 19.1 yrs | £970 |
| 6 kW | 5647 kWh | 4348 kWh | 1299 kWh | £1,106 | £130 | £1,236 | £21,657 | 17.5 yrs | £3,054 |
| 7 kW | 6588 kWh | 5073 kWh | 1515 kWh | £1,290 | £152 | £1,441 | £23,692 | 16.4 yrs | £5,138 |
| 8 kW | 7529 kWh | 5797 kWh | 1732 kWh | £1,474 | £173 | £1,647 | £25,726 | 15.6 yrs | £7,222 |
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.