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 917 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: £772, Upfront: £10,173, 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 | 1834 kWh | 733 kWh | 1100 kWh | £199 | £110 | £309 | £4,069 | 13.2 yrs | £2,108 |
| 3 kW | 2751 kWh | 1100 kWh | 1650 kWh | £298 | £165 | £463 | £6,104 | 13.2 yrs | £3,162 |
| 4 kW | 3667 kWh | 1467 kWh | 2200 kWh | £398 | £220 | £618 | £8,138 | 13.2 yrs | £4,217 |
| 5 kW | 4584 kWh | 1834 kWh | 2751 kWh | £497 | £275 | £772 | £10,173 | 13.2 yrs | £5,271 |
| 6 kW | 5501 kWh | 2200 kWh | 3301 kWh | £597 | £330 | £927 | £12,207 | 13.2 yrs | £6,325 |
| 7 kW | 6418 kWh | 2567 kWh | 3851 kWh | £696 | £385 | £1,081 | £14,242 | 13.2 yrs | £7,379 |
| 8 kW | 7335 kWh | 2934 kWh | 4401 kWh | £795 | £440 | £1,235 | £16,276 | 13.2 yrs | £8,433 |
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: £929, 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 | 1834 kWh | 1100 kWh | 733 kWh | £298 | £73 | £372 | £6,169 | 16.6 yrs | £1,263 |
| 3 kW | 2751 kWh | 1650 kWh | 1100 kWh | £447 | £110 | £557 | £8,204 | 14.7 yrs | £2,945 |
| 4 kW | 3667 kWh | 2200 kWh | 1467 kWh | £597 | £147 | £743 | £10,238 | 13.8 yrs | £4,627 |
| 5 kW | 4584 kWh | 2751 kWh | 1834 kWh | £746 | £183 | £929 | £12,273 | 13.2 yrs | £6,308 |
| 6 kW | 5501 kWh | 3301 kWh | 2200 kWh | £895 | £220 | £1,115 | £14,307 | 12.8 yrs | £7,990 |
| 7 kW | 6418 kWh | 3851 kWh | 2567 kWh | £1,044 | £257 | £1,301 | £16,342 | 12.6 yrs | £9,671 |
| 8 kW | 7335 kWh | 4401 kWh | 2934 kWh | £1,193 | £293 | £1,486 | £18,376 | 12.4 yrs | £11,353 |
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: £1,007, 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 | 1834 kWh | 1284 kWh | 550 kWh | £348 | £55 | £403 | £7,569 | 18.8 yrs | £491 |
| 3 kW | 2751 kWh | 1925 kWh | 825 kWh | £522 | £83 | £604 | £9,604 | 15.9 yrs | £2,486 |
| 4 kW | 3667 kWh | 2567 kWh | 1100 kWh | £696 | £110 | £806 | £11,638 | 14.4 yrs | £4,481 |
| 5 kW | 4584 kWh | 3209 kWh | 1375 kWh | £870 | £138 | £1,007 | £13,673 | 13.6 yrs | £6,477 |
| 6 kW | 5501 kWh | 3851 kWh | 1650 kWh | £1,044 | £165 | £1,209 | £15,707 | 13.0 yrs | £8,472 |
| 7 kW | 6418 kWh | 4493 kWh | 1925 kWh | £1,218 | £193 | £1,410 | £17,742 | 12.6 yrs | £10,468 |
| 8 kW | 7335 kWh | 5134 kWh | 2200 kWh | £1,392 | £220 | £1,612 | £19,776 | 12.3 yrs | £12,463 |
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 | 1834 kWh | 1339 kWh | 495 kWh | £363 | £50 | £412 | £9,319 | 22.6 yrs | £-1,071 |
| 3 kW | 2751 kWh | 2008 kWh | 743 kWh | £544 | £74 | £619 | £11,354 | 18.4 yrs | £1,018 |
| 4 kW | 3667 kWh | 2677 kWh | 990 kWh | £726 | £99 | £825 | £13,388 | 16.2 yrs | £3,108 |
| 5 kW | 4584 kWh | 3346 kWh | 1238 kWh | £907 | £124 | £1,031 | £15,423 | 15.0 yrs | £5,197 |
| 6 kW | 5501 kWh | 4016 kWh | 1485 kWh | £1,089 | £149 | £1,237 | £17,457 | 14.1 yrs | £7,287 |
| 7 kW | 6418 kWh | 4685 kWh | 1733 kWh | £1,270 | £173 | £1,443 | £19,492 | 13.5 yrs | £9,376 |
| 8 kW | 7335 kWh | 5354 kWh | 1980 kWh | £1,452 | £198 | £1,650 | £21,526 | 13.0 yrs | £11,466 |
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: £1,047, 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 | 1834 kWh | 1375 kWh | 458 kWh | £373 | £46 | £419 | £11,069 | 26.4 yrs | £-2,696 |
| 3 kW | 2751 kWh | 2063 kWh | 688 kWh | £559 | £69 | £628 | £13,104 | 20.9 yrs | £-543 |
| 4 kW | 3667 kWh | 2751 kWh | 917 kWh | £746 | £92 | £837 | £15,138 | 18.1 yrs | £1,609 |
| 5 kW | 4584 kWh | 3438 kWh | 1146 kWh | £932 | £115 | £1,047 | £17,173 | 16.4 yrs | £3,761 |
| 6 kW | 5501 kWh | 4126 kWh | 1375 kWh | £1,118 | £138 | £1,256 | £19,207 | 15.3 yrs | £5,913 |
| 7 kW | 6418 kWh | 4813 kWh | 1604 kWh | £1,305 | £160 | £1,465 | £21,242 | 14.5 yrs | £8,066 |
| 8 kW | 7335 kWh | 5501 kWh | 1834 kWh | £1,491 | £183 | £1,675 | £23,276 | 13.9 yrs | £10,218 |
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: £1,062, 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 | 1834 kWh | 1412 kWh | 422 kWh | £383 | £42 | £425 | £13,519 | 31.8 yrs | £-5,020 |
| 3 kW | 2751 kWh | 2118 kWh | 633 kWh | £574 | £63 | £637 | £15,554 | 24.4 yrs | £-2,805 |
| 4 kW | 3667 kWh | 2824 kWh | 843 kWh | £766 | £84 | £850 | £17,588 | 20.7 yrs | £-590 |
| 5 kW | 4584 kWh | 3530 kWh | 1054 kWh | £957 | £105 | £1,062 | £19,623 | 18.5 yrs | £1,625 |
| 6 kW | 5501 kWh | 4236 kWh | 1265 kWh | £1,148 | £127 | £1,275 | £21,657 | 17.0 yrs | £3,840 |
| 7 kW | 6418 kWh | 4942 kWh | 1476 kWh | £1,340 | £148 | £1,487 | £23,692 | 15.9 yrs | £6,055 |
| 8 kW | 7335 kWh | 5648 kWh | 1687 kWh | £1,531 | £169 | £1,700 | £25,726 | 15.1 yrs | £8,270 |
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.