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 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 | 1833 kWh | 733 kWh | 1100 kWh | £199 | £110 | £309 | £4,069 | 13.2 yrs | £2,107 |
| 3 kW | 2750 kWh | 1100 kWh | 1650 kWh | £298 | £165 | £463 | £6,104 | 13.2 yrs | £3,161 |
| 4 kW | 3667 kWh | 1467 kWh | 2200 kWh | £398 | £220 | £618 | £8,138 | 13.2 yrs | £4,215 |
| 5 kW | 4584 kWh | 1833 kWh | 2750 kWh | £497 | £275 | £772 | £10,173 | 13.2 yrs | £5,269 |
| 6 kW | 5500 kWh | 2200 kWh | 3300 kWh | £596 | £330 | £926 | £12,207 | 13.2 yrs | £6,322 |
| 7 kW | 6417 kWh | 2567 kWh | 3850 kWh | £696 | £385 | £1,081 | £14,242 | 13.2 yrs | £7,376 |
| 8 kW | 7334 kWh | 2933 kWh | 4400 kWh | £795 | £440 | £1,235 | £16,276 | 13.2 yrs | £8,430 |
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 | 1833 kWh | 1100 kWh | 733 kWh | £298 | £73 | £372 | £6,169 | 16.6 yrs | £1,262 |
| 3 kW | 2750 kWh | 1650 kWh | 1100 kWh | £447 | £110 | £557 | £8,204 | 14.7 yrs | £2,943 |
| 4 kW | 3667 kWh | 2200 kWh | 1467 kWh | £596 | £147 | £743 | £10,238 | 13.8 yrs | £4,624 |
| 5 kW | 4584 kWh | 2750 kWh | 1833 kWh | £746 | £183 | £929 | £12,273 | 13.2 yrs | £6,305 |
| 6 kW | 5500 kWh | 3300 kWh | 2200 kWh | £895 | £220 | £1,115 | £14,307 | 12.8 yrs | £7,987 |
| 7 kW | 6417 kWh | 3850 kWh | 2567 kWh | £1,044 | £257 | £1,300 | £16,342 | 12.6 yrs | £9,668 |
| 8 kW | 7334 kWh | 4400 kWh | 2933 kWh | £1,193 | £293 | £1,486 | £18,376 | 12.4 yrs | £11,349 |
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 | 1833 kWh | 1283 kWh | 550 kWh | £348 | £55 | £403 | £7,569 | 18.8 yrs | £490 |
| 3 kW | 2750 kWh | 1925 kWh | 825 kWh | £522 | £83 | £604 | £9,604 | 15.9 yrs | £2,484 |
| 4 kW | 3667 kWh | 2567 kWh | 1100 kWh | £696 | £110 | £806 | £11,638 | 14.4 yrs | £4,479 |
| 5 kW | 4584 kWh | 3208 kWh | 1375 kWh | £870 | £138 | £1,007 | £13,673 | 13.6 yrs | £6,474 |
| 6 kW | 5500 kWh | 3850 kWh | 1650 kWh | £1,044 | £165 | £1,209 | £15,707 | 13.0 yrs | £8,469 |
| 7 kW | 6417 kWh | 4492 kWh | 1925 kWh | £1,218 | £193 | £1,410 | £17,742 | 12.6 yrs | £10,464 |
| 8 kW | 7334 kWh | 5134 kWh | 2200 kWh | £1,392 | £220 | £1,612 | £19,776 | 12.3 yrs | £12,458 |
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 | 1833 kWh | 1338 kWh | 495 kWh | £363 | £50 | £412 | £9,319 | 22.6 yrs | £-1,072 |
| 3 kW | 2750 kWh | 2008 kWh | 743 kWh | £544 | £74 | £619 | £11,354 | 18.4 yrs | £1,017 |
| 4 kW | 3667 kWh | 2677 kWh | 990 kWh | £726 | £99 | £825 | £13,388 | 16.2 yrs | £3,106 |
| 5 kW | 4584 kWh | 3346 kWh | 1238 kWh | £907 | £124 | £1,031 | £15,423 | 15.0 yrs | £5,195 |
| 6 kW | 5500 kWh | 4015 kWh | 1485 kWh | £1,089 | £149 | £1,237 | £17,457 | 14.1 yrs | £7,283 |
| 7 kW | 6417 kWh | 4684 kWh | 1733 kWh | £1,270 | £173 | £1,443 | £19,492 | 13.5 yrs | £9,372 |
| 8 kW | 7334 kWh | 5354 kWh | 1980 kWh | £1,451 | £198 | £1,649 | £21,526 | 13.1 yrs | £11,461 |
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 | 1833 kWh | 1375 kWh | 458 kWh | £373 | £46 | £419 | £11,069 | 26.4 yrs | £-2,697 |
| 3 kW | 2750 kWh | 2063 kWh | 688 kWh | £559 | £69 | £628 | £13,104 | 20.9 yrs | £-545 |
| 4 kW | 3667 kWh | 2750 kWh | 917 kWh | £746 | £92 | £837 | £15,138 | 18.1 yrs | £1,607 |
| 5 kW | 4584 kWh | 3438 kWh | 1146 kWh | £932 | £115 | £1,047 | £17,173 | 16.4 yrs | £3,758 |
| 6 kW | 5500 kWh | 4125 kWh | 1375 kWh | £1,118 | £138 | £1,256 | £19,207 | 15.3 yrs | £5,910 |
| 7 kW | 6417 kWh | 4813 kWh | 1604 kWh | £1,305 | £160 | £1,465 | £21,242 | 14.5 yrs | £8,062 |
| 8 kW | 7334 kWh | 5500 kWh | 1833 kWh | £1,491 | £183 | £1,674 | £23,276 | 13.9 yrs | £10,213 |
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 | 1833 kWh | 1412 kWh | 422 kWh | £383 | £42 | £425 | £13,519 | 31.8 yrs | £-5,021 |
| 3 kW | 2750 kWh | 2118 kWh | 633 kWh | £574 | £63 | £637 | £15,554 | 24.4 yrs | £-2,807 |
| 4 kW | 3667 kWh | 2823 kWh | 843 kWh | £765 | £84 | £850 | £17,588 | 20.7 yrs | £-592 |
| 5 kW | 4584 kWh | 3529 kWh | 1054 kWh | £957 | £105 | £1,062 | £19,623 | 18.5 yrs | £1,622 |
| 6 kW | 5500 kWh | 4235 kWh | 1265 kWh | £1,148 | £127 | £1,275 | £21,657 | 17.0 yrs | £3,836 |
| 7 kW | 6417 kWh | 4941 kWh | 1476 kWh | £1,340 | £148 | £1,487 | £23,692 | 15.9 yrs | £6,051 |
| 8 kW | 7334 kWh | 5647 kWh | 1687 kWh | £1,531 | £169 | £1,700 | £25,726 | 15.1 yrs | £8,265 |
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.