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 1019 kWh per year on a south-facing roof. We value self-used electricity at 26.9p 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: £854, Upfront: £10,173, Break-even: 11.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2037 kWh | 815 kWh | 1222 kWh | £219 | £122 | £342 | £4,069 | 11.9 yrs | £2,764 |
| 3 kW | 3056 kWh | 1222 kWh | 1834 kWh | £329 | £183 | £512 | £6,104 | 11.9 yrs | £4,146 |
| 4 kW | 4075 kWh | 1630 kWh | 2445 kWh | £439 | £244 | £683 | £8,138 | 11.9 yrs | £5,527 |
| 5 kW | 5094 kWh | 2037 kWh | 3056 kWh | £548 | £306 | £854 | £10,173 | 11.9 yrs | £6,909 |
| 6 kW | 6112 kWh | 2445 kWh | 3667 kWh | £658 | £367 | £1,025 | £12,207 | 11.9 yrs | £8,291 |
| 7 kW | 7131 kWh | 2852 kWh | 4279 kWh | £768 | £428 | £1,196 | £14,242 | 11.9 yrs | £9,673 |
| 8 kW | 8150 kWh | 3260 kWh | 4890 kWh | £878 | £489 | £1,367 | £16,276 | 11.9 yrs | £11,055 |
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: £1,026, Upfront: £12,273, Break-even: 12.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2037 kWh | 1222 kWh | 815 kWh | £329 | £81 | £411 | £6,169 | 15.0 yrs | £2,043 |
| 3 kW | 3056 kWh | 1834 kWh | 1222 kWh | £494 | £122 | £616 | £8,204 | 13.3 yrs | £4,114 |
| 4 kW | 4075 kWh | 2445 kWh | 1630 kWh | £658 | £163 | £821 | £10,238 | 12.5 yrs | £6,185 |
| 5 kW | 5094 kWh | 3056 kWh | 2037 kWh | £823 | £204 | £1,026 | £12,273 | 12.0 yrs | £8,256 |
| 6 kW | 6112 kWh | 3667 kWh | 2445 kWh | £987 | £244 | £1,232 | £14,307 | 11.6 yrs | £10,328 |
| 7 kW | 7131 kWh | 4279 kWh | 2852 kWh | £1,152 | £285 | £1,437 | £16,342 | 11.4 yrs | £12,399 |
| 8 kW | 8150 kWh | 4890 kWh | 3260 kWh | £1,316 | £326 | £1,642 | £18,376 | 11.2 yrs | £14,470 |
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: £1,113, Upfront: £13,673, Break-even: 12.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2037 kWh | 1426 kWh | 611 kWh | £384 | £61 | £445 | £7,569 | 17.0 yrs | £1,332 |
| 3 kW | 3056 kWh | 2139 kWh | 917 kWh | £576 | £92 | £668 | £9,604 | 14.4 yrs | £3,748 |
| 4 kW | 4075 kWh | 2852 kWh | 1222 kWh | £768 | £122 | £890 | £11,638 | 13.1 yrs | £6,164 |
| 5 kW | 5094 kWh | 3565 kWh | 1528 kWh | £960 | £153 | £1,113 | £13,673 | 12.3 yrs | £8,580 |
| 6 kW | 6112 kWh | 4279 kWh | 1834 kWh | £1,152 | £183 | £1,335 | £15,707 | 11.8 yrs | £10,996 |
| 7 kW | 7131 kWh | 4992 kWh | 2139 kWh | £1,344 | £214 | £1,558 | £17,742 | 11.4 yrs | £13,412 |
| 8 kW | 8150 kWh | 5705 kWh | 2445 kWh | £1,536 | £244 | £1,780 | £19,776 | 11.1 yrs | £15,828 |
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: £1,138, Upfront: £15,423, 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 | 2037 kWh | 1487 kWh | 550 kWh | £400 | £55 | £455 | £9,319 | 20.5 yrs | £-211 |
| 3 kW | 3056 kWh | 2231 kWh | 825 kWh | £601 | £83 | £683 | £11,354 | 16.6 yrs | £2,308 |
| 4 kW | 4075 kWh | 2975 kWh | 1100 kWh | £801 | £110 | £911 | £13,388 | 14.7 yrs | £4,828 |
| 5 kW | 5094 kWh | 3718 kWh | 1375 kWh | £1,001 | £138 | £1,138 | £15,423 | 13.5 yrs | £7,347 |
| 6 kW | 6112 kWh | 4462 kWh | 1650 kWh | £1,201 | £165 | £1,366 | £17,457 | 12.8 yrs | £9,867 |
| 7 kW | 7131 kWh | 5206 kWh | 1925 kWh | £1,401 | £193 | £1,594 | £19,492 | 12.2 yrs | £12,386 |
| 8 kW | 8150 kWh | 5949 kWh | 2200 kWh | £1,602 | £220 | £1,822 | £21,526 | 11.8 yrs | £14,906 |
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: £1,156, Upfront: £17,173, 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 | 2037 kWh | 1528 kWh | 509 kWh | £411 | £51 | £462 | £11,069 | 23.9 yrs | £-1,823 |
| 3 kW | 3056 kWh | 2292 kWh | 764 kWh | £617 | £76 | £693 | £13,104 | 18.9 yrs | £765 |
| 4 kW | 4075 kWh | 3056 kWh | 1019 kWh | £823 | £102 | £925 | £15,138 | 16.4 yrs | £3,354 |
| 5 kW | 5094 kWh | 3820 kWh | 1273 kWh | £1,028 | £127 | £1,156 | £17,173 | 14.9 yrs | £5,942 |
| 6 kW | 6112 kWh | 4584 kWh | 1528 kWh | £1,234 | £153 | £1,387 | £19,207 | 13.8 yrs | £8,530 |
| 7 kW | 7131 kWh | 5348 kWh | 1783 kWh | £1,440 | £178 | £1,618 | £21,242 | 13.1 yrs | £11,119 |
| 8 kW | 8150 kWh | 6112 kWh | 2037 kWh | £1,645 | £204 | £1,849 | £23,276 | 12.6 yrs | £13,707 |
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: £1,173, Upfront: £19,623, Break-even: 16.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 2037 kWh | 1569 kWh | 469 kWh | £422 | £47 | £469 | £13,519 | 28.8 yrs | £-4,135 |
| 3 kW | 3056 kWh | 2353 kWh | 703 kWh | £633 | £70 | £704 | £15,554 | 22.1 yrs | £-1,478 |
| 4 kW | 4075 kWh | 3138 kWh | 937 kWh | £845 | £94 | £938 | £17,588 | 18.7 yrs | £1,179 |
| 5 kW | 5094 kWh | 3922 kWh | 1172 kWh | £1,056 | £117 | £1,173 | £19,623 | 16.7 yrs | £3,837 |
| 6 kW | 6112 kWh | 4706 kWh | 1406 kWh | £1,267 | £141 | £1,408 | £21,657 | 15.4 yrs | £6,494 |
| 7 kW | 7131 kWh | 5491 kWh | 1640 kWh | £1,478 | £164 | £1,642 | £23,692 | 14.4 yrs | £9,151 |
| 8 kW | 8150 kWh | 6275 kWh | 1874 kWh | £1,689 | £187 | £1,877 | £25,726 | 13.7 yrs | £11,809 |
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.