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 792 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: £667, Upfront: £10,173, 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 | 1584 kWh | 634 kWh | 950 kWh | £172 | £95 | £267 | £4,069 | 15.3 yrs | £1,267 |
| 3 kW | 2376 kWh | 950 kWh | 1426 kWh | £258 | £143 | £400 | £6,104 | 15.3 yrs | £1,901 |
| 4 kW | 3168 kWh | 1267 kWh | 1901 kWh | £344 | £190 | £534 | £8,138 | 15.3 yrs | £2,534 |
| 5 kW | 3960 kWh | 1584 kWh | 2376 kWh | £429 | £238 | £667 | £10,173 | 15.3 yrs | £3,168 |
| 6 kW | 4752 kWh | 1901 kWh | 2851 kWh | £515 | £285 | £800 | £12,207 | 15.3 yrs | £3,802 |
| 7 kW | 5544 kWh | 2218 kWh | 3326 kWh | £601 | £333 | £934 | £14,242 | 15.3 yrs | £4,435 |
| 8 kW | 6336 kWh | 2534 kWh | 3802 kWh | £687 | £380 | £1,067 | £16,276 | 15.3 yrs | £5,069 |
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: £803, Upfront: £12,273, 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 | 1584 kWh | 950 kWh | 634 kWh | £258 | £63 | £321 | £6,169 | 19.2 yrs | £251 |
| 3 kW | 2376 kWh | 1426 kWh | 950 kWh | £386 | £95 | £482 | £8,204 | 17.0 yrs | £1,427 |
| 4 kW | 3168 kWh | 1901 kWh | 1267 kWh | £515 | £127 | £642 | £10,238 | 15.9 yrs | £2,603 |
| 5 kW | 3960 kWh | 2376 kWh | 1584 kWh | £644 | £158 | £803 | £12,273 | 15.3 yrs | £3,778 |
| 6 kW | 4752 kWh | 2851 kWh | 1901 kWh | £773 | £190 | £963 | £14,307 | 14.9 yrs | £4,954 |
| 7 kW | 5544 kWh | 3326 kWh | 2218 kWh | £902 | £222 | £1,124 | £16,342 | 14.5 yrs | £6,130 |
| 8 kW | 6336 kWh | 3802 kWh | 2534 kWh | £1,031 | £253 | £1,284 | £18,376 | 14.3 yrs | £7,305 |
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: £870, Upfront: £13,673, Break-even: 15.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1584 kWh | 1109 kWh | 475 kWh | £301 | £48 | £348 | £7,569 | 21.7 yrs | £-607 |
| 3 kW | 2376 kWh | 1663 kWh | 713 kWh | £451 | £71 | £522 | £9,604 | 18.4 yrs | £840 |
| 4 kW | 3168 kWh | 2218 kWh | 950 kWh | £601 | £95 | £696 | £11,638 | 16.7 yrs | £2,287 |
| 5 kW | 3960 kWh | 2772 kWh | 1188 kWh | £751 | £119 | £870 | £13,673 | 15.7 yrs | £3,733 |
| 6 kW | 4752 kWh | 3326 kWh | 1426 kWh | £902 | £143 | £1,044 | £15,707 | 15.0 yrs | £5,180 |
| 7 kW | 5544 kWh | 3881 kWh | 1663 kWh | £1,052 | £166 | £1,218 | £17,742 | 14.6 yrs | £6,627 |
| 8 kW | 6336 kWh | 4435 kWh | 1901 kWh | £1,202 | £190 | £1,392 | £19,776 | 14.2 yrs | £8,074 |
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: £891, Upfront: £15,423, Break-even: 17.3 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1584 kWh | 1156 kWh | 428 kWh | £313 | £43 | £356 | £9,319 | 26.2 yrs | £-2,194 |
| 3 kW | 2376 kWh | 1735 kWh | 642 kWh | £470 | £64 | £534 | £11,354 | 21.2 yrs | £-666 |
| 4 kW | 3168 kWh | 2313 kWh | 855 kWh | £627 | £86 | £713 | £13,388 | 18.8 yrs | £862 |
| 5 kW | 3960 kWh | 2891 kWh | 1069 kWh | £784 | £107 | £891 | £15,423 | 17.3 yrs | £2,390 |
| 6 kW | 4752 kWh | 3469 kWh | 1283 kWh | £940 | £128 | £1,069 | £17,457 | 16.3 yrs | £3,918 |
| 7 kW | 5544 kWh | 4047 kWh | 1497 kWh | £1,097 | £150 | £1,247 | £19,492 | 15.6 yrs | £5,446 |
| 8 kW | 6336 kWh | 4625 kWh | 1711 kWh | £1,254 | £171 | £1,425 | £21,526 | 15.1 yrs | £6,974 |
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: £904, Upfront: £17,173, Break-even: 19.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1584 kWh | 1188 kWh | 396 kWh | £322 | £40 | £362 | £11,069 | 30.6 yrs | £-3,836 |
| 3 kW | 2376 kWh | 1782 kWh | 594 kWh | £483 | £59 | £543 | £13,104 | 24.2 yrs | £-2,253 |
| 4 kW | 3168 kWh | 2376 kWh | 792 kWh | £644 | £79 | £723 | £15,138 | 20.9 yrs | £-671 |
| 5 kW | 3960 kWh | 2970 kWh | 990 kWh | £805 | £99 | £904 | £17,173 | 19.0 yrs | £911 |
| 6 kW | 4752 kWh | 3564 kWh | 1188 kWh | £966 | £119 | £1,085 | £19,207 | 17.7 yrs | £2,493 |
| 7 kW | 5544 kWh | 4158 kWh | 1386 kWh | £1,127 | £139 | £1,266 | £21,242 | 16.8 yrs | £4,075 |
| 8 kW | 6336 kWh | 4752 kWh | 1584 kWh | £1,288 | £158 | £1,447 | £23,276 | 16.1 yrs | £5,658 |
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: £918, Upfront: £19,623, Break-even: 21.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1584 kWh | 1220 kWh | 364 kWh | £331 | £36 | £367 | £13,519 | 36.8 yrs | £-6,177 |
| 3 kW | 2376 kWh | 1830 kWh | 546 kWh | £496 | £55 | £551 | £15,554 | 28.2 yrs | £-4,541 |
| 4 kW | 3168 kWh | 2439 kWh | 729 kWh | £661 | £73 | £734 | £17,588 | 24.0 yrs | £-2,904 |
| 5 kW | 3960 kWh | 3049 kWh | 911 kWh | £827 | £91 | £918 | £19,623 | 21.4 yrs | £-1,268 |
| 6 kW | 4752 kWh | 3659 kWh | 1093 kWh | £992 | £109 | £1,101 | £21,657 | 19.7 yrs | £368 |
| 7 kW | 5544 kWh | 4269 kWh | 1275 kWh | £1,157 | £128 | £1,285 | £23,692 | 18.4 yrs | £2,005 |
| 8 kW | 6336 kWh | 4879 kWh | 1457 kWh | £1,323 | £146 | £1,468 | £25,726 | 17.5 yrs | £3,641 |
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.