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 805 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: £677, Upfront: £10,173, 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 | 1611 kWh | 644 kWh | 966 kWh | £174 | £97 | £271 | £4,069 | 15.0 yrs | £1,350 |
| 3 kW | 2416 kWh | 966 kWh | 1450 kWh | £261 | £145 | £406 | £6,104 | 15.0 yrs | £2,025 |
| 4 kW | 3221 kWh | 1288 kWh | 1933 kWh | £349 | £193 | £542 | £8,138 | 15.0 yrs | £2,700 |
| 5 kW | 4026 kWh | 1611 kWh | 2416 kWh | £436 | £242 | £677 | £10,173 | 15.0 yrs | £3,375 |
| 6 kW | 4832 kWh | 1933 kWh | 2899 kWh | £523 | £290 | £813 | £12,207 | 15.0 yrs | £4,051 |
| 7 kW | 5637 kWh | 2255 kWh | 3382 kWh | £610 | £338 | £948 | £14,242 | 15.0 yrs | £4,726 |
| 8 kW | 6442 kWh | 2577 kWh | 3865 kWh | £697 | £387 | £1,084 | £16,276 | 15.0 yrs | £5,401 |
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: £815, Upfront: £12,273, Break-even: 15.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1611 kWh | 966 kWh | 644 kWh | £261 | £64 | £326 | £6,169 | 18.9 yrs | £349 |
| 3 kW | 2416 kWh | 1450 kWh | 966 kWh | £392 | £97 | £489 | £8,204 | 16.8 yrs | £1,574 |
| 4 kW | 3221 kWh | 1933 kWh | 1288 kWh | £523 | £129 | £652 | £10,238 | 15.7 yrs | £2,798 |
| 5 kW | 4026 kWh | 2416 kWh | 1611 kWh | £654 | £161 | £815 | £12,273 | 15.1 yrs | £4,023 |
| 6 kW | 4832 kWh | 2899 kWh | 1933 kWh | £784 | £193 | £978 | £14,307 | 14.6 yrs | £5,248 |
| 7 kW | 5637 kWh | 3382 kWh | 2255 kWh | £915 | £225 | £1,141 | £16,342 | 14.3 yrs | £6,472 |
| 8 kW | 6442 kWh | 3865 kWh | 2577 kWh | £1,046 | £258 | £1,304 | £18,376 | 14.1 yrs | £7,697 |
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: £883, Upfront: £13,673, Break-even: 15.5 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1611 kWh | 1127 kWh | 483 kWh | £305 | £48 | £353 | £7,569 | 21.4 yrs | £-501 |
| 3 kW | 2416 kWh | 1691 kWh | 725 kWh | £458 | £72 | £530 | £9,604 | 18.1 yrs | £998 |
| 4 kW | 3221 kWh | 2255 kWh | 966 kWh | £610 | £97 | £707 | £11,638 | 16.5 yrs | £2,498 |
| 5 kW | 4026 kWh | 2818 kWh | 1208 kWh | £763 | £121 | £883 | £13,673 | 15.5 yrs | £3,997 |
| 6 kW | 4832 kWh | 3382 kWh | 1450 kWh | £915 | £145 | £1,060 | £15,707 | 14.8 yrs | £5,496 |
| 7 kW | 5637 kWh | 3946 kWh | 1691 kWh | £1,068 | £169 | £1,237 | £17,742 | 14.3 yrs | £6,996 |
| 8 kW | 6442 kWh | 4510 kWh | 1933 kWh | £1,220 | £193 | £1,414 | £19,776 | 14.0 yrs | £8,495 |
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: £904, Upfront: £15,423, Break-even: 17.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1611 kWh | 1176 kWh | 435 kWh | £318 | £43 | £362 | £9,319 | 25.8 yrs | £-2,086 |
| 3 kW | 2416 kWh | 1764 kWh | 652 kWh | £477 | £65 | £542 | £11,354 | 20.9 yrs | £-505 |
| 4 kW | 3221 kWh | 2351 kWh | 870 kWh | £636 | £87 | £723 | £13,388 | 18.5 yrs | £1,077 |
| 5 kW | 4026 kWh | 2939 kWh | 1087 kWh | £795 | £109 | £904 | £15,423 | 17.1 yrs | £2,659 |
| 6 kW | 4832 kWh | 3527 kWh | 1305 kWh | £954 | £130 | £1,085 | £17,457 | 16.1 yrs | £4,241 |
| 7 kW | 5637 kWh | 4115 kWh | 1522 kWh | £1,114 | £152 | £1,266 | £19,492 | 15.4 yrs | £5,823 |
| 8 kW | 6442 kWh | 4703 kWh | 1739 kWh | £1,273 | £174 | £1,447 | £21,526 | 14.9 yrs | £7,404 |
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: £918, Upfront: £17,173, Break-even: 18.7 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1611 kWh | 1208 kWh | 403 kWh | £327 | £40 | £367 | £11,069 | 30.2 yrs | £-3,726 |
| 3 kW | 2416 kWh | 1812 kWh | 604 kWh | £490 | £60 | £551 | £13,104 | 23.8 yrs | £-2,090 |
| 4 kW | 3221 kWh | 2416 kWh | 805 kWh | £654 | £81 | £734 | £15,138 | 20.6 yrs | £-453 |
| 5 kW | 4026 kWh | 3020 kWh | 1007 kWh | £817 | £101 | £918 | £17,173 | 18.7 yrs | £1,184 |
| 6 kW | 4832 kWh | 3624 kWh | 1208 kWh | £981 | £121 | £1,101 | £19,207 | 17.4 yrs | £2,821 |
| 7 kW | 5637 kWh | 4228 kWh | 1409 kWh | £1,144 | £141 | £1,285 | £21,242 | 16.5 yrs | £4,457 |
| 8 kW | 6442 kWh | 4832 kWh | 1611 kWh | £1,307 | £161 | £1,469 | £23,276 | 15.9 yrs | £6,094 |
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: £932, Upfront: £19,623, Break-even: 21.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1611 kWh | 1240 kWh | 370 kWh | £336 | £37 | £373 | £13,519 | 36.3 yrs | £-6,067 |
| 3 kW | 2416 kWh | 1860 kWh | 556 kWh | £503 | £56 | £559 | £15,554 | 27.8 yrs | £-4,375 |
| 4 kW | 3221 kWh | 2480 kWh | 741 kWh | £671 | £74 | £745 | £17,588 | 23.6 yrs | £-2,683 |
| 5 kW | 4026 kWh | 3100 kWh | 926 kWh | £839 | £93 | £932 | £19,623 | 21.1 yrs | £-991 |
| 6 kW | 4832 kWh | 3720 kWh | 1111 kWh | £1,007 | £111 | £1,118 | £21,657 | 19.4 yrs | £700 |
| 7 kW | 5637 kWh | 4340 kWh | 1297 kWh | £1,175 | £130 | £1,304 | £23,692 | 18.2 yrs | £2,392 |
| 8 kW | 6442 kWh | 4961 kWh | 1482 kWh | £1,342 | £148 | £1,490 | £25,726 | 17.3 yrs | £4,084 |
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.