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 938 kWh per year on a south-facing roof. We value self-used electricity at 25.4p 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: £758, Upfront: £10,173, Break-even: 13.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1876 kWh | 750 kWh | 1126 kWh | £191 | £113 | £303 | £4,069 | 13.4 yrs | £1,999 |
| 3 kW | 2814 kWh | 1126 kWh | 1688 kWh | £286 | £169 | £455 | £6,104 | 13.4 yrs | £2,998 |
| 4 kW | 3752 kWh | 1501 kWh | 2251 kWh | £382 | £225 | £607 | £8,138 | 13.4 yrs | £3,997 |
| 5 kW | 4690 kWh | 1876 kWh | 2814 kWh | £477 | £281 | £758 | £10,173 | 13.4 yrs | £4,997 |
| 6 kW | 5628 kWh | 2251 kWh | 3377 kWh | £572 | £338 | £910 | £12,207 | 13.4 yrs | £5,996 |
| 7 kW | 6566 kWh | 2626 kWh | 3940 kWh | £668 | £394 | £1,062 | £14,242 | 13.4 yrs | £6,996 |
| 8 kW | 7504 kWh | 3002 kWh | 4502 kWh | £763 | £450 | £1,214 | £16,276 | 13.4 yrs | £7,995 |
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: £903, Upfront: £12,273, 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 | 1876 kWh | 1126 kWh | 750 kWh | £286 | £75 | £361 | £6,169 | 17.1 yrs | £1,057 |
| 3 kW | 2814 kWh | 1688 kWh | 1126 kWh | £429 | £113 | £542 | £8,204 | 15.1 yrs | £2,635 |
| 4 kW | 3752 kWh | 2251 kWh | 1501 kWh | £572 | £150 | £723 | £10,238 | 14.2 yrs | £4,213 |
| 5 kW | 4690 kWh | 2814 kWh | 1876 kWh | £716 | £188 | £903 | £12,273 | 13.6 yrs | £5,791 |
| 6 kW | 5628 kWh | 3377 kWh | 2251 kWh | £859 | £225 | £1,084 | £14,307 | 13.2 yrs | £7,370 |
| 7 kW | 6566 kWh | 3940 kWh | 2626 kWh | £1,002 | £263 | £1,264 | £16,342 | 12.9 yrs | £8,948 |
| 8 kW | 7504 kWh | 4502 kWh | 3002 kWh | £1,145 | £300 | £1,445 | £18,376 | 12.7 yrs | £10,526 |
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: £976, Upfront: £13,673, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1876 kWh | 1313 kWh | 563 kWh | £334 | £56 | £390 | £7,569 | 19.4 yrs | £236 |
| 3 kW | 2814 kWh | 1970 kWh | 844 kWh | £501 | £84 | £585 | £9,604 | 16.4 yrs | £2,103 |
| 4 kW | 3752 kWh | 2626 kWh | 1126 kWh | £668 | £113 | £780 | £11,638 | 14.9 yrs | £3,971 |
| 5 kW | 4690 kWh | 3283 kWh | 1407 kWh | £835 | £141 | £976 | £13,673 | 14.0 yrs | £5,839 |
| 6 kW | 5628 kWh | 3940 kWh | 1688 kWh | £1,002 | £169 | £1,171 | £15,707 | 13.4 yrs | £7,707 |
| 7 kW | 6566 kWh | 4596 kWh | 1970 kWh | £1,169 | £197 | £1,366 | £17,742 | 13.0 yrs | £9,574 |
| 8 kW | 7504 kWh | 5253 kWh | 2251 kWh | £1,336 | £225 | £1,561 | £19,776 | 12.7 yrs | £11,442 |
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: £997, Upfront: £15,423, 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 | 1876 kWh | 1369 kWh | 507 kWh | £348 | £51 | £399 | £9,319 | 23.4 yrs | £-1,341 |
| 3 kW | 2814 kWh | 2054 kWh | 760 kWh | £522 | £76 | £598 | £11,354 | 19.0 yrs | £614 |
| 4 kW | 3752 kWh | 2739 kWh | 1013 kWh | £697 | £101 | £798 | £13,388 | 16.8 yrs | £2,568 |
| 5 kW | 4690 kWh | 3424 kWh | 1266 kWh | £871 | £127 | £997 | £15,423 | 15.5 yrs | £4,523 |
| 6 kW | 5628 kWh | 4108 kWh | 1520 kWh | £1,045 | £152 | £1,197 | £17,457 | 14.6 yrs | £6,478 |
| 7 kW | 6566 kWh | 4793 kWh | 1773 kWh | £1,219 | £177 | £1,396 | £19,492 | 14.0 yrs | £8,432 |
| 8 kW | 7504 kWh | 5478 kWh | 2026 kWh | £1,393 | £203 | £1,596 | £21,526 | 13.5 yrs | £10,387 |
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: £1,012, Upfront: £17,173, Break-even: 17.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1876 kWh | 1407 kWh | 469 kWh | £358 | £47 | £405 | £11,069 | 27.4 yrs | £-2,975 |
| 3 kW | 2814 kWh | 2110 kWh | 704 kWh | £537 | £70 | £607 | £13,104 | 21.6 yrs | £-963 |
| 4 kW | 3752 kWh | 2814 kWh | 938 kWh | £716 | £94 | £809 | £15,138 | 18.7 yrs | £1,050 |
| 5 kW | 4690 kWh | 3518 kWh | 1172 kWh | £895 | £117 | £1,012 | £17,173 | 17.0 yrs | £3,062 |
| 6 kW | 5628 kWh | 4221 kWh | 1407 kWh | £1,073 | £141 | £1,214 | £19,207 | 15.8 yrs | £5,075 |
| 7 kW | 6566 kWh | 4924 kWh | 1642 kWh | £1,252 | £164 | £1,416 | £21,242 | 15.0 yrs | £7,087 |
| 8 kW | 7504 kWh | 5628 kWh | 1876 kWh | £1,431 | £188 | £1,619 | £23,276 | 14.4 yrs | £9,100 |
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: £1,026, Upfront: £19,623, Break-even: 19.1 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1876 kWh | 1445 kWh | 431 kWh | £367 | £43 | £410 | £13,519 | 32.9 yrs | £-5,309 |
| 3 kW | 2814 kWh | 2167 kWh | 647 kWh | £551 | £65 | £616 | £15,554 | 25.3 yrs | £-3,239 |
| 4 kW | 3752 kWh | 2889 kWh | 863 kWh | £735 | £86 | £821 | £17,588 | 21.4 yrs | £-1,168 |
| 5 kW | 4690 kWh | 3611 kWh | 1079 kWh | £918 | £108 | £1,026 | £19,623 | 19.1 yrs | £902 |
| 6 kW | 5628 kWh | 4334 kWh | 1294 kWh | £1,102 | £129 | £1,231 | £21,657 | 17.6 yrs | £2,972 |
| 7 kW | 6566 kWh | 5056 kWh | 1510 kWh | £1,286 | £151 | £1,437 | £23,692 | 16.5 yrs | £5,043 |
| 8 kW | 7504 kWh | 5778 kWh | 1726 kWh | £1,469 | £173 | £1,642 | £25,726 | 15.7 yrs | £7,113 |
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.