Wind Turbine Payback in San Francisco County, CA
Wind turbine payback in San Francisco County
Only just. The money comes back late in the turbine's life.
At 30 m, the height a home turbine tower usually reaches, the wind in San Francisco County, CA averages 6.53 m/s (14.6 mph). A 10 kW turbine there would make about 23,628 kWh a year, worth $7,698 at CA's 32.58¢/kWh. Against an installed cost of about $100,000, that is a payback of 13 years, and the turbine is built to last about 20.
What to do in San Francisco County
It is close enough that your own site decides it. If you have open land with no trees or buildings upwind, ask an installer to log the wind at 30 m or higher; anything above 5.4 m/s pays back in time. Per kW, solar panels would make about 1,276 kWh a year here against the turbine's 2,363, so get a solar quote first.
What would have to change
- Power already costs enough here: break-even is 21¢/kWh and CA pays 32.58¢.
- The wind clears the break-even speed of 5.4 m/s at today's price.
Against the rest of CA
San Francisco County is the 165th windiest of 3,144 US counties at turbine height; the national middle is 4.79 m/s. It is the windiest county in CA.
Month by month in San Francisco County
June is the strongest month here, at 7.90 m/s and about 2,728 kWh. November is the weakest, 5.71 m/s and 1,445 kWh, so the best month makes 1.9 times the worst. November to March brings in 39% of the year's output in San Francisco County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.00 m/s | 1,671 kWh | $544 |
| February | 6.74 m/s | 1,928 kWh | $628 |
| March | 6.84 m/s | 2,199 kWh | $716 |
| April | 7.35 m/s | 2,426 kWh | $790 |
| May | 7.69 m/s | 2,703 kWh | $881 |
| June | 7.90 m/s | 2,728 kWh | $889 |
| July | 6.33 m/s | 1,880 kWh | $613 |
| August | 5.93 m/s | 1,630 kWh | $531 |
| September | 5.80 m/s | 1,496 kWh | $487 |
| October | 5.68 m/s | 1,476 kWh | $481 |
| November | 5.71 m/s | 1,445 kWh | $471 |
| December | 6.41 m/s | 1,934 kWh | $630 |
What a taller tower would buy
Measured at 10 m the wind in San Francisco County averages 5.81 m/s; at 50 m it is 6.89 m/s. That gives a shear exponent of 0.106, typical of very open, smooth ground where height adds little. Going from 20 m to 50 m takes output from 21,575 to 26,253 kWh a year, 22% more, before counting the extra cost of the taller tower.
| Hub height | Average wind | Output | Payback |
|---|---|---|---|
| 20 m | 6.25 m/s | 21,575 kWh | 14 years |
| 30 m | 6.53 m/s | 23,605 kWh | 13 years |
| 40 m | 6.73 m/s | 25,085 kWh | 12 years |
| 50 m | 6.89 m/s | 26,253 kWh | 12 years |
Counties around San Francisco County
None of the 6 closest counties is windier than San Francisco County.
- Marin County, CA: 4.37 m/s, 8,575 kWh, payback 36 years (27 mi)
- San Mateo County, CA: 5.02 m/s, 12,670 kWh, payback 24 years (42 mi)
- Sonoma County, CA: 4.66 m/s, 10,320 kWh, payback 30 years (55 mi)
- Contra Costa County, CA: 4.85 m/s, 11,537 kWh, payback 27 years (60 mi)
- Alameda County, CA: 4.17 m/s, 7,461 kWh, payback 41 years (61 mi)
- Napa County, CA: 3.97 m/s, 6,428 kWh, payback 48 years (66 mi)
Sun versus wind in San Francisco County
San Francisco County gets 4.37 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,276 kWh a year; one kW of the turbine above makes 2,363. This is one of the rare places where a kilowatt of turbine out-produces a kilowatt of panels, by 1.9 times. Panel output assumes an 80% system performance ratio.
How this is worked out
Wind is NASA's Power climate record, the 2001-2025 average at 10 m and 50 m for the county's centre, carried to 30 m with this county's own measured wind shear and spread into hours with a Rayleigh distribution. The turbine is a generic 10 kW, 7 m rotor machine with 10% losses. Cost is $10,000 per kW installed with no tax credit, because the federal one ended in 2025. One county-centre number cannot see your hilltop or your tree line, so treat it as the starting point for a site survey, not a substitute.