Drive by a multi-tower wind farm and some of the blades may not be turning. Why?

I wondered, and reached out to Katharine Kollins, President, Southeastern Wind Coalition. “Like any large machines, wind turbines require regular maintenance. The turbines are turned off while maintenance is taking place. Regular maintenance takes place during daylight hours, so it would be more common to see some turbines turned off during the day versus at night. There are also times where the wind blowing is below the cut in speed, which is the minimum wind speed required to generate electricity.”

Cut-in and cut-out speeds

The cut-in speed is typically between 6 and 9 mph. Blades start rotating to make power. More electricity is generated as the wind speed goes up until it reaches a limit, the rated speed. This is the when the turbine produces its maximum, or rated power. After that as wind speed increases, the power generated by the turbine remains constant until it eventually hits a cut-out speed and shuts down to prevent strain on the rotor. Different turbines have different cut out speeds.

The diagram below shows the power output of a turbine against steady wind speeds.

The potential for using wind as a power source varies because the amount of wind varies across the nation. Generally the wind is stronger farther north rather than closer to the tropics.

Onshore wind units were first and now offshore wind installations are likely to be developed. Installations can be placed well outside the view of seashore residents’ windows. It is a market thing, too. “Developers are investing in the East Coast because of its reliable supply of wind and proximity to populous markets.” (Source)

The Southeast has not had the amount of wind built as places that are windier. The top five states for installed wind energy are Texas, Iowa, Oklahoma, Kansas and California. The Southeastern Wind Coalition has useful economic resources about wind energy.

How Wind Turbines Work

  • Small sensors at the top of turbines measure the speed and direction of the wind. This indicates to the yaw motors which direction to point the nacelle or nose so that it is facing into the oncoming wind.
  • The kinetic energy in the wind causes the blades to rotate, which, in turn, causes a shaft to spin at a low speed.
  • This shaft is connected to a gearbox that increases the speed.
  • The second, high-speed shaft, holds the generator. The fast rotational power converts the kinetic energy into electricity.
  • A frequency converter synchronizes the electricity to the power grid where a transformer amps up the voltage before it can be used. (Source)