Wind Turbine Basics:

Wind turbines generate electricity by converting the wind's kinetic energy into electrical form.Wind turbines typically consist of a tower, three rotor blades, a drive train system, and an electrical (asynchronous) generator. Wind speeds tend to increase with increasing altitude, so the tower’s height is very tall and typically ranges from 50-100 meters.

There are two categories of commercially-used wind turbines: horizontal axis and vertical axis. The main difference between these models is the axis of rotation. A horizontal axis wind turbine looks like the modern equivalent of a windmill and its axis of rotation is perpendicular to the tower. Vertical wind turbines, on the other hand, come in many different designs that somewhat resemble egg beaters and its axis of rotation is in-line with the tower and the generator is located at the base of the tower. Because the majority of commercially-used wind turbines are horizontal axis, we will consider these types of turbines in our analyses.

There are also different classes of wind turbines that are used for different wind conditions. IEC Class 1 turbines are generally for wind speeds greater than 8 m/s, Class 2 turbines are for 7.5 m/s to 8.5 m/s, and Class 3 for winds less than 7.5 m/s. Lower class wind turbines have different tower heights, bases, and gear ratios to ensure that they can withstand the force of higher winds.

Wind Data

The National Renewable Energy Lab (NREL) has complied wind speed estimates for 6,461 sites in the Eastern half of the United States as part of the Eastern Wind Integration and Transmission Study (EWITS). These sites include 1513 on-shore sites from 34 different states and 4948 off-shore sites from 17 different states. The EWITS files contain 10-minute time series wind estimates for each site, the site's rated capacity, the power output for the turbine using different turbine classes, and the power output for the turbine class that NREL recommends for the site. It is important to note that the data do no consist of actual measurements, but are wind speed estimates based off of sophisticated mesoscale models. To learn more about the data simulation process and power conversion process, consult the NREL EWITS website or refer to our final research paper for a synthesis.

Problems With the Wind Data Files

Although the EWITS study provides a wealth of information about the wind conditions specific sites within the United States experience, the data is not well-suited to projects that need to synthesize the data across a large number of sites, much like our project. The EWITS study has one file per state per year, which totals over 19,000 files. In addition, it only contains wind speed estimates, which is not the value we wanted to use as a metric for determining the availability of natural resources. To calculate the values we needed, we would have to open over 19,000 files and then enter formulas into an Excel spreadsheet.