In this video, we examine the characteristics of an ideal wind energy site and outline how to undertake a wind site evaluation. The characteristics of an ideal wind energy site can be divided into three broad categories, wind characteristics, site characteristics, and operating characteristics. Ideal wind site attributes include steady winds with mean speeds of greater than seven meters per second, little turbulence dense air, for instance, at sea level and cooler cold air, which is denser than warm air. Desirable site characteristics are extensive, open land, low surface roughness, low population density, and mild weather. Several operating characteristics that are important for wind energy include; easy transport accessibility, and proximity to the electric grid. Let's look at each of these in more detail. Wind energy, of course, requires wind. A careful assessment of local wind resources is essential. Wind evaluation into perspective site is called a wind measurement campaign with the objective of determining wind speed and direction, wind shear, turbulence, and roughness, air density and humidity. Data is collected with one or more meteorological met mast as shown here. Met mast ideally are at the same height as the planned wind turbines. A met mast will typically include anemometers to measure the wind speeds at different heights, a recording weather vane for wind directions, a barometer, thermometer and humidity sensors, and recorder or logger to capture data. When data is normally collected for at least one year and for as many as five to capture data over the months and seasons of several seasons or years. Data collected includes mean wind speed, variation in distribution when directions and intensity is needed to create a wind rose. When shear and turbulence data and air density, pressure and temperature information. In addition to wind resources, other location specific characteristics are important to understand. These include the terrain of the prospective site, including hills, drop-offs and micro-climates, and local soil and rock geology. Identification of the best turbine locations for exposure to the winds and to avoid turbulence. Obstacles that limit location choices such as buildings, residences, and existing roads. In-access to the pros site, including external roads leading to the site in the availability of connections to the electric grid. An important fact, not immediately apparent, is that wind turbines create their own downwind wake turbulence, as shown in the dramatic picture to the right. In particular, note the obscured turbines into downwind turbulence created by upwind turbines. Downwind wake turbulence reduces the performance of downwind turbulence, just as turbulence creates problems for the smooth functioning of an aircraft. Turbine wake turbulence requires that wind turbines be located far apart from one another. A general rule of thumb requires that wind turbines should be spaced about or at least seven rotor diameters apart from one another. As an example, turbines with rotor diameters of 100 meters should be spaced at least 700 meters from one another. That's quite a distance. Consequently, land requirements for wind farms are large, requiring substantial tracks of land to be productive. The direct land use of an individual turbine is about 0.4 hectares per megawatt of turbine capacity required for its concrete pad access roads, substations, and other infrastructure. For example, a two-megawatt turbine would need about 0.8 hectares of land, which is about one-and-a-half acres. However, the total land use per turbine is much greater since turbines must be spaced far apart. The total land required can be estimated at about 50 hectares per megawatt considering turbine spacing, terrain limitations and existing uses such as agriculture or ranching. For example, the same two-megawatt turbine above is a total of about 100 hectares or 250 acres when located on a large wind farm. That's a lot of land. Another challenge for wind farm siting is access to the site, especially as turbine sizes grow larger and larger. Increasing turbine sizes presents substantial transportation problems. Proximity to manufacturing locations is desirable. Contemporary blade links there as long as a 100 meters with larger blades soon coming. The photos to the right illustrates some of the challenges of moving large blades from their point of manufacture to a wind site. Further the volume of materials required for construction of a wind farm places substantial demands on transportation systems. For example, a relatively small 150-megawatt wind farm requires about 650 truckloads of materials, plus the use of a 140 rail cars and six ships. Finally, transportation costs are increasing at a rate of about 25 percent annually, adding to transportation challenges. Of course, when farms must connect to an electric grid to be useful. However, in many cases, excellent wind locations are far from establish electrical grids. This requires the construction of long distance high-voltage electricity transmission lines, which are expensive to construct, maintain into secure. For example, the photo to the right shows some of the turbines at a 310-megawatt Lake Turkana wind power project in Northwestern Kenya. The site is far away from existing electricity grids and requires construction of a 530 kilometer, 400 kilovolt transmission line to make connections with the Kenyan National Grid. Another challenge when citing a wind farm is the availability of specialized equipment and labor. Specialized equipment includes bespoke trucks, cranes, and rigging designed for wind turbine construction, plus skilled drivers, operators, and riggers to operate that equipment. Also needed a specialized workforce, including wind engineers, skilled wind technicians, electricians. These personnel must be physically strong for climbing, able to work at large heights, and willing to work in remote locations for extended periods of time. Summarizing, evaluating perspective wind sites has many dimensions and challenges. First, the site must be evaluated over an extended period of time to characterize wind resources, turbine locations and turbine spacing must be chosen. Land requirements must be determined. Access to the site must be evaluated and planned, as must access to the electrical grid. Finally, equipment and labor resources for construction must be located, planned, and secured. Planning in constructing a wind farm is a lengthy, extensive, and costly endeavor to be sure. In the next video, we'll extend our discussion to offshore wind, the next frontier of wind energy. We'll see you there.
