Wind Energy

As moving air, wind is a nondepleting source of renewable energy. Wind can be of devastating power. Storms and hurricanes are proof of strong winds having the power to uproot trees and destroy homes and other infrastructure. That wind power can be used as a source of energy has long been known to humanity. The utilization of wind energy is not a new technology; the generation of electricity from wind power took place many years ago. Electricity generation (energy conversion) from fossil fuels is largely contributing to greenhouse gas (GHG) emissions, primarily carbon dioxide (CO2), which have been identified as the main driver of global warming and climate change. Wind is a clean energy source with the potential to replace other polluting, electricitygeneration technologies.

How much energy the wind is carrying depends on several factors: the amount of wind energy flowing through a given area, or area swept by a turbine (A) during a fixed time; the time to pass the turbine (t); the wind’s velocity before the turbine (v); and its density (ρ). The wind’s kinetic energy (Ekin) is calculated using the formula: Ekin = ρ/2 A v3 t. The wind speed (v) is normally measured in meters per second (m/s) using an anemometer (wind speed meter). Practical wind power density (WPD) maps are established to provide the mean annual power available per sq. m of swept area of a turbine for different heights in watts per square meter (W/m2) and serve as a reference as to the best location to install and operate wind turbines.

Wind is produced by differences in air pressure, which are the result of the unequal heating of the Earth’s surface by the sun (which in turn heats the air above it). This unequal heating of the Earth’s surface is the result of the difference between outgoing and incoming radiation at high and low latitudes of the Earth, which rotates around a shifted axis. Heated air expands and decreases in density.

Following the second law of thermodynamics, the air then flows from areas of high pressure to areas of low pressure until the air pressure is balanced (and the entropy is maximized). The higher the pressure difference and gradient, the stronger the wind that seeks to balance the difference. Because the Earth is rotating, the angular momentum is conserved with the wind, which is shifted along a longitudinal direction resembling a circular movement (Coriolis effect). On a local scale, the geographic and topographic properties of the Earth’s surface largely influence how uniformly and consistently the wind is flowing.

Offshore and onshore winds are generated along the shores of large lakes and ocean beaches. Those winds blow very regularly as they are created by the different heat absorption and storage properties of the land and water surfaces. Likewise, mountain-valley breezes arise from the unequal heating properties of the mountain-valley topography. Surface wind speeds tend to be lower when the movement of air is obstructed by geographical features, vegetation, or buildings. Therefore, coastal and offshore sites are ideal locations for wind-turbine installations.