Wind resource assessment is the primary factor considered when determining a wind farm site. Accurate wind resource assessment allows wind farm developers to select sites that will supply maximum power output. The developer also gains insight into the types of turbine that should be deployed based on wind speed and turbulence. Of course, the final placement of turbines relies in part on other factors including permitting, accessibility and willing landowners. However, wind resource assessment is the most significant driver behind wind farm siting.
Onshore and offshore wind resource assessments follow the same general guidelines, with differences stemming from the techniques used to collect similar data. Using meteorological information from the National Oceanic and Atmospheric Administration (NOAA) or the National Renewable Energy Laboratory (NREL) (see Figure 1 for an example), both land-based and offshore wind farm developers choose promising locations for study further.
Once an area is selected, land-based project developers then build several local meteorological towers, radars, and lasers to study the wind speed, direction, temperature, air pressure, turbulence, humidity and more, which are tracked for at least one year.
Offshore measurements are collected using survey buoys instead of towers, and these instruments collect additional information on the water temperature, currents, wave height and more. Data is gathered for at least a year, and then this short-term information is adjusted using decades of information from nearby weather stations to reflect the long-term trends. From here, the developers can project wind resource levels for the lifetime of the wind farm (20 years or more) and optimize the turbine layout throughout the site.
Figure 1: U.S. Wind Power Resource at 100m Hub Height (source: NREL's WINDExchange)
Besides wind resource assessment, wind farm developers must consider a host of other factors. These include: proximity to appropriate transmission lines, residential homes, property lines and roads; airplane radar and flight path interference; accessibility; geological and ecological conditions; permitting; and a variety of other community-driven factors.