By: Vaughn Nelson, Kenneth Starcher
Electricity from a wind farm is now amongst the cheapest forms of renewable energy and less expensive than that produced by new coal and nuclear power plants. As installations have increased, capacity has grown at an average rate of 28% per year from 1995 to 2012, and 14% per year from 2013 to 2017.
The numbers for wind power to date and for the future are astounding. Capacity is expected to reach 600 GW in 2019 and grow to around 1,000 GW by 2030 to meet the goals for wind power set by China, Europe, and the United States.
Siting a Wind Turbine
The crucial factor in siting a wind farm (also called wind park or wind plant) is the annual energy production and how the value of the energy produced compares to other sources of energy. Using long-term is data therefore critical. Data should be collected at a potential site for 2–3 years, after which other questions arise:
- What is the long-term annual variability?
- How well can we predict the renewable energy production?
Data on Wind Power
To determine whether historical data from a site is adequate to describe long-term wind resources at another site, a rigorous analysis should be done. The annual hourly linear correlation coefficient should be at least 0.90 between the reference site and off-site data. Wind shear must also be factored in if the heights are different at the two locations. If the two sites do not exhibit similar wind speed and direction trends and lack similar topographic exposures, they will probably not have sufficient correlation value.
These wind power stations should continue to collect data even after a wind farm is installed. The data improves siting of a wind farm and also provides reference sites for delineating wind resources for single or distributed wind turbine in the region.
Renewable Energy Production
The number of met stations and duration of data collection to predict the energy production for a wind farm vary depending on the terrain and the availability of long-term base data in the vicinity. In general, numerical models of wind flow will predict wind speeds to within 5% for relatively flat terrain and 10% for complex terrain, which means an error in energy of 15–30%. A wind measurement program is therefore imperative before a wind farm is installed. However, if a number of wind farms are already in the region, one year of data collection may suffice.
For complex terrain, one met station per three to five wind turbines may be needed. For more homogeneous terrain, a primary tall met station and one to four smaller met stations may suffice.
The money spent on micrositing (siting of wind turbines over an area the size of a wind farm, about 5–20 km2) is a small fraction of project cost, but the value of the information gained is critical for estimating energy production accurately. Many problems with low energy production are the results of poor siting.