Wind resource assessments are used to estimate a wind farm's power production during the planning process. It is important that these estimates are accurate, as they can impact financing agreements, transmission planning, and environmental targets. Here, we analyze the challenges in wind power estimation for onshore farms. Turbine wake effects are a strong determinant of farm power production. With given input wind conditions, wake losses typically cause downstream turbines to produce significantly less power than upstream turbines. These losses have been modeled extensively and are well understood under certain conditions. Most notably, validation of different model types has favored offshore farms. Models that capture the dynamics of offshore wind conditions do not necessarily perform equally as well for onshore wind farms. We analyze the capabilities of several different methods for estimating wind farm power production in 2 onshore farms with non-uniform layouts. We compare the Jensen model to a number of statistical models, to meteorological downscaling techniques, and to using no model at all. We show that the complexities of some onshore farms result in wind conditions that are not accurately modeled by the Jensen wake decay techniques and that statistical methods have some strong advantages in practice.
KEYWORDSonshore wind farms, statistical modeling, turbine wakes, wind power assessment
INTRODUCTIONWind energy is a fast-growing segment of the energy sector worldwide. As wind starts to play a larger role in our electricity systems, there is increasing interest in using it efficiently. Wind power is, for the most part, not a dispatchable form of energy; forecasts are not perfect, and an individual wind farm cannot be set to a desired production level unless the wind conditions are sufficient for that level of power. Managing a farm's variability and intermittency is still a big challenge, but recent research shows promising results in optimizing farm production. 1-4 Knowledge of the amount of power that a wind farm will produce in a given hour, day, or year will improve the way that the farm is operated and financed. Perfect knowledge of future wind power production is impossible, but recent research has made great strides in estimating these quantities. Power estimation and prediction is important for multiple applications within the timeline of a wind energy project. In the initial planning stages of a farm, one must develop accurate estimates of what the wind conditions will be once the farm is built. This typically involves the installation of meteorological towers (or met towers) for data collection. This information is used to determine the turbine layout and alignment within the farm that will best capture the available energy. Initial estimates of long-term wind conditions are used to assess the financial viability of a wind farm. Thus, the decision of farm design and resource assessment is critical, as the return on investment depends on the ability of the wind farm to generate enough en...