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Calculating the wind energy input to a system using a spatially explicit method that considers atmospheric stability
Citation:
Campbell, Dan AND Mike Charpentier. Calculating the wind energy input to a system using a spatially explicit method that considers atmospheric stability. Emergy Synthesis 10. The 10th Biennial Emergy Research Conference, Gainesville, FL, January 24 - 27, 2018.
Impact/Purpose:
The purpose of this research was to develop a method for considering atmospheric stability in the calculation of the wind energy absorbed by landscapes. Specifically, this method will result in improved assessments of the wind energy input to a system and is of particular benefit to those scientists performing emergy assessments. This evaluation will also help us determine the relative error that might be incurred by assuming neutral stability, as has often been done in the past..
Description:
Atmospheric stability has a major effect in determining the wind energy doing work in the atmospheric boundary layer (ABL); however, it is seldom considered in determining this value in emergy analyses. One reason that atmospheric stability is not usually considered is that a suitable method for making this determination is not readily available. Another difficulty is that determining the stability of the atmosphere requires data on the vertical profiles of wind speed and potential temperature that are not often available at the times and places needed to make these calculations. The problem of estimating atmospheric stability can be simplified by using the Pasquill-Gifford method of defining stability categories. This method requires data on wind speed at a known height, an estimate of the solar heating regime and an estimate of the quantity of cloud cover. In this study we used the Pasquill-Gifford method of determining atmospheric stability to develop a method to calculate the wind energy absorbed in the boundary layer under stable, neutral and unstable atmospheric conditions. Atmospheric stability was calculated using data from the National Aeronautics and Space Administration global weather dataset, which reports all of the necessary variables as 22-year or 10-year averages for 1 degree grids of latitude and longitude. We combined estimates of the time that the atmosphere was in stable, unstable, or neutral conditions and the average wind velocity at a height of 50 m obtained from the NASA data with landscape roughness elements, z0’s, determined for each land use land cover (LU/LC) type in the National Land Cover Database. These data were substituted into the equations governing the wind profile under stable, unstable and neutral conditions, which were then integrated over the average height of the ABL for the given stability conditions to estimate the wind energy doing work on the surface for each LU/LC type. These estimates were applied to the landscapes of the States of Illinois, Indiana, and to the Chicago Metropolitan Areas including the 7 counties of the Chicago Metropolitan Agency for Planning (CMAP), the 14 county (2007) and the 19 county (2012) Chicago Metropolitan Statistical Areas defined by the U.S. Census Bureau to determine the wind energy doing work on the systems within these spatial boundaries.