Method of evaluation wind flow based on conservation of momentum and variation in terrain
A method of modeling the spatial variation in wind resource at a prospective wind farm site. The method involves a simplified analysis of the Navier-Stokes equation and utilizes data from all of the met sites simultaneously to develop site-calibrated models. The model coefficients, m UW and m DW , describe the sensitivity of the wind speed to changes in the upwind and downwind terrain exposure and are defined for downhill and uphill flow. The coefficients are a function of terrain complexity and, since terrain complexity can change across an area, the estimates are performed in a stepwise fashion where a path of nodes with a gradual change in complexity is found between each pair of sites. Also, coefficients are defined for each wind direction sector and estimates are performed on a sectorwise basis. The site-calibrated models are created by cross-predicting between each pair of met sites and, through a self-learning technique, the model coefficients that yield the minimum met cross-prediction error are found.
1. A method of predicting wind speed at one or more target sites comprising the steps of:
measuring a wind speed and a direction at one or more meteorological towers;
defining a location of said one or more target sites;
calculating exposure at the one or more meteorological towers;
calculating terrain complexity;
selecting a wind flow model based on the terrain complexity wherein the wind flow model relates change in wind speed to change in exposure;
calculating exposure at said one or more target sites;
calculating a difference in exposure between the one or more meteorological towers and said one or more target sites; and
applying the wind flow model using the wind speed at the one or more meteorological towers and the difference in exposure between the one or more meteorological towers and said one or more target sites to predict a wind speed for said one or more target sites.
2. The method of claim 1 , wherein the step of selecting a wind flow model based on the terrain complexity comprises creating a log-log relationship between the terrain complexity and model coefficients.
3. The method of claim 2 , wherein the model coefficients comprise an uphill coefficient, a downhill coefficient, and a speed-up coefficient.
4. The method of claim 1 , wherein the step of calculating terrain complexity comprises creating a grid of exposure and selecting the terrain complexity as an upper percentile of exposure values for the grid of exposure.
5. The method of claim 4 , wherein the upper percentile of exposure values is a P10 value.
6. The method of claim 1 , wherein the wind flow model comprises coefficients for uphill wind flow, downhill wind flow, and speed-up of wind flow over a hill.
7. The method of claim 6 , where each of the coefficients is selected based on terrain complexity.
8. The method of claim 1 , wherein the step of calculating terrain complexity comprises calculating terrain complexity at the one or more meteorological towers and at said one or more target sites; and
further comprising the steps of:
calculating a difference in terrain complexity between the one or more meteorological towers and said one or more target sites;
comparing the difference in terrain complexity to a predetermined value; and
if the difference in terrain complexity exceeds the predetermined value, creating a path of nodes between the one or more meteorological towers and said one or more target sites and calculating a wind speed for each node in the path of nodes.
9. The method of claim 8 , wherein the path of nodes is created with gradual changes in terrain complexity and elevation along the path of nodes.
10. A method of predicting wind speed at one or more target sites comprising the steps of:
measuring a wind speed and a direction at one or more meteorological towers;
defining a location of said one or more target sites;
calculating exposure at the one or more meteorological towers;
calculating terrain complexity by creating a grid of exposure and selecting the terrain complexity as an upper percentile of exposure values for the grid of exposure;
selecting a wind flow model based on the terrain complexity wherein the wind flow model relates change in wind speed to change in exposure, the wind flow model comprising coefficients for uphill wind flow, downhill wind flow, and speed-up of wind flow over a hill;
calculating exposure at said one or more target sites;
calculating a difference in exposure between the one or more meteorological towers and said one or more target sites; and
applying the wind flow model using the wind speed at the one or more meteorological towers and the difference in exposure between the one or more meteorological towers and said one or more target sites to predict a wind speed for said one or more target sites.
11. The method of claim 10 , wherein the step of selecting a wind flow model based on the terrain complexity comprises creating a log-log relationship between the terrain complexity and model coefficients.
12. The method of claim 11 , wherein the model coefficients comprise an uphill coefficient, a downhill coefficient, and a speed-up coefficient.
13. The method of claim 10 , wherein the upper percentile of exposure values is a P10 value.
14. The method of claim 10 , where each of the coefficients is selected based on terrain complexity.
15. The method of claim 10 , wherein the step of calculating terrain complexity comprises calculating terrain complexity at the one or more meteorological towers and at said one or more target sites; and
further comprising the steps of:
calculating a difference in terrain complexity between the one or more meteorological towers and said one or more target sites;
comparing the difference in terrain complexity to a predetermined value; and
if the difference in terrain complexity exceeds said predetermined value, creating a path of nodes between the one or more meteorological towers and said one or more target sites and calculating a wind speed for each node in the path of nodes.
16. The method of claim 15 , wherein the path of nodes is created with gradual changes in terrain complexity and elevation along the path of nodes.
17. A method of predicting wind speed at one or more target sites comprising the steps of:
measuring a wind speed and a direction at one or more meteorological towers;
defining a location of said one or more target sites;
calculating exposure at the one or more meteorological towers;
calculating terrain complexity by creating a grid of exposure and selecting the terrain complexity as an upper percentile of exposure values for the grid of exposure, the upper percentile of exposure values being a P10 value;
selecting a wind flow model based on the terrain complexity wherein the wind flow model relates change in wind speed to change in exposure, the wind flow model comprising coefficients for uphill wind flow, downhill wind flow, and speed-up of wind flow over a hill, each of the coefficients is selected based on terrain complexity;
calculating exposure at said one or more target sites;
calculating a difference in exposure between the one or more meteorological towers and said one or more target sites; and
applying the wind flow model using the wind speed at the one or more meteorological towers and the difference in exposure between the one or more meteorological towers and said one or more target sites to predict a wind speed for said one or more target sites.
18. The method of claim 17 , wherein the step of selecting a wind flow model based on the terrain complexity comprises creating a log-log relationship between the terrain complexity and model coefficients; and
wherein the model coefficients comprise an uphill coefficient, a downhill coefficient, and a speed-up coefficient.
19. The method of claim 17 , wherein the step of calculating terrain complexity comprises calculating terrain complexity at the one or more meteorological towers and at said one or more target sites; and
further comprising the steps of:
calculating a difference in terrain complexity between the one or more meteorological towers and said one or more target sites;
comparing the difference in terrain complexity to a predetermined value; and
if the difference in terrain complexity exceeds said predetermined value, creating a path of nodes between the one or more meteorological towers and said one or more target sites and calculating a wind speed for each node in the path of nodes.
20. The method of claim 19 , wherein the path of nodes is created with gradual changes in terrain complexity and elevation along the path of nodes.