Wind speed and direction estimation for different hub height

Hello,

I am using own weather files based on MERRA-2 which provides wind speed and direction at 2, 10, 50 m and I want to simulate energy yield at different hub heights, for example, ranging from 80 to 120 m.

As per SAM help manual,

(1) for wind speed data, I need additional column(s) in my weather files to simulate hub heights higher than 85 m and using power law manually, I can add column(s) either as many as the number of different hub height or just one which is either 120 or 85 m and let SAM interpolate wind speed between 50 and 120 m. Could you recommend me the way with lower uncertainty?

(2) for wind direction data, should I also have additional column(s) with measurement height within 10 m from additional height(s) used in (1)? Could you recommend me a method to estimate wind direction at different height such as power law for wind speed?

Best regards,
Seyong

Dear Seyong,

1. I think either method would give similar results because, as described in SAM's Help system, SAM uses the wind shear coefficient on the turbine page with the Wind Power Law to calculate the wind speed at different hub heights. SAM limits the difference between the measurement height and hub height to 35 m. If you want to use 50 m wind speed data with hub heights above 85 m, then you can use the method you describe, as long as you are aware of the limitations of the Wind Power Law.

2. I am not aware of a method for estimating wind direction data from data measured at different heights.

Here are links to a couple of NREL publications on wind resource assessment:

Clifton, A. et al. (2016). Wind Plant Preconstruction Energy Estimates: Current Practice and Opportunities . NREL/TP-5000-64735.

Olsen, T. et al. (2015). Small Wind Site Assessment
Guidelines. NREL/TP-5000-63696.

Best regards,
Paul.