I am trying to compare the land use efficiency (kWh / m2) between fixed tilt and single axis tracking in SAM, and I'm getting some unexpected results. When I change the tilt angle, the "Total array area projected onto ground" value does not change.
As stated in the help files, Ground Coverage Ratio (GCR) is defined as:"The ratio of the photovoltaic array area to the total ground area. For an array configured in rows of modules, the GCR is the length of the side of one row divided by the distance between the bottom of one row and the bottom of its neighboring row. An array with a low ground coverage ratio (closer to zero) has rows spaced further apart than an array with a high ground coverage ratio (closer to 1).The ground coverage ratio must be a value greater than 0.01 and less than 0.99."
SAM should be taking an overhead view of the solar array, measuring the distance between the front of a string and the back, multiplied by the width of each string multiplied by the number of strings, and then dividing that area by the area derived from measuring the distance between the front of the first string and the back of the last string multiplied by the width of the average string. Therefore, if I change the tilt angle higher with a fixed GCR, the estimated land use should go down, but it doesn't.
When I do this calculation for a single axis tracker, it should calculate GCR based on a 0 degree tilt when the array is completely flat. When I compare the same GCR for single axis tracking and a fixed tilt array with a tilt angle between 0 - 90, the estimated land use is the same. For example, a 30 degree fixed tilt array with the same system capacity (i.e. default of 100 kW) as a single axis tracking array, which should measure GCR at 0 degrees tilt, both yield the same land use. The model should not be behaving this way. It's not taking the tilt angle into effect.Please let me know if I'm misunderstanding anything, or if there's some other way to get an accurate measure of kWh / m2.
Thank you very much for your help.
