Self shading of sawtooth PV array on a sloped roof

1. PV Array: 18 mod., 3 rows of 6, portrait, 1.64m X 1.0m ea., 6 mod./string.

2. Orientation: array azimuth: 186 deg. (6 deg. w of s), array el.: 20 deg.

3. Array sits on a roof with orientation: azimuth 77 deg. (13 deg. n of east), roof el.:20 deg. Flat roof.

Question 1: Does self shading module in SAM assume arrays sit on a horizontal surface?

Question 2: If the answer to question 1 above is yes,is there any way to modify input so SAM will give reasonable guess as to required spacing between rows for minimum/reasonable self shading for non horizontal mounting surface ?

Question 3: If the answer to question 1 above is no, how does SAM account for mounting surface azimuth and elevation ?

The attached is not my array, but its similar to what I'm trying to explain. My latitude is 33.2 deg. n.

Thank you,

J.P.M.

Dear J.P.M.,


1. Yes. The flat-plate PV self-shading model assumes that the photovoltaic array is on a horizontal surface. In other words, the bottoms of all of the modules in the array lie in the same horizontal plane.

2. I am not aware of a way to estimate the effect of a non-horizontal mounting surface on the self-shading model.

3. SAM does not have any information about the mounting surface orientation. It only has information about the subarray tilt angle with respect to the horizontal, and its azimuth angle with respect to a line perpendicular to the equator. For subarrays with no tracking, SAM assumes that all modules in each subarray have the same orientation.

Note that I'm using the term "subarray" because it is possible to model an array that consists of subarrays with different orientations and tracking.

Best regards,
Paul.

Paul:

Not what I wanted to read, but thank you for the thorough answer. Maybe I'll see if I can do something with the geometry/profile angles, etc.

Regards,

J.P.M.