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# In Generator:PVWatts, how do you know what surface the solar panels are on if you choose TiltAzimuth for Array Geometry Type?

Also, is the size of the solar array determined by the surface it's on?

I've tried changing the Surface Name input, which clearly has an effect when Geometry Type is surface, but isn't required for TiltAzimuth. Even then, though, the output doesn't seem to be determined by the size of that surface, only by its orientation. Are the orientation, shade, and rated capacity all that determine output of the panels?

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When you use the TiltAzimuth option, the irradiance calculation is detached from your model geometry. It assumes shade-free PV modules with the tilt and azimuth you specify. If you use the Surface option, the irradiance on the specified surface is used, shading included. The capacity is determined by the DC System Capacity input parameter, therefore the area of the array is not needed. See I/O reference on page 2239.

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If you choose TiltAzimuth for Array Geometry Type, the solar panels do not get associated with a surface. The tilt angle and azimuth angle are supplied directly by the user.

If you choose Surface, the tilt and azimuth are inferred from the specified surface but the size of the surface is not taken into account for capacity. The array capacity is set in the "DC System Capacity" field. For shading, it will assume the array occupies the entire surface.

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