</h2><div><ul><li><b><tt>SurfTilt</tt></b> - a scalar or vector of surface tilt angles in decimal degrees.     If SurfTilt is a vector it must be of the same size as all other vector     inputs. SurfTilt must be &gt;=0 and &lt;=180. The tilt angle is defined as     degrees from horizontal (e.g. surface facing up = 0, surface facing     horizon = 90)</li><li><b><tt>DHI</tt></b> - a scalar or vector of diffuse horizontal irradiance in W/m^2. If DHI     is a vector it must be of the same size as all other vect