Solar Engineering of Thermal Processes, 4th Edition

2.21 Effects of Receiving Surface Orientation on

The methods outlined in the previous sections for estimating average radiation on surfaces of various orientations can be used to show the effects of slope and azimuth angle on total energy received on a surface on a monthly, seasonal, or annual basis. (Optimization of collector orientation for any solar process that meets seasonally varying energy demands, such as space heating, must ultimately be done taking into account the time dependence of these demands. The surface orientation leading to maximum output of a solar energy system may be quite different from the orientation leading to maximum incident energy.)

To illustrate the effects of the receiving surface slope on monthly average daily radiation, the methods of Section 2.19 have been used to estimate for surfaces of several slopes for values of °, °, and ground reflectance 0.2. Here, is a function of , which in turn is a function of the average clearness index . The illustration ...