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250   ECONOMICS OF SOLAR POWER SYSTEMS


                array templates then can be used to establish a desirable output of dc power. Note that,
                when laying blocks of PV arrays, consideration must be given to the desirable tilt
                inclination to avoid cross shadowing. In some instances, the designer must also
                consider trading solar power output efficiency to maximize the power output produc-
                tion. As mentioned in Chapter 2, the most desirable mounting position for a PV mod-
                ule to realize maximum solar insolation is the latitude minus 10 degrees. For example,
                the optimum tilt angle in New York is 39 degrees, whereas in Los Angeles it is about
                25 to 27 degrees. The sun exposures caused by various insolation tilts over the course
                of the year in Los Angeles are shown in Figures 9.1 through 9.5.  To avoid cross
                shading, the adjacent profiles of two solar rows of arrays can be determined. Simple
                trigonometry can be used to determine the geometry of the tilt by the angle of the asso-
                ciated sine (shading height) and cosine (tandem array separation space) of the support
                structure incline. Note that flatly laid solar PV arrays may incur about a 9 to 11 percent
                power loss, but the number of installed panels could exceed 30 to 40 percent on the
                same mounting space.
                  An important design criterion when laying out solar arrays is grouping the proper
                number of PV modules that would provide the adequate series-connected voltages
                and current required by inverter specifications. Most inverters allow certain margins
                for dc inputs that are specific to the make and model of the manufactured unit.
                Inverter power capacities may vary from a few hundred to many thousands of watts.
                When designing a solar power system, the designer should choose the specific PV
                and inverter makes and models in advance, thereby establishing the basis of the
                overall configuration.
                  It is not uncommon to have different sizes of solar power arrays and matching invert-
                ers on the same installation. In fact, in some instances, the designer may, for unavoidable



























                 Figure 9.1  Insolation graph for Los Angeles PV panels mounted
                 at a 0-degree tilt angle.
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