APV system designer can conduct a detailed site assessment for you. To save the dealer time (and possibly save yourself some money), you can conduct a preliminary assessment to determine whether your site has potential for a PV system. There are three factors to consider when determining whether your site is appropriate. First, systems installed in the United States must have a southern exposure. For maximum daily power output, PV modules should be exposed to the sun for as much of the day as possible, especially during the peak sun hours of 10 a.m. to 3 p.m. Second, the southern exposure must be free of obstructions such as trees, mountains, and buildings that might shade the modules. Consider both summer and winter paths of the sun, as well as the growth of trees and future construction that may cause shading problems. Finally, the unobstructed southern exposure must also have appropriate terrain and sufficient space to install the PV system. Aflat, grassy site is appropriate terrain, whereas a steep, rocky hillside is not.
Unlike utility power plants, which produce electricity constantly despite the time of day and year or the weather, the output of PV modules is directly related to these two factors. Where you live will affect the number of PV modules you will need for power, because different geographic regions experience different weather patterns. Seasonal variations affect the amount of sunlight available to power a PV system. The above map shows annual average “peak sun hours” for regions in the United States.
Module temperature also affects output. The conversion efficiency of crystallinesilicon modules falls significantly at elevated module temperatures. When designing a PV system, be sure your PV installer obtains data specific to your area, rather than relying on general data. The National Oceanic and Atmospheric Administration began collecting solar data nearly 20 years ago. Some state energy offices have solar data-collection programs to assist solar designers. Finally, books are available that contain solar data on most major cities in the United States: