determine the economic feasibility of concepts, it is important to have specific design criteria. Design criteria developed during the study of low cost structures for photovoltaic arrays addressed types of load, nature of the loading function (known/ unknown, variable, upper bound) and risk of occurrence of the loads. The design criteria were developed along the lines of the above codes and used, in addition to those codes, the results of current research in assessment of risk and wind loading of civil engineering structures. Cost Trends and Costs: A number of factors affect cost trends. Some of these are: • cost of labor to install support components such as posts and beams declines as a function of 1/n where n is the number of panels supported per span • material required for beams increases as a function of L2, where L is the distance between supports • material required for foundations increases as a linear function of load on the columns or posts The effects of combining these trends are shown in the attached figures... Wind Design Studies: Usual design procedures like those given in ANSI A58.1- 1972 are not adequate for accurate wind design of repetitive arrays of sloping solar panels set at a low height above the terrain. The technical literature provides little information even for a single array. Hence the wind tunnel test program was performed in 1979 for single flat panel arrays and for a field of such arrays. The 1:24 scale models were tested in the Meteorological Wind Tunnel at the Colorado State Fluid Dynamics Laboratory at Fort Collins, utilizing a boundary layer feature to generate terrain turbulence. Measurements were made of the effects of panel slopes, wind azimuth, panel porosity and height above the ground, and for the effects of wind barriers. The height above ground and changes in panel porosity, to the amount deemed reasonable for solar panels, were found not to have much effect on wind forces. On the other hand, porous fences provided large reductions in wind forces on either single arrays or on parts of array fields. Wind force coefficients derived from these studies are recommended for the wind design of similar solar panel installations. These are intended to represent mean wind effects and do not include wind dynamics. Existing methods for gust force design are recommended at this time.
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