Page 362 - Handbook of Energy Engineering Calculations

FIGURE 19 Steps in the interconnection of a cell to a module to a

panel to an array. (U.S. Department of Energy.)

Photovoltaic systems are a useful form of renewable energy. Thus, the
modules have no moving parts, are east to install, require little maintenance,
contain no fluids, consume no fuel, produce no pollution, and have a long life

span—more than 20 years—and they are equally or more reliable than
competing power sources, such as batteries and generators. However,
components, such as the load and controls, also affect the reliability of the
entire system.

3. Determine the number of modules required

Reference data show that the winter average peak wattage for a module in
Albuquerque, NM, is 6.1 W-h; for Pittsburgh, PA, a cloudier area, the same
module will produce 2.4 W-h. To determine the peak Watts of the system,
divide the total energy consumption by the W-h for the location. Then divide

the result by 0.8 to account for inefficiency; multiply the result by 1.2 (a 20
percent factor of safety) to account for any items you might have overlooked.
Thus, for Albuquerque, NM, we have (506 W-h/6.1/0.8)(1.2) = 124.4 peak
Watts. If we’re using 50-W modules, a standard and convenient size, we

would need 124.4/50 = 2.488 modules. Since modules are made only in
whole sizes, three modules would be used for this application.
For Pittsburgh, PA, following the same procedure, we have: (506 W-