Solar electric systems convert sunlight to “DC” or direct current electricity—the same type of electricity that is produced by every-day batteries where electrons flow in one direction. Solar cells, generally consisting of 2 layers of silicon (semi-conductor material) and a separation layer, are wired together and assembled into panels or modules. When the cells are exposed to sunlight, photons from the sun interact with electrons in the upper silicon layer, basically knocking them loose from their associated atoms. The loose electrons are attracted to atoms in the lower layer of silicon and travel through the wire to get there. This movement of electrons from one side of the cell to the other through the wire is electrical current.The term “photovoltaic” (or PV for short) is nicely descriptive of this process.
When a solar panel is manufactured, the PV cells are wired together in “series”. The output voltage of the panel depends on the number of cells in the series. Common nominal output voltages are 12, 18, and 24 volts DC. The output wattage is dependent on the efficiency of the cells and the size or area of each cell in the panel. The larger and more efficient the cells, the greater the wattage will be per square foot. Panels made using more efficient cells tend to be more expensive.
When the installer assembles a PV system, an exact number of panels are wired in series strings to achieve the target voltage required by the inverter or other load.Then groups of panel strings are often wired together in “parallel” in order to increase the wattage of the system. Once all these components are in place, the sun provides the energy and the system simply manufactures electricity!
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