Photovoltaics (PV), or solar electricity, is the simplest form of battery charging available. A photovoltaic module is used to convert the sun's energy into electricity. There are no moving parts in photovoltaic modules and little maintenance is required. Solar electric systems are modular, allowing you to start with a small system. As your power requirements grow, you can add more modules.
PV Module Construction
There are three types of silicon used to construct PV modules: single crystal, multicrystalline and amorphous silicon. Single crystal silicon cells are extremely thin wafers of silicon cut from a single silicon crystal. These are the most efficient silicon cells and have a life expectancy exceeding 25 years. The cells are fragile so they must be mounted in a rigid frame. Multicrystalline silicon cells are also extremely thin wafers of silicon but are cut from multiple crystals grown together in an ingot. They are similar to single crystal cells in life expectancy and fragility. However, they are slightly less efficient than single crystal cells and require more surface area to produce a given amount of electricity. Amorphous silicon cells are made by depositing a micro thin layer of silicon directly onto a sheet of glass or other substrate. They can also be mounted on a flexible backing, making them ideal for portable use.
Sunshine and Shading
It is very important to note that shading even one cell of a module will reduce the output of the entire module. The only exception to his is the Uni-Solar modules which have built in diodes between the cells to reduce this effect, but it is better to mount the solar modules so shading is avoided.
For example: the peak power point of the Solec SQ-75 is at 16.5 volts and the panel will produce 4.6 amps at this voltage. Since volts x amps = watts, the rated power for the SQ-75 is 75 watts (16.5 volts x 4.6 amps).
Rated power is a measurement of ideal performance. However, it is important to note that a panel may produce less than its rated power when charging a battery. Battery voltage averages about 13.5 volts when charging.
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