A typical Solar pv electrical system is described to refresh our basic electrical knowledge. This knowledge will allow us to be comfortable with the design of our pv solar system and have confidence that it is not over or under designed.

The pv Solar Energy System: A pv Solar system has the four major components.

1) THE SOLAR PANEL: This is the component that receives photons from the sun and converts the photon energy into electricity. The panels are rated in Watts.

2) CHARGE CONTROLLER: This component insures that the storage batteries are not overcharged and damaged.

3) STORAGE BATTERIES: The batteries store our collected electricity until we use the energy to power our appliance. Our electricity is store as the potential energy rated in Volts.

4) INVERTER: This component changes the current from our batteries, which is stored in direct current (DC), to an alternating current (AC) which is compatible with our household appliance.

Conversion of Sunlight to Electricity: Photovoltaic energy is the conversion of sunlight into electricity through a photovoltaic (pv) cell, commonly called a solar cell. A photovoltaic cell is a non mechanical device usually made from silicon alloys.

Sunlight is composed of photons or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.

The output of a solar panel is usually stated in watts, and the wattage is determined by multiplying the rated voltage by the rated amperage. The formula for wattage is Volts times Amps equal Watts. So for our example, a 12 volt - 60 watt solar panel measuring about 20 X 44 inches has a rated voltage of 17.1 and 3.5 amps .

V X A = W

17.1 volts times 3.5 amps equals 60 watts.

Our solar panel rated as 60 watts exposed to 6 hours of peak sun will produce 360 watt hours of power per day. An typical; home will require 4000 watts of DC generating power to produce sufficient kwh to cover annual electrical consumption. This equates to 67 - 20 X 44 inches solar panels from the example above.

Wiring the System:

Solar panels can be wired in series or parallel to increase voltage or amperage respectively, and they can be wired both in series and in parallel to increase both volts and amps. Series wiring refers connecting a positive terminal of one panel to the negative terminal of an adjacent panel. This connection will produce voltage as the sum of the two panels and the amperage will remain the same as the output panel. Two 12 volt and 3.5 amp panels wired in series will produce 24 volts at 3.5 amps.

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