SOLAR ENERGY
LESSON 3
Solar Cells:
Solar cells convert sunlight directly to electricity, which is measured in kilowatt-hours. A Solar cell is a semi-conductor device that is light sensitive in that it produces an electric charge or voltage when light strikes its surface. Most cells are made of silicon, a material that comprises 28 percent of the Earth's crust.
Solar cells are also known as photovoltaic cells - or PV cells for short - and can be found on many small appliances, like calculators, and even on spacecraft. They were first developed in the 1950s for use on U.S. space satellites.
These individual solar cells are arranged together in a PV module and the modules are grouped together in an array. Some of the arrays are set on special tracking devices to follow sunlight all day long.
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The electrical energy derived from solar cells can be harnessed directly at home for producing light and for other appliances. Also it can be used in a business.The solar energy can be stored in batteries for aaplications such as emergency roadside cellular telephone use , for lighting a roadside billboard at night. Some experimental cars use PV cells which convert sunlight directly into electrical energy to power the motors inside the car .
But when most of us think of solar energy, we think of satellites in outer space. Here's a picture of solar panels extending out from a satellite
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An electrical equivalent model can be created to understand the electronic behavior of a solar cell. This model is modeled based on discrete electrical components whose behaviour is well known.An Ideal solar cell may be modeled by a current source in parallel with the diode. Practically no solar cell is ideal and hence a shunt resistance and a series resistance component are added to the model. The resulting equivalent circuit of a solar cell is shown on the left. A schematic representation of a solar cell for use in circuit diagrams is also shown on the right.
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A solar cell may operate over a wide range of voltages (V) and currents (I). By increasing the resistive load on an irradiated cell continuously from zero a short circuit to a very high value (an open circuit) one can determine the maximum-power point i.e the point at which the maximum V×I value is obtained, that is, the load for which the cell can deliver maximum electrical power at that level of irradiation.
The maximum powerpoint of a photovoltaic is a function of incident illumination. The maximum power point can be tracked using a tracker which tracks the instantaneous power by continually measuring the voltage and current (and hence, power transfer), this information can be used to dynamically adjust the load so maximum power is always transferred regardless of the variation in lighting.