ECOPAGE

     “Solar” is the Latin word for “sun” – and it’s a powerful source of energy.  In fact, the sunlight that shines on the Earth in just one hour, if collected, could meet world energy demands for an entire year!  We can use solar power in two different ways: as a heat source, and as an energy source.  People have used the sun as a heat source for thousands of years.  Families in ancient Greece built their homes to get the most sunlight during the cold winter months.  In the 1830s, explorer John Herschel used a solar collector to cook food during an adventure in Africa.  You can even try this at home!  Today we can use solar collectors for heating water and air in our homes.  If you’ve seen a house with big shiny panels on the roof, that family is using solar power.

     We can also use solar energy to make electricity. The process is called "photovoltaics." If you have a solar powered watch or calculator, you're using photovoltaics! In 1954, scientists at Bell Telephone discovered that silicon (an element in sand) created an electric charge when it was exposed to lots of sunlight. Just a few years later silicon chips were used to help power space satellites. Today, more than 10,000 American families get ALL of their electricity from solar power. Silicon from just one ton of sand used in photovoltaic cells could produce as much electricity as burning 500,000 tons of coal! You might be wondering, "Why we do not use solar electricity all the time?" Solar power systems make a different kind than big power plants do, so different wiring is needed which can be very costly.

     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.  When the electrons leave their position, holes are formed.  When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery.  When the two surfaces are connected through an external load, electricity flows.
The photovoltaic cell is the basic building block of a photovoltaic system.  Individual cells can vary in size from about 1 centimeter to about 10 centimeter across.  However, one cell only produces 1 or 2 watts, which isn't enough power for most applications.  To increase power output, cells are electrically connected into a packaged weather-tight module.  Modules can be further connected to form an array.  The term array refers to the entire generating plant, whether it is made up of one or several thousand modules.  The number of modules connected together in an array depends on the amount of power output needed.