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Ask A Scientist

How do solar panels work?

Asked by: Ethan Valentine
School: Maine- Endwell Middle School
Grade: 6
Teacher: Kevin Wagstaff
Hobbies/Interests: Soccer, reading and karate
Career Interest: Building/design engineer

Answer from Tara Dhakal

Postdoctoral research associate, Binghamton University

Research Area: Photovoltaics, spintronics, nanotechnology Ph.D. School: University at Florida Family: Wife and two daughters Interests/hobbies: Soccer, traveling, movies

A solar panel is an assembly of solar cells.  Each solar cell absorbs sunlight and converts it into electricity.  In a way, a solar cell is similar to a battery with very low voltage.  In a solar panel, several of them are connected in a series so that a usable voltage is achieved.  For example, a typical solar cell has a voltage of around 0.5 V and a current of 100 milliamps.  Power (multiply voltage and current) that comes out of this cell is 50 milliwatts.  Average power usage per household in the US is around 500 watts.  If a solar panel has 1000 solar cells, you can estimate how many solar panels you need for your house.

Let me now give you some basics about how a solar cell performs like a battery.  The most commonly used material for solar panels is silicon.  The silicon atom has four electrons in its outermost orbit, but requires eight electrons to completely fill it.  If it shares four electrons from silicon nearby, it will make a strong bond, but the resulting stable silicon is neutral. 

If we bond the silicon element with some other element like phosphorous, which has five electrons in its outermost orbit, an extra electron, which is a negative charge, will be created.  So, by mixing some impurities of phosphorous in silicon, we create negatively charged silicon, or n-type.  Similarly, if we make silicon bond with elements like Boron, which has only three electrons in its outermost orbit, there will be a void of an electron.  In essence, we call this silicon positively charged or p-type. The n-type and p-type silicon plates join together to make the building block of a solar panel.

By bringing n-type and p-type silicon plates together, we create an electric force field at the junction.  Without the presence of this force field, a solar cell doesn't work.  When light shines on the cell, the energy of the light can knock out electron (negative charge) from its orbit leaving behind hole (positive charge) in its place.  The electric force field separates the electron and the hole at the junction. As the light keeps shining, the process repeats and you will see an accumulation of more negative charges in one side of the junction and positive charges on the other.  The separation of charges is what gives voltage to the cell, as in the battery. Fossil fuels like coal, petroleum (gasoline is what we call it), etc. contain a high percentage of carbon, which causes pollution. Fossil fued reserves are depleted as days go by and are not renewable since they take millions of years to form.  Solar energy is clean (causes no pollution) and renewable. It is estimated that the total amount of evergy that falls from the sun upon our planet in one hour is enough to fulfill our energy needs for one year.  So, solar energy is our future source of energy.

Last Updated: 9/18/13