How Photovoltaic Cells Turn Sunlight into Solar Power
Photovoltaic cells have been used for solar powered calculators for years. Even before that, they were used in space. Now they are being used in many ways, including powering houses. The way photovoltaic cells work is interesting.
The photovoltaic cells themselves are made out of a special kind of material called a semiconductor. Silicon is most often used. When light strikes this substance, the semiconductor takes in some of the energy.
The incoming energy is enough to push some electrons loose. These free-floating electrons flow in the same direction in the semiconductor. This produces an electrical current. The next step is to use contacts that have been placed on the photovoltaic cells and run a circuit from the top contacts, through the item to be powered, and back to the bottom contacts.
The silicon is, surprisingly, impure. This is because silicon in its natural crystalline state does not allow for much movement of electrons. Each of the silicon atoms is unstable on its own because there are four places for electrons that can be filled. Yet, every silicon atom is usually locked up with the other silicon atoms by sharing electrons on the outer valance.
In order to make the silicon material more conductive, it is necessary to dope it, or mix in some other substance. To make N-type silicon, phosphorous is used. It has five electrons in its outer ring, so that when it mates up with the silicon atoms surrounding it, there is one free electron for every phosphorous atom.
P-type silicon is made by doping with boron. It has only three electrons in its outer shell. This leaves a hole, which is a place where an electron can jump in, for every atom of boron. The key to using silicon in photovoltaic cells is to use both P-type and N-type silicon.
The two types of silicon are set up side by side. At first, the electrons and holes near the shared border fill in rapidly. Then, equilibrium is reached where the electrons can no longer interact in that way.
An electric field is created separating the two halves. In this field, it is easy for electrons to flow from the P-side to the N-side. Electrons on the N-side cannot make it over to the P-side. This creates a one-way flow of electrons.
Photons are units of energy from the sun. Photons keep the energy flowing by bumping into the atoms of the solar cell and freeing electrons and holes. This perpetuates the movement of electrons from hole to hole and establishes current. The field created at the site of the N-type and P-type silicon junction makes the voltage that completes the power picture.
Using photovoltaic cells to harness the sun’s energy is still fairly new. The cells are being used in more and more applications, both commercial and residential. Photovoltaic cells are fairly easy to understand and they can be used by anyone who can take the time to learn about them. The use of photovoltaic cells puts solar power within reach.