Solar

The solar panels you see on top of houses, imbedded in your calculators, and riding on top of Martian rovers are what are known as photovoltaics. The basic principles that this technology builds upon were discovered throughout the 19th century, and later theoretically explained by Albert Einstein in 1904. Since then, scientists have heavily researched photovoltaics and they have been labeled as the future of clean technology.

How They Work

Photovoltaics convert solar energy (light) into a form of energy that is useful to us: electricity. The process through which this is done starts in something called a photovoltaic (solar) cell. Those big sheets you normally call solar panels are nothing more than large arrays of solar cells lined end to end under a glass covering to protect them from the harsh elements of nature.

The Solar Cell

Solar cells are classically made of silicon wafers. The fundamental nature of silicon atoms causes them to bond in groups of five, forming a crystalline structure, so that the material as a whole carries a neutral charge. This neutral silicon wafer is not very useful by itself, but when 'impurities' are added through a process called doping they become useful in many practical applications.

There are two types of silicon produced by this doping process, N-type silicon and P-type silicon. Adding phosphorous atoms to the silicon compound produces N-type silicon, or 'Negative'-type silicon. This is because phosphorous has five electrons to share with other atoms whereas silicon only has four. So when all the atoms combine the resulting molecules carry a net negative charge because the boron atom′s extra electron is not bonded to another atom. This electron can be thought of as free.

On the other hand, adding boron produces P-type silicon, or 'Positive'-type silicon. This is because boron atoms have three electrons to share compared with silicon′s four. Again, when the boron atoms combine with silicon atoms what is produced is a molecule with a net positive charge (called holes), due to the absence of an electron.

When you take these two different types of silicon and sandwich them together, all the free electrons in the N-type silicon want to neutralize the positive molecules in the P-type silicon by combining with those molecules. However, this neutralization process never fully happens. As the material near the junction begins to neutralize, an electric field is created that allows free electrons to travel in only one direction (toward the N-type silicon) and holes to travel in only the other direction (toward the P-type silicon). This means that any free electrons stay in the N-type silicon and any holes stay in the P-type silicon.

• An electron or hole travels close enough to the junction so that the electrical field can "transport it" to the other side.
• 1.The silicon wafer absorbs the energy from sunlight and the resulting absorbed energy creates an electron, hole pair by dislodging free electrons. When one of these pairs floats close enough to the electrical field, they are separated to their respective sides.

Attaching conducting elements from the N-type silicon to the P-type silicon creates a 'bridge' over which an electron can travel to reunite with the hole. This traveling electron is an electrical current. In solar cells, this process happens at a very fast rate and a significant electrical current is created. Furthermore, the junction between the two silicon wafers acts to create voltage. Electrical power is created by the combination of voltage and electrical current.