Posts published in July 2011
Renewable Energy Fundamentals (continued).
Next we’ll discuss how solar panels, also known as Photo Voltaic (PV) panels work.
Our journey must begin back in high school chemitsry. The part of PV panels we are concerned about are manufactured from silicon (Si), Si atoms have room for 8 electrons in their outter most bands, but naturally carrying only 4 electrons, leaving room for 4 additional electrons. Electricity in it’s most basic form can be described as the flow of electrons though a conductor. Can you see where this is going? When one Si atom comes into contact with another each receives the others 4 electrons, creating a very strong bond. There is no charge positive or negative as the 8 electrons satisfy both atoms.
Here’s where science enters the picture. Two plates of pure silicon would not generate electricity in solar panels, because they have is no positive or negative charge. Solar panels are created by combining silicon with other elements that do have positive or negative charges.
Phosphorus, for example, has five electrons to offer to other atoms. If silicon and phosphorus are combined chemically, the result is a stable eight electrons with an additional free electron along for the ride. It can’t leave, because it is bonded to the other phosphorus atoms, but it isn’t needed by the silicon. Therefore, this new silicon/phosphorus plate is considered to be negatively charged.
In order for electricity to flow, a positive charge must also be created. This is achieved in solar panels by combining silicon with an element such as boron, which only has three electrons to offer. A silicon/boron plate still has one spot left for another electron. This means the plate has a positive charge. The two plates are sandwiched together in solar panels, with conductive wires running between them.
With the two plates in place, it’s now time to bring in the ’solar’ aspect of solar panels. Natural sunlight sends out many different particles of energy, but the one we’re most interested in is called a photon. A photon essentially acts like a moving hammer. When the negative plates of solar cells are pointed at a proper angle to the sun, photons bombard the silicon/phosphorus atoms.
Eventually, the 9th electron, which wants to be free anyway, is knocked off the outer ring. This electron doesn’t remain free for long, since the positive silicon/boron plate draws it into the open spot on its own outer band. As the sun’s photons break off more electrons, electricity is generated. The electricity generated by one solar cell is not very impressive, but when all of the conductive wires draw the free electrons away from the plates, there is enough electricity to power low amperage motors or other electronics. Whatever electrons are not used or lost to the air are returned to the negative plate and the entire process begins again.
One of the main problems with using solar panels is the small amount of electricity they generate compared to their size. A calculator might only require a single solar panels, but a solar-powered car would require several thousand. If the angle of the solar panels is changed even slightly, the efficiency can drop 50 percent.
Some power from solar panels can be stored in chemical batteries, but there usually isn’t much excess power in the first place. The same sunlight that provides photons also provides more destructive ultraviolet and infrared waves, which eventually cause the panels to degrade physically. The panels must also be exposed to destructive weather elements, which can also seriously affect efficiency.