The Physics of Solar Power

In my previous post, I discussed how President Obama is helping to fund the development of Solar Energy. I thought I would then take the opportunity to explain a bit of the physics behind solar power.

Don’t worry, you won’t find any equations here :)

First, lets start with the sun. That big bright thing up in the sky.

The sun generates light, and light can be thought of as a bunch of tiny packets of energy. These packets are called “photons”. The different amounts of energy in a photon will correspond to the colour of the light that is emitted. For example, photons of the colour blue have more energy than photons of the colour red.

Energy increases from left to right (Source: Opensource Handbook of Nanoscience and Nanotechnology)

 

So how do we harness the energy in these photons? We can use Photovoltaic cells. Put simply, they convert solar energy into electricity. Let’s see how…

A photovoltaic cell is made of special materials called semiconductors, which are made of things like silicon (Yes, that stuff used to make fake boobs. Isn’t science awesome?).

Now, all atoms are made up of a nucleus (which is made of protons and neutrons) and electrons which circle around the nucleus.

Electrons can actually absorb the energy from a photon, but this happens only if the photon has a very specific amount of energy (a specific colour). When an electron does absorb a photon, it causes the electron to “jump”, and sometimes even break free of the entire atom! Electricity is a constant flow of electrons, which we refer to as an electric current.

Silicon structures like to hold onto their electrons. They don’t normally let them move around which makes silicon what we call an insulator. But in a Photovoltaic cell we add impurities, little bits of stuff that doesn’t belong there. The impurities will actually encourage the silicon to release its electrons and let them move around.

Now the magic happens. So a photon (those little packets of energy from the sun) hits the Photovoltaic cell. If the photon has just the right energy, it will knock loose one of the electrons in the silicon atoms. And, because of the impurities, that electron will move around.

If you get enough electrons moving around, you get an electric current which we can then use to power all of our awesome toys!

Thats it in a nutshell. If you want to read about this stuff in a bit more detail, check out the links spread all through this post, or some of the cool sites below.

Hooray for Physics!

Further Reading:

http://science.howstuffworks.com/solar-cell.htm

http://www.physlink.com/Education/AskExperts/ae451.cfm

http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/