Producing Power from the Sun

Intro to Photo-Voltaic Cells & Photons

Did you know that on bright and sunny days that the Sun shines around "1000 watts of power per square meter"? (5) If we were able to capture all of that energy, we would be able to easily power our homes, offices, and anything else with lots of power to spare! This would be an incredible feat if we were to ever be able to fully utilize the Sun's energy in this way, which seemed like a dream not even twenty years ago, is working its way into reality. Photo-voltaic cells (PV) are becoming much more common place to find as their technology has continued to improve. For years, PV cells were only able to produce enough power to run small electronics such as calculators, which in the presence of light, it did a fine job of. But now that a set of solar panels are capable of supplementing a home with power, people are beginning to have much more respect for these devices. But how does a photo-voltaic cell work and how does it get the power from the Sun?

This discussion now moves towards packets of energy called photons. To understand a photon, we must first discuss electrons moving about an atom's nucleus. For every atom of a particular element, the electrons that fly around it are bound to certain "energy levels" in which the electrons can remain or fall from. When an electron falls from one energy level to a lower energy level, it gives off a certain amount of energy in the form of electromagnetic radiation called photons which act sometimes like a particle and sometimes like a wave. These packets of energy can be all forms of light, ranging from infrared to ultraviolet, and some even fall into our visible spectrum for light (5). These photons travel at the speed of light, around 160,000 miles per second, arriving at Earth to give us the light to see what we are doing during the day. Light from lightbulbs work in this way also, as photons are given off as visible light to give us the ability to see. However, why some light seems much more intense than others is because the energy of the photon is based entirely on how many levels the electron falls. If an electron at level four, were to fall all the way to level zero, this would give off a much more powerful photon than one in which the electron originated at level one, and fell to level zero. For an interesting explaination of photons, I have included another Steve Jones video for you to watch.

How Photo-Voltaic Cells Work

Photo-voltaic cells are most commonly made of the element silicon, the same stuff used to make computer chips. Creating a PV cell involves using crystaline silicon and performing an action called "doping" in which impurities are added to the silicon to allow for the flow of electrons when warmed by energy. There are two types of doped silicon: p & n. P stands for "positive" because boron is added as the doping element to the silicon and allows for "holes" or places in which electrons want to fill in this substance. This is due to the fact that silicon has four electrons in its top shell, and boron only has three. This "shell" is capable of holding eight electrons, and so is constantly searching for another to complete this shell. The other kind of doped silicon is n for "negative" and as you may have guessed, this is looking to get rid of an electron because it has too many to hold "comfortably" in this shell, because the silicon which has four electrons in this shell, has been doped with phosphorus which has five electrons in this shell (5). This makes the n-doped silicon give up electrons rather easily, but can not directly pass its electrons to the p-doped silicon due to an electric field which forces these electrons to remain on their own side. However, if this is attached to a circuit, when a photon hits the PV cell, energy is passed to the cell, and an electron is released. This electron rushes through the circuit and back to the p-doped silicon to fill holes that are found there, and a hole is actually created in the n-doped silicon, allowing for this reaction to continue well into the future as long as there are photons to cause this movement of electrons (5).