How does Solar Energy Work?
The world is facing an energy crisis. Energy resources such as oil and coal not only continue to cost more, but when burned contribute to polluting the environment and – as many scientists beli– also contribute to global warming. While most people agree that the world needs to use less fossil fuels and turn to renewable forms of energy, these forms of energy have been incredibly difficult to develop mainly because of their exorbitant cost compared to traditional energy. One type of energy that is renewable and has made great strides in technology over the years is solar energy.
Solar energy is a kind of renewable energy that comes in the form of radiation from the sun. Everyday, millions upon millions of watts of power reach the earth’s surface. Much of this energy is used to heat our planet, but up to a third is wasted, reflected back out to space. In fact, each meter of the earth’s surface during a sunny day receives about 1,000 kilowatts of energy, more than enough energy to power a home or office. It is estimated that solar energy is so abundant, that in just 20 days, all the solar energy that reaches the earth exceeds that of the energy that can be produced by all the oil, coal and gas in the earth’s crust.
While solar energy does have enormous promise, over the years, harnessing this energy in an economically and environmentally practical way has been difficult. However, today’s technology has finally made inroads that should lead to an impressive future for solar energy in the years to come.
Solar energy as stated above is energy from the heat of the sun. It is already in use in many common devices such as solar powered calculators, solar powered highway communication systems and other devices that can be exposed to the sunlight and that use very low amounts of electricity. These devices use photovoltaic cells to convert sunlight into electricity in order to power the device.
Photovoltaic stands for Photo which means light and voltaic which means electricity. Photovoltaic cells are grouped together to make photovoltaic modules. These modules have been used in the past to power satellites in space, but now are being engineered to fulfill energy needs of homes, businesses and industries.
How Photovoltaic Cells Work
Photovoltaic cells are also called PV cells for short. They are made from silicon which is used to form semiconductors. When PV cells are exposed to the sun the semiconductors within each cell absorb some of the sunlight and change it into electricity. The change from sunlight to electricity occurs by energy knocking electrons loose on the semiconductor. Once these electrons are knocked loose, they are allowed to flow. Once electrons can flow, they are pulled into a specific direction by one or more electronic fields. When there are enough electrons flowing in one specific direction, this flow becomes an electrical current. Simply by catching this electrical current, we can now use it externally to power various electronic devices such as a lamp, calculator, etc.
Silicon is used in PV cells. Silicon is an element that has specific properties that make it easily attach to other silicon atoms. Silicon in its crystalline structure is not a good conductor of electricity, however in a PV cell, the silicon has impurities, and it is these impurities that give this substance the ability to efficiently produce electricity.
Since silicon alone does not produce enough electricity, the PV cell is doped with the chemical phosphorus. Doping means adding impurities. Phosphorous atoms are used to create a negative charge called N-type silicon. The reason is that silicon atoms bond together using their atomic structure, making it very difficult for light to knock them loose and cause energy. However, when you add phosphorous which doesn’t bond well with other phosphorous atoms or silicon, when light hits these atoms, it is easy for them to knock off electrons to create electricity. While phosphorous doped PV cells create N-type cells, boron is used to dope silicon to create a positive charge called P-type silicon.
When you put N-type silicon together with P-type silicon, the free electrons on the N side find a match with the P side and create a field of energy. This creates a diode which allows the electrons to flow one way – from the positive side to the negative side. As electrons flow, current is produced. In addition, the electric field created by both the P and N create voltage. Now that we have current and voltage, we essentially have power that can be tapped to run electronic devices.
Parts of a PV Cell
A PV cell usually consists of 6 parts. They include:
Cover Glass - The cover glass is used to protect the PV cell from the elements, while allowing photons (sunlight) to penetrate and hit the silicon.
Antireflective Coating – Silicon is a very reflective substance; the goal of a PV cell is to absorb as many photons as possible. Unfortunately, only about 15% of photons are utilized. While not all due to reflection, reducing reflection is important to maximize energy absorption.
N Type Silicon – This is the silicon cell that is doped with phosphorus.
P Type Silicon – This is the silicon cell that is doped with boron.
Contact Grid – The contact grid harnesses the electricity being created and sends it to a wire to power devices
Back Contact – Most PV cells are affixed to exterior roofs and walls. The back contact allows each PV cell to be attached to a structure.
Today, a peak watt generated by solar PV cells costs about $9, far more expensive than traditional forms of energy. However, more research is being done in the field of solar energy and it is expected that in the coming years, the price per peak watt will come down considerably. For many in the solar energy industry, it is possible that in the next 20 years, solar energy will be a viable economic alternative to fossil fuels for producing energy for homes and businesses.