How Solar Panels Work

What is a photovoltaic solar cell (PV cell) and how do solar panels work to convert light to electricity? Quite simply they rely on the photoelectric effect. This is a quantum electronic phenomenon where electrons are emitted from matter after electromagnetic radiation, like light, is absorbed. When a photon of light hits matter it does one of three things. It either passes through it, is reflected by it, or absorbed. In this third situation an electron from the material will be knocked loose by the energy of the absorbed photon. This creates both a free electron and an electron hole which is simply an open spot for an electron to fill which can move around similar to the electron.

The most popular type of solar cell is called a P-N junction solar cell. This type of solar cell is made from two different types of doped silicon. It must be “doped” with impurities such as boron in the case of P-type or phosphorus for N-type because silicon alone is not a good conductor of electricity. Silicon does have a good chemical structure that makes it ideal for use with the photoelectric effect though. The P/N stand for positive and negative which refers to the excess of electrons in N-type and lack of electrons in P-type. This imbalance of electrons is a result of the atomic structure of the impurities added to either side.

When these two types of silicone are combined you get the P-N junction which is simply where the layer of P-type meets N-type. When these two materials are combined the electrons from the N-type attempt to cross to the N-type. As these electrons all start to cross into the N-type material they create an electric field that actually repulses further electrons due to the accumulation of electrons along this barrier. Now when the photoelectric effect occurs electrons are freed in the P-type silicon layer and the electric field that exists pushes the electrons away while attracting the electron hole.

P-N Junction equilibrium.

P-N Junction equilibrium. Image by TheNoise. License: GNU FDL

With the addition of an external pathway the electron-hole pairs can connect by getting around the electric field created at the P-N junction. The flow of electron-hole pairs through this external pathway creates an electrical current and the field created by the P-N junction creates voltage thus creating power from the photoelectric effect. This power is used by adding a load, such as a battery, along the external pathway and thus power is harnessed from sunlight.

Another type of technology you might hear of is called multijunction solar cells. These cells simply use multiple P-N junctions stacked up to allow for different frequencies of light to be absorbed by different layers resulting in higher efficiency. As you might imagine these are significantly more expensive than P-N junction cells but they are also incredibly efficient and a three junction cell currently holds the efficiency record at 42.4% of light converted to electricity.

Below is a video about how these solar cells are combined into a solar panel for consumer and industrial use.


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