How does a solar panel (Solar Photovoltaic) works?

  

        Solar energy is one of the most efficient and renewable sources of energy. The term solar energy means; the energy generated through the power of solar radiation (that is given out by the sun). By collecting this solar radiation, a large amount of electrical power can be generated. This process is usually done by solar panels. Thus a solar panel is used to collect the radiation given out by the sun to convert it into electricity. The way electricity generated through solar panels is generally classified into two types, they are:

                   1.       Solar thermal

                   2.       Solar photovoltaic

 

Difference between Solar thermal and Solar photovoltaic

 

   

    Solar photovoltaics directly converts visible radiation (light) into electricity, whereas solar thermal uses infrared radiation (heat) of the sun to generate electricity. In this article let’s see the power generation through solar photovoltaics. Solar Photovoltaic is a type of panel, in which blue-colored solar cells are placed. It is usually found at the top of houses and many buildings. It is used in very large amounts in power stations, for a huge amount of power generation. It also requires low maintenance compared to other renewable resources. Now let’s look at the construction and operation of solar photovoltaics.

 

Different layers of a solar cell

    A solar photovoltaic panel is generally a semiconductor. A semiconductor is a material that partially conducts electricity and partially does not. A solar panel is generally made up of two types of semiconductors, one is a P-type semiconductor also called a Positive semiconductor, and the other one is an N-type semiconductor also called a Negative semiconductor. These semiconductors are primarily made up of silicon, as it acts as a conductor under certain conditions and acts as an insulator under certain conditions. It is also an abundant material found on earth. So it is cheap.

    The semiconductors are classified as P and N-type semiconductors based on the amount of doping added to them. Doping is the process of adding another material to the primary material, which is also mentioned as adding impurities. At first, the P-type semiconductor is formed by adding Boron to silicon. As Silicon has four electrons in its valence band (last orbit shell) and the boron has only three electrons in its valence band there will be a missing electron when it is bonded together. So one more electron is needed to make a perfect bond with silicon, and that missing electron is considered as a hole. So, when more boron material is mixed with silicon, more holes are generated and that particular semiconductor gains a positive charge because electrons possess a negative charge. So the absence of a negative charge makes it a positive charge and makes the semiconductor a P-type semiconductor.

Positive (P-type) Semiconductor

   At next, the N-type semiconductor is formed by adding phosphorous to the silicon material. When bonded together, an excess electron will be created, as phosphorous has five electrons in its valence band and silicon has only four electrons in it. So a negative charge is created, due to the excess free electron. When more phosphorous is added, there will be more excess electrons created in the semiconductor, which makes it to gain more negative charge and makes it an N-type semiconductor.

Negative (N-type) Semiconductor

Atomic Structure of Different atoms

    When these two types of semiconductors are combined together, a junction is formed at the center called the PN junction. Now the excess electrons in the N-type semiconductor start to flow to the P-type semiconductor and combine with the holes, thereby leaving a positive charge on the N-type (as the electrons are decreasing). Similarly, the excess holes in the P-type semiconductor start to flow to the N-type semiconductor and combine with the electrons, leaving a negative charge on the P-type (as the holes are decreasing). The process of combining electrons and holes is called diffusion. The diffusion process only occurs near the junction. Due to this action, a layer called the depletion layer is formed around the junction, and an electric field is formed at the junction. This electric field acts like a barrier thereby stopping further combination of electrons and holes. So the diffusion process also stops.

Formation of the Depletion Region

    When these semiconductors are placed in the sunlight, the photons from the sun strike the barrier at the junction, thereby splitting the electron-hole pair. The N-type semiconductor is always made thin so that the photons are made to reach the junction freely by passing the N-type. As a free electron and a hole is created, it again starts to combine. But due to barrier potential (which means the electric field that is acting as a barrier in the junction), the hole moves towards the P-type, and the electron moves towards the N-type. When more photons from the sun strike the junction, more electrons and holes are generated in their corresponding semiconductor. These electrons and holes are free to move. When we place metal conductors over the N-type semiconductor, we can collect these free electrons and make them do some useful work by connecting the conductors from the N-type to the P-type through a load. The electrons from the N-type will pass to the load through the metal conductors, and then reach the P-type semiconductor, and combine with the holes again. As the splitting occurs constantly at the junction, the depletion layer decreases around the junction. So again the diffusion happens as it from the first, and the depletion layer is formed again, and the electricity is generated continuously. This is how a solar cell works. The average voltage generated by a solar cell is 0.5v. When we connect so many solar cells to form a solar panel and we can achieve the desired voltage as per our wish.

Operation of a solar cell

           Solar thermal is another concept that will be explained in another post. Solar thermal

 

 

 

 

 

Written by [Jerine Victor]