What is the photovoltaic effect Solar Power Energy 2020 Part 6 of 12

Welcome to "What is the photovoltaic effect?". 📜Get your course certificate📜 ********************************** http://bit.ly/solar-crash-course-ipolytek SUBSCRIBE to see more courses like this one *********************************************** https://www.youtube.com/channel/UCYYX... This is the 6th video in our online course on Solar Energy. In it we discuss: What is the photovoltaic effect? How does a high ambient temperature affect the power output of a solar module? This video is part of iPolytek's online course on solar energy. iPolytek, Professional Development Courses for Engineers. When a photon hits a solar cell, one of three things can happen: - The photon can pass straight through the cell. This happens to low energy photons. - The photon can be reflected by the surface of the solar cell. - Or the photon can be absorbed the silicon to create electricity. This is known as the photovoltaic effect. Let's look at how this happens. When a photon is absorbed its energy is given to an electron in the crystal lattice. This energy excites an electron from the P-type silicon and "kicks" it into the conduction band where it is free to move around within the semiconductor. When the electron leaves the P-type silicon, it leaves its place empty, creating a "hole". An electron from neighbouring atom moves into the "hole", leaving another hole behind. In this way, holes are propagated throughout the lattice. As this happens, electricity begins to flow in the circuit that the solar cell is connected to. Ideally, a photon with an energy equal to that of the bandgap hits the solar cell and excites an electron from the valence band to the conduction band. Note that different materials have different bandgap energies as shown in this table. Most solar panels today are made of silicon solar cells. However, much of the sunlight reaching the Earth is composed of photons that have energies greater than that of the bandgap of silicon. This type of higher energy photon is still absorbed by the solar cell, but its "extra energy", that is, the difference between its energy and the silicon bandgap, is converted into heat rather than electricity. The internal temperature of the photovoltaic cell is a factor that influences the amount of power it produces. For a given current, when the temperature decreases, the generated voltage increases. This results in more power production since, Power (W) = Current (I) x Voltage (V) The Pmax temperature coefficient of a photovoltaic cell indicates by how much its power output will decrease as its temperature rises above the nominal temperature of 25 degrees Celcius. In this example, the temperature coefficient is -0.39%. This means that the power produced by the solar module decreases by 0.39% for every degree it is above 25 degrees Celsius. In general, most solar modules have Pmax temperature coefficients ranging from —0.2% to -0.50% per degree Celcius. The closer this coefficient is to zero, the less the solar module is affected by temperature. In summary, PV systems consist of three interdependent and successive physical phenomena : 1. The absorption of photons. 2. The transfer of energy from the photons to the semiconductor. 3. The collection of electrons in the form of electricity In this video, we've learned how solar cells produce electricity. Now let's see how good they are at it by asking the question, How is the efficiency of a solar cell measured? Find out in our next video! See you soon and thanks for watching. References: ************ 1. GianniG46—Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.... (Accessed 5 May 2017) 2. Electrons and Holes in Semiconductors (EECS at UC Berkeley). https://people.eecs.berkeley.edu/~hu/.... (Accessed July 2, 2018). 3. Yann (2015). Panneau photovoltaïque : Caractéristiques. http://www.dekloo.net/projets/photovo.... (Accessed July 16, 2018) #PV #SolarPV #HowDoSolarCellsWork #HowDoSolarPanelsProduceElectricity