The Maximum Possible Efficiency of a Solar Cell Solar Energy Course 2020 Part 10 of 12

Welcome to "What is the Maximum Possible Efficiency of a Solar Cell?". 📜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-pqg9CoVhjtC4cW4DIA?sub_confirmation=1 This is the 10th video in our online course on Solar Energy. In it we discuss: Is there a theoretical limit for the efficiency of a solar cell? What is it? How are scientists overcoming it? Find out in this video. This video is part of iPolytek's online course on solar energy. iPolytek, Professional Development Courses for Engineers. What is the maximum possible efficiency for a solar cell that has just one PN junction? In 1961, William Shockley and Hans Queisser calculated this limit based on the second law of thermodynamics which states that the maximum efficiency of a "heat engine" is a function of the temperature of the hot reservoir (sun) and of the cold reservoir (the cell) - and the following assumptions - The cell does not make use of the entire solar spectrum - meaning that part of the radiation that falls on the solar cell is systematically transformed into heat. - The sunlight is not concentrated by mirrors or lenses. The figure on the right summarises their findings. It shows how the energy of a photon is distributed as a function of the bandgap energy of the semiconductor. The majority of the energy that falls on the solar cell is lost, yielding a Shockley-Queisser maximum efficiency limit of about 30% for a cell having just one PN junction. Here we see the Shockley-Queisser Efficiency Limits for Various Semiconductors with 1 PN junction. At one sun, meaning without the use of concentration by mirrors or lenses, a maximum efficiency of about 30% can be obtained from solar cells made of Copper Indium Selenium, crystalline silicon, Indium phosphide, Gallium arsenide, and cadmium telluride. Amorphous silicon has a slightly lower max efficiency of 29%. Researchers are working on several solutions to overcome the Shockley-Queisser limit. Here are three examples, Multi-junction (MJ) solar cells have multiple p-n junctions made of different semiconductor materials that produce an electric current in response to different wavelengths of light. The theoretical SQ efficiency limit of MJ cells is on the order of 80%. Here's why. On the left, we see the energy absorbance spectrum of crystalline silicon having only one junction. The area shaded in gray is the AM1.5 spectrum supplied. The energy actually absorbed by the cell is shaded in red. As you can see, much of the energy falling upon the solar cell is wasted. On the right, we see the performance of a multijunction solar cell. As you can see, this solar cell is able to absorb a wider range of wavelengths and wastes much less energy. This is thanks to the use of different types of semiconductors, each having a bandgap energy chosen to absorb a specific part of the solar spectrum. When combined together, they allow more energy to be absorbed from sunlight yielding a much higher efficiency. Up to 40% efficienct has been obtained in the lab so far. A second approach to increasing solar cell efficiency is to use lenses to focus sunlight onto multijunction solar cells. Lenses placed above the multijunction solar cell concentrate the sunlight by a factor of 100 to 1000. An average of 300 "suns" is used. The active solar cell surface is significantly reduced using this technique. To date, efficiencies exceeding 45% have been measured in the lab. Here is a closer look at a typical set-up. On the left we see that sunlight hits a cell and lense assembly. References: ************ 1. TU Delft OpenCourseWare. Losses and Efficiency Limits. https://ocw.tudelft.nl/wp-content/upl.... (Accessed 22 July 2018). 2. WIREs Energy Environ 2016, 5:543–569. doi: 10.1002/wene.204. https://onlinelibrary.wiley.com/doi/f.... (Accessed 22 July 2018.) 3. Ncouniot - Fraunhofer Institute for Solar Energy Systems, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.... (Accessed 23 July 2018.) 4. Natalya V. Yastrebova, Centre for Research in Photonics, University of Ottawa, April 2007. High-efficiency multi-junction solar cells: Current status and future potential. http://sunlab.eecs.uottawa.ca/wp-cont.... (Accessed 23 Aug 2018). 5. Solarpedia. http://fr.solarpedia.net/wiki/index.p... . (Accessed 23 July 2018.) 6. Grumerr434. https://commons.wikimedia.org/wiki/Fi.... (Accessed 23 July 2018.) #SolarEnergy #SolarCell #SolarSystem #Shockley-Queisser #Photovoltaics