Running head: PHOTOSYNTHESIS VS. SEMICONDUCTOR BASED SOLAR CELL

Photosynthesis Vs. Semiconductor Based Solar Cell
Biology – SCI 115
23 January 2012
Abstract
This paper discusses photosynthesis and how it is used by plants to harness solar energy. It also discusses semiconductor-based solar cells and how they are able to harness solar energy and convert it to electricity. This paper also compares the two types of solar energy systems and provides an overview of how the two systems are alike and how they are different. In closing, this paper will briefly explain how the laws of thermodynamics apply to each of the two energy systems.

Photosynthesis Photosynthesis is a process that transfers solar energy, or energy from the sun, into a chemical energy that provides nutrients to plants and animals all over the world. Without these important nutrients, plants, animals and humans would not be able to survive on earth. “Animals and plants get energy by metabolizing nutrient molecules made by photosynthesizers.” (Mader, 2010)
Semiconductor-Based Solar Cell Before discussing what a semiconductor-based solar cell is, I would first like to define a semiconductor and then explain how it is used in a solar cell type environment. A semiconductor is, “a class of materials, such as silicon and germanium, whose electrical properties lie between those of conductors (such as copper and aluminum) and insulators (such as glass and rubber).” (Seale, 2003, Semiconductor). After many years of experimenting with solar energy, scientists were able to discover that semiconductors were the main component necessary to build non-moving parts that could be joined together in a manner that would radiate light and transform it into electrical energy. “Charles Fritts constructed the first true solar cells using junctions formed by coating semiconductor selenium with an ultrathin, nearly transparent layer of gold. Fritts's devices were very inefficient, transforming less than 1 percent of the absorbed light into electrical energy.” (Seale, 2003, Solar Cell)
Similarities of Photosynthesis and Solar Cell Energy The most obvious similarity between photosynthesis and solar cell energy is that they both get their energy from the sun. “The first two steps of photosynthesis involve capturing photons released from the sun and using that energy to create a flow of electrons. From there, photosynthesis involves using that electrical energy to create chemical energy, from which ultimately the products of photosynthesis are created (e.g., sugars to feed the plant).” (Stier, 2009). Similarly to photosynthesis, solar cell energy also captures photons and uses that energy to create a flow of electrons, which creates electricity. A third similarity between photosynthesis and solar cell technology is that “a semi conductor has solar cells that trap energy from the sun and convert it into electricity. Plants have cells that trap energy from the sun and convert it into useful products.” (Haile & O’Connell, 2005)
Differences between Photosynthesis and Solar Cell Energy I believe that the main difference between photosynthesis and solar cell energy is that photosynthesis converts solar energy to chemical energy, which provides nutrients to plants, animals and humans; while solar cell converts solar energy to electrical energy which is considered a luxury item in today’s society to save money in electrical energy bills. In order to use solar cell energy, you have to “develop silicon-based solar cells, and they use a great deal of energy to produce. They are developed from energy that typically comes from polluting fossil fuels. Processing silica (SiO2) to produce silicon is an energy-intensive process. At current efficiencies, it takes one to two years for a conventional solar cell to generate as much energy as was used to make the silicon it contains.” (Stier, 2009) Photosynthesis comes for our natural resources, and therefore doesn’t require any man-made products to produce chemical energy. In addition, there is no cost to develop chemical energy and it is produced on a daily basis from all natural ingredients. Finally, photosynthesis that occurs in plants, leaves, and trees has been around for billions of years. “It originated in organisms that date back roughly 2.8 – 3.5 billion years, making it one of the oldest technologies on Earth. This technology successfully converts photons striking the Earth from 93 million miles away into electrical and finally chemical energy, enabling the construction of chemical molecules that otherwise would not exist on the planet, and upon which virtually all life depends.” (Stier, 2009) In contrast, the man-made invention of semiconductor solar cells has only been around for approximately 200 years, or since “Charles Fritts created the first solar cell in 1883.” (Stier, 2009)
Law of Thermodynamics “The first law of thermodynamics, also called conservation of energy, states that the total amount of energy in the universe is constant. This means that all of the energy has to end up somewhere, either in the original form or in a different from. The second law of thermodynamics states that the disorder in the universe always increases. As the disorder in the universe increases, the energy is transformed into less usable forms. And the third law of thermodynamics tells us that all molecular movement stops at a temperature we call absolute zero, or 0 Kelvin (-273oC).” (ESD Bulgaria, Ltd., 2005) “The laws of thermodynamic apply to photosynthesis and semi conductors. In photosynthesis, plants transform energy. They transform light energy into food energy. This shows that plants obey the first law of thermodynamics. Also, during the process of photosynthesis, plants loose energy. They do not convert all the energy trapped from the sun into food energy. Some of it is lost in the process. So, plants obey the second law of thermodynamics. Plants need a constant supply of energy to make food and produce. They need to trap energy from the sun constantly. Hence, plants obey the third law of thermodynamics. Semiconductors obey the first law of thermodynamics as they transform energy trapped from the sun into electricity. Also, energy is lost as the semiconductor transforms energy trapped from the sun into electricity. Thus implies that semi conductors conform to the second law of thermodynamics. Lastly, the semi conductors need to trap energy from the sun constantly so as to produce electricity. Therefore, the semiconductors follow the third law of thermodynamics.” (Haile & O’Connell, 2005)

References

ESD Bulgaria Ltd. (2005). Kids and Energy. Retrieved January 21, 2012, from http://www.kids.esdb.bg/ basic_principles.html
Haile, J.M., & O’Connell, J.P. (2005). Thermodynamics: fundamentals for applications. Cambridge University Press. Retrieved January 20, 2012 from http://www.academicwritingtips.org/ component/k2/item/1134-assignment. html?tmpl=component&print=1
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York: McGraw Hill, pp. 3-82.
Seale, Eric. (2003, July). Semiconductor. Retrieved January 22, 2012, from http://encyclobeamia.solarbotics.net/articles/ semiconductor.html
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Stier, Sam. (2009). The Biomimicry Institute. Learning from Nature. Solar Cell Inspired by Plants. Retrieved January 23, 2012 from http://www.beyondbenign.org/ community/Solar%20Cell%20 Inspired%20by%20Plants.pdf, pp. 2-3.