THE COMPARISON OF PHOTOSYNTHESIS AND SOLAR CELLS 1

The Comparison of Photosynthesis and Solar Cells

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Abstract

This paper will compare and contrast photosynthesis and the semiconductor based solar cell.
This will be accomplished by detailing three similarities, and three differences between the two.
The first of the similarities being the absorption of solar energy, the second being the transformation of solar energy into a different more useable form of energy, and finally the third being that they both use organic colorants to attract the sun’s rays. The three differences being that one produces chemical energy and the other electrical energy. The second difference is that one occurs naturally and the other is manmade, and the third difference is that one is cost effective and the other are expensive to produce. This paper will also describe how the laws of thermodynamics apply to each of the systems, giving the reader even further insight on the topic at hand.

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The Comparison of Photosynthesis and Solar Cells

Photosynthesis is the process in green plants and other organisms by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source. Semi-conductor based solar cells, also known as photovoltaic cells, are a man made device that converts the energy of the sun into electric energy. Both of these systems absorb, and transform the suns energy into a more usable form. Photosynthesis does this when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane.
Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate, (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria, this is done by a sequence of reactions called the
Calvin Cycle, which is simply the reduction of carbon dioxides to a carbohydrate, or the sugars that the plants use (Smith A.L. 1997). Similarly a solar cell works when, the silicon of a solar cell absorbs the suns energy and frees up electrons. The electrons are able to be released because the silicon is purposefully full of impurities that break up the molecular bonds in the rays.
Phosphorous is often used as an impurity that creates a negative electron charge. Once the negatively charged electrons are freed, they seek out positive connections that can be found on another side of

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the solar cell that is positively charged with boron. The electrons will continue to flow towards that side, creating an electrical current. This current travels down the electrical contacts on the cell creating voltage, the energy that humans can better use. (Bright, 2011) The final similarity is that they both use organic colorants to attract the sun’s rays. Plants obviously are organic and use mostly the color green, being able to absorb all of the colors in the spectrum except green. Solar cells also use organic colors in the form of blackberry extracts. This actually is a little more efficient being that black absorbs all of the colors in the spectrum. The differences between the two begin with the type of energy produced. Photosynthesis produces a chemical energy in the form of carbohydrates (sugars) that the plants use and store for food. Solar cells on the other hand produce electrical energy in the form of voltage, that humans us for a variety of different things. The next difference is that photosynthesis occurs naturally and plants are made up of organic material, while solar cells are manmade, mostly they are made of silicon, as well as other components that are similar to computer chips. And finally we have cost. Obviously photosynthesis does not cost anything, however semiconductor based solar cells are expensive to produce. Over the years the cost has steadily declined, and the efficiency has improved, but the bottom line remains that solar power is not as cost effective as other sources of power.

THE COMPARISON OF PHOTOSYNTHESIS AND SOLAR CELLS 5 The first law of thermodynamics applies to photosynthesis and solar cells because it is a prime example of how in both cases energy is transformed from one form to another, but it is neither created nor destroyed. The second law of thermodynamics which is a little more complex can relate to photosynthesis and the solar cell because it states that any time that work is done, or energy is converted or transferred, some of the beginning energy is going to be lost as heat, and this is true in photosynthesis and in the process that the photovoltaic cell goes through to convert energy.(Three Laws of Thermodynamics 2004-2010) Obviously there are many more similarities and differences between photosynthesis and the semiconductor based solar cell, but I thought these to be most note worthy in a brief essay. There are a tremendous amount of resources in the world today, to research this topic further, i.e. the internet, being the first that comes to mind, because not only do you have web sites, but there are also chat rooms, message boards, e-libraries, ect. That one can gain more information from and further insight on the topic

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References

1. Smith, A. L. (1997). Oxford dictionary of biochemistry and molecular biology. Oxford [Oxfordshire]: Oxford University Press. p. 508. ISBN 0-19-854768-4. "Photosynthesis – the synthesis by organisms of organic chemical compounds, esp. carbohydrates, from carbon dioxide using energy obtained from light rather than the oxidation of chemical compounds."
2. Bright, Paul (2011) How does a solar cell work? Retrieved from http://www.ehow.com/how-does_4965169_solar-cell-work.html#ixzz1CA02k3Gd
3. Three Laws of Thermodynamics (2004-2010) Retrieved from http://www.physicsplanet.com/articles/three-laws-of-thermo