Why Not Solar Panels?

Photovoltaic solar panels might make ecological sense, but they don’t make economic sense. It is for this reason we are still extremely reliant on fossil fuels. To this day, humans make more energy burning wood than from solar panels.

While the second law of thermodynamics forbids a 100%-efficient solar cell, there is much room for progress. The second law of thermodynamics states that in any cyclic process, the entropy will either increase or remain the same. Entropy, in this case, can be most specifically defined as a measure of the amount of energy that is unavailable to do work.

The result is, for a system with sunlight concentration (lenses and mirrors and motors to follow the sun as it moves in the sky), the maximum efficiency is ~85%, and for a system that does not track the sun, the maximum efficiency is ~55%.

However, these are ideals, and the actual efficiency of solar panels do not reach these values – even in the laboratory. On the market today, the best solar panels money can buy have an efficiency of only 35%.

The essential question is this: How can we make photovoltaic solar panels more efficient?

One such solution draws from an old childhood pastime: holding a magnifying glass up so that sunlight is filtered through it and concentrated on a small surface area.

The magnifying glass has falling upon its surface area a certain amount of sunlight. As it passes through the lens, the sunlight – a form of energy – is then focused on a much smaller surface area. All this concentrated light means a high localized energy, which is enough to heat up and burn, say, a piece of paper. Its not so much the light itself, as what the lens does by focusing it.

Though magnifying lenses are too expensive to use on such a scale, mirrors can serve much the same purpose. However, even with this technique, solar panels can only produce energy equivalent to $0.11 per. Kilowatt-hour. As such, solar panels - as they currently exist - are far too inefficient and expensive to be used on a large scale.

References

     Byrnes, S. (2013, December 1). Maximum possible efficiency of a solar thermal energy system. Retrieved November 23, 2015, from http://sjbyrnes.com/ultimate_PV.html 

     Cummings, T. (2013, June 8). Lens Experiment. Retrieved November 24, 2015, from http://laser.physics.sunysb.edu/~thomas/report1/lens_report.html 

     Hall, N. (2015, May 5). Second Law of Thermodynamics. Retrieved November 25, 2015, from https://www.grc.nasa.gov/www/k-12/airplane/thermo2.html 

     Lewis, N. S. (2007). Toward cost-effective solar energy use. science,315(5813), 798-801.

Why Solar Panels?

A dessert collects more energy in six hours than the world uses in a year. So, why do we still use fossil fuels and other environmentally harmful energy sources?

Almost all of current human sources of energy originate from the sun. Coal, for example, is comprised of the fossilized remains of plants and animals, which got their energy directly from the sun. Following logic, because these forms of energy originate in the sun, and solar energy does the same but skips the mid-steps, it should be more efficient. It is more efficient, but it is not less expensive.

The photoelectric effect, or the observation that many metals emit electrons – and thus, energy – when light shines upon them was discovered as early as 1839 by Edmond Becquerel at 19 years old. 

When a rod of silicon is exposed to the sun, it emits electrons. However, it emits them in an amount not nearly enough to produce meaningful energy. Scientists then discovered that if the silicon is doped with phosphorus – giving it an abundance of electrons – and then is exposed to the sun, it emits many more. This is called N-type silicon, because it is negative. If the wafer is silicon is doped with Boron, it does not have enough electrons and is called P-typed silicon, where P stands for positive.

A typical solar panel is comprised of a wafer of N-type silicon and P-type silicon connected by a wire: 

Then, the system as a whole can be linked with any machine to which you'd like to supply energy. This can range from calculators to space stations. According to NASA, "more than an acre of solar arrays provide power to the station, and also make it the next brightest object in the sky after the moon."

References

        Davidson, M. (2015, November 13). Molecular Expressions: Science, Optics and You - Timeline - Alexandre Edmond Becquerel. Retrieved November 22, 2015, from http://micro.magnet.fsu.edu/optics/timeline/people/becquerel.

       Garcia, M. (2015, November 6). About the Space Station: Facts and Figures. Retrieved November 22, 2015, from http://www.nasa.gov/mission_pages/main/onthestation/facts_and_figures.

       Redarc Electronics. (n.d.). Retrieved November 22, 2015, from http://www.redarc.com.au/solar/about/solarpanels/.

       The Science of the Silicon Solar Cell. (n.d.). Retrieved November 22, 2015, from http://science.sbcc.edu/~physics/flash/siliconsolarcell/index.html.

Silicon Valley?

This year, I will be working in Jian Shi's research group - based in Rensselaer Polytechnic Institute's Department of Materials Science and Engineering.

This group is currently focused on studying and ameliorating the inefficiencies of solar panels. Solar panels have much potential as a more ecologically friendly method of harnessing energy, but are - as of now - far too inefficient to replace fossil fuels. Of course, the Second Law of Thermodynamics. According to Forbes, the highest theoretical efficiency of a solar panel is 85%. However, solar panels on the market are currently capped at 35%. This is, in part, due to the inefficiency of silicon, which is a photovoltaic solar panel's main component.

It will be exciting, as the year goes on, to test and study different ways in which we can increase the efficiency of solar panels - with a focus on discovering or creating alternatives to silicon.