Science of Energy: Solar
Solar energy is really hot these days, but many people don’t understand how solar panels create electricity from sunlight. The sun provides a huge amount of heat and light every day that can be converted into useable forms of electricity. In fact, the sun has been used by people since ancient times for keeping track of time and making fires.
Science of Energy: Solar
By Matthew Novak
Solar energy is really hot these days, but many people don’t understand how solar panels create electricity from sunlight. The sun provides a huge amount of heat and light every day that can be converted into useable forms of electricity. In fact, the sun has been used by people since ancient times for keeping track of time and making fires. Modern day applications use the sun’s energy to produce electricity that can be used to charge laptops, smartphones, and household appliances. According to the U.S. Energy Information Administration, only 1% of electricity generation comes from solar energy sources, but fortunately there is a lot of room for growth.
Back in the 19th Century, French scientist Edmond Becquerel discovered the process of converting sunlight to an electric current, using a positively charged semiconductor and negatively charged semiconductor. That conversion, known as the photovoltaic (PV) process, can be a highly technical process, and when used in modern day solar applications, involves solar cells made of silicon crystals, boron, and phosphorous that are grouped together on a solar panel. When light hits the solar panel, electrons within the silicon crystals get “excited” and are freed. Silicon is not a very good conductor of electricity, so it relies on other compounds within the cell to produce electricity. To create the electric current, you need a positive charge on one side and a negative charge on the other side. The positive charge is formed when boron is bonded to the silicon, and to produce a negative charge, phosphorous is added to the silicon crystals. Finally, an external electric circuit is added and the stage is set for electricity production from the sun. Excited, free electrons travel from the negative layer to the positive layer through the external circuit, which provides the owner with electricity. These photovoltaic solar panels are the main source of solar power used today.
Source: Union of Concerned Scientists, “How Solar Panels Work”
The other main, modern solar technology is concentrated solar power (CSP), which uses a simpler process with larger scale systems to harness solar energy for electricity generation. Two designs in CSP systems that have become the leading technologies are parabolic troughs and central receivers. Parabolic troughs are curved mirrors that concentrate light onto heat-transfer fluid in a horizontal tube that runs from the mirror to a central collector. The liquid is so hot that it produces steam, which turns a turbine that generates electricity. Similarly, the central receiver design uses a series of mirrors to concentrate sunlight onto a central tower. The heat produced boils a mixture of water and molten salt, which creates steam that spins a turbine to produce electricity. Molten salt is used in both designs, since the salt mixture can stay excessively hot for hours, allowing electricity generation to happen during periods of temporary cloud cover. The electricity produced by CSP travels through transmission lines to a power station, before being sent to residents and businesses.
PV and CSP systems provide electricity on different scales; therefore they are more suited for different applications. PV panels can be placed on rooftops or in urban solar parks, where they provide more direct access to the electricity, while CSP systems need a lot of open land with as much sunlight as possible, such as in the desert areas of the southwest U.S. CSP technology is often more efficient than PV, but must be located further from areas that use electricity. Distance is a major drawback to CSP, since electricity is lost over long distances, decreasing its overall efficiency. Both systems have issues with reliability, having low energy efficiency compared to fossil fuels, and being comprised of fragile materials that could be expensive to replace if broken.
Other drawbacks to solar energy include the often unstated environmental impacts. Large scale solar projects can pose land use issues and disrupt habitats for some animals nearby. CSP mirrors can become so hot they can hurt birds flying through the area. CSP systems also use a large amount of water, especially during steam cooling, but this has been mitigated in some cases by cooling the steam using air, instead of water. With increased understanding of site placements, habitat variability, and resource use, some of these impacts can be avoided.
While all of these drawbacks may seem daunting, there are many benefits to solar power that make it a great resource. It is renewable, meaning that the sun can provide an inexhaustible amount of energy and is considered a clean energy because it does not increase greenhouse gas emissions. The deployment of solar power is increasing rapidly with grants and incentives available for residents and businesses that want to install solar systems, which means that it is well suited for distributed generation. Distributed power generation is when power is produced on or near the site where it will be used so its production is spread out around a region. This would help avoid large scale blackouts and other problems that can come from an overload of demand on a centralized power plant. Currently, solar only accounts for a small percentage of total energy production, and while this is mainly due to the historically high price of solar energy systems, government subsidies such as the Solar Investment Tax Credit (ITC), plus growing concern for the environment, have significantly increased solar energy investment. This increased investment has more than doubled the amount of workers in the solar industry, which currently employs over 200,000 people in the United States.
Solar energy systems and the solar industry are growing rapidly, despite high costs and drawbacks. Since PV and CSP systems provide electricity generation on different scales, there is no definitive better system for every situation. Learning about an area’s possible urban and rural applications could provide answers about solar electricity generation for that city or region. Concern for the environment coupled with an increase in global electricity use will make solar energy (along with other sources of renewable energy) ever more important. Dare I say, solar energy has a bright future!
“How does solar power work?” Scientific American. Accessed September 22, 2016. http://www.scientificamerican.com/article/how-does-solar-power-work/
“How Solar Energy Works” Union of Concerned Scientists. Accessed September 22. 2016. http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-solar-energy-works.html#.V-RCn_ArLIU
“Solar Explained” U.S. Energy Information Administration. Accessed September 22, 2016. http://www.eia.gov/energyexplained/index.cfm?page=solar_home
“Solar Industry Data” Solar Energy Industries Association. Accessed September 22, 2016. http://www.seia.org/research-resources/solar-industry-data
“Solar Photovoltaics: Pros and Cons” Triple Pundit. Accessed September 27, 2016. http://www.triplepundit.com/special/energy-options-pros-and-cons/solar-photovoltaics-pros-cons/
“The History of Solar” U.S. Department of Energy. Accessed September 29, 2016. https://www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf
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