March 12, 2013
The Life Cycle of a Solar Panel: An Evaluation of Prime Materials
From 92,960,000 miles away, the sun’s radiation reaches earth and provides more energy in one hour than the global economy uses in one year, according to NASA (Gies 1). It is no surprise why humans have tried to harness this free, clean, renewable, and consistent energy source since the seventh century BCE (The History of Solar 1). Even so, after thousands of years, this energy source remains virtually “untapped” due to the inability to efficiently harness, convert, and transport the sun’s radiation in an efficient, inexpensive, or replicable manner. Today, solar power supplies less than 0.01% of America’s electricity (Zehner 20). Ozzie Zehner, author of the book Green Illusions, blames the lack of tangible success on the enormous economic, environmental, and unrealistic costs that accompany solar power’s widespread use.
Zehner estimates that powering the world with solar panels would cost upwards of $64 trillion plus an additional $694 billion per year of maintenance expenses. The GDP of the United States is only worth about $14 trillion (Zehner 9). Even with improvements in technological advances and economies of scale, the California Energy Commission claims that cheaper photovoltaic cells will not offset non-technological costs such as insurance, warranties, materials, transportation, labor, and environmental externalities. Zehner concludes that the environmental and economic benefits of solar cells are “insignificant compared to the expense of realizing them” (Zehner 30). Despite high praise from scientists, environmentalists, and politicians alike, the future looks bleak for the solar industry.
To construct a solar panel, a company must access and process prime materials, demand energy to manufacture, install, and maintain its infrastructure, and control its emissions and waste throughout the solar panel’s life. However, as sustainable as solar power claims to be, the prime materials needed for construction will limit our ability to produce clean energy. Metals used in technology require mining, collecting, cleaning, purifying, refining, melding, cutting, and assembling to be of any use. These processes are extremely energy intensive and harm our environment to the extent that wide use of solar power should be in question. It all goes back to materials that go into the fabrication (Williams 2).
A standard photovoltaic cell is an electricity-producing device that uses the photoelectric effect to absorb light and convert it to usable electricity. The absorbed light excites the cell’s electrons and causes them to flow in an electrical circuit. The size of a cell can range from a postage stamp to about 4 inches across. Several cells juxtaposed become a photovoltaic module system complete with electric connections, mounting hardware, and batteries ("Photovoltaic Cells" 3). Historians credit the technological development to Alexandre-Edmond Becquerel for the discovery that certain light-induced chemical reactions produce electrical currents. However, it was not until 1940 that solid-state diodes emerged, and the scaffolding of modern photovoltaic cells was formed (Zehner 7).
The cell is composed of seven thinly sliced layers. The first surface is a layer of tempered anti-glare glass. Tempered glass is much stronger than standard glass and prevents clouding from excessive heat and breakage from harmful weather. Clouded glass restricts the amount of radiation penetrating the cell and broken glass can lead to detrimental moisture exposure and possibly electrical fires. Tempered glass is industrially produced from annealed glass heated to over 720 degrees, then quickly cooled with air drafts. An alternative method involves chemically inducing a sodium and potassium ion exchange to strengthen the material (Long 2). The glass itself is derived from silica sand, also known as quartz sand. With the addition of soda (sodium carbonate) as well as manganese dioxide, the mixture will become glass at approximately 1,500 degrees Celsius. The glass is then cut to about three millimeters thick (Fthenakis 4).
Under the glass is a second protective module encapsulate of ethylene vinyl acetate, also known as EVA. EVA is a copolymer of ethylene and vinyl acetate that is soft and flexible, yet processed by vacuum lamination like other thermoplastics. The material is known for its glossy clarity and serves as an excellent moisture barrier and adhesive. Its chemical properties include resistance to UV radiation and heat-induced stress cracking (Kempe 2160). However, studies from the Photovoltaic Energy Conversion in 2006 found that excessive exposure to atmospheric moisture along with UV radiation can cause EVA to decompose, producing acetic acid, a corrosive substance that can damage solar cells. Also, EVA may transition into an inflexible glass solid at temperatures below -15 degrees Celsius, therefore increasing the likelihood to break in extreme weather. EVA is relatively inexpensive, but the compound might not be a sufficient encapsulate for newer thin silicon cells (Kempe 2161). Developments are necessary to create a safe and temperature independent substance that can properly protect the cells.
The third layer consists of the antireflective coating with conductor lines made of several rare metals such as cadmium, gallium, germanium, indium, selenium, and tellurium. Almost all cadmium is derived as a byproduct from processing sphalerite, a zinc sulfide ore, which contains large amounts of cadmium, indium, lead, and several other trace elements. In 2008, China, Peru, and Australia dominated cadmium production (Bleiwas 4). 19,600 metric tons were produced internationally in 2008, and 20% of the production was from the recycling of nickel-cadmium batteries. However, thousands of tons of cadmium are not recovered and discarded as waste because of its relatively low price and low demand. The availability of cadmium is generally not a present concern, but the purification necessary for application needs to be 99.999% pure (Bleiwas 4).
Gallium is an impure byproduct that is recovered during the processing of bauxite ore into alumina, a precursor to aluminum. In 2008, only 111 metric tons were produced, which is 30% below production capacity. Most gallium is also disposed of as waste because of low international demand. A demand increase is expected, as more products require the metal, such as LED lights and solar cells. Unfortunately, less than 1% gallium is recycled from obsolete materials (Bleiwas 5). Another metal, germanium is recovered while refining zinc. In 2007, there was an international germanium shortage because zinc production reduced due to the global financial crisis (Bleiwas 5).
In 2008, 570 metric tons of Indium was retrieved as a side product of refining zinc ores mined and refined in China, Peru, and Australia. China alone recovers 55% of the world’s supply of indium and use it for domestic production. LCD screen production dominates 50% of primary indium output and an increase in the production of photovoltaic cells will consequently augment demand. The U.S. Department of the Interior and U.S. Geological Survey suggests that the recycling of electronic waste could lessen the gap in the supply (Bleiwas 5). The last two metals, selenium and tellurium, are retrieved from slimes that are produced from copper concentrates (Bleiwas 5). Both price and production of these metals will increase as technological demand grows exponentially. Unfortunately, nearly 100% of these rare metals are recycled once used.
The forth and fifth layers of the cell contain the essential silicon wafer. Silicon is a non-metallic semi-conducting metal that occupies 25.7% mass of the earth’s crust and is the second most abundant material on earth, second to oxygen (Islam 1). Silicon is found in nature as silicon dioxide (SO2), and is also known as silica or quartz, a common component of sand. Availability is not generally a concern, but mining has harmful environmental effects and also requires a great amount of energy driven by additional primary materials (Islam 1). The Mammoth Lakes Geothermal Plant in California has developed a cost-effective method to extract silica (Bourcier 1). The process is a type of solution mining, concentrating the silica to over 600 ppm using a reverse osmosis process. The collection of the compound would provide additional revenue for the plant, reducing the cost of geothermal energy production by about 1.0 cent per kilowatt-hour annually (Bourcier 3). Solution mining requires little energy and eliminates the environmental damages that accompany typical surface mining. The concentration method could possibly be used for Lithium, Cesium, and Rubidium as well. Geothermal is another reliable source of renewable energy, so the accompaniment with silica solution mining is a sustainable way to access primary materials (Bourcier 4). However, in order for silica or any other metal material to be usable for metallurgical or electrical needs, the material must be purified through an extremely energy intensive process (Islam 2).
Metallurgical grade is 98-99% pure silicon and is produced by a reaction of high purity silica and charcoal, heated by either wood or coal in an electric arc furnace with graphite electrodes. The furnace is heated to over 1900 degrees Celsius. The metal melts and the carbon reduces the molten silica and collects at the bottom of the furnace. The impurities that remain include iron, aluminum, titanium, canadium, boron, and phosphorus (Islam 1). To further purify silicon to solar-grade (99.9999%), there are several competing processes, but the most common is the Siemens process. The Siemens process is the hydrogenous reduction of tricholosilane (SiHCl3). The reaction involves highly corrosive and toxic materials such as hydrochloric acid (Islam 3). Overall, the process is costly and has low productivity. Researchers are looking for alternative methods of production that skip the formation of energy intensive chlorosilanes to increase the efficiency of the reaction by five times (Islam 4).
Next, the solar-grade silicon is made into monocrystalline silicon crystal, multicrystalline silicon ingot, or multicrystalline silicon ribbons, depending on the desired result. The material is sliced into 0.2 mm thick wafers then bombarded with atoms to adjust its conductivity through a process called “doping” (Fthenakis 4). The fourth layer is doped with phosphorus and the fifth layer is doped with boron, creating the cell’s p-n junction, that act similarly to the plus and minus ends of a battery. The flow of electrons within the doped silicon semi-conductor is how the electric current is established (Fthenakis 5). In 2009, silicon-based photovoltaic cells held 57% of the market share (Gies 1). On average, silicon photovoltaic cells convert about 15% of absorbed light to electricity (Islam 2).
Following the silicon wafer is an additional layer of ethylene vinyl acetate for protection. The protective layer also contains the rare metals mentioned above. The final layer is the back sheet of the cell, made out of a polyvinyl fluoride film, primarily used to reduce flammability in airplane interiors and in photovoltaic cells. Polyvinyl fluoride film has a low permeability for vapors, burns slowly, and has excellent resistance to weathering and staining. The material is inert, meaning resistant to chemical reactions, and flexible (Simril 62). Now that the solar cell is constructed, the installation of the solar panel’s infrastructure also calls for additional raw materials (Fthenakis 5).
Several solar cells fused together create a photovoltaic module and are installed with an inverter, cabling, and mounting system (Fthenakis 6). Copper is used for electrical wiring, and the mounting structure is composed of iron, zinc, aluminum, nickel, steel, and zinc. Concrete is used for stability or planting the module into the ground (Islam 4). Countless more materials are involved in the delivery, wiring, and transportation that go beyond the scope of a photovoltaic life cycle. One of the major limiting restrictions to establishing solar panel plants is that the electricity must be transported to cities with major infrastructure, land use investments, and delivery networks. Lack of funding and financial incentive has prevented infrastructure development and would require enormous additional energy and material contributions.
The life expectancy of a solar panel is about 20 to 30 years due to intense weathering and damage from haze, humidity, soiling, misalignment, temp sensitivity, and aging. These unavoidable problems decrease output by about 1% or more per year (Zehner 22). Since the widespread use of solar panels only became popular in recent decades, modules are just now becoming obsolete. A uniform recycling system has yet to be established, but new companies, such as PV Recycling, are emerging to dispose and reuse old panels. Solar cells contain toxic and environmentally harmful substances, including silicon tetrachloride, selenium, cadmium, and sulfur hexafluoride, so careful processing and disposal are necessary to remain beneficial to society. In 2009, Greentech Media predicted that United States’ demand for solar will increase by about 50% per year through 2012, which will eventually create immense waste and must be met by large, centralized processing facilities (Gies 1). Incentive to recycle is low due to little research and the external reprocessing costs, however, Sheila Davis, executive director of the Silicon Valley Toxics Coalition, states that:
If you don’t look at the recycling when you’re designing the product, then it’s really, really difficult to recycle. But if you know you’re going to have to pay for recycling at the end of life, you might make the necessary design changes in your product now to reduce the cost. (Gies 1)
Manufacturers now look to designers to not only reduce costs and materials, but also create a sustainable and readily recyclable product.
Grand improvements in material and energy utilization in manufacturing will help solar panel’s environmental profiles. Although renewable energy is not as economical as coal, natural gas or nuclear power, a decrease in “price per watt” must occur for any alternative energy source to achieve a notable role in commercial usage (Mitrašinović 3603). Engineers are developing several innovations to increase efficiency and reduce material usage and emissions; for example, efforts are being made to reduce silicon wafer thickness (Fthenakis 4). The reduction would decrease the amount of materials being processed or recycled, but according to Zehner, these newer thin film cells degrade even faster (Zehner 22) and would require a replacement of EVA as an encapsulate (Kempe 2160).
In addition, designers need to develop a low energy, high capacity process for solar-grade silicon purification that avoids the energy demanding Siemens process. A direct metallurgical route would be five times more energy efficient according to Hammond and Gamble’s findings in the Renewable and Sustainable Energy Reviews published in 2011 (Mitrašinović 3604). Already, companies like Calisolar and 6Nsilicon are refining with metallurgical techniques. These improvements with increased production capacities and improved quality of feedstock silicon caused solar-grade silicon’s price to drop from six to three dollars in the last ten years (Mitrašinović 3605).
At present, the sun excites one electron per photon of light that strikes the solar panel. Solar panel efficiencies would increase substantially if the next cell generation could excite more than one electron. The National Renewable Energy Lab in Golden Colorado is working on silicon nanocrystals that can excite two or three electrons per photon, but the results are still theoretical (Mitrašinović 3606). Some developers are shifting from silicon-based cells because of the metal’s limited peak theoretical efficiency at 29%. Inexpensive alternative solar cells are created from thin films of semiconductors such as cadmium telluride and copper-indium diselenide. Scientists are even conducting research to create an organic solar cell (Mitrašinović 3606). The conquest for the solar power’s future is in the hands of designers, scientists, and engineers to create a 100% sustainable product from cradle to cradle. Even if solar power is not the answer to the earth’s energy needs, continuous research and awareness of truly renewable sources are vital for our society’s sustainability.
It is important to remember that society’s best attempt at being environmentally friendly is to consume less, not to produce more, even if the product is “more efficient.” As a society, we should not let clean energy and technology act as an excuse to avoid reducing our waste. When the earth eventually runs out of prime materials, our society will cease to exist as we live today. Several private billionaire-backed companies, such as Planetary Resources, are going so far as to mine the moon and asteroids for materials (David 1)! Does our exploitation have to continue like this? We need to dramatically rethink the way our society uses prime materials. Less is more!
Bleiwas, Donald. United States of America. U.S. Department of the Interior and U.S. Geological Survey. Byproduct Mineral Commodities Used for the Production of Photovoltaic Cells: U.S. Geological Survey Circular 1365. USGS: Science for a Changing World, 2010. Web.
Bourcier, W., W. Ralph, M. Johnson, C. Bruton, and P. Gutierrez. Silica Extraction at Mammoth Lakes, California. Rep. no. UCRL-PROC-224427. Lawrence Livermore National Laboratory, 14 Sept. 2006. Web.
David, Leonard. "MNN - Mother Nature Network." MNN - Mother Nature Network. SPACE.com, 26 June 2012. Web. 13 Mar. 2013.
Fthenakis, V., H. C. Kim, R. Frischknecht, M. Raugei, P. Sinha, and M. Stucki. Life Cycle Inventories and Life Cycle Assessment of Photovoltaic Systems. Rep. no. T12-02:2011. International Energy Agency (IEA), Oct. 2011. Web.
Gies, Erica. "Solar Waste Recycling: Can the Industry Stay Green?" The Huffington Post. TheHuffingtonPost.com, 11 Aug. 2010. Web. 13 Mar. 2013.
Islam, Md Saiful, Muhammad A. Rhamdhani, and Geoffrey A. Brooks. "Solar-Grade Silicon: Current and Alternative Production Routes." Swinburne University of Technology, Melbourne, Victoria, Australia, 2011. Web.
Kempe, M.D.; Jorgensen, G.J.; Terwilliger, K.M.; McMahon, T.J.; Kennedy, C.E.; Borek, T.T., "Ethylene-Vinyl Acetate Potential Problems for Photovoltaic Packaging," Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on , vol.2, no., pp.2160,2163, May 2006
Long, Bernard. "Tempered Glass Article and Method." U.S. Patent No. 2,177,324. 24 Oct. 1939.
Mitrašinović, Aleksandar. Photo-catalytic properties of silicon and its future in photovoltaic applications, Renewable and Sustainable Energy Reviews, Volume 15, Issue 8, October 2011, Pages 3603-3607, ISSN 1364-0321, 10.1016/j.rser.2011.05.017.
"Photovoltaic Cells." Energy Basics: Energy Efficiency and Renewable Energy. U.S. Department of Energy, n.d. Web. 06 Mar. 2013.
Simril, V. L., and Barbara A. Curry. "The Properties of Polyvinyl Fluoride Film." Journal of Applied Polymer Science 4.10 (1960): 62-68. Print.
United States of America. U.S. Department of Energy. The History of Solar. Energy Efficiency and Renewable Energy, 2002. Web.
Williams, Tyler, Jon Guice, and Jennifer Coyle. "Strengthening the Environmental Case for Photovoltaics: A Life-Cycle Analysis." Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on. Vol. 2. IEEE, 2006.
Yewdall, Zeke, and Sam Ley. PV Module Anatomy. Digital image. Renewable Energy & Efficiency Technologies. Home Power Magazine, n.d. Web. 06 Mar. 2013.
Zehner, Ozzie. "Chapter 1: Solar Cells and Other Fairy Tales." Green Illusions: The Dirty Secrets of Clean Energy and the Future of Environmentalism. Lincoln: University of Nebraska, 2012. 3-30. Print.
Des 40 A Winter 2013
Wastes and Emissions of Solar Panels
It has almost become a cliché at this point, but still the phrase, “don't believe everything you read on the Internet” holds true. This phrase holds true because the internet is flooded with opinionated blogs, articles, and stories that are often uncredible. While the Internet may have its fair share of unreliable sources, it remains an enormous trough of knowledge, covering almost any subject. In researching a subject that is easy to find the “right” side to argue on, finding academically sound papers criticizing the use of solar panels was a difficult task. So difficult in fact, that the first academic source I found mentions the “end of the internet” on the subject. While it can be difficult to find credible sources on controversial subject matter, the information is out there, and I have thoroughly enjoyed researching and learning about the darker shades of green in renewable energy.
Aside from the initial start up cost, solar panels seem like a no brainer. they are much more environmentally friendly than the burning of fossil fuels, and they provide site specific energy. So instead of producing energy at a plant using coal or natural gas, and piping the energy over miles, which reduces efficiency, solar panels are placed on top of or near the building they will provide energy for. Once installed, the solar panels generally last 20-25 years, providing renewable energy for the lifetime of the panels. This in addition to the savings, doesn't leave much to question: as a capable citizen, the opportunity to help the planet free itself from dependence on fossil fuels seems it should be taken with little hesitation. But, like we learned with the Prius, eventually information will come out regarding the dark and dirty secrets that are in fact far from green, and are in fact harming the planet in different ways.
The purpose of this paper is to explore the wastes and emissions produced during all three phases of the life of a solar panel. From production, to use, and finally to disposal, I seek to explore the wastes and emissions produced, and their impact on humanity, the environment, and the atmosphere. While solar energy only provides a very small percentage of our national energy production, the effects are there nonetheless. Solar panels are far better to the environment during their use than any form of fossil fuel energy, emitting extremely low levels of pollutants and toxins. However it is in their production that solar panels pose a threat to the environment, additionally after 25 years those solar panels only add to the growing amount of electronic waste on this earth. By looking at the three phases of a solar panels life, one will find that solar panels are a double edge sword, with drawbacks that can harm the environment as much as they benefit it.
While the use of solar panels can reduce ones CO2 emissions immensely, the manufacturing process of solar panels produces greenhouse gas giants that you’ve never even heard before, and if you have, you already know their astronomical impact. Additionally, the assembly of a solar panel system includes transportation, which contributes to Co2 emissions, and requires a number of other resources to build the facilities. During the manufacturing process of the solar cells a number of chemical compounds are produced, in a cloud of a very dangerous dust. While production is contained, it is inevitable that some of these chemicals get out. One of the most significant of the chemical compounds is Nitrogen Trifluoride, or NF3, a greenhouse gas giant 17,000 times more potent than carbon dioxide. Additionally, the production of some panels even involves the use of the gas Sulfur Hexafluoride, the most potent greenhouse gas known to science. In addition to greenhouse gasses, toxins produced during the construction of solar panels are even labeled carcinogens, specifically Cadmium, which is characterized as an extreme toxin by the U.S. Environmental protection agency, and a Group 1 carcinogen by the International Agency for Research on Cancer. Additional raw materials required for the production of solar panels include: Silica, Gallium, Germanium, indium, Selenium, Tellurium, Phosphorus, and Boron. Scientist have noticed an increase in the atmospheric presence of some of these chemicals, although they do not directly relate this increase to solar panels, the production processes of solar panels does not help these numbers.
While the facts on the toxins are beginning to become more common knowledge, and U.S. companies are trying to lessen their environmental impact, because solar panels are often produced in countries with less stringent rules governing the production process and disposal, these negative effects are still significantly higher than they should be. For example, in china it was found that a company was cutting costs by dumping its toxic wastes in farmland over a period of years. According to the Washington post article that broke the story, the chemical was silicon tetrachloride, a bubbling white, highly toxic chemical that burns human skin on contact, destroys all plant life it comes near, and violently reacts with water. This example is an extreme and rare case, but it gives a disturbing visual to the environmental impact that solar panel production can have.
While the production of solar panels may harm the environment, their popularity can no doubt be attributed to their environmental benefit during their use. When compared to conventional energy methods, solar panels are far better to mother earth. The burning of fossil fuels produces a number of chemicals that are big contributing factors to acid rain, a thinning of the ozone layer, and Global Climate Change. When we compare the emissions of various chemicals by conventional energy methods and by solar panels, it is evident that across the board solar panels have far fewer emissions than do conventional energy methods. Although solar panels are significantly better to the environment than fossil fuels, no energy source is without its emissions, including solar panels. Kalogirou’s paper states that in the case in which a solar system with an electrical back up will produce only .40 tons of CO2 per year compared to the 1.982 tons produced by conventional energy methods. In the same table Kalogirou compares the emissions of solar systems and conventional energy methods, with solar systems generally emitting about 1/5th than that of conventional energy methods. Without a doubt, during their use, solar panels are a far greener alternative to any fossil fuel, and will also help you reduce your energy bill.
However, solar panels produce energy entirely dependent on the weather. Not only do the solar panels need to be in a location that will receive enough sun, but they also must me sure that the environment will not affect the performance of the panels. For instance, solar panels in the desert have been found to lose efficiency due to sand and debris pile up, and overheating of all things. Additionally, for most the people that have access to solar energy, it only provides seasonal energy. This however does not disregard the fact that solar panels reduce ones fossil fuel consumption and in turn helps reduce one’s Co2 emissions, and in the long term, help save money.
Although it is not something that is thought of everyday, electronic waste, or e-waste, is a growing problem. If you didn't already know the the reason why you get fined if you just throw your TV away in the trash, its because of the numerous chemical compounds and materials than go into the production of electronics such as TV’s, computers, and solar panels. As we noted earlier in the production portion of the paper, there are a number of chemical compounds, some of which are greenhouse gasses and carcinogens that cannot simply be disposed of or burned to be gotten rid of. If companies can set up effective recycling standards, the e-waste should not be an issue, however if this precaution is not taken, the risk of those disposed electronics being sent to third world countries for disassembly and disposal becomes significantly higher. While nobody can say for certain which disposal and recycling methods will be used, the problem e-waste is a train on the tracks, coming faster and louder with each solar panel produced. You can either get on or be left behind.
The problems associated with solar panel disposal are largely speculative at this time, simply because this is such a new technology. We can’t definitively say what the effects of solar waste will be, because we do not have solar waste yet. However, as noted with the case in China, if proper disposal or recycling techniques are not established, solar panels have the potential to greatly harm the environment. The best thing we can do is look at the raw materials that go into production, current electronic waste trends, and prepare a sound recycling method. If every solar company invested in a sound recycling method, it is likely that the harms associated with production and disposal would be reduced, creating an even greener energy.
When we take a step back to look at the bigger picture, solar panels are barely a blip on the national energy radar. With solar energy production contributing to less than one percent of the annual unites states energy consumption. While solar energy does provide better alternative to fossil fuels in term of emissions during their use, they are not perfect. The production of solar panels insoles chemicals compounds and gases far more harmful than Co2, as well as a number of additional chemicals and materials necessary production and assembly. Furthermore, the production of solar panels only adds to the tidal wave of electronic waste that future generations will have to deal with by establishing proper disposal and recycling techniques. Furthermore, solar panels only offer seasonal energy, and can only be effective in specific environments. Additionally, efficiency is drastically decreased if maintenance is neglected. Although all of this may seem very negative, the fact remains that solar panels are often a worthy investment. They offer a cheaper alternative to fossil fuels, and can save a family quite a bit on their electric bill. Often paying off their investment in less than ten years. In order to reduce the harm that solar energy production has on the environment, solar investors should be sure to work with a company with an established disposal or recycling plan.
Solar Panels Research Project
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Parkinson, Jonathan. "The Not-So-Sunny Side of Solar Panels." Voice of San Diego. Voice of San Diego, 16 Feb. 2009. Web. 02 Mar. 2013. <http://www.voiceofsandiego.org/science/article_37811382-9d69-5936-adeb- 5db1395225e3.html>.
Kalogirou, Aoteris A. "Environmental Benefits of Domestic Solar Energy Systems."ScienceDirect.com. Energy Conversion and Management, Nov. 2004. Web. 02 Mar. 2013. <http://www.sciencedirect.com/science/article/pii/S0196890404000160>.
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Benson, David B. , “Understanding Solar” Senior Sales Manager, Suntech America, 2/27/13
Tsoutsos, Theocharis, Nike Frantzeskaki, and Vassilis Gekas. "Environmental Impacts from the Solar Energy Technologies." ScienceDirect.com. Energy Policy, Feb. 2005. Web. 6 Mar. 2013. http://www.sciencedirect.com/science/article/pii/S0301421503002416
Beloin-saint-Piere, D. "Environmental Impact of PV Systems." Hal-ensmp.archives-ouvertes.fr. N.p., 2009. Web. 5 Mar. 2013. <http://hal-ensmp.archives- ouvertes.fr/docs/00/48/73/49/PDF/ Beloin-Saint- Pierre_Blanc_EU_PV_Hamburg_2009.pdf>.