Figure 1Mechanism of electron flow in solar cell 3
Figure 2 Structure of typical Photovoltaic solar cell 3
Figure 3 Types and efficiency of different PV cells 4
Figure 4: Laboratory scale efficiency associated with size of different PV cells in China 5
Figure 5 Working mechanism or Principle of Solar Cell (Rongqiang.2006) 6
Figure 6 Efficiency for different silicon cells having varying combinations 7
Figure 7: Pricing of different installed PV systems 9
Photovoltaics Solar Power
1. Introduction
The sun has been seen for decades as the center of the universe instead of an energy powerhouse. The immense energy of the sun serves a number of purposes ranging from triggering photosynthesis to the creation/or development of vitamin D in the human body. However, the researches in the field of solar power revealed that the sun is one of the major solutions needed by mankind in the quest to solving the problem of electric power.
The major source of power today is fossil fuel that pose an immense threat to man and his environment. These are producing pollutants, greenhouse gases that deplete the ozone layer, melt the polar caps, raises global temperature and cause untold health hazards. In order to exploit the immense energy of the sun, sustainable and clean power can be produced. Quite interestingly, solar power is already being commercially produced in numerous parts of the world and holds great prospect. Photovoltaic system is one of the fundamental concepts of solar energy conversion besides solar thermal system. Kuhne and Aulich (2013) explained that photovoltaic systems absorbs certain wavelengths of light in the solar spectrum and hence generates an electric current directly in the absorbing material. This study delineates at the past, present and future of photovoltaics as well as its relevance.
2. The Development of Photovoltaics
2.1 Discovery of the Photovoltaic Phenomena and First Solar Cell
In the early part of the 1900, scientists could not imagine how an object other than a black body could emit radiations when exposed to light. This made the development of the photoelectric effect rather slow even after William Grylls Adams and his student Richard Evans Day had discovered that the selenium exhibit photoelectric effect. Alexandre – Edmond Becquerel, a Frenched physicist, is given the credit as the first person to discover the photovoltaic effect. The experiment conducted in 1839, Becquerel discovered the photovoltaic effect by placing silver chloride in acidic solution and connecting platinum electrodes.Later on other scientists such as William Grylls and Willoughby Smith began researching on this phenomenon but many others were not interested in the research (“A Short History of Photovoltaic”,).
2.2 Theoretical Explanation and First Silicon Solar Cell
The work done by Albert Einstein in 1905 brought photovoltaic effect to limelight. Einstein, who won a noble prize for the work, explained that light consists of tiny packets also known as photons that have wavelength and frequency. He explained the wave-particle paradox nature of light and how light particles can knock off electrons from materials like silicon and selenium. These electrons flow through wires to produce electricity (“A Short History of Photovoltaic”, ). On their bid to improve silicon transistors for electrical equipment, Bell Laboratories scientists Calvin Fuller and Gerald Pearson accidentally created the first PV cell. This opened up a new possibility owing to the unique features of silicon and its ubiquity. Figure 1 and 2 are presenting the view and internal structure of solar cell.
Figure 1Mechanism of electron flow in solar cell (“The Benefits of Solar.”2011)
Figure 2 Structure of typical Photovoltaic solar cell (Rongqiang.2006)
2.3 First Usage of Photovoltaics
At preliminary stage of photovoltaic, scientists were feared that its deployment could have some negative consequences. However, the National Aeronautics and Space Administration termed "NASA" deployed the first photovoltaic in March 17, 1958. The PV cell powered radio transmitters that went on a satellite called Vanguard-I. The PV cell worked well and hence other countries such as Russia also followed suitability of PV cells in space (“A Short History of Photovoltaic”, 2009).
2.4 More Advanced Research
The success achieved in the deployment of photovoltaic power in the space spurred a number of advanced researches in this field. Till date, numerous researches still going on in the field of photovoltaics. One of the researches of interest is the high-speed copper-indium-gallium-selenium (CIGS) compounds. According to European Commission (2009), solar cells based on CIGS involved two main strategies namely evaporative and selenisation (“Photovoltaic Solar Energy” 2009. However, both processes have a drawback of being slow and hence low productivity. The productivity can be increased by gradually augmenting each module, but this leads to a very costly process, and it could be a very complex process. European Commission (2009) also pointed out other ongoing researches, some of which have been completed, in the field of photovoltaic. It includes PV-MIPS -photovoltaic module with integrated power conversion and interconnection system. Further examples include SELFLEX (SELF-formation based flexible solar cells manufacturing technology), Solar Plots, Solsilc Demonstrators, Tellurium, CdTe PV, Indium and germanium. (“Photovoltaic Solar Energy” 2009; Fthenakis et al., 2009).
Figure 3 Types and efficiency of different PV cells (Rongqiang)
2.5 Main Milestone for PV Deployment and Booming of PV Market
Photovoltaic is one of the most promising technologies in the twenty-first century. That is driven by numerous factors especially because of its nature as a clean technology. European Commission outlined that the photovoltaic is increasingly attractive as mankind explore avenues to reduce the menace of fossil fuel in the human environment. The burning of fossil fuel release a lot of pollutants and poisonous substances into the environment. The photovoltaic is clean, and it is one of the best alternatives to leverage (“Photovoltaic Solar Energy” 2009).
European Commission also mentioned that the photovoltaic market grew extensively in 2009 in countries like Germany, Greece, Spain, Italy and so forth. Irrespective of the extensive growth, there are still some barriers against the growth of photovoltaics and this is predominantly the high cost of electricity production with this system.
Nogarin (2010) reports a milestone photovoltaic project in Chile on the Calama 1 photovoltaic project. The project involves a 9MW plant which was approved by the government in January 2010. This was the first multi-megawatt solar facility in South America with an environmental license.
A greater milestone in Chile photovoltaic project is their recent 70 MW solar farm under construction. China is the leading country in photovoltaic as it deployed solar PV and wind in 2013 having capacity of 27.3 GW. The deployment of photovoltaics in the world today continues to rise alongside with other renewable powers. Renewable power capacity over the past 10 years has grown 85% reaching 1700 GW in 2013 (“Rethinking energy.” 2014).
Figure 4: Laboratory scale efficiency associated with size of different PV cells in China (Rongqiang)
3. Main Working Principle of Photovoltaic Cells
Photovoltaic cells, also known as photoelectric cells, operate on the principle of the photoelectric effect. Studies explained that during photoelectric effects, electrons are released from the surface of a metallic conductor by virtue of absorbing energy from light shining on the metal surface. The Figure 5 below explain the working principle of photovoltaic modules.
Figure 5 Working mechanism or Principle of Solar Cell (Rongqiang.2006)
Albert Einstein explained that the light consists of particles and behave both as a particle and as a wave. He explained that the energy of the light is dependent on its wavelength. Furthermore, if the light particles exceed a certain threshold frequency or wavelength depending on a particular material, they would be able to knock of electrons from that material. This is the principle on which photovoltaic cells function. When light fall on the cathode, electrons are liberated which are then attracted to the anode of opposite charge and hence current flows through the system
4. Types of PV Technologies
PV technologies comprise of many types of PV cells. The commercially available types include amorphous or thin film, polycrystalline, monocrystalline or single-crystal silicon.
Single-crystal and polycrystalline PV cells are categorized under crystalline silicon. The University of Queensland Australia stated that these PVs are classified based on the nature of the silicon that is used to create their substrates (“PV Cell Technology”.2014)
Single-crystal was first invented in 1955 followed by invention of polycrystalline silicon in 1981. In order to produce single crystalline silicon, continuous cylindrical crystals are sliced into circular wafers. One advantage of this particular type of cells is uniformity in color due to the utilization of same crystal material.
Polycrystalline cells are also made from the similar silicon material but apart from being grown into a single crystal, it is melted followed by pouring into a mold. The advantage of polycrystalline silicon over single-crystals is minimum wastage of material ("Types of PV," 2012). However, polycrystalline cells have a higher temperature de-rating factor than mocrystalline cells (“PV Cell Technology”.2014).
Amorphous, also known as thin film, solar panel is produced by the deposition of a thin layer of silicon using a base material such as metal or glass. In this case, the silicon has no regular crystalline structure and the manufacturing process is reasonably straightforward and also the panel produced relatively cheap. However, the major downside of amorphous silicon is its inefficient behavior as single-crystal silicon. More so, amorphous silicon has a disadvantage of having uncertain durability. The silicon is less stable than crystalline silicon and hence degradation can occur over time ("Types of PV," 2012). Efficiency of different silicon combinations is presented in Figure 7.
Figure 6 Efficiency for different silicon cells having varying combinations (“PV Cell Technology”.2014)
5. Advantages of PV over Conventional Methods of Generating Electricity
Photovoltaic cell technology has many benefits not only for being a sustainable technology but also for many other reasons.
Eco-friendly
The burning of fossil fuels like oil, coal and natural gas are the major cause of environmental pollution today. The use of a sustainable energy such as photovoltaic is the major solution to this menace. Our fragile environment can be protected if we take advantage of photovoltaic and other clean, sustainable and renewable energies (“The Benefits of Solar.”2011).The renewable energy such as photovoltaic offers a route to reducing greenhouse gas emissions which is a major cause of global warming today. In addition, renewable sources such as solar, wind, geothermal, bioenergy, nuclear, and hydroelectric are across their lifetime up to 10-120 times less carbon intensive than the cleanest fossil fuel. (“Rethinking energy.” 2014).
Low Maintenance Requirements
One of the major advantages of photovoltaic is its nominal or no cost for maintenance to run and operate unlike another source of power such as fossil fuel. This goes a long way to saving cost and ensure efficiency in the use of PV. The photovoltaic enjoys long life span. In other words, one can be rest assured that it would serve efficiently for quite a long time before requiring maintenance. More specifically, photovoltaics can last as much as 30 years and beyond (Rongqiang, 2006; “The Benefits of Solar.”2011)
No Moving Parts
Unlike other conventional sources of power, solar panels do not contain any moving part. This implies that the panels do not produce noise pollution. In contrast to solar panels, wind turbines require noisy gearboxes and blades and thus this is one of the edges solar energy has over wind power (Gromicko, 2014).
Renewable Raw Materials
The world supply of fossil fuel is running out with the passage of time. In fact, studies estimate the world supply of fossil fuel to last about 40 years. This is simply because fossil fuel is a non-renewable energy source. The reverse is the case with photovoltaics that is a renewable source of energy. Due to renewable, it implies that PV is simply limitless. Moreover, renewable energies reduce the risk of ecological disasters and do not deplete finite resources, although they may need water that becomes a problem in arid regions. Solar energy is quite abundant, even much more than what we need (“Rethinking energy.” 2014).
Provision of Employment Opportunity
One of the major benefits of renewable energies, which photovoltaic solar power facilitating is the creation of employment opportunity. The renewable energies facilitated in generating about 6.5 million direct and indirect jobs which include 2.6 million jobs in China. Among major renewable energies like solar PV, liquid biofuels, wind power, biogas, and geothermal; the solar PV has the highest statistics of employment as it generated up to 2, 273, 000 jobs. It is followed by liquid biomass that generated up to 1,453,000 jobs (“Rethinking energy.” 2014).
6. Environmental Impacts of PV
Even though photovoltaics are seen to have benign environmental impact, there are still some issues to be concerned with in the deployment of this technology.
Land Use
Tsoutsos et al. (2004) outlined that the construction of PV on land can result to some menaces. For instance, an application of a PV system in once-cultivable land is possible to effect soil productive areas. This is a major reason for the social disagreements and displeasures with the deployment of PVs. PV installation on cultivable lands have downsides including the fragmentation of the countryside, reduction of cultivable land, plant degradation. It also has a visual impact on the landscape, interference with fauna and flora and so forth (Chiabrando et al., 2009).
Routine and accidental discharge of pollutants
PVs does not emit any pollutant during their normal operations with the exception of the CIS and CdTe modules which include some toxic substances. However, “in large-scale central plants a release of these hazardous materials might occur as a result of abnormal plant operations, and it could pose a small risk to public and occupational health." (Tsoutsos et al. 2004).
Depletion of Natural Resources
Solar energy is a renewable source but the materials required in the construction of solar panels such as In/Te/Ga, Si PV modules and so forth are not renewable. Electricity generation with PV is energy intensive and thus large bulk materials are needed for the process. In addition, most of the materials required for the construction of PV are scarce. This leads to the depletion of the materials. Furthermore, some of the materials are toxic and hence the emission of these substances may harm the environment although the impact is significantly low when compared to fossil fuel.
7. Cost for Generating Electricity for PV
High initial cost of PV is the major drawback to its deployment. However, increased efficiencies and technology facilitate against cost. Moreover, increased electricity prices have boosted development PV cell. The decreasing cost of PV has made it viable solution in the context of price compared to fossil fuel in many nations of the world. The cost of renewable energies continues to plummet with passage of time. They argued that the reduced cost of renewable sources continues to be deployed irrespective of the 22% reduction in global renewable investments in the year 2013 (“Rethinking energy.” 2014).
Feldman et al. (2012) reported the continued decline in residential and commercial PV systems in the United States of America. The report outlined that cost of installed PV systems decrease with increase size of the system. In US, it declined 5 to 7 percent and 11 to 14 percent during the period of 1998 – 2011 and 2010 – 2011 respectively. The statistics provided in Figure 7 are illustrating this particular trend. The prices for solar PV cells declined by 65% - 70% between 2009 and 2013 irrespective of the stabilizing module prices in 2013. The cost also declined by 53% in Germany during this period, and similar cost reduction was observed in many other countries including France, Italy, Mexico and Spain (“Rethinking energy.” 2014).
Figure 7: Pricing of different installed PV systems (Feldman et al. 2012)
8. Conclusion
The paper examined the development and usage of photovoltaics. It talked about the discovery of solar cell, its theoretical explanation, and advanced research, milestones, working principles, types, benefits and environmental impacts. Solar cell is highly beneficial as it is eco-friendly, has low maintenance requirement, no moving parts, leverage renewable raw materials and also provides employment opportunity for a lot of people. Photovoltaics has a benign impact on the environment, but this does not imply that they do not have some impacts. Some of the impacts include the depletion of natural resources required in its construction, routine and accidental discharge of pollutants as well as the issue of land use.
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