Proceedings of the Fall 2018 ELEC 7830/36 Class Presentations

1) Zabihollah Ahmadi 2) Arthur Bond 3) Carl Bugg 4) Prattay Chowdhury 5) Jeff Craven 6) Kyle Daniels 7) Tanner Grider 8) Donald Hughes 9) Grant Kirby 10) Markus Kreitzer 11) Sanfwon Seo 12) Minseok Song 13) Wendong Wang 14) Shane Williams 15) Yuqiao Zhang

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Fabrication Methods of Photovoltaic Devices Zabihollah Ahmadi

A simple configuration of Solar Cells is a P-N junction, but even for fabrication of this simple configuration there are several experiments that should be done. In other words, fabrication processes involve the steps such as oxidation growth, etching oxides, photolithograph, and metal deposition. As an example, ion implantation is used for making n+ or p+ doping in Si wafer. In general, there are different kind of materials that are used for fabrication of Solar Cells. The most popular materials are Multijunction Cells ( lattice matched, metamorphic, inverted metamorphic, …), Single-Junction GaAs (Single crystal, Concentrator, thin-film crystal), Crystalline Si Cells, Thin films like CIGS and CdTe and Emerging PV (Dye-sensitized cells, Perovskite cells, Organic tandem cells, Inorganic cells, Quantum dot cells.) Recently, some groups used 2D mateirals like Graphene and Transition Metal Dichalcogenides (MoS2) in fabrication of Photovoltaics devices. So, these materials need to be synthesized on substrate using different methods. For example Metal Organic Chemical Vapor Deposition is the best method for deposition of GaAs. This presentation will talk about how these methods work in fabrication of PV.

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Photovoltaic Sensors

Arthur Bond

Photovoltaics or PV is the process of converting into a DC electrical current through the use of semi conductive materials. This technology has had a significant impact in the fields of energy and environmental protection, but one lesser known area that photovoltaics is found is in electronic sensors. This presentation will discuss the use of photovoltaic technology in sensor applications. The presentation will begin with an introduction to photovoltaics. This section will provide a brief description of the design and function of common photovoltaics cells types. After the introduction, additional material will be built on to the base design of the photovoltaic cells to derive the working principle of photovoltaic sensors. There are different iterations of this technology so a few common sensors designs will be presented. To see the use of this technology, real world examples will be introduced. How and why these sensors are used will discussed as well as the limitation that they have in their roles. The next section of the presentation will focus on how photovoltaic sensors compare to other types of sensors. These other types of sensor are devices that are used in the same role, but operate on a different design principle. The comparison will be based on the strengths and weaknesses of each sensor and their performances in various circumstances. The final section will discuss the opportunity that photovoltaic sensors have in future applications. This section will also present potential advancements that may improve the existing technology. Most of this section will be a speculation and may not go into substantial detail. Concluding the presentation will be brief recap of key points of photovoltaic sensors and references to outside material resources.

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A SINGLE FAMILY HOUSE IN THE U.S. with GRID TIED ROOF-TOP SOLAR PANELS

Carl R. Bugg

This project is a description of a single family house in the United States, with roof-top solar panels connected to the grid. I will provide a detailed explanation of all the components involved, starting with the selection of the solar panels, all the electronics, breakers, etc. A grid-tied solar system generates energy from the sun and stores it in the utility grid, so you can use it anytime you need it. With access to the utility grid, your main concern is getting the most value from your investment; grid-tied solar is the way to go. It has the lowest upfront cost because you don’t have to buy batteries to store the power you generate. The grid takes care of storage for you. During peak hours, you may generate more electricity than you need to power your home. In most states, you can sell this excess power to the utility company, which stretches the value of your investment even further. This project defines the home size and location, the PV Panels selected, the mounting system, the wiring from the PV Panels, arrangement of strings, DC anti-surge devices, PV combiner units, DC disconnect switches, Grid tie inverters with MPPTs, Islanding prevention system, AC breakers, AC anti-surge device and the power utility’s net metering system. The project summary includes the PV system performance, net income and return on investment.

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The in Europe and its Current Status

Prattay Chowdhury

Major power sources like coal, oil, natural gas and other petroleum are being used extensively by the human. It will lead to the shortage of petroleum, and so sources for power generation is becoming popular day by day. Of all the renewable energy sources solar energy is the most popular as its readily available. Extensive research is going on photovoltaics throughout the world to exploit , and it has started contributing to the total world power generation. But no other region in the world is more successful in photovoltaics than Europe. In the last two decades, Europe has been a prominent example of solar power generation using photovoltaics. Germany, a leader in the photovoltaics power revolution, shares a significant contribution (about 42% of total EU solar power) to it. Approximately 1.5 million is installed in this country. European Union countries produce the highest amount of photovoltaics power in combined in the world. Major projects are being installed to increase the amount, and per capita consumption in the European area is also higher than the rest of the world. Two countries: Germany and Italy are the dominant player in photovoltaic power generation. Even smaller European countries are developing photovoltaics very fast. Denmark has already reached its goal of generating 200MW power from photovoltaics by 2020 in 2012. It is forecasted to reach 1000MW by 2020 in Denmark. Croatia which lags behind the other European countries in photovoltaic has targeted to generate at least 500MW by 2020. Some other motivating factors are helping to boom photovoltaic in Europe. For example, the French government is planning to reduce nuclear power reduction from 75% to 50% by 2025 and photovoltaic is expected to replace it. European companies are performing research to manufacture cheaper PV cell to meet the growing demand. Recently EU has lifted the five-year-old restrictions on Chinese import to meet up the demand of photovoltaics in the region. The presentation includes Europe’s photovoltaics history and the major projects and plans that made Europe a leader in PV power. It contains the current scenario of PV power generation and usage. It also shows the future of PV in Europe from generation and demand forecast.

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Solar Power: A Solution to the Fossil Fuel Problem, But Not the Only or Best Solution Jeff Craven II

Photovoltaic devices offer much promise and hope to the fossil fuel problem. The devices are becoming more readily available, efficient, and cheaper every day. They also are a great alternative to fossil fuels in that the sun is always shining and is, for all intents and purposes, a limitless source of clean energy. However, the positives of photovoltaic devices do not come without their drawbacks, as is the same for most promising technologies. For the most part, the drawbacks of solar cells are only problematic at large scales. Unfortunately, in order to solve the fossil fuel dependence of not only the United States but also other countries, a large-scale solution is the only solution. Because of this a large drawback of solar cells is simply unavoidable: practicality. On smaller scales solar cells offer much cheaper energy and can even allow for residents to make enough electricity that they can, in fact, sell the energy back to the power companies in some instances. But on larger scales, solar cells become problematic in that they require larger and larger areas for solar coverage. Not only this, but the solar energy available at different latitudes can also very significantly, particularly at higher latitudes in which the sun shines less intensely and for shorter amounts of time during the day. One solution to this is to simply place the cells in a sunnier location and send the power to the other parts of the country. Unfortunately, this is not only not practical, but it is also extremely inefficient. The reason for this is line loss from the transmission lines- as transmission lines get longer, they lose more and more of their energy and it is dissipated as heat, which is precisely what clean energy is supposed to prevent in the first place. Thus, due to losses more energy will be required which leads to a larger area required. In the presentation I will cover the basic mathematics behind solar cells, their average energy absorbed by the sun, and what energy requirements are required to power the United States alone for a year. I will also discuss the problem of scale with the solar panels, primarily by showing varying images of the sizes of the necessary solar array sizes in comparison to maps of the United States and Alabama. In the presentation it will become readily apparent that solar energy as the only alternative is simply not the solution to the fossil fuel problem based on the scale of the arrays, but it is very much one of the solutions to the problem.

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History of Photovoltaic Technology

Kyle Daniels

Photovoltaic technology has been around longer than most people think. The technology has evolved a lot over the centuries. Photovoltaic technologies started with making fires with magnifying glasses and advancing to tiny solar panels being stitched into the fabric of clothing. Photovoltaics technologies have been created by some highly distinguished, some unfamiliar and even ancient individuals. Horace De Saussure created the Solar Cooker which is normally credited with being the first milestone of solar technologies. Albert Einstein won a Nobel Prize in Physics for his discovery of the law of the . De Saussure, Einstein, and many more lead the way for the birth of photovoltaic technology. 1954 the first silicon photovoltaic cell was created by Daryl Chapin, Calvin Fuller and Gerald Pearson at . The technology just keeps evolving. Solar energy has an abundance source (sun) and is clean for the environment. Unfortunately, solar panels can be considered eye sores and take up space. Many modern photovoltaic technology applications are solar panels to power houses, solar farms and solar reflectors to light up dark roads. Many investments are being made in this technology. Therefore, there is much to research and develop for photovoltaic technologies. It is important to understand past photovoltaic technologies in order to advance and improve ideas. Photovoltaic technology future is bright and here to stay.

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Power Electronics for Photovoltaic Devices and Systems

Tanner Grider

Power Electronics are a necessity in order to increase the application of Photovoltaic devices and systems. They allow us to change the magnitude of voltage up or down depending on our need and allow us to convert between DC and AC voltage values. These are accomplished using Buck, Boost, Buck/Boost and DC-AC Converters. In this presentation, we will limit the scope to H- Bridge and Six-step DC-AC inverters for use in Three phase PV Systems, and examine the use of the three types of DC-DC converts listed above in these systems. The result being identifying appropriate areas to implement each technology.

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Use and Integration of Photovoltaic Systems In Industrial Power Systems

Donald G Hughes

As the technology for photovoltaic (PV) systems has evolved in recent years, not only has the efficiency of the cells improved, but the cost of purchasing and installing a PV system has dropped to the point where adding a PV system to an existing system can be an economically beneficial endeavor. PV systems have experienced an increased usage in all market segments. Because of their lower power demand and slowly varying load profile, PV system usage in residential and commercial applications are easier to justify and design. However, integration into industrial power systems require careful consideration from both economic and technical perspectives.

Industrial facilities usually have processes that involve large, varying power loads that can have poor power factor and generate harmonics. Coordinating the addition of a power supply system such as photovoltaic which itself has a varying supply characteristic can be challenging.

This presentation will contain information regarding the history and current trend in incorporating photovoltaic systems into power systems at industrial facilities. The information will include typical economic considerations for adding a photovoltaic system as well as information on the technical considerations and regulations for interconnecting the photovoltaic system into the facility’s power system. In addition, I will present information from a case study at Daikin America in Decatur, AL. The justifications used at this facility will be compared to another facility where a PV system cannot be justified.

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Auburn University’s Electrical Energy Consumption and PV Supplementation Grant Kirby The campus of Auburn University is comprised of nearly 2000 acres of land, housing over 300 buildings, and has a student enrollment of more than 30,000. Consequently, Auburn consumes a tremendous amount of electrical energy; however, the institution does not generate any of its own power. Three main substations, operated and maintained by Alabama Power, serve as the primary grid supply source for the campus’ electrical needs. Alabama Power has shifted away from coal- fired energy generation, which contributes to harmful greenhouse gas emissions. However, it would benefit Auburn to explore alternative, environmentally-friendly energy sources, such as a photovoltaic (PV) solar array to supplement its overall energy consumption. The primary aim of this project was 2-fold: 1.) Assess the overall electrical energy consumption of the campus highlighting the building or college that consumes the largest amount of electricity, and 2.) Examine an existing PV proposal for Auburn that includes the following parameters: cost, payback timeline, overall power output, efficiencies, and layout. These aims were approved by the Auburn University Utilities and Energy (U&E) Department. eSight Energy Express, an online energy analysis software, was utilized to glean data regarding total and building-specific energy consumption on campus. The PV proposal was provided by U&E’s onsite energy engineer. For fiscal year 2017, the entire campus consumed 188,340,185 kilowatt hours (kWh). Certain campus buildings consume a disproportionately large amount of electrical energy when compared with the total consumption overall. Not surprisingly, the largest consumers of electrical energy were the central energy plants, which consumed more than twenty-five percent of the total electrical energy for the campus. They are tasked with heating and cooling the campus, a significant energy load. Outside of this consumption, however, certain buildings still represent a notable portion of the consumption, typically between one and three percent. Jordan-Hare Stadium, for instance, is just over three percent of total consumption. In 2016, a project proposal for a photovoltaic carport system was presented to Auburn University. The proposed cost for the project was $18.5 million and would have directly supplemented the electrical needs of the campus with more than 6.5 million kilowatt hours of electricity annually, representing greater than three percent of total consumption. This proposal illustrates the meaningful energy contribution that PV systems can provide for Auburn University. However, the costs for a project of this magnitude would not be recouped for nearly 20 years which represents a significant barrier to implementation.

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Abstract Markus Kreitzer As the price of photovoltaic cells continues to drop, other parts of the system's price per watt, and therefore efficiency, becomes increasingly important. Traditional methods for maximum power point tracking (MPPT) are effective for controlling the output power to batteries, microgrids, and national level smart grids. However, new robust and reliable machine learning methods using "artificial intelligence" are bringing faster performance to maximum power point tracking, especially under conditions which are hard to predict. We will review some of the machine learning based mathematical approaches to solving this problem, and highlight some of their advantages and disadvantages. We will also go over the basic theory of some of these methods. The methods include: Artificial Neural Networks, Fuzzy Logic Control, Particle Swarm Optimization, Anto Colony Optimization, Genetic Algorithms, Differential Evolution, and if time permits, Radial Movement Optimization, Cuckoo Search, Grey Wolf, and Firefly Optimization.

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Investigation on voltage stability of a grid-connected PV with battery energy system in distribution network

Sangwon Seo

With decreasing price of photovoltaic (PV) panels and rapid deployment of PV technology to the distributed network, there are more large-scale PV plants being established. Simultaneously, integration of significant levels of PV generation induces the high penetration levels of solar energy, and it causes some power quality issues such as voltage rises or voltage fluctuation to the power grid, which limits the maximum PV energy generation. Especially, the weak grid within the distributed network, where has low X/R ratios, would provide severe voltage fluctuation and make the reactive power compensation method less effective on voltage regulation. Hence, this presentation will propose the battery energy storage system (BESS) to regulate voltage fluctuation and investigate its effectiveness in the weak grid within distributed network. The BESS will charge and discharge the fluctuating active power caused by solar power disturbance and fault in the grid, so it provides voltage regulation to the point of common coupling of PV power conversion system. The effectiveness of the BESS on the voltage stability of a grid-connected PV power system will be investigated by PSCAD, and the simulation is subjected to power disturbance caused by step changes in or temperatures and the different grid status by differentiating short circuit ratio and X/R ratio. In order to verify the effectiveness of the BESS on voltage regulation, the simulation will capture short-term voltage fluctuation, and the result will be compared with base control scheme of PV power system.

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Passivation – improvement of Si cell efficiency and Fast charging algorithm for lithium ion battery Minseok Song Solar cells made with thin wafers are very sensitive to surface recombination. Suppressing recombination at both surfaces permits to compress a higher number of electrons and holes, which augments their concentration and hence their electrochemical potential. Mainly there are two passivations that are widely used in order to suppress recombination, which are chemical passivation and field effect passivation. Also, different approaches are introduces for each top and rear sides of the cell. For the top side of the cell, chemical passivation is mainly applied. The silicon atom possesses four valence electrons and therefore requires four bonds to fully saturate the valence shell. At the surface of the silicon crystal, atoms are missing and traps are formed, which is called unsatisfied dangling bonds of surface silicon atoms. Typically, a certain amount of interface defects remains after an oxidation process or after thin film deposition. The density of defects or traps can be drastically reduces by attaching atomic or molecular species. The presence of hydrogen, preferably in atomic form, is a common denominator of all the approaches that have led to high quality surface passivation, including semiconductors like a-Si:H and dielectrics like SiO2, SiN2 etc. In case of rear side of the cell, where their structure is more important, filed effect passivation is usually used. The reaction rate of recombination is highest when the concentration of the two reactants is similar to each other. Therefore, it is possible to control electron-hole recombination by manipulating their respective concentration, which can be done by doping or deposition of materials or using hydrogen-rich semi-insulator. For the deposition at rear side, Si dissolution in Al plays an important role in the formation of the contacts. Since many years, crystalline Si solar cells industry is using Al for creating the back contact of the cells. The incorporating of an electric field under the contacts is useful to repel the minority carriers from the surface thereby avoiding their recombination. An easy and straightforward way to create electric field is by alloying Al and Si, called aluminum back surface field (Al-BSF). A full Al-BSF is the standard which is used in the industry nowadays, where the bulk Si and Al are in full contact. This Al layer is applied on top of the bare Si depositing a paste by the screen printing technique with 25~60um to form a continuous BSF layer. On the other hand, the local Al-BSF has a clear advantage over the full Al-BSF case, due to the improved passivation and reduced recombination for the smaller contacted area, which is called passivated emitter and rear cell (PERC). Also, another material can be applied instead of aluminum that is boron. Using diffused localized boron region, the doping underneath the contact is made. The higher solubility of boron compared to Al allows a higher doping level providing a higher field effect at the BSF and therefore a reduced recombination of the minority carriers. This type of cell is called passivated emitter and rear locally diffused (PERL). Lastly, new material to improve cell efficiency is introduced, where one of the example is aluminum oxide (Al2O3) that is well known to be a negatively charged dielectric. Contact passivation of the aluminum-silicon interface by thin aluminum oxide layers grown by thermal atomic layer deposition (ALD) can increase effective lifetime with the number of ALD cycles for both p and n type Si. Reduction of charging time is one of challenging issues for different applications of lithium ion batteries. Increased charging current can reduce the charging time, but adversely accelerates degradation. A study conducted by U.S. Army research laboratory showed the fact that charging protocols (constant current (CC) charging, constant power (CP) charging, and multistage constant

13 current (MCC) charging) for lithium ion battery have a significant impact on their cycle life. In this presentation, different charging protocols are introduced and compared in terms of charging time and the battery degradation. Aging phenomena of lithium ion battery are complex, affected by electrochemical, heat generation and mechanical stress. Among them, the most dominant causes are electrochemical reactions that include side reactions and lithium deposition reaction. Detailed research of these degradation reactions are studied using an electrochemical model and characteristics of each reaction are compared. The side reactions take place on the whole anode electrode and the degradation from side reactions is linear if the charging profile is same during cycling. On the other hand, the lithium deposition reaction takes place locally and it accelerates degradation. The lithium deposition only take place when the lithium deposition overpotential against a reference of Li/Li+ is less than 0V, which is depend on charging current, state of charge, battery’s degradation rate, temperature and so on, however once it starts to take place, battery is aged exponentially. Therefore, it is possible to reduce battery degradation by controlling side reaction rate and prevent lithium plating by controlling charging current. A fast charging algorithm is proposed by estimating battery’s inner variables that directly leads to the degradation reactions, consequently battery can be charged with low degradation reaction rate, while being charged with high current. Additionally, reverse reaction of lithium deposition reaction, lithium stripping reaction is introduced as one of the solutions for reduction of degradation. Experimental results show that discharging pulses during promote lithium dissolution reaction.

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Photovoltaic in China

Wendong Wang

Photovoltaic (PV) technologies become a very promising and important renewable energy source in China. The total electrical output from photovoltaic in china is increase every year. In 2017, the total electrical output have been increased 75.4% compared with previous year [1]. However, currently the major electricity contribution is not come from Photovoltaic. In 2017, only 1.5% electricity throughput comes from photovoltaic. For future development of photovoltaic in china, the throughput and the cost of photovoltaic in china should be decreased. Some researchers build a model to calculate the future electricity output of photovoltaic, by fully take advantage of the free space, etc. desert and roof-top and façade, the photovoltaic can fully support the electricity consume of china in the future [2]. In order to achieve this, three aspects have been analyzed deployment of photovoltaic in china, the potential photovoltaic technology, the cost of photovoltaic. For deployment of photovoltaic, China still have a lot of area have not been applied the photovoltaic, for example, the province Anhui Sichuan [3]. The roof-top is another area for photovoltaic but it is barely taken advantage now in china. For potential photovoltaic technology, currently PV market is dominated by based on the mono or multi- wafers. But there are still other technology is coming, for instance, the thin-film is one of them with lower cost but lower efficiencies. The multi-junction device has maximum efficiencies but it is still at test level and cannot be deployed in large volume. For future development of PV technology, the multi-junction device maybe a promising technology to improve throughput of photovoltaic. For cost of photovoltaic, in [2], if the cost of photovoltaic can be reduced by factor 2, the PV power generation can be competitive to the tradition source, for example, fuel. In order to reduce the cost, one promising trend is that more integration will happen in PV supply chain. If one company can do wafer production and silicon production at same time or most cell manufacturer can be integrated with module manufacturer. The cost will drop due to these manufacturer can export at lower price. The other important factor of PV in china is the policy. In general, the government of china pay attention to development of PV but R&D support has been comparatively weak.

[1] "2015年光伏 发电相关统计数据---国家能源局 ". www.nea.gov.cn. Retrieved 2016-02-08.

[2] Grau, Thilo, Molin Huo, and Karsten Neuhoff. "Survey of photovoltaic industry and policy in Germany and China." Energy policy 51 (2012): 20-37.

[3] Evans, Annette, Vladimir Strezov, and Tim J. Evans. "Assessment of sustainability indicators for renewable energy technologies." Renewable and sustainable energy reviews13.5 (2009): 1082-1088.

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Additive Manufacturing for Photovoltaic Technologies

Shane Williams

The development of photovoltaic technologies that are compatible with additive manufacturing opens up a new paradigm of energy generation. Portable, wearable, and/or on-chip energy generation devices are close to a consumer reality thanks to the customization afforded by additive manufacturing processes. This paper shall begin with a discussion of the roll-to-roll (R2R) printing process, which has already been widely commercialized for thin-film photovoltaics, highlighting advancements in R2R printing of perovskite solar cells and alternative electrode designs. The commercialized use of roll-to-roll printing takes advantage of economies of scale, often being used to fabricate high-surface-area electronics in high volume. The solar cells produced by the R2R process are flexible and can be cut into the shape desired for specific applications such as wearable electronics or on-device energy generation. This cutting process, however, can introduce error in the process and thus reduce the economic favorability of the R2R process. The ink-jet printing process is more suitable for smaller, more specific photovoltaic applications. After discussing the advancements in R2R processing, this paper shall investigate the specifics of ink-jet printing photovoltaic technologies, discussing various ink chemistries and how they relate to the printing process and the efficiency of the final photovoltaic cells. After discussing ink-jet printing, this paper shall present a brief discussion of the impact that electrode architecture plays in the design of solar cells. The paper shall then conclude by highlighting the strengths and weaknesses of the current state of additive manufacturing for photovoltaic technologies, and present suggestions for future research into the field.

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Photovoltaic hazards and safety issues

Yuqiao Zhang

Photovoltaic (PV) are usually believed to be reliable and safe enough in the early stage. At the beginning, the systems were mostly standalone with low voltage and just one or few modules. Furthermore, the usage may be focused on the battery charging for in remote areas. The reason why the PV cells and modules are safe is that the whole system is till operated on there I-V curve. However, with the popularity of the grid-connected PV system since the mid-90’s, the issue of the fire safety of PV modules is emerging due to the employed high voltages of 600V to 1000V. In 2011, it was expected to be the first year in which the utility-scale photovoltaics would rank as the largest segment of the US solar market. Based on the report and plan, more utility scale PV will be installed than the residential and commercial PV combined. In the real life examples, open circuiting of the DC and the bypass diodes and ground faults are two main factors to be responsible for the fire in PV systems. In a well matched PV system, when all the cells are connected in series and illuminated uniformly, each cell will be flown with the equal amount of the current. Thus, the voltages will be added together. One reason that the overheating leading to the fire due to the partial of full shading of single/multiple cells connected in series. The shaded cell will generate a lower power or no current, which forms a reverse biased diode in the system. Here, bypass diodes are used to avoid accidental application of high reverse voltages to those individual cells that are series connected in the PV modules. As for the open circuits, a documented accident is occurred in an open circuit where the system voltage can occur across a small gap. When the high voltage is exploited in the discontinuous circuit, if the gap is narrow enough the arc will be generated and initiated. Moreover, if the two electrodes are mechanically held in place, the arcing may be continued for a long time which increase the risk of the fire. Also, the PV modules are supposed to provide high resistance stand- off between the electric circuit and the ground plane, which means that a low resistance path to ground can lead to overheating, arcing, and fire. Any ground fault may cause the catastrophic consequence. In the paper and presentation, recommendations are provided for preventing the fire hazards such as designing the PV array mounting system to minimize the effect, having proper bypass and blocking diodes with a proper ungrounded system.

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