Lightning is one of the main factors that cause Photovoltaic (PV) systems to fail. The PV modules inside PV systems, like any other electric equipment, will be degraded under electrical stress. The effect of electrical degradation of the PV modules caused by lightning induced voltage has been rarely reported. In the dissertation, the electrical properties degradation of a polycrystalline silicon module was studied. Firstly, lightning impulse voltages of positive polarity ranging from low to high are applied on different groups of the testing modules. All these lightning impulse voltage tests are conducted in the same experimental condition except for their stress voltage magnitudes. The maximum power output, I-V characteristics, and dark forward I-V curve are measured and reported periodically during the lightning impulse voltage tests. By comparing the maximum output power and changes in the internal electrical properties, it could be concluded that lightning impulse voltages, even medium voltage levels, will cause degradation to the sample. The relationship of the maximum output power and the number of applied impulses for different testing voltage levels are compared. An analysis of the electrical property changes caused by the lightning impulse voltages is presented. Secondly, a group of samples are tested with lightning impulse voltage of negative polarity. A comparison of the impulse voltage aging effects at the same voltage level with positive polarity is made. The maximum power output drop caused by positive and negative lightning impulses are compared. Laboratory results revealed that positive and negative lightning impulses will not only influence the degree of degradation, but also lead to different electrical property changes. Finally, a comparison of the effect of lightning impulses combined with other stress factors are discussed. The study simulates a field-aged sample’s behavior at lightning impulse voltage testing conditions. The result suggests that the degradation caused by lightning impulse voltage is greatly accelerated when the sample has bubbles and delamination. Electrical breakdown of the module is caused by the failure of the insulation.

abstract: This is a two part thesis: Part – I This part of the thesis involves automation of statistical risk analysis of photovoltaic (PV) power plants. Statistical risk analysis on the field observed defects/failures in the PV power plants is usually carried out using a combination of several manual methods which are often laborious, time consuming and prone to human errors. In order to mitigate these issues, an automated statistical risk analysis (FMECA) is necessary. The automation developed and presented in this project generates about 20 different reliability risk plots in about 3-4 minutes without the need of several manual labor hours traditionally spent for these analyses. The primary focus of this project is to automatically generate Risk Priority Number (RPN) for each defect/failure based on two Excel spreadsheets: Defect spreadsheet; Degradation rate spreadsheet. Automation involves two major programs – one to calculate Global RPN (Sum of Performance RPN and Safety RPN) and the other to find the correlation of defects with I-V parameters’ degradations. Based on the generated RPN and other reliability plots, warranty claims for material defect and degradation rate may be made by the system owners. Part – II This part of the thesis involves the evaluation of Module Level Power Electronics (MLPE) which are commercially available and used by the industry. Reliability evaluations of any product typically involve pre-characterizations, many different accelerated stress tests and post-characterizations. Due to time constraints, this part of the project was limited to only pre-characterizations of about 100 MLPE units commercially available from 5 different manufacturers. Pre-characterizations involve testing MLPE units for rated efficiency, CEC efficiency, power factor and Harmonics (Vthd (%) and Ithd (%)). The pre-characterization test results can be used to validate manufacturer claims and to evaluate the product for compliance certification test standards. Pre-characterization results were compared for all MLPE units individually for all tested parameters listed above. The accelerated stress tests are ongoing and are not presented in this thesis. Based on the pre-characterizations presented in this report and post-characterizations performed after the stress tests, the pass/fail and time-to-failure analyses can be carried out by future researchers. / Dissertation/Thesis / Masters Thesis Engineering 2015

The aim of the Thesis is theoretical clarification of the issues of photovoltaic power plants, their diagnostics, inspection and performance measurement, including negative impacts on their operation and subsequent application of theoretical knowledge during practical inspection and diagnostics of PV power plants. In its introductory part, the Thesis deals with design, manufacturing and development of PV cells and panels and describes other necessary elements and components, including their use in individual types of photovoltaic systems. Another part describes electric parameters of PV cells and panels, especially the parameters that can be found out by measurement of V-A characteristics and also the parameters affecting the shape of the V-A characteristics. The third part is focused on failures of photovoltaic systems, which include various defects of photovoltaic cells and panels, it also provides for adverse factors affecting operation of the entire system, associated not only with weather influences but also with the actual design of the photovoltaic system. The fourth part deals with possibilities of increasing the cost-effectiveness of electricity generation by PV power plants on the basis of practical experience of their operators. The subsequent part determines, on the basis of technical standards, procedures for PV power plant inspections, the procedures for measurement and diagnostics of PV power plants and also other prerequisites connected with inspections and measurements. This part includes also a description of requirements for measuring devices, most frequent measurement errors, adverse impacts affecting measurements and methods of assessment of the data measured. The last part of the Thesis is practical. At first it deals with verification of the impact of defects of PV modules on the shape of their V-A characteristics, then with execution of inspections and diagnostics of a particular PV power plant, evaluation of the data identified and measured, as well as with a proposal of optimisation measures to increase cost-efficiency of the operation of that particular PV power plant.

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abstract: This study evaluates two photovoltaic (PV) power plants based on electrical performance measurements, diode checks, visual inspections and infrared scanning. The purpose of this study is to measure degradation rates of performance parameters (Pmax, Isc, Voc, Vmax, Imax and FF) and to identify the failure modes in a "hot-dry desert" climatic condition along with quantitative determination of safety failure rates and reliability failure rates. The data obtained from this study can be used by module manufacturers in determining the warranty limits of their modules and also by banks, investors, project developers and users in determining appropriate financing or decommissioning models. In addition, the data obtained in this study will be helpful in selecting appropriate accelerated stress tests which would replicate the field failures for the new modules and would predict the lifetime for new PV modules. The study was conducted at two, single axis tracking monocrystalline silicon (c-Si) power plants, Site 3 and Site 4c of Salt River Project (SRP). The Site 3 power plant is located in Glendale, Arizona and the Site 4c power plant is located in Mesa, Arizona both considered a "hot-dry" field condition. The Site 3 power plant has 2,352 modules (named as Model-G) which was rated at 250 kW DC output. The mean and median degradation of these 12 years old modules are 0.95%/year and 0.96%/year, respectively. The major cause of degradation found in Site 3 is due to high series resistance (potentially due to solder-bond thermo-mechanical fatigue) and the failure mode is ribbon-ribbon solder bond failure/breakage. The Site 4c power plant has 1,280 modules (named as Model-H) which provide 243 kW DC output. The mean and median degradation of these 4 years old modules are 0.96%/year and 1%/year, respectively. At Site 4c, practically, none of the module failures are observed. The average soiling loss is 6.9% in Site 3 and 5.5% in Site 4c. The difference in soiling level is attributed to the rural and urban surroundings of these two power plants. / Dissertation/Thesis / M.S.Tech Engineering 2013

The purpose of this bachelor thesis is to investigate different outcomes of the usage of photovoltaic (PV) power for electric vehicle (EV) charging adjacent to workplaces. In the investigated case, EV charging stations are assumed to be connected to photovoltaic systems as well as the electricity grid. The model used to simulate different scenarios is based on a goal of achieving constant power exchange with the grid by adjusting EV charging to a solar irradiance forecast. The model is implemented in MATLAB. This enables multiple simulations for varying input parameters. Data on solar irradiance are used to simulate the expected PV power generation. Data on driving distances are used to simulate hourly electricity demands of the EVs at the charging stations. A sensitivity analysis, based on PV irradiance that deviates from the forecast, is carried out. The results show what power the grid needs to have installed capacity for if no PV power system is installed. Furthermore, appropriate PV power installation sizes are suggested. The suggestions depend on whether the aim is to achieve 100 percent self-consumption of PV generated power or full PV power coverage of charging demands. For different scenarios, PV power installations appropriate for reducing peak powers on the grid are suggested. The sensitivity analysis highlights deviations caused by interference in solar irradiance.

As the world strives towards finding alternative sources of power generation, photovoltaic generation has become an increasingly prevalent alternative energy source on power systems world-wide. This paper studies the effects that incorporating photovoltaic generation has on the existing power systems and their power system protection schemes. Along with the addition of this emerging alternative energy source comes the volatility of PV power generation as cloud-cover produces erratic variations in solar irradiance and PV power production. Such variations in PV power may lead to unfavorable operating conditions and power system failures. The issues addressed in this paper include a study of inverter harmonic levels for variations in DC voltage and power, and a study of power system protection failures caused by cloud-induced PV power variations. Such issues are addressed so as to provide a better understanding of the effects that cloud-induced PV power generation variability has on power systems and its protection schemes.

This study aims to examine and quantify the impact from increasing penetration of electric car chargers and solar cells in Mälarenergi's distribution grids. Four different types of low voltage grids are examined: a small rural grid, an older suburban grid, a modern suburban grid and a modern urban grid with multi-dwelling houses. The networks are modeled in Matpower, a MATLAB Power System Simulation Package with grid and metering data from Mälarenergi's NIS (Network Information System), insolation data from Swedish Meteorological and Hydrological Institute (SMHI) and simulated data from an electrical vehicle Home-charing model based on residential activity patterns. The idea has been to use as few assumptions as possible and as much real measurements as possible. The results show that problems such as unwanted voltage levels at the customer's connection points and increasing power flux in the low voltage substation's is to be expected based on aforementioned increasing penetration. The various low voltage networks are affected to varying degrees due to its different structure and type of customers. Measures to increase acceptance for the above mentioned changes have also been reviewed. Line gain shows best properties to reduce both losses and voltage variations. Reactive power compensation in the solar cell's inverters can reduce voltage increases, but with the disadvantage that network losses increase. The use of smart chargers that can control when the charging of electrical vehicles begin charging can both reduce network losses but also the risk of unwanted voltage drops.

The purpose of this bachelor thesis is to assess whether it is possible to create a simplified model that estimates the hosting capacity of a low-voltage grid. The Simplified model is compared with a more elaborate model created by the Built Environment Energy Systems Group (BEESG) at Uppsala University. The Simplified model takes three easily obtainable variables into account. The model created by BEESG allows us to observe both the amount of photovoltaic (PV) power that is installed as well as the voltages in each bus in a grid. The hosting capacity is found by gradually increasing the amount of PV power installed in a low-voltage grid until overvoltage is reached. Simulations with BEESG’s model are done for a week in July when the PV generation has its peak and the load is generally low. The Simplified model is created using linear regression with the calculated values from the BEESG’s model as a reference. The report shows that the Simplified model will give an estimation of the low-voltage grid’s hosting capacity that is comparable to the value calculated with BEESG’s model. The results show that it is rarely the low-voltage grid that restricts the installation of PV facilities and that a high self-consumption is advantageous regarding to the grids hosting capacity.

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