The diploma is divided into two parts. The first part is a theoretical explanation of the solar cell. It begins with a brief presentation of renewable energy sources, including solar cells. The composition and the operation of solar cells are described in detail, as well as the PN junction obtained when the P and N type semiconductors are "connected". We did some research on the division of solar cells and determined which are more appropriate for the customer from the economical and practical point of view. For the user of solar cells, it is necessary that the solar cells have the highest possible efficiency, so that the initial investment is met as soon as possible. We can improve efficiency by tracking the Sun. We know two types of tracking systems. They differ from each other in the way they follow the Sun. Regular maintenance of solar cells is very important to reduce mechanical damage. Each building that has solar cells must be specially marked and must have the fire escape plan. Before connecting to the public network, the user must meet certain conditions.
The second part of the diploma thesis consists of theoretical and practical part. In the theoretical part, we performed a solar cell simulation in the Matlab-Simulink program, which we also described in more detail in the diploma thesis. The simulation of photovoltaic systems has been evolving over the years. With the help of simulation, we can dimension photovoltaic systems and predict what the electricity consumption will be. The research is based on increasing conversion efficiency and reducing manufacturing costs. It is very important to find the best possible material-geometric parameters of the cells, as the initial investment is very expensive and very time consuming. Solar cell models are based on experimental and theoretical findings of science from several fields, such as static mechanics, chemistry, and quantum mechanics. The goal of modeling is to develop a model that incorporates the entire physical operation of a solar cell, is simple, and allows fast calculation. Approximation of the voltage-current I-U characteristic is the basis of modeling. We use a mathematical model of the photovoltaic module. Today, various computer programs help us with calculations. A computer program uses numerical methods to solve a system of equations captured by the model. With the help of the measurements we perform, we obtain various material-geometric parameters, which are used for numerical evaluation of the model and for simulating the output characteristics of solar cells, such as voltage-current I-U characteristic and efficiency. The most important results of the simulations are the open terminal voltage, the charging factor, the short-circuit current and the efficiency. The analysis allows us to determine which set of parameters gives us the desired output characteristics of the solar cell.
The practical part of the task is related to a concrete photovoltaic power plant with a total power of 86 kW, partly on the roof (41 kW) and partly on the southern facade of the packaging warehouse (45 kW). The cells are polycrystalline, type YL230P-29b, manufactured by Yingli Solar. The electrical parameters given under Standard Test Conditions (STC) are an open-circuit voltage of 37 V; short-circuit current 8,4 A; voltage at Pmax 29,5 V and current at Pmax 7,8 A. With the help of these and some other parameters, we performed a simulation of a photovoltaic power plant in the Matlab-Simulnik program. The results of the simulation were compared with the real measurements performed in the company. Measurements were performed using a two-channel oscilloscope. With the simulation, we found out how well the simulation program simulates real conditions in nature or how accurate we were when performing measurements. The measurements showed a very small deviation, with an average error of 2,6 %. The simulation curve and the points of the real measurements matched nicely.
|
