Abstract
For Photovoltaic systems designers and manufacturers, it is very important to develop suitable models to closely emulate the characteristics of PV cells, predict their behavior and evaluate their efficiency. So the main contribution of this chapter is to propose an improved and accurate method for identifying and determining the equivalent circuit elements values of photovoltaic module using only exact analytical equations and four manufacture's data reference, i.e., the open-circuit voltage (VOC), the short-circuit current (ISC), the current and the voltage at the maximum power point (IM, VM). In order to extract the five-parameter Single or Double-Diode models of photovoltaic module, the authors try initially to determine analytically all parameters according to RS (the value of the series resistance). Thus, all these parameters are calculated once RS is determined. Rapid and iterative algorithm is then designed to solve a strongly nonlinear equation in order to extract the value of RS in a precise manner and without any mathematical simplification used usually by many other authors.
TopIntroduction
The most powerful natural energy resource is the sun and the solar technologies offer clean and sustainable options for generating electrical energy without pollution. Photovoltaic (PV) technologies have distinct environmental advantages for generating electricity over conventional technologies. The operation of photovoltaic systems does not produce any noise, toxic-gas emissions, or greenhouse gases. Photovoltaic electricity generation, regardless of which technology is used, is a zero-emissions process.
The basic unit for converting solar energy into useful electrical energy is the solar cell. Grouped cells form photovoltaic (PV) modules with the aim of increasing energy production and make the process more practical. However, due to the high investment cost on PV modules, optimal utilization of the available solar energy has to be ensured. This necessitates a precise and reliable simulation of the designed PV systems prior to installation.
For Photovoltaic systems designers and manufacturers, it is very important to develop suitable models to closely emulate the characteristics of PV cells, predicting their behavior and evaluating their efficiency (Majdoul et al., 2015). It can be used also to study the interaction between the power converter and the PV arrays. Climate and solar radiation affect both on PV system supply side issues and on system demand side issues. Designers need both solar data and temperature data. The modeling tool must allow the analysis of the behavior of electrical characteristics in accordance with environmental changes such as temperature and irradiance. It is verify that these extrinsic factors influence strongly the photovoltaic efficiency.
In practice, in order to describe the current-voltage (I-V) relationship for PV simulators, the most popular approach is to use the electrical equivalent circuit with both linear and non-linear components (Ishaque et al., 2011). According to what has been said, it is clear that these components have to be adjusted automatically when the operating conditions change. Over the years, many models have been proposed, but two main equivalent circuit models have been widely used: the single diode model also called simple exponential model and the double diode model or double exponential model. These models differ in the accuracy and number of parameters involved in the calculation of PV current-voltage characteristics. To use these models in the simulation and evaluation of PV systems, one needs to determine the models parameters. However, parameter identification of such models is a challenging problem, since the derived equations for the estimation of a PV model parameters are implicit and nonlinear and may not be analytically solved (Hejri et al., 2014).
This chapter aims to give at first a summary overview of many aspects of photovoltaic cells modelling used and the different parameters estimation methods explained and promoted by many researcher authors. In a second phase, the authors proposes and develops an improved and accurate method for identifying and determining the equivalent circuit elements values of photovoltaic module. They use in this approach, only exact analytical equations and four manufacture’s data reference, i.e., the data of three remarkable points: the open-circuit voltage (VOC), the short-circuit current (ISC) and the current and the voltage at the maximum power point (IM, VM). This approach is presented in a way that it can be easily accessed by the expert and the non-specialist of photovoltaic systems.
Key Terms in this Chapter
Stand-Alone Power System: (SAPS or SPS), also known as remote area power supply (RAPS), is an off-the-grid electricity system for locations that are not fitted with an electricity distribution system. Typical SAPS include one or more methods of electricity generation, energy storage, and regulation. Electricity is typically generated by one or more of the following methods: Photovoltaic system using solar panels, Wind turbine or Diesel or bio fuel generator.
Partial Shading: Shading effects is due to dusts, clouds, leafs, branches of trees and buildings causing shading on part of cells, modules or panels.
Fill Factor: Abbreviated FF, is a parameter which characterizes the non-linear electrical behavior of the solar cell. Fill factor is defined as the ratio of the maximum power from the solar cell to the product of Open Circuit Voltage and Short-Circuit Current.
Grid-Connect PV System: Or grid-connected photovoltaic power system is an electricity generating solar PV system that is connected to the utility grid. It consists of solar panels, one or several inverters, a power-conditioning unit and grid connection equipment.
Buck Converter: A type of DC-DC converter that has an output voltage magnitude less than the input voltage magnitude.
Photovoltaic System: Also: solar PV power system, or PV system, is a power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to change the electric current from DC to AC, as well as mounting, cabling and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system's overall performance and include an integrated battery solution, as prices for storage devices are expected to decline. Strictly speaking, a solar array only encompasses the ensemble of solar panels, the visible part of the PV system, and does not include all the other hardware, often summarized as balance of system (BOS). Moreover, PV systems convert light directly into electricity and should not be confused with other technologies, such as concentrated solar power solar thermal, used for heating and cooling.
Thin Film Solar Cell: A second generation solar cell that is made by depositing one or more thin layers or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal.
Air Mass: It defines the direct optical path length through the Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e. at the zenith. The air mass coefficient can be used to help characterize the solar spectrum after solar radiation has traveled through the atmosphere. The air mass coefficient is commonly used to characterize the performance of solar cells under standardized conditions, and is often referred to using the syntax “AM” followed by a number. “AM1.5” is almost universal when characterizing terrestrial power-generating panels.
Multi-Junction Solar Cell: Solar cells with multiple (three or four) P-N junctions made of different semiconductor materials. Each material's P-N junction will produce electric current in response to different wavelengths of light. The use of multiple semiconducting materials allows the absorbance of a broader range of wavelengths, improving the cell's sunlight to electrical energy conversion efficiency.