The primarily focuses on the modeling of photovoltaic cells, batteries, and supercapacitors. It delves into the working principle of photovoltaic cells and the cause of the “hot spot effect.” Additionally, it investigates the output characteristics of photovoltaic arrays under partial shading to ascertain the relationship between the number of peak points in the output characteristic curve and the shading situation, with a particular emphasis on the role of hybrid energy storage in this context.
Photovoltaic cells convert solar energy into electrical energy through the photoelectric effect of the P – N junction. A practical photovoltaic cell model often includes the ideal circuit model and the single / double diode circuit model. The single diode model, which is relatively simple, can effectively simulate the internal actual loss and space charge diffusion effect of the photovoltaic cell. To achieve greater output power, photovoltaic cells are typically connected in series and parallel to form a photovoltaic array. The manufacturer specifies the basic parameters of the cell under standard working conditions, including the open – circuit voltage, short – circuit current, and maximum power point voltage and current. However, in actual use, the working environment of the photovoltaic cell is variable, and therefore, the model needs to be adjusted according to the standard working environment.
The output power of the photovoltaic cell is positively correlated with solar irradiance, and the short – circuit current and open – circuit voltage also increase with the increase in irradiance. Conversely, the output power is negatively correlated with the surface temperature. As the surface temperature rises, the short – circuit current of the photovoltaic cell increases, while the open – circuit voltage decreases.
When a single photovoltaic cell has a low output power, it is common to form a photovoltaic array by connecting multiple photovoltaic cells in series and parallel to meet the power demand. As the scale of the photovoltaic array expands, the number of required photovoltaic cells increases, and the occupied area also enlarges, making it more susceptible to partial shading. Factors such as building shadows, fallen leaves, and dust can all cause partial shading, resulting in different output characteristics for some components of the photovoltaic array compared to the overall array. In such cases, the shaded components become loads, consuming the energy generated by the remaining normally illuminated components, and the shaded components also generate heat, leading to the “hot spot effect.”
To explore the output characteristics of the photovoltaic array under partial shading, a 5 * 4 photovoltaic array model is constructed. It is found that when the photovoltaic array is under uniform shading or longitudinal shading, its P – U characteristic curve has only one peak point. However, when the photovoltaic array is under transverse or irregular shading, its P – U characteristic curve exhibits multiple peak points. The number of peak points in the photovoltaic array is solely related to the shading situation of the series components and is independent of the shading situation of the parallel components.
To further investigate the relationship between the number of peak points in the P – U characteristic curve of the photovoltaic array and the shading situation, a 5 * 1 photovoltaic array is formed. It is concluded that the multi – peak phenomenon in the P – U characteristic curve of the photovoltaic array is caused by the different shading degrees of the series components. In other words, the number of peak points corresponds to the number of different shading situations. Moreover, the number of peak points in the P – U characteristic curve of the photovoltaic array is related to the number of series photovoltaic cells.
In distributed power generation, which is widely utilized with the development of clean energy, there are inherent issues of instability and uncontrollability. The hybrid energy storage system plays a crucial role in effectively addressing these problems. It not only enhances the reliability of distributed power generation but also enables bidirectional energy flow. Batteries, as the most commonly used energy storage devices, are widely employed in distributed power generation. Common battery types include lithium – ion batteries, lead – acid batteries, and nickel – chromium batteries. Currently, lithium – ion batteries are widely used in new energy power generation scenarios as energy storage elements due to their relatively high energy density, low self – discharge rate, and long lifespan.
Supercapacitors, also known as double – layer capacitors, are energy storage elements positioned between batteries and capacitors. They store energy through the polarization of the electrolyte. Although supercapacitors are electrochemical energy storage elements, their energy storage process does not involve chemical reactions, making the energy storage process reversible. They have a life of repeated charging and discharging for more than 100,000 times.
In summary, this chapter lays the foundation for the subsequent study of the maximum power point tracking algorithm under partial shading and the application of hybrid energy storage in the three – phase photovoltaic grid connection. The hybrid energy storage system, comprising batteries and supercapacitors, is of significant importance in optimizing the performance and stability of photovoltaic power generation systems. By combining the advantages of both energy storage types, the hybrid energy storage system can effectively manage the intermittent and fluctuating nature of photovoltaic power generation, ensuring a more stable and reliable power output. Additionally, the proper design and control of the hybrid energy storage system can enhance the efficiency and longevity of the energy storage components, further contributing to the overall sustainability and cost – effectiveness of the photovoltaic power generation system. Therefore, further research and development in the field of hybrid energy storage are essential to advancing the widespread adoption and effectiveness of photovoltaic power generation in the quest for clean and sustainable energy sources.