4 energy storage technologies in photovoltaic power generation
With the rapid development of the economy, the energy shortage is becoming more and more serious. Faced with the dual pressure of energy demand and environmental protection, countries around the world have adopted strategies such as increasing energy utilization, improving energy structure, and developing renewable energy. As a representative of new energy power generation, solar photovoltaic power generation has been formally applied in actual production. Photovoltaic power supply is different from traditional power supply. Its output power changes drastically with changes in light intensity, temperature and other environmental factors, and it is uncontrollable. Therefore, if photovoltaic power generation is to replace traditional energy sources to achieve large-scale grid-connected power generation, it will The impact of power grid impact cannot be ignored. Moreover, as the proportion of photovoltaic systems in the grid continues to increase, its impact on the grid must be effectively managed to ensure the safety and reliability of power supply. The application of energy storage system in photovoltaic power generation system can solve the problem of unbalanced power supply in photovoltaic power generation system to meet the requirements of normal operation. Energy storage systems are crucial to the stable operation of photovoltaic power plants. The energy storage system not only ensures the stability and reliability of the system, but also is an effective way to solve dynamic power quality problems such as voltage pulses, inrush currents, voltage dips, and instantaneous power interruptions.
Energy storage technology in photovoltaic power generation system
battery energy storage
Battery energy storage is one of the most promising energy storage methods among various energy storage technologies. It has the characteristics of high reliability and high degree of modularization, and is often used in distribution networks in load areas that require high power supply quality. Battery energy storage mainly uses the oxidation-reduction reaction of the positive and negative electrodes of the battery to charge and discharge. The battery energy storage can solve the power demand of the system during the peak load, and the battery energy storage can also be used to assist the reactive power compensation device, which is beneficial to suppress voltage fluctuations and flicker. At present, common batteries include lead-acid batteries, lithium-ion batteries, sodium-sulfur batteries, and flow batteries. Literature [9] analyzed the role of the battery in the photovoltaic power generation system: energy storage, clamping the working voltage of the solar cell, and providing a large instantaneous current. Literature [10] focuses on several common chemical energy storage technologies at present, selects key technical indicators, collects the latest application data of chemical energy storage technologies up to 2011, and combines data envelopment (DEA) analysis methods to explore various chemical energy storage technologies. The advantages and application effects of the technology provide suggestions and references for the future research direction of chemical energy storage technology.
Supercapacitor energy storage
A supercapacitor is a porous medium made of special materials. Compared with ordinary capacitors, it has a higher dielectric constant, greater withstand voltage capacity and greater storage capacity, and maintains the characteristics of fast energy release of traditional capacitors. It is gradually accepted in the field of energy storage. According to different energy storage principles, supercapacitors can be divided into electric double layer capacitors and electrochemical capacitors. As an emerging energy storage element, supercapacitor has many advantages compared with other energy storage methods. Compared with batteries, supercapacitors have the characteristics of high power density, long charge and discharge cycle life, high charge and discharge efficiency, fast charge and discharge rate, good high and low temperature performance, and long energy storage life. However, supercapacitors also have many disadvantages, mainly including low energy density, relatively large fluctuation range of terminal voltage, and voltage equalization of capacitors in series. Judging from the characteristics of batteries and supercapacitors, the two are highly complementary in technical performance. Mixing supercapacitors with batteries will greatly improve the performance of energy storage devices. Literature [14] found that the parallel connection of supercapacitors and batteries can improve the power output capability of hybrid energy storage devices, reduce internal losses, and increase discharge time; it can reduce the number of charge and discharge cycles of batteries and prolong their service life; The size of the device, improving the reliability and economy of the power supply system.
flywheel energy storage
Flywheel energy storage technology is a mechanical energy storage method, which can have the advantages of high efficiency, short construction period, long life, high energy storage, etc., and it can be charged quickly, with unlimited charge and discharge times, and has no pollution to the environment. However, the maintenance cost of flywheel energy storage is much more expensive than other energy storage methods. In literature [15], on the basis of analyzing the structure and characteristics of the photovoltaic flywheel energy storage system, a fuzzy control-based active power smoothing control of the photovoltaic flywheel energy storage system is proposed. Using the Matlab/Simulink platform, the photovoltaic flywheel energy storage system is simulated and analyzed The flywheel speed, power output status and smoothing coefficient of the flywheel energy storage system are compared with those of no flywheel energy storage and simple flywheel energy storage. Literature [16] is based on the maximum power tracking of photovoltaic power generation and grid-connected inverter control, and introduces a flywheel energy storage system to achieve stable power output to the grid. In order to enable the photovoltaic power generation system to output dispatchable and stable electric energy to the grid, the current inner loop, voltage outer loop control mode is used for charging and current inner loop, voltage outer loop control mode for discharging, so that the entire system outputs stable and dispatchable active power. It effectively suppresses the fluctuation of active power output from the photovoltaic power generation system to the grid due to fluctuations in sunlight and ambient temperature.
Superconducting energy storage
The superconducting energy storage system (SMES) uses coils made of superconducting wires to store the magnetic field energy generated by the grid-powered excitation, and then send the stored energy back to the grid when needed. Superconducting energy storage systems usually include superconducting coils placed in a vacuum-insulated cooling container, cryogenic and vacuum mercury systems, and power electronics for control. The current circulates continuously in the closed inductance formed by the superconducting coil and will not disappear. Compared with other energy storage technologies, superconducting energy storage has significant advantages: because it can store energy without loss for a long time, the energy return efficiency is very high; the energy release speed is fast, usually only a few seconds; the use of SMES can make the grid voltage, Frequency, active and reactive power are easily adjusted. Literature [17] proposes to use a superconducting energy storage unit to stabilize the output voltage and frequency of the wind turbine. The SEMS unit is connected to the busbar of the asynchronous generator. The active power controller of the SEMS uses the speed deviation of the asynchronous generator as the control signal. Literature [18] proposed a strategy of using voltage deviation as the control signal of the SEMS active power controller for the frequent short-circuit faults of the tie line and the wind speed disturbance of the wind farm. Various studies have shown that SEMS devices have excellent performance in improving the stability of wind farms.
