By zhanqun1 
The technological innovation of energy storage has emerged as a key link during the wave of energy transformation in recent years. As the new star of energy storage, hybrid energy storage develops gradually and brings about new ways for both efficient use and stable supply.
A hybrid energy storage device refers to organically combining several different kinds of energy storage technologies, fully exerting advantages of all kinds of energy storage methods and making up for deficiencies in one certain energy storage technology. For example, the Xinjiang Huadian Hami Yandun new hybrid energy storage demonstration project involves flywheel energy storage, super-capacitor energy storage, and lithium iron phosphate battery energy storage. Its advantages are long-life in that during long-time running, it can work stably and reliably. That’s to say, the general lithium iron phosphate battery storage has a large capacity that is able to store enormous electric quantity, so it can meet electricity demand in different scales. The supercapacitor also possesses fine performance in fast-charging speed, good performance in high-current discharge, and very long cycle life, therefore does a good job of responding to instantaneous high-power charge/discharge demand.
It’s really not easy for so many energy storage techniques to be integrated all together. Coupled multiple energy storage functions, very complex debugging, and efficient coordination of centralized control form only a few of the many issues in project implementation. It was, however, through the unremitting efforts of the scientific research team that was composed of Huadian Xinjiang Power Generation Co., LTD., Huadian Electric Power Research Institute Co., LTD., and the active participation of Tsinghua University, Xi ‘an Jiaotong University, Beijing University of Aeronautics and Astronautics, North China Electric Power University, and other colleges and universities in technical research and demonstration implementation that the three energy storage technologies have successfully completed the frequency modulation service of the power system. And share with the new energy station. This breakthrough is of great significance, not only fills the gap in the field of technology application, but also provides valuable practical experience for Xinjiang to build a national energy resources strategic security base and a new power system.
From a broader perspective, the application prospects of hybrid energy storage are very broad. New energy power can effectively solve the problem of new energy consumption. Together with the increase in renewable energies like solar energy and wind energy in structure, intermittency and volatility in power generation may lead to a certain effect on power grid operation stability. The Hybrid Energy Storage would store electric energy when there is excess new energy generation and releases electric energy when power generation or peak consumption falls short in order to smoothen out the fluctuation in the supply of power to ensure stable operations of the grid and therefore enhance large-scale access and efficiency in the utilization of new energy.
Hybrid energy storage also has possible applications within the industrial sectors. The so-called hybrid energy storage in such an industry could refer to, say, an electronic chip manufacturing or a precision instrument processing, where the power should be supplied stably and in high quality to avoid possible problems that may include a rise in defective product rates caused by power grid fluctuations. In the field of electric vehicles, hybrid energy storage technology is also expected to apply, optimize the combination of batteries and supercapacitors, improve the endurance and power performance of electric vehicles, reduce charging time, and further promote the popularity of electric vehicles.
Hybrid energy storage indeed has great potential in many challenges of the energy sector, being an advanced energy storage solution that leverages the advantages of several energy storage technologies. With the development of continuously improved technology, in all aspects, hybrid energy storage will be more powerful in energy production, transmission, distribution, and use, hence contributing powerfully to our movement toward a cleaner, more effective, and stable energy future. This would contribute to the sustainable development of the global energy industry and bring us closer to realizing the goal of green, low-carbon life.
Hybrid energy storage system has a very broad application prospect in the field of renewable energy, mainly reflected in the following aspects:
1, smooth renewable energy output power
Renewable energy sources, such as solar and wind, are intermittent. For instance, solar photovoltaic depends on sunshine, whereby it can only generate during the daytime with sunny conditions and where cloudy or rainy conditions prevail, affects the generated quantity; wind power generation would depend on the velocity and steadiness of the wind. In a situation where one generates more renewable energy than can be consumed, hybrid energy storage systems store the produced electricity and release it upon shortfall conditions.
For example, taking a system that includes wind power generation and hybrid energy storage, such as battery energy storage combined with supercapacitor energy storage, when the wind speed is big and the output power of the wind generator surpasses the grid demand, the excess energy can be stored in the energy storage system. When the wind speed suddenly decreases and the output power of the wind turbine decreases, the energy storage system can quickly release electric energy and supplement the power shortage of the grid, so as to effectively smooth the output power of renewable energy and reduce the impact on the grid.
The volatility of new energy sources may cause power quality problems, such as voltage fluctuations or frequency deviations. The hybrid energy storage system will respond quickly to these changes in voltage and frequency due to the characteristics of fast charge/discharge-for example, high-power density of ultra-capacitors-and thus regulate voltage and frequency to feed stable and high-quality power to users.
2. Improve renewable energy absorption capability
The problem of spatiotemporal matching with power load has become increasingly evident as the proportion of renewable energy generation increases. Hybrid energy storage systems can work like “energy buffers” to shift electricity generated by renewable energy over time.
For example, during peak hours of photovoltaic power generation, normally around noon, excessive electrical energy is stored until evening peak. Where the photovoltaic power generation lowers its power, electrical energy previously stored is released to the grid in order to supply the demand from users, which thereby increases the proportion of renewable energy within the grid and cuts down on the “light” and “wind” phenomenon.
Hybrid energy storage systems help distributed renewable energy systems, including distributed photovoltaics and small wind power systems, connect with the local grid in a better way or work independently. A hybrid energy storage system balances on-site supply and demand in a distributed energy system owing to its small power generation scale and large fluctuation resulting from environmental impacts, hence enhancing the autonomy and reliability of the system.
3. Improve the stability and flexibility of the power grid
Hybrid energy storage can provide a variety of ancillary services for the power grid, such as frequency modulation, peak regulation, and so on. When the frequency of the grid changes, the energy storage system can make a quick response and then modulate the frequency by releasing or absorbing electricity.
For instance, it can quickly charge the energy storage system to absorb extra energy when the grid frequency is raised; on the other hand, when the grid frequency is lowered, it is capable of releasing the same amount of energy in electrical form. The function of the hybrid energy storage system in peak load balancing service is to store electric energy during the load off-peak period and release it during the load peak period, thus relieving the peak load pressure of the grid.
The application of a hybrid energy storage system is not restricted to the concept of microgrids and virtual power plants alone. A micro-grid generally represents a small power system, comprising distributed energy, storage systems, and loads. Hybrid energy storage systems are able to provide energy balance and a stable power supply in isolated operation for microgrids.
Virtual power plants integrate multiple distributed energies and storage resources to meet electricity demands of the grid just like a conventional power plant. A reasonable configuration for the hybrid energy storage system in the virtual power plants will enhance their performance to flexibly face different kinds of power market demand and dispatching requests from the grid.
4. To reduce the expenses of renewable energy systems
By smoothing the output power of renewable energy with hybrid energy storage systems, the mechanical and electrical stress brought about by the frequent power fluctuation in renewable generation equipment-such as wind turbines and photovoltaic panels-can be reduced to extend its service life, thereby reducing costs related to the replacement of equipment.
Different energy storage technologies have different cost structures. For example, the cost of battery storage is relatively low, with limitations to cycle life and power response speed, while the cost of supercapacitor energy storage is correspondingly high, featuring higher power density and longer cycle life. Hybrid energy storage systems combine several energy storage technologies with optimal cost-effectiveness while satisfying all system performance requirements. By the rational capacity and power configuration of different energy storage components, the whole cost of the energy storage system can be reduced.
The hybrid energy storage system has an especially promising application prospect in renewable energy utilization, and it will be playing an increasingly important role in improving the efficiency of renewable energy utilization, enhancing the stability of the power grid, and promoting energy transformation.