Energy storage systems: innovations and advantages

Energy systems are dynamic and in transition due to alternative energy resources, technological innovations, demand, costs and environmental consequences. Fossil fuels are traditional sources of energy production, but they have gradually given way to today’s innovative technologies, with an emphasis on renewable resources such as solar and wind energy.

Energy storage can enable flexible generation and stable electricity supply to meet customer demands. This article can contribute to the selection of the latest and most innovative energy storage devices and systems for their networks and other related uses such as automobiles and portable devices.

Energy storage techniques

Flow batteries

Flow batteries replace conventional batteries, composed of two electrolytes in a liquid state, unlike the solid compounds of standard batteries, which have a limited energy storage capacity. Different types of electrolytes are used in a flow battery; bromine as the core element with zinc (ZnBr), sodium (NaBr), vanadium (VBr) and many others as the anode, while a recent addition is sodium polysulfide. Flow batteries have relatively higher capacities for energy storage and subsequent release. Other good features are fast charging, long life (about a decade), full discharge capability, non-toxic materials in the structure and low-temperature operating functions.

Superconducting Magnetic Energy Storage (SMES)

Another energy storage technology is “superconducting magnetic energy storage (SMES),” which is characterized as instantaneous and highly efficient. The flow of direct current in a coil of superconducting material creates a magnetic field that stores energy. However, the system must be continuously cooled. It is particularly suitable for providing constant and instantaneous power and for regulating grid stability with very high output power in a short time.

Energy storage in the flywheel (FES)

It is one of the most promising and innovative forms of kinetic energy storage. FES devices consist of several types of flywheels (solid or composite), a motor-generator and magnetic holders located in a housing. Flywheel systems usually operate in high vacuum and have the characteristics of: no friction losses, low wind resistance, long life, no harmful effect on the environment and require negligible maintenance. The FES system can help control the frequency of the grid and ensure the quality of the electricity supplied. It is mainly used for renewable energy generation where electrical fluctuations are large and frequent. Low energy density and higher costs to ensure system security are the main disadvantages. Currently, its main use is battery system integration.

Pumped hydroelectric energy storage (PHES)

Two water bodies (natural or artificial) located/constructed at higher and lower elevations are the key points of the pumped hydroelectric storage system to realize the energy storage process. The water is pushed into the water body located at a higher height using additional electricity during peak hours, while during peak hours, water from the upper reservoir is piped at a lower level to a hydroelectric generator, which is finally stored in the lower reservoir. The operation of the generators produces electricity again. The water is pumped back into the upper body of water outside of peak periods. The operating cost per unit of energy was found to be the lowest among the PHS. However, the construction of reservoirs and other infrastructure requires very high investment costs.

Thermal Energy Storage (TES)

Thermal energy storage (TES) has been widely adopted where materials that can be stored at high or low temperatures in isolated captivity are used. The energy stored in the form of heat is recovered when the cold or hot material returns to normal conditions, which is again used to generate electrical energy with the help of thermal motor devices. The energy input into this system is electrical resistance during heating or cooling. This energy storage system can be considered a low-carbon or high-performance system for powering buildings. However, research is expected to find efficient, stable and less expensive storage materials. However, TES has limited storage capacity for energy storage.

Compressed Air Energy Storage (CAES)

In the CAES system, air is pressurized in an underground tank using electricity during peak hours. During peak hours, compressed air is released which pushes the turbine/generator unit to produce electricity again. CAES is the only energy storage system (other than hydropumping) that has very broad commercial scalability. This technology is adopted by many companies in Europe to store electricity in the electricity grid. The CAES system stores energy in the form of intermolecular gas, which is compressed in a tank, then released again to spin the turbine and generator to produce electricity. However, this problem has been controlled in advanced adiabatic CAES systems due to the ability to produce electricity without fossil fuels because there is no combustion process. Therefore, not only can the efficiency of the system be increased by up to 70%, but the modified system has proven to be optimal for medium and small installations.

Hybrid Energy Storage Systems (HESS)

When an energy storage system is developed by integrating multiple devices and established in a grid network, the system is called a hybrid energy storage system (HESS). As a result, the benefits of each integrated system technology are added to meet specific needs, to cope with challenging conditions and to increase system performance and efficiency. The role and use of HESS has been identified in several sectors. In the electrified transportation sector, the hybridization of batteries and supercapacitors has proven successful when used in electrified propulsion vehicles. Many fuel cell vehicle researchers have proposed fuel cell HESS with batteries and/or supercapacitors. Energy smoothing and grid integration are more practical through the use of supercapacitor batteries in wind energy systems. It has been widely proposed to support photovoltaic systems with battery-supercapacitor or battery-fuel cell hybrids. Wind-PV hybrid renewable energy systems can be well supported by combinations of fuel cells and batteries. Therefore, the use of HESS could be considered a favorable solution for various future applications. However, to demonstrate the feasibility and functionality of HESS, further research and development needs to be carried out.

There are some constraints and challenges during energy storage processes. None of the devices and systems return 100% of the stored energy, which means there must be losses (10%-30%). It is necessary to do research and develop devices with higher yields. Concerted efforts should be made to increase renewable energy production resources in order to reduce emissions and environmental impact. All stakeholders, including customers, should be aware of the impact of energy storage.

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