ENERGY STORAGE SYSTEMS

Energy storage systems are employed to store energy for future use. They also help to balance power supply and demand thereby enabling the efficient and optimal performance of energy systems.

Energy storage systems may be classified into mechanical, electrical, chemical, and thermal and hybrid storage systems.

Mechanical energy storage consists of the following; pumped hydro storage (PHS), compressed air energy storage (CAES), flywheel energy storage (FES) and hydraulic energy storage (HES) systems.

Pumped hydro storage stores energy by pumping water from a lower reservoir to an upper reservoir during off peak hours. During peak hours the water flows back to the lower reservoir generating electricity through hydroelectric turbines.

Compressed air storage involves the use of off peak power to pressurize air into underground reservoir or storage mediums like steel, which is then released during peak electricity to power a turbine to generate electricity.

Flywheel energy storage stores energy kinetically in rotating flywheels. Electrical energy is converted into mechanical energy spinning the flywheel. When energy is needed, the flywheel’s kinetic energy is converted back into electricity

Hydraulic energy storage, stores energy by compressing fluids at high pressure in closed cylinders. When energy is needed the high pressure fluid is released to do work.

Electrical energy storage, consist of the following; capacitor energy storage, superconducting magnetic coil (SMES) energy storage and super capacitor or double layer capacitors (DLC).

Capacitor energy storage, stores energy electrostatically in capacitors, superconducting magnetic coils(SMES), stores energy magnetically in superconducting coils while double layer capacitors(DLC) stores energy electrostatically in double layer capacitors(DLCS).

Super capacitors are electrochemical double layer capacitors that store energy as electric charge between two plates, metal or conductive material, separated by a dielectric material. When a voltage differential is applied across the plates they store energy. This energy is released to bridge instant power needs before the main storage takes over.

Superconducting magnetic storage systems store energy in the magnetic field created by the flow of direct current in a coil of cryogenically cooled superconducting materials. The fast response time of these systems make them ideal for regulating network stability as power is released instantly.

Chemical energy storage, consist of the following; battery energy storage, hydrogen energy storage, and fuel cell energy storage.

Battery energy storage stores energy electrochemically in batteries (e.g. lithium ion, lead acid, nickel cadmium). Chemical reactions convert electrical energy into chemical energy. When energy is needed the battery terminals are connected to the load thereby releasing electric energy.

Hydrogen energy storage stores chemically in hydrogen gas. Electrolysis splits water into hydrogen and oxygen. The hydrogen is stored and later used in fuel cells or internal combustion engine to generate power.

Fuel cells stores energy chemically in Hydrogen or an hydrocarbon fuel like methane. The fuel cell subsequently uses that hydrogen or an hydrocarbon like methane stored, as fuel and air to generate peak hour electricity.

Thermal energy storage consist of the following; molten salt thermal energy storage, phase change material (PCM) storage and thermal energy storage tanks. Molten salt thermal energy storage, stores energy thermally in molten salts, phase change materials (PCMS) storage, stores energy thermally in PCMS while ice storage stores energy thermally in ice and thermal energy tanks stores energy thermally in fluids.

Phase change material stores energy thermally in PCMs, PCMs change phase for example from solid to liquid or vice-versa as they absorb and release heat energy.

Ice storage stores energy in ice during off peak hours and melted during peak hours to provide cooling.

Thermal energy storage systems stores energy in a storage medium which is usually a fluid at high temperature in insulated containment and recovered later to be used for electricity generation using heat engine cycles.

Hybrid energy storage consists of the following; hybrid battery capacitors systems and hybrid mechanical electrical systems. While hybrid battery and capacitor combine both technologies, hybrid mechanical electrical system combines also both mechanical and electrical storage technologies.

The application of energy storage system is a vital aspect of the power supply infrastructure, particularly in the incorporation of renewable energy system as support for the grid infrastructure. The use of energy storage solution helps in various ways to mitigate the inefficiencies in the grid network.  it use helps to smooth solar and wind power output, voltage regulation, peak savings, backup power and for electric vehicles to drive and power the charging infrastructure.

The benefit of energy storage systems cannot be overemphasized; their use will result in improved grid optimization, stability, enhanced energy security and probably reduced dependence on the main grid infrastructure. The only limitation in their use is the large amount of upfront cost, scalability to large energy system and the technical limits in enforcing a uniform standard for safe operational use.

The future of renewable storage systems will depend on the development of low cost, reliable and safe energy storage solutions and this will depend on several factors; continued decline in rechargeable battery cost, increased adoption of solid state batteries, advancement in sodium ion and other alternative battery chemistry, increased deployment of renewable energy supply systems and the expanded use of energy storage in electric vehicles.

Definitely, the future belongs to advances in the following storage technologies; solid state batteries, sodium batteries, lithium air batteries, grapheme based batteries, hydrogen energy storage, superconducting magnetic coil storage and so on.

 

 

 

SOURCES:

• Energy storage: A key to renewable energy by peter F. Varadi.
• Energy storage systems for renewable energy by Umamaheswara Reddy Kari.
• Battery technology: A handbook for engineers and innovators by Homi Tehrani.
• Energy storage in smart Grids: concept, technologies and methods by Tao Ma, Hongcai Zhang.
• Mechanical energy storage: Technologies and applications by Andreas Sumper.
• Advances in energy storage research by Li Lu, Xingjiang Li.