1.2 Types of energy storage systems

Energy storage systems come in various forms, each with unique characteristics. From mechanical systems like pumped hydro and flywheels to electrochemical solutions like batteries and supercapacitors, these technologies play crucial roles in managing energy supply and demand.

Thermal and chemical storage methods, including phase change materials and hydrogen, offer additional options. Electrical storage technologies like superconducting magnetic energy storage round out the diverse array of solutions available for different energy needs and applications.

Mechanical Energy Storage

Pumped Hydro Storage and Compressed Air Energy Storage

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• Pumped hydro storage utilizes two water reservoirs at different elevations to store energy
  • During off-peak hours, water is pumped from the lower reservoir to the upper reservoir, converting electrical energy into potential energy
  • During peak demand, water is released from the upper reservoir, driving turbines to generate electricity (hydroelectric power)
• Compressed air energy storage (CAES) involves compressing air and storing it in underground caverns or tanks
  • Off-peak electricity is used to compress air, which is then stored in a reservoir
  • During peak demand, the compressed air is released, heated, and expanded through a turbine to generate electricity

Flywheel Energy Storage

• Flywheel energy storage systems store energy in the form of kinetic energy using a rotating mass (flywheel)
  • Electrical energy is used to accelerate the flywheel, which stores energy in its rotational motion
  • When energy is needed, the flywheel's rotation drives a generator to produce electricity
• Flywheels are typically made of high-strength materials (carbon fiber composites) to withstand high rotational speeds
• Advantages of flywheel energy storage include high power density, fast response times, and long cycle life

Electrochemical Energy Storage

Batteries

• Batteries store energy through electrochemical reactions, converting chemical energy into electrical energy
• Consists of one or more electrochemical cells, each containing an anode, cathode, and electrolyte
  • During discharge, electrons flow from the anode to the cathode through an external circuit, while ions move through the electrolyte
  • During charging, the process is reversed, converting electrical energy back into chemical energy
• Various types of batteries are used for energy storage, including lead-acid, lithium-ion, and flow batteries (vanadium redox flow batteries)

Supercapacitors

• Supercapacitors, also known as ultracapacitors or electrochemical capacitors, store energy in an electric field between two electrodes
• Consist of two conductive plates (electrodes) separated by an insulating material (dielectric)
  • Energy is stored by accumulating opposite charges on the electrodes' surfaces
• Offer high power density, rapid charge/discharge cycles, and long lifetimes compared to batteries
• Suitable for applications requiring quick bursts of energy (regenerative braking in electric vehicles)

Thermal and Chemical Energy Storage

Thermal Energy Storage

• Thermal energy storage (TES) systems store energy in the form of heat or cold for later use
• Sensible heat storage materials (water, molten salts) store energy by increasing their temperature without changing phase
• Latent heat storage materials (phase change materials, PCMs) store energy during phase transitions (solid-liquid, liquid-gas)
  • PCMs absorb or release large amounts of energy during phase change while maintaining a constant temperature
• TES can be used for space heating, cooling, and industrial process heat applications

Chemical Energy Storage and Hydrogen Storage

• Chemical energy storage involves storing energy in chemical bonds of substances
• Hydrogen storage is a form of chemical energy storage where hydrogen gas is stored for later use
  • Hydrogen can be produced through electrolysis using excess renewable electricity
  • Stored hydrogen can be used in fuel cells to generate electricity or burned directly for heat
• Hydrogen storage methods include compression, liquefaction, and storage in metal hydrides or other materials (carbon nanotubes)

Electrical Energy Storage

Electrical Energy Storage Technologies

• Electrical energy storage directly stores electricity without conversion to other forms of energy
• Superconducting magnetic energy storage (SMES) systems store energy in a magnetic field created by the flow of direct current in a superconducting coil
  • Superconductors allow current to flow with virtually no resistance, enabling efficient energy storage
• Capacitors store energy in an electric field between two conductive plates separated by an insulating material (dielectric)
  • Capacitors offer high power density but relatively low energy density compared to batteries

Supercapacitors (Electrochemical Capacitors)

• Supercapacitors bridge the gap between conventional capacitors and batteries
• Store energy through both electrostatic storage (like capacitors) and electrochemical reactions (like batteries)
• Consist of two high-surface-area electrodes separated by an electrolyte
  • Energy is stored in the electric double layer formed at the electrode-electrolyte interface
• Offer higher energy density than conventional capacitors and higher power density than batteries
• Suitable for applications requiring rapid charge/discharge cycles and long lifetimes (electric vehicles, grid stabilization)