Wind power storage development is essential for renewable energy technologies to become economically feasible. There are many different ways in which one can store electrical energy, the following outlines the various media used to store grid-ready energy produced by wind turbines. For more on applications of these wind storage technologies, read Solving the use-it-or-lose-it wind energy problem
Electrochemical batteries consist of two or more electrochemical cells. The cells use chemical reaction(s) to create a flow of electrons – electric current. Primary elements of a cell include the container, two electrodes (anode and cathode), and electrolyte material. The electrolyte is in contact with the electrodes. Current is created by the oxidation-reduction process involving chemical reactions between the cell’s electrolyte and electrodes.
When a battery discharges through a connected load, electrically charged ions in the electrolyte that are near one of the cell’s electrodes supply electrons (oxidation) while ions near the cell’s other electrode accept electrons (reduction), to complete the process. The process is reversed to charge the battery, which involves ionizing of the electrolyte. An increasing number of chemistries are used for this process.
Some electrochemical batteries (e.g., automobile batteries) contain electrolyte in the same container as the cells (where the electrochemical reactions occur). Other battery types – called flow batteries – use electrolyte that is stored in a separate container (e.g., a tank) outside of the battery cell container. Flow battery cells are said to be configured as a ‘stack’. When flow batteries are charging or discharging, the electrolyte is transported (i.e., pumped) between the electrolyte container and the cell stack. Vanadium redox and Zn/Br are two of the more familiar types of flow batteries. A key advantage to flow batteries is that the storage system’s discharge duration can be increased by adding more electrolyte (and, if needed to hold the added electrolyte, additional electrolyte containers). It is also relatively easy to replace a flow battery’s electrolyte when it degrades.
Capacitors store electric energy as an electrostatic charge. An increasing array of larger capacity capacitors have characteristics that make them well-suited for use as energy storage. They store significantly more electric energy than conventional capacitors. They are especially well-suited to being discharged quite rapidly, to deliver a significant amount of energy over a short period of time (i.e., they are attractive for high-power applications that require short or very short discharge durations).
Compressed Air Energy Storage
Compressed air energy storage (CAES) involves compressing air using inexpensive energy so that the compressed air may be used to generate electricity when the energy is worth more. To convert the stored energy into electric energy, the compressed air is released into a combustion turbine generator system. Typically, as the air is released, it is heated and then sent through the system’s turbine. As the turbine spins, it turns the generator to generate electricity. For larger CAES plants, compressed air is stored in underground geologic formations, such as salt formations, aquifers, and depleted natural gas fields. For smaller CAES plants, compressed air is stored in tanks or large on-site pipes such as those designed for high-pressure natural gas
transmission (in most cases, tanks or pipes are above ground).
Flywheel Energy Storage
Flywheel electric energy storage systems (flywheel storage or flywheels) include a cylinder with a shaft that can spin rapidly within a robust enclosure. A magnet levitates the cylinder, thus limiting friction-related losses and wear. The shaft is connected to a motor/generator. Electric energy is converted by the motor/generator to kinetic energy. That kinetic energy is stored by
increasing the flywheel’s rotational speed. The stored (kinetic) energy is converted back to electric energy via the motor/generator, slowing the flywheel’s rotational speed.
Key elements of a pumped hydroelectric (pumped hydro) system include turbine/generator equipment, a waterway, an upper reservoir, and a lower reservoir. The turbine/generator is
similar to equipment used for normal hydroelectric power plants that do not incorporate storage. Pumped hydro systems store energy by operating the turbine/generator in reserve to pump water uphill or into an elevated vessel when inexpensive energy is available. The water is later released when energy is more valuable. When the water is released, it goes through the turbine which turns the generator to produce electric power.
Superconducting Magnetic Energy Storage
The storage medium in a superconducting magnetic energy storage (SMES) system consists of a coil made of superconducting material. Additional SMES system components include power
conditioning equipment and a cryogenically cooled refrigeration system. The coil is cooled to a temperature below the temperature needed for superconductivity (the material’s ‘critical’ temperature). Energy is stored in the magnetic field created by the flow of direct current in the coil. Once energy is stored, the current will not degrade, so energy can be stored indefinitely (as long as the refrigeration is operational).
Thermal Energy Storage
There are various ways to store thermal energy. One somewhat common way that thermal energy storage is used involves making ice when energy prices are low so the cold that is stored can be used to reduce cooling needs – especially compressor-based cooling – when energy is expensive.
Filed Under: Energy storage