The way energy is stored depends primarily on the source of energy. According to the latter, we know the following methods of energy storage:
1. Chemical energy storage. Chemical energy is a form of potential energy, storage of which further depends on its source. We know the following methods or mediums for chemical energy storage:
Hydrogen. Although the colourless, odourless, tasteless and non-toxic gas has potentials as a source of energy, it is primarily used as an energy storage medium for subsequent use. Examples include underground hydrogen storage involving the use of underground caverns and empty gas and oil fields to store grid energy for intermittent energy resources such as wind power and solar energy for instance.
Biofuels and biomass. They do not refer to energy storage as such but are rather examples of chemical energy storage. When wood logs or biofuels are burned, they release energy that is stored in the bonds of molecules and atoms.
Liquid nitrogen. Just like hydrogen, liquid nitrogen shows potentials as a source of energy but instead, it is used as a form of energy storage. It can be used to generate electricity or refrigeration and cooling.
Oxy-hydrogen. It is a mixture of oxygen and hydrogen which when ignited, releases high pressure and high temperature steam that can be used to generate electricity.
Other. There are many other mediums to store chemical energy. Examples include:
- hydrogen peroxide; it is best known for its uses as bleach and cleaning agent although it is also used as rocket fuel
- vanadium pentoxide; it is used in vanadium redox batteries, a type of flow batteries that are used to store various forms of chemical energy including electric power produced by wind farms
2. Electrochemical energy storage. It involves the use of various devices which convert chemical energy into electricity. Examples include:
Battery. It is a widely used device that converts stored chemical energy into electricity. Two basic types of batteries exist which known as the primary batteries or non-rechargeable batteries and secondary batteries which can be recharged and used multiple times.
Fuel cell. It refers to a device which converts chemical energy into electricity through chemical reaction. Several different types of fuel cells exist but all feature a cathode, anode and an electrolyte.
3. Electrical energy storage. It involves the use of an electric field to store energy. Examples include:
Capacitor and supercapacitor (double-layer capacitor). Both are electrical components that are used to store electric charge but as its name reveals, supercapacitor can store more electric charge. Capacitor is typically used a a short-term backup power, while supercapacitor can also be used to power large engines including vehicles. But it is also often used to run low-power devices such as portable media players, PC Cards, etc..
Superconducting magnetic energy storage (SMES). It refers to a relatively new technology which stores electricity from the grid within a magnetic field that is created by the flow of current in a coil.
4. Thermal energy storage. It refers to methods that are used to store thermal energy in order to use it to cool or heat buildings when the temperature inside is above or below the internal energy in the stored substance.
Hot water storage tank. It refers to a water tank that stores hot water for space heating, washing, bathing, etc.. Hot water storage tanks are a common feature of wood furnaces and solar thermal collectors.
Storage heater. It is an electric heater that stores energy during the evening or night and releases heat during the day when the price of base load electricity is higher. Storage heaters work by accumulating heat in ceramic material or clay bricks.
Steam accumulator. It refers to a steel tank that contains steam under pressure. It is used to balance between supply and demand by accepting steam when the supply is greater than demand and to release it when demand exceeds the supply.
5. Mechanical energy storage. Methods to store energy that is produced by motion include:
Hydraulic accumulator. It is a storage reservoir which stores non-compressible fluid under pressure. There are several types of hydraulic accumulators but the most widely used is the so-called compressed gas accumulator which contains gas under pressure, usually nitrogen.
Flywheel energy storage. Like its name suggests, it is a method to store energy through a flywheel. This type of mechanical energy storage is used to store grid energy and energy that is generated by wind farms but it also shows potentials in transportation and as an emergency power source.