Enipedia

The second generation of Compressed Air Energy Storage deals with the thermal issues to achieve higher efficiences. Currently, there are a number of companies and demonstration plants. Efficiencies between 70 and 80% are forecasted.

Applications: long term-storage, short-term storage, arbitrage, distributed/off-grid storage, frequency or voltage regulation, reserve grid capacity, mobility

Compressing air is a way to store energy, and combining this with a generator yields a way of storing electricity. Systems have been in use in applications such as starting large engines or in the propulsion of mine locomotives. At a larger scale, the technology is used to shift the energy demand for smaller and larger electricity grids, providing storage. Air heats up when compressed, and cools down when decompressed, generating a natural barrier for efficiency. To counter this, some installations use an external source of heat, like natural gas. Efficiencies up to 45% are attainable.

The nickel–iron battery (NiFe battery) is a rechargeable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. The active materials are held in nickel-plated steel tubes or perforated pockets. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated. The battery needs maintenance, as hydrogen builds up when (dis)charging.

A flow battery is a type of rechargeable battery where rechargeability is provided by two chemical components dissolved in liquids contained within the system and separated by a membrane. Ion exchange (providing flow of electrical current) occurs through the membrane while both liquids circulate in their own respective space. Cell voltage is chemically determined by the Nernst equation and ranges, in practical applications, from 1.0 to 2.2 Volts. A flow battery is technically akin both to a fuel cell and an electrochemical accumulator cell (electrochemical reversibility).

Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy; adding energy to the system correspondingly results in an increase in the speed of the flywheel. Most FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are being developed.

Hydrogen is being developed as an electrical energy storage medium. Hydrogen is produced, then compressed or liquefied, stored, and then converted back to electrical energy or heat or used as an input to (industrial) processes. Hydrogen can be used as a fuel for portable (vehicles) or stationary energy generation. Compared to pumped water storage, CAES and batteries, hydrogen has the advantage that it is a high energy density fuel that can be fed into the grid, stored or converted in ammonia and then stored. Hydrogen can be directly converted to electrical energy using an electrolyser.

The lead–acid battery was invented in 1859 by French physicist Gaston Planté and is the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, makes it attractive for use in motor vehicles to provide the high current required by automobile starter motors.

Applications: short-term storage, arbitrage, distributed/off-grid storage

The lithium-air battery, Li-air for short, is a metal-air battery chemistry that uses the oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow. Originally proposed in the 1970s as a possible power source for electric vehicles, Li-air batteries recaptured scientific interest in the late 2000s due to advances in materials technology and an increasing demand for environmentally safe and oil-independent energy sources.

The lithium–sulfur battery (Li–S battery) is a rechargeable battery, notable for its high energy density. By virtue of the low atomic weight of lithium and moderate weight of sulfur, Li–S batteries are relatively light; about the density of water. They were demonstrated on the longest and highest-altitude solar-powered airplane flight in August, 2008.

Applications: short-term storage, arbitrage, distributed/off-grid storage, mobility

A lithium-ion battery (sometimes Li-ion battery or LIB) is a member of a family of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, no memory effect, and only a slow loss of charge when not in use.

The nickel–cadmium battery (NiCd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. The abbreviation Ni-Cd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd): the abbreviation NiCad is a registered trademark of SAFT Corporation, although this brand name is commonly used to describe all Ni–Cd batteries.

A nickel–metal hydride battery, abbreviated NiMH or Ni–MH, is a type of rechargeable battery. Its chemical reactions are somewhat similar to the largely obsolete nickel–cadmium cell (NiCd). NiMH use positive electrodes of nickel oxyhydroxide (NiOOH), like the NiCd, but the negative electrodes use a hydrogen-absorbing alloy instead of cadmium, being in essence a practical application of nickel–hydrogen battery chemistry.

Applications: short-term storage, arbitrage, distributed/off-grid storage, mobility

Pumped-storage hydroelectricity (PSH) is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power.

Sodium-ion batteries are a type of reusable battery that uses sodium-ions as its charge carriers. This type of battery is in a developmental phase. Sodium-ion batteries can be made portable and can function at room temperature (approx. 25˚C).

Applications: long term-storage, arbitrage, distributed/off-grid storage, reserve grid capacity

A sodium–sulfur battery is a type of molten-salt battery constructed from liquid sodium (Na) and sulfur (S). This type of battery has a high energy density, high efficiency of charge/discharge (89–92%) and long cycle life, and is fabricated from inexpensive materials. However, because of the operating temperatures of 300 to 350 °C and the highly corrosive nature of the sodium polysulfides, such cells are primarily suitable for large-scale non-mobile applications such as grid energy storage.

Applications: short-term storage, arbitrage, mobility

Supercapacitors are divided into three families, based on electrode design:

Superconducting Magnetic Energy Storage (SMES) systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature.

Applications: frequency or voltage regulation

Electrical Vehicles can be connected to the grid, and used to balance the (local) power distribution network. This is a feasible solution for an energy system with a higher penetration rate of intermittent renewable energy generation. Take for example the Netherlands: 6M electric vehicles with an average capacity of 20 kWh, with 20% connected to the network at any given time, providing 50% of the charging rate yields about 6M * 20 * 50% * 30% = 18 GW of instantaneous power, allbeit for a small time-frame.

Zinc–air batteries (non-rechargeable), and zinc–air fuel cells (mechanically-rechargeable) are metal-air batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. Sizes range from very small button cells for hearing aids, larger batteries used in film cameras that previously used mercury batteries, to very large batteries used for electric vehicle propulsion. During discharge, a mass of zinc particles forms a porous anode, which is saturated with an electrolyte.