What are the three types of energy storage?

Storage options include batteries, thermal, or mechanical systems. All of these technologies can be paired with software that controls the charge and discharge of energy.

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There are many types of energy storage; this list serves as an informational resource for anyone interested in getting to know some of the most common technologies available. You can learn more about these and other energy storage technologies in the U.S. Department of Energy&#;s Energy Storage Handbook .

Batteries

There are various forms of batteries, including: lithium-ion, flow, lead acid, sodium, and others designed to meet specific power and duration requirements.

Initially used for consumer products, lithium-ion batteries now have a range of applications including smaller residential systems and larger systems that can store multiple megawatt hours (MWh) and can support the entire electric grid. These systems typically house a large number of batteries together on a rack, combined with monitoring and management units. These systems have a small footprint for the amount of energy they store. For example, a system the size of a small refrigerator could power an average home for several days. A utility-scale system of 100 MWh could fit on less than 0.5 acres.

Lithium-ion batteries have received a lot of press for their rapidly declining costs, due to the growing popularity of electric vehicles.

A different type of battery is a flow battery in which energy is stored and provided by two chemicals that are dissolved in liquids and stored in tanks. These are well suited for longer duration storage.

Thermal

Thermal systems use heating and cooling methods to store and release energy. For example, molten salt stores solar-generated heat for use when there is no sunlight. Ice storage in buildings reduces the need to run compressors while still providing air conditioning over a period of several hours. Other systems use chilled water and dispatchable hot water heaters. In all cases, excess energy charges the storage system (heat the molten salts, freeze the water, etc.) and is later released as needed.

Mechanical Systems

Flywheels

Flywheels store energy in a rapidly spinning mechanical rotor and are capable of absorbing and releasing high power for typically 15 minutes or less, although longer duration systems are being developed. These systems can balance fluctuations in electricity supply and demand where they respond to a control signal adjusted every few seconds. They also recapture braking energy from electric trains in some installations or provide short-term power until backup generation comes online during a grid outage, such as in a critical manufacturing process where product would be lost by a momentary electric interruption.

Pumped Hydro Power

Pumped hydroelectric facilities are the most common form of energy storage on the grid and account for over 95% of the storage in use today. During off-peak hours, turbines pump water to an elevated reservoir using excess electricity. When electricity demand is high, the reservoir opens to allow the retained water to flow through turbines and produce electricity. Siting these systems can be difficult because of the terrain needed (an upper and lower pool of water) and large footprint.

Emerging Technologies

Compressed air, superconducting magnets, underground pumped storage, and hydrogen storage are all forms of emerging energy storage that are in different stages of development. Like NYSERDA, many storage vendors are technology agnostic&#;they can use their software to dispatch different storage technologies and will procure the storage technology from a manufacturing partner that best suits the requirements of the site.

Energy storage technologies are technologies that store energy through devices or physical media for later utilization when needed. Energy storage technology can be categorized according to the storage medium, can be divided into mechanical energy storage, electrical energy storage, electrochemical energy storage, thermal energy storage and chemical energy storage.

This paper focuses on three of the main electrical energy storage technologies. They are pump energy storage, compressed air energy storage and electrochemical energy storage.

1. Pumped Storage

This is currently the most widely used large-scale power storage technology.

(1) Basic Principle

Pumps and turbines are set up between two reservoirs at different heights. At times of low power loads, electrically driven pumps are used to pump water from the lower reservoir to the higher reservoir. At peak loads, water is released from the high reservoirs to generate electricity through the turbine-generator units.

(2) Characteristics

• It belongs to large-scale, centralized energy storage, and the technology is quite mature, which can be used for energy management and peaking of the power grid.

• Efficiency is generally about 65%~75%, and can reach up to 80%~85%.

• Fast load response (10% load change takes 10 seconds), from full stop to full load generation in about 5 minutes, from full stop to full load pumping in about 1 minute.

• Has the ability of daily regulation, suitable for cooperation with nuclear power plants, large-scale wind power generation, ultra-large-scale solar photovoltaic power generation.

(3) Disadvantages

• Needs upper and lower pools.

• The choice of plant site depends on geographical conditions, which has certain difficulties and limitations.

• There is a certain distance from the load center, long distance transmission is required.

(4) Application

Currently, the world average for the share of pumped storage units in a country&#;s total installed capacity is about 3%. As of the end of , the total capacity of energy storage units in the world was 184.6GW, of which pumped storage was 171.0GW, accounting for 92.63%.

2. Compressed Air Energy Storage

Compressed air is stored in cylinders or underground storage tanks to store the potential energy of compressed air. When electricity is needed, the compressed air is released to drive the turbine to generate electricity.

(1) Basic Principle

Compressed air energy storage using air as a carrier of energy. Large-scale compressed air energy storage using excess electricity will be compressed air and stored in an underground structure (such as underground caves). When needed, the compressed air is then mixed with natural gas and burned and expanded to power a gas turbine.

Currently there are various forms of compressed air energy storage systems. Which can be categorized according to the working medium, storage medium and heat source: conventional compressed air energy storage systems (which require fossil fuel combustion), compressed air energy storage systems with heat storage devices, and liquid-gas compression energy storage systems.

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(2) Advantages

It has a peak shifting function and is suitable for use in large-scale wind farms. Because the mechanical work generated by wind energy can directly drive the compressor to rotate, reducing the intermediate conversion into electricity, thus improving efficiency.

(3) Disadvantages

Requires a large cavern to store compressed air, is closely related to geographical conditions, and is suitable for a very limited number of locations.

Requires a gas turbine and a certain amount of gas as fuel, and is suitable for energy management, load leveling, and peak shaving.

A non-adiabatic compressed air energy storage technology has been developed in the past. The heat released when the air is compressed is not stored and is dissipated through cooling. Instead, the compressed air needs to be reheated before entering the turbine. The efficiency of the whole process is therefore low, usually below 50%.

(4) The significance of compressed air energy storage power plant:

Air is the best choice for &#;energy multimedia&#;. It is a global trend to vigorously develop solar, wind, wave and nuclear energy, but supply and demand are often asynchronous and unbalanced. The only &#;energy multimedia&#; capable of converting, storing, and accessing all forms of energy is &#;air&#;. And it is the &#;best candidate&#; for this &#;role&#;.

Huge economic and social benefits calculated on the basis of one-third of the power generation capacity, can save four or five hundred million tons of coal per year. This is equivalent to the annual output of dozens of medium and large coal mines. And year after year, the economic and social benefits are huge, saving a lot of resources and promoting sustainable economic and social development.

3. Electrochemical Storage

Electrochemical storage mainly includes a variety of secondary batteries, lead-acid batteries, lithium-ion batteries, sodium-sulfur batteries and liquid current batteries. Application of various batteries (mainly lithium-ion batteries) chemical storage principle to store electrical energy. When charging the electrical energy is converted into chemical energy of the battery, and when discharging the chemical energy is converted into electrical energy output.

In which lead-acid batteries and lithium batteries are more widely used.

3.1 Lead-acid Batteries

(1) Basic Principle

Lead-acid battery is one of the most widely used batteries in the world. Lead-acid batteries within the anode (PbO2) and cathode (Pb) immersed in the electrolyte (dilute sulfuric acid), between the two poles will produce a potential of 2V.

(2) Advantages

• Technology is very mature, simple structure, low cost, easy maintenance; -Cycling life can be up to about times.

• Cycle life up to about times; -Efficiency up to 80% to 90%.

• Efficiency up to 80% to 90%, cost-effective.

(3) Disadvantages

• Decrease in usable capacity in deep, fast and high power discharge; -Lower energy density, lower life time.

• Lower energy density, shorter life.

• Lead metal has a greater impact on the environment

(4) Application

Lead-acid batteries are often used as accidental or backup power for power systems, and in the past, most stand-alone photovoltaic power generation systems were equipped with such batteries. Currently there is a trend to gradually be replaced by other batteries (such as lithium-ion batteries).

3.2 Lithium-ion Battery

(1) Basic Principle

Lithium-ion battery is actually a lithium-ion concentration battery, positive and negative electrodes are composed of two different lithium ion embedded compounds.

When charging, Li + from the positive electrode de-embedded through the electrolyte embedded in the negative electrode, the negative electrode is in the lithium-rich state, the positive electrode is in the lithium-poor state.

Discharge is the opposite, Li + from the negative electrode de-embedded, through the electrolyte embedded in the positive electrode, the positive electrode in the lithium-rich state, the negative electrode in the lithium-poor state.

(2) Advantages

• Lithium-ion battery efficiency can reach more than 95%.

• Discharge time can be up to several hours.

• Cycling up to times or more, fast response.

Lithium-ion batteries are practical batteries with the highest specific energy in batteries. And there are a variety of materials that can be used for its anode and cathode. For example: lithium cobaltate lithium-ion batteries, lithium manganate lithium-ion batteries, lithium iron phosphate lithium-ion batteries and so on.

(3) Disadvantages

• The price of lithium-ion batteries is still high.

• Sometimes overcharging can lead to heat, combustion and other safety issues.

(4) Application

Because of the application of lithium-ion batteries in portable and mobile devices such as electric cars, computers, cell phones, etc.. It has now become almost the most widely used battery in the world.

The high energy density and power density of lithium-ion batteries is the main reason why it has been able to gain wide application and attention. Its technology is developing rapidly, and in recent years, mass production and multi-occasion applications have led to a sharp decline in its price, and thus its increasing use in power systems.

Lithium-ion battery technology is still under continuous development, and current research is focused on further improving its service life and safety, cost reduction, and the development of new positive and negative electrode materials.

In addition, there are flywheel energy storage, super capacitor energy storage, superconducting energy storage and other technologies, but the current application scale is small. The above three are the current mainstream large-scale power storage technology. With the development of technology, a variety of energy storage methods will continue to improve and application.

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