Compressed-air energy storage (CAES) is a commercialized electrical energy storage … Contact online >>
Compressed-air energy storage (CAES) is a commercialized electrical energy storage
Covers advances in mechanical energy storage systems, both electricity and
Block diagram of mechanical energy storage systems.
An illustration of pumped hydroelectric storage [8].
An illustrative topology of a CAES [8].
An illustrative topology of a FES [8].
Advanced science. Applied technology.
Mechanical energy storage works in complex systems that use heat, water or air with compressors, turbines, and other machinery, providing robust alternatives to electro-chemical battery storage. The energy industry as well as the U.S. Department of Energy are investing in mechanical energy storage research and development to support on-demand renewable energy that can be stored for several days.
Mechanical energy storage research and development at Southwest Research Institute (SwRI) is helping to develop and commercialize several emerging technologies. Our services span the spectrum of energy storage with expertise in fluids, machinery, chemistry, materials and electrical engineering. Mechanical energy storage integrates with several disciplines, including:
Science and engineering services that support development of mechanical storage and other emerging energy storage technologies include:
Pumped heat energy storage converts electric energy from the grid into thermal energy that is stored as a thermal potential. At full capacity, the system can store energy in tanks for hours or up to several weeks before converting it back to electrical energy. The system can then provide greater than 10 hours of electricity at rated power. The capacity of the system can also be extended by increasing the volume of the storage tanks.
SwRI is currently building a pumped heat energy storage demonstration system with the support of the U.S. Department of Energy, and also has broad expertise in the design, development and operation of supercritical carbon dioxide power systems that are also compatible with energy storage systems.
Electric power systems use pumped storage hydropower (PSH) for load balancing. The method uses the gravitational potential energy of water, pumped from a lower-elevation to a higher-elevation reservoir using low-cost, off-peak surplus electric power to run the pumps. During periods of high electrical demand, the stored water is returned to the lower reservoir, driving turbines to produce electric power. Although the losses of the pumping process make it a net consumer of energy, the system creates value by providing more electricity during periods of peak demand, when electricity prices are highest.
Compressed air energy storage (CAES) plants work similarly to pumped storage hydropower plants, but rather than pumping water between reservoirs, these types of plants compress and store ambient air in an underground cavern during periods of excess power. When power is needed, the air is heated and expanded in a turbine to drive power generation.
SwRI is involved in many different projects advancing CAES technology, including the development of heat exchangers and isothermal compression technology in addition to reciprocating and centrifugal compressor technologies for improving machinery efficiency and range. The Institute is the assignee of a patent for a piston that generates compressed air in a CAES cavern.
Flywheel energy storage systems store energy as kinetic energy in a high-speed rotor connected to a motor or generator, typically in a vacuum environment. The flywheels decelerate in discharge mode and are ideal for short-duration fast-response backup power.
SwRI is involved in projects advancing flywheel component technologies including magnetic bearings, auxiliary bearings and rotordynamic modeling.
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Mechanical energy storage can be added to many types of systems that use heat, water or air with compressors, turbines, and other machinery, providing an alternative to battery storage, and enabling clean power to be stored for days.
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While the physics of mechanical systems are often quite simple (e.g. spin a flywheel or lift weights up a hill), the technologies that enable the efficient and effective use of these forces are particularly advanced. High-tech materials, cutting-edge computer control systems, and innovative design makes these systems feasible in real-world applications.
A flywheel is a rotating mechanical device that is used to store rotational energy that can be called up instantaneously. At the most basic level, a flywheel contains a spinning mass in its center that is driven by a motor – and when energy is needed, the spinning force drives a device similar to a turbine to produce electricity, slowing the rate of rotation. A flywheel is recharged by using the motor to increase its rotational speed once again.
Flywheel technology has many beneficial properties that enable us to improve our current electric grid. A flywheel is able to capture energy from intermittent energy sources over time, and deliver a continuous supply of uninterrupted power to the grid. Flywheels also are able to respond to grid signals instantly, delivering frequency regulation and electricity quality improvements.
Flywheels are traditionally made of steel and rotate on conventional bearings; these are generally limited to a revolution rate of a few thousand RPM. More advanced flywheel designs are made of carbon fiber materials, stored in vacuums to reduce drag, and employ magnetic levitation instead of conventional bearings, enabling them to revolve at speeds up to 60,000 RPM.
You can learn more about flywheel technologies below.
Flywheel energy storage systems (FESS) use electric energy input which is stored in the form of kinetic energy. Kinetic energy can be described as "energy of motion," in this case the motion of a spinning mass, called a rotor.
The rotor spins in a nearly frictionless enclosure. When short-term backup power is required because utility power fluctuates or is lost, the inertia allows the rotor to continue spinning and the resulting kinetic energy is converted to electricity. Most modern high-speed flywheel energy storage systems consist of a massive rotating cylinder (a rim attached to a shaft) that is supported on a stator – the stationary part of an electric generator – by magnetically levitated bearings. To maintain efficiency, the flywheel system is operated in a vacuum to reduce drag. The flywheel is connected to a motor-generator that interacts with the utility grid through advanced power electronics.
Some of the key advantages of flywheel energy storage are low maintenance, long life (some flywheels are capable of well over 100,000 full depth of discharge cycles and the newest configurations are capable of even more than that, greater than 175,000 full depth of discharge cycles), and negligible environmental impact. Flywheels can bridge the gap between short-term ride-through power and long-term energy storage with excellent cyclic and load following characteristics.
Typically, users of high-speed flywheels must choose between two types of rims: solid steel or carbon composite. The choice of rim material will determine the system cost, weight, size, and performance. Composite rims are both lighter and stronger than steel, which means that they can achieve much higher rotational speeds. The amount of energy that can be stored in a flywheel is a function of the square of the RPM making higher rotational speeds desirable. Currently, high-power flywheels are used in many aerospace and UPS applications. Today 2 kW/6 kWh systems are being used in telecommunications applications. For utility-scale storage a ''flywheel farm'' approach can be used to store megawatts of electricity for applications needing minutes of discharge duration.
More advanced FESS achieve attractive energy density, high efficiency and low standby losses (over periods of many minutes to several hours) by employing four key features: 1) rotating mass made of fiber glass resins or polymer materials with a high strength-to-weight ratio, 2) a mass that operates in a vacuum to minimize aerodynamic drag, 3) mass that rotates at high frequency, and 4) air or magnetic suppression bearing technology to accommodate high rotational speed. Advanced FESS operate at a rotational frequency in excess of 100,000 RPM with tip speeds in excess of 1000 m/s. FESS are best used for high power, low energy applications that require many cycles.
Additionally, they have several advantages over chemical energy storage. They have high energy density and substantial durability which allows them to be cycled frequently with no impact to performance. They also have very fast response and ramp rates. In fact, they can go from full discharge to full charge within a few seconds or less. Flywheel energy storage systems (FESS) are increasingly important to high power, relatively low energy applications. They are especially attractive for applications requiring frequent cycling given that they incur limited life reduction if used extensively (i.e., they can undergo many partial and full charge-discharge cycles with trivial wear per cycle).
FESS are especially well-suited to several applications including electric service power quality and reliability, ride-through while gen-sets start-up for longer term backup, area regulation, fast area regulation and frequency response. FESS may also be valuable as a subsystem in hybrid vehicles that stop and start frequently as a component of track-side or on-board regenerative braking systems
Compressed air energy storage (CAES) is a way to store energy generated at one time for use at another time. At utility scale, energy generated during periods of low energy demand (off-peak) can be released to meet higher demand (peak load) periods.
Since the 1870''s, CAES systems have been deployed to provide effective, on-demand energy for cities and industries. While many smaller applications exist, the first utility-scale CAES system was put in place in the 1970''s with over 290 MW nameplate capacity. CAES offers the potential for small-scale, on-site energy storage solutions as well as larger installations that can provide immense energy reserves for the grid.
Compressed air energy storage (CAES) plants are largely equivalent to pumped-hydro power plants in terms of their applications. But, instead of pumping water from a lower to an upper pond during periods of excess power, in a CAES plant, ambient air or another gas is compressed and stored under pressure in an underground cavern or container. When electricity is required, the pressurized air is heated and expanded in an expansion turbine driving a generator for power production.
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