Compressed air flywheels and batteries
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Compressed Air, Flywheels and Batteries. Nabil Reza. Compressed Air Energy Storage. Off-peak electricity is used to power a motor/generator that drives compressors to force air into an underground storage reservoir.

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Compressed Air, Flywheels and Batteries

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Compressed air flywheels and batteries

Compressed Air, Flywheels and Batteries

Nabil Reza

Compressed air energy storage

Compressed Air Energy Storage

  • Off-peak electricity is used to power a motor/generator that drives compressors to force air into an underground storage reservoir.

  • When the demand for electric power peaks, The compressed air is returned to the surface, and is fed into a gas turbine, allowing the turbine to produce electricity more efficiently.

  • Natural Gas is burned to preheat air.

  • Storage reservoirs can be large underground caverns, depleted wells, or aquifers.



Co 2 reductions

CO2 Reductions

  • CAES power plant system can achieve >85% reductions in fossil fuel use.

  • Can achieve over 80% reduction in CO2 output

  • Adiabatic Compressed-Air Energy Storage recovers the heat that emerges during air compression.

  • The stored thermal energy replaces the need for natural gas, causing the entire system to run on renewable power alone

Adiabatic caes

Adiabatic CAES



Current installations

Current Installations

  • 280 MW plant in Hunthorf, Germany - been active since 1978

  • 110 MW plant at McIntosh, Alabama - operating since 1991

Cost efficiency

Cost & Efficiency

  • Insatallation cost - Depending on hours of storage, $750/kW to $1,200/kW.

  • Running cost at about 10.5 cents/kWh

  • Diabatic storage efficiency is around 55%

  • 70% for adiabatic CAES



  • CAES systems can be used on very large scales. CAES is ready to be used with entire power plants.

  • Fast start-up time – 9 min, compared to 20 min for conventional combustion turbine

  • Helps solving peak load crisis



  • A flywheel is a flat disk or cylinder that spins at very high speeds, storing kinetic energy.

  • When required, the flywheel then delivers rotational energy to power an electric generator until friction dissipates it.



Kinetic energy

Kinetic Energy

  • Ef = (1/2) x I x ω2


    Ef = flywheel kinetic energy (Nm (Joule), ftlb)

    I = moment of inertia (kg m2, lb ft2)

    ω = angular velocity (rad/s)

  • I = k x m x r2


    k = inertial constant

    m = mass of flywheel (kg, lb)

    r = radius (m, ft) 

Physical characteristics

Physical Characteristics

  • Tensile strength - the stronger the disc, the faster it may be spun, and the more energy the system can store.

  • Energy storage efficiency - 50% for mechanical bearings, 85% for magnetic bearings

Current installations costs

Current Installations & Costs

  • Beacon Power - 20 MW plant in Pennsylvania

  • Installation cost - around $1,500 per kilowatt



  • Little affected by temperature fluctuations,

  • Take up relatively little space

  • Have lower maintenance requirements than batteries

  • Very durable.



  • Storage devices that convert Chemical Energy to Electrical Energy

  • Batteries are made up of cells, containing a chemical called an electrolyte.

  • Each cell has two electrically conductive electrodes immersed into its electrolyte, one releases electrons into the electrolyte, and the other absorbs them.

  • When an electrical device is connected to the electrodes, an electrical current flows through it and provides electric power for its operation.

Battery types

Battery Types

  • Lead-Acid

  • Lithium-ion

  • Lithium polymer

  • Nickel metal hydride

  • Sodium sulfur

  • Flow Battery

Flow battery

Flow Battery

  • Electrolyte is stored in external containers and circulated through the battery cell stack as required.

  • Flow batteries use two liquid electrolytes that react when pumped through a cell stack. The battery is broken down into a cell stack and two large electrolyte tanks.

  • As the electrolyte flows past a porous membrane in each cell, ions and electrons flow back and forth, charging or discharging the battery.



Sodium sulphur battery

Sodium Sulphur Battery

  • The active materials in a NaS battery are molten sulfur as the positive electrode and molten sodium as the negative.

  • The electrodes are separated by a solid ceramic, sodium - alumina, which also serves as the electrolyte.

  • During Charge and Discharge cycle, electrons flow from Na to S and vice versa through an external circuit.



Current installations1

Current Installations

  • Flow Batteries

    • 250 KW installation in Castle Valley, Utah

  • NaS Batteries

    • 4 MW installation for Texas Power Grid

    • 270 MW installation in Japan by Tokyo-based NGK Insulators

Cost efficiency1

Cost & Efficiency



  • Electricity storage can be deployed throughout an electric power system—functioning as generation, transmission, distribution, or end-use assets.

  • Sometimes placing the right storage technology at a key location can alleviate a supply shortage situation, relieve congestion, defer transmission additions or substation upgrades, or postpone the need for new capacity.















Thank you


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