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Flywheel energy storage

News International-French

9 Oct 2013

Beacon Power introduces a carbon-fiber rotor for energy storage.

Flywheel energy storage works by accelerating a cylindrical assembly called a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. The energy is converted back by slowing down the flywheel. The flywheel system itself is a kinetic, or mechanical battery, spinning at very high speeds to store energy that is instantly available when needed.

At the core of Beacon's flywheel is a carbon-fiber composite rim, supported by a metal hub and shaft and with a motor/generator mounted on the shaft. Together the rim, hub, shaft and motor/generator assembly form the rotor. When charging (or absorbing) energy, the flywheel's motor acts like a load and draws power from the grid to accelerate the rotor to a higher speed. When discharging, the motor is switched into generator mode, and the inertial energy of the rotor drives the generator which, in turn, creates electricity that is then injected back into the grid. Multiple flywheels may be connected together to provide various megawatt-level power capacities. Performance is measured in energy units - kilowatt-hours (kWh) or megawatt-hours (MwH), indicating the amount of power available over a given period of time.

Beacon's Smart Energy 25 flywheel has a high-performance rotor assembly that is sealed in a vacuum chamber and spins between 8,000 and 16,000 rpm. At 16,000 rpm the flywheel can store and deliver 25 kWh of extractable energy. At 16,000 rpm, the surface speed of the rim would be approximately Mach 2 - or about 1500 mph - if it were operated in normal atmosphere. At that speed the rim must be enclosed in a high vacuum to reduce friction and energy losses. To reduce losses even further, the rotor is levitated with a combination of permanent magnets and an electromagnetic bearing.

Beacon Power's grid-scale Smart Energy Matrix is made up of multiple integrated systems of (10) Smart Energy 25 flywheels, interconnected in an array, or matrix, to provide energy storage for certain utility applications. The Smart Energy Matrix can absorb and deliver megawatts of power for minutes, providing highly responsive frequency regulation capabilities for increased grid reliability.

A word about sustainability and energy storage
Sustainability is a philosophy and set of practices that have gained considerable acceptance among global organizations in recent years. The concept of sustainability refers to business conduct that addresses the economic, social and environmental impacts of operations; the so-called "triple bottom line." More than 50% of Fortune 100 companies have adopted sustainable business practices and issue comprehensive annual progress reports. These companies, including many in the energy sector, are taking a longer-term view that considers the total impact of a product or service, from development through end-of-life.

Flywheel-based energy storage systems, unlike fossil-fuel power plants that are used on the grid for frequency regulation, are sustainable "green" technology solutions that consume no fossil fuel, nor produce CO2 or other emissions during operation.

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