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Compressor energy storage system could lead to wind power on demand: Ricardo and General Compression collaborate to develop compressor to overcome wind power intermittency.

RICARDO is working with American firm General Compression to overcome the problems of wind power intermittency, developing a storage system it reckons can offer "wind on demand".

In a traditional windfarm the turbines are used to generate DC current, which is passed to an inverter, matched to the system frequency and fed into the electricity grid. Power transmission is immediate, so the wind energy provider has to take whatever the current market clearing price is for grid electricity.

The Dispatchable Wind system under development uses a compressor-based energy storage concept that could act as a buffer for windfarm output peaks. The DC generator on the wind turbine is replaced by an array of compressors and intercoolers that take atmospheric air and raise it to a given storage pressure. This high-pressure air is piped to a reservoir and stored, ready to be expanded through a turbine to produce electricity whenever needed.

Much of the development work has revolved around building a compressor capable of delivering a required service pressure of around 100bar within the structure of a wind turbine, yet light enough to be fitted in the nacelle immediately behind the rotor.


The compressor must also match the power input of the wind turbine almost instantaneously.

General Compression felt none of the then-available compressor technologies met the combination of performance, cost, power density and reliability requirements identified. So, with the help of Ricardo, it set about developing the Dragonfly high-power density compressor.

As a first step a small-scale 37kW proof-of-concept demonstrator, the V0, was made. While this machine confirmed the basic principle of operation, a production device of 10 times this rating was required to enable the Dragonfly to form one of the four compressor stages in the nacelle which would be capable of handling 1.5MW--the typical power rating of a commercial wind turbine--and delivering reservoir compressed air in excess of 100bar.

Ricardo was used in the detail design and development process, with its computer-aided engineering technology used to examine overall gas dynamics and possible drive mechanisms. Like any compressor, the Dragonfly generates its own pulsed flow with consequent pressure wave dynamics.

Ricardo's Wave software simulated the complete system of four compressor stages and associated manifolds, ducting and intercoolers installed in the nacelle. Its Valdyn software was also used to enable engineers to calculate critical parameters such as bearing loads, contact stresses, and resonant vibration modes.

While the detail design of the compressor is subject to patent applications, Ricardo said it appeared to offer a viable solution. The first full-size prototype Dragonfly will be tested this year in parallel with engineering design work on the next-stage prototype.

General Compression said that analysis indicates that Dispatchable Wind will have a system efficiency of around 55%. The company aims to bring Dispatchable Wind to market in 2010.

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Title Annotation:TECHNOLOGY
Publication:Professional Engineering Magazine
Geographic Code:4EUUK
Date:Feb 27, 2008
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