Abstract
For decades, maximum power coefficient limit, known as the Betz limit, has been accepted as a theoretical optimum value for wind turbine power extraction; nevertheless, some reports, exceeding this limit, have already been published. To explain this phenomenon and show a different point of view, a novel theoretical and ideal analysis based on flow conservation law and areas’ quotient is presented, supported by a review of works related to surpassing the power coefficient limit approached from different perspectives.
Highlights
Wind power has become an important source of energy for humanity; in recent years, the installed capacity has grown considerably to reach hundreds of Giga Watts as it was reported in [1]. e importance of wind energy nowadays is crucial to face the energetic problems around the world; as established by [2], wind energy has evolved from an emerging technology to a near-competitive technology. is fact, combined with an increasing global focus on political desire in the energy supply diversification and environmental concern, promotes wind energy has an important role in the future electricity market
Energy efficiency is a highlight; because of this, new and sophisticated control equipment is currently developed to extract the most energy from the wind, and several works about overviews of emerging technologies of wind energy conversion systems (WECS) have already been published in recent years, for example [7,8,9], but it is necessary to move back 100 years to the past to identify and understand the origin of wind turbine power extraction limit, or at least, as it has been known for decades
The analysis of the power coefficient resulted in two equations based on the relationship among ideal wind tunnel cross-sectional areas with no dimensional limits. e maximum value of curves generated by the models derived from the analysis in this work overcame the Betz limit, providing an alternative to explain published papers dealing with surpassing power coefficient classical limit, a reality that needed an explanation and cannot be denied
Summary
Wind power has become an important source of energy for humanity; in recent years, the installed capacity has grown considerably to reach hundreds of Giga Watts as it was reported in [1]. e importance of wind energy nowadays is crucial to face the energetic problems around the world; as established by [2], wind energy has evolved from an emerging technology to a near-competitive technology. is fact, combined with an increasing global focus on political desire in the energy supply diversification and environmental concern, promotes wind energy has an important role in the future electricity market. Another study, published by Khamlaj and Rumpfkeil [21], states that some wind turbine models have been developed based on experimental data to highlight their potential to surpass the Betz limit. It is mentioned that shrouded turbines equipped with a flange can overcome the Betz limit As it can be seen, several studies existed and experimental results were reported which establish that the Betz limit has been surpassed; in this paper, an explanation about this phenomenon is presented.
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