Wind Turbines: Vertical vs. Horizontal Axis

Why are the wind propellers of wind generators always in the vertical position and never horizontal? It would seem they could be stacked horizontally, could be enclosed easily and would be more aesthetic for building tops. — Bill V., San Clemente, CA.

Bill, Horizontal “axis” wind turbines (vertical blades) are the traditional conventional design. They consist of a rotor with one to twenty blades driving a generator or a pump either directly or through a gearbox, chain or belt system. A tail vane or fantail is required to direct the machine. These turbines are usually more efficient than vertical-axis units. Savonius and Darius are two designs of vertical-axis machines, and these types of units do not have to be directed into the wind. The Savonius windmill was the brainchild of Sigrid Savonius of Finland, racecar driver of the 1930s. The design produces a low-speed high-torque unit that can be used for pumping water through a gearing mechanism, generating electricity — and the design also has the advantage of an aerodynamic effect called the “Magnus principle,” whereby suction is formed by the air moving over the convex face of the rotor. The Darius windmill was named after its French inventor. It is also known as “catenary” because of its profile when operating. Darius units, also known as “egg beaters,” will often not start to turn by themselves and need either an electric start or use a small Savonius unit attached to the top. As the blades revolve they lose some energy as they head into the wind, reducing the output. Some newer versions are coming on the market that can “self start” but they are not as widely commercialized. Southwest Windpower (AZ) and Bergey Windpower (OK) have tens of thousands of horizontal-axis wind turbines globally, and you can be sure they would have adopted vertical-axis designs if they were more viable. — Scott Scott Sklar is President of The Stella Group in Washington, DC, a distributed energy marketing and policy firm. Scott, co-author of “A Consumer Guide to Solar Energy,” uses solar technologies for heating and power at his home in Virginia.
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Scott, founder and president of The Stella Group, Ltd., in Washington, DC, is the Chair of the Steering Committee of the Sustainable Energy Coalition and serves on the Business Council for Sustainable Energy, and The Solar Foundation. The Stella Group, Ltd., a strategic marketing and policy firm for clean distributed energy users and companies using renewable energy, energy efficiency and storage. Sklar is an Adjunct Professor at The George Washington University teaching two unique interdisciplinary courses on sustainable energy, and is an Affiliated Professor of CATIE, the graduate university based in Costa Rica. . On June 19, 2014, Scott Sklar was awarded the prestigious The Charles Greely Abbot Award by the American Solar Energy Society (ASES) and on April 26, 2014 was awarded the Green Patriot Award by George Mason University in Virginia.

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