Low Wind Speed Technology Phase I: Clipper Turbine Development Project

Clipper Windpower Technology, Inc.

Project Description: Design studies conducted by the U.S. Department of Energy, its 

subcontractors, and others have indicated that several new design configurations offer 

significant opportunities for reducing cost over current wind turbine configurations. 

These technologies include reduction in the cost of and improvements in the efficiency 

of the drivetrain; increases in energy capture by increasing rotor diameter; and 

improved active wind turbine controls. Several techniques can be used to achieve 

these results. Many, such as decreasing drivetrain weight to make taller towers more 

cost effective, or advanced rotor designs that decrease loads and allow greater rotor 

diameter, are interrelated. 

This project is developing a new turbine design that incorporates a number of advanced 

elements. This new design, designated the Clipper C-93 Liberty turbine, uses a highly 

innovative multiple-drive path gearbox feeding four advanced permanent magnet 

generators. The multiple-drive path design radically decreases individual gearbox 

component loads, which reduces gearbox weight and size. The new generators significantly reduce component mass by eliminating much of the copper that would be 

required for windings in the rotor. The machine will also take advantage of advanced 

feedback controls to reduce load excursions in turbulent wind conditions and optimize 

pitch schedules to reduce drivetrain loads and improve energy capture. The new 

machine, with its 93-meter rotor, 75-meter hub height, and 2.5-MW rating promises 

to be significantly lighter, less costly, and easier to maintain than other machines in 

this rating.

Project Type: Prototype Development 

Total Project Budget: $18,955,065

Industry Cost Share: $9,359,147 

DOE Cost Share: $9,595,918

Planned Project Duration: October 2002–December 2006

Contacts:

NREL/Sandia: Clipper Windpower Technology, Inc.:

Alan Laxson, NREL Amir Mikhail, Clipper Windpower Technology, Inc.

1617 Cole Blvd. 6305 Carpinteria Avenue #300

Golden, Colorado 80401 Carpinteria, California 93013-2901

303-384-6944 805-690-3275

alan_laxson@nrel.gov amikhail@clipperwind.com

Current Status: NREL began field tests on the prototype in 2005.

Clipper 2.5-MW Liberty Turbine installed in 

Medicine, Wyoming.

This Clipper 2.5-MW drivetrain underwent 

dynamometer testing at the National Wind 

Technology Center.

A Strong Portfolio for a Strong America • Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment, and greater energy 

independence for America. Working with a wide array of state, community, industry, and university partners, the U.S. Department of Energy’s Office of Energy Efficiency 

and Renewable Energy invests in a diverse portfolio of energy technologies.

For more information contact EERE Information Center • 1-877-EERE-INF (1-877-337-3463) • www.eere.energy.gov

Produced for the U.S. Department of Energy by the National Renewable Energy Laboratory, a DOE national laboratory

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste.

DOE/GO-102006-2199

March 2006