Environmental Energy
Research Collaboration

The Windmil Blade Project 

Conventional windmills are limited in size by the gusts and storm winds that exceed the ability of the generator and tower to absorb power. The problem of excess forces caused by wind gusts limits the size of rotors. In essence, large rotors capture light winds and low wind speeds, but large rotors also capture too much wind at high wind speeds. If the rotors could dump wind easily, then larger rotors can be used to capture energy at lower wind speeds.

In large windmills this ability to dump wind is accomplished by having the blades stall, turn out of the wind, or hydraulically feathering the blades to prevent overpowering the mill. Each of these techniques has problems. Some current technology stalls the blades limiting over-powering. However, stalling leaves a large wind capture cross section intact in the rotor, and this produces large resulting forces.

The research undertaken in this project addresses a non-hydraulic - automatic feathering technique. Feathering produces a similar decrease in power output with wind speed, but the resulting horizontal forces are much smaller than stalling. This allow for a larger rotor for any tower/generator size. All feathering to date has been with mechanically feathering of blades. This works well for large windmills, but the cost of hydraulics is prohibitive in smaller units that are more useful for distributed generation.

The specific research is to design, build and test a series of self feathering blades. These blades could be used as retrofit to existing mills or could be part of a new low-cost windmill design that has only one.

Currently, a proposal to do this work is before the DOE. A summary of this proposal is also available. A Patent is being submitted on this IP.