through the design of less expensive, longer-lived, and higher-efficiency rotor blades. A guiding principle in creating this design should be that knowledge of aerodynamic forces must be carefully integrated with the structural response of the material, all balanced by the practicalities of field experience and tempered by the need to manufacture a consistently high-quality product at reasonable cost.

This committee has examined the experience base accumulated by wind turbines and the accompanying R&D programs sponsored by the Department of Energy. We have concluded that a wind energy system such as described above is within the capability of engineering practice. But certain gaps in knowledge exist, so achieving the goal without costly and inefficient trial and error requires certain critical research and development. Because of the fragile nature of the wind power equipment producers in the United States, this will require an R&D investment from the Department of Energy.

The committee cannot conclude without commenting on the status of the wind power equipment industry. Because of the decrease in the rate of installation of machines in the last 5 years (since the tax incentives expired), there currently is only one major integrated manufacturer in the United States; only a few companies are actively producing blades. In recent years a major Japanese manufacturer has entered the world market, joining the European manufacturers who have been participants for some time. As a result, the U.S. industry is not in a financial position to engage in the R&D necessary to gain worldwide technological leadership for what the committee sees as a future growing worldwide market for wind power. The committee believes that the United States is facing a future reduction in most fossil fuel sources of energy. When this is coupled with a resurgence of public concern over environmental issues in energy production, the need to develop wind power energy to the fullest extent possible seems compelling.

RESEARCH RECOMMENDATIONS

The committee has identified four goals to guide the research needs in wind turbine rotor technology:

Goal 1 To improve the material properties and design capability so that the structure will either withstand higher stresses or the same level of stress for a much longer period of time.

Goal 2: To lower the operating stress levels by altering the structural/configuration design.

Gual 3: To improve the blade manufacturing process so that quality variations and cost are minimized.

Goal 4: To reduce the cost of blades enough so that periodic replacement becomes cost-effective.

The details of specific research recommendations are given in Chapter 7 (Conclusions and Recommendations) and, in greater depth, at the ends of Chapters 2, 3, 4, 5, and 6. The main research tasks are summarized below.

MATERIALS

Initiate a program to generate long-term (10-year-equivalent), high-cycle fatigue (108-109) data for candidate structural materials: glass-reinforced plastic, wood/epoxy, and advanced high-modulus composite materials under appropriate environmental conditions. The program would contribute an element in a needed databank for wind turbine blade materials.

DESIGN

The wind turbine industry needs design tools that are beyond the capability for development by the private sector. For example, it is necessary to be able to compute laminate stresses in three dimensions and to



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