The Next Generation Wind Turbine Development Project

Publication Number: 500-02-031F
Publication Date: March 2002

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Executive Summary

It has long been recognized that commercially available, utility scale wind turbines are not able to produce competitively priced electricity. Recently, the Federal Production Tax Credit for wind energy was again extended. Further, under the Commission’s Renewables Program, many wind energy producers in the State also receive production payments ranging from 0.5¢ to 1.5¢ per kilowatt-hour (KWH).

In 1994, the Department of Energy (DOE) created the "Next Generation Turbine Development Project" to help develop a new wind turbine capable of generating lower cost electricity. In 1995, The Wind Turbine Company (WTC) won a competitive solicitation under this program and began work on its new turbine. In June 1998, the Commission, again through a competitive solicitation, chose to support WTC’s project with the intent of accelerating the development of this new design in order to achieve a more rapid entry into the commercial marketplace.

The goal of the DOE and the Commission was a commercial wind turbine that could produce electricity at good wind resource sites for an unsubsidized price of 3.0-3.5¢ per KWH. WTC believes this goal can be attained by 2005, if not sooner. The DOE’s target is 2010. The overall project goal identified in Contract No. 500-97-032 Work Statement was "to design, develop and demonstrate a 350 Kilowatt (KW) rated-capacity wind turbine that will produce electricity at prices that do not need subsidies or premiums to compete in the emerging electricity market-place. This overall project goal supports PIER program objectives by; improving energy cost/value of California’s electricity, causing substantial reduction in air pollution deriving from fossil-fuel electricity generation, and providing positive impacts to California’s state and local economies by the creation of new jobs and new tax revenues."

Objectives

Two technical objectives were identified:

• Demonstrate the feasibility of employing all the wind turbine concepts (the proof of concept (POC) and the Wind Turbine Company (WTC) 350).
• Achieve the identified weight reduction targets. This target will provide comfort that WTC’s targeted "should cost" objectives for the commercial WTC 350 can be achieved.

The economic objective was:

• To develop a 350 KW wind turbine capable of producing electricity at prices competitive with the lowest cost sources of conventional electricity generation. The specific economic objective is to produce electricity for $0.035 per KWH or less when installed in annual quantities of 100 units or more in windfarms featuring Class 5 wind resources (or at 6.7 meters per second (15 mph) sites).

In a collaborative effort between WTC, the Commission, and the DOE, through the National Renewable Energy Laboratory, two prototype wind turbines were developed.

Wind Turbine Company’s POC turbine, rated at 250 KW was installed in February 2000 near Denver, Colorado, and has operated successfully since May 2000. Although minor system bugs have occurred, they have for the most part been eliminated. The POC has accomplished all design objectives. Most importantly, through measurement of stress loads at approximately 60 locations on the turbine it has been demonstrated that

1. the computer models used to predict loads and to establish component configuration and system design were slightly conservative in their predictions, and
2. the stress loads encountered by the POC are significantly (approximately 3 orders of magnitude) less that theloads encountered by conventional wind turbines. The POC has also demonstrated the turbine control system works as desired.

A 500 kW prototype was installed in December 2001 in Los Angeles County. This "pre-commercial" turbine was grid connected in February 2002 and began initial testing in early March. This turbine will be placed in a commercial operating mode in May/June 2002.

In addition to test objectives, WTC’s commercial objective is to develop engineering and manufacturing plans that will demonstrate a clear path to the manufacturing cost targets for this turbine and its commercial derivatives. Based on the cost of the 500 kW turbine and the DOE’s goal of producing 3.0¢/kWh wind power when cumulative production reaches 500 turbines, WTC determined it must achieve a production learning curve of 88 percent (every time cumulative production doubles the average cost of the new machines decreases by 12 percent from the previous level), which is well within the range achieved by manufacturers of large scale equipment.

Outcomes

It is too early to demonstrate that the overall project goal, development of a wind turbine that does not need subsidies or premiums to produce competitively priced electricity has been or can be met; however, there is evidence to suggest WTC is on the right track. Technical Objectives

• WTC accomplished the first technical goal identified above. Since May 2000, when the POC began test operation, the turbine has operated almost 1,400 hours. Data gathered to date provides valuable information about stress and fatigue loads encountered by the machine.
• The identified turbine weight objective was not achieved. This is attributable to the fact that the rated capacity of the final turbine objective has more than doubled from 350 kW to 750 kW.
• Although the absolute weight target identified in Contract No. 500-97-032 has been exceeded, the relative weight relationship is strong evidence that the turbine weight objective has been reached.

Economic objective

• WTC’s turbines have yet to attain the PIER Program economic goals, however, as will be discussed in the Program Outcomes section, WTC believes these goals are in reach and could even be attained within the targeted timeframe.

As was painfully demonstrated during the 12 months from May 2000 to May 2001, California needs a significant amount of new electricity generating capacity that does not depend on the vagaries of the natural gas markets. Wind energy clearly has a major role to play in creating a long-term, stable supply of electricity for the State from a non-polluting source. Although California already has a considerable number of wind turbines installed in the main wind energy resource areas, the potential for future development is much larger and only now beginning to be better understood. The availability of a commercially viable wind turbine that does not require subsidization will only increase the potential for wind energy.

Not only will stable, low-cost supplies of wind energy benefit the State’s residents, businesses, and governmental agencies, the resulting new production facilities and the local manufacture of wind turbines will provide important new jobs. This is particularly true in rural regions of the state where higher winds are usually found and which often suffer from higher unemployment and fewer job opportunities than the more urbanized parts of the state.

Achievement of the cost reduction goal will require one additional hardware development effort, the development of a new, purpose-designed rotor blade for use on the turbine. This new blade set will increase the turbine’s rated capacity to 750 kW with no additional cost and therefore will result in an immediate, significant improvement in the turbine’s economic performance.

Conclusions

The following conclusions were reached.

• The principle conclusion of the NGT Project was that WTC’s wind turbine concept works very well. Data gathered to date incontrovertibly supports the conclusion that WTC’s hinged-blade coupled with its proprietary flap motion restraint system significantly reduces the largest source of fatigue stress loading on a wind turbine - the loads resulting from the wind bending rigidly attached blades in the downwind direction.
• A finding important for all future wind turbine development efforts is that the predictive system structural dynamics models used to design the POC and WTC 500 wind turbines were surprisingly accurate in loads prediction. The ADAMS and BLADED models, have convinced WTC’s engineering team of their value. It is critical for the future of the wind industry that hardware designers take advantage of and benefit from the most sophisticated tools available and that the tools get better.
• During the execution of this program WTC’s engineering team moved steadily away from the simpler is better school of thought to the school that relies on understanding the complexity of the environment in which wind turbines operate. Better understanding is required in order to achieve better results, and such understanding is not possible in the absence of better tools such as the dynamic analysis models ADAMS and BLADED.

Commercialization Potential

WTC believes the case for a commercially viable version of its new wind turbine is stronger today than ever. Although it is clear that the WTC 500, configured with all components designed for application on a 750 KW capacity turbine thus incurring the additional expense of a machine with 50 percent greater capacity, would struggle commercially, once the purpose designed blade set is available the turbine will quickly achieve its commercial potential. This machine will be commercially available in 2003 and within a year if not sooner will be capable of beating the COE target of 3.5¢/KWH contained in WTC’s proposal to the Commission by up to 1/2 cent per KWH. Subsidies will then no longer be necessary.

Recommendations

• The PIER Program is a powerful source of funding for new technology development in the renewable energy industry. WTC encourages the State of California make every effort to assure that the DOE’s renewable programs are lined up in support of the Commission’s programs.
• During the execution of contracts, WTC suggests that, depending on contract duration, the Commission require a regular, or semi-annual sit-down debriefing on project progress and plans with critical Commission staff and management.
• To enable the Commissioners to obtain a better first hand understanding of the agency’s programs, the Commission should strongly recommend contractor attendance at important policy and program review meetings involving the Commissioners.
• The Commission’s Contract Manager position changed hands three times in four years. Thus there was some discontinuity and re-education. As suggested in the Observations above, a good balance is required to achieve a desirable level of project involvement by an agency’s Project/Contract Manager. It seems the Commission’s staffing limitations may, unfortunately, preclude a deeper involvement in the Commission’s PIER projects.

Benefits to California

Although California has yet to see the major benefit of the NGT Project - lower cost wind energy - several less consequential benefits have already occurred:

• WTC has identified and worked closely with a number of component suppliers and these relationships are expected to continue into future commercial production.
• WTC has California-based employees and will add to its California payroll as quickly as commercial considerations permit.
• The Company has identified one promising location where it could establish a wind turbine assembly facility as soon as commercial business opportunities develop.
• Within its resource constraints, WTC has made a concerted effort to identify opportunities to deploy its wind turbines in commercial developments in the state.
• WTC has an agreement with a Los Angeles-based developer to develop one or more wind projects totaling approximately 100 MW of installed capacity with the electricity to be sold to the DWP.
• WTC is working with a major utility-affiliated wind development company to evaluate the feasibility of deploying WTC’s new 750 kW wind turbines in a major project in Southern California. WTC believes the lower cost and increased capacity factor achievable by its turbines will make the difference between a decision to go forward with the project or not.
• WTC believes it has helped, to a limited extent, enhance the role of the Commission PIER Program Renewables Group with NREL’s Wind Program organization.

The longer term and major benefit to California remains the goal of lower cost wind energy that does not require subsidies for either on going operation or for project development in the first place.

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Abstract

The Wind Turbine Company’s new wind turbine is based on concepts employed in earlier wind turbines. It incorporates a proprietary, hinged-rotor-blade, a concept from the helicopter industry that operates with a blade "Flap Motion Restraint System" which controls movement of the blades in the out of plane direction. This concept was expected to significantly reduce the major source of wind induced stress loading on the machine - that associated with bending rotor blades that are rigidly attached to the rotor shaft. Computer models predicted this configuration would reduce loads by three orders of magnitude compared with conventional upwind turbines. By reducing loads the turbine designer can safely eliminate material required in conventional wind turbines to absorb them. Material reduction means cost savings. The initial cost of a utility scale wind turbine represents about 70 percent of the resulting electricity cost. Significant reductions in the cost of wind-generated electricity must come from turbine cost reductions. The goal of the "proof-of-concept" turbine was to demonstrate predicted load reductions could be achieved and measured loads are less than were predicted. With this finding, it is possible to reduce material requirements across all major turbine structural components by approximately 40 percent compared with similarly rated upwind turbines. This will translate into a 20-25 percent cost reduction. Combined with a guy-cable supported tower, a more economic means of elevating the rotor hub height to capture higher winds aloft to produce more energy, which can only be effectively employed on downwind turbines (blades operate downwind of the tower), the effect is expected to result in an electricity cost reduction of 30 percent or more compared with upwind turbines. Goals for the second prototype turbine are to demonstrate the technology on a commercial scale and provide the basis for manufacturing economic analyses to assure manufacturing cost targets can be achieved.

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Table of Contents

Executive Summary

Abstract

1.0 Introduction

2.0 Project Outcomes

3.0 Conclusions and Recommendations

4.0 Glossary

5.0 References

Appendices

Appendix I - Turbine Checkout and Commissioning Checklist

Appendix II - POC Test Matrix

Appendix III - POC Measured vs. Predicted Loads (Consultant Reports, Not Available for Public Release)

Appendix IV - Turbine Manufacturing Costs Summary

Appendix V - NGT Project Cost Sharing Details

List of Figures

Figure 1: WTC Proof-of-Concept

Figure 2: WTC 500

Figure 3: Timeline for Development of WTC Wind Turbines under DOE/NREL NGT Project

Figure 4: Relationship between proposed CEC PIER Program project to develop WTC 350 and DOE/NREL project to develop WTC 1000

Figure 5: Vestas V-47, 660 kW, leading 3-blade upwind turbine

Figure 6: California Energy Commission Next Generation Turbine Project Work Plan

Figure 7: Comparison of Annual Cumulative Blade Root Fatigue Cycles

Figure 8: Proposed WTC 1000 Featuring Hinged Blades and Teetering Hub

Figure 9: Cut-away illustration of POC drive train

Figure 10: Comparison of WTC expected power curves with Vestas power curve

Figure 11: Turbine Sales Price/kW Required to Achieve COE Values

Figure 12: Learning Curve WTC Will Have to Obtain to Achieve COE Goals

List of Tables

Table 1: Weight comparison - WTC 350 versus 3-blade, upwind, 350 kW turbine

Table 2: Weight comparison - proposed WTC 350 versus WTC 750

Table 3: Figures of Merit - Vestas V-47 versus WTC Turbines

Table 5: Comparison of Economic Performance - Vestas V-47 versus WTC 750

Table 6: Planned and Actual Duration of Project Activities