NASA's Contributions to Aeronautics, Volume 1 by National Aeronautics & Space Administration. - HTML preview

CASE

13

Good Stewards: NASA’s Role in Alternative Energy

Bruce I. Larrimer

Case-13 Cover Image: A full-pitch, fiberglass Vestas wind turbine in Rome in 2009. The Danish company remains the largest in the wind turbine industry. R.P. Hallion.

This case study reviews two separate National Aeronautics and Space Administration (NASA) programs that each involved research and development (R&D) in the use of alternative energy. The first part of the case study covers NASA’s participation in the Federal Wind Energy Program from 1974 through 1988. NASA’s work in the wind energy area included design and fabrication of large horizontal-axis wind turbine (HAWT) generators, and the conduct of supporting research and technology projects. The second part of the case study reviews NASA’s development and testing of high-altitude, long-endurance solar-powered unmanned aerial vehicles (UAVs). This program, which ran from 1994 through 2003, was part of the Agency’s Environmental Research and Aircraft Sensor Technology Program.

Wind Energy Program and Large Horizontal-Axis Wind Turbines (1974–1988)

The energy crisis of the 1970s brought about renewed interest in the development of alternative energy sources, including harnessing wind power for the generation of electricity. This renewed interest led to the establishment of the Federal Wind Energy Program in 1974 as part of the Nation’s solar energy program. The initial program overview, technical analysis, and objectives were formalized by the Project Independence Interagency Solar Task Force that was formed in April 1974 and chaired by the National Science Foundation (NSF). Approximately 100 individuals—representing various Government agencies, universities, research laboratories, private industries, and consulting firms—participated in the task force project. Thirteen of the participants were from NASA, including six from NASA Lewis (now NASA John H. Glenn Research Center). The task force’s final findings were outlined in the November 1974 “Project Independence Blueprint” report. The task force identified the six following “most promising” technologies for converting solar energy to a variety of useful energy forms: (1) solar heating and cooling of buildings, (2) solar thermal energy conversion, (3) wind energy conversion, (4) bioconversion to fuels, (5) ocean thermal energy conversion, and (6) photovoltaic electric power systems. The task force noted that the objective of the wind energy conversion part of the program was to improve the efficiency of wind turbine systems in a variety of applications and to reduce their costs. In regard to site selection, the task force concluded that the first attainment of economic viability in the United States would occur in areas such as the Great Plains, Alaska, the Great Lakes, the Atlantic and Pacific coasts, New England, and Hawaii. It concluded that the key to large-scale application of wind energy conversion systems was the reduction of costs through advanced technology, new materials, mass production, and the use of field fabrication techniques. Finally, the task force noted that a closely monitored program of proof-of-concept experiments was expected to reduce cost and constraint uncertainties.[1]

As a prelude to the formation of the wind energy program, NASA Lewis made significant contributions to a wind energy workshop that reviewed both the current status of wind energy and assessed the potential of wind power. This workshop was held as part of the Research Applied to National Needs (RANN) project that led to the National Science Foundation’s role in the initial planning of a 5-year sustained wind energy program. In January 1975, the wind energy program was transferred to the newly formed Energy Research and Development Administration (ERDA), which was incorporated into the newly formed U.S. Department of Energy (DOE) in 1977.

Pursuant to the initial agreement between NASA and the NSF, which had no research centers of its own, NASA’s Lewis Research Center at Lewis Field in Cleveland, OH, was given overall project management for the portion of the Wind Energy Program that involved the development and fabrication of large experimental horizontal-axis wind turbines. NASA Lewis’s responsibilities also included the conduct of supporting research and technology for the wind turbine conversion systems. This sponsorship continued under the Department of Energy once DOE took over the Federal Wind Energy Program. Louis Divone, who initially selected NASA Lewis to participate in the program, was the wind energy program manager for the NSF and later for ERDA and DOE. The program goal was the development of the technology for safe, reliable, and environmentally acceptable large wind turbine systems that could generate significant amounts of electricity at costs competitive with conventional electricity-generating systems.

NASA Lewis engineers were very interested in getting involved in the Wind Energy Program and realized early on that they could make significant contributions because of the Research Center’s long experience and expertise in propeller and power systems, aerodynamics, materials, and structures testing. The selection of NASA Lewis also represented an interesting historical context. Over 85 years earlier, in 1887–1888, in Cleveland, OH, an engineer by the name of Charles F. Brush constructed a 60-foot, 80,000-pound wind-electric dynamo that is generally credited as being the first automatically operating wind turbine for electricity generation. Brush’s wind turbine, which supplied power for his home for up to 10 years, could produce a maximum 12,000 watts of direct current that charged 12 batteries that in turn ran 350 incandescent lights, 2 arc lights, and a number of electric motors. His dynamo made 50 revolutions to 1 revolution of the wind wheel, which consisted of 144 wooden blades and was 56 feet in diameter, accounting for 1,800 square feet of total blade surface swept area. The wind dynamo had an automatic regulator that prevented the power from running above 90 volts at any speed. Brush later dismantled his wind dynamo, apparently without attempting to develop a unit that could feed into a central power network.[2]

The use of wind power to generate electricity achieved a degree of success in rural and remote areas of the United States in the 1920s and 1930s. These generators, however, were small, stand-alone wind-electric systems such as those designed and marketed by Marcellus and Joseph Jacobs, who built three-bladed systems, and the Windcharger Corporation, which built two-bladed generators. Most of these efforts were abandoned in the 1940s and 1950s because of the expansion of electrical utility networks, especially in response to passage of the Rural Electrification Act of 1937 and the availability of low-cost fossil fuels.

The first American effort to build a large wind turbine to feed into a power network was undertaken by Palmer Cosslett Putnam. This effort was funded by the S. Morgan Smith Company, which constructed and installed a 1.25-megawatt wind turbine at Grandpa’s Knob, VT. Prior to fabrication of his turbine, Putnam considered a number of questions that were still being debated years later, including whether to build a vertical- or horizontal-axis wind turbine; if horizontal, how many blades should there be; whether the generator should be aloft or on the ground; whether the drive should be mechanical or hydraulic; whether the tower should rotate or be stationary; and what size generator should be used. He noted that examples of all of these configurations existed in writings on wind power. Putnam, with the concurrence of both Beauchamp and Burwell Smith, decided on using the horizontal-axis, two-bladed stainless steel configuration, with a mechanically driven synchronous generator mounted aloft. He then concluded that the optimum size of a wind turbine generator (WTG) was close to 2 megawatts and noted that studies indicated that increased efficiency appeared to be flat between 2 and 3 megawatts.[3] The Smith-Putnam wind turbine, which supplied power to the Central Vermont Public Service Corporation’s power network, started operations on October 19, 1941, and operated intermittently for a total electric generation period of approximately 16 months. A bearing failure caused a blade separation accident, and the project was terminated in March 1945. While the turbine was not rebuilt, the system’s operation demonstrated that wind could be harnessed on a large scale to produce electricity. The power company, as well as others, envisioned that wind turbines would operate in conjunction with hydroelectric power systems.[4]

In the late 1950s, a German engineer by the name of Ulrich Hütter also built a smaller, 100-kilowatt wind turbine generator (the Hütter-Allgaier wind turbine) that was tied into a power utility grid. Hütter’s machine used a 112-foot-diameter, two-bladed downwind rotor with full span pitch control. The blades were mounted on a teetered hub. In preparation to commence work on its own wind turbines, NASA purchased the plans from Hütter and considered or incorporated a number of design criteria and features of both the Smith-Putnam and Hütter-Allgaier wind turbine generators.[5] NASA also participated in a joint NASA–Danish financing of the restoration of the wind turbine, which was completed in 1977. NASA Lewis later did aerodynamics testing and modeling of the Gedser wind turbine information using the Mod-0 testbed turbine.

NASA Lewis’s involvement in wind energy leading up to its selection to oversee the wind turbine development portion of the Federal Wind Energy Program included designing, at the request of Puerto Rico, a wind turbine to generate electricity for the Island of Culebra. This project grew out of an unrelated NASA Lewis 1972 project to take wind measurements in Puerto Rico. Later on, under the Wind Energy Program, NASA returned to Puerto Rico to build one of the Agency’s first-generation (Mod-0A) wind turbine machines. NASA Lewis’s involvement in the Wind Energy Program also was enhanced by its research of past wind energy projects and its projection of the future feasibility of using wind power to generate electricity for U.S. power utility networks. NASA’s overview and findings were presented as a paper at a symposium held in Washington, DC, that brought together past developers of wind turbines, including Palmer Putnam, Beauchamp Smith, Marcellus Jacobs, and Ulrich Hütter, as well as a new group of interested wind energy advocates.

1973 RANN Symposium Sponsored by the National Science Foundation

In reviewing the current status and potential of wind energy, Ronald Thomas and Joseph M. Savino, both from NASA’s Lewis Research Center, in November 1973 presented a paper at the Research Applied to National Needs Symposium in Washington, DC, sponsored by the National Science Foundation. The paper reviewed past experience with wind generators, problems to be overcome, the feasibility of wind power to help meet energy needs, and the planned Wind Energy Program. Thomas and Savino pointed out that the Dutch had used windmills for years to provide power for pumping water and grinding grain; that the Russians built a 100-kilowatt generator at Balaclava in 1931 that feed into a power network; that the Danes used wind as a major source of power for many years, including the building of the 200-kilowatt Gedser mill system that operated from 1957 through 1968; that the British built several large wind generators in the early 1950s; that the Smith-Putnam wind turbine built in Vermont in 1941 supplied power into a hydroelectric power grid; and that Germans did fine work in the 1950s and 1960s building and testing machines of 10 and 100 kilowatts. The two NASA engineers noted, however, that in 1973, no large wind turbines were in operation.

Thomas and Savino concluded that preliminary estimates indicated that wind could supply a significant amount of the Nation’s electricity needs and that utilizing energy from the wind was technically feasible, as evidenced by the past development of wind generators. They added, however, that a sustained development effort was needed to obtain economical systems. They noted that the effects of wind variability could be reduced by storage systems or connecting wind generators to fossil fuel or hydroelectric systems, or dispersing the generated electricity throughout a large grid system. Thomas and Savino[6] recommended a number of steps that the NASA and National Science Foundation program should take, including: (1) designing, building, and testing modern machines for actual applications in order to provide baseline information for assessing the potential of wind energy as an electric power source, (2) operating wind generators in selected applications for determining actual power costs, and (3) identifying subsystems and components that might be further reduced in costs.[7]

NASA–Industry Wind Energy Program Large Horizontal-Axis Wind Turbines

The primary objective of the Federal Wind Energy Program and the specific objectives of NASA’s portion of the program were outlined in a followup technical paper presented in 1975 by Thomas, Savino, and Richard L. Puthoff. The paper noted that the overall objective of the program was “to develop the technology for practical cost-competitive wind-generator conversion systems that can be used for supplying significant amounts of energy to help meet the nation’s energy needs.”[8] The specific objectives of NASA Lewis’s portion of the program were to: (1) identify cost-effective configurations and sizes of wind-conversion systems; (2) develop the technology needed to produce cost-effective, reliable systems; (3) design wind turbine generators that are compatible with user applications, especially with electric utility networks; (4) build up industry capability in the design and fabrication of wind turbine generators; and (5) transfer the technology from the program to industry for commercial application. To satisfy these objectives, NASA Lewis divided the development function into the three following areas: (1) design, fabrication, and testing of a 100-kilowatt experimental wind turbine generator; (2) optimizing the wind turbines for selected user operation; and (3) supporting research and technology for the systems.

The planned workload was divided further by assignment of different tasks to different NASA Research Centers and industry participants. NASA Lewis would provide project management and support in aerodynamics, instrumentation, structural dynamics, data reduction, machine design, facilities, and test operations. Other NASA Research Centers would provide consulting services within their areas of expertise. For example, Langley worked on aeroelasticity matters, Ames consulted on rotor dynamics, and Marshall provided meteorology support. Initial industry participants included Westinghouse, Lockheed Corporation, General Electric, Boeing, and Kaman Aerospace.

In order to undertake its project management role, NASA Lewis established the Center’s Wind Power Office, which consisted initially of three operational units—one covering the development of an experimental 100-kilowatt wind turbine, one handling the industry-built utility-operated wind turbines, and one providing supporting research and technology. The engineers in these offices basically worked together in a less formal structure, crossing over between various operational areas. Also, the internal organization apparently underwent several changes during the program’s existence. For example, in 1976, the program was directed by the Wind Power Office as part of the Solar Energy Branch. The first two office managers were Ronald Thomas and William Robbins. By 1982, the organization consisted of a Wind Energy Project Office, which was once again under the supervision of Thomas and was part of the Wind and Stationary Power Division. The office consisted of a project development and support section under the supervision of James P. Couch (who managed the Mod-2 project), a research and technology section headed by Patrick M. Finnegan, and a wind turbine analysis section under the direction of David A. Spera. By 1984, the program organization had changed again with the Wind Energy Project Office, which was under the supervision of Darrell H. Baldwin, becoming part of the Energy Technology Division. The office consisted of a technology section under Richard L. Puthoff and an analysis section headed by David A. Spera. The last NASA Lewis wind energy program manager was Arthur Birchenough.

NASA’s Experimental (Mod-0) 100-Kilowatt Wind Turbine Generator (1975–1987)

Between 1974 and 1988, NASA Lewis led the U.S. program for large wind turbine development, which included the design and installation of 13 power-utility-size turbines. The 13 wind turbines included an initial testbed turbine designated the Mod-0 and 3 generations of followup wind turbines designated Mod-0A/Mod-1, Mod-2, and Mod-5. As noted in the Project Independence task force report, the initial 100-kilowatt wind turbine project and related supporting research was to be performed in-house by NASA Lewis, while the remaining 100-kilowatt systems, megawatt systems, and large-scale multiunit systems subprograms were to be performed by contractors under NASA Lewis direction. Each successive generation of technology increased reliability and efficiency while reducing the cost of electricity. These advances were made by gaining a better understanding of the system-design drivers, improving the analytical design tools, verifying design methods with operating field data, and incorporating new technology and innovative designs. However, before these systems could be fabricated and installed, NASA Lewis needed to design and construct an experimental testbed wind turbine generator.

NASA’s first experimental wind turbine (the Mod-0) was constructed at Plum Brook Station in Sandusky, OH, and first achieved rated speed and power in December 1975. The initial design of the Mod-0 drew upon some of the previous information from the Smith-Putnam and Hütter-Allgaier turbines. The primary objectives of the Mod-0 wind turbine generator were to provide engineering data for future use as a base for the entire Federal Wind Energy Program and to serve as a testbed for the various components and subsystems, including the testing of different design concepts for blades, hubs, pitch-change mechanisms, system controls, and generators. Also, a very important function of the Mod-0 was to validate a number of computer models, codes, tools, and control algorithms.

The Mod-0 was an experimental 100-kilowatt wind turbine generator that at a wind speed of 18 miles per hour (mph) was expected to generate 180,000 kilowatthours of electricity per year in the form of 440-volt, 3-phase, 60-cycle alternating current output. The initial testbed system, which included two metal blades that were each 62-feet long from hub to blade tip located downwind of the tower, was mounted on a 100-foot, four-legged steel lattice (pinned truss design) tower. The drive train and rotor were in a nacelle with a centerline 100 feet above ground. The blades, which were built by Lockheed and were based on NASA’s and Lockheed’s experience with airplane wing designs, were capable of pitch change (up and down movement) and full feather (angle of the blade change so that wind resistance is minimized). The hub was of the rigid type, meaning that the blades were bolted to the main shaft. A yaw (deviation from a straight path) control aligned the wind turbine with the wind direction, and pitch control was used for startup, shutdown, and power control functions. When the wind turbine was in a shutdown mode, the blades were feathered and free to slowly rotate. The system was linked to a public utility power network through an automatic synchronizer that converted direct current to alternating current.[9]

A number of lessons were learned from the Mod-0 testbed. One of the first problems involved the detection of larger than expected blade bending incidents that would have eventually caused early fatigue failure of the blades. The blade bending occurred for both the flatwise (out-of-plane) and edgewise (in-plane) blade positions. Followup study of this problem determined that high blade loads that resulted in the bending of the blades were caused by impulses applied to the blade each time it passed through the wake of the tower. Basically, the pinned truss design of the tower was blocking the airflow to a much greater degree than anticipated. The cause of this problem, which related to the flatwise load factors, was confirmed by site wind measurements and wind tunnel tower model tests. The initial measure taken to reduce the blocking effect was to remove the stairway from the tower. Eventually, however, NASA developed the soft tube style tower that later became the standard construction method for most wind turbine towers. Followup study of the edgewise blade loads determined that the problem was caused by excessive nacelle yawing (side-to-side) motion. This problem was addressed by replacing a single yaw drive, which aligns the rotor with the wind direction, with a dual yaw drive, and by adding three brakes to the yaw system to provide additional stiffness.[10]

Both of the above measures reduced the bending problems below the predicted level. Detection of these problems on the testbed Mod-0 resulted in reevaluation of the analytical tools and the subsequent redesign of the wind turbine that proved extremely important in the design of NASA’s subsequent horizontal-axis large wind turbines. In regard to other operational testing of the Mod-0 system, NASA engineers determined that the wind turbine controls for speed, power, and yaw worked satisfactorily and that synchronization to the power utility network was successfully demonstrated. Also, the startup, utility operation, shutdown, and standby subsystems worked in a satisfactory manner. Finally, the Mod-0 was used to check out remote operation that was planned for future power utility systems. In summary, the Mod-0 project satisfied its primary objective of providing the entire Federal Wind Energy Program with early operations and performance data and through continued experience with testing new concepts and components. While NASA Lewis was ready to move forward with fabrication of its next level Mod-0A and Mod-1 wind turbines, the Mod-0 testbed continued to provide valuable testing of new configurations, components, and concepts for over 11 more years.

First Generation DOE–NASA Wind Turbine Systems (Mod-0A and Mod-1) (1977–1982)

The Mod-0 testbed wind turbine system was upgraded from 100 kilowatts to a 200-kilowatt system that became the Mod-0A. Installation of the first Mod-0A system was completed in November 1977, with one additional machine installed each year through 1980 at four locations: Clayton, NM; Culebra, PR; Block Island, RI; and Oahu, HI. This first generation of wind turbines completed its planned experimental operations in 1982 and was removed from service.

The basic components and systems of the Mod-0A consisted of the rotor- and pitch-change mechanism, drive train, nacelle equipment, yaw drive mechanism and brake, tower and foundation, electrical system and components, and control systems. The rotor consisted of the blades, hub, pitch-change mechanism, and hydraulic system. The drive train included the low-speed shaft, speed increaser, high-speed shaft, belt drive, fluid coupling, and rotor blades. The electrical system and components were the generator, switchgear, transformer, utility connection, and slip rings. The control systems were the blade pitch, yaw, generator control, and safety system.[11]

Similar to the Mod-0 testbed, the Mod-0A horizontal-axis machines had a 125-foot-diameter downwind rotor mounted on a 100-foot rigid pinned truss tower. However, this more powerful first generation of turbines had a rated power of 200 kilowatts at a wind speed of 18 miles per hour and made 40 revolutions per minute. The turbine had two aluminum blades that were each 59.9 feet long. The Westinghouse Electric Corporation was selected, by competitive bidding, as the contractor for building the Mod-0A, and Lockheed was selected to design and build the blades. NASA and Westinghouse personnel were involved in the installation, site tests, and checkout of the wind turbine systems.

The primary goal of the Mod-0A wind turbine was to gain experience and obtain early operation performance data with horizontal-axis wind turbines in power utility environments, including resolving issues relating to power generation quality, and safety, and procedures for system startup, synchronization, and shutdown. This goal included demonstrating automatic operation of the turbine and assessing machine compatibility with utility power systems, as well as determining reliability and maintenance requirements. To accomplish this primary goal, small power utility companies or remote location sites were selected in order to study problems that might result from a significant percentage of power input into a power grid. NASA engineers also wanted to determine the reaction of the public and power utility companies to the operation of the turbines. The Mod-0A systems were online collectively for over 38,000 hours, generating over 3,600 megawatthours of electricity into power utility networks. NASA determined that while some early reliability and rotor-blade life problems needed to be corrected, overall the Mod-0A wind turbine systems accomplished the engineering and research objectives of this phase of the program and made significant contributions to second- and third-generation machines that were to follow the Mod-0A and Mod-1 projects. Interface of the Mod-0A with the power utilities demonstrated satisfactory operating results during their initial tests from November 1977 to March 1978. The wind turbine was successfully synchronized to the utility network in an unattended mode. Also, dynamic blade loads during the initial operating period were in good agreement with the calculation using the MOSTAB computer code. Finally, successful testing on the Mod-0 provided the database that led the way for private development of a wide range of small wind turbines that were placed in use during the late 1980s.[12]

Closely related to the Mod-0A turbine was the Mod-1 project, for which planning started in 1976, with installation of the machine taking place in May 1979. In addition to noise level and television interference testing (see below), the primary objective of the Mod-1 program was to demonstrate the feasibility of remote utility wind turbine control. Three technical assessments were planned to evaluate machine performance, interface with the power utility, and examine the effects on the environment. This system was a one-of-a-kind prototype that was much larger than the Mod-0A, with a rated power of 2,000 kilowatts (later reduced to 1,350) and a blade swept diameter of 200 feet. The Mod-1 was the largest wind turbine constructed up to that time. Considerable testing was done on the Mod-1 because the last experience with megawatt-size wind turbines was nearly 40 years earlier with the Smith-Putnam 1.25-megawatt machine, a very different design. Full-span blade pitch was used to control the rotor speed at a constant 35 revolutions per minute (later reduced to 23 rpm). The machine was mounted on a steel tubular truss tower that was 12 feet square at the top and 48 feet square at the bottom. General Electric was the prime contractor for designing, fabricating, and installing the Mod-1. The two steel blades were manufactured by the Boeing Engineering and Construction Company. There was also a set of composite rotor blades manufactured by the Kaman Aerospace Corporation that was fully compatible for testing on the Mod-1 system. The wind turbine, which was in Boone, NC, was tested with the Blue Ridge Electrical Membership Corporation from July 1979 to January 1981. The machine, operating in fully automatic synchronized mode, fed into the power network within utility standards.[13]

One of the testing objectives of this first-generation prototype was to determine noise levels and any potential electromagnetic interference with microwave relay, radio, and television associated with mountainous terrain. These potential problems were among those identified by an initial study undertaken by NASA Lewis, General Electric, and the Solar Energy Research Institute. An analytical model developed at NASA Lewis of acoustic emissions from the rotor recommended that the rotor speed be reduced from 35 to 23 revolutions per minute, and the 2,000-kilowatt generator was replaced with a 1,350-kilowatt, 1,200-rpm generator. This change to the power train made a significant reduction in measured rotor noise. During the noise testing, however, the Mod-1, like the Mod-0A, experienced a failure in the low-speed shaft