Mukund Patel

Wind and Solar Power Systems—Design, Analysis, and Operation

The author had wide experience as an electrical engineer in major US companies before becoming an academic professor. His expertise led him to study power generation from renewables, especially wind and photovoltaic power. This textbook has been developed from his teaching and research, and from his experience as an associate editor of the Solar Energy Journal, published by the International Solar Energy Association. This background explains the electrical engineering character of the book, and its nominal division into four parts: wind, photovoltaic, system integration and ancillary power. The division is ‘nominal’, because various fundamental aspects of power generation and analysis pop-up somewhat indiscriminately throughout the text. The book will be well used in mid-year degree courses in engineering, but, by keeping close to present reality, it will also be interesting and informative for professional engineers. Thus

Instability of the continuously transposed cable under axial short-circuit forces in transformers

The axial instability of the winding conductor is one of the principal modes of mechanical failure in large power transformers. It is caused by axial compressive forces generated by the electromagnetic interaction of the short-circuit current and the radial leakage flux. It is a buckling type of mechanical instability that occurs under compression. Two possible modes of failure in the layer type coil wound with the continuously transposed cable are identified and analyzed in this paper. The critical design loads leading to instability of the individual strands as well as of the whole cable are separately derived. The actual instability threshold of the coil would be the lesser of the two critical loads. For the through-fault integrity of the transformer design, this threshold must be greater than the peak compressive force on the cable under the worst case short-circuit current.

Wind Power Systems

Wind has been utilized as a source of power for thousands of years for such tasks as propelling sailing ships, grinding grain, pumping water, and powering factory machinery. The world’s first wind turbine used to generate electricity was built by a Dane, Poul la Cour, in 1891. It is especially interesting to note that La Cour used the electricity generated by his turbines to electrolyze water, producing hydrogen for gas lights in the local schoolhouse. In that regard we could say that he was 100 years ahead of his time since the vision that many have for the twenty-first century includes photovoltaic and wind power systems making hydrogen by electrolysis to generate electric power in fuel cells. In the United States the first wind-electric systems were built in the late 1890s; by the 1930s and 1940s, hundreds of thousands of small-capacity, windelectric systems were in use in rural areas not yet served by the electricity grid. In 1941 one of the largest wind-powered systems ever built went into operation at Grandpa’s Knob in Vermont. Designed to produce 1250 kW from a 175-ft-diameter, two-bladed prop, the unit had withstood winds as high as 115 miles per hour before it catastrophically failed in 1945 in a modest 25mph wind (one of its 8-ton blades broke loose and was hurled 750 feet away).

Energy-momentum-wheel for satellite power and attitude control systems

In an earlier paper by the author on a 2500 W low Earth orbit satellite, such as NASA Goddard Space Flight Centers EOS-AM, the mass and volume reductions by replacing the battery with a flywheel were estimated to be 35% and 55% respectively. Further savings are possible by using a dual function flywheel that stores energy for the electrical power system and momentum for the attitude control system of the satellite. This paper analyzes the operation of such a dual function flywheel, termed the energy-momentum-wheel. As the spacecraft cannot discharge energy without discharging momentum, the maximum depth of energy discharge is limited by the minimum momentum storage requirement on a given axis. Such mission level operating constraints are analyzed and presented in the form of circle diagrams.

Photovoltaic Power Systems

Solar photovoltaic power systems weight reduction and reliability noting applicability to propulsion, attitude control and stationkeeping missions

Integrated energy-momentum wheels for spacecraft

The spacecraft energy storage requirement has been traditionally met by using rechargeable electrochemical batteries. NASA-Glenn Research Center and a few industry partners are investigating the flywheel to replace battery in the spacecraft power system. With moderate component development, the flywheel offers potential benefits of longer life, reduced mass and lower cost. For greater benefits, the flywheel is being considered for dual function of energy storage for the electric power system and also momentum storage for the attitude control system. This paper presents a point design estimate of mass and volume savings in a 2500 watts low earth orbit satellite by using an integrated energy and momentum storage system. The study shows that such a system has a potential of reducing 40 percent solar array area compared to the conventional design with existing NH/sub 2/ battery and reaction wheels.

Solar Thermal System

Characterize and upgrade a solar thermal system. Work on the 2007 Cornell Solar Decathlon House. Map out and thermally model the existing system in the house. Troubleshoot existing system to improve performance. Project will include creating a research presentation on solar thermal systems, use of home energy thermally modeling software, site visits to house and interaction with home owner. One or two semesters.

Power System Requirements

An overview of electrical power requirements for each mission of a baseline and alternate plan for space activities in the 1990-2035 timeframe is presented. The specific missions included low earth orbit (LEO), geosynchronous earth orbit (GEO), lunar, Mars, and asteroid related projects.