PARABOLIC DISH CONCENTRATOR DESIGNS AND CONCEPTS

Compiled by Brian Beveridge

December 1980

Jet Propulsion Laboratory California Institute of Technology

Pasadena, California

Prepared by the Jet Propulsion Laboratory, California Institute of Technology, for the U.S. Department of Energy through an agreement with the National Aeronautics and Space Administration. This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

The Solar Thermal Power Systems (TPS) Project at the Jet Propulsion Laboratory (JPL), sponsored by the U.S. Department of Energy, is assisting private Industry in the development of cost-effective, modular solar power systems for both thermal and electric applications. The development for which JPL Is responsible is generally referred as the parabolic dish technology. This solar collection concept Is a two-axis tracking system that employs a concentrator (reflective surface, support structure, foundation, and control system); a receiver; and for electric power production, a power conversion subsystem (engine and generator or alternator). The dish modules may be used individually to provide thermal and/or electric energy to small users, or may be clustered to provide a greater power capacity for applications up to and including central power generation. This technical summary, for the first time, consolidates descrip-tions of all known parabolic dish concentrator designs and advanced parabolic dish concentrator concepts for those Investigating solar ther-mal power systems. The emphasis is on the concentrator subsystem;

FORWARD however. available information about the receiver and thermal transport subsystems is also provided. The first section of this summary describes ten known dish system designs, currently in production or under detailed development. The second section includes descriptions of the advanced concepts, which are approaching the full conceptualization and design stage. These designs and concepts represent potential commercial units.

The technical information provided relates only to the design or concept of the parabolic dishes. It does not include, either expressly or implicitly, any performance characteristics of the component or module hardware.

Revisions will be made periodically to include new and

updated parabolic dish designs and concepts, as the information becomes available to the TPS Project. If additional information is required about a particular parabolic dish system design or concept, write to the address provided at the end of Its description.

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Electropolished, aluminum mirror segments on foam substrates (petals) make up a 6-m (20-ft)-diameter parabolic dish, with an effective reflective surface area of 25.9 m2 (279 ft2). This reflective area differs from the geometrical area of 28.3 m2 (304 ft2) due to the receiver shadow hole that is actually cut out of the surface. CONCENTRATOR

REFLECTIVE SURFACE – Eighteen petals are formed from a reflective, electropolished, aluminum sheet called ALZAK. This sheet is pressed into shape and bonded to a polyurethane foam substrate, which adds strength while providing lower weight. Each petal is approximately 2-m (7-ft) long x 1-m (3.4-ft) wide at the outside radius, and 30-cm (12-in.) wide at the inside radius. These are secured to the spaceframe for sun tracking. SUPPORT STRUCTURE - Lightweight aluminum tubing and a steel truss ring form the spaceframe. Counterweight, for ease of elevation. is provided by steel wings. A steel arm supports the spaceframe at an elevation bearing located just forward of the reflective surface to reduce counterweight requirements. The steel arm is anchored to the roof of the base structure, which rides on a circular track for azimuth motion. This base structure, a steel enclosure mounted on a concrete pad, serves as an anchor against wind loading and a storage unit for electronic hardware. Four support arms position the receiver in front of the reflective surface at Its focal plane. DRIVE MECHANISMS - Elevation drive is accomplished by an electric motor, which rotates the spaceframe about the forward-positioned elevation bearing. Azimuth drive is provided by rotating the steel support arm and roof around the track by using another electric drive motor. CONTROL SYSTEM - Integrated circuits provide the safety and tracking functions for automatic operation. If high winds are

detected, the system Is commanded to a stow (zenith) position. Defocusing of the unit protects the receiver from overheating. Coarse or open-loop tracking is provided by an ephemeris clock/function generator. Fine or closed-loop tracking is provided by nulling the output from a dual photosenser detector.

RECEIVER The water-steam receiver consists of an lnconel cone that is backed by a copper-zinc alloy block in which the heat transfer coil is embedded. The block is encased in stainless steel. This assembly is surrounded with mineralwool insulation and encased in more stainless steel. Embedded thermocouples protect the receiver from overheating. The receiver can be adapted for use with organic fluids. An air receiver has been designed, but not built. THERMAL TRANSPORT Fluids are directed to and from the receiver through tubing attached to the receiver support arms. A flexible hose provides the interface between the movable spaceframe and the stationary ground tubing CURRENT STATUS

The OMNIUM·G dish is undergoing system-level testing by JPL and Solar Energy Research Institute (SERI). For further information contact:

Stanley H. Zeliinger, President OMNIUM·G Co. 1815½ North Orangethorpe Park, Complex B Anaheim , California 92801