The integration of subsystem components and the testing of a Parabolic Dish Module (PDM) to convert solar energy to grid compatible electric power is examined. System components are selected on a basis of current and projected performance efficiencies, technology readiness, future production probabilities and prices, current cost and availability. Potential for a near-term, 8 kW derivative of the PDM is adjudged to be superior to that of a 20 kW system. The PDM is suited to both grid connected and standalone applications, and it may be fired by solar, fossil, or solar/fossil hydrid means

Davis, S. B.

English

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Near-Term Brayton Module Status
S.B. Davis
Sanders Associates, Inc.
Nashua, New Hampshire
Summary
Sanders Associates, Inc. was selected as system integrator for this
program with the responsibility of integrating subsystem components and
testing a Parabolic Dish Module (PDM) to convert solar energy to grid
compatible electric power.
By March 1983 Trade Studies had been completed and the PDM system
components were selected. System components were selected on a basis of
current and projected performance efficiencies, technology readiness, future
production probabilities and prices, current cost and availability. Though
the PDM program was originally oriented toward an 11-12 meter reflector with
a 15-20 kw electric output, the trade study conclusion led us to downsize
the system to include a smaller lightweight reflector and to output a rated
8 kw electric. Potential for this near-term, 8 kw derivative of the PDM is
adjudged to be superior to that of a 20 kw system.
Major system components are: 1, the AiResearch/GRI Mark III
subatmospheric Brayton cycle power conversion assembly; 2, the LaJet LEC-460
point focusing concentrator; 3, the Abacus 8 kw DC-AC inverter; 4, the
Sanders/JPL low pressure, high temperature ceramic matrix receiver; and 5,
the Sanders 8086 microprocessor based control system.
The PDM is suited to both grid connected and standalone applications,
and it may be fired by solar, fossil, or solar/fossil hybrid means.
Current program plans call for delivery by AiResearch of two engines.
The early engine will be utilized in The Development Test Model (DTM) which
will be tested in March of 1984 at Sanders, in Merrimack, NH. DTM
objectives are to complete:
• System Integration
• Development of Control Algorithms and system operating logic
• Establishment of System Performance Baselines
• Demonstration of System Feasibility
Following the PDM Critical Design Review (CDR) in April 1984, assembly of a
Final System will commence. An improved engine will be delivered directly
to Sandia Laboratories, Albuquerque, NM and final system integration is
scheduled for September 1984. Testing will be concluded in the fourth
quarter of calendar 1984.
113
https://ntrs.nasa.gov/search.jsp?R=19840020177 2020-03-22T10:11:24+00:00Z
Status
The Parabolic Dish Module (PDM) Experiment is being conducted by
Sanders Associates under contract (956039) with Jet Propulsion Laboratories,
Pasadena, Ca. With the major technology development near completion, the
contract will be transferred to Sandia National Laboratories, Albuquerque
(SNLA), New Mexico, in early 1984 f9r testing and improvement. Development
Test Model (DTM) experiments, design updating, and performance validation
tests (PVT) will occur under the aegis of SNLA through calendar 1984. See
Figure 1.
The DTM testing in early 1984 is oriented toward completing subsystem
integration. The control system will be integrated with the major system
components: 1, engine assembly; 2, concentrator controller; 3, inverter;
and 4, the operator control terminal. The nTM will be extensively
instrumented to collect baseline performance data against which the improved
system will be measured in the fall. System feasibility will be
demonstrated during these tests and will provide the experimental proof of
concept needed to pursue widespread deployment of the PDM system.
The DTM test results will be used to define control and hardware
improvements that will be incorporated in the second unit, the PDM, along
with the already planned improvements: 1, improved engine; 2, simplified
controller; 3, corrosion resistant heat sink exchanger; 4, optimized
recuperator ducting; 5, lighter weight receiver; 6, and (tentatively) the
electric start.
The validation of system improvements and increased efficiency are
primary goals of the PVT. Additionally, the testing of automatic algorithms
essential for unattended operation is planned. During extended testing,
lifetime and reliability data will be collected to identify improvements
necessary for large scale deployment of this new alternate energy source.
The current PDM system is comprised of advanced components which will
provide economic conversion of sunlight to grid compatible AC power with the
high reliability and low maintenance costs characteristic of Brayton (jet)
power plants. The engine is a subatmospheric Brayton cycle engine recently
developed by AiResearch Manufacturing Company of California for the Gas
Research Institute to drive natural gas fired heating/air conditioning heat
pumps. The engine employs air bearings to achieve life expectancies beyond
30,000 hours and advanced versions will operate in the 8 - 10 kilowatt
range. While the engine is currently developmental, it has successfully
operated several hundred hcurs and has no major technical uncertainties.
The MOD IlIA engine that will be used in the DTM test sequence uses a vacuum
air start system. The more advanced MOD IIIB engine uses a shaft-mounted
alternator integral to the compressor turbine shaft. This IIIB engine will
be capable of automatic electric starting.
The ceramic matrix receiver designed and built by Sanders is an
inherently long-life component. Developmental work continues to improve its
already high efficiency and to reduce cost to production level goals.
114
EVALUAnON Ua&JW.cr...cwJr
CONCEPT .."",..
TRADES ."Aft
SAGT-1A .,.....
DESIGN ""~
ASSEMBLY Fl•
....
.... TESTVI ~
DESIGN ......
FAB .,..
TEST ..~.
81 82 83 84 85 86
Figure 1. Parabolic Dish Module (PDM) Experiment is Nearing Completion
The lightweight concentrator is equivalent toa 7.4 meter diameter dish
and employs 24 closely packed quasi-spherical circular facets to reflect the
solar energy through an 8 inch (diameter) aperture into the receiver. The
dish has been built in moderate quantities (700+) and meets design to cost
(DTC) goals.
The PDM uses an integrally mounted shaft-speed 8 kw permanent-magnet
alternator with torque characteristics that allow it to double as a starting
motor. The DTM 5 kw alternator from which the 8 kw version is derived has
performed reliably during engine testing.
The inverter uses microchips to digitally synthesize the grid-locked
output AC from the rectified alternator output. The inverter logic allows
signals from the system controller to vary inverter input power requirements
and thereby control engine loading.
The PDM control system operates as an executive processor to command
the subsystem on-board controllers (concentrator, inverter, and start
sequencer.) The controller that was developed for the DTM test will
communicate to the operator via a video terminal and will offer a high
degree of flexibility to facilitate the developmental testing. Production
controllers will be programmed to a more restricted command menu and will
consolidate functions to reduce system cost.
The DTM receiver is shown in cutaway Figure 2. It is conceptually
similar to the follow-on receiver that will be used with the PDM. Preheated
air enters through a central inlet duct and flows through the radiation
cavity to the segmented honeycomb silicon carbide panels. The honeycomb
panels are heated to approximately 1850 0 F by the concentrated sunlight that
enters the receiver through the fused quartz window. As the 1200°F
preheated air flows through the honeycomb, it is further heated to 1600°F.
The hot air is then collected in the tapered plenum and delivered to the
outlet duct via a stainless steel particulate filter.
The front of the receiver is protected by a passive graphite shield
assembly that is inexpensive and requires no parasitic power.
Two DTM receivers have been assembled; one is being used for
development tests -- the other has been delivered to AiResearch for
integration into the power conversion assembly (PCA).
Packaging and aperture/cavity modifications will be incorporated into
the PDM receiver to reduce its weight and improve its thermal performance.
The solar concentrator for the PDM system is an LEC-460, supplied by
Lajet Energy Company of Abilene Texas. In this application the PCA is, at
1300#, heavier than the design load for the concentrator. The concentrator
was, therefore, analyzed to determine the modifications that would be
required to sustain the heavier PCA and expected snow loads. The structure
proved to be generally adequate and only limited modifications were required
116
MEETS DESIGN TO COST GOALS
Figure 2. Low Pressure-Brayton Cycle Solar Receiver
117
to meet the desired safety margins with the heavier loading. The
modifications have been incorporated and the concentrator is currently being
assembled and installed at Sanders' Merrimack, NH facility. Installation
will be complete by mid-January and characterization will occur during the
ensuing four weeks before DTM testing.
The control system is organized as an executive processor (EP) to
expedite the DTM testing and follow-on PVT at Albuquerque. By configuring
and programming the EP to use the existing on-board controllers in the
inverter, start sequencer, and concentrator, duplication of effort was
avoided. This approach reduces contract cost by allowing us to hold to a
compressed schedule and complete testing in 1984. Eventually, however, the
control system functions will be reallocated to reduce hardware costs and
achieve DTC targets. According to Figure 3, the EP:
1, communicates with the operator via CRT or hand~held terminal;
2, commands and monitors the inverter and concentrator;
3, commands the fuel valve and start sequencer:
4, monitors the engine, safety circuits, and weather; and
5, relays data to the recorder for subsequent analysis.
Conclusion
Over the course of this contract, the system has evolved from concept
to hardware that will be practical in the near term, figure 4. The smaller
8 kw system that has been developed will provide the market base to support
the development of larger systems as more advanced components become
available.
By our commitment to the aggressive schedule of Figure 5, we will
advance toward the generation of substantial quantities of truly renewable
energy and take a crucial step toward the DOE goal of reducing America's
energy vulnerability by the year 2000.
118
INVERTER
VRJELVALVE
8086 CPU > START 'SEQUENCER
CONCENTRATOR
ENGINE
SAFETY CIRCUITS
WEATHER
CRT
HAND HELD
DATA
Figure 3. Control System Executive Processor
PARABOLIC DISH MODULE DESIGN
HAS EVOLVED FROM CONCEPT
TO NEAR TERM PRACnCAUTY
pressurized receiver atmospheric receiver
I-' 11 meter dish 7.5 meter dish
~
0
regenerated' recuperated
15 - 20 kW 7-8kW
computer controlled 8086 mp
Figure 4. System Evolution
INSTALUNG 8,000 kW BY 12/85
1,000 units on line by 8188
2,500 units built by 12/88
5,000 units per ye. In '87 -
Figure 5. Development Schedule Objective
121


Near-term Brayton Module Status

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