Activities planned for phase 2 Of the Small Community Solar Thermal Power Experiment (PFDR) program are summarized with emphasis on a dish-Rankine point focusing distributed receiver solar thermal electric system. Major design efforts include: (1) development of an advanced concept indirect-heated receiver;(2) development of hardware and software for a totally unmanned power plant control system; (3) implementation of a hybrid digital simulator which will validate plant operation prior to field testing; and (4) the acquisition of an efficient organic Rankine cycle power conversion unit. Preliminary performance analyses indicate that a mass-produced dish-Rankine PFDR system is potentially capable of producing electricity at a levelized busbar energy cost of 60 to 70 mills per KWh and with a capital cost of about $1300 per KW

Grigsby, C. E.

Pons, R. L.

English

NASA Technical Reports Server

N80 2478.2
THE DISH-RANKINE SCSTPE PROGRAM
(Engineering Experiment No. 1)
by
R. L. Pons and C. E. Grigsby
Ford Aerospace & Communications Corporation (FACC)
Aeronutronic Division
Newport Beach, CA 92663
ABSTRACT
Paper summarizes the activities planned for Phase II of the Small
Community Solar Thermal Power Experiment (SCSTPE) program. A Dish-
Rankine Point Focusing Distributed Receiver (PFDR) solar thermal elec-
tric system will be designed and developed and a single power module
tested at the JPL Solar Thermal Test Facility, Edwards ATB, California.
Major design efforts will include: development of an advanced concept
indirect-heated receiver; development of hardware and software for a
totally unmanned power plant control system; implementation of a hybrid
digital simulator which will validate plant operation prior to field
testing; and the acquisition of an efficient organic Rankine cycle. (ORC)
power conversion unit (PCU). Preliminary performance analyses indicate
that a mass-produced Dash-Rankine PFDR system is potentially capable of
producing electricity at a levelized busbar energy cost of 60 to 70 mills
per KWh and with a capital cost of about $1300 per TW.
INTRODUCTION
FACC will be the Systems Contractor for Phase II of the SCSTPE pro-
gram, under contract to JPL. The Phase III effort, as currently
envisioned, will consist of the fabrics l•fi on, installation and test of
multiple powe?7 modules comprising a complete power plant -- in the range
of 1/4 to 1 MWe - at a site to be selected by DOE.
The phase T studies ;tarried out by FACC considered PFDR solar thermal
electric syatems employ;ng Stirling, Brayton and Rankine cycle engines.
Given the benefits of mass production, all of these concepts were shown
potentially capable of producing electricity at a cost competitive with
the energy cost projected for fossil- and nuclear-fueled plants in the
near future. The Dish/Rankine PFDR concept was chosen for the Phase IT
SCSTPE program primarily because it offered the best performance for the
lowest program risk. In general., Rankine cycle engines represent a
well-developeda technology and should prove to be very reliable equipment.
At the module power levels of interest (-20 We) to the SCSTPE program,
however, there is a lack of data on representative hardware, and an
experimental, program is necessary to obtain operating experience and
provide a valid data base for accurate projections of performance,
reliability and (maintenance) cost of the ultimate commercial systems.
https://ntrs.nasa.gov/search.jsp?R=19800016289 2020-03-21T18:58:25+00:00Z
PROGRAM REQUIREMENTS AND PLANS
The overall milestone schedule for the SCSTPB program is shown in
Figure 1, The major constraint is the customer requirement to hive the
FY 74	 FY44 FY41 FY42	 IFY43	 lY4i
MILESTONES CY70
Cy
40 CY41 CYr3 CYII- CY44
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PHASE
—
DOE CONTROL POINTS
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PHASE it
PRELIMINARY DESIGN
SUBSYSTEM DES & DEV "►Y
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DETAILED DESIGN 47 RTyam,
SYSTEM VERIFICATION TESTS t1	 Af t AqT TI l 7 4
:,PHASE III 	 N
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SITE PREPARATION
FAA PLANT HARDWARE
SUB SYS INSTALL 6 CHECKOUT
SYSTEM LEVEL CHECKOUT
PLANT ON LINE
,
PLANT TEST & OPERATION S
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CONCENTRATOR - LCG £ifltlit^ItT^I
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FIG, 1. OVERALL MILESTONE SCI!EDULE FOR SCSTPE PROGRAM
plant "on-line" by mid-FY83, The critical path for Phase II i,s acquisi-
tion of the organic Rankine PCU during month 15 for integration with
the FACC receiver and subsequent installation inti th y; power ,todule at
the JPL Solar Thermal. Test Facility. This schedule assumes a 12-month
development cycle for the organic Rankine PCU.
The Preliminary Design Review will be held after 4 months; the Sys-
tems Design Review after 12 months, and completion of the Phase 11 pro-
gram after 23 months. In addition to program schedule and cast con-
siderations, subsystem and component selection will be based on economics
of a commercial, mass-produced PFDR system (circa 1990) designed for
1 We rated power without storage. The remote (unmanned) plant will
interconnect with a utility grid network. The Barstow, California,
site will be employed for preliminary design computation, Subsequent
analyses will use the Phase III site currently under source selection.
Effort during design of t'he major subsystems will address the follow-
ing key issues:
Concentrator - The General Electric prototype 12-meter Low Cost
Concentrator (LCC) will be provided by JPL as the baseline. The
JPL/E-System Test Iced Concentrator (TBC) will remain as backup for the
System Verification Tests at the JPL Solar-Thermal. Test Facility.
1.60	 OF 1'0
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Power Conversion Unit - A detailed presentation of this subsystem
has been given previously by Mr. dada. Among the key issues to be
addressed are the rather tight development schedule discussed previously
and the lack of operating experience on toluene at the desired operating
temperature range of 700-800°F. The baseline. PCU will be hermetically
sealed to avoid leakage, oxide contamination, etc. A parallel steam
Rankine engine system is under consideration as program backup.
Receiver - Detaila of this subsystem were given previously by
Mr, Osborn. Key issues relate to the selection of an acceptable second-
ary working fluid within the relatively short time available prior to
the scheduled decision date at PDR. The direct-heated receiver concepts
currently under development as a part of the JPL PFDR program remain as
backups.
Plant Control FACC will design the plant control subsystem for
remote, unmanned operation. The detailed design of the hardware and
software for complete control of a multi-module plant; is a major task
of the Phase 11 program. A complete hardware-in-loop system simulator
will be constructed so that complete dynamic simulation of plant opera-
tion can be achieved; varying solar insolation, start-up, shut--down,
transient cloud cover, forced outages and the like will be simulated
and bhoroughl,y examined. An additional bene i.t e£ this simulator is its
applicability to other PFDR systems, regardless of the type of engine
employed,
Energy Transport - The Energy Transport subsystem is a conventional.
DC electrical. network. The program decision to go DC is based on exten-
sive studies which show no significant difference in system efficiency
between the AC or DC design, whereas the DC network permits an easier
interface Cone point) with the utility grid, and, if storage were
desired, permits a more efficient interface with batteries since the
DC-DC interconnection does not require additional conversions.
BASELINE SYSTEM
The baseline system for SCSTPE has been established consisting of the
collector subsystem, the energy transport subsystem and a central plant
control subsystem. Details of these subsystems are given in the follow-
ing paragraphs.
Collector Subsystem
The collector subsystem consists of multiple power modules. Each
power module contains a 2-axis tracking parabolic dish concentrator, a
cavity receiver and an ORC Power Conversion Unit (ORC engine and elec-
trical generator). The control rectifier is also part of the PCU, but
is mounted at ground level near the base of the dish concentrator. Fig-
ure 2 shows the prototype power module which uses the 12-meter General
Electric Co. Low Cost Concentrator (LCC) currently under development as
a part of the JPL PFDR program. The LCC is a lightweight, advanced
design unit which employs injection-molded plastic dish segments,
161
e
integral reflector surface, front structural bracing and a wheel/track
type of azimuth/elevation mount with the unique capability to achieve
an inverted stow position in order to reduce survival wind loads and
provide easy access to the power conversion assembly and the reflecting
surface. The prototype LCC will use an aluminized plastic reflecting
surface; later designs may use silvered glass mirror elements with
substantially higher reflectivity and longer life. Sun tracking is
accomplished by a combination open loop/closed loop system. A more
detailed discussion of the LCC has been given by Mr. Zimmerman of the
General Electric Company,
A cutaway view of the power conversion assembly consisting of the
receiver, ORC engine, alternator and plumbing is shown in Figure 3.
Complete weight of the assembly is 490 'Kg (1078 lb); it is 2.60m
(8.52 ft) long and fits within a 1-meter-diameter circle. The receiver*
is an indirect-heated design based on the pool-boiling or thormosyphon
concept thoroughly studied by FACC during the Phase I program. It is
essentially a double-walled cylindrical. container with a secondary
fluid boiling in the annulus. (The Leading candidates for the secondary
fluid are sulphur mixed with 10-15 percent iodine and a terphenyl
organic compound.) The cylindrical container is connected by a short
pipe to a heat exchanger which contains the circulating toluene. The
vaporized secondary Fluid is transported up the pipe b, natural convec=
Lion, condenses on the toluene heat exchanger surfaces and returns to
the boiler by gravity.
The PCU has not been selected although preliminary designs have been
submitted by a number of firms including Sundstrand, Barber-Nichols,
Garrett/AiResearch, Thermo-Electron and General Electric. Both
Sundstrand and Barber-Nichols have had contracts from FACC to provide
high-performance ORC engine designs. The Barber-Nichols design (Fig-
ure 3) has an electrical, output of about 16 KWe at rated power conditions.
FIG. 2. POWER MODULE INCORPORATING
LOW COST CONCENTRATOR AND
ORC POWER CONVERSION ASSEMBLY
*Patent Applied or
162
FIG. 3. ORC POWER CONVERSION ASSEMBLY
An air-cooled condenser is packaged concentrically about its turbine/
alternator/regenerator components as shown in Figure 3. Toluene opera-
ting supercritically is the working fluid with a maximum temperature of
427°C (800°T). Consideration has been given to the effect of the 427%
maximum Qperating temperature on the long-term stability ol toluene.
Estimates have been made which indicate that the working fluid will
have to be changed only about every 30,000 hours or twice during the
30-year life of the plant. It should be noted that the rate of fluid
degradation is low since the bulk of the toluene fluid inventory is at
much lower average temperature than the 427 00 maximum operating tempera-
ture. Note further that the use of a hermetically sealed system mini-
mizes oxide formation and attendant scale deposition on the plumbing.
Energy Transport Subsystem
The overall SCSTPE system schematic shown on Figure 4 illustrates the
major elements of the Energy Transport Subsystem. A DC electrical sys-
tem interconnects the individual power modules and converts the collec-
ted energy into AC power by a central inverter. Standard interface
POWER CONVERSION ASSEMBLY
COLLECTOR	
r
POWER CONVERSION UNIT 1PCUI 	 ENERGY TRANSPORT SUBSYSTEM
	 O"IG^lSUBSYSTEM	 ^.V
+ RECTIFIER	 CENTRAL,
	 I 
POOR'
OO QU Lr,I r
RECEIVER
	 SWITCHBOARD	
INV RTER n
CONCENTRATOR	 TURBINE	 INTERFACE
EOUIPMEN7
11
r-
POWER I
MODULE
	 HIGHSPEED	 I I	 UTILITY
ALTERNATOR ( I I	 OHID
I PLANTCONTROL
PUMP	 ( i I BUILDING
4	 i 	 I
AIR-COOLED	 REGENERATOR
	 I I I
CONDENSER	 I I	 PLANT CONTROL(I	 SUBSYSTEM
- - -ADDITIONAL POWER MODULES - - - .- - I I
FIG. 4. -SCS'fPE SYSTEM SC—HEMATXC
equipment: is used to connect to a utility grid. Overall efficiency of
the SCSTPE Energy Transport Subsystem from PCU output to the utility
grid is estimated at 93.4 percent. All components are off-the-shelf
items with demonstrated performance and minimum risk.
Plant Control. Subsystem
The Plant Control Subsystem is designed to permit remote, unmanned
operation of the SCSTPE. A central microprocessor serves as the
supervisory-level controller and centralized interface for communica-
tions among all plant subsystems and the central plant control room.
The general functions performed by the control subsystem include
163
164
M1^
k
K (1) Automatic/Manual control of all plant subsystems.
(2) Coordinated sequencing of plant subsystems for its various
operating modes such as; start-up, shutdown, normal opera-
tion, intermittent operation and emergency operation.
(3) Plant system protection against failures (grad faults,
environmental conditions, etc.) by means of monitoring key
measurement variables and commanding automatic emergency
sequencing.
(4) Status monitoring of relevant plant variables for control
room terminal display and recording.
Most control functions will be implemented as algorithms in the micro-
processor software; however, in certain cases local analog electronic
control loops may be used and only supervisory level control will be pro-
vided. The microprocessor speed and memory have been sized to permit
sequential communication with each powav module through a serial-
multiplexed da;:a bus.
SYSTEM PERFORMANCE
A major variable in the ORC system is the working fluid temperature
at the inlet to the engine expander (turbine). Figure 5 shows the influ-
ence of turbine inlet temperature (TIT) on the pertinent component
efficiencies. Note that overall system efficiency (from sun to electric
grid) is maximum ( rQ l%) at 427°C (800"F), which is the upper limit for
the data, corresponding to an upper limit estimated for reliable opera-
tion with toluene. As shown later, it is possible to operate at some-
what lower temperature, if an added safety factor is desired, with only
a small increase in energy cost. The performance data presented herein,
however, have been computed at a temperature of 427°C.
System annual output was determined by calculating performance in
15-minute intervals for a Barstow, CA, site during CY1976; all plant
parasitic losses are included. Figure 6 shows the power budget for an
individual module as a function of time for a typical Barstow day.
Figure 7 showa power delivered to the grid, per module, for three repre-
sentative days of the year. For a I. MWe system, nominally rated at a
solar insolation of 800 W/m2
 and an ambient temperature of 27% (80°F),
approximately 68 power modules are required and annual energy output is
54.5 MWH/Dish, for a total system output of 3706 MWh/year. This corres-
ponds to an Annualized Capacity Factor (ACF) of 0.418 without storage
and adjusted for computed System Availability.
These computations were carried out for a spatial arrangement of
modules corresponding to 25 percent packing fraction, i.e., the ratio
of concentrator aperture area to land area. At 25 percent packing frac-
tion, the annual energy loss due to mutual shading/screening of concen-
trators is negligible (Reference 1) and total system cost, including
electrical cabling and land (at $5000/acre) is minimum.. Corresponding
i s{
0.90
300	 400	 560	 000	 700	 800 °F
0.	 ..-.—_.^	 ' I	 .._L...J..^...
100	 2N1	 300	 d00	 500
EXPANDER INLET TEMPERAT4)RE,OC
FIGURE. 5. EFFECTS OF TEMPERATURE
ON COMPONENT EFFICIENCY
(OPTIMIZED I MWe - ORC
SYSTEM)
ORIGINAL PAGE IS
OF POOR QUALITY
t
SUNRISE	 NOON	 SUNSET
TIME
...4-u
FIGURE. 6. INDIVIDUAL POWER MODULE
SYSTEM PERFORMANCE FOR
A TYPICAL DAY
044.A
FIGURE. 7. SYSTEM PERFORMANCE BY
SEASON (INDIVIDUAL
POWER MODULE)
NUMBER OF DISHES (PCU POWER XVQ
x
Y
. 1 MWe PLANT
• ACF-0.418iW'OSTORAGE!
H . 105 UNITSMAR
J_
w
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m
OU}
s 100 '°
W
2
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5(43)
4 22449)
m
W 201541
N
!	 144GOI
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WJ
300	 400	 500 600	 700	 800OF
50 1 1 '1	 1 '	 1	 f
100 200 300	 400	 50
EXPANDER INLETTEMPERATUREOC
FIGURE. 8. OPTIMIZED ORC SYSTEM
PERFORMANCE
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land area for a prototype 1 MW e plant is 7.6 acres. Higher packing
fractions are achievable, but with some loss in energy, For example, at
50 percent packing, annual energy loss is about 6 percent, but land costs
would have to exceed about $30,000/acre to achieve minimum system cost
at this density.
SYSTEM ECONOMICS
A generalized economic analysis was carried out for the Dish-Rankine
concept, assuming optimized components* and the benefit of mass
production/installation techniques. Life cycle cost analysis techniques
(Reference 2) were employed to determine System Levelized Busbar
Energy Cost (BBEC), which is used as the sole comparative parameter.
Figure 8 shows the influence of TIT on BBEC for a production rate of
100,000 modules/year. The benefits of high er temperature are obvious,
but very non-linear since the reduction in BBEC for the last 55°C
(100°F) difference in TIT is only about 5 mills/kWh (N7%). Note that
lowest BBEC is on the order of 70 mills/kWh despite use of the relatively
conventional FACC concentrator design. Use of m ore advanced concentra-
tors currently in the design stage could .reduce BBEC below 50 mills/kWh.
Figure 9 shows the effect of power module production rate on BBEC.
Note that modest producti,ii rates (-1000/year) result in energy costs
low enough to be attractt,ve at the present time for certain special
applications, e.g., isla,,zds, military facilities and remote sites.
Figure 3.0 shows the sensitivity of BBEC to plant size. For plant
rated power on the order of 1/2 MWe and above, the maximum variation in
BBEC is only about 10 mills/kWh (-15%). Below 1/2 MWe there is a sub-
stantial increase in energy cost - due primarily to the influence of the
fixed cosh elements.
CONCLUSION
The Dish-Rankine PFDR concept projects excellent performanae; an ACF
of 0.418 without storage reflects the very good part-load performance of
the ORC engine. The concept also projects very good economic potential,
given the benefit of mass-production and the use of optimized components.
The SCSTPE program is a challenge, particularly with regard to schedule,
but will offer many benefits toward development of the ultimate, opera-
tional PFDR small community power system.
REFERENCES
1. Osborn, D. B., "Generalized., Shading Analysis for Parabolic
Concentrator Fields," ASME Paper 80-RET-33, 1980 Energy Source
Technology Conference, New Orleans, 3-7 February 1980.
*An FACC concentrator design was employed since it is the only design for
which suitable parametric performance/cost data are currently available.
166
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POWER MODULE ANNUAL PRODUCTION RATE	 PLANT RATED POWER, KW,
	FIGURE. 9. EFFECT OF POWER MODULE
	
FIGURE. 10. EFFECT OF PLANT SIZE
	
ANNUAL PRODUCTION RATE
	
ON SYSTEM ENERGY COST
ON (MIN) ENERGY COST
2. Doane, J. W., et al, "The Cost of Energy from Utility-Owned Soler Thermal
Electric Systems" JPL Report 5040-79 ERDA/JEL 1012-76/3., June 1976.
0111IINAL PAGE', IS
OF POOR QUALffY
167


The dish-Rankine SCSTPE program (Engineering Experiment no. 1)

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