A 150 kW solar thermal electric power plant which includes over 2100 square meters of parabolic trough type collectors and an organic Rankine cycle turbine engine was constructed on an irrigated farm. The plant is interconnected with the electrical utility grid. Operation is providing an evaluation of equipment performance and operating and maintenance requirements as well as the desirability of an on farm location

Larson, D. L.

English

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COOLIDGE SOLAR POWERED IRRIGATION PUMPING PROJECT
D.T. Larson
Soila, Water and Engineering Department
University of Arizona
Tucson, Az	 85721
XBSTRACT
Construction of a 150 KW solar thermal-electric power plant on an
irrigated farm near Coolidge was completed in autumn, 1979. The plant,
designed by Acurex Corp., includes over 2100 m 2 of Acurex made parabolic
trough type collectors and an organic Rokine cycle turbine engine built by
Sundstrand Corp. The plant is inter.onnected with the electrical utility
grid. The installation is being operated by the University of Arizona with
Sandia Laboratories direction. Operation is providing, an evaluation of equip-
ment performance and operating and maintenance requirements as well as the
desirability of an on-farm location.
BACKGROUND
Approximately 13 percent of the energy used on 'U.S. farms is used for
pumping to irrigate about 20 million hectares (50 million acres) or 13 percent
of the total cropland (5,9). About 85 percent of the irrigated cropland is
located in 17 western states. On farms with deep subsurface water sources,
70-90 percent of the crop production energy may be used for pumping (8). The
magnitude of irrigation energy requirements, potential natural gas shortages
and greatly increased energy costs motivated a request to examine the use of
solar energy to drive irrigation pumps by Arizona farmers after the oil em-
bargo of 1974.
A University of Arizona feasibility study in 1975-76 listed a r,"riber of
engineering and economic factors to be considered and conditions to ,b , met for
successful marketing and use of solar powered pumping plants (7). These included
development of lower cost solar devices, improved energy use management and
availability of capital at a modest price. During the past three years, four
known solar power plants have been constructed to evaluate the use of solar
energy to drive irrigation pumps. The first three units began operation in
1977; construction of the fourth was completed in autumn, 1979.
Photovoltaic cells are used to provide up to 25 kilowatts (KW) of elec-
trical energy to drive irrigation pumps at the University of Nebraska farm near
Meade (10). Parabolic trough type solar collectors and Rankine cycle turbine
engines are the principal components of the other earlier systems (1,3). The
two plants, a 50 KW installation located on a farm near Gila Bend, Arizona
and a 25 KW plant on a Willard, New Mexico farm, are directly coupled to
pumps with electric motor backups. The Willard installation includes consider-
able thermal energy storage capacity for nighttime operation while the Gila
Bend plant has none.
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COOLIDGE PLANT
The fourth experiment encompasses design, construction, operation, and
evaluation of a 150 KW solar power plant. Plant size was selected to meet
the energy requirements of deep well pumping to provide irrigation water for
a quarter section or 65 hectares (160 acres) of Arizona cropland. The plant
generates electricity since existing pumps were electrically driven and the
power can be readily used in other applications.
The 150 KW plant is located on the D41ton Cole farm southwest of Coolidge
in central Arizona. The cooperator was selected from among a group of volun-
teer farmers by a governor-appointed committee. An important factor in site
selection was cooperation of the local utility company.. "ae'kup energy is re-
quired to assure pump operation; full , utilization of so'-^ plant output is
economically desirable. Electric District Dumber Two, the local, utility com-
pany, is supplying or purchasing energy as required.
The Arizona experiment is funded by the U.S. Department of Energy and
technically supervised by Sandia Laboratories. Additional funding and technical
support have been furnished by the Arizona Solar Energy Commission and the
University of Arizona, respectively. In the first phase of the project con-
ducted in 1977, competing conceptual designs were developed by three firms:
Honeywell, Black and Veatch, and Acurex. Honeywell proposed use of several
lartre parabolic dish collectors. A Brayton cycle turbine engine and electri-
cal generator, set were to be mounted adjacent to each collector receiver. Black
and Veatch proposed a field of heliostats or individually tracking reflectors,
central receiver type collector, and Rankine cycle engine. Acurex proposed
use of a field of single axis tracking, parabolic trough type collectors and
Rankine cycle turbine engine.
The Acurex Corporation concept was selected for design and construction
in late 1977, appearing to have the fewest technical unknowns and be most
economical. The solar power plant plans consisted of collector, energy storage
and energy conversion sub-systems, Figure 1.
THERMAL STORAGE
SUBSYSTEM
	
POWER GENERATION
C11Ar,VST1:M POWER DISTRIBUTION
SUBSYSTEM
Power
ISO kWe	 grid
,ator
I,
t
>l
Pump
FIGURE 1 Schematic diagram of the 150 KWe solar
powered pumping facility (2).
230
The collectors, 1.83m wide by 3.05m long (6 feet by 10 feet), have
reflective parabolic surfaces of aluminum (Coilzak) and concentration ration
of about 36 to 1. Collector receiver tube is coated with a selective black
chrome surface and surrounded by a pyrex tube. The collectors, manufactured
by Acurex, are arranged in a series of north-south oriented rows. Solar col-
lector area is greater than 2100 square meters (23,000 square feet). An addi-
tion is being planned which will nearly double the collector area.
A heat transfer oil, Caloria HT43, is being used as the collector fluid.
This oil remains stable and in fluid state at the 288 0C (550 0F) temperature to
which it will be heated permitting low pressure flow. Energy storage is a 113
cubic meter (30,000 gallon) tank of hot oil. Initial collector area permits
only daytime operation. The planned collector addition will permit about 20
hours of operation on a sunny June day.
Energy conversion is accomplished by a Rankine cycle turbine engine through
expansion of the organic fluid toluene. The engine, made by Sundstrand Corpora-
tion, is a scaled down version of one developed for other relatively low temp-
erature applications such as conversion of power plant waste heat. Net  engine
efficiency is expected to be 17 percent; overall system energy collection and
conversion efficiency is expected to average seven percent annually..
EVALUATION ORIGINAL PAGE IS
OI+' POOR QUALM
The Arizona experiment is providing an evaluation of a relatively small
sized power plant located on a farm in Arizona and interconnected with the
electrical utility company grid. The economies of scale for solar power plants
are not well known; different designs might be more appropriate with different
sized plants. This experiment is evaluating a design using distributed, para-
bolic trough type, concentrating solar collectors and Rankine cycle, turbine
engine to generate 150 KW of electrical energy.
Location on a farm in central Arizona provides an evaluation in that
environment; some of the characteristics being sunny,hot, and dusty. Solar
plant operating and maintenance requirements, competing land uses and energy
use management all affect the desirability of an on-farm location. Land is
available in agricultural areas in central Arizona. However, operation and
maintenance of a power plant is a new and additional farm task. Minimum atten-
tion was a solar plant design objective; amount and type of attention will be
determined.
Since solar power plants are capital intensive, complete utilization of
output is desirable to minimize energy production costs. More complete solar
powered pumping plant utilization may be obtained through energy or water
storage or use of alternative energy sources during peak demand periods (7,11).
Crop residues and animal wastes are two potential energy sources. However,
pumping energy costs will not necessarily be reduced by the use of other energy
sources or storage. Interconnection with the electrical utility system could
require less management and perhaps be most cost effective. Mutually beneficial
operation might involve purchase of off-peak supplemental energy from the
utility company and controlled period generation and sale of energy to the utility.
231
The backup and utilization problem has been resolved in the Arizona experi-
ment since the local utility company is providing energy when solar plant output
is insufficient and purchasing energy not needed on the farri. Plant output and
farm use will be recorded and conservation and load shifting measures will be
examined to determine methods for improved matching of energy supply and demand.
The University of Arizona is operating the Coolidge solar plant with tech-
nical assistance from Sandia Laboratories and the manufacturers. This opera-
tion is evaluating new solar power plant components and determining operating
and maintenance requirements. A number of experiments also are being conducted
to evaluate solar collector, thermal storage and turbine generator operation.
Performance and operating and maintenance requirements data will be used to
suggest methods to improve performance, reduce servicing and increase reliability.
To date, the solar plant has been operated almost daily for over two months
and storage Yank thermocline stability and winter solstice energy collection
tests have been conducted.
Solar power plant production cost estimates are high, tentative and variable-
from less than $3,000 to over $10,000 per kilowatt of output (2,4). Prelimi-
nary analyses have indicated some necessary conditions for cost competitiveness
with alternative energy sources (6). These include low capital and operating
costs and high utilization. This experiment will provide additional information
on future capital and operating costs and plant utilization. Economic analyses
will be updated as information becomes available.
CONCLUSIONS
The Arizona 150 KW ;solar powered pumping experiment is providing an evalua-
tion of a medium sized solar power plant using distributed collectors and much
new technology. The application appears appropriate since irrigation demand
reaches a peak during the period of maximum insolati,on, a farm can provide a
good environment for solar devices including adequate land area, and farmers are
seeking alternative energy sources.
The experiment is expected to provide information on design, operation,
and maintenance which will lead to equipment improvements. The experiment also
is expected to indicate the practicality of locating a solar power plant on
a farm and provide comparative cost data. Thus, the experiment is an important
step in the development of solar power plants.
232
- "'GINAL PAGED IS
REFERENCES
	
OF POOR QUALITY
1. Abernathy, G.H. and T.R. Mancini. Design and installation of a solar
powered irrigation pump. Paper No. 77-4020, ASAE, St. Joseph, MI (1977).
2. Acurex Corp. 150 KWE solar-powered irrigation facility. Technical Status
Review Report to the U.S. Department of Energy. Acurex, Mountain View,
CA. (1978).
3. Alexander, G., et al. Modification and 1978 operation of the Gila Bend
solar-powered irrigation pumping system. Publ. No. SAND 79-7009, Sandia
Laboratories, Albuquerque, NM. (1978).
4. Barber, R. E. Current costs of solar-powered organic Rankine cycle engines.
Solar Energy 20 (1978) 1-6.
5. ERS,USDA. Energy and U.S. Agriculturc: 1974 Data Base, Volume 2. Federal
Energy Admin. Publ. FEA/D-77/140 (1977).
6. Katzman, M.G. and Matlin, R. W. The economics of adopting solar energy
systems for crop irrigation. Amer. J. Agr. Econ. 60 (1978) 648-654.
7. Larson, D.L. et al. Evaluation of solar energy for irrigation pumping.
Trans. Am. Soc. of Agr. Engr. 21 (1978) 110-115, 118.
8. Larson, D.L., and Fangmeier, D.D. Energy in irrigated crop production.
Trans. ASAE 21 (1978) 1075-1080.
9. Sloggett, G. Energy and U.S. Agriculture: Irrigation pumping, 1974.
Agr. Econ. Report No. 376, ERS, USDA, Washington, D.C. (1977).
10. Twersky, M., and Fishback, P.E. Consideration of irrigation systems in
the solar photovoltaic energy program. Paper No. 78-2551, ASAE, St.
Joseph, MI. (1978).
11. Williams, D.W., Larson, D.L., and McAniff, R.J. Load management of on-farm
solar electric power plants. Paper No. 79-3003, ASAE, St. Joseph, MI (1979).
233


Coolidge solar powered irrigation pumping project

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