The 50 horsepower solar powered irrigation facility near Gila Bend, Arizona which includes a Rankine cycle demonstrates the technical feasibility of solar powered pumping. The design of a facility specifically for the irrigation farmer using the technology that has been developed over the last four years is proposed

Alexander, G.

Busch, D. F.

Smith, W. A.

English

NASA Technical Reports Server

t. N80 24793
THE SO-HORSEPOWER SOLAR-POWERED IRRIGATION
FACILITY LOCATED NEAR GILA BEND, ARIZONA
W. A. Smith
G. Alexander
D. F. Busch
BATTELLE, Columbus Laboratories, Columbus, Ohio
ABSTRACT
The operation of the 50-horsepower solar-powered irrigation facility near Gila Bend, Arizona over three years
demonstrates the technical feasibility of solar-powered. pumping, The Rankine cycle facility was built using
1976 technology, The requirement now is to use the'technology that has been developed over the last four years
to design a facility specifically for the irrigation farmer. Considerations to meet his needs and to demonstrate
whether solar thermal conversion Is a potentially viable application for pumping Irrigation water in the United
States are suggested.
INTRODUCTION
The initial program to develop the 50-horsepower solar-powered irrigation facility was funded at Battelle Memorial
Institute by The Northwestern Mutual I,ife Insurance Company as one of several programs undertaken to accelerate
the development of practical applications of solar energy.
The installation is on a 76,000-acre ranch west of Gila Bend, Arizona. The ranch represents an agricultural invest-
ment in one of this country's most arid regions where intensive irrigation is required to produce crops on the 25,000
acres that are irrigated.
The solar irrigation pumping system serves to return tail water from a collection sump to concrete lined distribution
ditches. Water supplied to the irrigation system from a number of deep wells is applied to the fields from the distri-
bution ditches by siphons in an amount approximately 10 percent in excess of that required by the crop; the result-
ing 10 percent runoff is recovered from the graded fields in a network of tail water ditches. The solar irrigation pump
returns the tail water, which collects in a sump, to irrigation ditches servicing an area of approximately 5000 acres.
The lift from the tail water sump to the distribution ditches varies daily, ranging from 7 to 12 feet.
In 1975 when the design of the facility was initiated, the following were guidelines:
(1) Select off-the-shelf equipment or equipment that was as near to off-the-shelf as possible
(2) Take every advantage of available technical information with proper exercise of experience and judgment
(3) Design a system to produce 50 horsepower but include the potential for applying the same design practices to
scale up to 250 horsepower
(4) Include in the design the potential for operating the system in remote locations with only minor modification.
The thrust of these guidelines was that our program was not to be a research effort; it was a development and appli-
cation effort.
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System definition, design work, component selection, procurement, assembly, testing, and Installation were com-
pleted In about 18 months; the system was dedicated In April,1977. The basic components of the system are
shown In Figure 1,
72,000 L//HR
A
002 F
100 Palo
SOLAR COLLECTOR
Zt{ f	 (CONCENTRATOR TYPE)
274 F
-"^
2t0 F
BOILER
126 PSIG
FREHEATER
^11,700 LO/HR
.	 Y
;ONPABENGINE6PSI 6 IN.
-12.6  ^^
IN.	 IRRIGATION
FEED PUMP	 WATER
FIGURE 1. A SCHEMATIC OF THE SOLAR-POWERED
IRRIGATION SYSTEM: 1977
7lle figures are design values.
The collector field (5785 sq ft) heats the water, which in turn is used to flash the working fluid (R-113) to drive
the Rankine cycle turbine at a maximum speed of 30,500 rpm; this is then geared down to 1755 rpm. The SO-
horsepower system can deliver a maximum of 10,000 gpm.
In this paper, there is no attempt to cover all of the activities In the three years of operating the facility and mak-
ing modifications to it, The purpose is to highlight some observations dealing with the pragmatic use of solar
power in a particular agricultural application,
x
236
OPERATIONS
The system was operated for a total of 800 hours during part of the 1977, 1978, and 1979 irrigation seasons,
On several occasions the water pumped exceeded 9000 gpm over short periods and an average of 7000 gpm for
several entire solar days.
Collectors
When the collectors were new, well-focused, and tracking under bright sun conditions, they regularly delivered
48-52 perc^;nt average efficiency (design was 55 percent). After several months, and several ,problems which In-
eluded the over tempo raturing of two absorber tubes, typical efficiency dropped to 46 percent.
To reduce convection losses, the absorber tube/receiver assembly was originally fitted with halt-round, sections of
glass set into a seal. Dirt and dust which built up on the outer surface, though serious on its effect on operations,
could be readily removed. However, within one month, the dust buildup on the interior surface of the glass was
such that the covers had to be removed to be cleaned. The a. lendant problems with cleaning the glass n- removal,
replacement, seal alignment, breakage -- Immediately created an incentive to operate without the glass. We ran
some tests comparing adjacent rows with and without clean glass covers; we were not able to measure individual
flow rates. On the basis of our tests we found there was actually an Increase In AT without the glass covers, The
results would have been even more significant If the glass covers had been lust a little bit dirt y on the Inside or the
outside. We discontinued the use of the glass because In our system --- operating around 300 F Av It was far from
cost effective to operate with them.
Dust is a normal environmental feature In Gila Bend. The dust, whether from dust storms, dust devils, or agricul-
tural operations will collect on reflector surfaces. From a practical viewpoint the dust 4„ at least our dust - did not
reduce performance nearly as much as one would think. In the first year of operation the reflecting surface ap-
peared very dusty after about one month - particularly when viewed from a flat angle. The reflectors were im-
mediately washed, There was no noticeable difference in the energy output of the field before and after wash-
ing. The field was washed twice more during 1977 with the principal difference still being aestlnctic, From August
1977 through the five months of operation In 1978 and until August 1979 the collectors were not washed again,
By this time the dust accumulation was such that performance was Improved by washing. It will be significant to
the farmer to know what the washing requirements are for his application. Washing is expensive; "excess" dirt
accumulation will affect output. The farmer will want a definition of "excess" that lie can use.
During 1978 a number of changes were made in the receiver assemblies. Some of the coatings on the receiver
tubes appeared to have degraded; powdering and flaking were evident, A new receiver assembly design was avail-
able which had overall system Improvement as well as Improved thermal features. Combinations of old coatings,
new coatings, black chrome, old housing, and new housings were a part of the 11778 and 1979 system. The per-
formance of the various combinations of components does not appear to be markedly different, but detailed
examination would have to be made to evaluate tile efficiencies of the individual rows. If, as we suspect, there
are only modest differences in efficiencies, the long-term effect of this in terms of initial costs and maintenance
costs is significant.
Generally, the collectors appear to be holding up fairly well, There is one place on the reflector side where the
metal backing is breaking away from tine honeycomb core material, The manufacturer has looked at the separa-
tion; it is his judgment it is the result of a manufacturing error rather than degradation, Additionally, there are
several places where the aluminized reflector surface is not adhering to the substrate as it should. Most of this,
which is new tlus year, is occurring at seams but there are several places where there is some delamination in the
middle of a. panel. Tills degradation does not represent a large percentage of the total surface area, It does, how-
ever, represent a potential maintenance cost either in terms of repair or replacement.
237
The remaining components of the collectors do not appear to be degrading In any way that affect performance
or require maintenance.
Tracklot
The subsystem that has caused the greatest problem Is row tracking. It was, and still is, difficult to maintain
consistently accurate tracking in conditions of changing cloud cover and hate. We have made modifications to
our On/Off switching to incorporate serniproportlonal control on the motor speed and have replaced the mechani-
cal relays with solid-state switching devices. Other Improvements can be made and systems newer than ours offer
substantial improvements. One problem with the newer systems Is that the costs are going In the wrong direction.
Meat Exchangers
There Is one feature of the Gila Bend facility on which we have little information. Data is available to calculate
the performance of the heat exchangers — boiler condenser, regenerator, and preltcater; the calculations made In
1977 and for part of 1978 indicated design or near design performance. information Is not available, however, on
what is happening to the Inside surfaces of the heat exchangers. This information must be developed to determine
the maintenance requirements and to provide a design for the components that will enable the maintenance to be
carried out.
RECOMMENDATIONS
The Gila Bend facility is basically a 1976 design. It was designed to demonstrate an application using state-of--the-
art equipment. It has demonstrated that application, What is required now is an update to use the current state
of the ,art (which is significantly advanced over 1976) and design an overall facility whch will best fit the needs
of the Irrigation farmer.
It has yet to be demonstrated for the United States market whether the use of solar thermal conversion is (or Is
not) a viable application when the principal use is for pumping water. To date, most, If not all, of the demonstra-
tion systems have been built by engineers to be run by engineers. The real, world need will be to deliver a system
that is acceptable to the farmer In terms of meeting his operating and maintenance requirements .
	 . and parti-
cularly because of today's interest rates — first cost, A demonstration unit should be built with the following
in mind.
(A) Components used must have the potential for significant cost reduction.
(B) The farmer wants water "on demand" day or night. The primary pumping will be by electric motor (or
gas or diesel engine). Solar power, when available, will be used to reduce other forms of power consumed.
This approach is equally applicable to low lift, shallow well, and deep well requirements. Furthermore,
the potential solar output does not need to match the power requirements of the pump motor; the solar
power portion can be substantially smaller and still be effective.
(C) The collector operating temperature needs to be examined carefully, The pros and cons of temperatures
requiring glass covers for absorber tubes need to be examined in terms of field use by the farmer, not
laboratory use by the engineer.
238
(D) A sump application, such as the one at GilaBond, Is less desirable than an application on a well. The water
from a well which will be diverted for the condensor cooling water Is better than the water from a sump for
two reasons.,
(1) The temperature of the well water Is lower and does not have the temperature variation over time
that is characteristic of sump water,
(2) The well water does not have the solid debris characteristic of sump water,
(E) Tracking systems must provide the capability to follow the sun accurately when It can provide thermal In-
puts to the system. As mentioned before, systems are Improving but costs are not. There have been many
advances In the last four years In control technology and timing devices, for this specific application, a
detailed examination should be made of the relative advantages of tracking the sun on the basis of where
It actually Is and where it is calculated to be.
(P) The master control system needs not only to start and stop the system under normal conditions but also
to provide diagnostic Information to the user for causes of shutdown or preventable falloff in performance.
This suggests a well-conceived instrumentation and signaling system,
(G) In the design process, consideration must be given to how the farmer wants to operate and maintain his water
pumping systbrn.
(1) When the pump is running, the solar portion of the unit should start automatically when there Is
sufficient energy from the sun; conversely, it should shut itself off automatically.
(2) The system should run automatically and reliably without the need for an operator in attendance,
One or two checks a day by the farmer (similar to the checks he currently makes on Iris motor
driven pumps) should be sufficient,
(3) The levels of skills required to operate and maintain the system should be little different than
those currently employed. It is reasonable to assume that one week or less of training would provide
the level of skills required for maintenance,
The foregoing does not necessarily define a large-scale system. In fact, quite the opposite may be true. For demon-
stration purposes, a 25 to 50-horsepower system could be used, coupled with a well-tread pt,mp.
The two existing systems that have any similarity to the system suggested are circa 1976 technology, With the ad-
vances that have taken place since, then, not only In solar technology but also In control technology, there Is now
the opportunity to really test the viability of solar thermal conversion for pumping water In U.S. Irrigation
operations.
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The 50-horsepower solar-powered irrigation facility located near Gila Bend, Arizona

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