Final report on the modification and 1978 operation of the Gila-Bend solar-powered irrigation pumping system

ABSTRACT:
The 1978 program for modification and operation of the solarpowered irrigation system at Gila Bend, Arizona was intended to upgradethe system using state-of-the-art components, modify the system to achieve more mature capabilities, and use the system to evaluate operating and maintenance

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requirements. Five separate tasks were undertaken to achieve these goals. Three of the tasks involved physical alteration of the system, the fourth involved developing extensive evaluation capabilities, and the final task, which was in progress through the majority of the program, was to operate the facility to obtain maintenance and operating experience. Some of the collector unit absorber tubes and housings were replaced with new components, and some of the original tubes were recoated with an improved compound. Insufficient data is available to judge the relative efficiency of these new components, but operating life and mechanical performance appear to be superior to the original units. Experience indicates that visible deterioration may not indicate serious loss of performance. A new tracking system was placed on order to reduce the requirements for operator attention and adjustments. After delivery and spending substantial time making modifications in the new system and trouble shooting it--both of which caused a serious loss in overall system operating time- the new system, to date, does not appear to be any better than the system it replaced. The problems in the new system are not the same problems that existed in the original system; however, satisfactory progress towards unattended operation was not made. Design work was completed and components were purchased to allow the irrigation pump to be driven by either the solar system, an electric motor, or both simultaneously. The electric motor and the gearbox required to drive the pump were installed, and operation on solar-power-only and on electric-power-only was demonstrated. Leakage in the turbine/gearbox unit prevented operation in the hybrid mode. Resolution of this leakage problem and installation of remaining components were postponed to permit operation for the duration of the season, since initial problems with the electric motor and irrigation pump had further reduced operating time. An extensive system of instrumentation and data recording and transmission equipment was installed and verified. A computer procedure • for automated storage and analysis of data was developed. Although several deficiencies still exist in this area, these capabilities, developed for this program but applicable to programs with similar requirements, proved valuable for monitoring and evaluating the performance of the equipment. The problems associated with various subsystems still in development and, surprisingly, with components of proven reliability, seriously affected the total amount of operating time during which useful operating data could be gathered. Even so, the solar-powered irrigation system was operated for 188 hours and pumped 32.8 million gallons of water, and significant information was gathered on hardware performance, component life, and maintenance requirements. Economics aside, modest development work and extensive field testing operations are still required before the farmer accepts solarpowered irrigation hardware as a part of his irrigation system. The Gila Bend facility will be maintained, at no cost to the government, in a temporary shutdown condition for 6-12 months to facilitate the initiation of any follow-on program or demonstrations in connection with additional work.

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