Investigation of a Solar Thermal Powered Pump for Agricultural Application. Final Report

摘要

A simple solar thermal powered water raising device, for irrigation applications, has been investigated. The concept is based on the use of a closed piston system comprising a condensable working fluid and an array of solar collector panels in conjunction with a mechanical system comprising a cable, lever, pulley and water bucket. The alternate heating and cooling of the solar panels in turn evaporates (expands) and condenses (contracts) the working fluid thereby moving the piston in a vertical direction. This vertical movement is transmitted through the cable, lever and pulley assembly to a vertical movement of a second cable which raises a bucket of water, dumps it on the solar panel thus cooling it and allowing the bucket to lower back to the water, where the cycle begins again. A computer model of the operational cycle of the water raising device has been developed. The model addresses the transient heat transfer, thermodynamic, fluid mechanics and economic aspects of the problem. The model was used to simulate the yearly operation of a nominal 2 ft. diameter x 5 ft. stroke piston operating with a 10 ft. head. The location of operation was assumed to be at a latitude of 32 exp 0 , which corresponds roughly to San Diego, California. Freon 21, Freon 12 and butane were investigated as the working fluid, with Freon 12 providing the maximum yearly pumping capacity. The economic model was used to compare the yearly cost of the solar pump with that of conventional pumps using available electricity, and conventional pumps with gasoline and diesel powered generators. It was determined that the solar pump would be competitive with the conventional pump for electrical power costs of about $0.10/kW-h, while if operating in areas where generators must be used, the solar pump will have significantly lower yearly costs. (ERA citation 05:013323)