Optimization of photovoltaic powered deficit irrigation
Abstract
Photovoltaic (PV) powered irrigation systems can be used to supply water to crops in remote locations. Optimally sizing a PV irrigation system is challenging because of the complexity the system's components and crops' water requirements. The objective of this project is to develop a method to optimize the design and performance of a PV irrigation system, and minimize the required cost. A simulation of the performance of the system's components has been developed. This includes: the PV cell and module performance for varying solar radiation, ambient temperature, array slopes, and array tracking; hydraulics and friction losses of the pipe flow; and performance of a pump/motor subsystem at varying dynamic heads, operational speeds and loads. Crop growth and water requirements have also been modeled to calculate the daily soil moisture, determine irrigation scheduling, and calculate any reductions in the relative crop yield that result from water stress. The irrigation system is optimized using three steps. The first step determines the planting dates for each crop within input bounds and the planting locations if a multiple water storage reservoir system is used. A method is developed to approximate the weekly irrigation load, and the genetic algorithm (GA) is used to minimize the peak load. The second step uses the simulation program to optimize the pipe diameter, reservoir volume, PV mounting slope, and PV array for a determined required crop yield. The final step determines the optimal irrigation and pumping schedule for periods of the year when there is a water deficit. The GA is used for this step and pumping times and locations as well as irrigation days and durations for each crop are calculated. This analysis is applied to a 3 hectare (7.4 acre) farm in Gashora, Rwanda. Multiple pumps, PV modules, tracking methods, and reservoir combinations are analyzed. A system consisting of three 70 m3 storage reservoirs, a 340 m pipeline with a diameter of 90 mm, a 2.73 kWp PV array, and a 2.2 kW Grundfos SP17-4 submersible pump is determined to be the optimal solution. The total system cost is $30,644. The results also show that the system is resistant to decreases in the average rainfall, solar radiation, and PV module performance. The system is economical and competitive with traditional irrigation systems.
Degree
M.S.M.E.
Advisors
Hirleman, Purdue University.
Subject Area
Mechanical engineering
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