Performance evaluation and optimal design of a stand-alone direct pumping sprinkler system

Abstract

Irrigation has attained increasing importance world over attributed to the growing demand for food by a rapidly growing world population. Many solar powered irrigation schemes in Uganda are faced with irregular daily solar radiation, which later affects irrigation water pumping to meet the crop water demand. For example, Abera irrigation scheme with an off-grid solar direct pumping sprinkler system with no reservoir tank situated on a 15-acre receives intermittent solar energy, affecting irrigation uniformity. When water is required, mainly in the morning and evening, solar radiation is not available, causing stress to the crops. The system being far away from Utility Grid, a diesel generator was used as an alternative source of power to cover up during irrigation times when the radiation is not enough or unavailable. However, operation costs for the generator are overwhelming in addition to environmental concerns; hence there was a need to evaluate the direct pumping sprinkler system. This study therefore aimed at determining the farm's scheme water demand using CropWat software, which was used in determining the pumping requirements using the Grundfos sizing tool. The Homer Pro software was used to optimize the PV-Diesel configuration, and a sensitivity analysis was conducted. The results show that the area requires at least 339.93m3 of water daily to irrigate its cropping pattern of tomatoes, cabbages, watermelon and small vegetables. The appropriate sizing of solar panels by the Grundfos sizing tool gave results of a solar array rated 14.58 kW and 569V with the Average daily water production of 300m3/day, but since this was less than the scheme water demand, solar alone could not provide all the water throughout the year. Simulation results from the HOMER software showed that the optimum configuration that could meet irrigation and other requirements on the farm is a 10.8 kW all-PV system and 17.0kW diesel generator. Solar energy was the only renewable energy resource. Adding other sources of renewable energy to determine optimal configurations is recommended for future studies to avoid adding Diesel generators which due to the raising of fuel is costly and its impact on the environment.