Can Low-Cost Solar-Powered Drip Irrigation Systems for Smallholders Be Smart? A Case Study in Sub–Saharan Africa

Abstract

Smart irrigation, which ensures precise water delivery to crops, is essential for the economic sustainability of irrigated agriculture. Yet, most irrigation schemes in sub–Saharan Africa (SSA) are not smart; instead, water is applied without regard to crop water needs, leading to sub-optimal crop water productivity, low water and nutrient use efficiencies and, ultimately, reduced crop yields. This study aimed to (i) improve an existing automated solar-powered irrigation system, enabling it to be smart by meeting crop water needs, and (ii) assess the impact of meteorological variables on reference evapotranspiration (ETo) in Ghana. The previous system utilized a low-tech siphon device for automation, supplying water at specific intervals regardless of crop water needs. Integrating siphon automation with solar pumps offers the potential to design the irrigation system for automatic ETo-based scheduling. In the present study, hourly ETo data were correlated with corresponding solar radiation (Rs) values. Similarly, linear regression compared the hourly volume of water pumped (VWP) from a 12V pump powered by a 50-watt solar panel to corresponding ETo values. Separately, partial correlation analyses were conducted to understand the relative influences of Rs, wind speed (U2), relative humidity (RH), and air temperature (Tair) on ETo in ten locations distributed across the agroecological zones of Ghana. There was a strong linear correlation between Rs and ETo in hourly contexts (R2 > 0.99). Similarly, hourly VWP exhibited significant and strong linear relationships with Rs (R2 = 0.79). Solar radiation consistently emerged as the primary meteorological factor exerting the most influence on ETo in Ghana’s agroecological zones. In conclusion, the clear linear relationship observed among the solar energy provided for pumping (Rs), water demand by crops (ETo), and water delivery to crops (VWP) allows for the implementation of built-in irrigation scheduling throughout all of Ghana's agroecological zones.

Keywords: Irrigation scheduling, Evapotranspiration, siphon, solar radiation driven automated irrigation, smallholder farmer