LOW HEAD MICRO-HYDRO TURBINES USED FOR EFFICIENCY INCREASE OF SOLAR POWERED IRRIGATION SYSTEMS

This paper presents an improved solution for solar powered irrigation systems by integrating low-head micro-hydro turbines for energy recovery when discharging the water from the storage tank. The proposed solution is justified by the potential energy available when storing water in a tank using pumps powered by PV panels. This energy can be used to provide additional electricity when discharging the water, by placing a low-head micro-hydro turbine at the bottom of the tank. The energy produced can be used for pumping back a fraction of the consumed volume of water, or to ensure the pressure for longer distance irrigation networks. The energy surplus provided by the turbine is necessary especially when irrigating during mornings and evenings, when PV system power production is reduced. A low head micro-hydro turbine suitable for a small scale solar powered irrigation systems was tested on a dedicated testing stand in order to demonstrate its efficiency. The turbine was designed to generate 1 kW of power operating at 2.4 m head and 360 m3/h flow. The tested model reached a maximum output of 526 W at 2 m head and 240 m3/h flow. The rotor is made from thermoplastic by 3D printing, thus the flow through the turbine was limited to avoid damaging the blades. The experimental data was compared to the specific data of a small-scale solar powered irrigation system to determine the total efficiency of a hybrid irrigation system. The calculation takes into account the medium flow rate needed for turbine operation during irrigation phase, correlated with the electricity requirements of the pump for obtaining specific flows. The additional power output can increase the global efficiency of a solar powered irrigation system by feeding the electricity back to the pumping unit. For a PV power system that provides 20 kWh/day, the turbine can ensure around 22.5% of the energy needed for irrigation.