Adapted Irrigation Pump Load in Solar PV and Wind Energy Systems through Stepped Variable Frequency Drives

Abstract

Wind and solar photovoltaic (solar-PV) power are highly variable and intermittent as exhibited by corresponding generation profiles. When this power is utilized directly for water pumping, the availability and reliability of water automatically follow the Renewable Energy Sources (RES) characteristics. On the other hand, Deferrable Irrigation Load (DIL), follows a specific irrigation water need profile. The DIL profile is determined by crop cycles and corresponding water needs. It is also affected by aspects of weather mainly precipitation, temperature, and wind. In this research, discrete switches and Variable Frequency Drives (VFDs) are applied as a combined solution. Combined discrete and continuous switching through VFDs is applied to separately adapt pump load to DIL and RES profiles. Discrete switches are applied to engage the exact number of pumps required to match an expected irrigation load. A VFD is further used to ensure continuous matching of irrigation pump load to the anticipated DIL curve, through adjustment of pump speed points. Finally, the system is repeated to adapt the pump power to the RES curve. The adapting technique was implemented to improve elasticity, hence the efficiency of the system. The results showed that the adapted system to the DIL curve was 94.7% compared with a discrete-only system (91.4%). This represented a slight improvement of 3.3%. The results demonstrated the smoother operation of the pump system and increased energy utilization efficiency. A further improvement on the control strategy for VFD coupled with the re-design of irrigation pipe networks was required to improve efficiency beyond 94.7%.