Solar-powered water pumping systems are a saving grace in areas that are not grid-connected or where the power supply fluctuates a lot.

In a solar-based water pump, the solar energy is converted into electrical energy for operating through either direct current (DC) or alternating current (AC). In the case of a solar AC motor water pump, energy conversion happens in two stages (DC-DC and DC-AC), leading to increased size, cost, and complexity. It also decreases the efficiency of the entire system. The two-level inverter (DC–AC) stage generates higher harmonics in output voltage and higher electromagnetic interference that deteriorates the AC motor performance.

Researchers from Tamil Nadu’s Vellore Institute of Technology have come up with a multi-level inverter for solar water pumps.

The seven-level solar inverter with five power semi-conductor switches for the operation of a single-phase induction motor pump and can provide a lesser harmonic voltage that reduces filter requirements.

According to the report, solar-powered water pumping systems are mostly used in areas where there’s plenty of sunshine and scarce power generation systems.  The system is an assembly of a solar PV array, inverter, and a motor-pump set.

During the research, the framework of the solar PV standalone water pumping system comprised a PV array, a five-switch seven-level inverter and an induction motor water pump.

The multilevel inverter with reduced switches was used to provide pulse width modulated voltage to the input of induction motor and pump assembly with a single-stage solution.

According to the research team, the operation of a seven-level inverter with five switches inverter had been tested experimentally with a 0.5 HP (horsepower) single-phase induction motor water pump.

“A switching frequency of 2 kHz had been applied to the first leg of three switches, and 50 Hz was applied to the other two switches,” said the report titled, ‘Investigation of Standalone Solar Photovoltaic Water Pumping System with Reduced Switch Multilevel Inverter.’

The research team stated that the topology uses an insulated-gate bipolar transistor (IGBT), as power switches and gate signals are given through a sinusoidal pulse width modulation technique. This proposed system eliminates the need for the DC (direct current) conversion stage and provides a single-stage solution through the MLI (multilevel inverter) topology.

The scientists also used a small resistor that was connected between the programmable DC supply and the seven-level inverter’s five switches. The kind of pulse pattern generated helped reduce the switching losses significantly, added the research paper.

Published in Frontiers in Energy Research, the study further states the experiment showed that the induction motor pump operated smoothly as it received quality output voltage with lesser total harmonic distortion (THD) and with reduced switching losses from seven-level five-switch topology.

According to scientists, the major advantages of induction motor include high starting torque, less cost durability, speed variation, low maintenance cost, and easier operation.

The study observed that the proposed multilevel inverter topology obtained a total power loss of 1.6034 W and an efficiency of 98.11%.

Solar-powered water pumps are a great way to solarize India’s agriculture sector and over recent years, the government has focused on the wider adoption of such pumps by India’s farmers.

In the recently released Budget 2020, the government said it plans to provide two million farmers to set up standalone solar agricultural pumps and 1.5 million farmers to set up grid-connected pumps.

As the Government of India earlier announced that it has a target of adding over 10,000 MW of solar capacity to solarize the agriculture sector, the government, until October 2019, has installed over 181,000 solar water pumps across the country.  Chhattisgarh accounted for the highest number of installations of 60,430 solar pumps, followed by Andhra Pradesh, a distant second, with 28,267 installations.

Image credit: JREDA