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PV-driven drip irrigation system with compressed air storage

Source：pv-magazine

The proposed system uses compressed air to store energy, as well as for the prevention of clogging in the irrigation tubes. Two experimental systems were built and tested in China and clogging was reduced by up to 93%.

The system

Image: Northwest A&F University, Agricultural Water Management

Researchers from China's Northwest A&F University have developed a novel drip irrigation system powered by PV, which stores energy in the form of compressed air. The use of compressed air not only regulates the system's performance but also ensures uniformity in irrigation outflow and enhances the anti-clogging of the pipes.

“This innovative photovoltaic irrigation model effectively addresses the fluctuations in photovoltaic output, which often hinder the provision of stable and reliable energy for drip irrigation systems. Furthermore, the processes of energy storage and release generate a pulsed dynamic water pressure that enhances the anti-clogging performance of the drip irrigation systems while ensuring uniformity in water distribution,” corresponding author Dr. Maosheng Ge told pv magazine. “Our findings indicate that small-scale off-grid solar resources can be seamlessly combined with drip irrigation technology through this straightforward approach.”

In order to maximize the water-energy balance of the system, the researchers have utilized a sealed pressure tank with a mixture of air and water. That tank is located in between a pump and the drip tubes. The tank is initially filled with air, and once solar energy is available, the pump pushes water to the tank, effectively compressing the air in it. Once a certain pressure is reached, a valve opens, releasing the stored water in pulses. Once water is released, the air expands again, enabling the repetition of the cycle.

“During the cycle process, the air volume in the pressure tank undergoes expansion during each pulse drip irrigation process, thereby guaranteeing the consistency of both the pulse jet time and discharge flow,” said the group. “Although the output of the solar panel and the water lifting performance of the pump vary due to variations in solar irradiance or cloud occlusion during different periods of the day, these differences only alter the water lifting and injection time of each pulse period in different time of the day, without affecting the pulse jet process.”

To test the novel system, the scientists built two experimental setups in Yangling, China. For the analysis of the hydraulic performance, they used a 374 W PV panel that powered a 16 L/min pump. The pump drove water through a 48-meter central tube, to which eight lateral pipes were connected, each six meters long. On each pump, six emitters were placed, resulting in a total of 48 emitters throughout the system. Under each of them, a measurement cup was placed.

The layout of the system

Image: Northwest A&F University, Agricultural Water Management

The second experimental system focused on anti-clogging performances. For that, muddy water with a sand content of 2 g/L was flowing into four drip tapes. One tape received its water directly from the contaminated water tank using a pump, while the three others had a pressure tank between the pump and the tape. In those later three, the system used the same water-air pressure technique as in the first setup.

“The system operates in intermittent cyclic pulse drip irrigation mode, with the emitter's flow rate varying as a power function of peak pressure to ensure a flow uniformity not less than 91.76%,” the group explained. “Furthermore, the dynamic pulse pressure generated by the system significantly enhances emitter anti-clogging performance. During intensified clogging tests, sediment deposition in the lateral tube was reduced by 78.95% – 93.36% compared to constant pressure continuous drip irrigation systems.”

Moreover, the team conducted an economic analysis of the system, finding that system implementation will cost $373.13, equivalent to the initial investment of $103.84 in traditional drip irrigation. However, only considering operating energy consumption and environmental benefits can result in annual operating benefits of up to $19.41 per mu, which is the traditional Chinese unit of land area, equivalent to approximately 667 m2.

“The system offers substantial economic and environmental benefits without significant increases in system investment costs while providing clean, readily available energy for efficient operation of drip irrigation systems, thus contributing positively to food security,” the scientific team concluded.

The system was presented in “The incorporation of solar energy and compressed air into the energy supply system enhances the environmentally friendly and efficient operation of drip irrigation systems,” published in Agricultural Water Management.

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