PV-driven solar water pumping system based on supercapacitor buffer

Scientists have proposed a novel design for standalone solar PV water pumping systems, using an intermediate supercapacitor buffer to temporarily store solar energy and release it in high-power pulses. Daily water productivity has grown by 64%, based on a simulation. An experimental setup was also tested.

Researchers from Ukraine's Lviv Polytechnic National University have proposed a novel design for standalone solar PV water pumping systems (SPVWPSs) that reportedly achieve higher efficiencies.

While traditional SPVWPSs with direct drive are not very efficient due to fluctuations in solar radiation, the team has suggested a system that uses an intermediate supercapacitor module (SCM) buffer to temporarily store solar energy, later releasing it in high-power pulses to the pump, enabling the pump to operate at a better capacity.

“Taking into account that the water pumping process itself is an accumulation of energy, this work proposes applying a pulsating mode of pump operation with nominal power in each pulse enabled by the introduction of an SCM,” the team said. “It is permanently connected to the PV module and periodically connected to the brushless DC motor (BLDCM) with the centrifugal pump (CP) using an electronic switch. The on-off algorithm of this switch operation is designed in such a way as to ensure the maximum power point tracking (MPPT) of the PV module.”

To test the novel system, the scientists simulated three systems on the Matlab/Simulink environment. The first was of a traditional SPVWPS – that includes the PV module connected to a DC-DC converter that performs the function of MPPT, providing a voltage value for the corresponding angular velocity of the BLDCM with CP.

In contrast, two novel designs were also simulated. In the first, an SCM is installed between two DC-DC converters. At the same time, the first converter adjusts the operating point with MPPT, and the second manages the pulsating operation by connecting and disconnecting the pump when the SCM reaches specific charge levels. The other novel designs give up the DC-DC convertors altogether, connecting the SCM directly to the panel. Instead, the MPPT function is achieved by turning the pump on and off to maintain the PV panels near their maximum power point.

In all of the simulations, four PV panels with a power of 500 W each and an efficiency of 20.3% were used. The CP had a motor power of 1.5 kW and an angular speed of 2,800 rpm. The BLDCM had a rated voltage of 1.6 kW and an efficiency of 90%. The DC-DC converter is a step-down type, and its MPPT subsystem implements the perturb & observe (P&O) search algorithm.

“In the particular simulated studied case (July in Ukraine), the developed system showed the increase of daily water productivity of 64% compared to SPVWPS of traditional configuration with MPPT and the same components and operating conditions,” the results found. “We can hope for an even higher advantage of the proposed approach compared to the known ones in the case of estimating the annual performance of the SPVWPS, taking into account the decrease in solar intensity in other months compared to summer.”

In addition to the simulated results, the team has also constructed an experimental setup of the novel system. “Experimental studies conducted on the created SPVWPS sample confirmed the effectiveness of the proposed pulsating operation of the CP: in conditions of reduced insolation, the efficiency of the operation of the CP together with its electric drive was 25% higher than in the basic configuration,” they found.

The results were presented in “Efficiency improvement in standalone solar PV water pumping system by pulsating pump operation based on intermediate supercapacitor buffer,” published in e-Prime – Advances in Electrical Engineering, Electronics and Energy.