An international research team has proposed a new testing method for photovoltaic water pumping systems (PVWPS) used for domestic water applications and irrigation in developing regions.
“No prior studies have proposed such a method for evaluating the evolution of boreholes throughout the lifespan of PVWPS,” the research's lead author, Simon Meunier, told pv magazine. “It notably leverages the system’s photovoltaic panels as a power source to conduct regular borehole pumping testing, rather than relying on diesel generators, and can be applied across diverse contexts, benefiting communities, governments, NGOs, and other stakeholders dedicated to sustainable water and energy solutions.”
In the paper “Photovoltaic pumping tests: A novel supervision method for photovoltaic water pumping systems,” published in Heliyon, Meunier and his colleagues explained that the novel testing approach offers innovative and practical benefits such as continuous and cost-effective monitoring, reduction of emissions and logistical complexities, as well as enhanced system longevity and groundwater sustainability.
“Conventional borehole testing in PVWPS typically requires diesel generators and substantial manpower, making it costly and often feasible only before the installation of the PVWPS,” Meunier said. In contrast, our method enables ongoing borehole monitoring without additional fuel costs or interruptions to the water supply.
They also stressed that many countries in Africa currently require pumping tests before the installation of a pumping system on the borehole or at the borehole recommissioning, noting that these tests are usually conducted in a few days. Furthermore, some countries also require tests after deployment to protect the borehole over time.
“Most of the focus is on water contamination, with regulations on minimum distances between the borehole head and other facilities, on the borehole cap, on the gradient of the slope around the borehole head to prevent surface water from entering the borehole, and on the presence of waste near the borehole,” the study notes.
The proposed methodology monitors borehole water levels at various flow rates without disrupting the operation of the PVWPS, according to its creators. The testing setup utilizes a “non-intrusive” clip-on flow sensor that can be de-installed after the test is completed. It measures the hydrostatic pressure induced by the height of water above it.
“The installation of the equipment is carried out approximately 1 h before sunrise to be ready to start the measurements when the water in the borehole is still at its static depth,” the scientists said, noting that the test could be easily conducted by one technician alone. “The data collection starts 30 min before sunrise. The measurement is stopped around 2–3 h after sunset, in order to collect data throughout the whole day, and to observe the recovery of the water level without pumping.”
These tests, according to Meunier, allow early detection of issues such as borehole clogging. “Regular supervision through photovoltaic pumping tests supports sustainable groundwater management, preventing over-extraction and extending the operational life of both the borehole and PVWPS,” he added.
The proposed methodology was tested in a 600 W PVWPS installed in 2018 in Gogma, Burkina Faso, where there is no centralized water supply network. The system supplies around 7 m3 of water per day for around 280 inhabitants. “The borehole is 56 m deep, has an interior diameter of 0.11 m and the motor-pump is at a depth of 30 m,” the scientists specified. “The height between the ground level and the level at which the water enters the tank is 7.6 m.”
They found that the proposed testing method accurately determines borehole parameters, achieving a model fit with an average coefficient of determination (R2) of 0.99. They also estimated the cost of a photovoltaic pumping test at $43, which compares to $511 for the multiple-step drawdown test and $2,050 for long-term tests.
“Furthermore, over a 10-year period (the estimated motor-pump lifespan), the cumulative cost of conducting photovoltaic pumping tests every two years is less than 10 % of the expense of replacing the motor-pump prematurely,” they added. “Over a 50-year period (the estimated borehole lifespan), the total cost of biannual photovoltaic pumping tests amounts to only 13 % of the cost of drilling a new borehole.”
“By using solar power instead of diesel, this method reduces emissions and logistical complexities, aligning with sustainability goals,” Munier concluded.
The research team comprised academics from France's Université Paris-Saclay, the Sorbonne Université in France and Institut Photovoltaique d’Ile de France, as well as from Stanford University in the United States and the Imperial College London in the United Kingdom.
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