Membrane tech boosts PV desalination

Written by: Andrew Wade | Published:
(Credit: KAUST)

Researchers in Saudi Arabia have demonstrated how tweaking the membrane in their solar desalination system can boost its performance.

The breakthrough builds on previous work carried out at King Abdullah University of Science and Technology (KAUST), where excess heat from photovoltaic (PV) systems was harnessed to desalinate seawater. PV panels in the Middle East can harvest huge amounts of solar energy, but the panels also get incredibly hot, sometimes more than 40°C above the ambient air temperature. This not only affects PV performance, it shortens the lifespan of the panels.

To address this problem, the KAUST team devised a system that draws seawater into a series of layered channels beneath the PV panels, distilling it through three stages of purification to produce drinkable water and cooling the panels in the process. The system was found to produce up to 1.6 litres of freshwater per hour, but the PV panels remained stubbornly hot even with the addition of the cooling channels.

Now, the KAUST team has made changes to the thickness of its desalination membrane to enhance both the cooling and desalination processes. Experiments, including outdoor tests on the KAUST campus, showed that the new membrane design boosted electricity generation by eight per cent while at the same time doubling the rate of potable water produced. The work is published in Joule.

“Realising a lower solar-cell temperature relies on regulating heat transfer through the hydrophobic membrane in the multistage device,” explained research lead Pen Wang.

“Simply by modulating the membrane parameters, we found that utilising a thinner hydrophobic membrane with higher porosity enables higher desalination performance and lower solar-cell temperature to be achieved simultaneously.”

Taking inspiration from infusion technology used in intravenous lines, the researchers developed a gravity-driven system that feeds seawater into the solar-cell device without external pumps. A special fabric also wicks away solid salts and minerals, avoiding the release of toxic liquid brine.

“Because our device aims to desalinate seawater and provide electricity for off-grid communities, relying on a mechanical pump to control the flow rate of source water is not a good choice,” said Wang.

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