Scientists develop device that produces fresh water and electricity simultaneously solving two global problems in one stroke
Researchers have been able to invent a single device that might bring both clean power and water to millions of people across the globe as it is capable of producing electricity from sunlight while simultaneously purifying saline water.
A study published in Nature Communications says the device provides an alternative to prevailing water purifying technologies, which often consume huge amounts of electricity and require large infrastructure.
According to the team of researchers from the King Abdullah University of Science and Technology in Saudi Arabia, if the technology demonstrated by them is scaled up, and if the device could be installed on a four billion square meters of land, approximately four billion cubic meters of fresh water could be produced every year - which is equivalent to 10% of the total global drinking water consumption in 2017.
“The generated clean water can be used for many highly desired and niche purposes, such as cleaning solar panel to remove dust particles, irrigation of plants and crops, drinking water, especially in semi-arid and arid areas, and potable water production from highly contaminated surface and groundwater, among others,” say the researchers, adding that the device will be particularly useful in areas where land and resources are scarce.
So, what is this technology?
The team of researchers used a solar panel for their study and below it, they attached a three-stage membrane distillation device through which saline flows. The heat from the solar panel warms the water passing beneath it and the process is repeated for the next membrane.
“The simultaneous production of fresh water and electricity was achieved by an integrated solar PV panel-membrane distillation (PV-MD) device, in which a PV panel was used both as a photovoltaic component for electricity generation and photothermal component for clean water production,” says the paper.
The researchers explain that in a typical solar cell, 80–90% of the absorbed solar energy is "undesirably" converted to heat, and after that, it is “passively and wastefully” dumped into the ambient air. The device at the back side of the solar cell directly uses this waste heat as a heat source to distill and purify water. "It (device) was used to recycle the latent heat of water vapor condensation in each distillation stage,” says the paper.
The team believes the device could produce clean water by without compromising the performance of electricity generation. The water production rate of the device, according to the analysis, is three times higher than that of conventional solar stills. At the same time, the PV panel generates electricity with energy efficiency higher than 11%, which is the same as that recorded on the same PV panel without the device.
“To reduce heat loss into the ambient environment, the sides of the device were sealed by polyurethane foam with low thermal conductivity. Each stage of the device was composed of four separate layers: a top thermal conduction layer, a hydrophilic porous layer of water evaporation layer, a hydrophobic porous layer of MD membrane for vapor permeation, and a water vapor condensation layer,” says the study.
The energy shortage and clean water scarcity are two key challenges for global sustainable development. Nearly half of the total global water withdrawals are consumed by power generation plants, while water desalination consumes lots of electricity.
“Water and energy are inextricably linked, and the intimate water-energy nexus is being increasingly felt globally, as water security is becoming a threat to energy security and vice versa. In the US and Western Europe, about 50% of water withdrawals are for energy production. On the other hand, clean water production, especially seawater desalination, consumes a huge amount of electricity. In Arab countries, for example, over 15% of the total national electricity is consumed by the freshwater production industry. It has been reported that 1~10% of clean water produced in the electricity-driven seawater desalination process is fed back to the power plant to generate the electricity consumed during the desalination process,” say the researchers.
According to them, the composite device can significantly reduce capital investment costs by sharing the same land and the same mounting system. “(It) thus represents a potential possibility to transform an electricity power plant from otherwise a water consumer to a freshwater producer,” the study says.