Combined System Gives Abundant Solar Electricity And Clean Water
A new device that can produce electricity from sunlight while simultaneously purifying water has been produced by researchers, an invention they say could solve two problems in one stroke.
The scientists adapted a solar panel that not only generated power, but used some of the heat energy to distil and purify sea water.
The findings may one day help to mitigate the shortage of energy and clean water in arid and semiarid regions.
The increasing demand for energy and clean water globally represents a challenge for sustainable development. Current technologies for purifying water often consume large amounts of electricity and require infrastructure beyond the reach of many communities that lack basic access to safe drinking water – a situation thought to affect more than 780 million people worldwide.
The lead author expects that a commercial device could be available in five years.
Clean energy and clean water are among the major challenges for sustainable development especially in emerging countries. But traditional approaches to electricity generation consume huge amounts of water. In the US and Europe about 50% of water withdrawals are for energy production.
It's estimated that in Arab countries around 15% of electricity production is used to produce drinking water.
Now, researchers believe they have found a way to combine these actions in a single device.
The team has high hopes for the future of the project. The paper notes that solar installations are set to increase to 969 gigawatts by 2025. These panels require four billion square meters of land for sunlight. If all of the panels are outfitted with water-generating devices as well, that could mean a maximum of four billion cubic meters of water also produced annually, or 10 percent of the world’s water consumption in 2017.
Existing state-of-the-art solar panels face physical limits on the amount of sunlight they can actually turn into electricity. Normally about 10-20% of the sun that hits the panel becomes power. The rest of this heat is considered as waste.
Peng Wang and colleagues combined two existing solar-driven technologies - photovoltaics and multi-stage membrane distillation - to simultaneously produce electricity and clean water. Membrane distillation is an advanced solar-driven process requiring relatively low temperatures to efficiently evaporate and collect water. The authors designed a three-stage membrane distillation unit mounted on the rear side of a photovoltaic panel so that the heat normally dissipated by the latter is used to evaporate water. The device maintains the efficiency of a commercial solar cell, while at the same time providing clean water at a higher production rate than most existing devices.
"The waste heat from PV panels has really been ignored, no one has thought about it as a resource," said lead author Prof Peng Wang from King Abdullah University of Science and Technology in Saudi Arabia.
"We use the heat to generate water vapour that gets transported across the membrane and then it condenses on the other side."
The team found the device can be used to purify saltwater as well as seawater contaminated with heavy metals, with the water collected containing levels of lead, copper, sodium, calcium and magnesium all below the levels deemed safe for drinking water by the World Health Organisation.
"Because it is a multiple stage distillation device, it also allows the latent heat in the condensation to be utilised to drive the second cycle of water evaporation. So that is why we can get a very high fresh water production rate by this device."
According to the authors if the technology was scaled up and used globally, it could, in theory, produce 10% of the total amount of drinking water consumed in 2017.
However there are many tricky steps to go through to develop and commercialise this type of device. There are some inherent drawbacks in that it needs a large area of land to collect enough solar light to be effective at producing water.
"It can be used for coastal areas as long as you are not talking about delivering drinking water for a city of over one million people," said Prof Wang.
With solar farms often located in arid regions, the device could provide clean water where it is needed most. What is more, the team say it could be used in a backyard or on an industrial scale.
"It is a suitable technology to deliver drinking water at the small to medium scale," he explained.
The study has been published in the journal Nature Communications.