Electricity and drinkable water in one device

12 July 2019

OCEAN-SEA

Ocean and an island

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Scientists in Saudi Arabia have designed a solar panel device that produces electricity and creates clean water at the same time.

It uses heat energy - generally wasted when it comes to solar panels - to evaporate salt water, with no reduction in efficiency of the electricity generation.

According to Paul Coxon from the University of Cambridge, “the device is like a sandwich, made of stacked layers. On the top layer you have a little silicon solar panel.”

Salt water flows through a set of pipes and evaporates in the heat. This vapour then passes through a membrane, a little filter, and it condenses. The condensed clean water flows out through a second set of pipes. This process occurs in each of the four layers, producing a sample of concentrated salt water at one end and a sample of clean water at the other.

The device addresses the rising demand for drinkable water that comes with population growth. Current water sources - rainfall, spring water and rivers - have become insufficient to meet this demand in many nations.

As a result, some countries are turning to the sea as a further source of water. It takes a lot of energy to reduce the concentration of salt in the water to make it safe to drink - a process called desalination. In Arab countries, over 15% of the nationally produced electricity is used to desalinate water.

The researchers were based at the King Abdullah University of Science and Technology in Saudi Arabia - a country relying more and more on solar power. Until it fell through last year, Saudi Arabia had been planning to build the world's largest solar farm.

Solar power uses photovoltaic cells to convert visible light into electricity. Meanwhile wavelengths not used for electricity, in the infrared part of the light spectrum, get absorbed by the solar cell and cause it to heat up. In a normal cell this heat energy goes to waste - but not here.

In theory, this device could turn solar power plants into fresh water producers. The water can be used to clean the solar panels, irrigate nearby crop fields, or go straight into the drinking water system. According to Coxon, “it does lend itself to being scaled up; it’s making about one to one and a half litres of water every hour.”

The article, published in Nature Communications, did not make it clear what happens to the concentrated salt water byproduct after the device has been running. This could be crucial. A recent study in the journal Water Research showed that the waste brine from desalination may be toxic where it's deposited into ecological systems.

As demand for drinkable water increases, hot countries are desalinating more and more seawater. Whilst this new device may reduce electricity consumption for production of drinkable water, scaling them up may come at a cost for marine life.

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