12 September 2018
Harnessing solar and geothermal energy for desalination
Published online 20 December 2017
Scientists are looking for new ways to desalinate water using energy resources that reduce dependence on dwindling fossil fuels.
The Middle East relies heavily on fossil fuels to drive modern desalination technologies that are used to grow food. Currently only 1 percent of desalinated water comes from renewable resources.
Intermittent or low energy supplies are a problem for agricultural settings, where grid networks may not always stretch. Better ways to capture and store renewable energy resources could increase the sustainability of using desalinated water, making it cheaper and easier to use.
“This is a moment of innovation. You can see that in Saudi Arabia, in Oman, in the Emirates and Qatar and in North African countries. New practices and policies are being developed around water,” said Shannon McCarthy, General Secretary of the International Desalination Association, who has worked extensively in the Middle East throughout her career.
Solar energy is a particularly attractive option for an arid region like the Middle East with a reliable supply of sunlight.
Solar energy has been a key area of research in Oman, where the Middle East Desalination Research Centre (MEDRC) is based. The Research Council, Sultan Qaboos University, the Omani Ministry of Agriculture and Fisheries and MEDRC have installed a desalination unit powered directly by photovoltaic solar panels to treat brackish water irrigation purposes.
The unit contains 20 solar cells and can produce up to 3,000 gallons of water per day, brines are treated in evaporation ponds close the to the desalination system. MEDRC aims to organize a workshop in small desalination units for agriculture sustainability in March 2018, mainly for Omani farmers.
Other autonomous photovoltaic reverse osmosis plants are operational on small scale in remote areas of Morocco and Tunisia, and on medium scale in combination with MED/MSF at Umm Al Nar Abu Dhabi and Layyah in Sharjah.
The King Abdullah Initiative for Solar Desalination at Al Khafji Saudi Arabia, set to become operational by 2020, is the largest plant to date. It will produce 60,000 m3/day using polycrystalline photovoltaics and reverse osmosis. The design of this plant is decoupled: RO will be fuelled by energy from the grid, and the solar panels will feed back to this grid.
It is expected to reduce costs to as little as 3-4 cents per kilowatt hour. In November, recent tenders for the new 300 megawatt solar powered plant at Sakaka Al Jouf brought in bids at a record low of under 2 cents per kilowatt hour among the three top competing companies. Abu Dhabi's Masdar — which hosts a sustainability research institute and the UAE’s first carbon-free city — eventually won the bid at 1.79 cents per kilowatt hour.
“The question for the future is not about whether fossil fuels will be expended, but whether they are competitive at this price,” says Carlos Cosin, treasurer of the IDA and CEO of Almar Water Solutions, a Spanish company focused on sustainable development in the water sector. “We will see in the coming years a big revolution in the sector.”
Masdar has since 2013 developed research partnerships in renewable desalination technology with four commercial partners -- Abengoa, Suez, Sidem/Veolia and Trevi Systems. Results of the pilot phase are yet to be announced but three solar collector systems were installed in 2017 to evaluate their suitability for the provision of low temperature process heat for desalination.
For Cosin, who is the former CEO of Abengoa Water, the future is about solar. The resource’s major drawbacks — intermittent supply, and lack of storage capability — will be solved, he says, in the next five years by improvements in batteries and salt storage.
Geothermal – a new frontier
Of increasing interest in desalination is geothermal energy, which would provide a constant source of stable ‘base-load’ power for continuous, long-term periods. It could be used directly for membrane distillation, while thermal distillation like MED and MSF could be powered using the electricity it generates.
To date there is no industrial scale geothermal desalination plant, but it is a mature technology that has been used for generating electricity in Italy, Iceland, China, New Zealand and beyond.
“The world is producing about 12,000 MWe of electricity from hydrothermal power only, why not use it in desalination,” says Dornadula Chandrasekharam, geothermist and visiting professor at the Indian Institute of Technology Hyderabad, India. Now adjunct professor at King Saud University, Chandrasekharam has analysed the opportunities of tapping geothermal systems from Saudi Arabia. The hot springs and radiogenic granites in the west provide huge potential.
“Immediately Saudi Arabia can develop 40 MWe [about 254 million kWh] from just two thermal springs — Jizan and Al Lith,” he says. If you translate that into desalinated water for say, wheat production, assuming 5700 kWh is for one tonne of wheat and 5.6 tonnes are grown per hectare, about 20 hectares can be brought under irrigation. That’s 120 tonnes of wheat.
Combining high temperature (above 150 degrees Celsius) geothermal energy with a big industrial scale technology, such as hybrid MED-MSF would bring the cost of one metre cube of this water to less than 1.5 Euro, Chandrasekharam says. Tapping the high resources available, he says, could make Saudi Arabia a water surplus country in the near future.
There is a high initial investment needed for deep well drilling, using technologies developed by the oil sector. Environmental engineer, Noreddine Ghaffour, of the King Abdullah University of Science and Technology and Thomas Missimer, of Florida Gulf Coast University have been looking at lower temperature, more shallow geothermal resources for standalone desalination processes.
The direct use of steam would make for efficient membrane distillation or adsorption desalination. These resources include thermal springs, mines and existing hydrocarbon wells. While there are a few pilot models in seas around Mexico and Greece, detailed economic modelling and a commercial-scale showcase is necessary.
The technologies for renewable energy driven desalination and partial desalination are in place. The question is now one of regulation and implementation. “This is one of the most water scarce parts of the world, but it has the some of the highest use per capita," says Ghaffour.
But today, he is hopeful. “Politically everything is positive, towards supporting technologies that reduce the use of fossil fuels. Getting solutions is part of the socio-economic development and the food security of the region.”
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