Converting ocean water into fresh water is energy intensive, and therefore expensive. Saudi Arabia is a desert kingdom with plenty of oil but very little fresh water. The Saudis burn 1 million barrels of oil a day to produce 60% (4 billion cubic meters) of its total fresh water supply through desalination. If exported onto the world market, those 1 million barrels of oil would bring Saudi Arabia $115 million a day, but it is worth it to them to forgo the profits and have the fresh water. From an environmental standpoint, burning 1 million barrels of oil a day sends close to a half million tons of CO2 emissions into the atmosphere every day, contributing greatly to the pace of global warming.
To deal with these problems, the Saudis have joined with IBM to build a series of solar-powered desalination plants that could by mid-century produce a large share of the kingdom’s water needs.
However, the largest solar-powered desalination plant yet designed will be built in the United Arab Emirates. The Ras Al Khaimah plant, scheduled to start production in 2015, will produce 100,000 cubic meters (approx. 22 million gallons) of fresh water a day, and in addition, provide 20 megawatts of electrical power daily. The developers estimate they will be able to deliver water at a cost of $0.75 per cubic meter. Average cost per cubic meter of water delivered to households in the United States runs between 0.35 and 0.40. Most of the desalination plants run by solar energy are situated in the Middle East where there is an abundance of year round sun and a scarcity of water.
The largest desalination plant run by wind power is near Perth in Western Australia. The Kwinana Desalination Plant produces 144,000 cubic meters of water a day (approx. 38 million gallons), about 17% of Perth’s water supply. The Kwinana plant is powered by the 80 Megawatt Emu Downs wind farm located 200 miles away. Because electrical power has to be supplied evenly 24/7, and because the wind stops blowing from time to time, the power from the wind farm goes into the grid on a trade-off basis. The wind farm contributes 270 Gigawatt hours a year into the power grid, more than offsetting the 180 Gigawatt/h year required to operate the desalination plant. There are a number of smaller desalination plants run by wind-generated electrical power that goes directly from the wind farm to the plant, but Perth has opted for the offset arrangement.
Most desalination plants are still operated with grid power generated by coal, oil, or natural gas because it is less expensive than spending hundreds of millions to construct solar arrays or wind farms. For example, Australia’s other desalination plants providing fresh water to Sydney, Melbourne, Adelaide, and other coastal areas use fossil fuel power from the grid. But more and more, new desalination plants around the world are being planned to operate on alternative power. At some point in the future, all our electricity will have to come from those sources.