The Desalination Energy Dilemma

Desalination plants consume a significant amount of energy, and the question now is how much energy should we expend on boosting clean drinking water supplies?

There are now 17 desalination plants in the proposal process in the US, and each would consume about 15,000 kilowatt-hours of power for every million gallons of clean drinking water they produce, according to a new report by the Pacific Institute. As much as half of the total cost of desalination is represented by energy.

What rankles here for desalination leaders is the fact that recycling waste water uses about half the energy. And with the growing number of desalination plant proposals out there, analysts are concerned that this future increase in clean water supplies will come at the expense of increased energy price volatility.

Desalination leaders, who are not keen on the Pacific Institute's mathematics, point out that we are wasting tons of energy on non-essentials like TVs and air conditioners-or even the energy cost of driving. Cutting down on these non-essentials, they say, would be preferable to not having enough clean drinking water. It's all a matter of perspective-and priorities.

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They will also point out that desalination plants are much more energy efficient than other plants, while at the same time recognizing the considerable amount of energy consumed and the resultant greenhouse gas emissions. 

The US is on the verge of pursuing large-scale desalination, for which it has gotten off to a slow start compared to the world's water-poor regions, where desalination has been a necessity. Things have been slow because there are too many questions surrounding this massive venture, and developers have had a hard time proving that it's worth all the energy, emissions and expense.

Earlier this year, construction began on one of the largest desalination plants in the US, Poseidon Resource's $1 billion Carlsbad plant in Southern California. The Carlsbad plant will use reverse osmosis to divert saltwater through microscopic sieves inside cylindrical filters. The fresh water is thus separated from the salt water and other impurities. The entire process requires a lot of energy. 

San Diego has already agreed to buy massive amounts of water every year from Carlsbad. The local authorities are gambling that the cost of this water, which is double the cost of available water, will level off eventually. Indeed, as things stand, it will be a hefty bill: around $3 billion over 30 years for 7% of the county's water requirements. That these prices will fall is a big unknown.

As such, all eyes are now on Carlsbad, which should be considered the litmus test for the US' desalination future. San Diego aside, will there be a guaranteed market for this water? Some experts believe the gamble is a good one and that desalinated water supplies will indeed be cheaper than existing supplies by 2024. Plenty of others disagree, and say the best path for now is conservation and recycling waste water.

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Perhaps the best hope for desalination is the possibility of using renewable energy technology in the process. This is already being done in Abu Dhabi.

At a recent summit of the International Renewable Energy Agency (IRENA), experts noted: "While the initial focus, particularly in the Middle East, was to provide a reliable source of fresh water to ensure the beginning and blossoming of the region's economy, the emphasis now includes making desalination a sustainable and environmentally responsible industrial solution …"

In the US, MIT and the US Navy are experimenting with desalination energy efficiency, the former working on a filtration system based on atom-thin sheets of grapheme, and the latter developing a prototype for a transportable energy-efficient desalination unit that uses 65% less energy than conventional units.

By. Charles Kennedy of Oilprice.com