If photovoltaics show promise to totally replace coal as a clean source of electricity, how would they perform to provide fresh water from seawater?

Photo: water-technology.net

Desalinating seawater is not cheap.  Based on costs for a state of the art desalinization facility in Ashkelon, Israel, as reported in WaterTechnology.net, it costs about US $2.0 billion to build a plant with capacity to desalinate 1.0 cubic kilometer per year of seawater.  In reality, that size plant has not yet been built.  The one in Ashelon is the largest of its kind on earth, and its output at 320,000 cubic meters per day, only equates to about .117 cubic kilometers of fresh water per year.

But the costs are what is most interesting.  The Ashekelon plant cost 250 million US dollars, and assuming a larger plant would produce desalinated water at least as efficiently as this plant, this means a plant that can desalinate one cubic kilometer of seawater per year would cost about 2.0 billion US dollars to build.  If the plant only lasts 50 years - 100 years is a more reasonable expectation - that means the cost of the capital investment, amortized over the life of the plant, is only 4.3 cents per cubic meter of fresh water.

The math gets even more fun if one considers the costs to power this plant using photovoltaic cells, which have an ever improving energy payback (lifetime energy produced divided by energy required to manufacture) that now stands over 20x.

It takes 2.0 kilowatt-hours of electricity, powering a reverse-osmosis system, to desalinate one cubic meter of seawater.  According to a study by Uri Lachish “Optimizing the Efficiency of Reverse Osmosis Seawater Desalinization,” this power consumption efficiency could be more than doubled.

If, in a reasonably developed country, the average per capita water usage for all requirements - residential, industrial and agricultural - is about 2,000 meters per year, then at 10.0 cents per kilowatt-hour and 2.0 kilowatt-hours per meter, desalinated seawater would cost $400 per person per year.  Add to that around $100 per year for the lifetime amortized installation costs of the plant, and at this point desalinated water is not very expensive - maybe double those costs for operating and maintenance costs, and desalinated water costs maybe $.50 per cubic meter.  Desalinization appears to be an idea whose time has come.

Returning to photovoltaic power as an energy source for desalinization, at 10.0 cents per kilowatt hour, assuming a yield of one-third (eight hours of sun), and a 25 year life, the installed cost of the photovoltaics would have to be about $7.00 per watt, a price they are well on track to achieve.