Julie Rehmeyer is right to say that "the best desalination plant is one that runs cheaply off its own renewable energy source" but she does not mention the best source of all: the solar energy that is so plentiful in the arid regions where fresh water is most needed.

Instead of using relatively expensive photovoltaic solar panels - the technology that gets most attention - a much better idea is to use mirrors to concentrate sunlight and create heat. The heat may be used directly in a desalination plant, but an even better idea is to use it first to raise steam to drive a steam turbine and electricity generator and then to use the waste heat from electricity generation to desalinate sea water - killing two birds with one stone.

Power plants that concentrate sunlight using mirrors have been generating electricity successfully in California for nearly 20 years (see the website of the US Department of Energy, www.eere.energy.gov/solar/csp.html).

The idea of using waste heat from such plants to desalinate sea water is described in a new study from the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). The final report may be downloaded from www.dlr.de/tt/trans-csp.

Menai Bridge, Anglesey, UK

From issue 2561 of New Scientist magazine, 22 July 2006, page 27

Last updated: 2009-08-20 (ISO 8601)