Concentrating solar powered desalination - a water solution?

Wednesday, 11 March 2009
By Stewart Taggart

Australia needs electricity and Australia needs water. Concentrating solar power can help provide both.

Unlike solar photovoltaics, which creates electricity directly from sunlight, concentrating solar power first creates heat. This heat can then be used either to generate electricity or to desalinate water. Properly configured, concentrating solar power can switch back and forth from creating electricity to water.

Given these attributes, Concentrating solar powered desalination is a technology with hugely positive potential implications for global drinking water supplies. With futurists warning that water could emerge as a 21st Century flashpoint for strife, solar desalination is an avenue that should be explored aggressively.

Australia is ideally suited to take a global lead in concentrating solar-powered desalination. Australia has sunshine, seafront land, an advanced industrial economy and pressing water and energy needs. More favorable conditions for developing an infant industry like solar desalination are hard to imagine.

One solar powered desalination plant is already in development in Australia.

Known as 'Acquasol 1,' the plant will be located outside Port Augusta, South Australia. It will mesh together parabolic trough concentrating solar power, combined cycle gas turbines, multi-effects desalination and solar salt harvesting. In so doing, it will achieve the closest thing yet to a 'closed loop' in desalination.

The plant is being built by Acquasol Infrastructure Ltd., an Adelaide-based company of which I'm a director. To better understand 'Acquasol 1,' it pays to look at the underlying technologies.

Concentrating solar power

There are four main technologies in concentrating solar power: parabolic troughs, solar dishes,solar towers and compact linear fresnel reflectors. Of the four, parabolic troughs are the most commercially proven, with plants operating in California, Nevada and Spain.

Solar thermal storage and combined cycle natural gas

Solar thermal energy storage allows excess solar heat gathered during morning hours to be stored for use during afternoon electricity demand peak periods. Adding a combined cycle natural gas turbine provides provides redundancy and the ability to double up power production when needed, for instance on hot afternoons when grid demand spikes.

Desalination

There are two main forms of desalination: reverse osmosis and multi-effects distillation. Reverse osmosis uses electricity to push seawater through screens to separate water from salt. Multi-effects uses heat to boil seawater under pressure and then recondenses the vapor. Given that concentrating solar power can create temperatures of 400-1,000+ degrees Celsius, the thermal energy can be used as a direct input to desalination.

Solar salt harvesting

Solar salt harvesting involves putting hypersaline byproduct waste brine from the desalination process into land-based holding ponds and then allowing the sun to evaporate the water. This leaves only salt which can be sold as an additional revenue stream. Solar salt harvesting keeps brine out of sensitive coastal marine environments where its impact remains poorly understood.

By bundling existing technologies in a novel way, 'Acquasol 1' aims to create lower cost power for consumers, enhanced grid stability, more assured water supplies and safeguarded marine environments.

Solar-powered desalination is benefiting from favorable cost trends. Desalination technology costs are falling by about 5-7 per cent per year and concentrating solar power costs are falling at about the same rate. Meanwhile, depletion and pollution of natural water resources is causing the cost of traditional water extraction to rise.

Research conducted for the Western Australian government in 2004 estimated the three cost trends could mean that desalinated water becomes cheaper than groundwater in some parts of that state as early as 2020. The 'cross-over' point for other states may not be far behind.

Australia needs solutions to its energy and water problems. Australia is a 'smart country.' But what Australia needs is a sense of adventure, a sense of open frontiers and a sense of prudent risk-taking in pursuit of climate change and environmental problems in pressing need of solutions.

'Acquasol 1' is just one good idea. There are many others, including those in wave energy, tidal energy, geothermal and hydrogen creation -- all of which may yield 1+1=3 solutions down the track similar to the potential of solar powered desalination.

Stewart Taggart is a director of Acquasol Infrastructure Ltd., a developer of environmentally-friendly power and water solutions building a municipal-scale solar desalination plant in South Australia's Upper Spencer Gulf. Stewart is also founder/administrator of DESERTEC-Australia, DESERTEC-USA and DESERTEC-China. DESERTEC promotes the concept of "Clean Power From Deserts."