|29 March 2017|
By Dr Chris Sansom, Associate Professor in Concentrated Solar Power at Cranfield University
Desalination plants – converting seawater into drinking water and water for agriculture – have been used since the 1950s in the Middle East and tropical regions of the world. But while the technology has met urgent needs for clean water supplies, the environmental cost has been heavy, dependent on oil and gas-powered plants. It’s been estimated, for example, that the thirty desalination plants in Saudi Arabia rely on around 300,000 barrels of crude oil each day. The World Bank has said it is critical that the desalination industry makes the shift away from fossil fuels. More than the fuels involved there are also the environmental risks presented by the large-scale traffic in oil tankers.
The current output of desalination plants globally is more than 70 million cubic metres per day, and growing populations and their demands for higher standards of living mean this figure will need to grow exponentially to meet needs – and wants. In the Middle East and North Africa the gap between demand for water and actual supply is said to be around 42 cubic kilometres per year, according to the World Bank figures, and expected to increase by five times that by 2050. The problem is shared by other desert regions like Australia and parts of the USA – as well as regions where there’s rainfall but the water supply can be contaminated like in India and South America.
Solar-powered desalination plants, theory and practice, have been under development since the start of the 21st century. The challenge is all around gaining hard evidence of viability in terms of costs and scale. The entrepreneur Malcolm Aw founded his firm Waterl’eau to move forward with his vision of using solar enhanced greenhouses for desalination. Concentrated solar energy from strategically-arranged banks of mirrors – equivalent to the power of 20,000 suns – are used to speed up the natural process of evaporation within the domed greenhouse structures, up to 80 metres in diameter. The inflow of seawater travels into the dome via enclosed glass aqueducts, drawn in by gravity, where it is distilled in the dome and collects in cauldrons and boiled. The dense steam produced becomes like a tropical rainstorm, falling within the dome as clean and pure water which is piped to reservoirs and wetland areas as needed for uses in the local region. As a result the domes provide a carbon neutral and sustainable solution.
At Cranfield University a team of researchers has been evaluating this patented technology by building a working scale model at 1:100 size, looking at expected productivity and costs as well as the most efficient materials for the structure and for heat storage within the dome. From this work we’ve been able to estimate that each Waterl’eau dome would deliver up to 40,000 litres of clean water every day. In practice that means a single dome would meet the ongoing water needs of 8,000 people, based on World Health Organisation figures, including their needs in terms of water for agriculture and farm animals.
Based on this analysis and a simulation of the full scale plant we have also been able to estimate costs. A problem so far with early zero-carbon desalination technologies has been the relatively high cost compared with fossil fuel-based approaches. World Bank figures claim that using current technologies, each litre of desalinated water costs around $1 more. Our research found that over the 35 year life cycle of a dome each litre of clean water would cost under 2 US cents a litre to produce – and in terms of added-value this would come with high environmental savings for governments, communities and industry.
A field demonstrator at a scale of 1:20 has been designed and cost analysis completed, with detailed recommendations made for design, layout, technical solutions, materials and maintenance. The next step is to build and test the demonstrator at a site already identified in Spain. Cranfield and Waterl’eau are looking for partners to invest in the project, contributing to the £350,000 needed for this final demonstration stage before full working plant is available commercially. Interest has already been shown by governments in Australia and North Africa to purchase a working plant and business plans – worked up by Cranfield’s School of Management – have predicted a business value of £40 million after five years of operation.
For more information please contact Dr Chris Sansom: c.l.sansom@cranfield.ac.uk, 01234 752955
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