Energy-intensive desalination plants have traditionally run on fossil fuels, but renewables, particularly solar power, are now beginning to play a part.

Around half the operating cost of a desalination plant comes from energy use, and on current trends Saudi Arabia and many other countries in the region would consume most of the oil they produce on desalination by 2050.

The dominant desalination technology at present, with around 60% of global capacity, is Reverse Osmosis (RO), which pushes brine water through a membrane that retains the salt and other impurities.

Thermal desalination uses heat as well as electricity in distillation processes with saline feedwater heated to vaporise, so fresh water evaporates and the brine is left behind. Cooling and condensation are then used to obtain fresh water for consumption.

Multi Stage Flash (MSF), the most common thermal technique accounting for around 27% of global desalination capacity, typically consumes 80.6 kWh of heat energy plus 2.5-3.5 kWh of electricity per m³ of water. Large scale RO requires only around 3.5-5 kWh/m³ of electricity.

According to the International Renewable Energy Agency (IRENA), desalination with renewable energy can already compete cost-wise with conventional systems in remote regions where the cost of energy transmission is high. Elsewhere, it is still generally more expensive than desalination plants using fossil fuels, but IRENA states that it is ‘expected to become economically attractive as the costs of renewable technologies continue to decline and the prices of fossil fuels continue to increase.’

Solar Reducing Costs

SWCC has taken a long view and aims to gradually convert all its desalination plants to run on solar power as part of a drive unveiled by the Saudi government earlier this year to install 41 GW of solar power by 2032.

The Al-Khafji solar desalination project, near the border with Kuwait, will become the first large-scale solar-powered seawater reverse osmosis (SWRO) plant in the world, producing 30,000 m³ of water per day for the town’s 100,000 inhabitants.

Due for completion at the end of 2012, it has been constructed by King Abdulaziz City for Science and Technology (KACST), the Saudi national science agency, using technology developed in conjunction with IBM. Innovations include a new polymer membrane to make RO more energy efficient and protect the membrane from chlorine – which is used to pretreat seawater – and clogging with oil and marine organisms.

The use of solar power will bring huge cuts to the facility’s contribution to global warming and smog compared to use of RO or MSF with fossil fuels, according to the developers.

Al-Khafji is the first step in KACST’s solar energy programme to reduce desalination costs. For phase two, construction of a new plant to produce 300,000 m³ of water per day is planned by 2015, and phase three will involve several more plants by 2018.

Desalination’s Future

Historically, desalination plants have been concentrated in the Persian Gulf region, where there is no alternative for maintaining the public water supply. The region has excellent solar power prospects, suggesting that coupling of the two technologies may become commonplace. A pilot project to construct 30 small-scale solar desalination plants by the Environment Agency Abu Dhabi has already seen 22 plants in operation, each producing 25 m³ of potable water per day.

But population increases and looming water scarcity have also prompted widespread investment in desalination. It is now practised in some 150 countries including the US, Europe, Australia, China and Japan and it is becoming an increasingly attractive option both financially and for supply security.

Over the past five years the capacity of operational desalination plants has increased by 57% to 78.4 million m³ per day, according to the International Development Agency. Sharply falling technology costs have been a key driver of the trend and an EU-funded project is examining the case for expanding solar-powered desalination.

Solar power may even offer a solution to an impending crisis in Yemen, where water availability per capita is less than 130 m³/year. Yemen’s capital Sana’a, with a population of two million, faces running out of groundwater before 2025. It is estimated that a solar plant powered by a 1250 MW parabolic trough to desalinate water from the Red Sea and pump it 250 km to Sana’a could be constructed for around $6 billion.

Around 700 million people in 43 countries are classified by the UN as suffering from water scarcity today – but by 2025 the figure is forecast to rise to 1.8 billion. With the global population expected to reach nine billion by 2050 and the US secretary of state openly discussing the threat of water shortages leading to wars, desalinated water has never been more important.

Demand for desalinated water is projected to grow by 9% per year until 2016 due to increased consumption in the Middle East and North Africa (MENA) and in energy-importing countries such as the US, India and China.Population growth and depletion of surface and groundwater means desalination capacity in the MENA region is expected to grow from 21 million m³/day in 2007 to 110 million m³/day in 2030, according to the International Energy Agency.

US President John F Kennedy, speaking in 1962, said: ‘If we could produce fresh water from salt water at a low cost, that would indeed be a great service to humanity, and would dwarf any other scientific accomplishment.’ In the half century since, the need for innovation to satisfy humanity’s demand for clean water has become ever more urgent. While technological advances continue to improve the efficiency of desalination methods, it is vital that the sources of power used by desalination plants also continue to evolve.