Water from the sun Making Seawater Desalination Green! Solar Power as Key for more Sustainability

From Maria Muelbaier, Markus Wallinger*

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How a desalination plant uses the most sustainable and available energy source to generate fresh drinking water — Seawater desalination has a large ecological footprint, as the processes used to generate fresh water from brine or seawater are energy intensive an often rely on fossil fuels. Luckily, the arid regions that rely on desalination the most have one resource in abundance: sunlight. Can solar power bring green drinking water to the Middle East?

The Al Khafji desalination plant uses reverse osmosis to produce 60,000 m³ of fresh water per day.
The Al Khafji desalination plant uses reverse osmosis to produce 60,000 m³ of fresh water per day.
(Source: Siemens)

Traditionally, saltwater has been processed into fresh water by various methods of distillation, a thermal process in which water is evaporated to separate fresh water from saltwater. Distillation is still widely used — but it is quite energy-intensive, consuming up to 25 kWh of total equivalent electrical energy per cubic meter of water produced. This is why most new desalination plants employ a more energy-­efficient process in which fresh water is separated from saltwater through semipermeable membranes and applied pressure.

This process, called reverse osmosis, uses much less electrical energy per cubic meter of water, with the most advanced plants achieving a total equivalent electrical energy consumption of less than 4 kWh per cubic meter. Nevertheless, water desalination is still one of the major consumers of power in the Near and Middle East, and a large share of that power is produced by burning fossil fuels — meaning that reverse osmosis water desalination is also a major cause of carbon dioxide (CO2) emissions.


Using Power from Sun

But the Near and Middle East have another power source in vast abundance that — unlike oil and gas — remains mostly untapped: the sun. Large parts of Saudi Arabia are desert, and the country has enough space for building large-scale solar parks as well as more than enough sunshine, making it the ideal site for solar-powered seawater desalination.

Until recently, solar-powered desalination plants were a niche application at best, but with a growing population that needs fresh water for human consumption, agriculture, and industrial use, as well as increasing concern about the impacts of global warming, the Saudi Arabian utility company Rawafid Systems decided to build the first large-scale solar-powered water desalination plant near the city of Al Khafji on the coast of the Arabian Gulf.

The plant has a capacity of 60,000 m3 per day, with an option for a future extension to 90,000 m3 per day. All infrastructure and piping systems have already been designed to enable the later extension, says Eng. Ali Awadallah, CEO and project director at Rawafid Industrial, and “together with ­Siemens we achieved to finish this project in 14 months, which is a great breakthrough.”

Sustainable Desalination

This ambitious project was designed and executed by Rawafid together with the water desalination experts from Advanced Water Technology (AWT). The new plant employs a two-stage reverse osmosis process and receives power from a neighboring solar power plant with a connected capacity of 20 MVA. Peak solar power production is sufficient to fully meet the power needs of the desalination plant. During the night, the plant is powered through the public grid. Plant operation is aligned with the available solar power to maximize the use of sustainable energy for water production. This not only results in significant CO2 emission savings but also reduces operating costs.

Facing a Rigid Timetable

However, Rawafid and AWT had to work with a very tight schedule, including having only six months available for the delivery of the major electrical and automation packages. The technical equipment had to be designed in just two months, and after delivery all systems needed to be installed, commissioned, and readied for operation in just seven months.

Faced with this schedule, Rawafid and AWT selected their project partners based on reliability and industry expertise. For the electrical, automation, and instrumentation packages, the project team chose Siemens as the main contractor. “Our policy to be successful in such a project is to give the complete package of electrical, control, and instrumentation to one company. We contracted Siemens as they are a big company in the market of electromechanical supply for power and water production, producing all the components for electrical power transmission and distribution, low-voltage boards, and control systems,” says Eng. Ali Awadallah, CEO and Project Director Rawafid Industrial.

“Moreover, the Siemens control system is universal and utilized in different industries like oil and gas, petrochemicals, refineries, and water treatment. And finally, we had already worked with Siemens Austria in the United Arab Emirates, and we have been very successful together with them.”

With its extensive experience in the fields of automation, electrification, and digitalization as well as its desalination process–related expertise gained in numerous pro­jects worldwide, Siemens was able to demonstrate that it could engineer, manufacture, and deliver all the systems and components within the required short time frame. After receiving the order, Siemens designed a comprehensive solution for the electrical and automation equipment, including transformers; Sivacon switchgear systems; Siprotec protection systems; Sinamics converters; and process instrumentation for monitoring flow, level, pressure, and temperature.

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Electrical and automation systems are networked using Scalance industrial communication technology. The control system for power generation and distribution as well as water processing is based on the Simatic PCS 7 process control system. Altogether, the equipment shipped to Al Khafji weighed 425 tons and comprised 37,000 items. Mastering this logistical challenge was another major achievement of the Siemens team, and all systems were ready for installation on time.

Compelling Expertise

Considering the complexity of the installation, the Siemens engineers had to execute the design and engineering in a fast-track project. The team was even able to accommodate a significant change during the project, when the power supply was changed from 34.8 kV to 13.8 kV. Partnering with a large global technology provider as the main contractor paid off for Rawafid and AWT, as Siemens was able to provide the resources needed for engineering and manufacturing all the systems in the time available, and the elimination of interfaces further streamlined the project management.

Having Siemens as a main contractor for the design, engineering, manufacturing, installation, supervision, and commissioning of all electrical, instrumentation, and control systems ensured short response times and good communication between all parties. In addition, the Siemens solution enables seamless vertical and horizontal integration of all electrical components, thus reducing operational and maintenance costs.

Since start-up, the Siemens systems have performed extraordinarily well. The drivetrains with their Sinamics GH180 and G150 converters ensure reliable and efficient plant operation while exceeding the strict requirements for line harmonics specified in the IEEE 519:1992 standard and the Saudi Arabian Grid Code for electricity transmission.

The Simatic PCS 7 process control system not only provides superior plant availability and efficiency but also enables central monitoring and control of all plants and systems and supports the operators in their daily work. For Eng. Ali Awa­dallah, the system’s major benefits are its versatility and openness: “It is not dedicated to a certain specific process, and it is not customized. We can adjust all the parame- ters by ourselves without calling ­Siemens for changes in the software. For example, if we want to add additional safety measures or additional equipment we can do so, because the control system is universal and expandable.”

The automation system is designed as a fully redundant system, which improves plant and process performance and enables the Al Khafji plant to achieve an availability of up to 98 %. Another benefit is that Simatic PCS 7 is very user-friendly and flexible. For example, it enables the pressure of the high-pressure pump to be automatically adjusted according to the water temperature and salinity via a variable-speed drive, which saves a great deal of energy compared to conventional flow control by control valve. In the winter, when the water temperature is low and the required pressure is high, the production of the second pass will be reduced and a higher portion of low-salinity water from the first pass will be fed directly to the product water tank, bypassing the second pass. This significantly reduces operational expenditures, as it reduces consumption of both power and chemicals. Simatic PCS 7 also helps the plant operator to optimally deploy staff during both regular plant operation and maintenance, resulting in additional savings.

Outperforming expectations

Since its commissioning, the plant has been running without a hitch, producing even better-quality water than expected. Consequently, both Rawafid and AWT are very satisfied with the project outcome. The world’s first large-scale solar-powered desalination plant will also serve as a lighthouse project for similar plants. Under the King Abdullah Initiative for Renewable Energy Desalination, Al Khafji is intended to be the first of a series of such projects in Saudi Arabia. In addition, the plant is a milestone in the drive toward sustainability and in the ability to meet a growing demand for fresh water.

By cutting both operating costs and CO2 emissions through the use of renewable energy, desalination becomes an increasingly viable and sustainable means of providing clean water. This success story was made possible not least thanks to the excellent collaboration with the Siemens project team, says Awadallah: “I would state that you could hardly get a better partner. With Siemens, it
is engineer talking to engineer — 
you understand each other, and that is what makes a project a
success. We always want to achieve the best result in the
project, and we can achieve this with Siemens.” Based on the great success and high customer satisfaction, Advanced Water Technology awarded Siemens with a contract to equip eight more seawater reverse osmosis plants in Saudi Arabia.

* * Ms. Muelbaier is VSS for water & waste water Contact: Phone +49-162-4227671, Mr. Wallinger is Project Lead at Siemens. Contact: Phone +43-664-6154512