Sustainable Future: Alternative Energy Source From Rivers Flowing Into Oceans
July 29, 2012

Sustainable Future: Alternative Energy Source Could Come From Rivers Flowing Into Oceans

redOrbit Staff & Wire Reports - Your Universe Online

Many energy experts envision a future that includes a variety of green energy solutions. Wind, hydroelectric, and solar power currently dominate the renewable power sector, but a new process described in the latest episode in the American Chemical Society's (ACS) award-winning Global Challenges/Chemistry Solutions podcast series could usher in a new genre of electric power-generating stations.

According to the podcast, which was based on a report by Yale researchers Menachem Elimelech and Ngai Yin Yip in the ACS journal Environmental Science & Technology, these stations could generate electricity for over half billion people by tapping just 10 percent of the global potential of a little-known energy source that takes advantage of the salinity difference located where freshwater rivers meet the ocean.

In the report, Elimelech and Yip describe the process, called pressure-retarded osmosis (PRO) that requires no fuel, is sustainable and releases no carbon dioxide. To generate energy via PRO, freshwater flows through a selective membrane and dilutes seawater on the other side. The pressure created by the flow spins a turbine and generates electricity.

The process was first invented by Sidney Loeb in 1973 at the Ben-Gurion University of the Negev in Israel. The system devised by Loeb, called a closed loop system, is different than the process described by the two Yale scientists, known as an “open loop” system. Loeb´s original system, which relied on converting PRO-related heat to energy, is considered sustainable, but not renewable.

Because of its resemblance to a process used to purify water called reverse osmosis (RO), initial PRO prototypes relied on membranes and membrane modules originally created for RO. This expedited early experiments since it eliminated the need for a specifically tailored apparatus, but also resulted in suboptimal power generation. However, advancements in membrane technology eventually made PRO a more realistic green energy option.

In the early 2000s, Loeb and a team of researchers looked at the Great Salt Lake in Utah as a potential place to install a PRO facility. They determined that the energy produced would cost 15 cents per kilowatt-hour. By comparison, energy produced by burning coals costs less than 1 cent per kilowatt-hour.

The world's first PRO prototype power plant installation was opened in Norway in 2009. The small scale installation, built by Statkraft, is intended to generate 10 kW of power and has already generated widespread interest. Statkraft has announced plans to build a full-scale 25 MW osmotic power plant by 2015.

With PRO technology developing at a rapid pace and appearing to have great potential, the Yale scientists set out to understand how much it could realistically contribute to future energy needs under real-world conditions.

“PRO power-generating stations using just one-tenth of the global river water flow into the oceans could generate enough power to meet the electricity needs of 520 million people, without emitting carbon dioxide,” said Elimelech in the ACS podcast.

“The same amount of electricity, if produced by a coal-fired power plant, would release over one billion metric tons of greenhouse gases each year.”