Osmosis: In Search of the Perfect Membrane

Osmosis: In Search of the Perfect Membrane

An interview with Statkraft's head of osmotic power Stein Erik Skilhagen

Osmotic power is not the first thing that comes to mind when you think of renewable energy, nor is it a new concept. However, thanks to some initial research and development in Norway under Europe's largest renewable energy provider, Statkraft, the technology is gaining momentum around the world. Pursued for its mere potential, developers of innovative technologies are coming together in an effort to create systems that could potentially fill the renewable energy gaps of the likes of solar and wind power.

Based on the phenomenon of osmosis, the energy is created through the transport of water through a semipermeable membrane, similar to how plants absorb water through their leaves. In this case, when fresh water meets salt water, usually in areas where a river runs into a sea, monumental amounts of energy are released. That energy can then be utilized to generate power using a manmade membrane—the most critical piece of the process.

The flow of water is predictable, and therefore reliable, whereas wind and solar depend on the timing of sunlight and wind conditions. Areas where rivers meet water are also generally around industrialized centers, which would mean osmotic plants would be placed where consumers live. In areas like Northern Alaska or in developing countries lacking an operating infrastructure or a sufficiently functioning grid, osmotic power would be particularly beneficial.

In an osmotic power plant, fresh water and salt water are guided into separate chambers on the sides of an artificial membrane. The salt molecules on the sea water side suck fresh water through the membrane, increasing pressure that creates a waterfall that is used to generate a turbine for power. Although Statkraft's first system in 2008 was successful and generated a lot of excitement, it was incredibly small—generating only enough electricity to power a coffee machine.

“With the membrane we were using, we realized there was a large gap in taking an idea from the laboratory and scaling up,” says Statkraft's head of osmotic power Stein Erik Skilhagen.

One big issue concerning membranes is finding the right thickness, capable of withstanding extreme pressure without getting clogged up with salt. Last summer, Statkraft announced it would begin working with Japan-based Nitto Denko, the world's largest manufacturer of membranes. Unable to comment on the materials of the membrane, Skilhagen believes that by the end of 2012, the technology will be good enough to build a system that is significantly larger than one Statkraft has today.

With a promising market opportunity, supporters claim that the technology is unlimited. According to Statkraft, osmotic power has an estimated global potential of 1600 to 1700 Twh, based on figures from surveys of areas around the world where fresh water meets the ocean. That's roughly equal to China's total electricity consumption in 2002.

After Statkraft held an invitation-only event in Amsterdam to initially discuss the developments, it attracted over 100 participants in an event held in San Diego in 2010.

“The quality in presentations had significantly increased at that point and the global awareness and momentum in development of this technology had increased beyond belief from when he had met just two years earlier in Amsterdam,” says Skilhagen.

Following that conference, more initiatives have been procuring globally, which has led to an even larger event coming up this April in Barcelona, Spain.

“We have had so many requests, it's hard to believe how many people there are wanting to present their developments and technologies,” says Skilhagen. “We are looking forward to once again hosting a venue where the global leaders of this industry will come together and share their knowledge and results.”

Osmosis, also known as reverse electrodialysis (RED), has spurred other similar technologies. Researchers at Pennsylvania State, for instance, have developed a new device that combines two forms of renewable energy—using bacteria and saltwater—to generate more electricity than either alone, while cleaning wastewater at the same time.

While RED requires a large number of membranes and must be located by the sea, researchers have come up with a device that reduces the amount of membranes used to create an electric current. Using microbial fuel cells (MFCs), the system bypasses the need for salt water by using ammonium bicarbonate solution as a substitute, allowing it to be used in areas far from the ocean. The technique could be adopted in developing countries to provide clean water and power for homes.

Of course, osmotic power is still, for the most part, in the pilot phase and it could be a few years before the technology becomes a commercial reality. Regardless, figures of its potential are fueling motivation for more R&D.

“The more companies there are working on this, the more the competition grows and the higher the likelihood is to find solutions in reducing the costs and spreading the technology,” says Skilhagen. “In our upcoming conference, people are working together to get to the solutions we need in this field.”

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