‘Blue energy’ is the name given to electricity produced by harnessing the difference between fresh water and salt water. And by going blue, the Netherlands could generate ten times the amount of power it currently gets from wind farms. It may sound like a fanciful claim, but it’s a very serious possibility. “Thanks to advances in the electrical modification of plastics, the special membranes needed for blue energy can now be made very cheaply. Which in turn means blue energy has become affordable,” says KEMA’s Rob Ross. “But energy production is just one of the many applications of electrically modified plastics.” KEMA is working with the Dutch building firm VolkerWessels to bring this particular application on line.

Fresh and salt water

One of these valuable new materials can be used to make plastic membranes for osmosis (mixing). An osmosis membrane will let fresh water through, but hold salt water back. Ross elaborates: “What you do is put two tanks side by side, one filled with fresh water, the other with salt water, separated by one of these membranes. The fresh water will naturally try to mix with the salt water. But, once the fresh water has passed through the membrane and mingled with the salt water, almost nothing will flow back the other way. So the water level in the one tank gradually rises above that in the other. In other words, you have potential energy, which you can harness using water turbines.” Another related technique involves making membranes through which only one type of charged particle (either positive or negative) can pass. Once separated, of course, the charged particles can be used to generate electricity.

Both techniques were shown to work on the laboratory scale long ago. Until recently, however, the ideas hadn’t been taken any further because of the prohibitive cost of making suitable membranes. The arrival of electrically modified plastics has changed all that. The cost of making membranes has been brought down so far that power generation based on these techniques is now a commercially attractive option. KEMA and VolkerWessels are currently working to create a plant made up of modules each with a capacity of 250 kW. “Each module is the size of a sea container,” says Ross. The aim of the project isn’t just to develop practical applications for the process, but also to bring the cost of making the special membranes right down.

“In countries that have river deltas, and therefore plenty of fresh and salt water, such as the Netherlands, Brazil, China and Bangladesh,” continues Ross, “much of the energy demand could be met using blue energy. This would have huge environmental benefits, because blue energy is very clean; no greenhouse gases are released either making the membranes or generating the electricity.”  

Countless applications

‘Energy from water’ is just one of the many potential applications for the electrical modification of plastics. “It is possible to incorporate substances with particular properties into a plastic,” says Ross. “So you can make plastics that are fluorescent or repel algae.” Alternatively, the properties of the plastic itself can be modified, making it super-strong, for example. “You could impregnate plastic with a particular dye or with a fire-resistant material. You could incorporate a ‘detector substance’ into packaging material, enabling you to see at a glance whether a frozen product had thawed out at some point. Other possibilities include water desalination , fuel cells, super-capacitors, to name but a few. The potential applications of electrical modification are endless.”

The 250 kW blue energy module that KEMA is developing with VWS should be operational by 2005, when it will probably be set up at a coastal test site. Several months of trials will then follow. The ultimate aim is to have a complete plant consisting of several modules with a combined capacity of around 200 MW. Plants of this kind could be created at every river mouth.