Saline Power

Electricity from the difference in salt concentration

Blue energy is a special way of harnessing solar energy. The sun evaporates sea water, leaving the minerals behind in the sea. The evaporation creates clouds, which then fall back onto the earth as rain and snow, creating rivers of fresh water that flow back into the sea. The difference in the salt concentration between the river water and sea water can be used to generate electricity.

Two techniques

One option is to use osmotic membranes that hold salt water back and let fresh water through. Two water tanks, one with salt water and one with fresh water are coupled via such a membrane. The fresh water will naturally try to mix with the salt water. However, once it has passed through the membrane, almost nothing will flow back. The water level in one tank will gradually rise above that in the other, and this potential energy can be harnessed by small water turbines.

Another technique is to use membranes through which only positive or negative ions can pass. Once separated, the charged particles can be used directly to generate electricity.

Both techniques have demonstrated long ago that they work on a laboratory scale, but only recently have they become commercially attractive thanks to the arrival of electrically modified plastics. This new process has substantially reduced the cost of membrane production.

A prototype at the Dutch coast

A 250 kW prototype using the second technique is currently being built by the Dutch Energy Research Centre KEMA and by the Dutch contractor VolkerWessels (VWS). The ultimate aim is to assemble a complete 200 MW power plant out of 250 kW modules, each about the size of a sea container. If plants of this type and capacity were to become operational at every Dutch river mouth, the result would be a total generation capacity for the Netherlands of 3,300 MW.