Osmotic power

An osmotic power plant ( Salzgradientenkraftwerk ) is a power plant that uses the difference in salinity between fresh water and sea water, in order to extract energy and generate electricity. Proposals for a power plant, the technical advantage of the osmotic power ( salt gradient ), were first published in the 1970s. Specific research and development projects there since the second half of the 1990s. As the world's first prototype osmotic power plant, a micro power station was on 24 November 2009 in Norway Tofte on the Oslo Fjord put into operation.

Principle of operation

The energy uses the physical principle of osmosis: Are fresh and salt water through a semi-permeable membrane in contact with each passing pure water through the membrane to the salt water side, on the pressure builds up, with the aid of a turbine can be driven to generate electricity. With a salt content of 3.5 % is obtained at a temperature of 10 ° C an osmotic pressure of about 28 bar, but decreases within the plant through the incoming dilution. Osmosis achieves maximum performance when the static pressure differential is half of the osmotic pressure and the other half is to overcome the resistance of the membrane are available.

The technical realization requires special membranes that retain salts efficient, but at the same time are highly permeable to water. Due to lack of suitable membranes, the principle in the 1970s could not be realized. Since the mid- 1990s, there are new approaches to develop suitable membranes from polymers.

The direct energy supplier for an osmotic power plant is the difference in salinity ( the salinity gradient ) of two solutions, which tend to approximate their concentrations. In contrast to conventional hydropower plants is the driving force in energy not the potential energy (as in storage power plants ) or the combination of kinetic and potential energy of large bodies of water (such as hydroelectric power plants), but the higher thermodynamic potential of fresh water.

In a more indirect, parent observation, the energy for an osmotic power plant is supplied by the sun: By contributing through their radiation for evaporation of water from the sea, it allows for the separation of ( remaining in the sea) salt water ( evaporated ) freshwater. The evaporated water is flowing through cloud formation, rainfall and flows back into the sea, where in re- mixing energy that can be recovered in an osmotic power plant part, which was originally applied by the sun. The osmotic power is so " topped up " by the sun and is inexhaustible by human standards. It is therefore a form of renewable energy, which by their mention in the German Renewable Energy Sources Act has been found (under the name salt gradient, see § 3) before its technical realization official recognition.

Potential for energy

Possible locations for osmosis power plants are located where rivers flow into the sea. In addition, as are locations all conceivable points where two streams occur at different salinities, for example, the direct discharge of highly saline waste water into rivers. The recoverable energy gain is larger, the higher the flow rate and the greater the difference in salt content. When considering energy potentials of osmosis power plants is to be noted that a full exploitation of an entire flow in osmosis power plants in practice is not feasible - for technical reasons, as well as out of consideration for the shipping and the ecology of rivers. For these reasons, the consideration of ecological potentials is useful, which include in addition to the technically induced conversion losses, but also limiting the maximum allowable water withdrawal amount with.

The potential- most location on German soil is the mouth of the Elbe into the North Sea. The ecological potential of the use of all German rivers that flow into the North Sea and the Baltic, is specified with approximately 42 MW and 330 GWh / a. This results in a share of only about 0.05 % of Germany's electricity needs could be met through which osmosis power plants. The runoff of the Rhine and Danube are not counted, as they lead outside Germany. At the global level, the ecological potential to about 65 GW, or about 520 TWh / yr is estimated. The division of the potential into continents and regions is thereby analogous to the division of the outflow values ​​.

Based on the operating flow rate higher specific power plant benefits waters could be achieved, which have a higher salt content than Baltic and North Sea, especially in the Mediterranean and especially in salt lakes such as the Dead Sea or the Great Salt Lake in Utah, USA. The potential at the Kara- Bogaz - Gol east of the Caspian Sea estimates of the Heidelberg physicist Florian Dinger on more than five gigawatts.

Implementation

The Basics of a sufficiently stable for large-scale use of membrane were created in a project funded by the EU research program since 2004. System partners Statkraft SF ( Norway), Instituto de Ciencia e Tecnologia de Polimeros (Portugal ); Norwegian Institute of Technology SINTEF (Norway ); Helsinki University of Technology (Finland ) and the Helmholtz -Zentrum Geesthacht ( Germany ). Currently an electrical output of three watts per square meter of membrane can be achieved.

In the fall of 2007, the Norwegian state-owned company Statkraft announced the world's first construction of such a power plant at Hurum, at an estuary in the southern foothills of the Oslo Fjord. On 24 November 2009 the world's first prototype took to the operation. In this case, membranes were used that instead of the current, can provide 0.2 watts of electrical power per square meter, 3 watts. A project group at the Helmholtz -Zentrum Geesthacht operates under an EU-funded project on the development of membranes with higher performance. Their project Peinemann denotes a power of five watts per square meter as a prerequisite for the economic operation of an osmotic power plant.

Next, in 2015 planned target is a 25 - megawatt power plant with 5 million square meters of membrane area. Statkraft estimates that Norway in the long term can cover 10% of its electrical energy from osmotic power plants.