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Can you make enough energy to run a household by mixing salt water and river water? If you thought that is a bad idea, think again. Scientists in Norway and The Netherlands are working on this method for quite sometime.

Their theory is quite simple. They bank on osmosis. Osmosis power was shown in 1748 when French physicist Jean Antoine Nollet put a pig s bladder filled with alcohol in a trough of water. The bladder swelled and burst the more concentrated liquid draws pure water into it.

With the help of this method, two tiny projects to create energy through mixing of sea water and river water are being implemented in Oslo and Dutch seaside lake.

The projects are expected to become operational this year.

This traditional knowledge has not yet been proved to be economically viable but would help in fighting global warming. The process imitates osmosis used by trees to suck water from their roots.

And rivers flow around the clock, an advantage compared to variable wind or solar power.

The UN Climate Panel said in 2007 energy sources such as waves, tidal power or salt are a long way off unlikely to make a significant contribution to overall power needs by 2030.

When salt and fresh water mix at river mouths, they are typically warmed by 0.1 degree Celsius (0.2 Fahrenheit). Dutch scientists say such energy at all the world s estuaries is equivalent to 20 per cent of world electricity demand.

The plants may support hopes the technology can overcome hurdles, the most significant of which is poor cost effectiveness of the membranes used in the process.

Statkraft based in Norway and a leading top producer of hydro and wind energy alongside Electricite de France, is building a test plant costing $20 million.

The company claims it will be the first saline power plant based on osmosis.

The plant, at Tofte on the Oslo fjord, will have output of up to about 5 kilowatts enough to run household appliances such as washing machines or heaters or a few dozen lightbulbs.

The Dutch Centre for Sustainable Water Technology (Wetsus) is planning a pilot blue power test at IJsselmeer in the Netherlands, from where water flows into the sea.

The objective is to obtain 1 5 kilowatts within one year.

The Norwegian and Dutch plants use different systems but both depend on membranes placed between the salt and fresh water, which are currently prohibitively expensive and highly energy intensive to produce.

The Norwegian project will include 2,000 square meters (21,530 sq ft) of plastic membranes, through which fresh water will be sucked into salt water by osmosis.

At Tofte, the power exerted by salt water sucking in fresh water is equivalent to water falling 270 metres in a waterfall. The only emissions are brackish water.

Unlike the osmosis of the Norwegian system, the Dutch scheme captures salt particles which give off electrical currents.

Filters have to be in place to avoid sucking in fish and there are environmental concerns about drawing water away from estuaries, perhaps threatening plants and creatures in the area.

The Dutch project is close to producing two watts per square meter of membrane.

The Dutch government, utility Eneco and Redstack research group are also making a feasibility study of a plant on the Afsluitdijk dam between the IJsselmeer and the Wadden Sea, with a 10 50 kilowatt installation to be built that could lead to a 200 megawatt capacity if it works.