Osmosis—An Alternative Energy Idea Gone Bust

In September 2013, after four years of operation of the pilot facility, Statkraft announced its intention to build a much larger osmosis pilot plant with a design output of 2 MW (2000 kW), likely at Sunndalsøra. However, a few months later they changed their mind entirely. The company was not going ahead with the larger system and after working on the osmosis project for over a decade was abandoning the idea altogether. You might ask why?

Osmosis Power—Theory

The osmotic force or osmotic pressure was discovered a long time ago and is well understood. The principle is that a saltwater solution will take on water from salt-free water when the two are separated by a “semi-permeable” membrane. The pores in such membranes are small enough to let water molecules pass through it but not the larger salt ions. Over some time then, the surface of the saltwater column will rise above that in the freshwater column and create a “head” that can be used to drive a turbine. The above graphic demonstrates the principle.

Such systems are widely used in the opposite way, called “reverse osmosis” to create freshwater from salty ocean water. You find them on most navy ships and in other places where plenty of salty or impure water may be available but little clean potable water, like the large communities at the shores of the Persian Gulf. Of course, the reverse osmosis water purification does not provide but consumes energy.

Osmosis Power—Practice

The osmosis pilot plant in Tofte, Norway is situated right at the ocean shore and not far from a small river delivering the necessary freshwater. In many aspects, the plant was situated at an ideal location for that kind of system. The plant’s low elevation above the sea level would minimize the energy requirement for pumping the seawater to the site and the freshwater would arrive more or less by its own volition from the river.

While one would not expect to get any net power from a pilot test facility like that, careful observation of all energy inputs and outputs will show whether or not the idea is viable. However, even if a pilot project works out well and is found to be producing a net energy gain, it may be impossible to scale it up to a size that could support a commercially viable operation. For example, a requirement of one cubic meter of freshwater per second for a 2 kW plant would translate into one thousand cubic meters of freshwater for a 2 MW plant. That’s about half the flow of the mighty Niagara River.

Then there are other critical elements such as the semi-permeable membranes. In 2012 a company representative claimed that “The membranes we are testing at Tofte this summer are ten times more efficient than the ones we installed during the opening of the prototype in the autumn of 2009.”

The membranes’ microscopic pores can easily get clogged by the always present microscopic suspended clay particles and tiny organisms in the freshwater. Even the most pristine water contains such and they would lead to an increased time requirement for the passage of water through the membrane. Therefore, the membranes need regular cleaning by back-flushing or other means also requiring time and energy. Then there is more time needed for the equilibration of the (now diluted) saltwater in its compartment. The latter time requirement can be shortened by mechanical pumping of the saltwater along the membrane surface but that comes with its own energy cost.

As I wrote in CONVENIENT MYTHS in 2010, the osmosis idea should work in principle, but the actual “osmosis energy windfall” will likely be disappointing for two reasons; namely the cost of building and maintaining the facility and the limiting step of the osmotic energy-extraction process, which is the time required for the passage of water from one side to the other of the semi-permeable membrane.

Wise Decision

Statkraft’s decision to cancel any further work on the osmosis front confirms my earlier assessment of this power generation idea. More importantly though is that it shows that a well-run private company makes wise decisions when unencumbered by promises of free money (from taxpayers) for political or financial gain.

The company is to be congratulated for recognizing the practical limitations of the osmosis idea and stopping to pursue it any further rather than throwing good money after bad and bilking the country’s taxpayers out of millions of Norwegian Kroner with promises of free energy that cannot be delivered like the (in 2009) claimed potential of 12 TWh or 12 million MWh annual osmosis-power-generation capacity from Norway alone.

Isn’t it about time the purveyors and promoters of other “alternative energy” schemes were just as forthright?