Why Tidal Power is Europe’s Best Near-Term Ocean Energy Technology

The news that the world’s largest tidal turbine – 1 MW in size – will be installed off the coast of Scotland near Orkney should come as no surprise.

Primitive tidal mills operated in the England date back to the 11th century. During the 18th century, several tidal mills popped up in Western Europe. The first modern tidal plants borrowed from conventional hydropower concepts by relying upon dams or barrages. La Rance, France still boasts the largest such system in the world, supplying 240 MW of capacity since 1966.

Scotland is the hot spot for tidal power in all of northern Europe, with the Pentland Firth often described as the “Saudi Arabia of tidal power.” The U.K. and Ireland also feature among the best tidal sites in the world, because they are relatively close to people. Some from these islands near the European coast may argue with this assessment, but when compared to the U.S. — where 95% of the nation’s tidal resources rise and fall off the coast of remote Alaska — it becomes clear it is all a matter of perspective.

Tidal stream turbines often look suspiciously like wind turbines placed underwater. Tidal projects comprise over 90 percent of today’s marine kinetic capacity totals, but the vast majority of this installed capacity relies upon first generation “barrage” systems still relying upon storage dams (see forecast below.)

Pike Research will be issuing a revised forecast of ocean energy technologies next year, with lower capacity totals given the lack of progress on carbon regulations and the lingering recession, but this 2009 forecast shows how tidal systems dominate the near-term market for ocean energy technologies.

What is the scientific basis of tides?

Tides result from the gravitational forces of the moon and sun interacting with oceans. (Because of its proximity to the earth, the moon actually exerts about twice as much influence on tidal patterns as the sun.) The ever-changing relationship between the moon, sun, and earth causes the ocean to rise and fall at regular intervals. These bulges are frequently referred to as “semi-diurnal” tides.

These tidal streams become concentrated pools of kinetic energy ideal for power generation, when passing through narrow channels, an inlet into a bay or other passages between two land masses. While the tidal resource is much less abundant than wave energy resources, its power density is greater. Most waves move at the pace of approximately one meter per second; tides typically move at least twice that speed at two meters per second. A doubling of the speed of tidal streams will result in eight times the amount of potential energy since power density is determined by the cube of water speed.

The Electric Power Research Institute has projected that a 100 MW tidal stream turbine project could generate power at a cost of 6 to 9 cents per kilowatt hour, which is competitive with wind, geothermal and other mainstream renewable technologies.

The basic selling points for tidal as follows:

• Tidal resources have the highest power density of any of the marine renewable technologies, hence the lowest cost estimates.

• Unlike many renewable resources including solar and wind power, tidal resources can be accurately predicted literally years in advance.

• Tidal devices are typically sited below the ocean surface: they can’t be seen; can’t be heard; and, in most instances, would not interfere with shipping or other maritime uses.

While physics is on the side of tidal streams if compared to wave energy resources, the size of the resource is much smaller. Most experts estimate the wave resource to be two to three times the size of the world’s tidal stream resource.

Article by Peter Asmus, appearing courtesy Matter Network.