The revolving of the earth, moon and sun creates tidal differences in the sea level. Tidal energy takes advantage of the energy that is created through ebb and flow. The energy can be extracted from the level difference between ebb and flow, or from utilizing the fast-flowing tidal streams that exist at some locations.

Status for tidal energy
The technology for tidal energy is still quite new, and the use of tidal energy for electricity generation is small. But some plants exist, as for example La Rance in France. This is the world's biggest plant for tidal energy, and is of the barrage type, taking advantage of the level difference at ebb and flow. It consists of a large dam, that collects water during flow, and a set of turbines that generate electricity as the water flow in or out of the dam.

In Norway the difference between ebb and flow is not so large, but there are some strong tidal streams. The energy in such streams can be extracted in floating or ground-fixed turbines, that have much in common with wind turbines on-shore. The tidal streams are, however, more reliable and predictable than the wind, and the energy density is higher. The technological challenges are connected to the harsh environment that sea water represents, that gives e. g. corrosion or growing on the installations.

The total potential for production of electricity from tidal streams in Norway is limited to 2 TWh/year, according to the Norwegian Directorate for Water and Energy. That is not so much, but with the great experience Norway has in offshore technology, there should be a good basis for driving innovation on the international market for tidal energy.

Research at NTNU and SINTEF
NTNU and SINTEF have been involved in the development of a tidal turbine in cooperation with Hammerfest Strøm. The prototype has been installed outside Hammerfest, and has produced electricity for four years. A full-scale turbine is planned for installation in Scotland in 2010. The further development of the project takes place in Scotland due to the better framework conditions.

Installation of the tidal turbine in Kvalsundet, developed by the Norwegian company Hammerfest Strøm in cooperation with NTNU and SINTEF. (Illustration: Hammerfest Strøm)

More information
Hammerfest Strøm

Contacts
Professor Ole Gunnar Dahlhaug, +47 91 89 76 09 (NTNU)