1.2        Geographical assessment

The tidal energy resource that could realistically be developed is confined to a few select regions of the world, which have exceptional tidal ranges. Within the EU only two countries, France and the UK, have sufficiently high tidal ranges. In France, a 240 MW demonstration plant which was built on the Rance estuary during the 1960s has now completed 35 years of successful operation. Some experimental stations have also been implemented in Russia, China and Canada. Beyond the EU, potential sites, which have been periodically investigated, are Canada, the CIS, Argentina, Western Australia and Korea. It is likely that economic criteria and commercially more competitive options (for example large-scale hydropower in Canada) will determine whether tidal energy will be developed on these sites or not.

Data on marine currents are sparse. In most places the movements of seawater are too slow - and the energy availability is too diffuse - to permit practical energy exploitation. However there are specific locations where the water velocity is speeded up by a reduction in cross-section of the flow area, such as straits between islands and the mainland, around the ends of headlands, in estuaries and other such topographical features. A major study by the European Commission evaluating the tidal current resource for 106 locations around Europe estimated an exploitable resource of 48 TWh per year from these sites. The U.K. government recently came up with an estimate of about 320 MW of installed capacity for the United Kingdom by 2010. There is a potential to install several Giga-watts of tidal turbines at identified locations of United Kingdom. The worldwide potential is obviously much larger.

 

Energy can be extracted from waves all over the world. As an example, in deep water off the northwest coast of Scotland (having one of the most intense wave climates in the world) the average energy along the prevailing wave front can be 70 kW a metre (or more). Closer to the inshore this falls to an average of around 20 or 30 kW a metre, and along the shoreline to about 10 kW a metre or less. The energy availability is thus sensitive to the distance from the shoreline.

Many wave energy devices remain at the research and development stage and have not yet entered the market. However, several shorelines, near shore, and offshore demonstration projects have been built worldwide and a number of companies are planning their first commercial schemes. EU is in the forefront of the developments in the field, with Denmark, Ireland, Norway, Portugal, Sweden and UK being the most active. In the CEE, CIS, NAFTA, Middle East and Mediterranean regions there are no wave energy machines currently deployed, and only a small amount of work has been undertaken in the USA. On the other hand, Japan has several small-scale wave energy schemes, while China, India and Indonesia have built (or are about to built) some demonstration ones.

 

As regards ocean energy, the laws of thermodynamics demand as large a temperature difference as possible to deliver a technically feasible and reasonably economic system. OTEC requires a temperature difference of about 20 degrees Celsius, and this limits the application of this technology to a few tropical and sub-tropical regions between the latitudes of 25^oS to 32^oN with very deep water.