ESRU

Marine Resources and Market Size

Marine Energy

Marine energy generally refers to all forms of renewable energy derived from the sea and are classified into three major categories; tidal, wave and gradient.

Tidal energy is a type of marine energy that occurs as a result of the gravitational forces of the moon and the sun on the surface of the sea which causes the water to move to and from the coast producing what is known as a tidal range.

Wave Energy

Wave energy is another type of marine energy that occurs due to the water movements near the surface of the sea. Waves are the resultant effects of wind blowing over the surface of the sea. The amount of energy transferred, and the size of the resulting waves, depends on the wind speed, the length of time for which the wind blows, and the distance over which it blows. Coasts with exposure to the prevailing wind direction and long distances over which this winds blow tend to have the most energetic wave climates, the western coasts of the Americas, Europe and Australia/New Zealand being typical examples.

This vast global wave power potential as estimated by Isaacs and Seymour in 1973 is between 1-10 TW (8000-80,000TWh/year). With specific reference to the UK, the theoretically available accessible offshore resource is 600-700 TWh/year, with the nearshore resource estimated to be between 100-140 TWh/year and the Shoreline resource 2 TWh/year.

Shoreline wave energy resources are usually lower because of energy dissipation but are attractive because of the advantage they have in terms of easy accessibility for installation and maintenance. In terms of locations, UK’s most promising nearshore sites can be found in the North of Scotland and Orkney which have an estimated annual energy intensity level of about 452.7 kW/m. Scotland’s Shetland sites also have an equally excellent resource size of about 300.7kW/m according to Richard Boud et al 2002.

Gradient

Gradient, perhaps the least popular of the three marine energy sources occurs as a result of the temperature or salinity difference between surface and bottom of the ocean. Marine energy available due to temperature difference is popularly known as ocean thermal and the term Ocean Thermal Energy Conversion is used to generally refer to its conversion technologies.

Tidal Energy

Tidal energy is the first ocean energy technology to have attained maturity probably due to its similarity to conventional hydropower plants. The rotation of the earth within the gravitational fields of the moon and the sun results in the generation of tides. These tides move the huge amount of water which is seen as a periodical rise and fall on the surface of the sea for each occurring cycle. The two commonly occurring cycles being the half – day and 14 – day cycles.

When the gravitational field of the sun reinforces that of the moon, maximum tides occur and this is called spring tides. On the contrary when the gravitational attraction of the sun partially cancels that of the moon, minimum tides called neap tides occur.

The typical period between two successive high waters in a half day cycle is 12 hours 25 minutes.

Harnessing tidal energy can be done through two main means; stream and the barrage methods. The tidal barrage method involves constructing a dam across an estuary. As the tides move the water through the sluice gates of the dam, they turn a turbine to generate electricity. The first and largest commercial tidal barrage plant in the world is the 240MW La Rance tidal barrage scheme in France.

The tidal stream method of harnessing tidal energy involves extracting power from the kinetic energy of the sea using turbines that work on a similar principle to conventional wind turbines and is in its development stages.

Reference:

Guide to Marine Energy www.thecarbontrust.co.uk/CTMarine1/page2.htm

Opportunity for marine energy in Scotland by Richard Boud, Scott Gerrard and Madeline Cowley, Future Energy Solutions, AEA Technology, November 2002.

Wave Energy, World Energy Organisation www.worldenergy.org/wec-geis/publications/reports/ser/wave/wave.asp

“Ocean Energy Conversion” by Pontes T. M and Falcao A

"The Ocean as a Power Resource" by Isaac J. D. and Seymour R. J. (1973), International Journal of Environmental Studies, Vol. 4(3), P 201 - 205

Why is Marine Energy Important to Scotland?

Global concerns about climate change, greenhouse emissions and dwindling fossil fuel reserves have enhanced the search for alternative energy generation options of which renewable energy technologies have been a major target to help address the above issues. According to the DTI, presently less than 3% of UK’s electricity supply comes from renewable sources. The UK government has thus set a renewable energy generation target of 10% by the year 2010. From DTI projections, if all reasonable exploitable estuaries were to be utilised, the annual generation of electricity from tidal power alone could meet 15% (50 TWh) of current electricity consumption.

Specifically in reference to Scotland, the government has pledged its commitment to ensuring that by 2020, 40% of Scotland’s electricity is generated from renewable sources. The 2010 target is 18% with the primary focus being on established renewables technologies, such as on-shore wind and hydro but to meet the longer term target, new technologies would have to be brought on board especially marine technologies.

Reference:

Renewable Energy: DTI website www.dti.gov.uk/renewables/

Tidal Power: DTI website www.dti.gov.uk/renewables/renew_1.5.2.2.htm

Opportunity for marine energy in Scotland by Richard Boud, Scott Gerrard and Madeline Cowley, Future Energy Solutions, AEA Technology, November 2002.