Methodology for a Decision Support Tool for a Tidal Stream Device

Energy Resource

“The 2011 Tidal Current Resource and Economics report suggests a total of 20.6 TWh per year could practically be extracted from the 30 key tidal stream sites in the UK” (Black & Veatch LTD, 2011)

A tidal stream flow is generated due to the interactions of gravity force between the sun, the moon, and the earth. In small channels between land masses the flow of water is constricted in a “bottle neck” causing the velocity of the flow to increase. In these regions it is possible to place underwater tidal turbines to extract the energy in electrical form.

Relative positions of the sun, moon and Earth during spring and neap tides - Pearson Prentice Hall, Inc

The tidal stream resource around the UK comprises of a number of potential sites. These include: the Pentland firth, Western Islands, and Islay (Scotland); the Coast of Anglesey (North Wales); the Bristol Channel and various regions of the English Channel (England) which all retain large resources of tidal stream energy.

Having selected sites which have sufficient tidal stream flow speeds, the depth of water and waves experienced in these areas must be evaluated. Large waves in shallow water create extreme velocity variations over the length of the blade. These velocity fluctuations can cause structural loading problems linked to fatigue failure. Locations which are sheltered between islands or in estuaries are often the sites which have the best potential for tidal turbines because the waves are generally smaller.

Hammerfest Strom HS1000 Tidal Turbines

In the highlighted study [1], the University of Edinburgh assessed the total amount of energy which could be extracted including technical and practical constraints. This value of 20.6 TWh per annum illustrates the vast resource which is possible to extract from sites around the UK, and the significant contribution of electrical energy tidal resources could supply to the national grid. Potential issues which can affect the viability of the resource are:

         •   Grid connections and transmission
         •   Waves
         •   Depth of water
         •   Environmental impacts
         •   Variation between springs and neap flows

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References:
        ➙   [1] Carbon Trust, Black & Veatch UK Tidal resource and Economics Study. Retrieved April 15th, 2014.