Green Economy in a Blue World-Full Report

Spots of potential for wave energy harvest

5 15 25 35 45 55 65 75 85 95 105 115 125 Mean power in Kilowatt per metre

in a Blue World

Source: Cornett, 2008

or through channels. Tidal currents can be harnessed using technologies similar to those used for wind-energy conversion (horizontal or vertical-axis turbines, also known as ‘cross flow’ turbines). However, in contrast to atmospheric airflows the availability of tidal currents can be predicted very accurately, as their motion corresponds to local tidal conditions. While still in a nascent stage of development, commercially attractive sites have been identified in the UK, Ireland, Greece, France and Italy. Outside Europe, there is potential in the Republic of Korea, China, Canada, Japan, the Philippines, New Zealand and South America. China, for instance, has estimated a tidal power current potential of 14 GW (IPCC, 2011) Tidal energy has the potential tobecome a viable option for large-scale, base-load generation in some countries due to their advantageous location. However, current competitive capacity when compared to fossil-fuel based energy is still a concern. 1.4 Wave energy Wave energy is captured directly from surface waves or from pressure fluctuations below the ocean surface. Wave power varies considerably in different parts of the world, making it more economically feasible to harness in some parts than in others, hence making wave energy a region-specific energy source. For example, strong winds variations are observed within the band between 30 and 60 degrees latitude, and circumpolar storms near the southern latitudes, which account for high-energy ocean waves in those areas (IEA, 2008). Similarly it has been

observed that annual wave power distribution is greater on the western coasts of temperate countries (IPCC, 2011). For instance in the figure above, offshore average annual wave power distribution is highlighted. It can be seen from the figure that the largest power levels occur off the west coasts of the continents in temperate latitudes, where the most energetic winds and greatest fetch areas occur. Wave energy is predictable, because satellites can measure waves out in the ocean that will later impact on devices around the coast. This predictability will allow for less spinning reserve than is often required to support more intermittent renewable energy sources (WEC, 2007). Many different wave energy converter types have been, and continue to be, proposed and tested but they are still at the pre-commercial phase (Holmes & Nielsen, 2010). A very few pilot projects have been translated into working prototypes, and even fewer into devices which are sufficiently robust. Some estimate that more than 50wave energy devices are at various stages of development (IPCC, 2011), often tailored to specific site conditions. They range from small 10 kW generators standing on the seabed to large floating structures generating 1.5 MW. The total theoretical wave energy potential is estimated to be 1 300 million MW/yr (Mørk, et al., 2010), roughly twice the global electricity supply in 2008 (700 million MW/yr). This figure is unconstrained by geography, technical or economic considerations. However the technical potential of wave energy will be

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