Executive Summary
Energy can be retrieved from the oceans in five basic
ways: tides, waves, tidal or marine currents, temperature gradients, and salinity gradients. Of these, wave energy is the most significant resource, followed by power from salinity and thermal gradients. Tidal and marine current offer the smallest potential capacity by a wide margin. According to the British government-funded research group The Carbon Trust, ocean energy resources in their entirety have the potential to generate 4000 TW of electricity and will likely constitute up to 20% of Europe's total renewable resources by 2020.
Still mostly in the experimental stage (apart from the 40-year-old tidal barrage at La Rance in France), more than 300 wave and tidal systems have been proposed, and more than over 25 countries and 100 small companies are engaged in the process. Nonetheless, few devices are advanced enough for commercial development. The key scientific challenges to be addressed are resource assessment and predictability, engineering design and manufacturability, installation requirements, operation and maintenance, survivability, reliability and cost reduction. Tidal barrages are generally agreed to be the most established and developed commercial systems, though only a small number have been built because of cost and environmental concerns.
The visible success of wind and solar power - coupled with rising concerns about the environmental, economic and strategic costs of relying on fossil fuels - have breathed new life into ocean energy development. By some estimates the potential world energy produced by tides alone could be 1 million GWh per year (5% of the world's current production). According to the Electric Power Research Institute (EPRI), Canada could generate 25% of its electric needs from tidal power, the UK and Portugal 20%, and the US 10%. However, only a fraction of that overall potential will be developed due to accessibility, difficulty of grid integration, and uncertain financial returns. Of the two sources, tidal power has more limited potential than wave power, since only about 40 sites on the planet have enough tidal differential to make electricity generation possible.
Despite the enthusiasm, very little electricity has actually been generated through tidal power aside from scattered test sites around the world. Beyond the technical questions, significant challenges are posed by funding and financing, government will, and utility support. Experts seem to agree that the next five years will be critical to the industry's survival. Developers must demonstrate that tidal power technologies are commercially viable, that environmental concerns are unjustified, and that unwieldy regulatory processes are counter-productive to growth and not in the interest of the general public.
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