Once something of a minority interest, wind power has rapidly become a firmly established part of the mainstream alternative energy strategy in Britain and across the globe over the last decade. By contrast, the huge potential resource represented by ocean currents remains largely overlooked and under developed, with no commercial installations of any size currently in operation around the world.
As Tim Cornelius, the Chief Executive of Atlantis – the UK-based world leader in this technology – puts it, “tidal power today is what wind energy was 10 years back,” and practical ocean current generation is even further away from becoming reality. Gradually, however this huge, and almost entirely unexploited, source of energy is beginning to be tapped.
The Potential
Ocean currents score over wind power as a source of renewable energy in two important ways. Firstly, if there’s one question that simply doesn’t apply, it’s the age-old one about what happens when the wind doesn’t blow. The waters of the world’s seas and oceans are constantly in motion, flowing in complex patterns that are driven by the warming effect of the sun at the equator, the rotation of the Earth, surface winds and variations in water temperature and salinity.
Unlike the more familiar tidal currents which ebb and flow daily, and vary in intensity with the phases of the moon, ocean currents – such as the Gulf Stream – travel only one-way, remaining relatively constant throughout the year, making them a highly reliable potential resource.
Secondly, although these currents move very much more slowly than a typical wind, sea water is over 800 times more dense than air, which means that ocean currents carry a huge amount of kinetic energy. As a result, a current travelling at just 10mph equates to a wind blowing at around 100mph over the same area – and as mentioned before, unlike the wind, that’s going on constantly, 365 days a year. If we can harness even a small part of all the energy on offer, the possibilities are clearly enormous.
Harnessing the Sea
Unsurprisingly, Britain is not alone in looking to the sea as a potential new source of power; a number of European countries, China, Japan and the US are just a few of the other nations taking an active interest in exploiting ocean currents.
Although a variety of technologies have been put forward to achieve it, and some prototypes have been demonstrated – mostly in tidal, rather than oceanic, currents – there is broad agreement that submerged water turbines are the most likely approach for commercial development. Sited in areas where fast ocean currents flow, and arranged in clusters of up to 50 per square mile of the sea bed, these underwater turbines would be the ‘wind farms’ of the sea.
Technical and Environmental Challenges
Inevitably, any attempt to make use of the ocean’s energy must overcome a number of technical and environmental challenges. Any structure that is to be semi-permanently installed in the sea, faces the obvious problems of salt-water corrosion and the likelihood of fouling by the growth of a whole variety of marine life, such as barnacles, limpets and algae. In addition, from a technical point of view, reliability and a long-life are essential, since maintenance of deeply submerged turbines in mid-ocean is almost guaranteed to be a costly and difficult thing to achieve.
From an environmental standpoint, protecting marine life from disturbance and injury from the turning blades will, of course, be one of the key factors to consider – but there are less obvious potential problems too. Other important uses of the water, including shipping, fishing and diving, will also need to be taken into account to avoid damaging the local economy, while careful thought will have to be given to the effect of slowing the flow of the current by extracting significant amounts of energy from it.
Estimates suggest that there are 18 terawatt hours (TWh) per year of potentially extractable current power in British waters alone, with almost 40 per cent of this concentrated in the Pentland Firth, between the far north of Scotland and the Orkney Islands. Globally, there is very much more; it is hard to believe that ocean current energy will not have a major role to play in the future.
