There has been an explosion of tidal stream technologies being trialled and tested in recent years, in preparation for what is set to be a new age of renewable power.
For a long time, electricity powered by the sun and the wind has stood at the forefront of the green energy sector, but the attraction of a more predictable, inexhaustible resource has shifted the industry focus towards the seas.
One of the largest and most-talked-about projects has already been approved by the Scottish Government and will see ten tidal turbines, at 10MW capacity, being installed in the Sound of Islay.
And, over the next five years, this tidal project and many more like it will be deployed onto the seabed around the UK, a region that will surely be followed by the rest of the world.
Something in the water
So far, the rise and fall of the tides have generated electricity via dams and barriers installed in the sea. Now though, industry heavyweights are working hard to create technologies that can work with the current; that is to say the speed and the flow of the tides.
Many prototypes of such a technology have been tested in waters around the world, but the first and only commercial-scale turbine was placed off the coast of Northern Ireland, in 2008, by Marine Current Turbines (MCT), a UK-based company with strong ambitions for the tidal sector.
MCT's turbine, SeaGen, was deployed in the Strangford Narrows, a channel which runs through the largest sea inlet in the UK, the Strangford Lough. It is a 1.2MW machine, which, during the course of the day, generates electricity onto the grid for an average of 20 hours.
SeaGen has already attracted private and public investment in MCT, including EDF Energy, the Carbon Trust, and Siemens Energy. And, with such powerful backing, MCT has set its sights on Kyle Rhea, a strait of water between the Isle of Skye and the Scottish mainland, where it hopes to build an array of tidal turbines.
MCT spokesman Paul Taylor explains the progress that has been made so far, "We have signed an agreement for lease, which means we have passed the certain criteria and reached a commercial agreement with the Crown Estate to take our plans forward.
"We hope to submit a planning application this year and aim for the deployment of four units at 8MW capacity in 2014."
An even larger project is the 10MW array, which MCT, in partnership with RWE npower renewables, hopes to deploy off the north-west coast of Anglesey in 2015.
Last month, the firm submitted a consent application to install seven twin rotor turbines, which are set to power over 10,000 homes on the Welsh island.
But MCT isn't alone in the tidal energy race; ScottishPower Renewables is also moving forward with its Sound of Islay project, the world’s only tidal array to gain planning permission, explains the firm's head of renewables policy Alan Mortimer, "Potentially, when it's installed, it will be the first in the world.
"We call it a tidal array of ten tidal technology devices, each one of which is best described as an underwater windmill. They have three blades with a total diameter of 24 metres and they sit on a support foundation, which in turn sits on the sea bed."
ScottishPower is looking to use Hammerfest Strom turbines, which have been operating as a prototype in Norwegian waters for more than five years, but at around £3m per MW built, turbines don’t come cheap.
Swimming through barriers
Tidal energy has not yet been proven to reduce the overall costs of electricity, and this issue has stalled the progress of many projects, admits Pulse Tidal CEO Bob Smith, "The biggest challenge is to develop a commercially attractive technology solution. Nobody has done this yet.
"If somebody came along with a truly cost effective solution tomorrow then you would see a dramatic increase in the number of devices deployed," says Smith.
It is hoped that by installing a number of turbines together, the potential to cut costs will become clear, and Taylor adds, "It’s a new industry but the momentum is picking up and it's quite an exciting time to be involved in it."
One of the biggest obstacles for renewables is installation and, compared to wind farms, tidal arrays are much more difficult to deploy, particularly in fast-flowing water. The Hammerfest Strom device in Norway, for example, had to be placed on the seabed in less than 30 minutes, a rare time period when the tide was slack.
Renewable energy companies are reluctant to install turbines in areas with very high tidal flows such as the Corryvreckan Whirlpool in Scotland, as it would be too dangerous. But, equally, lower flow areas can create their own problems.
Mortimer explains, "In the lower flow areas, the amount of energy, available for the devices, drops off quite rapidly, so there is a balancing act to be done. Within the range of what we think is viable, there is a huge resource and there is potential power to generate many thousands of megawatts around the UK.
"We are looking to develop devices that will be most effective in these sorts of ranges of tidal flow conditions."
Gaining planning permission for renewable energy projects can also prove to be a daunting task. Onshore wind applications are frequently rejected because locals object to the visual impact. Tidal generators installed on the seabed don’t incur this problem, but when it comes to environmental impact, they can cause quite a stir.
Strangford Lough, the home of SeaGen, is heavily populated by seals and MCT had to assure the Northern Island Environmental Heritage Service that this device would have minimal impact on the mammals and other marine life.
So far, the company has proved this to be true, insists Taylor, "To date the studies show that there has been minimal impact. We even had environmentalists standing on the SeaGen."
Because of the density of the sea, turbines rotate around a dozen times a minute when placed in the water, and so most tidal machines are benign to the surrounding environment. To put this in perspective, each blade must push through around 35t of water before it can turn.
Smith also insists that Pulse Tidal's 1.2MW turbine currently being built for Scottish waters is safe to be installed, "Studies tend to indicate that marine mammals will swim around the devices rather than cut through them, but in the case of our own machine, if they did swim through them they would survive."
Tidal power: going global
At the moment, it seems the UK is leading the way in terms of deploying tidal projects, but it may not be too long before the rest of the world follows suit.
Indeed, MCT is already working with Minas Basin Pulp & Power to place a single SeaGen system in Canada's Bay of Fundy, between the eastern provinces of New Brunswick and Nova Scotia. The firm is also eyeing further potential hot spots off the country's west coast.
Areas around the US, Korea, China, Norway and France are also seen to have huge tidal resources, which, in the future, could power vast areas of land.
"The point is that nowhere has been exploited yet," says Mortimer. "It's happening first and foremost in the UK, but it is correct to say that there are resources elsewhere in the world."