As the moon spins around the earth, its gravity creates a bulge in the oceans that causes tides. Researchers are working out ways to tap into this immense power, and smart sensors could help them do it cost-effectively.
One of the main expenses in tidal power is maintenance – the salt water corrodes the metal parts, and generators are hard to reach because they are often deep underwater.
That’s why researchers are working on long-range sensors that can monitor the integrity of tidal turbines and alert engineers before the equipment is damaged.
‘The industry currently takes action when necessary - usually after a critical failure occurs, which can lead to serious and costly repairs,’ said Dr Nico Avdelidis, the coordinator of TidalSense Demo, an EU-funded project.
TidalSense Demo is specifically making technology for an emerging method of generating tidal power known as tidal stream generation, where turbines are placed underwater in places where the tidal current moves quickly.
The project, which began in February 2012, uses long-range ultrasonic sensors to pick up any signs of wear and tear on the underwater turbines, and then alert engineers so they can decide whether to take action.
‘There is no standard condition monitoring technique available that can provide details of the tidal blade integrity,’ said Dr Avdelidis, who works for InnotecUK, the British company leading the TidalSense Demo project.
The condition monitoring system being developed by the project constantly checks the integrity of the exposed rotor blades, meaning that operators can save money by fixing problems quickly, and by adapting their designs if part of the rotor is particularly prone to breakage.
The system the project is developing can work for rotor blades, or for underwater hydrofoils such as the ones being developed by the EU-funded project PULSE STREAM 1200.
PULSE STREAM 1200, which finishes at the end of October 2013, is experimenting with rod-like oscillating hydrofoils that move with the water to generate energy.
Researchers believe that the hydrofoil design can capture more energy than a turbine, and operate in wide, shallower water, meaning it is more suited to estuaries which are often too shallow for high-power turbines. They’ve already successfully tested them in a small-scale trial, and they are now looking for further investment to build a full-scale protoype.
‘This 1.2 megawatt machine that’s been designed as part of the EU project is able to be deployed in 20 to 25 metre water depth, and there are very few other 1 megawatt turbines out there that you can deploy in quite so shallow water,’ said project coordinator Joe Hussey.
The most established method of generating energy from the tides is by using barrages - long barriers built across estuaries that channel the water through sluice gates to feed generators. The world’s first tidal power station, opened in 1966, lies across the Rance estuary in Brittany, France.
Within Europe the UK is one of the countries that stands to benefit the most from tidal energy due to its abundant coasts, and tidal power could supply a third of the UK’s energy needs, according to Tidal Energy, an industry organisation. A planned barrage across the estuary of the River Severn in the west of the UK alone could generate 5 % of the UK’s energy needs, Tidal Energy said.
Tides move along coastlines as well as in and out of estuaries, and another possible future method of generating power from the tides, called dynamic tidal power, would exploit this by building a long wall straight out into the sea.
As the water swells with the tide, it would be higher on one side of the wall than the other. That fact can be exploited by engineers by placing turbines along the wall that turn as the water flows from one side of the wall to the other.
No dynamic tidal power installation has ever been built. However, a project involving Dutch and Chinese researchers called POWER is looking into the practicalities and hopes to have completed a feasibility study by 2015.
The contrasting salinity of freshwater and seawater creates a pressure difference which could be used to generate energy, while the thermodynamic cycle between warm shallow water and colder deep sea water could also be exploited to generate electricity.
A wave breaking. © Shutterstock/ Galyna Andrushko
Power from the movement of waves alone could supply 1.1 % of the projected EU-28 electricity consumption by 2030, the EU said.
Overall, the EU has spent over EUR 55 million supporting research into ocean energy since the 1980s.
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