Background


Tidal streams are created by the gravitational pull of the moon and sun on the world’s oceans. Tides never stop, with water moving first one way, then the other, the world over. Tidal stream technologies capture the kinetic energy of the currents flowing in and out of tidal areas. Tides, unlike waves, can be predicted. It is this predictability that makes tidal energy such a valuable resource.

Tidal stream resources are generally largest in areas where a good tidal range exists, and where the speed of the currents are amplified by the funnelling effect of the local coastline and seabed, for example, in narrow straits and inlets, around headlands, and in channels between islands, as shown in the map below.

One of the largest business opportunities for ocean energy is presented in Europe as it has a high tidal energy potential, with some areas experiencing some of the largest tidal flows in the world: the Atlantic-facing coasts of the UK, France, Spain and the North Sea. Combining this with Europe’s advanced research and development in ocean energy capture systems, a major potential for ocean energy extraction has arisen.

Tidal stream resource map based on velocity of currents
Tidal stream resource map based on velocity of currents

Image courtesy of AQUARET - www.aquaret.com

One of the key characteristics of tidal energy capture systems is that they deliver large but locally fluctuating output torque and rotational speeds, leading to poor sustained reliability of generator gearboxes. The torque transfer requirements are demanding and such gearboxes are complex, expensive to manufacture and not compact. Repair, renewal and maintenance of any failed components often require the gearbox to be removed from the subsea environment and brought ashore: a time-consuming and expensive operation. Larger and more complex gearboxes typically require pressured lubricating oil systems with a large oil reservoir. Any mechanical failure can result in leaks of lubricating oil into the water. Even under ideal operating conditions the oil must be replaced and/or disposed of regularly.

A low rpm, gearless system can be a solution to these issues. To assist the transition of the many renewable marine energy capture systems from concept to useful energy contributor, a low-speed, reliable, gearless generator needs to be available on the market. This is what the MAGNETIDE project focuses on: the development of suitable soft magnetic materials for use in such a generator and the development and modelling of concept designs for the generator.