A new era for marine energy?

A new era for marine energy?

Arianna Pescini
Share
Only 5 percent of the force of the ocean flows would bring electricity and energy to millions of homes. Tens of projects and encouraging data, aboveall in the US

A wave is not just a wave. It has a speed, height, direction. And a great energy potential. That might even meet the power needs of the entire planet. Already in 2012 an analysis of the Intergovernmental Panel on Climate Change (IPCC), spoke of a 30 thousand terawatts (TW) per year energy capacity of wave power around the world, 31% of which concentrated in North America. Indeed, it is the United States that is focusing on wave energy, with the aim of obtaining 80% of electricity from renewable sources by 2035. But in Europe too countries like Britain, Denmark, Italy, Portugal, Ireland, France and Norway are becoming increasingly involved in the industry.

The advantages of a wave

A wave is not just a wave. It has a speed, height, direction. And a great #energy potential

More predictable and consistent, wave power has ten times the potential of solar power, and five times that of wind power: One only has to consider that an hour of wave motion is equivalent to an hour of gusts of wind running at 160 kph. Furthermore, as a resource wave power can be used day-in-day-out, by night the same as by day. In the world of clean energy, seas and oceans have been the sources least tapped up to now, both because of the high costs of conversion facilities and their maintenance and for the many variables that need to be considered in the study of water movement. Yet research in recent years has gone ahead and suggests a future of experimentation and new relaunch of the sector. Marine energy development is inevitably linked to several factors: "We must take into account the financial, environmental and technical aspects - explains Marcus Lehmann, researcher and collaborator at the Theoretical and Applied Fluid Dynamics Laboratory (TAFLab) of the University of California at Berkeley, USA - but in the near future we will be able to make great strides forward, as has happened in recent years with solar and wind power. There are basically two key elements: technological progress and the resorting to economies of scale, meaning small energy systems that are more easily usable and controllable."

Power plants and "wave farms"

There are mainly three types of facilities, installed on the water surface or about 40 meters under the sea, that capture wave motion: attenuators, serpentine structures composed of cylinders that activate generators (thus transforming the mechanical energy into electrical energy); buoy systems, which follow the wave and trigger turbines; and terminals, tanks positioned perpendicular to the flow that capture the energy before compressing it, like the pistons in an engine.

The marine power plants set up so far have had mixed results: the "Pelamis", created in 2008 in the north of Portugal, provided electricity to 1500 homes, but was closed down after just two months due to financial problems. However, the first "wind farm" opened in Australia in 2015, that produces electricity and is connected to a water desalination plant, and the "Azura System" converter, built on the Hawaiian island of Oahu in collaboration with the American Navy, are working successfully. In the latter case the wave energy is captured by a special 45 ton floating device, which rotates 360° and is able to draw power from both the horizontal motion and the vertical flow.

In Europe, Asia and North America, over a thousand patents for converters that use kinetic, thermal and chemical energy of seawater were filed in 2015 alone. That is to say we are dealing with a potentially inexhaustible store, associated with other forms of renewable energy: "This field will never be a 'monoculture', but a healthy mix - continues Lehmann - The goal is to lower the costs, and make wave power competitive."

There are mainly three types of facilities, installed on the water surface or about 40 meters under the sea, that capture wave motion

The wager of the USA

The development of wave energy in the United States is encouraged, in academia and beyond, by ad hoc funded scholarships, competitions and workgroups. One of the most important is the  "CalWave" project research team, guided by Lehmann himself: "We have created under water "carpets" (hence sheltered from the effects of rain and storms) inspired by the muddy seabeds. These structures absorb wave energy and generate electricity more efficiently than other systems on the surface," he explains. The first prototype dates back to 2012 and has evolved into two variants: moving in contact with the waves pistons are activated that in turn activate a hydraulic motor to produce electricity; but these pistons can also "drive" the flow through a desalination plant. "Our objectives are mainly to provide an affordable solution for generating sustainable and reliable electricity and to get fresh water from ocean waves," Lehmann concludes. The US Department of Energy has released encouraging data on the potential energy capacity of North American waters, also considering tidal energy and exploitation of the currents: up to 3200 TW a year, enough to power more than 200 million homes, or that is provide electricity to 90 thousand homes annually with one single TW. This is also why investments totalling over 40 million dollars has been allocated for the construction, in an area yet to be determined, of the first wave power test center, in order to accelerate the development of the sector and the commercialisation of marine energy in the United States.