How to generate electricity from waves – knowledge

Like a huge pear painted black and yolk yellow, the monster lies in a workshop in the northern Portuguese port of Aguçadoura, the interior full of rails and rods, cables and electronics. In the spring, the manufacturer, the Swedish company Corpower, wants to load the construction onto a ship and place it on four pillars anchored to the seabed off the coast. There the pear becomes a buoy, according to the plan: moved by the ups and downs of the waves, it should dance on the water and let the pillars slide up and down. The movement drives a generator inside, which produces electricity. According to Corpower, the 19-metre high power buoy can draw up to 300 kilowatts of power from the waves, almost a thirtieth as much as a modern offshore wind turbine delivers at peak.

Energy generating buoy

(Photo: SZ graphics: Schubert)

It is seldom that the world’s seas are as smooth as glass, mostly the waves swell incessantly. Because they are formed by the wind blowing across the water, their energy is inexhaustible. But while the wind itself has long since become a key source of electricity generation, the waves remain unused. Their potential is gigantic: around 500 gigawatts of power, as much as 1,000 medium-sized coal-fired power plant blocks, could be generated if the energy of the waves were skimmed off just two percent of the world’s coasts. That has the International Renewable Energy Agency Irena of all things.

Energy: Black and yellow bulb: Corpower's buoy in the workshop.

Black and yellow bulb: Corpower’s buoy in the workshop.

(Photo: Ralph Diermann)

Around 15 years ago, researchers from industry and science dealt intensively with wave power plants. They launched a number of pilot plants – a snake-shaped system called the Pelamis, for example, which consisted of several floating bodies designed to generate electricity by rocking. However, the project partners, including Eon, soon stopped development. Other concepts were also not pursued further.

“In addition to the technical challenges in the harsh environmental conditions on the high seas, there was probably a lack of investors at the time who wanted to accompany the next steps on the way to commercializing the technology,” says Christian Keindorf from the Institute for Shipbuilding and Maritime Technology at Kiel University of Applied Sciences.

The EU Commission wants more marine power plants

With the EU’s Green Deal, however, new impetus has now come into the subject. The EU Commission has set the goal of using marine power plants by 2050 – which also include floating solar parks and current power plants to install a total of 40 gigawatts of power. Well-filled funding pots should help. Corpower also benefits from these funds. The company plans to install four power buoys off Portugal for test purposes. By 2026, the first power plant with 100 turbines and an output of 30 megawatts is to be built off the west coast of Ireland.

“Compared to offshore wind farms, our systems have the advantage that they can generate three to five times more energy on the same area,” says Corpower boss and co-founder Patrik Möller. But he doesn’t want to play the two technologies off against each other. “On the contrary, because they complement each other well. Wave power plants usually continue to supply electricity even when the wind turbines are weak,” he explains. In any case, the systems could easily be installed within the wind farms. “This has the advantage that the two technologies can share the connection to the power grid,” says Möller.

Keindorf sees it that way too. “We have to use the sea areas designated for energy production as efficiently as possible,” he says. However, wind turbines could not be arranged even more densely because the greater turbulence effects would result in significant yield losses. “Wave power plants represent a way of using the space between the towers of wind turbines without reducing the yields of the wind turbines.” With his institute, Keindorf has developed its own concept for a wave power plant that works on the same principle as Corpower’s. The researchers are currently working on a prototype.

An international project team, also funded by the EU and in which the Fraunhofer Institute for Energy Economics and Energy System Technology IEE is also involved, is pursuing a different approach: The partners are relying on a concept that works with air pressure generated by waves in a hollow chamber. The facility is in the form of a large cuboid, part of which protrudes out of the water and has openings above and below the waterline. “When a wave hits the hollow body, the water column inside rises, so that the air is pushed out of the chamber,” explains Fabian Thalemann from Fraunhofer IEE. It flows through a turbine installed in the opening. “When the wave pulls back, the water column falls, creating a negative pressure and sucking air through the turbine.” So-called Wells turbines are used, which maintain their direction of rotation, even if the direction of the air flow changes constantly as the water rises and falls. Smaller systems of this type have already been tested off the coast of Ireland. In the future, the project partners want to install a system with one megawatt of power off the Scottish Orkney Islands.

However, it is far from certain whether the new generation of wave power plants will actually prove themselves in practice. Because the conditions on the high seas are rough. During a storm, enormous forces act on the systems, and the salt in the water and air threatens corrosion. However, Corpower boss Möller points out that processes, technologies and materials are available today that did not exist 15 years ago. “Our integrated controller, for example, can use algorithms to align the systems during a storm so that they are exposed to the forces as little as possible,” says Möller. Whether this actually works will soon be seen off the coast of Portugal.

source site