How is electricity generated from waves 3

Energy from the sea

Tidal power plant

As early as the 11th century, the power of the tidal range was used in tide mills in England and France. And in 1897, electricity was generated for the first time in France with the help of turbines and generators, powered by ebb and flow.

Around 20 years later, the first plans for a tidal power station were made at the mouth of the French river Rance near St. Malo in Normandy. The bay is particularly suitable with a tidal range of up to 12 meters. However, it was not until December 4, 1967, before the world's first tidal power plant could go into operation.

The principle is very simple. A 750 meter long dam separates the bay from the open sea. The water can only get to the other side through 24 bulb turbines. The turbines generate electricity both when the water enters (high tide) and when it leaves (ebb). Depending on the power requirement, the drain can also be slightly delayed.

The power plant generates a total output of 240 megawatts. There is a comparably powerful power plant in South Korea. There are otherwise only a few, smaller plants in the world with around one to three megawatts.

Ocean current power plant

However, energy cannot only be generated by using the tidal range. Because the fact that the sea is higher at high tide does not mean that it is raised there, at least not in the sense that one would lift a bucket of water from the ground.

The water of the sea is drawn from one place to another by the forces of the tides. Where it flows away, there is ebb, where it flows, the tide comes. There are currents. And these can also be used to generate electricity.

The world's first ocean current power plant was built off the coast of Great Britain. The German-British pilot project was called "Seaflow".

It looked like an underwater wind turbine and it worked almost the same way. The difference: Instead of the wind, i.e. the flow of air, the tidal flow of the water was used.

In 2008 "Seaflows" successor "Seagen" went into operation off the coast of Northern Ireland. With its two turbines, the tidal power plant actually produced electricity, unlike its predecessor. The output was 1.2 megawatts, with which a good 1000 households could be supplied. It was the world's first commercially used tidal power plant. In 2019, the operator took it out of service after eleven years.

The most powerful ocean current power plant to date is "MeyGen", located between the Scottish mainland and the Orkney Islands. The first turbines have been supplying electricity since 2016. When fully expanded, MeyGen should be able to generate almost 400 megawatts of power.

Wave energy

The weather is an unpredictable factor, but it is crucial in another form of energy transport in the ocean: wave energy. There are different approaches to using this energy.

One of the oldest is the principle of the oscillating water column. The constant up and down of the water drives a column of air in a kind of chimney. As in an air pump, when the water rises, the air is pushed upwards through a turbine. When the water sinks, the air is sucked in through the turbine.

Sophisticated technology ensures that the turbine always rotates in the same direction in both cases. This avoids friction losses. The first prototype of a wave power plant went into operation on the west coast of Scotland in 2000 and delivered a peak output of 500 kilowatts, but is no longer in operation.

In the summer of 2011, the first commercially operated wave power plant followed in Mutriku off the Basque coast. The 16 turbines were integrated into the harbor wall so that the power plant can hardly be recognized as such.

However, the current yield is much lower than initially assumed. The power plant generates almost 300 kilowatts, which can supply an average of 250 households with electricity.

"Wave Dragon" and "Sea Serpent"

Two other techniques tested were "Wavedragon" (wave dragon) and "Pelamis" (Greek for sea serpent). At "Wavedragon" waves on the high seas sloshed over ramps into a higher reservoir. From this reservoir, the water flowed back into the sea, driving turbines in the process.

"Pelamis" consisted of several steel pipes that were connected to one another by movable joints. This steel pipe snake lay on the surface of the water, adapted to the wave movements and converted the movement into electricity.

Solution to the global energy problem?

The energy supply in the tides is huge, but it can only seldom be used economically. To be able to operate a tidal power plant, for example, you need at least a tidal range of five meters and a suitable bay. It is estimated that there are only a few dozen such locations worldwide.

In purely mathematical terms, a total of twelve gigawatts (one gigawatt = one billion watts) of electricity could be generated. This could only replace ten coal-fired power plants.

In addition, the energy is not continuously available, the peak load shifts from day to day, as does the high and low tides. There would therefore have to be ways to store the energy.

The problem of continuous energy generation occurs more intensely with wave power plants, as the weather plays a decisive role in these. Only a flow power plant supplies a reasonably constant energy and is independent of the weather. However, there are only a few pilot plants.

Nevertheless, the experts see the combination of various marine power plants as an important pillar of renewable energies. Compared to wind, sun and biomass, the use of energy from the sea is only just beginning.