Rance tidal power plant (France)
Dani 7C3 [CC BY-SA 3.0]
What is Ocean energy?
Did you know that oceans could provide us with electricity? We often hear about wind turbines or solar panels, but the ocean is also becoming a more a more popular renewable energy source.
There are two ways of capturing energy from it: by capturing the tide (movement of the sea), or by interacting with the waves created by the wind blowing on the water surface.
Waves travel vast distances across oceans at great speed. The longer and stronger the wind blows over the sea surface, the higher, faster and more powerful the sea is. Wave energy has the potential to be one of the cleanest energy in the future. The amount of energy it provides can be considerable and more consistent than the ones provided by wind or solar energy. Only on very few days per year are waves too weak to generate electricity.
Wave energy converters are used to change wave movements into electricity. The most famous one is called the “Pelamis”. It gets its name for a snake which is able to swim in the sea; as its shape and its movement looks like it is a big red metal snake floating in the ocean. Its lower part is emerged while its upper part stays out of the water.
The water has to be deeper than 50 meters for this metal snake to be able to “swim”; at least 2 kilometers from the coast, at most 10 kilometers from it. Its movement is created thanks to joints keeping all its 5 different tube sections together, enabling it to follow waves’ movements. The joints can go in two various directions, so they adapt to the waves’ movements. As waves pass down, the sections bend in the water and transform their energy into electricity. Then power is transmitted to shore using standard sub-sea cables and equipment.
On average one machine will provide enough power to provide electricity for 500 homes for a whole year.
Tidal energy is often confused with waves’ energy. Tidal energy is about taking energy from the movements of the water and converting it into electricity or other useful forms of power. The tide is created by the gravitational effect of the sun and the moon on the earth, causing movement of the seas that are always repeated the same way and create “high” and “low tide”.
Two different types of devices are used to capture tidal energy: tidal dam and tidal stream turbine.
Tidal barrage systems trap water when its level is high (high tide) in a bay or using an estuary. Water is then carefully released back in the ocean, going through turbines and creating energy. Those installations have been used for a long time and are well-known in the ocean energy field.
Tidal stream turbines are paced under water in order to capture the ocean movements, weather the sea level is getting higher or lower. The tide flows through the stationary turbines, making them turn like wind turbines do.
Those devices are new and they have yet to prove their efficiency. However, the world’s first commercial tidal power generating device was installed in Strangford Lough, Northern Ireland and the market is developing.