It has become apparent that alternatives must be found to fossil fuels that are both renewable and kinder to the environment, of which the wind and tidal power are two possible alternative sources of energy to wean humanity from its dependence on fossil fuels. Tidal power is caused by the gravitational pull of the moon and the sun on the seas and oceans whereas wave power is generated by the wind. These examples of renewable energy are thought to have advantages over other types of renewable energy such as the wind and solar energy that can provide inconsistent results.
The power of waves is a promising source of sustainable energy, a resource of enormous potential considering the seas and oceans are in a continuous state of motion. Waves are generated by the transfer of wind energy onto the water surface. Therefore, the power of waves is dependent upon the force with which the wind interacts with the water while the wind’s power and direction are influenced by areas of low and high pressure caused by solar radiation. The apparatus required to harness the energy of waves is known as a Wave Energy Converter (WEC) and comes various forms.
One type of WEC is installed on the coast where the waves crash into the shore and involves a container with an opening at the bottom that allows seawater to enter and exit with the incoming and outgoing waves. As the water level in the tank rises and falls the air pressure inside the container increases and decreases. The airflow caused by the changes in air pressure drives a turbine that, in turn, generates electricity. The Islay Limpet, installed on the Isle of Islay in 2000, is an early example of this technology and is capable of producing 250 kilowatts of power.
In 2013, plans were drawn to create a wave energy farm off the shore of Lewis in the Outer Hebrides capable of producing 40 megawatts of electricity sufficient to power 30,000 homes. It is predicted that the infrastructure, including state-of-the-art Oyster devices and interconnector, will be up and running by 2017. The Oyster WEC, an earlier example being installed near Orkney and connected to the grid in 2009, operates in shallow coastal waters and consists of a shell attached to the seabed and a flap that catches waves and drives a piston that pumps water to an onshore generator.
The tides, controlled by the gravitational pull of celestial bodies and influenced by such factors as the tilt of the earth on its axis, are a clean, predictable and sustainable source of energy. Tidal energy, if utilised to its full potential, could revolutionise the future of power generation and prove one of the most reliable forms of renewable energy available. With investment in infrastructure, technological improvements and solutions to practical obstacles on the cards increasing numbers of future homes and workplaces look like they will be powered by tidal energy.
The Rance Tidal Power Station, straddling the Rance Estuary in the French province of Brittany, went down in history as the first tidal power station when it was opened in 1966. This tidal barrage, harnessing the tidal energy of the waters flowing into the river at high tide and ebbing out into the English Channel at low tide, functions in a similar fashion to a hydroelectric dam with the tidal energy driving 24 turbines that generate between 62 and 240 megawatts of electricity. Similar designs appeared at other locations such as Kislyaya Guba in Russia and Shiva Lake In South Korea.
Tidal Stream Generators represent the cutting edge of Tidal Energy Conversion technology and in simple terms can be compared to submarine wind turbines, harnessing the power of underwater tidal currents instead of the power of the wind. These contraptions are capable of generating several hundred times more power than wind turbines, with more predictable results, and could prove a major contender to traditional energy sources. Problems, other than initial installation costs, facing this technology include ongoing service expenses caused by such issues as salt water erosion.
The predictability of the tides makes tidal power a reliable form of renewable energy while the ubiquity of waves in the seas and oceans presents a nearly inexhaustible source of energy if exploited to its full potential. While the ebb and flow of the tides are poised to follow a similar course for millions of years, the winds that drive the waves are less predictable, meaning wave power could prove more chaotic than tidal power. The strength of tides is influenced by the lunar phases, with tidal power generated depending on the strength or weakness of the moon’s gravitational pull.