WAVE AND TIDAL POWER
Wave and tidal power are relatively undeveloped forms of renewable energy. The ocean covers 70% of the world's surface and is considered an untapped source of renewable energy. The potential of the ocean to supply the world with green energy has generated huge interest for years, with world governments and companies investing millions into this field.
Below explains the two different forms of energy, the various types of wave and tidal devices available and their potential for use in Ireland.
There are several issues that arise when renewable energy is installed out at sea rather than on land. The devices must deal with more extreme weather conditions which has the potential to greatly damage the systems. The salt water is corrosive towards most materials which makes it difficult to create a long lasting wave energy device. Marine life such as barnacles attaching to the devices could also me a major issue.
There are also concerns about the environmental impact of wave energy. Some devices employ the use of underwater turbines which could potentially damage all kinds of marine life. Further research is required to fully determine the effects.
Wave power is unique in that energy is created in pulses with each wave. The waves are used to spin turbines. It is proving to be difficult to effectively harness this type of energy as power generators require a continuous source of energy. Wave power only spins the turbines for several seconds at a time. This is not sufficient to generate enough usable electricity. Due to this limitation there have been many creative devices in efforts to successfully harness wave energy. A few examples are included below.
This device is known as an absorber and it extracts energy from the rise and fall of the waves using a buoy as is pictured The absorber is part of a category of wave energy devices known as oscillating bodies.
As the name suggests these devices capture the oscillating up and down motion of the waves. They use vertical motion to harness energy. Several of these devices can be linked up to generate electricity.
Wave overtopping devices consist of a reservoir which captures water as the waves break. The water then leaves the device through a hole in the bottom which contains a turbine, turning the turbine which results in the production of electricity.
Multi-story wave overtopping devices are being developed which allow for greater collection of water. They could also function as a buffer to waves if placed along the coastline.
Oscillating Water Column
These devices are partially submerged under the water. Incoming waves travel into the capture chamber and compress the air within. As the wave leaves the air depressurizes.
This constant cycle of pressurization and depressurization of the air turns a connected turbine, generating electricity.
Tidal turbines operate in the same way as wind turbines, and often look quite similar.
They consist of a large turbine situated underwater which is located within a tidal stream. When the tide changes the constant stream of water turns the turbine generating electricity. Most operating tidal power prototypes consists of a variation of a tidal turbine. The main tidal turbines being developed today are axial-flow, cross-flow and ducted turbines.
These turbines turn slower than wind turbines but water's greater density compensates for this, with tidal turbines capable of generating a similar amount of electricity as wind turbines.
Oscillating hydrofoils consist of a hydrofoil wing attached to a lever. The flow of a tidal stream over the hydrofoil generates lift underneath the wing which causes the lever to rise.
At the maximum of the rise the direction of lft changes, causing the arm to move in the opposite direction.
These oscillations can be used to drive hydraulic fluids which in turn can power a generator. thereby generating electricity.
This technology is not as researched as other forms of tidal power and so not much is known about their efficiency or practical application.
Tidal kites consists of a small turbine attached to a hydrofoil which is tethered to the seafloor. The device can move freely with the tether, allowing it to be directed into the tidal stream.
This increased motion increases the speed of the flow through the turbine, allowing for smaller turbines to be employed.
Tidal range devices take advantage of the natural height difference between high and low tide. Water at high tide is captured in a reservoir. This water is then released during low tide through a series of turbines, similar to a hydroelectric dam.
Tidal barrages are an example of a tidal range device, with several in use around the world today. These barrages essentially create a basin of water, although concerns exist due to environmental damage as well as high upfront capital costs.
There have been several attempts to install commercial wave-farms worldwide, in order to prove the viability of them as a renewable energy source. These have been met with mixed success. Some of these farms had to be shut down or deployment abandoned due to financial or technical difficulties. Wave power has been successfully generated, but has never resulted in sustained generation because of the aforementioned reasons.
Tidal power is in a similar position globally to wave power with regards to commercial use. A tidal power station has been successfully operating in Brittany, France since 1966. Environmental and financial concerns have hindered progress since then.
The wide-scale commercial use of wave and tidal power is still several years off although progress is positive and advancing quickly. Power from the ocean is still more expensive than other renewable energy sources but many organisations and governments are trying to change this. This is of particular interest to Ireland as our seas have been identified as a major potential producer of wave and tidal energy.
Below are links to several websites with some more details about the technologies and progress of research in Ireland and abroad.
IWEDA: Irish Wave Energy Developer's Association
The IWEDA is an organisation committed to the research and development of wave energy as a commercially viable sector in Ireland. They have great information on wave energy in Ireland, including a list of the various developers of new wave technologies.
Ocean Energy Ireland
Ocean Energy Ireland is a branch of SEAI that is heavily involved in ocean energy research. They have numerous test facilities which allow trialling of wave and tidal energy prototypes.
Ocean Energy is a US company which is leading the development of wave technologies. The website provides more information on the actual mechanics of their wave energy system.
They plan on setting up one of their devices on the West coast of Ireland in a joint collaboration between the Irish government and the US's Department of Energy.