Ocean energy has the potential to provide a substantial amount of sustainable, renewable energy around the world. Find out more about the key technologies.
Waves are formed by winds blowing over the surface of the sea. The size of the waves generated will depend upon the wind speed, its duration, and the distance of water over which it blows (the fetch), bathymetry of the seafloor (which can focus or disperse the energy of the waves) and currents. The resultant movement of water carries kinetic energy which can be harnessed by wave energy devices.
The best wave resources occur in areas where strong winds have travelled over long distances. For this reason, the best wave resources in Europe occur along the western coasts which lie at the end of a long fetch (the Atlantic Ocean). Nearer the coastline, wave energy decreases due to friction with the seabed, therefore waves in deeper, well exposed waters offshore will have the greatest energy.
Much like onshore wind energy, offshore wind energy provides a clean, sustainable solution to our energy problems. It can be used as an alternative to fossil fuels in generating electricity, without the direct emission of greenhouse gases. As there will always be wind, it is inexhaustible and renewable.
Ireland’s wave energy resource
A detailed assessment of Ireland’s wave energy resource was performed in 2005. This study looked at the theoretical and accessible levels of wave energy in Irish waters. The study indicated that a theoretical wave energy resource of up to 525TWh exists within the total limit of Irish waters. For comparison, in 2006 the Total Electricity Requirement for the Republic of Ireland (ROI) was 27.8TWh of electricity.
More recently the Offshore Renewable Energy Development Plan published in 2014 identified a total development potential of 31,100MW of wave energy in Ireland that could be extracted without having likely significant adverse effects on the environment.
The amount of this resource which Ireland ultimately realises will depend on the:
- The cost effectiveness of the wave energy technology.
- The amount of power which can be practically connected to the network from the western seaboard locations.
- The amount of capacity available on the network when other intermittent generation sources such as onshore/offshore wind energy are considered.
- Impacts on the environment and Interactions with other users of the marine resource.
Wave energy converters
There are a range of devices suitable for location in the nearshore and offshore environment. All wave energy converters (WECs) comprise a sub-surface component (moorings, lines, anchors, foundation) and some have a surface or above surface component). WECs may be installed as a single device or an array of devices depending on the technology. There are a range of devices currently being tested and the technology remains novel. Ireland's wave resource is greatest on the west, south and north coast where environmental conditions are more extreme.
- Point Absorber
- Over-topping Device
- Oscillating Water Column
- Submerged Pressure Differential
- Oscillating Wave Surge Converter
- Water Pressure/ Bulge Sytems
- Rotating Mass Point Absorber
Tidal streams are created by the constantly changing gravitational pull of the moon and sun on the world’s oceans. Tides never stop, with water moving first one way, then the other, the world over. Tidal stream technologies capture the kinetic energy of the currents flowing in and out of the tidal areas. Since the relative positions of the sun and moon can be predicted with complete accuracy, so can the resultant tide. It is this predictability that makes tidal energy such a valuable resource.
The highest (spring) tidal ranges are generated when the sun, moon and earth are in line. Water flows in greater volumes when attracted by this combined gravitational pull. The lowest (neap) tidal ranges are generated when the sun, moon and earth describe a right angle. The split gravitational pull causes water to flow in lesser volumes.
Tidal stream resources are generally largest in areas where a good tidal range exists, and where the speed of the currents are amplified by the funnelling effect of the local coastline and seabed, for example, in narrow straits and inlets, around headlands, and in channels between islands.
Ireland’s tidal energy resource
In 2005 SEAI undertook a review of the tidal resource in Ireland. This report identified a number of areas around Ireland coastline suitable commercial for tidal deployment, primarily the East coast, and Shannon estuary.
- In 2014 the Offshore Renewable Energy Development Plan, designated the following areas as suitable for tidal development:
- South East coast
- Shannon Estuary
- North West coast
A total development potential of 3000MW of tidal energy was identified across these areas. SEAI is now working to develop more specific resource assessments for these areas.
Tidal energy devices
Tidal devices are located in tidal streams, such as narrow straits and inlets, around headlands, in channels between islands. Devices are mainly subsurface but there may also be a surface component. A single or a number of devices may be located within a tidal stream. Ireland tidal stream resource is limited, the best locations being on the north and north east coast, and discrete sites such as the Shannon Estuary.
- Horizontal axis
- Vertical axis
- Reciprocating Devices (Oscillating hydrofoils)
- Venturi effect
- Archimedes Screw
- Tidal Kite
Offshore wind farms
Ireland has one of the best resources in Europe for harnessing offshore wind energy. The east coast of Ireland has sufficiently shallow water depths to allow for fixed foundations turbines, while floating structure may be more appropriate for many sites off the south, west and north-west coasts.
According to the Offshore Renewable Energy Development Plan(OREDP) Ireland has the potential for up to 4.5GW installed capacity of offshore wind by 2030, without having a likely significant impact on the environment. In general terms this means that Ireland’s offshore wind industry alone could power 4.5 million homes per annum
Currently there is only one offshore wind farm in operation in Irish waters. The SSSE Renewables Arklow Bank wind farm consists of seven turbines with a total installed capacity of 25 MW. The sites lease includes provision for up to 200 turbines (525 MW) in total. Other projects under development of the Irish east coast include:
- Oriel Wind Farm – consent for 55 turbines (330 MW)
- Dublin Array – application for 145 turbines (725 MW)
- Codling Wind Park – lease for 220 turbines (1100 MW), application for a further 200 turbine
Offshore turbine devices
Most offshore turbine devices are horizontal axis devices, however vertical axis systems have also been proposed and tested. The platforms on which the turbine sits can vary as per descriptions below. To date, all commercial offshore wind installations have been on fixed platforms- but more research is being done on floating platforms so that technology can move further offshore.
- Horizontal Axis Turbine
- Vertical Axis Turbines