- What is Tidal Energy?
- What are the different potential harnessing technologies?
- What are the latest developments both in Ireland and within the industry?
- How much of a contribution could Tidal energy make to Irelands' Future energy needs?
- Are there any commercial Tidal energy projects in operation?
- What are the potential environmental impacts that need to be considered
In the main, there are two types of tidal harvesting technology namely, tidal barrage and tidal stream turbines.
- Tidal barrage systems involve the trapping of water at high tide, most commonly at a point near the mouth of a river estuary or a bay, followed by the controlled release of the water back to the sea through turbines working on essentially the same basis as an upstream hydroelectric dam.
- Tidal stream turbines harness the power of both the inflows and outflows of tidal energy. The tide flows through the stationary turbines, causing them to turn using the same principal as a wind turbine. There are various different designs of tidal stream turbines such as seabed standing and surface floating designs
While tidal barrage technology is a firmly established technology* tidal stream technology is in its infancy.
Recently however**, the world's first commercial scale tidal power generating device has been installed in Strangford Lough, Northern Ireland. A UK company have designed and developed a tidal stream device known as SeaGen. The device is currently in the commissioning and testing phase. It is estimated that the 1.2 MW tidal stream device will be capable of providing enough clean electricity to power 1,000 homes.
*The Tidal Barrage system on the Rance River in France has been in operation fro over 30 years **Information correct on 07/07/08
Sustainable Energy Ireland’s report “Tidal and Current Energy Resources in Ireland” states that the majority of Ireland’s tidal power potential lies on the west coast of Ireland, with the most potential concentrated in the Shannon estuary.
Shaw, M. 2004, “Tidal and Marine Energy Resource in Ireland”, Sustainable Energy Ireland, estimates that the theoretical resource for tidal energy in Irish waters is predicted to be 230,000 GWh/year. However the practical resource is estimated at just 2633 GWh/year.
Furthermore, based on the currently available tested prototypes, the economically viable estimate for the resource is 915 GWh/year representing a mere 8% return for a 20 year project to provide 2% of future predicted needs. However, with further technological advancements, tidal energy may yet prove to be a crucial component of Ireland's renewable generation portfolio in the future due to its high predictability of peak and trough generation.
This predictability has the potential to offset the intermittent nature of other green renewables such as wind and wave energy, thus reducing the amount and scale of costly measures aimed at ensuring security or supply in times of very little or zero wind or wave generation.
While there are a number of tidal barrage systems currently in operating around the world, most notably on the Rance river in Bretagne in the north of France, there are currently* no commercial tidal turbine stream arrays fully in operation.
*As of 07/07/08
In terms of barrage tidal systems, all of the associated environmental impacts and risks associated with dam building and the creation of an artificial lake have to be considered. For example, will the barrage system have an adverse impact on certain fish species by cutting off access to spawning grounds?
Other impacts such as the change in nature of the habitat behind the dam, the possible presence of stagnant water and silt build ups need to be assessed in terms of their effect on the health of both the people and wildlife in the surrounding area. The possible impacts of tidal stream turbine systems are for the large part unknown. There has been little research on the long term effects of such structure due mostly in part to the infant nature of the industry. Possible impacts that should be considered when it comes to large scale deployment are: Navigational hazarding, fish mortality, disturbance of the complex current flows in shallow waters, proximity to leisure areas and effects on sand drift.