Renewable electricity generation in Ireland is provided by wind (35%); hydro 2.9%; and with solar gaining traction. Marine energy is not contributing to the national grid. While research into both tidal-stream and wave energy is ongoing, as described in the excellent Engineers Ireland webinar 'Preparing for the third wave of ocean energy' on May 31, 2024, we do not have, as yet, “turbines in the water”.
Tidal stream turbines are similar to wind turbines. However, due to the relative densities of seawater and air, they produce more electricity than wind turbines of similar size. Another advantage of tidal stream energy is its predictability as opposed to the intermittency of the wind.
Tidal-stream turbine deployment is slow worldwide, primarily because of maintenance issues. Research is ongoing to address those issues. Tidal-stream electricity is contributing, albeit to a limited extent, to the UK grid.
As previously stated, the contribution of tidal-stream electricity to the Irish grid is zero. This is a cause for concern as the first grid-connected tidal-stream turbine worldwide was deployed in Strangford Lough in Northern Ireland. The Strangford Lough site is now vacant. Is it now time to reactivate this local source of renewable electrical energy?
Peter Fraenkel and Marine Current Turbines
It may be stated with a high degree of certainty that the tidal stream electricity generation sector in the UK and Ireland was started by Marine Current Turbines Ltd (MCT) and its technical director, Peter Fraenkel. He became involved in harnessing tidal energy for the production of electricity in the 1970s and 1980s and was an early advocate for government involvement in the promotion of clean energy projects.
MCT was founded in 2002 and is based in Bristol. Siemens became the leading shareholder in MCT in 2012. Fraenkel reports on an early implementation (2003) of a turbine deployment, called Seaflow, by MCT in a depth of 25m some 1.1km off the Foreland Point Lighthouse in Devon, England. This is claimed to be the world’s first offshore tidal current turbine, this was experimental only and did not supply power to the national grid.
The Strangford Lough demonstration project
Informed by the experience gained from the Seaflow project MCT made an application in 2005 for a Food and Environmental Protection Act (FEPA) licence to the Northern Ireland Environment and Heritage Service, to allow the deployment of a demonstration tidal device in Strangford Narrows for an initial period of five years. Following an Environmental Impact Report by Royal Haskoning, the application was granted and the device, called SeaGen, was installed in 2008, see Figure 1. Strangford Lough was chosen for the project because of its fast flowing tidal currents (up to 4m/s).
The installation consisted of a fixed base with two 600KW turbines mounted on crossbeams which could be raised and lowered. The project was initially approved for a five-year life cycle. This was later extended by a further five years. Decommissioning started in 2016 and was completed in 2019.
Figure 1: SeaGen in Strangford Lough. Image: TETHYS.
An evaluation of SeaGen
This evaluation considers the environmental impact, the amount of power delivered to the grid, and the quality of that power. Power production started in 2008. Output was, initially, very limited for two reasons:
- Some initial technical problems
- Environmental restrictions
Regular production started in 2009. A study entitled 'Marine tidal energy: A case study in legislative challenges and environmental impacts', presented at an EEE Conference on Technologies for Sustainability (SusTech), in 2014 reported SeaGen as producing 8GW/h between 2008 to 2014.
A study 'Power Quality Performance of the Tidal Energy Converter, SeaGen', presented at the 30th International Conference on Ocean, Offshore and Arctic Engineering Sweden ASME 2011 was undertaken between 2008-2011. Data was collected over a 35-day period between January 9, 2010, and February 17, 2010.
In a 34-day period, 186.1MW/h was generated with one turbine being down for five days. During that time environmental restrictions allowed the turbine to be operative during daytime hours only. That restriction was removed in the summer of 2010.
The study reported on Power Quality (PQ); Frequency; Voltage imbalance; Flicker; and Third Harmonic Distortion (THD) are reported as being compliant to the relevant standard.
Fraenkel of MCT, presented a paper 'Development and testing of Marine Current Turbine’s SeaGen 1.2MW tidal stream turbine', at the third International Conference on Ocean Energy, on October 6, 2010.
Fraenkel reports that while that it took from July 2008 until March 2010 (20 months) to generate 1,000 MW/h into the grid, it then only took from March 2010 to the end of July 2010 (less than five months) to deliver a further 1,000MW/h. This indicates that as initial environmental restrictions were relaxed, and initial technical issues addressed, the system approached its potential.
Regarding the environmental impact, a report 'Strangford Lough and the SeaGen Tidal Turbine' published in Marine Renewable Energy Technology and Environmental Interactions stated that only minor statistically significant changes in animal behaviour patterns were recorded and that these changes were ecologically of little significance.
Conclusion
Strangford Lough presents as an ideal location to 'kick-start' the tidal sector in Ireland. There is no doubting the challenges of the marine environment. Dealing with those challenges requires taking the research from the laboratory to the marine environment. This provides the facility to generate electricity while researching the issues. The regeneration of a tidal-stream power station in Strangford would appear to have local support.
The MP for Strangford, Jim Shannon, speaking in the House of Commons on January 10, 2023, said: “With a current of more than 2.5 metres per second, Strangford Lough has obvious potential for a tidal stream, which is why there was a trial there with the 2008 SeaGen project.
"I was a member of the Northern Ireland Assembly then, as were some of my honourable friends, and a member of Ards Borough Council. It was an incredibly successful pilot scheme, but it never seemed to go anywhere.”
Since the deployment of SeaGen the technology has evolved. While SeaGen required to be fixed to the sea floor some of the latest systems such as Orbital 02, see Figure 2, provide floating platforms. Such systems are simply floated into a location in the tidal stream and secured to the seafloor by anchors. This provides a much faster deployment.
Figure 2: Orbital O2. Image: Orbital Marine Power.
According to the European Marine Energy Centre (EMEC) Orbital O2 has the ability to generate enough clean, predictable electricity to meet the demand of about 2,000 homes and offset approximately 2,200 tonnes of CO2 production per year.
In summary, Strangford has the tidal-stream resource, the environmental impact study is completed, and the technology is available, so surely now is the time to exploit it?
Author: Michael Barrett has 30 years of experience as a lecturer and researcher in electrical systems. His research interests focused on tidal-stream electricity generation for which he was awarded a PhD by the University of Sunderland.