OpenHydro and Alderney Renewable Energy intend to harness the energy in the notoriously dangerous waters around Alderney to generate enough electricity to power 150,000 homes, writes Michael Lewis
Elec

 

Author: Michael Lewis, project manager – development projects, OpenHydro

“The main navigational challenge in the Channel Islands is the very strong tidal streams. The notorious Alderney Race reaches 8 knots at times. The golden rule here is to work passages with tidal streams in your favour” – Channel Islands Navigation and Pilotage (courtesy alphatozulu.com)

Marine pilotage books and charts of the waters around Alderney urge mariners to proceed cautiously through the Alderney Race. For as long as people have been taking boats out on these waters, they have respected its massive energy. The key to operating successfully in these conditions is to work with these powerful tidal streams.

OpenHydro and Alderney Renewable Energy (ARE) have recently formed Race Tidal Ltd to do just that. Together, these two companies intend to harness the energy in the waters around Alderney in order to generate enough electricity to power 150,000 homes. The formation of Race Tidal is the first step in a complex and challenging process to develop a 300 MW tidal energy array. This will be one of the largest tidal energy arrays in the world when it is constructed in 2020.

The project we are embarking upon to achieve that goal will involve the integration of work packages carried out by a multi-disciplinary team located in Ireland, France, the United Kingdom and Alderney.

Taking advantage of the energy stored in the tides is certainly not a new concept. In fact, there is evidence that tidal barrage-style mills were in operation as far back as Roman times. These mills made use of the tide by trapping water in reservoirs when the tide was high, and then allowing the water to exit through waterwheels as the tide went out. The waterwheels provided the mechanical power to mill grain.

This barrage concept was developed further in the 1960s with the building of the Rance Tidal Power Station in France. Operational since 1966, this was the first large-scale tidal power station in the world and remains one of the largest. Operating on the same principle as the Roman mills described above, the ‘waterwheels’ at La Rance are 24 massive turbines, each rated to produce 10 MW.

Similar tidal power stations are now in operation across the world including Canada, Russia, South Korea and China. The power generated is renewable and clean, but the ecological and visual impact of these developments is significant. Large areas are flooded to create the reservoirs and significant ecological impacts result from the presence of the barrages.

IN-STREAM TIDAL

Image 1: OpenHydro deployment methodology overview (click to enlarge)

One technology that has recently emerged is in-stream tidal generation and OpenHydro is a world leader in the development of this industry. These turbines are located in the tidal flow, where they extract energy from the flow of water associated with the tides. This resolves many of the environmental issues associated with barrage generation, as there is minimal impact on the flows around the turbines and there is no requirement for significant civil works like dams or reservoirs. In the case of the OpenHydro technology, no infrastructure is visible above the surface of the water.

The OpenHydro Open-Centre Turbine is a horizontal axis device, which is placed directly on the seabed using a gravity base. No seabed preparation is required and the entire system can be deployed within a single tidal cycle. The turbine uses a permanent magnet generator, with magnets mounted around the outside of the rotor and electrical windings fitted in the support structure.

As it is seawater lubricated, the turbine requires no harmful lubricants or complex sealing and is an extremely simple means of extracting energy from the sea.

OpenHydro and ARE have a long-established relationship and will bring their complementary expertise to the project. Alderney is the most northerly and the third largest of the Channel Islands. It is separated from the French coast of Normandy by a 10-mile-wide stretch of water known as the Alderney Race, or the Raz Blanchard in French.

Image 2: Alderney Development Zones (click to enlarge)

OpenHydro and ARE have a long-established relationship and will bring their complementary expertise to the project. Alderney is the most northerly and the third largest of the Channel Islands. It is separated from the French coast of Normandy by a 10-mile-wide stretch of water known as the Alderney Race, or the Raz Blanchard in French.

ARE has secured rights to the seabed around the island, for the purposes of installing and operating tidal energy projects. The area in question is shown in Image 2, with the areas for which ARE has secured the rights highlighted in red.

DEVELOPMENT WORK

1.              Hydrodynamic conditions

Race Tidal is preparing to install a number of instruments called acoustic doppler current profilers to measure the flow characteristics at discrete points around the island. As well as the tidal flows, these instruments will capture information about the wave environment, turbulence phenomenon and the profile of the flow through the full depth of water.

These measurements will be supported by leading-edge 3-D modelling of the flow regime, which will allow a full picture of the characteristics of the tidal flows across the entire area under investigation. The data gathered from this work package is essential to ensure our detailed understanding of the site conditions, to inform equipment design and array location and to economically assess the project.

2.              Seabed conditions

Image 3: Typical bathymetry chart

It is essential that a detailed picture of all aspects of the seabed is established. To achieve this, we will complete complex surveys of the site. These surveys use multi-beam echo sounder, side scan sonar and magnetometer to accurately assess the bathymetry and geological characteristics of the area. This provides high-resolution depth and slope data, identifies seabed features and checks for the presence of any metallic objects on or under the seabed, such as cables, shipwrecks or unexploded ordinance. The data from these surveys can be used to create charts similar to the example shown in Image 3.

3.              Environmental baseline assessment

To accurately assess the potential impact of the project on the environment, it is essential to have an understanding of the baseline conditions. This baseline assessment will include surveys and studies of benthic habitats (understanding marine life on the seabed), abundance of seabirds, fish and mammals in the waters, assessing marine traffic and understanding any significant archaeological features.

The programme of work to establish this information will be carried out over a two-year period and will require the input of experts in all those fields.

4.              Consenting process

The consenting process for this project is about demonstrating to all relevant stakeholders that there will be minimal environmental impact resulting from the project. Important aspects to consider include the installation, operation, maintenance and decommissioning of the turbines, balance of plant and onshore infrastructure. In Alderney, the process will be governed by the States of Alderney, with input and guidance from the various environmental organisations in the region.

OpenHydro is currently going through the consenting process for two other major tidal energy projects, in Northern Ireland and Scotland. A key factor in both of these projects is the need to engage with the local stakeholders early in the process. Different needs and concerns must be addressed in the development of the project and in the consenting process.

5.              Grid access and connection

With fewer than 2,000 people resident on the island, the electricity load of approximately 1.5 MW is currently being served by three diesel generators. While there is a demand for this generation to be replaced by predictable, clean and renewable tidal energy, the local needs are a fraction of the generation potential from this project.

Therefore, we plan to align turbine installation with that of the FAB Link connector. This interconnector is being developed by ARE and Transmission Investment LLP, with the support of French grid operator Réseau de Transport d’Électricité (Electricity Transmission Network). This connector is expected to be in place by 2020 and will link the south coast of Britain, through Alderney, to the north coast of France. Linking the Race Tidal project into this interconnector will provide a route to two major markets for renewable energy.

PROJECT BUILD

Image 4: Artist’s impression of OpenHydro open-centre turbine array

After the completion of the development phase, the project build will be initiated. A development of this scale will result in a lot of activity on the site and at manufacturing facilities supporting the project. OpenHydro, through its parent company DCNS, is developing a manufacturing facility in the nearby French port of Cherbourg. This will be used as a manufacturing and mobilisation base for the turbines of this project.

Installation of the turbines will utilise OpenHydro’s unique deployment methodology. OpenHydro have extensive experience successfully installing turbines on the seabed. The technique employed allows the operation to be completed within a single tidal window, which is essential in very energetic locations like the Alderney Race.

As Race Tidal embarks on the development of one of the largest tidal energy arrays in the world, we are looking ahead to the challenges that this project will bring. The build of a 300 MW power station would be a significant project on land but at sea, the difficulties involved are multiplied many times over.

In an environment such as the Alderney Race, preparation is absolutely integral to the overall success of the project. In devoting time and resources to the development phase, we can harness the unique conditions that the Alderney Race provides and in doing so provide renewable energy that is silent, invisible and predictable, for generations to come.

After graduating from DIT Bolton Street with a degree in mechanical engineering in 2001, Michael Lewis left Ireland to work for Rolls-Royce in the UK. During his nine years there, he worked primarily in aircraft engine development and gained chartered status with Engineers Ireland and IMechE. After taking a year out to take part in a round-the-world yacht race, Lewis returned to Ireland in 2011 to work for OpenHydro, where he now works as project manager in its DevelopmentsProjects team. He is also studying part-time for a Master’s in Engineering Management in UCD.

 

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  Author: Michael Lewis, project manager - development projects, OpenHydro “The main navigational challenge in the Channel Islands is the very strong tidal streams. The notorious Alderney Race reaches 8 knots at times. The golden rule here is to work passages with tidal streams in your favour' - Channel Islands Navigation and Pilotage...