Wind energy, and wave energy, is driven by the heating and cooling of the planet as it rotates about its axis. Ultimately wind and wave energy are simply a converted form of solar energy from the sun’s rays falling on us and are dictated by the sun and the planets weather systems. There is huge energy potential to be extracted from these natural resources but as is frequently discussed one of the key problems is predicting the availability of this resource at any given time. It is relatively easy based on use of measurement and historical data to say for any given year how much energy a wind farm or a wave farm may produce. What is not easy is to predict how much energy it will be producing at any given moment

By contrast tidal energy is not converted solar energy it is driven by the rotation of the planet and the gravitational forces resulting from the proximity of the moon and to a lesser extent because of its enormous distance from us the sun. As navigators have known for many years this means that the tides can be predicted with great accuracy and not just a day ahead but years, or even tens or hundreds of years in the future. For a tidal farm then, once the relationship is determined between the speed of the tidal flows across the site, and the energy that the devices installed can extract from that flow yield predictions can be predicted many years ahead.

No these are entirely separate projects and separate developers. However, we are communicating with SSE Renewables in respect of the cumulative impact assessment which is necessary because of the close proximity of the proposals.

Given the disparity in size of the SSE Islay Wind Farm 690+MW and our current West Islay Tidal project at 30MW there is no common grid solution plan between the two projects. At a larger scale a common grid connection strategy might make sense but this would depend on timing of build. We understand that SSE Islay Wind Farm are looking at an HVDC convertor station but whether this is the best solution is something of an unknown.

There are many elements to this question but in relation to the available resource, the tides off West Islay are strong over a large area and are largely bidirectional i.e. the ebb and flood tides are almost 180degrees opposed. This is not always the case and a number of tidal sites have flows of 30 degrees different between the opposing tides. This can cause problems with yield loss because the technology needs to deal with quite different approach flows.

West Islay Tidal Energy is a joint venture between DP Marine Energy Ltd (DPME) a renewable energy developer part of the DP Group of companies and DEME Blue Energy (DBE) part of the DEME Group.

DP Marine Energy Ltd (DPME) is part of the DP Group and one of a number of privately owned energy companies which operate under the DP Energy name. All of these operate in the field of renewable energy and it is a fundamental principle of the businesses that all their developments are both sustainable and environmentally benign. The director/owners of the DP Energy businesses have been developing renewable energy projects for some 20 years.

DPME was formed in 2008 specifically to assess the resource and develop both tidal and wave energy sites worldwide albeit with an initial focus on UK, and Irish Waters. DPMEs initial focus has been on tidal energy generation and following a UK wide site selection exercise identified the West of Islay site as having potential for a commercial tidal energy development. F

or the West Islay project DPME will be managing site development and leading the consents process. Further information is available at www.dpenergy.com.

DEME Blue Energy (DBE) is part of the DEME Group. DEME is a marine construction group with roots going back 150 years. DEME is one of the leading contractors in the marine construction sector and one of the pioneers in the development of offshore wind energy. The DEME group has significant in-house resources for marine construction and installation works including a large specialised fleet and support plant and equipment. DBE was established to develop and invest in Blue Energy (wave and tidal energy) projects. DEME has gained direct tidal installation experience as part of the installation team for the SeaGen device, the first commercially operated tidal turbine at Strangford Lough in Northern Ireland. Further information is available at www.deme.be

The current proposal to build one of the world’s first commercial scale tidal energy parks at 30MWs in the waters off the tip of the Rinns of Islay – anticipating construction in 2016/2017.  Although the current proposal is for a 30MW project the ultimate goal is (subject to further consents and agreement from lease with The Crown Estate) to build a multi-hundred MW tidal farm (up to potentially 400MW). This larger aspiration is likely to be 2019+ subject to the consents, an agreement for a larger lease area and the availability of grid capacity.

One of the key objectives of the West Islay Tidal proposal was to develop a commercial scale project of multi-hundred MWs and that means having a large enough area to deploy multiple turbines without dominating the flow or the environment.

The West Islay tidal flow is generated by the waters flooding in and ebbing out of the Irish sea via the North Channel being forced vertically over the shallower waters formed by the Rhinns spur projecting out many kilometres into the sea. By contrast the flow developed across the Sound Of Islay project is derived from the physical horizontal constraint between the two land masses of Islay and Jura.

A number of other sites are being developed in similar constrained environments including the Siemens MCT projects at Kyle Rhea project further North, or the Strangford Lough Project in Northern Ireland both of which are either under development or in the case of Strangford Lough already have a deployed turbine.

The Strangford Lough resource is very strong but has space for only perhaps another 3 or 4 machines (6MW), Kyle Rhea is expected to be similar and proposed with 4 machines (8MW). The Sound of Islay project is limited on capacity currently to 10MW.

Horizontally constrained sites have significant advantages in respect of a very benign wave regime but are constrained on space and navigation. The West of Islay Tidal located as it is in open water is essentially unconstrained navigationally, has a large area of resource, and our assessment estimates there to be potential for up to 400MW of installed capacity.

The conditions are challenging for any kind of human activity in the waters off the west coast of Scotland whether that is for energy extraction, fishing or simply operating a vessel. The site has an excellent tidal resource but it also has significant potential for extraction of wave energy. The Limpet Wave Device one of the world’s first grid connected wave energy devices has been located and operating near Portnahaven for a number of years.

Stormy weather and the resultant heavy seas has a number of impacts on the development which necessitates planning and design consideration.

 

Interference with installation works during construction – increased downtime

Increased Surge loads on the turbine foundations – stronger designs

Increased fatigue loads on power train – stronger blades and operational constraints under severe conditions

Reduced vessel accessibility during operation – strategic and preventative  maintenance planning  

Ultimately engineering solutions can be provided to ‘almost’ anything and are under development. The challenge is to ensure that these solutions are cost effective and that is one of the reasons the approach to the consenting is technology neutral and with various options under consideration for support structures.

The application for consent will cover a number of different turbine types under a “design envelope”. This will provide some flexibility in selecting the most appropriate turbine for the site at a later date.

Although the tidal industry is starting to consolidate on a fundamental design for large machines which is a Horizontal Axis three bladed Open Rotor design (Siemens, Alstom, Voith, Andriz, Kawasaki, Atlantis etc.) there are still a number of areas where further development to reduce costs is important. This includes foundation and support structure design.

By a Technology Neutral Approach we mean that unlike many of the applications for consent for tidal farms we are not tied to any one manufacturer or to any one specific technology type. That means when we undertake an environmental assessment we have to consider a wider range of impacts than if we simply picked a Siemens MCT Seagen, or an Alstom TGL, or Hammerfest Strom (like that utilised in the Sound of Islay) device.

It is probably worth noting that although we are technology neutral it does not mean we have included all possible technologies because that would be simply impractical. We have a defined a Project Design Envelope which encompasses the turbine and design structure philosophies which we would consider to be most likely to reach commercial availability and those which currently to have substantive manufacturer support from a major Original Equipment Manufacturer (OEM). That does not mean other manufacturers and devices will not succeed but we would currently see these as lead technologies. Why? In short to maintain flexibility as the industry and technology develops.

The technology and the tidal industry as a whole is still in its infancy, and although there have been a number of single turbine demonstration projects including in the UK (at EMEC), Canada (in Bay of Fundy and Race Rocks), and most notably longer deployments in Strangford Lough (Siemens MCT – 1.2MW), and Kvalsund Norway (Hammerfest Strom – 300kW) there are at this time still no commercial scale sites in existence. Until tidal projects are successfully demonstrated at small array scale, larger projects will need to maintain flexibility in order to ensure their future success.

An example of the ‘why?’ technology neutral approach is that of the foundation support structure. One of the biggest challenges in the industry is in achieving a cost effective solution for the deployment and long term operation of the turbines. One of the potential solutions to this is the use of floating platforms to which the turbines can be attached and thereby easily maintained and installed using relatively cheap vessels.

Although ultimately it may be the case that an entirely subsurface tidal farm will be possible, there are a number of technical challenges that this philosophy introduces both in terms of the turbines but also in the tidal farm infrastructure. Key challenges are the difficulty of access to the equipment in the event of component failure or even just routine maintenance, and the electrical connection challenges brought about by introducing large numbers of high current electrical couplings into a harsh wet environment. The electrical coupling question is less of a problem where turbines can be individually cabled ashore as they can be on near shore sites such as the Sound of Islay but this becomes less practical at increased distances due to electrical losses and costs. (And obviously the further offshore a project is the less the visual impact of the surface penetration will be onshore).

Surface penetration by contrast to the subsurface philosophy brings with it significant advantages – a platform to provide dry electrical connections between machines, and with the right deployment mechanism a means of providing easy access to the turbines themselves without use of large and expensive vessel. This means that front line maintenance can be conducted closer to the operating asset minimising downtime and increasing project yield. This might for example be by using a workboat operating out of Islay as opposed to heavy vessel operating from Campbeltown or the Clyde on the mainland.

The Siemens MCT SeaGen S device which has operated in Strangford Lough was designed as a surface piercing device to enable easy access for maintenance and swift intervention in event of breakdown and this has proven to work well since its installation in 2008. The machine is maintained by rib by local service crews based at Portaferry minutes from the device whilst performance is monitored from the main MCT engineering base in Bristol.

The principle disadvantage of the fixed surface penetrating structure is that it is depth constrained. At increased water depths typically beyond 35-40 metres the cost of making a tower structure substantial enough to withstand the tide thrust loading and wave loadings starts to become disproportionate relative to the costs of the turbine element that actually generates the energy. This is one of the main reasons manufacturers have proposed seabed mounted non surface piercing technologies.

One approach to getting around the fixed structure surface penetrating load problem is to utilise a floating compliant mooring system where the structure is surface piercing but taut moored and the give in the mooring substantially reduces the dynamic loads on the structure. Examples of this would be the Bluewater BlueTec device or the Scot Renewable SRTT device.

We have produced a number of photomontages or photographic representations of which are displayed on the project website www.westislaytidal.com and these provide an indication of what the proposal might look like from a number of different locations on Islay if we do ultimately build the project with surface penetrating devices.

The photomontages are based on a surface piercing height of 21metres utilising the SeaGen S compared to the 151metres of a wind turbine at the SSE Islay Wind Farm. It is also worth noting that if a floating solution such as the BlueTec were to be adopted this will further reduce visibility since the height will be reduced further to around 6metres above sea level

Given the state of the industry and technology a flexible (and Technology Neutral) approach is important so that when a consent is obtained it provides enough flexibility to enable us to adopt the advances in technology and installation methodology that were considered not to be viable or at least unproven at the time of the original submission. This is achieved by defining a generic Project Design Envelope not simply providing one manufacturer’s specification and drawings and undertaking the Environmental Impact Assessment based on any one turbine.

The Project Design Envelope needs to encompass the key parameters of any turbine or support structure that the project might potentially utilise and it needs to do this in a defined way rather than as an entirely open envelope. One of the difficulties for the tidal industry is in defining a detailed enough envelope when there is still a degree of uncertainty relating to what is the best installation technique, the best foundation type and even the type and size of turbine.

As a part of our technical evaluation of the technology options we have focussed on horizontal axis open rotor machines with a variety of support structure options. This technology choice would currently support utilisation of a number of manufacturers: Siemens, Alstom, Voith, Andriz, Kawasaki, Atlantis etc. Our Project Design Envelope is designed around these turbine types with a variety of support structure types.

The adoption of the Project Design Envelope approach allows a meaningful Environmental Impact Assessment (EIA) to be undertaken by defining a ’realistic worst case’ scenario that decision makers can consider in determining the acceptability, or otherwise, of the environmental impacts of a project. As long as a project’s technical and engineering parameters fall within the limits of the envelope and the EIA process has considered the impacts of that envelope and provides robust and justifiable conclusions, then flexibility within those parameters is deemed to be permissible within the terms of any consent granted, i.e. if consent is granted on the assessed maximum parameters of a development, any parameters equal to or less than those assessed is permitted to be constructed.

The Rochdale Envelope is an approach to consenting and environmental impact assessment, named after a UK planning law case (relating to proposed a proposed business park in Rochdale), which allows a project description to be broadly defined, within a number of agreed parameters, for the purposes of a consent application.

This allows for a certain level of flexibility while a project is in the early stages of development. As development progresses and more detail and certainty are available, further information regarding potential impacts can be provided.

The UK’s Overarching National Policy Statement on Energy alludes to this approach, stating:

“In some instances it may not be possible at the time of the application for development consent for all aspects of the proposal to have been settled in precise detail… the [Environmental Impact Assessment (EIA)] should set out, to the best of the applicant’s knowledge, what the maximum extent of the proposed development may be… and assess, on that basis, the effects which the project could have to ensure that the impacts of the project as it may be constructed have been properly assessed.The 'Rochdale Envelope' approach”.

The detailed site layout depends on a number of factors, not least of which is the ultimate selection of turbine, and foundation or support structure type. Clearly the layout will be different between for example 15 floating support structure with twin rotors of 1MW each, and 30 completely subsea 1MW turbines. The objective of the project design envelope approach is to outline a number of indicative layouts within the proposed project area of 2 sq km, and to undertake environmental assessments on the basis of these various options. Clearly in a near shore navigationally constrained site such as the Sound of Islay knowing exactly where the turbines are proposed and whether they will be surface piercing or not is quite a significant factor. By contrast 6km offshore in open water this is not quite so critical provided before construction commences their precise location is known for purposes of safe navigation.

Before a precise layout is determined the localised tidal flows, turbulence, and wave conditions need to be assessed and it is perhaps not surprising that given the interaction between the West Islay tidal flows, the Atlantic swell and localised wind driven waves this is extremely complex. Defining a precise layout also requires a detailed localised video assessment of the seabed to identify large boulders or rock fissures which could interfere with the either the turbine foundation legs or the jack up feet, and an intrusive geotechnical assessment including core sampling survey to gain an understanding of the exact geology before designing the foundation pins and grout etc.

To date computer models have been generated in order to model the tidal flows and this has been calibrated against measured data from the Acoustic Doppler Current Profilers on site. A wave model has also been developed and one of the challenges is merging the models and including the effects of wind strength and direction to model local wind/tide effects. Water depth and turbulence on blades are also key issues as are the depths of water turbines can be placed in. This assessment has been ongoing in parallel with the site surveys and is likely to continue until the exact locations and type of turbines to be used has been defined.

Our goal is to fix the turbine sites by the end of 2014 but this is subject to a number of other factors.  Ultimately a construction method statement which included a detailed design will be required to be submitted to Marine Scotland for approval 3 months before construction commences and at this point everything will be fixed in detail.

There are several options for connecting turbines and bringing the electrical power ashore.

If the turbines are close to shore they can be individually cabled to a collection point or substation located on land and therefore interarray cabling between turbines isn’t required.

For projects further offshore or for larger projects this option becomes less attractive because of the high cost of subsea cabling. The seabed area occupied by multiple cables can also start to become significant environmentally, as can the electrical losses as the distance offshore increases. For these projects it would be normal to link the turbines together (via inter-array cabling) to form turbine clusters, and then join these to one or more collector stations depending on the project size.

For large offshore wind farms, and for future large tidal farms, a dedicated offshore substation platform is used where the turbine cables are connected, and the distribution voltage from the turbines is stepped up to a higher export voltage for one or more export cables to take the power ashore. The dedicated offshore platform provides easy access for maintenance crews to electrical equipment including transformers and switchgear but is an extremely expensive solution for small projects.

For the 30MW West Islay tidal project it is likely that either one of the surface piercing structures would be used as a collector station as well as a turbine support structure or a dedicated seabed mounted hub would be used. Work is ongoing on seabed mounted hubs but whilst there is experience in subsea electrical substations for the oil and gas industry it remains to be seen whether this technology can be successfully be translated to the wave and tidal industry at the level of MW’s and voltages required.

Currently the island is supplied from a very long 33kV connection from Port Ann and we are aware of the numerous problems that have been experienced over the recent years. In theory an additional connection across to the 132kV network on the Kintyre Peninsula should substantially reinforce the grid on Islay, minimise outages and potentially enable other generators such as the Islay Energy Trust wind project to connect and export onto the mainland.

BUT

The West Islay Tidal Farm currently has a grid connection offer from Scottish Hydro Electric Power Distribution (SHEPD) on the Kintyre Peninsula which means effectively it is not connected to the Islay network. However, our goal is also to connect to the Islay 33kV network and deliver at least some of the tidal power generated onto the island. If that becomes possible a connection will be made to the existing island network and that should provide the completely separate connection at 132kV to the mainland. This requires some further discussion with SHEPD but certainly forms part of our plans.