Codling Wind Park, one of Ireland’s largest offshore wind projects, is set to be the largest energy project ever undertaken in this country. When operational, it will contribute a little more than a quarter of Ireland’s target of 5GW offshore wind. As Ed Sly, the project’s engineering manager outlines here, while projects of this size present an array of challenges, the benefits to our climate, country and community are immense.

Global warming and energy security are deeply interconnected. The world is caught in a negative feedback loop, where burning of fossil fuels for energy drives up global temperatures and accelerates climate-related disruptions. 

Neart na Gaoithe wind farm – which is gaelic/Irish for ‘Strength of the Wind’ – is located off the east coast of Scotland. Photo: EDF Power Solutions UK and Ireland, and ESB.

This, in turn, challenges economies and creates risks to reliable and affordable energy. The resulting political churn undermines the societal consensus needed to transition economies away from fossil fuels. The status quo is not sustainable. We are at the very end of long and shaky oil and gas supply lines. Resolving the dual challenges of climate and security has never been more urgent. 

We are fortunate that Ireland’s government and opposition parties all recognise the need to address these issues. The Climate Act 2022 and the annually updated Climate Action Plan are notable pillars of the Irish response to the twin challenges of climate change and energy security.

Codling Wind Park, Ireland’s largest ever proposed energy project, is a joint venture between EDF power solutions and Fred. Olsen Seawind. The proposed offshore renewable energy project, which is located between 13km and 22km off the Wicklow coast, is the keystone project for Ireland’s offshore, climate and energy security ambitions.

Subject to planning permission, the wind farm will have a generating capacity of up to 1,300MW, supplying renewable electricity directly to the grid in the heart of Dublin’s docklands. Once operational, the project will contribute a little more than a quarter of the government's target of 5GW of grid connected offshore wind by 2030, supporting the country’s climate targets. The expected output of the offshore wind farm would be enough to supply the equivalent of more than a million Irish homes with clean, Irish electricity.

Representing one of the largest energy infrastructure investments in the republic, the project will also deliver substantial benefits to the regional and national economy, including a community benefit fund of up to €200m, more than 1,000 construction jobs and about 75 long-term jobs at its operations and maintenance base.

Problem overview

The challenges associated with developing an offshore wind farm are vast. The project has to develop a successful engineering solution spanning from the offshore generation via wind turbine generator’s (WTGs) all the way through to connecting into the Irish grid where this new source of home-grown power is delivered to the consumer.

Any infrastructure project has its challenges, but offshore wind brings some particularly complex ones, and they often defy neat classification. The following is just an attempt at providing a flavour of the multifarious challenges that typically need to be addressed:

• Projects at this scale require multidisciplinary co-ordination and alignment between, onshore and offshore project planning and associated structural, electrical, grid, construction and consenting considerations;
• The interplay between a complex geographical community of stakeholders, a new and untested policy infrastructure for Ireland, government agencies, national policy imperatives and political pressures along with local and national media interest in the new industry all need to be considered;
• A constrained global supply chain and international market uncertainty aggravated by adverse developments towards offshore wind in the USA;  
• Ever evolving technologies that regularly require offshore renewable energy (ORE) projects to consider and design for equipment that doesn’t yet exist. This industry dynamic is particularly evident in new iterations of WTGs and the associated, perennial focus on increasing capacity;
• The scale and footprint of ORE projects with sites that cover typically more than a 100 sq km and with long cable routes (Codling has a site area of 125 sq km) inevitably means projects are confronted with wide variability in ground conditions and consequently significant design complexity. This design complexity is further complicated by the need to maximise wind yields (a key underpinning of the business case) and minimise development costs on the site within a new, multifaceted and evolving regulatory envelope; 
• Layers of complexity in ORE projects means a single design will never fit all. This consideration creates unique commercial challenges for the delivery of project business cases, which in turn impacts financial planning and funding. As a result, a keen focus is required on optimising costs across the multiyear development cycle.

Maximising the yield through layout

Codling Wind Park has a site adjacent to the Codling Bank in the Irish Sea about 45km southeast of Dublin bay. The site is roughly rectangular running 25km north to south and extending a further 12km east into the Irish sea. Following careful environmental assessment the  site was identified as suitable for ORE development. It also had the advantage of suitable water depths to facilitate construction as well as the wind resources to ensure commercial viability.

The project was originally conceived in 1999 as two separate, adjacent developments. In those days WTGs would have been 2MW to 3MW and the total number of them would have been in excess of 400.

Now, as WTGs have evolved, with individual capacities of 15MW and above, there is a need for significantly fewer turbine generators. But the challenge remains, to extract as much energy out of the wind in this given area.

The engineer’s role at this stage of project design is to maximise the yield, the mega watt hours (MWh) that the wind farm will produce each year. Just by way of context the typical Irish household consumes circa 4.2MWh per year.

Yield starts with the wind, how much of it there is, the intensity, speed and direction in which it blows. Offshore wind speeds are typically higher and, more consistent than onshore as there is less to influence it, fewer physical obstacles, like hills, trees and buildings. This means you get a higher capacity factor; that’s the total installed capacity of the WTGs vs the actual energy produced. The measurement of what is actually generated when operational is expressed in MWh/yr (mega watt hours per year).

To understand the resource that is available to Codling, a series of measurement campaigns were undertaken between 2020 and 2022. The first of these was at the Newcastle aerodrome and measured the wind speeds onshore at a location close to the proposed wind farm.

Then two offshore surveys were performed using floating lidar to analyse wind speeds within the offshore site. LiDAR stands for light detection and ranging and is equipment that uses a laser to measure wind speeds at a given height in the atmosphere.

In addition to measuring the wind speeds, met ocean conditions such as current, sea states, water level and direction were measured, which provide the basis for designing the offshore structures.

The measurements taken cover a period of two years, whereas the offshore wind farm will be producing electricity for greater than 25 years. As such, a sequence of numerical modelling is required to extrapolate the data over a longer time frame. This extrapolated time series data is then reviewed and updated using additional sources of wind speeds and intensities from other sites within the Irish Sea and existing wind farms off the UK and other European countries.

Once the wind resource is understood the focus is then to arrange the wind turbines in a configuration that delivers the greatest wind yield before layering on environmental and technical constraints informed by site specific data collection.

Understanding the receiving environment

To determine the final design and WTG layout, a robust environmental impact assessment is required with the ultimate aim to mitigate any potential impacts the project may have on the environment through design and proactively enhance environmental conditions where possible. One example is the impact that the wind farms potentially have on bird species native to the area.

To mitigate any adverse effects to bird life, an optimum geometry of the wind turbine and specifically their rotating blades needs to be determined. Extensive modelling based on surveyed bird numbers and flight pattern details is used to determine a minimum blade tip clearance which is the distance between the sea and the bottom of the WTG rotor blades.

With the outline geometry of the WTGs established, extensive modelling on different wind turbine layouts is undertaken to determine which configurations produce the best yields. Orientation, spacing, and density of wind turbines in particular areas of the site are all refined to develop the best initial WTG layouts.

However, the layouts submitted for the planning application cannot be developed with these considerations alone, there are other factors that need to be borne to mind during this process:

1. The wind park will be visible from onshore and therefore considerations regarding seascape, landscape and visual impact need to be taken into account.
2. Accessibility through the wind park needs to be maintained for operations and maintenance, as well as in the event that search and rescue activities are needed, this requires a minimum spacing between wind turbines and a need for a uniform grid arrangement.
3. Constructability of the design and access to locations for installation vessels is a critical consideration. Due to increases in the size of the wind turbines there is a requirement for bigger WTGs, foundations and therefore bigger vessels to install them. Areas of the wind park with water depths deemed too shallow for these installation vessels is not suitable for the placement of wind turbines.
4. Then finally, one of the most critical considerations is the ground that the wind turbines are to be sited in and the foundations on which they are supported. The foundations are a key part of the overall development, and an optimised foundation is key in achieving an optimised return on capital expenditure (CapEx). In locations where poor ground exists, it is often more economical to re-site the WTG to a different location taking an impact on the potential yield but saving significant sums on the foundation structure and installation.

Variable ground conditions from the Ice Age

The ground conditions within the 125 km² Codling site are varied. During the last Ice Age, great forces were exerted on the ground creating incredibly dense soils at depth. Subsequently as the glaciers melted, large channels were gouged into what is now the ground beneath the seabed, these channels were subsequently filled with softer materials.

The infill contained the material that was carried by glaciers down to the sea, such as boulders and sediment. As a result of this process, the variability in ground conditions across the Codling site is significant, yet common with many other locations around Ireland and the Britain where similar Ice Age events occurred.

Coding will be built using monopiles for the foundation of the WTGs. A monopile foundation is a steel tube with a typical diameter of up to 10 metres and a length of up to 80m. Up to 40m of the monopile is inserted into the seabed to provide resistance to overturning.

Given the water depths, these offer the most economical solution for the Codling site. These will be fabricated and brought to site where they will be upended and driven into the seabed using piling hammers. In the event that the ground is too hard or an obstruction, such as a boulder is met, then the ground within the monopile will need to be drilled out.

As such ground conditions are one of the greatest risks within the codling project.

To understand this and best optimise the design, several geotechnical and geophysical surveys have and will be undertaken. The geophysical surveys map the subsurface strata using acoustic technology that helps to build a set of 2D lines taken across the offshore site. This offshore data is then processed and developed into a 3D model of the site.

Geotechnical surveys are then performed to extract samples from the seabed which are then tested in laboratories to determine the geotechnical properties that will be used for the design. The ground modelling is then updated to combine the subsurface models produced from the geophysical surveys and attribute geotechnical properties from specific borehole locations.

Some locations can have soft ground, which if a foundation were to be placed there would lead to significant increases in the size and installation that would be required. If we were to over size foundations anticipating soft ground but instead finding harder ground the risk of a premature pile refusal is increased.

The Coding project will be installed within tight environmental constraints for underwater noise to mitigate potential impact on marine mammals. This means the size and energy of piling hammers that are used will be tightly restricted and an engineering balance has to be achieved between what is known of the ground, the risk of variability within the ground, the energy required to install the monopiles and the environmental constraints.

Coding will continue to acquire geotechnical data from the site to minimise risks, however some risk always remains. As such, the design needs to be robust to deal with variability while delivering an optimised CapEx.

To help mitigate these risks Codling is investing significant hours and effort to understand as much about the ground as possible recognising that time spent now could prevent significant cost increases later.

Conclusion

The challenges presented here demonstrate some of the competing objectives and interdependencies of having multiple engineering elements within the project. These extend across the entire development and represent a small snapshot of what needs to be overcome to deliver a successful offshore wind farm development.

A successful project is one that meets a number of key objectives. Ultimately what is engineered needs to have acceptable impacts on the environment and deliver on the commercial objectives for the project while ensuring that they can be fabricated, installed, operated and decommissioned within safe parameters.

When delivered, Codling Wind Park will have a generating capacity of up to 1,300MW of sustainable Irish energy, enough to power 1.2 million Irish homes each year. The benefits to our climate, country and community are immense, as are the solutions the engineers and team at Codling Wind Park are bringing to meet the challenges of Ireland’s largest offshore wind project. 

Author: Ed Sly, Codling Wind Park engineering manager, is a chartered engineer and project manager. He has been with the project for more than four-and-a-half years and in that time the project has secured an ORESS contract, submitted its planning application and completed multiple engineering design and work scopes.