Partner: Fugro

The impact of greenhouse gases on our planet is a problem too large to ignore. Denmark alone has committed to a 70% reduction in greenhouse gas emissions by 2030. Engineers and scientists are striving to find a solution to our energy needs that is renewable and maintains the large power supply needed. In the recent Esbjerg declaration regarding the North Sea in Denmark, with Germany, the Netherlands, Belgium and the UK agreeing that more renewable forms of energy creation are necessary, particularly wind farms.

Denmark is embarking on the largest construction project in its history with the assembly of the first energy island in the North Sea. The 120,000sq.m site could serve as a hub for around 200 wind turbines, storing and supplying electricity to Denmark and its neighbours. The completion of this megaproject is some time away, but preparation is beginning now, all the way down at the seabed.

Aiming to ease the export of wind energy throughout Europe, the island will be developed by a public private partnership. Costing $34 billion to supply 3GW of power by 2030. Where offshore wind energy typically must be transformed onshore before distribution, requiring a proximity to land for maximum efficiency, the transformation will take place on this new island at the centre of the windfarm and go to neighbouring countries from here.

The Danish transmission system operator, Energinet, is responsible for carrying out the preparatory environmental studies and seabed surveys and will develop, construct, own and manage the heart of the Energy Island. They are already receiving questions from connections in Asia and across the world.

A multi-purpose island

What’s more, the new island could enable the creation of a whole range of new industries, from manufacturing and hydrogen production to data centres and scientific research stations – with accommodation for staff. These are just some current ideas, after construction the land can be adapted as necessary.

With so many potential uses for an energy island, the next stage is consideration of the design concept. There are different methods for building the island depending on the environment you’re building in and the depth of the water. The North Sea being approximately 25 metres deep, compared to the hundreds to thousands of metres in depth, allows the island to be fixed to the seabed.

Despite no main construction plans confirmed, preparatory work is underway. The Danish Energy Agency are considering a caisson structure, watertight retaining structures used to enable underground construction in saturated locations such as rivers, lakes and seas. Using the caissons you can enlarge the area in modularity, allowing them to construct the area as they deem necessary.

But what must be considered is the lack of reliability in the environment of the North Sea, the unpredictable decisions create challenges for designers. The huge waves can put the electrical gear on the island at risk, and this isn’t all the teams must contend with, but also the conditions of the seabed they’re building on. This is critical in terms of foundation design as the wrong type of support could lead to the collapse of the island as well as the wind farm.

Preparations begin

Geophysical and geotechnical investigations are a critical starting point in terms of knowing what is under the sea and then understanding how to design and construct the wind farm and the energy island. This means undertaking topographic and bathymetric analysis of the area to create a clear picture of the seabed conditions, before delving into the ground itself to analyse its composition. Both stages require a variety of tests and equipment.

These began in May 2021 with Fugro launching their dedicated survey vessel, the Pioneer. Using the fully mobilised geophysical spread and 2D Ultra-High Resolution (UHR) equipment, the team accurately mapped the seabed onsite for high resolution bathymetric data using their multi-beam system on board. The resulting bathymetric and seismic data gave the team a morphological map of the seabed showing natural features such as sand waves, boulders and reefs, alongside man-made features like shipwrecks and debris.

As these could be of some archaeological interest, Fugro had to inform their client Energinet, who in turn would inform the Danish Archaeological Society. But when it comes to actually looking at what was there in these surveys, they didn’t find everything they thought. The surrounding area they searched was the sight of the largest naval engagement of the First World War, the Battle of Jutland. Over 100 years later, a lot of the wrecks from this battle have been lifted and are now housed in museums.

There are still some archaeological finds, according to Hanne Storm Edlefson, Energinet’s Vice-President for the Energy Islands Project, “we found a vessel, a submarine from the Second World War, actually a British one. They think that it has up to 40 soldiers laying there. So it’s also a grave for them […] it’s totally intact.” So the team have been careful to avoid it, leaving the submarine and its soldiers to their final resting place.

But this isn’t all that has been found. In better alignment to the purpose of the survey they also found a huge hole couple of metres under the seabed. There is speculation that this is a remnant of the ice age, the result of a clash or corrosion. “It was quite good we found it,” Hanna says, “but it looks absolutely crazy when you see the pictures, because it looks like there’s just an empty hole in the middle of the seabed.”

Geo-hazards like this are why these UHR seismic surveys are so important. Project Manager, Padwalkar, was lead of the geophysical surveying, “we interpreted the layers 100 metres below the seabed,” he says, “So the 2D UHR survey was carried out for performing geo-hazard survey, like fault findings or accumulation of shallow gas, or even soft sediments. Now, these could be a potential hazard for the wind farm.”

Once the team had a good understanding of the general seabed morphology, next came the unexploded ordnance (UXO) surveys, and then the geotechnical surveys. To learn more about the UXO surveys, check out Episode 164.

They analyse the results from the geophysical phase for boundaries and basic geology, then go and test the seabed to discover the composition of the soil, the strength of different layers. The goal is to remove the uncertainty of the area so the designers know exactly what they can and cannot do at different locations within the space. To do this, they perform cone penetration (CPT) and borehole tests.

Kasper Spet, Project Manager of the geotechnical phase says, “we go in with the seabed phase, meaning we have sensors that are mounted on and are deployed from a frame. In this case the sensor is with the CPT test, which is very fast because we’re able to push straight from the surface as deep as we can go.”

The downside of these systems, however, is their limited push power. Typically, if an obstruction is hit, the test is terminated. To combat this, Fugro has designed specialist equipment called the SeaCalf deep drive. This innovation ensures the team have the deepest push with CPTs, but sometimes even this can’t reach the depths required.

“And then we come in with the downhole phase,” Spet explains, “the downhole phase means that we bring in drilling vessels. So these are geotechnical drilling vessels and they actually build in drill strength, as if you would be drilling for oil but in a much more delicate way, because you don’t want to disturb the soil. So it’s a very, very tricky balance between massive machines trying to delicately bring the soil to the surface without disturbing it.”

Although the hole created in this process will collapse, the team make use of it for as long as they can, by inserting sensors for tests such as geophysical logging. This allows the team to measure more components within the borehole than they would otherwise have been able to.

Testing on-ship

Back onboard ship, the samples are categorised and preliminary tests are undertaken. When combining the samples together from the site of the island they amassed about 900 metres. Compare this to the 50 locations sampled across the wind farm site, and they collected more than 3 kilometres of data. The team estimate that the tests will take them about a year to complete.

The initial tests that occur onboard ship are primarily for soil classification, analysing its type depending on various properties. “It’s important that you give the right information,” Spet says, because these findings are what inform the onshore, advanced laboratory testing, ensuring the right tests are undertaken on the right types of soil and in the right quantities.

Once the soil has been removed from its natural, underwater, environment, as it travels from the ship to the lab, it will dry out, thus giving different results and causing inaccuracies in the tests. Therefore, the samples must be returned to the same pressure and conditions that acted on them before they were removed from the seabed. This can be achieved by placing the samples in a pressure cell and saturating them with water, the requirements of which are noted down in the onboard testing. But for a material such as clay, the harder it is, the longer it takes to return it to its natural state, and this can take weeks.

So even in the preparation phases of this megaproject, building the wind farm and island certainly isn’t a quick process. The only way to speed the tests up is to gather samples quicker by mobilising more vessels. According to Spet, the geotechnical team had three of Fugro’s vessels working onsite at the same time, which posed logistical challenges.

Alongside this, the team had to liaise with the local fishing community to control fishing when the surveys were undertaken. Despite working on over 1000 square kilometres of sea, the occurrence of fishing could still cause problems.

“The interesting part is these fishing gillnets,” Padwalkar says, “These are the ones deployed at the seabed and not floating somewhere in the sea, but they don’t get picked up by sonar.” Due to their location, these gillnets pose a tangle risk to some of the equipment, like the 2D UHR streamers and side scan sonars. The resolution for this was to employ a fishing liaison officer from the fishing community. This person was situated onboard Fugro’s vessels to relay location information.

However, even without active fishing occurring, fish will be found in those areas of the sea. “So you have to understand,” Padwalkar details, “the marine life also needs to be protected onsite. So one of the things which our client requested us to perform was a noise monitoring test.” This is important as some of their equipment is acoustically loud and could be damaging to the marine mammals onsite.

Primarily occurring on Fugro’s Pioneer vessel, the test measures the underwater sound emissions of their equipment as a function of distance, frequency and direction. This sound source characterisation study was then provided to the environmental impact assessment study group to analyse how the noise sources could affect the marine mammals of interest onsite.

Fugro also incorporated a soft start procedure in which their equipment is started up gradually to dissuade any nearby marine life from remaining in the area, without causing them any damage. As another reassurance to ensure thorough searches, the company also employed non-dedicated but trained personnel to complete a marine mammal watch. Occurring prior to equipment start up, the personnel inspect the ships surroundings with binoculars to watch for visible marine mammals within 500 metres. Finally, they use a passive acoustic monitoring system (PAM) to detect animals underwater.

Furthermore, it is vital to remember that these tests are taking place in the difficult and unpredictable conditions of the North Sea. To mitigate this uncertainty the team deployed SeaWatch buoys; weather LIDAR, acoustic doppler current metre profilers (ADCP) and current density and temperature metres (CTDs).

This equipment monitors midocean data in real time, feeding it back to Fugro’s weather forecasting team who use the information to update a weather model. This ensures the models are very accurate while allowing them to be done twice a day. Going directly to the survey vessels and client the models are crucial for the safe working of offshore construction sites and allow efficient planning and safety.

The dream of the future

This level of planning is vital for a project of this scale, “it was a big project, so many vessels, so, so many people over such a long timescale. That’s what makes it,” says Spet.

For Padwalkar, it was the technology that was the most exciting, “not only does it give you more for less, or it takes away the risks from a project, but also adds risks as well, because it’s new technology. So how to manage around this and how to make the best out of it. Technology is what excites me.”

“I feel very lucky to be part of this,” Edlefson says, “It’s crazy difficult and some days I’m just thinking how are we going to do this? But we will. I’m quite sure we will, because we need it. But it’s just so enthusiastic to be working on something that will have such a huge, huge impact and I think that sort of drives everybody on this. So, even though we have quite a lot to do, and we’re running fast, I think we all try to sort of remember why we’re doing it. So, maybe the enthusiasm is sort of what warms my day the most.”

From its role as a step forward for the energy sector and bringing countries closer together, to allowing us appreciation of the past, as Spet says, “the deeper you drill, the further back in time you go.”

Finally, we can look to the future as someday, Edlefson will be able to fly from her home in Denmark over to England and on that journey look out the window to see the huge, world-changing energy islands that she has helped to create. “So, the whole vision really takes my breath away. Also that my colleagues and I will be able to show this to our kids and tell them the massive impact it will have because of its size,” she continues, “from now on, things will be done more across borders, it will be done in more parallel, it will be done larger because we need to do this faster, and also cheap, to make sure that it’s not too expensive for us. And this means that it has to be cross national. And there’s also something beautiful about that, especially taking into account the current situation with the Ukraine war etc. We need to stand shoulder by shoulder and do these things.”

This article is based on Episode #173 Europe’s First Energy Island, click here to listen