Offshore wind has become an increasingly popular source of renewable energy over the last decade. As the green transition accelerates, wind power is now firmly established as part of the global energy mix, providing clean and sustainable electricity to millions of people worldwide. However, the process of installing the wind turbines required to generate this energy is a complex and challenging undertaking. These massive structures require significant engineering expertise and logistical planning.
In this article, we take a closer look at the process of installing offshore wind turbines, as well as examining the essential role that standby vessels play in supporting these installations.
How many offshore wind farms are there in the UK?
There are currently 224 offshore wind farm projects in the United Kingdom. These are at various stages of development with 43 already operational, another one currently generating electricity, and two in the process of being built. Additionally, there are a further ten projects which have either been consented or have applied for consent.
With a combined total of 12.7GW of wind energy being produced by 2,652 turbines across 43 farms, the United Kingdom has the most offshore wind sites in the world. Furthermore, the country is home to seven of the world’s ten biggest offshore wind sites.
What does production at this scale look like in real terms? It means that the country’s wind farms generate enough electricity to power over 14 million homes and deliver around 13% of the UK’s electricity. This number is only rising. In 2021, the United Kingdom accounted for 70% of total installations in Europe with 2.3GW of new installations.
How do offshore wind farms work?
Offshore wind farms use large numbers of wind turbines to produce electricity. Each individual turbine has rotator blades which spin when the wind blows. As they spin, they create kinetic energy and turn a shaft that is connected to a generator. This generator then converts the kinetic energy to electrical energy, ready for it to be transmitted via a network of underwater cables to an offshore substation. The electricity is then moved onshore ready to be used via the grid.
Each turbine is anchored to the seabed using steel foundations and is usually installed at depths of around 20m to 60m. The decision of where to locate a wind farm is a strategic one: turbines need to be placed in areas with consistently high wind speeds to ensure they are capable of generating electricity efficiently.
The stronger winds experienced out at sea are also part of the reason that offshore wind farms are more productive than land-based ones. There is nothing obstructing – and therefore slowing down – the flow of wind in the ocean like there is on land (i.e. mountains, buildings and trees). The increased wind speeds experienced out at sea therefore deliver a greater energy yield than onshore wind farms. Furthermore, offshore wind turbines are often much larger than the land-based counterparts which, again, contributes to greater energy yield.
How offshore wind turbines are installed
While installing offshore wind turbines is a complex and nuanced process, it usually involves the following five key steps:
1. Pre-installation site preparation
The seabed needs to be surveyed before work can begin. This process allows for the identification of any potential hazards or obstacles and may flag the need for the seabed to be levelled or dredged to provide a stable foundation for the turbines.
2. Foundation installation
Specialized vessels with drilling equipment install the turbine’s steel foundations (usually large steel monopiles or jackets), drilling them into the seabed with hydraulic hammers.
3. Turbine installation
After fixing the foundations in place, specialized installation vessels transport the turbines to the site. At this point, the nacelle and rotor blades are lifted onto the tower, and the turbine is bolted to the foundation.
4. Cable installation
Using a range of techniques, specialized cable-laying vessels bury the cables in the seabed in order to create an underwater network that connect the turbines to an offshore substation.
Once the turbines and cables are installed, the wind farm is tested to ensure it is operating correctly. After passing all the necessary electrical, safety and performance tests, the system is commissioned.
The type of foundation that a wind turbine requires depends on the depth of the water where it’s being installed: For turbines installed at depths below 15 metres, monopiles are used. Relatively speaking, these are simple structures comprising a thick steel cylinder anchored directly to the sea bed. For turbines installed at depths below 30 metres, a gravity foundation system – using a concrete or steel platform - is advised. And for turbines installed at depths below 30 to 35 metres, a more complex support and anchoring structure is used. Typically, this involves using jackets (a lattice-framework foundation with three to four anchoring points) with a transition piece at the top which connects to the turbine shaft while the legs are anchored to the sea bed with piles.
How do standby vessels support offshore installations?
A number of different vessels are required for offshore installations. As well as the more obvious drillships and pipelaying vessels, perhaps surprisingly, one of the most crucial vessels for getting offshore wind projects up and running are Emergency Response and Rescue Vessels (ERRV). This is because offshore projects are subject to strict regulations that require every structure to have ERRVs on stand-by in case of an emergency.
In fact, the role of EERVs in offshore projects is so essential that they are required to be available at all times, providing a round-the-clock service to their assigned offshore structure. While it is advised they keep an approximate 1km distance from the rig, the idea is that they will be close-by to evacuate personnel from rigs and platforms should the need arise.
These specialist vessels need to have the facilities and capabilities to:
- Carry a range of specialist equipment, such as firefighting and rescue equipment, cranes, and accommodation facilities for personnel
- Operate fully during severe weather
- Rescue and/or recover people from the water and provide them with medical aftercare
- Act as a reserve radio station with state-of-the-art communication equipment
- Operate as a ‘place of safety’ and coordination point for rescue efforts during an emergency situation
- Monitor the safety zone and warn off any approaching vessels in a bid to prevent collisions
With a strong commercial and technical background in the Offshore and shipping industries, Clarksons is able to provide leading support to clients who are involved in offshore wind projects. Contact our expert team to find out more about our impeccable track record in providing a range of specialist vessels for the offshore renewables sector.