Why are offshore wind farms relevant in Belgium?
Belgium is one of the largest producers of offshore wind energy at a global level. The offshore wind farms in Belgian Continental Shelf (BCS) have a total installed capacity of 2.3 GW and occupy an area of approximately 238 km2. Today, Belgium has nine operational wind farms providing an average annual production of 8 TWh. The production is foreseen to increase with the development of a second area for offshore wind energy, with 285 km2, in the Western part of the BCS.
SUMES case study
In a nutshell, the offshore wind farm selected for the SUMES project is located between 30-55 km from the Belgian coast and covers an area of 14-20 km2. The offshore wind farm has 20-75 turbines with a capacity of 3-10 MW and monopile foundations. The wind turbines are connected to an offshore high-voltage substation via 30-50 km of infield cables. Electricity produced in the wind turbines is transmitted from the offshore high-voltage station to shore via a 40-60 km submarine export cable. This submarine cable is connected to a land cable, which transmits the electricity to a high-voltage substation on the mainland.
What are the main components of an offshore wind farm?
Offshore wind farms usually have seven main components: wind turbines, foundations, infield cables, an offshore high voltage station, a subsea export cable, a land cable and an onshore high voltage station. Each of these components play a crucial role in the production and transmission of electricity to shore, which at the end reaches Belgian households.
Wind Turbines
Without turbines, wind energy cannot be captured and converted in electrical energy, but how does this actually happen? Air currents carry kinetic energy making the turbine’s blades rotate. The blades are connected to a low-speed shaft located inside the nacelle, which is a box-liked cover housing different components of the wind turbine. To produce electricity, the speed of the low-speed shaft is increased thanks to a gearbox and then transferred to a high-speed shaft, which is connected to a generator and this way kinetic energy is converted into electricity.
Foundations
The foundations are large steel structures that connect the wind turbines to the seabed and support them to withstand strong winds. The tower of the turbines is connected to the steel structure with a transition piece. These structures can have a length of over 60 meters or more depending on the sea depth and rocks called “scour protection” are placed around them at the seabed to prevent erosion.
Infield cables
The electricity produced in the wind turbines is transported via infield cables to the offshore high voltage station (OHVS). These are submarine cables that connect the wind turbines in strings or chains and then each chain is connected to the offshore high voltage station.
Offshore high voltage station (OHVS)
The offshore high voltage station is the heart of an offshore wind farm. You can picture the chains (i.e. infield cables) being veins transporting electrical energy to its heart, namely a transformer. The transformer is responsible for accumulating and converting electrical energy that has a low voltage to a high voltage.
Subsea export cable
From the OHVS or heart, electricity is transported to shore via a submarine export cable. This cable, as well as the infield cables, are designed in a way to prevent the intrusion of salt water. The export cable also has fiber-optic technology; fiber optics is a way of sending information through very thin glass fibers, which have almost the thickness of a human hair. These fibers are like a nervous system sending data on, for example, temperature changes or vibrations.
Land cable and onshore high voltage station
The land cable is the onshore extension the subsea export cable. It also has fiber-optics and transport the electricity to the onshore high voltage station. The onshore high voltage station also has transformer, where the voltage from the electricity coming offshore is either stepped-up (increased) or stepped-down (decreased), in other words, the transformer “buffers” the electricity before being sent to the transmission grid and then to Belgian households.
Impacts of an offshore wind farm
Despite an obvious benefit from offshore wind farms, which is the production of renewable energy, these structures can have effects of various scale and nature, i.e. local to global positive and negative impacts on ecosystems. Which are these impacts?
Local impacts of an offshore wind farm
Own design, not scaled proportionality.
Offshore wind farms have an impact on the local marine ecosystem and its functioning. One of the most important changes is the introduction of hard substrate – i.e. the turbine foundations – in a predominantly sandy environment. These structures provide new habitat to different marine organisms, which leads to changes in marine biodiversity and biomass on the structures itself and in the seafloor surrounding the turbines. Eventually this may affect the functioning of the marine ecosystem and change the capacity of the marine ecosystem to provide ecosystem services. To quantify these impacts, methodologies such as ecological risk assessment and ecosystem services assessment are needed. More information can be found in the “Ecosystem services model” section.
Global impacts of an offshore wind farm
Own design, not scaled proportionality.
Besides local impacts, offshore wind farms also have global impacts which are associated to its value chain. What is a value chain? These are all the life cycle stages of an offshore wind farm, i.e. the extraction and supply of materials to manufacture all the components of an offshore wind, its installation, operation and maintenance, decommissioning and end-of life treatment. It also includes all the transportation required during each life cycle stage. Each of these life cycle stages will generate several stressors, such as emissions, land transformation and occupation, resource use and wastes, which eventually cause impacts on ecosystem quality (e.g. ecotoxicity, eutrophication, land-use change), human health (e.g. global warming, toxicity, radiation) and natural resources (e.g. depletion of mineral and fossil resources). For example, steel is the mostly used material to manufacture the components of an offshore wind farm, including the wind turbines and foundations. To produce steel, the extraction of iron ores is first needed and then the ores are transported to a steel manufacturing site to be processed. After the steel is produced, it is transported again to a wind turbine or foundation manufacturing site. Once the lifetime of the OWF is reached, the wind turbine and foundation are dismantled and their components are taken to an EoL treatment, for example, recycling, incineration and landfill. Through recycling, the steel can be recovered and its production with virgin material can be avoided. Ultimately, we have avoided a product. All these processes will eventually generate different impacts. To quantify the impacts of the value chain, a life cycle assessment is usually conducted.
Furthermore, the environmental sustainability performance of offshore wind energy is compared with another type of energy (cfr a benchmark) to better understand its positioning relative to competitors. More information on the benchmark is found in our recent paper.