The term landfall refers to the point at which the cables carrying power from an offshore wind farm reach the shore. This is where the offshore and onshore infrastructure is connected – an important step in bringing renewable wind energy into the power grid.
To make the cable sea-to-shore connection, we use horizontal directional drilling (HDD) to lay the export cable under the seabed and beach area. HDD can extend anywhere from 300 meters to approximately 1.000 meters out at sea.
Step 1: From sea to shore using HDD
The first stage of making landfall is for a cable to run from the seafloor to a location a short distance inland. To put this cable in place, a hole is drilled using a technique called horizontal directional drilling.
The hole starts in a small pit behind the dunes or a beach, and is then bored using a drill rig machine. Drilling can be measured and controlled precisely, keeping it well below the surface until the drill head emerges from the seabed 300 meters to approximately 1.000 meters out to sea.
The drill head is then pulled back through the hole, bringing with it a pipe from a cable installation vessel. After this, a cable can be fed through the pipe, establishing a safe path for the wind energy to be brought ashore.
Step 2: The transition joint bay
The site of the drilling pit becomes the home of the transition joint bay. This is an underground concrete box or tunnel where the cable from under the beach joins a cable leading to the onshore substation further inland.
Since it’s housed underground, the transition joint bay is basically invisible once constructed, except for some manhole covers in case access is needed in future.
Step 3: Underground transmission to the substation
The onshore substation transforms power generated by an offshore wind farm to the correct voltage before delivering it to the local grid, after which it can be sent to thousands of households and businesses.
Before building an onshore substation, we undertake extensive environmental, technical and feasibility surveys to determine the best location to build.
With regards to underground transmission, the onshore substation is linked to the transition joint bay by a transition line (containing piping and cables).
During construction of the line we also work with highway authorities to minimize disruption to traffic, residents and businesses, as well as to reduce construction waste.
Step 4: Connecting to the grid at the substation
The final stage in getting renewable power from the offshore wind farm to the distribution grid is the substation. This is where the physical connection is located, and where the current is converted to the right voltage and frequency to be fed into the grid of Transmission System Operator (TSO).
Substations can vary significantly in type, size and layout. The site includes associated roads, fences and landscaping, and may include an open yard as well as buildings.