Quick summary

The foundation is any structure below sea level and it may also extend to approximately 20 metres above sea level, where the tower is bolted on top.

The standard solution for most offshore wind farms is to use a “monopile” foundation, attached to a Transition Piece (otherwise known as a TP).  The monopile is essentially a large steel tube of around 8 metres in diameter which is hammered in to the seabed sometimes by many 10’s of metres depending on how stiff or soft is the mud/seabed.

The transition piece (TP) is fixed on top afterwards.  See the photo below.  This shows a fabricator manufacturing the yelllow TP’s.  Once the monopile has been installed the TP is fixed by bolting or the using of a concrete / grout type material which sets to secure it in place.

A large WTG installation vessel is required to install the foundation and Transition Piece (the yellow sections below).  We cover these components in more detail in later sections and in the online training videos.

focus on wind foundation offshore construction

1. Transition Piece (TP) key features

The Transition Piece (TP) sitting above the main foundation and directly below the Wind Turbine Generator (WTG) tower has a number of important roles:

  • Take the operational loads from the WTG tower down into the main foundation structure.  There is a large metal flange on the top which needs to match the flange pattern of the bottom tower when it is bolted together;
  • Provide landing access for technicians wanting to enter the WTG or the TP.  This is typically done using a Crew Transfer Vessel (CTV).  There is a ladder on the outside, and a work platform at the top with a davit crane for lifting components from a boat below;
  • Shelter the electrical equipment including the Inter-Array Cables.  There might also be a junction box or circuit breakers inside the TP;
  • Corrosion protection – The TP will typically house the system for preventing corrosion on the monopile, whether it is an ICCP (Impressed Cathodic Current Protection) solution, or metal anodes bolted to the outside.