An Offshore Port concept to reduce the Construction costs in offshore wind farm projects

Abstract

In the 25 years of existence, the offshore wind market has developed on many aspects. Among others, the dimension of the turbines increased by a factor 15 and the distance to shore increased by a factor of 50. The developments of the offshore wind farms increase the requirements for the installation vessels and as a consequence the present day rates can be up to $300.000. The global potential of the offshore wind market by the year 2030 is forecasted to be 60 GW for Europe and 22GW for the US Atlantic coast. The developments in the market, lead to demands during the construction of offshore wind turbines. The construction phase became more demanding over the years, while the logistical strategy of sailing back and forth to the offshore wind farm with a jack-up vessel, is similar as applied in 1991. The six demands can be fulfilled by performing four required activities at the offshore port. The potential of seven support structures that fulfil the boundary conditions for the offshore port are determined. Important boundary conditions are a maximum vertical load of 12.600 ton, suitability in a water depth range between 30 and 50 meter and a minimum surface area of 17.500 m2. Besides boundary conditions that have to be fulfilled, there are also maximum allowed conditions that determine the workability of a port concept. For a floating port concept the motion response is the leading workability condition. Based on the mobility, motion response and a cost indication, three port concepts are selected. These port concepts are a single barge, a single jack-up barge and a combination of a small jack-up barge and a single barge. The current logistical strategy for construction of an offshore wind farm is compared to various logistical concepts that include an offshore port. The logistical concept with a feeder vessel that sails from the onshore to the offshore port and an installation vessel that sails between the offshore port and the wind farm has the highest potential saving. Taking into account the assumptions made throughout this research, for each executed project by the offshore port the savings are expected to be €23.000.000. These savings consist of a sooner generation of energy and by savings on the construction of an offshore wind farm. The discounted cash flows for the three port concepts shows a potential for the offshore port concept. The net present value of the three offshore port concepts deviates between 52 and 216 million euro. The financial results are most sensitive to the ratio between wind farm capacity and the turbine capacity, also the market share that is interest in applying the offshore port and the day rate of the vessels. When the offshore wind market follows the tendency of developments of the last years, there is a market potential for an offshore port concept to reduce the construction costs. The main recommendations are to analyse the interest of potential port owners, perform a motion response into more detail and validate the financial assumptions.