A feasibility study for the installation of 10 MW offshore wind turbines with an SSCV

Abstract

Since the oil price collapse at the end of 2014, operators in the offshore industry experience a decline in revenues and a need for downsizing. Simultaneously, the wind industry is growing every year, as an increasing amount of companies and consumers are investing in green energy. This creates opportunities for Heerema Marine Contractors (HMC), as they have ample experience in offshore installations, operations and maintenance. Currently, in most cases a Jack-Up Vessel (JUV) is used to install offshore Wind Turbine Generators (WTGs). With the exception of Hywind, a wind farm of floating wind turbines commissioned with a Semi-Submersible Crane Vessel (SSCV) near shore and thereby protected from large waves, there is little experience in installing large WTGs with a floating vessel in offshore sea states. Current trends in Offshore Wind Farm (OWF) development are the upscaling of WTGs and installations in deeper waters, both resulting in more complex operations. In the current market however, there are many installation operators with lower priced JUVs. Therefore, to compete and make it economically viable for HMC to enter this industry, HMC must be able to install WTGs at a faster rate than the rate of conventional installation vessels.

The main objective of this master thesis is to determine the economic and technical feasibility for HMC to enter the offshore wind industry as an installation operator. First, the attractiveness of the offshore wind market is analyzed. For the analysis of the offshore wind market as a business environment the theoretical framework ‘PESTLE’ is applied. Through the application of the ‘Porter’s Five Forces’ model, the competitive position of HMC as an potential entrant to the offshore wind market is analyzed. Second, insight is gained under which conditions it is economically feasible to use a SSCV for the installation of 10 MW WTGs. Different logistical methods are compared in terms of installation time and installation costs, as a function of site particularities, and by comparing the use of a JUV, a purpose-build installation vessel and a SSCV. As the installation of WTGs makes up a significant percentage of the total costs of a project, the workability of the installation vessel is of great importance. To address the technical feasibility, this thesis aims to quantify the influence of wave forecast on the workability of installing a fully-assembled 10 MW WTG with a SSCV.

The offshore wind market in the North Sea as a business environment is evaluated to be attractive. Additionally, there is a large potential for building new OWFs in the North Sea and governmental support is significant and assumed to be stable in the future. The trends that OWF development moves into deeper waters and further offshore, as well as the increase in size of wind turbines are all positive for floating installation vessels with larger crane capacity, as many JUVs have reached their maximum capacities. Although the barriers to enter the OWE industry are high, the power of the OWF developers is significant and the price competition among installation operators is fierce, the threat of alternative WTGs becoming mainstream is small due to economies of scale and the enormous potential of new OWF development. It is recommended to enter the market with a HMC SSCV and focus on the installation of extra-large WTGs (≥10 MW) and thereby succeed in the offshore wind market by specialization.

Based on the current ECN Tool (version 2.1) and the assumptions made, it is economically feasible to use an SSCV for the installation of completely pre-assembled wind turbines in a large OWF (>1500 MW). In the scenario used in the ECN Tool, the duration of the WTG lift, installation and the SSCV sailing to the next TP should be less than six hours. According to the industry, a great concern is the movement of the SSCV during the set-down, and thereby making it a complex operation with impact loads that are more difficult to predict. Wave forecasting is the key that can take away this concern, however it is still an ‘unproven innovation’ in the industry. With the use of a 2 minute wave and motion forecast, the waiting on weather for the ‘WTG lift’ and ‘WTG set-down’ on the TP can be reduced from 28 hours per turbine to 7 hours for the ‘WTG lift’ and 48 minutes for the ‘WTG set-down’. Subsequently, based on a 2 minute wave and motion forecast, the impact load on the bottom of the tower and the TP can be reduced by 13 % by choosing an optimal sea elevation for the set-down moment. As the average waiting on weather time is relative high for installing the third blade and lifting the WTG, it is furthermore recommended to investigate the influence on wave radar forecast on these steps. The implementation of wave radar technology during the installation process, is to be investigated further.