Optimising offshore wind commissioning logistics

Transcription

1 THINK TANK Optimising offshore wind commissioning logistics Words: Dr. Marcel Wiggert and Maxim Hartung The development of appropriate logistic concepts is a key factor for an economically successful offshore wind park. In the past the analysis and optimisation of these concepts have mostly focused on either the logistics for transport & installation (T&I) or operation and maintenance (O&M). Less attention has been paid to the important phase of commissioning. Yet it is this phase which is decisive for the rapid connection of the wind turbines and the feeding of their wind electricity into the grid. 96

2 THINK TANK Copyright: Helmut Gross Copyright: Matthias Ibeler, DOTI 21/alpha ventus The commissioning process takes up much more time than the actual installation of the wind turbine. The various process workflows, the ships used, and the operating limits mean the installation and commissioning processes often diverge (Figure 3). A logistics concept must therefore optimize its resources paying due consideration to the weather risks in order to minimize this divergence. Methods used to analyse the weather risks In the COAST research project funded by the German Federal Ministry for Economic Affairs and Energy, the WaTSS Weather Time Series Scheduling method was developed at Fraunhofer IWES, together with partners from industry and implemented into the COAST Comprehensive Offshore Analysis and Simulation Tool software. The COAST software computes the weather risk of project plans taking into account the local weather conditions and operational limitations1. For the present investigation and the comparison, a specific model was Copyright: press picture Repower developed for commissioning. Before the commissioning model is explained, the WaTSS analysis and the simulation modes of the COAST software will be briefly presented. WaTSS Weather Time Series Scheduling method The aim of the WaTSS method is to analyse the weather risks of project plans in combination with the local weather conditions and the operating limits of the equipment used. To this end, the project plans investigated are aligned with long-term time series, e.g. 3-5 years, of local weather conditions, paying due consideration to the procedures and operating limits i.e. starting from the simulated project start, each step of the work is shifted depending on the weather conditions at the simulated point in time and the operating limits of this step. A statistical analysis of the project durations, over the years investigated, is then undertaken. This means the distribution of the project durations is available and can be used to derive the risk profile. The WaTSS method was implemented in the COAST software with two simulation modes: Yearly Simulation and Constant Interval Simulation. In the first approach, the project plan is started and adapted for each year at the defined starting date. With the Constant Interval Simulation, on the other hand, the starting date is continuously shifted by a selected interval, e.g. 1 day, each time and a simulation is undertaken for each starting date. To carry out the task introduced, the analysis of the logistics processes during commissioning, the problem is divided into three sub-tasks (Figure 1). The starting point is to examine the weather risk during the installation of the wind turbines using the COAST software and thus define the earliest starting point for the commissioning of the individual turbines. 1 Wolken-Möhlmann, Gerrit; Lilov, Hristo; Wiggert, Marcel: Offshore Logistik Wetterabhängigkeit und Prognoseverfahren für Bau und Betrieb von Offshore-Windparks Abschlussbericht 97

3 SCENARIOS LOGISTIC-CONCEPT ANALYZING ANALYZING W eather Risk Installation W eather Risk Commissioning Post Processing Analyzing/Optimizing COM BINED OPTIM IZATION Figure 1. Commissioning simulation project process COAST: Yearly Simulation Installation dates of the wind turbines per analyzed year Goal: Definition commissioning start dates COAST: Constant Interval Simulation (Δ=1 day) Success of the commissioning work for every day of the time series Goal: Definition of the turbine accessibility OW P IW ES Baltic Reference Regardless of the number of teams, the accessibility of the installation for the technicians is analysed again using the COAST software. In the third step, the individual results are analysed, in combination, as a function of the number of teams in the post-processing, e.g., in MS-Excel or MATLAB. This is followed by the evaluation of the ship, working, and bad weather days (WoW Waiting on Weather) required and the associated costs. The daily rates of the ships, teams, and the opportunity costs are integrated into the present model as costs. Case Study IWES Baltic The project presented here is based on the reference Offshore Wind Park (OWP) IWES Baltic (see location in figure 2). The considered parameters are presented in Table 1. The results for the three scenarios investigated have been simplified for this article. To analyse the logistic processes during commissioning, three sub-tasks needed to be executed: 1. The weather risk during the installation of the wind turbines was examined using the COAST software by Fraunhofer IWES and the earliest starting point for the commissioning of the individual turbines was defined. Figure 2. Wind farm cluster: IWES Baltic Sassnitz 2. Independent of the number of teams, the accessibility of the installation for the technicians was analysed using the COAST software. 3. The individual results were analysed in combination as a function of the number of teams. In addition the ship, working, and bad weather days (WoW-Waiting on Weather) required and the associated costs were investigated. The daily rates of the ships, teams, and the opportunity costs were integrated into the present model as costs. Boundary Conditions Assumptions Number of Turbines 6 Port Distance 4 km Start Date Commissioning (1Team) 16 h / turbine (net) Team costs 3, Euro / Day Opportunity costs 3, Euro / Day per turbine Weather data coastdat v1 ( ) [4] Duration of installation incl. weather risks (P5) 1 days (COAST) Table 1. Boundary conditions of the reference OWP IWES Baltic The COAST software analyses project plans using several decades of weather data for the area of interest. As a result, a significant number of different project durations throughout this period is calculated and statistically analysed. This allows further analysis regarding weather risk and risk profiles for different scenarios. It was assumed that the ships and teams were all available for the whole commissioning period. Furthermore, only full working days were taken into account. The opportunity costs were calculated from the net commissioning duration. Three different logistics scenarios were considered for the commissioning of the wind turbines (details in Table 2). 98

4 Copyright: Stiftung OFFSHORE-WINDENERGIE; Repower; Jan Oelker Nb. [Turbine] Installation Process Commissioning Team 1 Commissioning Team 2 Commissioning Team 3 Commissioning Team 4 Figure 3. Working progress-time diagram of the WEA installation and commissioning CTV HV SOV Time Type Crew Transfer Vessel Hotel Vessel Service Operation Vessel Operation time 12h/7 days 24h/7 days 24h/7 Capacity 3 Teams 2 Teams 2 Teams Base Case 6 Teams 6 Teams 6 Teams Operational Limits h s = 1.5m h s = 1.5m h s = 2.5m Costs 4, Euro /day 2, Euro /day 24, Euro /day Working time (on turbine) 8h/day 1h/day 1h/day Commissioning [net] 2 days 8 days 8 days Processes Transfer Harbor WTG Transfer OWP Harbor Table 2. Three logistical scenarios for the commissioning Transfer HV WTG Transfer WTG HV Transfer HV WTG Transfer WTG HV Transfer SOV WTG Transfer WTG SOV Transfer SOV WTG Transfer WTG SOV Basis for planning, logistics and contract drafting In the first scenario, Crew Transfer Vessels (CTV) sail directly from Sassnitz harbour to the wind turbines and the technicians transfer from here to the installations. After working for eight hours on the installation, they are collected again by the CTV and transferred back to the harbour. The work is only carried out during daytime in a 12 hour shift between 6: a.m. and 6: p.m. In the second scenario, a hotel vessel (HV) is used, and there is a switch to a 2 x 12 hour shift system. Accordingly, work is carried out at night as well, and the technicians remain in the OWP. This thus reduces the transfer time and the technicians can carry out the commissioning on the installation for 1 hours. In the third scenario, a Service Operation Vessel (SOV), with much higher operating limits, is used for the transport and the overnight accommodation of the technicians in the field. The technicians again work a 2 x 12 hour shift system. Further information on the three scenarios can be found in Table 2. Finding reasons for delay The three scenarios differ essentially in the operating limits, a 12/7 or 24/7 shift system, the times on the turbines and the costs. Starting with the basic scenario with 6 teams, the number of teams and the weather risk profile are determined for each logistics concept. An increased number of teams has a positive effect on the duration of the commissioning, but in some cases, further vessels are required in the CTV model. Longer durations, in turn, take the work into seasons where the weather is worse and involve a higher weather risk. Longer project duration is additionally penalised by opportunity costs. 1

5 Copyright: Image Source, Fotolia % 1 SOV HV CTV Risk Spectrum Costs [Million ] Figure 4a. Comparison base case with 6 teams: Cost and risk profile Construction (net) Commissioning (net) WoW Ressources 35 Project duration [days] Project duration [days] Costs [Million ] CTV HV 1 SOV HV CTV 15 SOV 1 5 NET DURATION Base case SOV HV Number of commissioning teams CTV CTV HV SOV Figure 5. Impact number of teams on the costs and project durations (P5) Figure 4b. Comparison base case with 6 teams: Project duration (P5) The commissioning periods are clearly too long compared to the installation times and the two processes drift widely apart. If the different parts of the project durations are investigated: construction (net), commissioning (net), bad weather commissioning (WoW), and delays due to resources, see Figure 4b, it quickly becomes clear that the missing resources are the main reason for the delays. Optimal number of commissioning teams The costs for various combinations were determined for the analysis of the optimal number of teams taking into account the weather risk (Figure 5). The costs for the individual concepts decrease with an increasing numbers of teams up to the point above which the use of new teams becomes inefficient. The commissioning cannot overtake the installation. The optimal number of teams can thus be derived for each individual vessel concept: SOV 1 teams, HV 12 teams, and CTV 14 teams. Most suitable vessel concept for commissioning In the presented model project, the order of the efficiency does not change as far as the costs and risk profiles of the three concepts are concerned when compared to the basic scenario. Even when the costs of the HV 12 concept are assumed to be the same, the negative cost risk range (P1 to P5) in the HV 12 concept is significantly higher than for the SOV 1 concept. Basically, the delay with the individual installations, in conjunction with the resources and weather risks, has the greatest impact on the costs. This also becomes clear in the course of the project durations and the commissioning costs (Figure 6). 11

6 Copyright: Stiftung OFFSHORE-WINDENERGIE; DOTI; Matthias Ibeler Summary and outlook In the presented investigation, three logistic scenarios: CTV, HV, and SOV, were analysed, optimised, and compared with respect to the number of teams and the associated weather risks for a model wind park in the Baltic Sea. The question of an optimal concept cannot be answered across the board, but always depends on the specific risk profile of the project and the appetite of the investor for accepting risks. % Copyright: Stiftung OFFSHORE-WINDENERGIE; Matthias Ibeler 1 SOV -1 HV-12 CTV Costs [Million ] Figure 6. Cost distribution in case of the team optimization The COAST software and the model used to analyse the commissioning logistics have shown themselves to be a suitable approach for a combined analysis, since costs and risks can be considered at the same time. The following three points were brought out in the work presented: 1. The optimal number of commissioning teams depends on the overall concept: ship, team, cost structure, and weather risks. 2. To assess the logistics concepts, it is not sufficient to consider only the costs, e.g., P 5 value; the cost risk range must enter into the decision as well. 3. Opportunity costs have a decisive impact on the optimal concept. The introduced example and analysis methods have been simplified compared to the original case. Other aspects can be considered e.g. effective team utilisation, combined approaches of teams/vessels and different working shift concepts. For studies regarding the North Sea with rougher weather conditions and larger port distances of the offshore wind parks, a more intensive impact of the weather in the results is expected. For the Baltic Sea, ice impacts and temperatures should be included in further works. 12