Offshore installations: Weather and project risk analysis at IWES

Here at IWES, we assess weather risks using the Advanced Weather Time Series Scheduling (AdWaTSS) method, which is more precise than just statistics, and frequencies of tasks. For the offshore wind industry, we analyze and verify the time schedules of offshore transport and installation (T&I) projects with regard to the weather risk assessment (weather downtime). Our unique selling point is that we work with our in-house tool and with project planning schedules provided directly by the client using project management software: we combine the topics of project simulation, weather systems, and project planning.

IWES consulting services for weather risks

Offshore wind farm installations face weather-related risks due to the harsh and unpredictable conditions at sea. To ensure the safety of workers and equipment, strict weather restrictions are in place for certain operations, such as limiting the maximum wind speed for blade installations or maximum current speed for cable laying. Waiting for favorable weather conditions can result in weather downtime and trigger knock-on effects, which ultimately lead to additional costs.

Assessing weather risks is standard practice in the installation and maintenance of offshore wind farms. The innovation here lies in using historical weather data to estimate available weather windows in a more precise manner – compared to weather window statistics – and therefore to minimize marine operation costs. While the wind industry has matured in recent years, the limited availability of installation vessels has resulted in exorbitant chartering fees: contractors and operators are required to engage in negotiations regarding who should bear the costs for the weather delays, with the aim of minimizing weather risks.

To mitigate these risks, the Fraunhofer IWES tool COAST employs a comprehensive approach to project planning. It delivers us a better assessment of the risks associated with the project such as predicting the extent of potential delays in the project schedule and calculating the final project costs. This approach provides valuable insights into the potential knock-on effects.

Precise calculations with the COAST software

What is COAST and what makes it so special?

The custom-developed COAST tool is able to calculate weather windows via discrete time series simulation, quantifying the relative and total delays in a project schedule. An offshore project typically consists of a series of activities or tasks connected to each other, some of which are subject to weather restrictions.

COAST simulates the project tasks with their operational limits into 12-month time series of historical weather data, searching for weather windows where all conditions are favorable. What makes it so special is that COAST integrates project planning schedules developed in project management software tools such as PRIMAVERA P6 and Microsoft Project with weather-related operational restrictions.

COAST can be tailored to consider different attributes of each task in a project plan:

  • its relationship to other tasks (i.e., the task can only start when its predecessor is finished);
  • its time-related limitations (i.e., the task should start as soon as possible or it cannot take place in a certain month because of fish spawning seasons);
  • its weather restrictions (the task cannot take place when the temperature is below zero degrees, otherwise the cable might break); and
  • its location, especially relevant for cable-laying activities where the weather conditions vary throughout the cable route.

Moreover, COAST is also able to split the placement of an activity into smaller weather windows if the activity can be carried out in that way.

One focus: minimize risks associated with the cable installation

Transmission system operators (TSO) establish the grid connection for German offshore wind farms. Installing export cables is a challenging process, as the cable route should be carefully planned to avoid rocky seabed and environmentally protected areas, special vessels are required to handle heavy and large cables and, in general, it is a process greatly dependent on weather conditions, see Figure 1.

Figure 1: Connecting wind farms in the Westlich Adlergrund. The challenge: different zones of water depths (shallow and medium water depths) and the island of Rügen have an influence on the environmental conditions – wind direction, waves [Figure generated using M_Map].

So how do the TSOs do it? They launch an EU-tendering procedure where manufacturers submit their project planning schedules for the supply and installation of the connection, including the time they need to wait for weather conditions to be suitable for work also known as waiting on weather (WoW) times. This allows the TSO to compare and select the best proposal, considering factors such as project efficiency, cost, and weather downtime.

The verification of the bidder’s estimation of weather downtime has already led to several collaborations between TSOs and Fraunhofer IWES. These collaborations include the evaluation and verification of weather and project risks from the tender proposals and the analysis of the quality of project planning schedules for cable-laying operations.

In the case of the risk evaluation of cable-laying activities for a TSO, we study the bidders’ proposals and present a comparison of all their results answering questions such as: How was their distribution of effort in each location? What would the effect of a task delay be on the entire project duration? How was their weather risk distribution? How much money does the TSO have to set aside to balance the delays caused by weather? And many other questions.

In the case of the quality assessment of project planning schedules, we carry out a thorough analysis of all the tasks in the schedule. The attributes of each task are studied, the task’s relationship to other tasks, the influence of weather on non-weather dependent tasks, as well as project controlling. In-depth understanding of project scheduling between T&I contractors and client allows us to identify the impact of weather downtimes and pinpoint bottleneck activities that cause significant delays. By analyzing the critical path of the project and identifying high-risk areas, we offer targeted recommendations to help mitigate delays and improve overall project performance.

In the end, our detailed analysis of weather risks and project planning schedules allows us to provide the TSO with a comprehensive understanding of the bids from potential contractors. This, in turn, enables the TSO to make an informed decision when selecting the winning proposal.

Our analyses with COAST are available for any planned offshore projects, including wind farm installation or decommissioning activities and large component replacements.

More information:

Large-Scale Wind Farm Effects – A Key Contributor for Economic Wind Farm Operation? (
Waves, buoys, offshore wind energy: Wind measurement in the German Bight (

Leave a Reply

Your email address will not be published. Required fields are marked *