Installing wind turbines offshore has a number of advantages compared to onshore development. Onshore, difficulties in transporting large components and opposition due to various siting issues, such as visual and noise impacts, can limit the number of acceptable locations for wind parks. Offshore locations are usually far enough away from populations to reduce objections from residents and can take advantage of the high capacity of marine shipping and handling equipment, which far exceeds the lifting requirements for multi-megawatt wind turbines. In addition, the winds tend to blow faster and smoother at sea than on land yielding more electricity generation per square meter of swept rotor area. Especially larger onshore wind farms tend to be in somewhat remote areas, so electricity must be transmitted over long power lines to cities. Offshore wind farms can be closer to coastal cities simplifying some transmission issues, yet far enough away to reduce visual and noise impacts.

Good wind resource, proximity to load centers, and expansion of development areas are some of the reasons why development of offshore wind energy is moving forward. By the close of 2005, 804 MW of offshore wind power plants were operating in Denmark, the Netherlands, Sweden, and United Kingdom.

Challenges for offshore development include higher initial investment costs for large machines and sea cables for the connection to land; more difficult access to the turbines resulting in higher maintenance costs; and more severe environmental conditions at sea due to salt water and additional loads from waves and ice.

Despite the difficulties of offshore development, it holds great promise for expanding wind generation capacity. In Europe, the space available for offshore wind turbines in many countries is larger than onshore. For example, in the Netherlands roughly 3 GW of wind power could be installed in areas available outside the 12-mile zone (about 22 km) with a water depth of less than 20 m. The Netherlands shares this advantage of shallow water with countries such as Belgium, Denmark, Germany, and the United Kingdom. Figure 1 below shows the cumulative installed offshore capacity to by the end of 2005 on the basis of 925-MW of total installed capacity.

Figure 1 – Offshore Wind Projects Installed through 2005
Based on a Total of 804 MW

Need to Collaborate Identified

Work is underway in many countries to address issues surrounding wind development offshore. To identify what the critical research issues were for offshore wind and to determine if a collaborative international research opportunity existed, several meetings and workshops were held between 2003 and 2004. First, in October 2003 and again in October 2004, workshops on deep-water technologies were held in Washington, D.C. with participants from the US and Europe, see: http://www.nrel.gov/wind_meetings/offshore_wind/. It was clear from these workshops that opening vast windy areas of deep-water ocean for electric power generation will require development of new technologies and strategies. Meanwhile in Europe, IEA Wind Annex XI sponsored a Topical Experts Meeting (#43) on Critical Issues Regarding Offshore Technology and Deployment in March 2004 in Denmark. The meeting gathered 18 participants, representing Denmark, Finland, the Netherlands, Sweden, the United Kingdom, and the United States. Presentations covered both detailed research presentations and more general descriptions of current situations in Denmark, Finland, the Netherlands, United Kingdom, and the United States. The result from all of these meetings recommended the IEA Wind Implementing Agreement as a framework for expanding international cooperation on critical research activities pertaining to offshore wind energy.

Task 23 Approved

In May 2004, the IEA wind executive committee approved a proposed research Annex to sponsor focused workshops and develop research tasks directed at understanding issues and developing technologies to advance the development of wind energy systems offshore.
The objectives of this annex are to do the following related to offshore development of wind energy systems:

• Conduct R&D activities of common interest to participants to reduce costs and uncertainties
• Identify joint research tasks among interested countries based on the issues identified at the Topical Expert Meeting #43 on Critical Issues Regarding Offshore Technology and Deployment
• Organize workshops on critical research areas for offshore wind deployment. The goal of the workshops is to identify R&D needs of interest to participating countries, publish proceedings, and define joint research activities for the Annex participants.

During the first year of the Annex, (May 2004 to May 2005) the goal was to identify interested participants, project leaders for each research area, and prepare Work Programs and Budgets for each collaborative research activity. Since then the annex membership has grown as shown in Table1.

OJECTIVES WITH PROPOSED SUBTASKS

This Task comprised of two subtasks with Risø National Laboratory in Denmark and the National Renewable Energy Laboratory in the United States serving as joint operating agents. Risø leads Subtask One: Experience with Critical Deployment Issues, and NREL will lead Subtask Two: Research for Deeper Water.

MEANS TO ACHIEVE OBJECTIVES WITH PROPOSED SUBTASKS

This annex is comprised of two subtasks with Risø National Laboratory in Denmark and the National Renewable Energy Laboratory in the United States serving as joint operating agents. Risø will lead Subtask One: Experience with Critical Deployment Issues, and NREL will lead Subtask Two: Research for Deeper Water.

SUBTASK ONE: EXPERIENCE WITH CRITICAL DEPLOYMENT ISSUES

Denmark, through RISØ National Laboratory, will serve as operating agent for this subtask, led by Jørgen Lemming. Workshops have been planned in three research areas including:

Research Area 1: Ecological Issues and Regulations
Research Area 2: Electric System Integration
Research Area 3: External Conditions, Layouts and Design of Offshore Wind Farms.

A volunteer host country will assume the responsibility for each research area until formal research plans are adopted.

The Netherlands has agreed to host the first workshop for Research Area 1 (Ecological Issues And Regulations) but a meeting date has not yet been set. The United Kingdon hosted the first workshop on Grid Interconnection and the meeting was held at Manchester University 12-13 September 2005. Denmark hosted the first workshop for Research Area 3 (External Conditions, Layouts and Design of Offshore Wind Farms) held on December 2005 at RISØ National Laboratory. A significant topic dealing with Operation and Maintenance Issues was also considered a high priority topic but at this time there are no plans to hold a workshop to cover this topic. Each research area is described below:

Research Area 1: Ecological Issues and Regulations
The areas of collaboration to be discussed at the first workshop are:

Research Area 2: Electric System Integration

The first workshop in Research Area 2, discussed the technical options and the role of enabling technologies in achieving reliable design of offshore connections. This includes the development of offshore grids for collection and transport of significant amounts of power to the shore and the integration with the onshore transmission network.

Also, cost effective integration of offshore wind generation will require the development of systematic and consistent approaches to resolving a number of technical, commercial, and regulatory issues. These include license conditions, offshore security standards, transmission charges, grid code, connection and use of system codes, all of which were included in the scope of the workshop.

Based on a number of presentations on experiences from existing offshore wind farms and the planning process, the delegates at the workshop in Manchester concluded that the following topics were the most important for further work under Task 13:

The working title for the working groups covering the subjects is suggested to be: Connection of Offshore Wind Farms to Onshore Grids.
Research Area 3: External Conditions, Layouts, and Design of Offshore Wind Farms
The purpose of the workshop in Research Area #3 is to explore the key issues and highlight the topics related to the following areas:

SUBTASK TWO: RESEARCH FOR DEEPER WATER

The second subtask will address issues pertaining to deployment of wind turbines in water depths greater than 30 m. This subtask is led by NREL, with the primary research area focused on a Codes Comparison Collaborative (OC3) that is sharing information, research, and data to advance the understanding of models that can predict the behavior of support structures that deviate from the present monopile technology.

Coupled turbine/substructure dynamic modeling - A Kick-off meeting was held in October 2004 in Washington D.C. United States. Representatives from Denmark, Japan, Norway, the United Kingdom, and the United States attended. To maximize the benefit to the research community and to take advantage of experience with current turbine modeling effort in shallow water, it was decided to include both shallow and deep-water modeling. Uncertainties associated with load prediction increase the risk for offshore machines, and the development of accurate dynamic models for load prediction is the best way to reduce these uncertainties. Participants will share their codes among the other participants and compare assumptions, model fidelity, and the results of model outputs for controlled cases determined by the group. Through this type of rigorous sharing and subsequent validation efforts, offshore researchers will accelerate the development of codes for modeling a wide range of offshore wind turbines systems. A research topic “Coupled turbine/substructure dynamic modeling” was discussed and targeted for detailed collaborations and planning at a follow up meeting held at Risø National Laboratory in Denmark in January 2005. The January meeting attracted 32 participants from 8 countries.

Results Expected

The results of the Subtasks One and Two in the first year are expected to be the following. Technical proceedings will be published from the workshops on critical research areas from the two Subtasks and made available to member countries only through this website. In addition, the results will be presented by the operating agents or their representatives to various conferences and to the IEA Executive Committee. Collaborative research activities under each Subtask will be defined with participating members, work program, and budget. A project leader for each research area will be designated who reports to one of the Operating Agents.

Time Schedule

The Annex shall continue for a period of four years beginning May 2004, when it was approved in-principle in Chester, UK. The Annex may be extended for such additional periods as may be determined by two or more participants, acting in the Executive Committee and taking into account any recommendation of the Agency’s Committee on Energy Research and Technology (CERT) concerning the term of the Annex. Extensions shall thereafter only apply to those Participants who agree to the extension. A preliminary time schedule is provided below.

Participation

Participation is open to any organization within a country belonging to the IEA Wind Implementing Agreement. No fees are required through May 2005. The United States and Denmark have agreed to bear the cost of shared operating agents through 2005 and the participants in the planned workshops bear their own costs. Fees for the coming years of operation will depend on the research tasks identified and approved by participants.

Authors: Jørgen Lemming, Risø National Laboratory, Denmark and
Walter Musial, NREL, United States.