POW WOW

Prediction Of Waves, Wakes and Offshore Wind

List of participants:

Project summary

Currently, a good number of research projects is underway on the European and national level in the fields of short-term forecasting of wind power, offshore wind and wave resource prediction, and offshore wakes in large wind farms. The purpose of this Action is to co-ordinate the activities in these related fields, to spread the knowledge gained from these projects among the partners, and to start the work on some roadmaps for the future. Therefore, the leaders of research projects are assuming the function of a hinge towards the larger research and user community. Additionally, in the fields of short-term forecasting and offshore energy resource, Expert Groups will be formed to act as the central focus point for external stakeholders (eg the EU commission). The liaison with other groups will also include groups outside of Europe.

To facilitate the spread of knowledge, a number of workshops is planned, being smaller and more focused than the usual conferences. In order to include more researchers from the new and accession states, they can get travel grants paid from the project.

Another important issue hampering the progress in our fields is the difficulty of getting access to good data. In most cases, data on offshore wind or power is strictly confidential, and also data on onshore wind power, especially in conjunction with numerical weather predictions, is not easy to come by. One example of a good testing procedure comes from the Anemos project, where in all 6 test cases were defined, to be run by all involved institutes. This idea is taken to the next level with the set-up of two Virtual Laboratories, one for offshore wake modelling, the other one for short-term forecasting.

In the end, this Coordination Action will also support preparation of next actions such as a Network of Excellence or an Integrated Project, connecting many additional partners within the European Research Area.

Scientific and technological objectives of the project

The trend towards building very large offshore wind farms is evident in many European Countries, with two 160 MW wind farms installed and even larger wind farms planned. In many countries in Europe, most of the good sites on land are already taken, so the large expansion needed to reach the EU target of 12% of renewable energy has to take place offshore. Two major problems remain, hampering progress: the resource estimate before erection of an offshore wind farm is relatively uncertain, due to the lack of a good understanding of offshore wind meteorology regarding the resource and the development of wakes behind turbines, and short-term forecasts of wind power for integration into the network are still not as good as load forecasts.

Based on a typical resource assessment using e.g. one years site measurements compared with decadal variations in wind speed at a nearby site, a point estimate of the wind resource at the measurement height is only accurate of the order ± 5%. While these estimates are state of the art, there are many other sources of uncertainty in the total power output of a wind farm including extrapolating wind speeds to turbine hub-height, power losses from wakes, and spatial variability of wind speeds over the area of very large wind farms. Wakes and multiple wakes in particular, are the major source of uncertainty in power output due to the importance of lower turbulence and varying atmospheric stability on wake development within and downwind of large offshore wind farms. Optimal financing depends on both an accurate resource assessment and an accurate forecast of wind several days in advance. State of the art wake models are not designed for this, rather focusing on averages but even for this purpose they have not yet been verified for multiple wakes.

The situation is similar in short-term forecasting (i.e., everything between a few seconds ahead to a week ahead). Utilities have used short-term forecasting for their power plant scheduling and for trading since the first time practical tools were available, and some utilities could not keep their grid stable was it not for the existing tools. Nevertheless, with more and more wind power coming to ever more countries, good short-term forecasting tools are indispensable for many utilities and market participants in the future. One problem is that utilities without much experience with wind power are only used to the accuracy of their load forecasts, which is usually an order of magnitude better than wind power forecasts. Often though, with the high penetrations found in some regions, the wind power variability is the main factor determining the risk for the grid. Since here, the offshore meteorology is only one variable among many, and since the installed wind power capacity offshore is not dominant yet, it makes sense to also look at the onshore performance.

The project will:

• bridge the gap between resource prediction and short-term forecasting by bringing together the wind and wave communities to compare and learn from methods used in the different disciplines.
• review the state of the art in offshore wind and wave resource prediction, focusing on how the communities from these two fields can benefit from the research carried out separately from both communities.
• form an Expert Group for input to the decision making process in the Framework Programme 7 and for having the direct contact and feedback from users (mainly utilities).
• organise a workshop to bring the two communities together to examine how wind and wave resource studies and short-term forecasts can be enhanced. This will likely focus on shallow water (<30 m) sites for wind farms and near shore wave energy devices although water depths of 50-80m will also be considered for wave energy and potentially future wind farms.
• organise a scientific session at a European conference (likely the European Geophysical Union annual conference) to further extend the expert group and then focus more on the practical details of how modelling approaches can be integrated at a final workshop.
• attempt to link between networks funded by the EU including Wavenet, WindEng and others which do not focus on the resource such as CA Ocean Energy and COD (CA on Offshore Wind Development). It will utilize also elements from other EU funded projects like ENVIWAVE.
• furnish a Virtual Laboratory, where other modellers can try their models on the same footing with everyone else, using identical data.
• address whether wind and wave forecasting can be improved for load predictions at offshore wind farms and for wave energy devices.
• list uncertainties in wind and wave prediction methods in order to understand where the largest errors arise and ultimately how these can be reduced.
• help on the better integration of modelling approaches for resource prediction and a more harmonised approach. It is also worth noting that we will consider the applicability of the different approaches in all European seas - we have partners with experience in the Atlantic, North, Baltic and Mediterranean seas. This will be the first project that considers also the geographical variability.

A major issue here is not just the long-term forecasting of wakes which is used for initial estimates of power output from wind farms (so mainly for planning and financing) but also the online prediction of wakes that links with short-term forecasts of power output from wind farms. Scientists and engineers need to work together to consider how short-term forecasting and wake modelling can be operationalised. The work will take the form of wake case studies via a virtual laboratory; an open workshop for scientists and engineers and finally a set of guidelines will be issued for best practise in including wake models in short-term forecasts. In addition to the overall theme of integration and harmonisation, this project will provide major benefits to the successful development of wind and wave energy by improving both long-term and short-term predictions of energy output which are fundamental to the success of renewable energy in the liberalised electricity market.

Currently there are operational facilities that provide wind and wave forecasts at different time scales and resolutions (e.g. the operational activities at http://forecast.uoa.gr). These facilities will be utilized for training and dissemination to end users.

Once an accurate forecast is obtained the largest single correction needed to capture power output is for wind turbine wakes. Wake effects have been studied in a number of projects incorporating both measurements and modelling. One of the project's objectives will be to assess which models can be operationalised in short-term forecasts, and to review the major sources of uncertainty. Uncertainty is a key factor in wind farm financing and should also be used to identify areas for future research.

IASA/AM&WFG contribution

IASA/AM&WFG will participate in several work packages and actions namely:

(i) WP1 - Coordination activities in offshore meteorology

• Set up of the expert group to study integration of wind and wave modelling for energy prediction and
• Study and benchmarking of resource models.

(ii) WP2 - Coordination activities in short-term prediction

• Contribute in the formation of an Expert Group Short-Term Prediction
• Contact the relevant operational meteorological centres in Europe, and perform an overview of the atmospheric and wave models used and the current strategies on forecast improvement in order to prepare a state-of-the-art document on numerical weather prediction applications for power production.
• Form a Virtual Laboratory for Short-Term Prediction. IASA will evaluate the submitted predictions and will make a synthesis of the results.
• Best Practice for the Use of Short-Term Predictions. IASA will contribute on the utilization of new products available from weather and wave forecasting operational centres.
• Contribute to International Liaison with a workshop in order to coordinate the research and disseminate the results of European research with relevant institutions outside of Europe.

(iii) WP4 - Dissemination and future activities

• IASA will contribute on training end users or commercial partners on the utilization of new products available from weather and wave forecasting operational centres.