Ana Estanqueiro

A Dynamic Wind Generation Model for Power Systems Studies

In this paper, a wind park dynamic model is presented together with a base methodology for its application to power system studies. This detailed wind generation model addresses the wind turbine components and phenomena more relevant to characterize the power quality of a grid connected wind park, as well as the wind park response to the grid fast perturbations, e.g., low voltage ride through fault. The developed model was applied to the operating conditions of the selected sets of wind turbine experimental benchmark data from Azores and Alsvik wind parks, both for steady and transient operation of the grid. The results show a fairly good agreement in the relevant range of frequencies and indicate the model may be used as a tool for power system studies.

Experience and Challenges With Short-Term Balancing in European Systems With Large Share of Wind Power

The amount of wind power in the world is quickly increasing. The background for this development is improved technology, decreased costs for the units, and increased concern regarding environmental problems of competing technologies such as fossil fuels. Some areas are starting to experience very high penetration levels of wind and there have been many instances when wind power has exceeded 50% of the electrical energy production in some balancing areas. The aims of this paper are to show the increased need for balancing, caused by wind power in the minutes to hourly time scale, and to show how this balancing has been performed in some systems when the wind share was higher than 50%. Experience has shown that this is possible, but that there are some challenges that have to be solved as the amount of wind power increases.

Barriers (and Solutions...) to Very High Wind Penetration in Power Systems

In this paper the existing technical barriers that prevent the accomplishment of a very high wind generation penetration in a power system are presented. Since several countries and regions in Europe are already experiencing such high wind penetration or, as a minimum, planning their grids and operation strategies to cope with wind penetration from a high to a very high level, the solutions already identified for the most common constraints are also identified.

Currents of change

The power systems in Denmark, Portugal, Spain, Ireland, and Germany have some of the highest wind penetrations in the world, as shown in the paper. In this article, the situations of five countries with high wind penetration are briefly presented, with special emphasis given to their future needs with respect to accommodating targeted wind power amounts. The final section provides an overview of offshore grid developments and plans in Europe.

On the use of Markov chain models for the analysis of wind power time-series

Wind energy is becoming a top contributor to the renewable energy mix, which raises potential reliability issues for the grid due to the fluctuating and intermittent nature of its source. This paper explores the use of Markov chain models for the analysis of wind power time-series. The proposed Markov chain model is based on a 2yr dataset collected from a wind turbine located in Portugal. The wind speed, direction and power variables are used to define the states and the transition matrix is determined using a maximum likelihood estimator based on multi-step transition data. The Markov chain model is analyzed by comparing the theoretically derived properties with their empirically determined analogues. Results show that the proposed model is capable of describing the observed statistics, such as wind speed and power probability density as well as the persistence statistics. It is demonstrated how the application of the Markov chain model can be used for the short-term prediction of wind power.

Impact of Weather Regimes on the Wind Power Ramp Forecast in Portugal

Short-term forecasting and diagnostic tools for severe changes of wind power production (power ramps) may provide reliable information for a secure power system operation at a small cost. Understanding the underlying role of the synoptic weather regimes (WRs) in triggering the wind power ramp events can be an added value to improve and complement the current forecast techniques. This work identifies and classifies the WRs over mainland Portugal associated with the occurrence of severe wind power ramps. The most representative WRs are identified on compressed surface level atmospheric data using principal component analysis by applying K-means clustering. The results show a strong association between some synoptic circulation patterns and step variations of the wind power production indicating the possibility to identify certain WRs that are prone to trigger severe wind power ramps, thus opening the possibility for future development of diagnostic warning systems for system operators use.

Multi-Agent Energy Markets with High Levels of Renewable Generation: A Case-Study on Forecast Uncertainty and Market Closing Time

This article uses an agent-based system to analyze the potential impacts of variable generation on wholesale electricity markets. Specifically, the article presents some important features of the agent-based system, introduces a method to forecast wind power, and describes a case study to analyze the impact of both wind forecast errors and high levels of wind generation on the outcomes of the day-ahead market. The case study involved two simulations: a base case, where the market closes at 12:00 noon and the bids of a wind producer agent are based on a forecast performed 12 to 36 hours ahead, and an updated forecast case, where the market closes at 6:00 p.m. and the bids of the wind producer agent are based on an updated forecast. The results indicate that wind power forecast uncertainty may indeed influence market prices, highlighting the importance of adaptations to the market closing time.

A methodology for the identification of the sustainable wind potential. The Portuguese case study.

The exponential grow of the wind sector in Portugal required the development of planning tools for the siting of the wind farms, its connection to the existing grid, as well as the assessment of the countrys existing wind resource capable of enabling an economic, social and environmental sustainable development. The methodology developed and presented in this paper was initiated a decade ago with the classification of the existing wind data adequate to wind energy resource assessment as well as the identification of the constraints to the deployment of wind power plants. This GIS based methodology was systematically applied to the Portuguese territory and resulted on the identification of the available optimum sites for wind plant development at the lowest grid connection costs. The methodology may be easily applied to other countries or regions, thus enabling a systematic and objective approach to the wind power deployment.

Assessment of Power Quality Characteristics of Wind Farms

In this paper the main parameters to assess the power quality of grid embedded wind farms are presented. International standards to assess and quantify the power quality of grid connected wind turbines exist for some years now, and are here extrapolated to wind farms aggregates when possible being the correspondent methodologies identified in the document. Recently, the grid code requirements posed a novel challenge to this technologic area, particularly since they were issued with national or local objectives and without particular normalized global concerns. The form how the international standards are evolving in order to cope both with the power systems industry local requirements, but also with the global wind turbine manufacturers principles is addressed in the paper.

Integration of renewable sources in the electric system using Virtual Renewable Power Plants

The concept of “Virtual Renewable Power Plants - VRPP” enables several positive factors for the electric integration of Renewable Energy Sources (RES), namely (a) the smoothing of time based fluctuation of the power delivered by the RES, (b) the use of the natural complementary of renewable resources availability (c) the establishment of synergies between different RES as well as the combination of their production. The present work aims to identify the synergies between wind and photovoltaic (PV) plants, regarding their daily profiles l complementarity and resource availability; as well as the technical and economic added value of a VRPP. Results show an increase of 5.3% in the capacity factor when 2 MWp of PV is added to an 8 MW wind farm, considering all infrastructural capacity limits. Moreover, additional results include the characterization and optimization of hybrid virtual wind-PV plants production profile.