European Wind Integration Study (EWIS) -Towards a Successful Integration of Wind Power into European Electricity Grids

The support of renewable energy sources (RES) is one of the key issues in European energy policy. In order to cope with this challenge, European Transmission System Operators launched a European wide grid study on the integration of wind power, focusing on measures needed to be taken by legislators, regulators, grid operators and grid users, aiming at establishing a harmonised set of rules for the integration of wind power. This set of rules is vital for the secure and reliable operation of the electricity networks in presence of variable generation. The scope of work covers all the technical, operational and market aspects related to the integration of large scale wind power all over Europe. Attention will be later focused on system interaction of various wind turbines types, the effects of their variable power output on the system and their ability to provide system service to enable the stable operation of an electricity grid. The final objective is to obtain the necessary information for the technical and operational measures for risk mitigation and the secure operation of the European electricity grid identified by the steady-state and dynamic investigations on electricity grid models which are established within the study. For this, market and regulatory aspects will be taken into consideration.

Selected Extracts


[A] Capacity Development of Wind Power installations and Geographical Allocation

As realisation of the Directive 2001/77/EC of the European Parliament and of the Council on the promotion of electricity produced from RES in the internal electricity market the wind power in Europe is expected to increase from 41 GW in 2005 to nearly 67 GW in 2008. The highest amount of wind power is concentrated in Germany, where ca. 40% of the total installed capacity is expected in 2008. This is followed by Spain and Great Britain. These 3 countries will represent more than 70% of the total installed capacity within Europe. Furthermore, Italy, France and Greece are expected to see strong increases in installed wind power capacity. Further increase of wind power integration is expected for the time horizon 2015.

[B] Impacts

Large load flows affect neighbouring transmission systems and reduce available cross border trading capacities

The expansion of variable wind power generation has significant effects on the European electricity system as a whole. A regional concentrated high wind power generation which is producing a high surplus of power generation such as in Northern Germany results in temporary large load flows through the neighbouring transmission systems. These unscheduled flows could reduce system stability and increasingly affect trading capacities.

Grid congestions – Need for additional/new grid infrastructure

New RES lead to local grid congestions and thus need new grid infrastructure. New wind farms are built on sites with high average of wind speed which are often far away from the main load centres. New overhead lines are therefore necessary to transport the surplus of electricity produced in these regions to where it is consumed. These investments are exclusively or at least mainly driven by the new RES generation sites. The variable contributions from wind power must be balanced almost completely with other back-up generation capacity located elsewhere. This adds to the requirements for grid reinforcements.


High wind power generation combined with high power production of conventional power plants in the North of Germany and additional large import from NORDEL result in large North-South power flows through the transmission system of Germany and neighbouring countries e.g. the Netherlands, Belgium, Poland and Czech Republic.

For the high wind scenario bottlenecks on internal and cross border lines in northern Europe are detected already for the time horizon of 2008. If a circuit is unavailable due to a disturbance in the grid the remaining lines can be overloaded up to 180%. Internal overloads are observed in Germany, Czech Republic, Poland, Belgium and the Netherlands for single circuit outages in case of high wind power production in northern Europe. Investigated measures to prevent these overloads are described in the detailed analysis.

Secure system operation at risk

Conventional power stations do not disconnect from the grid even following serious grid failures, instead they generally trip into auxiliary services supply and "support" the grid. Wind farms, however, have so far disconnected themselves from the grid even in the event of minor, brief voltage dips. Experience in grid operation showed that this can lead to serious power failures. In order to prevent the risk of large outages, manufacturers and operators must technically ensure that in the event of a fault, wind farms also support system stability.

Increasing need for balance power and reserve capacity

The day to day forecast of electricity production from wind energy is just possible to a limited extend. To balance the difference between generation and demand balancing power is needed. The need for balancing power increases proportionally with the growing wind power capacity. Depending on the different national rules different parties are responsible for providing the balance power. In case the TSO has to contract it the costs will be part of the tariff and by this be paid by all customers. As a consequence there is no incentive for the wind farms to reduce the costs of integration in the electricity system. Furthermore, a considerable amount of reserve capacity - being paid by the consumers - is needed for system adequacy and security.

Increasing grid losses and reactive power compensation

High wind power production remote from main electricity demand centres produces higher grid losses within the transmission system. Compared to scenarios with low wind power production the active grid losses e.g. in Germany are doubled in case of high wind power production in Northern Europe. In some other countries, e.g. Poland and the Netherlands, there is a noticeable increase.

High wind power production needs more reactive power because wind installations are built far away from the main load centres. Long distance transmission of wind energy leads to a higher load factor of the electric lines which thus consume more reactive power. In addition, in several parts of the system with a high reactive-power demand conventional power plants have been taken out of operation due to high wind power production. Before 2008 reactive-power generation must be installed directly at the extra high voltage level in order to provide the necessary reactive power.

Economic impact on conventional power generation

High wind power production causes regional overloading of transmission lines. Although the TSOs instituted grid expansion measures at an early stage, especially in the Northern region, it is unlikely that they will come entirely into operation by 2008. Therefore the existing priority rules for connection, purchase and transmission of RES-Electricity in some European countries will increasingly effect the power generation all over Europe. The investigation showed that in high wind situations a large proportion of cost effective power generation is pushed out of the market by renewable energy sources and/or the short-term auction capacity on congested channels must be reduced.

2007 01 15 Fina I Approved

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JAN 15 2007
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