Integrating wind power in the European power systems

Executive summary

Wind power is winning recognition as a valuable option for power generation. With a total of more than 20.000 MW of installed wind power capacity, more than the half of the worldwide energy production from wind power is located in Europe (Annex A). The huge success of this renewable and environmentally-friendly energy source and the respective energy output has to be handled by the Continental European transmission system operators (TSO) in their day-to-day operation of the European interconnected system..

UCTE (Union for the Co-ordination of Transmission of Electricity) is the TSO organisation, whose main role is to maintain the security of supply and the quality of the energy delivered. In this context UCTE and its member TSOs share the goal to promote renewable energies and reduce CO2 emissions according to EU and national targets.

TSOs and their synchronously interconnected power grids provide the reliable infrastructure to wind power generation. The challenges arising out of the integration of wind power were successfully mastered in the past and even in view of the already foreseeable massive increase in wind energy TSOs will remain focussed on their mission to facilitate wind energy.

The extension of wind power requires thorough redesign of the power infrastructure in Europe both on the generation side through additional need for balancing power and on the grid side. The framework shall take this into account, in particular by

• committing to binding wind power extension goals as indispensable inputs for infrastructural planning and designing activities of TSOs and other market participants (e. g. balancing power providers)

• creating combined procedures for wind parks and corresponding grid extension measures.

• ensuring remuneration of costs for the integration of wind power into the power systems as well as providing sufficient financial resources to the TSO for funding the investments in grid extension and for funding the additional operational expenses for balancing power

• Defining grid code requirements to be fulfilled by wind power plants to minimize their impact on the grid. A UCTE working group is preparing a proposal on this subject.

This position paper examines the profile of wind power, its impact on the network, security of supply and the quality of the energy delivered. It further deals with the reasons to establish certain technical requirements for the connection of wind power generation to the network.

Main characteristics of wind power

In some regions in Europe, generation from wind power already plays a significant role in meeting the electricity demand. Nevertheless, great challenges of wind power production are created by the limited predictability and the high fluctuations in production levels as the prime mover of wind turbines, i.e. the wind is hardly controllable and fluctuates randomly.

Location of resources, whether in-shore or off-shore poses additional logistic problems as they are in general located in remote areas far from population centers and transmission network facilities. In the case of off-shore plants the additional cost of constructing offshore and the longer distance to be covered for connecting to the grid must be considered.

Generating systems for wind power also differ from the synchronous generator used in conventional power plants. For major details on the different types of turbines commonly used in a wind energy converter and the impacts of wind power both locally and system-wide please refer to ANNEX B.

Wind power – overall availability of 20%

By nature, wind energy is only available as variable power depending on the weather conditions that may range from calm to stormy conditions. Based on the operational experience gained so far the following can be stated with regard to the power contribution of wind power plants (WPP):

a) An average of 20 per cent of the total wind power installed in a control area was available for electricity generation over the year.

b) For two thirds of the year less than 20 per cent of the installed power was available for electricity generation.

c) For one third of the year, less than 10 per cent of the capacity was available for electricity generation. This was particularly the case in peak consumption periods (annual peak load in winter) or under aggravated generating conditions (e. g. heat wave in the summer 2003).

Teaming-up for system stability: wind power and conventional back-up capacities

Forecasting the electricity production from wind power is possible only to a limited extent – and the forecasting quality significantly depends on the quality of the weather forecast. Despite the use of advanced tools, the average forecasting error for wind energy supply could only be reduced to some 10-12 per cent of the installed wind capacity. On certain days the forecasting deviations may be as high as 50%.

Maximum expected forecasting deviations increase with the rise in the installed wind capacity. It is not the yearly average but the individual maximum forecast deviation to determine the value of power/energy reserves to be programmed by the transmission system operators in order maintain system stability.

Plant operators could however contribute to more precise forecasts of wind energy production. In view of the growing number of wind power plants and the increasing sizes of these plants the operators of wind power plants should be induced to respect certain obligations, such as informing the transmission system operators about the availability of plants exceeding a certain size. Thus any further wind-related rises in balance power requirement could be avoided.

Back-up capacities from other power plants have to be kept in reserve for cases of total generation outages of WPP (e.g. summer heat waves) as well as for balancing variations in wind energy injections. It will be a big challenge for the future to always guarantee for sufficient amounts of backup and balancing energy to keep up with the massive expansion of wind power. The increasing demand for balancing power may also result in possible price impacts for final customers.