Two-step process for grid code harmonisation in Europe

There is considerable potential for improving the proc- ess of wind power integration by harmonising grid codes requirements for wind power. Such a process will benefit all the stakeholders involved in the inte- gration of wind power. A systematic approach to set- ting a European grid code harmonisation process in

motion was proposed by EWEA in 200815_{. Harmonisa-}

tion does not automatically mean that the maximum

and most stringent requirements should apply every- where, rather it is a process of cleaning out technically unjustified requirements and creating a transparent, understandable, comprehensive and well-defined set of requirements according to common definitions and specifications and optimised to the power systems where they apply.

A two-step harmonisation strategy introduced by EWEA consists firstly of a structural harmonisation, and sec- ondly a technical harmonisation. Together, the two forms of harmonisation should particularly benefit those system operators that have not yet developed their own customised grid code requirements for wind- powered plants.

Structural harmonisation consists of establishing a grid code template with a fixed and common structure (sequence and chapters), designations, definitions, parameters and units. The key aim of the structural harmonisation process is to establish an accepted framework for an efficient grid code layout. Such a

template was launched16 _{by EWEA in 2009.}

Technical harmonisation can be seen as a more long- term process which works by adapting existing grid code parameters following the template of the afore- mentioned new grid code. The process is to be imple- mented through co-operation between TSOs (ENTSO- E), the wind power industry and regulatory bodies (ACER). The implementation of the Third Liberalisation package as described below provides the proper ena- bling legal and institutional framework at EU level. europeandevelopmentsatowardseuropeancode In the developing European internal electricity market, national networks have to be interlinked in a more ef- ficient way. They must be operated as part of an inte- grated European grid to enable the necessary cross border exchanges. This requires harmonised codes and technical standards, including grid connection re- quirements. However, the national power systems in Europe today are so different that a full harmonisation cannot and should not be carried out straight away.

15 _{http://www.ewea.org/fileadmin/ewea_documents/documents/publications/position_papers/ 080307_WGGcr_final.pdf}

The implementation of further liberalisation measures in the energy sector in Europe, as imposed by the so- called Third Liberalisation Package, involves the crea- tion of a European network code for connection. This process involves several steps in which European TSOs and European regulators play a crucial role. Ba- sically, the regulators (ACER) set out the framework for the code in a so-called framework guideline. Conse- quently, the TSOs draft the European code according to the terms set out in the framework guideline. Once established, the code will be imposed throughout Eu- ropean and national legislation (comitology). The proc- ess asks for an open consultation with the relevant industry associations when drafting the codes. With

this, the legal framework has been set for further de- veloping harmonised grid code requirements through co-operation between TSOs and the wind energy sec- tor. At the same time, this creates the opportunity to strike a proper balance between requirements at wind plant and at network level, in order to ensure the most efficient and economically sound connection solu- tions. EWEA recommends that in this future European code for network connection, there is a clear grouping of wind power related grid code requirements in a sep- arate chapter to ensure the maximum level of clarity and an adequate valuation of the specific power plant capabilities of wind power.

SUmmary

State-of-the-art wind power technology with advanced control features is designed to enhance grid perform- ance by providing ancillary services. Using these pow- er plant characteristics to their full potential with a minimum of curtailment of wind power is essential for efficiently integrating high levels of wind power. Ad- vanced grid-friendly wind plants can provide voltage control, active power control and fault-ride-through ca- pability. Emulating system inertia will become possi- ble too. The economic value of these properties in the system should be reflected in the pricing in proportion to their cost.

Wind power provides variable generation with predict- able variability that extends over different time scales (seconds, minutes, hours and seasons) which are rel- evant for system planning and scheduling. The intra- hour variations are relevant for regulating reserves;

the hour by hour variations are relevant for load fol- lowing reserves. Very fast fluctuations on second to minute scale visible at wind turbine level disappear when aggregated over wind farms and regions. The remaining variability is significantly reduced by aggre- gating wind power over geographically dispersed sites and large areas. Electricity networks provide the key to reduction of variability by enabling aggregation of wind plant output from dispersed locations. Wind plant con- trol can help control variability on a short time scale. The latest methods for wind power forecasting help to predict the variations in the time scale relevant for system operation with quantifiable accuracy. Aggregat- ing wind power over large areas and dispersed sites and using combined predictions helps to bring down the wind power forecast error to manageable levels in the time frames relevant for system operation (four

to 24 hours ahead). Furthermore, well interconnected electricity networks bring many advantages. In order to control the possible large incidental forecast errors, reserve scheduling should be done in as short as pos- sible time frames (short gate-closure times), assist- ed by real time data on wind power production and site specific wind conditions. The significant econom- ic benefits of improved accuracy justify investment in large meteorological observational networks. The way grid code requirements in Europe have been developed historically has resulted in gross ineffi- ciencies for manufacturers and developers. As the amount of wind power in the system continues to grow in Europe, there is an increasing need to de- velop a harmonised set of grid code requirements. Harmonised technical requirements will maximise ef- ficiency for all parties and should be employed wher- ever possible and appropriate. However, it must be noted that it is not practical to completely harmo- nise technical requirements straight away. In an ex- treme case this could lead to the implementation of the most stringent requirements from each Member

State. This would not be desirable, economically sound, or efficient.

EWEA proposes a two step harmonisation approach for grid codes, namely a structural harmonisation fol- lowed by a technical harmonisation. The proposed har- monising strategies are urgently needed in view of the significant increase in foreseen wind power penetra- tion and should be of particular benefit to:

• Manufacturers, who will now be required only to de-

velop common hardware and software platforms

• Developers, who will benefit from the reduced costs

• System operators, especially those who have yet to

develop their own grid code requirements for wind powered plants

The technical basis for the requirements should be further developed in work carried out jointly between TSOs and the wind power industry in studies at Euro- pean and international level. If the proposals can be introduced at European level by means of a concise network code on grid connection, it will set a strong precedent for the rest of the world.

pOWerSyStemOperatIONS