European network codes and the national legislation

The grid connection of new electricity generators requires detailed knowledge of the standards that regulate it. These standards are based on higher standards defined at pan-European level. By way of introduction, in the following lines we will review where they come from and briefly go through their content, in the hope that they will be of use to our readers.

Grid codes (GC) are the national rules that regulate the operation of the different electricity systems since the liberalisation of the sector [1]. The GR are characterised by a high degree of heterogeneity and a lack of standardisation, with significant differences between countries [2]. This circumstance has historically been a clear barrier to the creation of a large European electricity system integrated into a single electricity market that would enable the objectives of reducing emissions, increasing renewable penetration and reducing energy consumption to be achieved.

The European Commission (EC), aware of this problem, initiated a process in 2010 to draft a single European CoR that would allow the harmonisation, integration and efficiency of the European electricity system as a whole [3]. To this end, it commissioned the Agency for the Cooperation of Energy Regulators (ACER) to prepare guidelines on which to develop the CoR. The latter task was carried out by the European Network of Transmission System Operators for Electricity (ENTSO-E), which brings together 43 transmission system operators (TSOs) spread across 36 countries. Following a public consultation process with the participation of the various sector players, the resulting regulations were reviewed by ACER and approved by the EC. They are currently in the process of being implemented in the legislation of the member states [4].

The GR was drafted following the basic principles of transparency, non-discrimination and balance between maximum efficiency for the system as a whole and minimum total cost for its participants, giving great importance to free competition, system security and the integration of renewables. Its purpose is to ensure the optimal management, coordinated operation and appropriate evolution of the European electricity transmission grid.

The formulation of the GR includes two types of requirements, namely closed and open. The former are exhaustive in nature, fully defined and self-executing in the member states. The latter are non-exhaustive, partially defined and need to be completed by national legislation in the individual member states. It is important to note that the latter requirements predominate over the former, so that each TSO can adapt the GR to the particularities of its network.

The European GR is made up of 8 codes grouped into 3 families as shown in Figure 1, where their names are shown together with their acronyms, which are widely used in the sector [5]:

The Grid Connection Family of codes deals respectively with demand, DC connections and generators. There are a total of three codes, namely:

• Demand Connection (DCC): This regulation affects both loads and the connection of the distribution grid to the transmission grid. It also regulates demand response to grid events.
• Connection of high-voltage direct current (HVDC) systems: This regulation applies both to direct current links and to power park modules connected to the grid in direct current.
• Requirements for generators (RfG): This regulation sets out the requirements that different types of generators must meet to connect to the grid in order to ensure a level playing field, system security, the integration of renewable sources and the electricity market.

The second Family of codes is the Exploitation Family. These codes deal with emergency operation, restoration and exploitation of the system. There are two codes:

• Emergency and Restoration (ER): This regulation ensures that the operation of the system is safeguarded by preventing the propagation or deterioration of an incident in order to avoid a blackout. It describes the mechanisms for reliable, efficient and rapid restoration after an emergency or blackout.
• System Operation (SO): This regulation is responsible for safeguarding operational security, load/frequency control, reserves, operational planning and scheduling. It also establishes the coordination between the different TSOs and the coordination of unavailability.

Finally, the Market Family of codes sets out the rules concerning capacity allocation, congestion management and ancillary services. All this is developed in a total of three codes:

• Capacity allocation and congestion management (CACM): This regulation sets out detailed rules for capacity allocation in the day-ahead and intraday markets, as well as congestion resolution.
• Electricity Balancing (EB): This code includes the regulation of primary, secondary and tertiary frequency power reserves. It includes detailed guidelines on common principles for the contracting and settlement of reserves.
• Forward Capacity Allocation (FCA): This regulation sets out detailed rules on the (forward) allocation, transmission and return of long-term cross-zonal capacity at European level.

A complete overview of the grid code set allows us to understand all the constraints that our projects will be subject to. In addition, the development process of national grid codes requires them to be aligned with the European code, so a good knowledge of the European code will give us a lot of information on future requirements in different countries for, for example, the grid connection of new renewable generators.

And what do the grid codes say about the connection of new generators? The RfG [6] divides generators into 4 groups according to their power, so that the generators in each group have increasing demands as they get larger. This creates greater complications in the grid connection process the larger the generating plant; it makes perfect sense as the larger the plant the greater its impact on the system as a whole.

In future articles we will unpack some of the requirements for the connection of new generators, which we hope will be of interest to engineering teams working on the development and design of new renewable generation plants.

References

1. Al-Sunaidy and R. Green, “Electricity deregulation in OECD (Organization for Economic Cooperation and Development) countries,” Elsevier Energy, vol. 31, pp. 769-787, 2006.
2. Díez-Maroto, L. Rouco y F. Fernández-Bernal, “Fault ride through capability of round rotor synchronous generators: Review, analysis and discussion of European grid code requirements”, Electric Power Systems Research, Vol. 140, 2016, pp. 27-36.
3. Official Journal of the European Union, Regulation (EC) No 714/2009 of the European Parliament and of the Council of 13 July 2009 on conditions for access to the network for cross-border exchanges in electricity and repealing Regulation (EC) No 1228/2003 available at http://eur-lex.europa.eu/legal-content/ES/TXT/PDF/?uri=CELEX:32009R0714&from=EN
4. REE, ‘Implementation of network connection codes’, available at http://www.esios.ree.es/es/pagina/codigos-red-conexion
5. Official Journal of the European Union, Commission Regulation (EU) 2016/631 of 14 April 2016 laying down a Network Code on grid connection requirements for generators, available at http://eur-lex.europa.eu/legal-content/ES/TXT/PDF/?uri=CELEX:32016R0631&from=EN