To keep an electricity system reliable, sustainable and stable, transmission system operators (TSOs) make plans in order to be prepared to operate a system in real time. This involves analysing whether there will be enough generation to meet demand (adequacy analysis), and whether the system can handle the resulting flows in a secure way (operational security analysis).

Scheduling is a task in which TSOs collect and manage the schedules of market participants (i.e. their plans, notably for generation levels, or for electricity trading) in order to prepare the system for stable real time operation.

The increasing volumes of renewable energy sources (RES) and distributed generation are presenting challenges for transmission system operators (TSOs) in the way they operate the network. Ensuring that the network is safe and secure at all times requires an understanding of the behavior of all actors within the system – be they grid operators or customers (such as generators).

This analysis, termed adequacy and security analysis, allows TSOs to plan and prepare for the conditions that the system will experience. There is also a need to perform maintenance on the different assets of the electrical system (grid elements, generation units, demand facilities), which requires them to be taken out of service for a certain period. This needs to take place at the best time for both generators and TSOs, and needs to be well planned. Not undertaking these planning and scheduling activities could jeopardise system security or impose unnecessary costs.

The Network Code on Operational Planning & Scheduling (NC OPS) introduces common methodologies for operational security and adequacy analysis. By doing so, it allows the different TSOs to work together in a coherent and coordinated way across Europe to efficiently prepare operational processes. It also allows TSOs to use transmission resources efficiently. The code provides procedures to handle the uncertainties which are inherent to studies of future operation conditions, in a coordinated way, from year-ahead to some hours ahead, and which tend to increase with the increasing amount of renewable generation.

The OPS code specifies the way in which the maintenance of assets is coordinated. Since all power plants and all transmission lines can’t be taken offline at the same time, TSOs make coordinated availability plans to ensure the adequacy of the grid, generation and demand. With the electricity flows increasingly crossing borders, these availability plans also affect operations in neighbouring countries. Therefore, the NC OPS improves efficiency by ensuring that the TSOs coordinate all availability plans, which prevent the need for costly measures that might otherwise be required.

Finally, the NC OPS ensures that every actor involved in system operations and electricity markets knows what is expected of them. It determines the roles and responsibilities for transmission system operators (TSOs), distribution system operators (DSOs), significant grid users and market players with regard to operational scheduling procedures and prescribes how the different parties exchange data.

The increase in renewable energy sources (RES) and distributed generation are presenting challenges for transmission system operators (TSOs) in the way they operate the network. The adequacy analysis and security analysis are now being influenced by the fluctuating weather conditions (wind and solar-power), which is not always easy to predict. Therefore, the first objective of the NC OPS is to reinforce the preparation of operational coordination across Europe to meet the changing generation environment.

Due to the development of European electricity market and the integration of intermittent renewable generation (fluctuating due to weather conditions), electricity flows are increasingly having cross-border effects. Transmission system operators (TSOs) need to work closely together to consider these flows when performing an operational security analysis of the system. Therefore, the second objective of the NC OPS is to ensure that the way TSOs prepare to operate the system occurs in a coherent and coordinated way across Europe.

In some cases, the NC OPS will impose new obligations on generators. In the majority of existing practices, many (but not all) generators are already coordinating their maintenance with the grid operators. However, this is not the case everywhere and additional coordination obligations will be put on those generators that have not previously coordinated their maintenance with the TSO.

Today’s existing rules are based on current best practice in the European system. These rules exist at regional levels via multilateral contracts between transmission system operators (TSOs) or bilateral contracts between TSOs, distribution system operators (DSOs), generators and demand facilities. These contracts are based on different principles and do not allow efficient planning on a pan-European level.

The request from the European Commission to begin drafting the code was received in April 2012, with ENTSO-E given a year to complete the task. The NC OPS was developed by a drafting team comprised of industry experts from across ENTSO-E member European transmission system operators (TSOs).

During the drafting process, several workshops were organised to gather stakeholder opinions and to discuss issues of concern. Three workshops were organised with the distribution system operator (DSO) technical expert group and four public stakeholder workshops.

A formal public consultation, which led to over 850 comments, was held in November-December 2012. The stakeholder comments were analysed and a significant majority were taken into account in the final draft version of the NC OPS. The NC OPS was approved by the ENTSO-E Assembly before submission to ACER in March 2013.