The security of the electricity system

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Ensuring the security of the Italian electricity system which is interconnected with the European grid is a sensitive task, which Terna performs through a series of actions based on a scrupulous assessment of operating risks.

The objective is to maintain the risk of service outage within pre-established limits and mitigate as much as possible the negative consequences of malfunctioningin the event this occurs.

To keep high security levels, Terna must maintain an excellent performance in all the phases of its activities, from the development and construction of infrastructures to plant maintenance and real-time operation. The benchmark for the criteria to adopt is the best European practices in the field of managing interconnected electricity systems. These practices are the result of the cooperation that has taken place for some time within the international organizations in which Terna participates as a transmission system operator (TSO). It is particularly in the ENTSO-E, the European Organization that groups TSOs, that Terna cooperates for writing international Grid Codes and the ten-year Development Plan for the European electricity grid, with the objective of managing service security and at the same time favoring the integration of renewable sources into the interconnected system and the development of electricity markets.

EU6For Terna, preventing and limiting the risk of outages means monitoring and protecting the physical integrity of its plants, preparing defense plans to limit the consequences of outages, carrying out preventive operation planning, improving real-time control, and training the employees involved also through modern simulation instruments that reproduce the system operation; it also means developing new methods for supporting the planning and control processes, improving the reliability of support tools and coordinating the management of the interconnected system with neighboring TSOs.

Terna’s commitment to continual improvement is expressed in the Plan for the Security of the Electricity System prepared by the Company and approved by the Ministry for Economic Development. The Plan is drawn up every year with a three year time horizon. In the different editions of the Plan since it was introduced in 2003, the approach to the security of the electricity system has become increasingly complex.

The initiatives that were presented in the past editions of the Security Plan regarding planning, control, regulation and protection, restoration and monitoring of the electricity system, have been confirmed and partly reviewed in order to better focus on new requirements, such as a more flexible management of the system, in coordination with neighboring TSOs and distributor companies.

The presence of a subject area dedicated to renewable sources, which was introduced during the previous edition of the Plan, was confirmed due to their importance with regard to the security of the system and the objective of ensuring the full integration of renewable energy plants into the interconnected system.

The following are the main objectives achieved in 2011:

  • consolidating optimization tools for the procurement of dispatching resources and the verification of congestions (of the following types: Optimal Power Flow and Optimal Reactive Power Flow);
  • improving the process of and the tools for the assessment of the risk conditions related to non meeting the demand (of the Advance Dispatching type);
  • improving the forecasting of wind power production and introducing the forecast of PV power generation also of the distributed type;
  • automatically correcting congestions occurring in the most critical segments of the grid also in the sub-transmission grid to which renewable energy plants are connected;
  • launching testing activities of the new control System;
  • strengthening the telecommunication infrastructure in support of the Control System and defense systems.

The 2011 Security Plan also highlights the need to identify ways to operate the electricity system over the medium term that are characterized by new elements such as the significant development of renewable energy sources, the widespread presence of electric vehicles and an active demand that is increasingly aware of price indications from energy markets.

These new elements indeed increase the complexity of managing the system and the need to adopt new control systems of the Smart Grid type. The initiatives that are currently under study include coordination proposals to be made to distributor companies for the control of the distributed power generation and the active demand, the management of energy storage systems for the management of the variability in the renewable energy production and the dynamic management of grid elements.

In 2011, the investments associated with the Security Plan totaled 96 million euro .

The eighth edition of the 2011-2014 Security Plan provides for investments of 206 million euro .

Terna and Smart GridEU8

The development of generation from renewable energy sources – which is bound to continue in the near future at high growth rates, also thanks to the European strategy for limiting CO2 emissions – poses new challenges for the transmission and distribution of electricity.

In particular, the unpredictable variability of wind and sun availability and the increasing production by small plants located along the distribution grids and the prospects of a greater role of active demand (daily consumption based on price variation), conflict with the traditional structure of the electricity system, which is based on a transmission grid that transfers huge quantities of power from large production centers concentrated in the connection points with the distribution grids, where it is consumed in a widespread way.

The need to change this structure renders it necessary to develop networks and control techniques capable of fostering the dissemination of renewable energy sources without lowering service security: the so-called Smart Grids. Multifunctional smart grids can regulate multi-directional power flows, integrate renewable sources, and make access to the electricity system more flexible for grid users.

Even though transmission grids are already capable of managing variable and multi-directional flows, the increased production of electricity from renewable sources also affects Transmission System Operators, requiring the introduction of innovative solutions for the security and efficiency of the dispatching service.

Furthermore, the system must be able to cope with malfunctions and other abnormal situations by redistributing power flows without suffering service outages and permanently violating the working limits of the equipment that forms the entire system.

It is on the basis of these objectives that Terna has concentrated its development priorities regarding Smart Grids on 4 main aspects:

  • Non conventional storage systems through which the coordinated management is ensured of production injections from renewable sources and energy storage, maximizing production from renewable sources and the system’s efficiency and increasing the regulation capability of the electricity system.
  • SPS – Special Protection Systems, i.e., technologically advanced automatic devices that react to large malfunctions. These systems require the construction on a large scale of immediate-remedial-action schemes that can limit the consequences of a malfunctioning and even trigger self-healing mechanisms.
  •  Advanced forecasting instruments for obtaining a more accurate prediction of production from renewable sources based on real time processing of meteorological data and of the production from wind and photovoltaic plants.
  • Dynamic line rating, i.e. the dynamic determination of the capacity limits of lines according to environmental conditions, aimed at maximizing the use of the transfer capacity or at a more efficient grid use, as opposed to fixed and excessively reductive limits in favorable meteorological conditions. 

 

Energy Storage, a solution to the problems associated with Non-Programmable Renewable Energy SourcesEU8

The sharp increase in power generation plants from Non-Programmable Renewable Energy Sources (NPRS), especially in Southern Italy and on the islands, has a significant impact on the management, operation and cost of the national electricity system.

A high concentration of production distributed by the NPRS compared to the amount of local power load often requires limiting its injection into the grid – in particular with regard to wind power production – to solve local congestions on the high voltage segments of the grid. The presence of NPRS often increases the number and extent of grid congestions. The result is higher production costs for the national electricity system which is linked to the need to resort to less efficient electricity production with higher marginal costs.

With regard to the security of the electricity system, the widespread presence of production from NPRS implies a reduced availability of primary reserve (that is the capability of automatic regulation, which is typical of thermoelectric groups, in case of deviation from the default parameters of grid frequency) caused by a reduction of regulating production units, based on equal electricity demand, which are excluded from the market by the presence of renewable generation with dispatching priorities. Moreover, scant predictability and high intermittency, especially of wind power, require the availability of greater secondary and tertiary reserve margins in order to allow for real time regulation.

Grid development activities planned by Terna only partially address the critical issues posed by the increase in production from NPRS, given that – due to the long implementation timetable – they can provide a solution to the congestions but not to the safe management of the National Electricity System. For this reason, Terna has identified storage systems – in particular electrochemical storage (batteries) and hydroelectric pumping – as a proper technical response to promote the development of electricity production from NPRS and improve the overall efficiency of the National Electricity System, along with the construction of new power lines and stations, based on the same security levels. There are in fact many advantages stemming from the use of storage systems.

The installation of energy storage systems in areas with the largest presence of NPRS’ would help reduce congestion during excessive power production times. Furthermore, storing energy during off peak hours (when the demand is low) followed by electricity output in peak hours (i.e., during periods of high demand) would reduce the problems associated with the management of “exhausted” electricity grids during off peak periods and avoid having to resort to less efficient systems during peak periods (a strategy called “peak shaving”). This method would have a positive impact on the costs and security of the system and would help reduce CO2 emissions.

Storage systems may also be used to satisfy the increased need for real-time regulation reserves. The capacity of storage systems to rapidly inject or withdraw electricity from the grid allows every MW installed to potentially generate twice the capacity amount in terms of reserves, since it can modulate the absorption or injection into the grid as well as quickly goes from full absorption to full injection of electricity into the grid. Storage systems could also guarantee primary frequency regulation where performance is higher than that of conventional power plants.

Considering both technical specifications and the implementation timetable, Terna’s technical experts and a group of professors from Massachusetts Institute of Technology performed an analysis which has allowed them to identify batteries as the storage system that can provide the best solution to current problems in a short period of time. Pumping units, indeed, cannot be built everywhere and require longer periods of time to be implemented.

Batteries not only allow for the storage of adequate amounts of electricity with a return capacity of the stored power lasting several hours each cycle, but they are also characterized by a high modularity, thus they are easy to install, and can be used with considerable flexibility. A very short timetable for implementation, especially if compared to that of other types of storage systems, the capability of widespread location on the grid also in the vicinity of the numerous NPRS injection points, and the fact that they are not dependent on the suitability of the site, are further elements playing in favor of batteries.

Overall, Terna's plans include the installation of a mix between batteries and pumping units that are properly deployed on the territory according to the specific needs of the electricity system, so as to increase the grid capacity to manage an electricity system where the NPRS play an increasing role.