Pumped-storage hydroelectric power station and operation of the electricity system

The General Manager of System Operation, Miguel Duvison, explains how reversible pumped-storage power stations help to ensure the continuity of the electricity supply.

  • Tribune

One of the main functions of the system operator is to ensure the balance between generation and demand at all times, as this is essential for security of supply.

Electrical energy, as such, is difficult to store on a large scale and, currently, electricity storage (batteries) is not a tool that is technically capable of meeting the needs of the system and neither is it economically competitive in the management of large electricity systems, such as the Spanish peninsular electricity system. Therefore, pumped-storage hydroelectric power stations, also called reversible hydroelectric power stations, become the only storage option which is available and efficient for the system operator.

These power stations play a vital role in ensuring the reliability and security of the electricity supply. They allow the demand curve to be "shaped", increasing consumption in valley hours, providing available power during peak hours and reducing ramp up demand in the peak-valley transitions.

Both the Spanish peninsular and non-peninsular electricity systems are characterised by a demand curve with a level of consumption at peak times that may, in some cases, be double the level of the valley period. This, together with the usual pattern of behaviour of wind power generation, with higher production during night-time hours compared to daytime, implies a very demanding requirement for conventional power plants in order to cover the demand of the system. Pumped-storage power stations allow a flattening of the demand curve and thus reduce the operating requirements of conventional power stations.

Moreover, reversible hydroelectric power stations are a key tool in the safe integration of renewables, greatly reducing the need for dumping of these energy sources. The importance of pumped-storage is more significant in isolated systems, such as non-peninsular ones, where it is not possible to export the excess of renewable generation at times of low demand, and in electricity systems that are weakly interconnected such as is the case of the Spanish peninsular system, where exports have certain limitations.

In short, the efficient management of pumped-storage power stations is key to achieving the 20/20/20 targets of the European Union, the National Action Plan for Renewable Energy and the Renewable Energies Plan 2011-2020.

Pumped-storage hydroelectric power stations are also a valuable resource for the system operator from the point of view of system security. This type of generation technology helps improve power-frequency regulation of the electricity system as it has the ability to provide a quick response to adjustments between generation and demand; a response that is much faster than that offered by conventional thermal power stations and other renewable generation technologies.

In weakly interconnected systems, such as the Spanish peninsular system, these power stations rapidly correct power deviations at the interconnections, thereby reducing the risk of incidents. In isolated systems, supply disruptions are reduced in the face of untimely failures regarding power generation stations. Furthermore, they represent an efficient resource for voltage control during valley hours and increase the inertia of the system, which is key during periods of low demand and high penetration of non-manageable renewable sources.

Pumped-storage power stations improve the energy efficiency of the system, especially in isolated systems, by reducing the number of hours that power stations work at low load where their performance is lower and avoid pull from more expensive power stations during peak demand. This translates into a cost reduction for the system.

In short, reversible pumped-storage power stations are an essential tool for the operation of the system in order to increase security of supply, maximise the integration of renewable energy and improve energy efficiency and the economic efficiency of the electricity system. The importance of pumped-storage power stations is greater when the interconnection capacity of the system is lower and the degree of penetration of renewable energies that are not based on hydroelectric power stations is greater.