Contemporary society is highly dependent on electric energy. Even short-term power failures can result in significant economic losses. To ensure an uninterrupted electricity supply, supply security must therefore be maintained at a high level. Supply security can be quantified according to security, reliability and availability.
The power supply system is secure when supply is guaranteed even if failures occur. To achieve this security, Germany has adopted the (n-1) principle in many areas. In addition, sufficient storage or alternative generation capacity must be available in the system to top up generation from renewable energy at times when it is insufficient. Conventional power plants will therefore remain necessary to provide back-up capacities.
The reliability of the power system quantifies the duration of an interruption in supply during or after a power failure. Reliability is broken down into voltage quality (voltage and frequency control ancillary services) and service quality. According to the dena study, products used in the provision of voltage and frequency control ancillary services can be supplied both by conventional power plants and through alternative provision. Where alternative provision of system services products represents the more cost-effective option for the macro-economy, the provision of so-called conventional must-run capacity in the case of high renewable energy feed-in is no longer necessary. Nevertheless, this does not affect the need for conventional power plants in a secure power supply system.
Availability quantifies the period during which an operational resource or power plant was available, or will most likely be available, throughout a longer operational period, for instance a year. The availability of operational resources and power generation units must be sufficient to guarantee the security and reliability of the power supply system.
The energy transition is fundamentally changing the supply of energy in Germany. Renewable energy sources like solar and wind power are being utilised, while the market shares of conventional, controllable power stations decrease more and more. Feeding energy at medium and low voltage levels can reverse the load flows from lower to higher voltage levels, and the increasing distance between the generation and consumption locations require increased transport and distribution capacities of the grid.
All these changes affect the provision of ancillary services which serve to stabilise the power supply. For example, conventional power stations not only provide most of the balancing energy required in the system, but the rotating mass of their generators also guarantees the provision of instantaneous reserves for immediate frequency support. Other important ancillary services include voltage control, operation management and re-establishment of power supply.
The goal of the study is to determine the scope of ancillary services with an increasing supply of renewable energy by 2030 and to identify and evaluate alternative concepts for provision. In particular, the analyses are to show the extent to which the distribution grids can contribute to grid stability for the transmission grid, and the role renewable energy systems, storage facilities and demand side management are to play.
The findings of the study were presented in Berlin on 18 February 2014 during an information event. You will find the presentations at: www.dena.de/SDL2030.
Research partners: Prof. Dr.-Ing. Christian Rehtanz, Technical University of Dortmund/ef.Ruhr