The electric power market in Europe is almost exclusively based on 1-hour-schedules with a constant power target value for each 1-h-interval. The corresponding current market boundaries and system rules lead to remarkable power imbalances arising from the power difference between the continuous ramp-wise physical load behaviour and step-wise power schedules – especially at the change of the hour. These in the long term increasing power imbalances entail equally increasing frequency deviations which result in considerable disadvantages for the power plant and power system operation already today. The resulting higher power plant stress which has to be included in the cost calculation for primary control, as well as the increasing amount of required secondary control energy are inevitably going to lead to higher control energy costs. Furthermore, especially during the evening hours, a large part of the primary control reserve power is repeatedly activated, which means that it cannot be ensured that the respective UCTE design hypothesis for the primary control reserve activation after a sudden loss of 3000 MW generating capacity is valid during these time periods.
Therefore, within the framework of this work, a comprehensive analysis of the origins of the frequency deviations is carried out. For the analysis of the origins of the current frequency behaviour, three aspects are decisive:
- Identification of the correlation between the frequency and load behaviour, based on long-term measurements,
- Evaluation of the current practice of load-coverage of the market participants,
- Simulations, starting from the boundary conditions above.
The results verify that the origins of the frequency deviations are system inherent, i.e. according to current market boundaries and system rules of the deregulated energy market.
Starting from the verified origins, counter measures are proposed. The presented proposals for improvement include a two-stage complementary realisation of measures, which
- lead to a better approximation of the ramp-wise physical load behaviour by the power trade through the introduction of a new power product and especially prevent large schedule steps, and
- entitle the TSO to order lower-priced control energy day-ahead, based on the power schedule resulting from the power trade and the physical load forecast.
Based on the results of the work, the German committees VGB POWERTECH and BDEW plan to put the proposed measures up for discussion on a national and European level.