Technology-Specific Contributions to Power Grid Instability in Germany

Technology-Specific Contributions to Power Grid Instability in Germany

In this study Filippos Sivorotka and I began by asking ourselves, “to what extent do coal power plants contribute to instability in the power grid?” This is a counter-intuitive question. Coal plants are suited to producing baseload power which has traditionally been the secure and dependable way of organizing the generation of electrical power. It is the volatile renewable energy generation systems (RES), and in particular solar and wind power, that have been the cause of concern for the future security of Germany’s energy supply. As, however, the so called “Energiewende” moves forward, regulations and market structures have been proposed to integrate RES generation into the price-signal-driven market system and to thus allow for RES to contribute to grid stability by flexibly adjusting (ie, reducing) power production if the grid is overloaded at the time. That is to say, the contribution of RES to grid stability, despite their volatile, unpredictable nature, has garnered attention in the market and at the level of regulation and government.

Coal power has also been at the forefront of debates in and around the Energiewende but in a completely different context. The developments in the German energy market associated with the Energiewende have brought into question the future role of coal power. The shift to a regime of relatively low wholesale power prices and relatively high surcharges for end customers has led to a situation in which base-load power generation is not profitable. Prominent projects for the construction of new coal plants in Germany were canceled in recent years and currently operating plants have also struggled to maintain profitability. The recent decision by the government to allow a group of mostly coal plants to participate in the market as special “strategic reserve power” highlights the level of urgency in the debate – coal power cannot compete competitively in the current (transitioning) market.

But what are exactly the reasons for hanging onto coal as a power generation technology? Besides the availability of coal as fuel, dependability is an often cited reason. In this study we test this thesis that coal only contributes to supply security by analyzing the dependability of the technology itself. We do this by looking at unexpected coal plant outages in Germany in 2014 and analyzing the amount and costs of ancillary services required to compensate and balance the grid for these outages.


Two primary sources of data are used in this study:

First, we use the publicized plant outages on the transparency website of the European Energy Exchange (EEX). The EEX publishes data daily on the amount of planned and actual generation by all relevant power sources for Austria, Hungary, Germany, Belgium, the Netherlands and Switzerland. The table containing all planned and unplanned plant outages is located here.

We link the timestamps of the plant outages from the above table to the actual grid demand for secondary reserve power in Germany. The demand in megawatts for secondary reserve power is available at a resolution of 4 seconds from the websites of the German transmission system operators (TSOs). We accessed the data from the website of transnetbw, the TSO in southwest Germany. The data can be accessed here. The demand data are for the entire grid control area (ger. “Netzregelverbund” abbreviated NRV) which includes all four German TSOs as well as those of Denmark (, the Netherlands (TenneT), Switzerland (swissgrid), Czech Republich (ČEPS), and Belgium (Elia System Operator).


We filtered the data on plant outages for duplicates and consistency and measured the change in secondary reserve power demand for the NRV. Inka Ziegenhagen analyzed the same plant outage data to obtain an estimate of the distribution of plant outages that needed to be compensated by grid reserve power. Her analysis assumed that coal plants would would be operating if spot prices for power were above 40 €/Mwh. She then assumed that reserve power would be necessary to compensate the missing power from the plant experiencing the outage. For planning purposes, the TSOs could then contract reserve power according to the estimated distribution of relevant outages. Our approach is similar: We also first begin by analyzing the reported plant outages (first focusing on coal plants).


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