2014-12-08 VGB Aufsatz Englisch
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English translation including amendments and the content of the following paper: Krüger, K., Rotering, N.: Energiewende erfolgreich gestalten durch Pumpspeicherausbau. p. 37-44, VGB PowerTech, 09/2014. Successful energy transition in Germany by pumped storage expansion Dr.-Ing. Klaus Krüger, Voith Hydro Holding GmbH & Co KG, Leiter F&E, Heidenheim; Dr.-Ing. Niklas Rotering, Institut für Elektrische Anlagen und Energiewirtschaft RWTH Aachen, Forschungsgruppe Versorgungsqualität & Regulierung 1 Abstract Operational flexibility in electrical energy generation and consumption as well as the provision of reliable available capacity are two major challenges of the German energy transition. The consistent deployment of cost-effective and proven pumped storage technology can provide significant contributions to meet both challenges. This paper shows that an expansion of pumped storage plants as part of the energy transition is a technically and macro-economically interesting option for Germany. Two future scenarios are investigated, one assumes an energy supply in 2030 with a 60% share of renewable energy and another expects a renewable energy share of 80% in 2050. A central result of the investigations is that the appropriate operation of the existing pumped storage inventory and its further expansion can provide significant system adequacy and reduces the necessary fossil fuel power plant capacity for providing reliable available capacity. In a scenario with 80% renewable energy 23 GW pumped storage plants replace up to 16.6 GW thermal power plants. In addition, the pumped storage power plants significantly reduce renewable energy curtailment and substitute generation from fossil fuels when releasing the stored energy. This also contributes to an overall reduction of CO 2 emissions. Furthermore the fleet of pumped storage plants actively compensates the volatility of renewable energy from wind and solar generation and allows for a smoother and more economical operation of the remaining fleet of thermal power plants. This compensation of volatility allows a safer operation of the power system and thereby helps to avoid blackouts. 1 2 Introduction In Germany, there have already been "energy transitions" in the form of the replacement of coal by oil in the 1960s and 70s or the replacement of oil and coal by nuclear energy in the 1970s to 1990s. What these transitions had in common was that there was only a change in the primary energy source while the system architecture remained unchanged. In the past system architecture, energy storage did not have any important functionality, because a sufficiently high and permanently available reserve capacity was provided by coal and nuclear plants (base load capability with reliable available capacity) [1] and because the residual load was never below zero. Energy storage was previously performed by nature in the primary resources of coal, gas, uranium or oil, while electricity was generated according to demand, meaning that storage took place before production. The production of renewable energy from wind and photovoltaics (PV) is detached from demand. As a consequence, in systems with a high share of production from volatile renewable sources, it becomes necessary to store electrical energy instead of fossil energy. This changes the sequence of storage and production. Currently, politicians assume that it will be possible to forego storage by focusing on grid expansion and the future flexibilisation of production and consumption. Many published articles (e.g. [6], [9]) propose compensating for the volatility of renewable energy by building controllable and highly flexible new thermal plants (e.g. gas power plants) and by promoting the use of demand side management (disconnecting consumers in the industrial and private sectors). This paper presents a completely different approach to the two main challenges of energy transition relating to system technology: The provision of sufficient flexibility when feeding in significant amounts of renewable energy (RE) and ensuring system adequacy (reliable available capacity) during periods of low production from renewable sources. In 2013, Voith Hydro commissioned a study with the Institute of Power Systems and Power Economics (IAEW) of RWTH Aachen University to examine scenarios in which pumped storage plants are used as "multifunctional power plants" to accomplish the necessary tasks as energy storages and for the provision of reliable available capacity. The study, which has since been published, is based on a simulation of the entire German power plant fleet using a dedicated plant scheduling optimization tool [2], which minimizes the costs of generation. A special feature of this study is the assessment of the combined usage options of pumped storage expansion from a macro- economical point of view. The study looks at two future scenarios offering a detailed analysis of a new role of pumped storage plants within the German electricity system. The first scenario considers power production in Germany in the year 2030 with an RE share of 60%, the second assumes an RE share of 80% in the year 2050. 2 3 Methodology and assumptions The ETG study [3] is recognized among specialists and is often cited. However, it only considers a simplified non-technology-specific storage model. It cannot be used to deduce detailed statements on pumped storage plants (PSPs). In addition, it assumes that a sufficient quantity of fossil-fuel power plants is always available to provide reliable available capacity. As a consequence, the potential contribution of storages to the provision of reliable available capacity has been underestimated. In contrast to the ETG study, the new IAEW study [2] does not assume that sufficient fossil-fuel power plant capacities are always available to cover the maximum national peak load. The new study rather aims to optimize the capacity of peak-load and storage power plants. The central assumption of both of the above mentioned studies is that the future storage requirement following RE expansion will be largely determined by generation costs. This assessment is based on an approach that is macro-economical rather than micro-economical. The provision of additional system services by storage applications, such as spinning reserve (primary control), compensation of forecast errors, congestion management, voltage control, ensuring grid stability and supply quality as well as islanding operation, have not been analyzed. The ETG study assumes a ratio of storage energy to power of 5Wh/W. In addition, the new IAEW study has also analyzed the ratios of 3Wh/W and 7Wh/W, arriving at the conclusion that a ratio of 7Wh/W is the most economical. Further assumptions are: • No national transmission grid limitations • Limited to Germany, i.e. import/export = 0, • Other consumption based on ENTSO-E data [4], • RE production based on the IWES model and 2007 weather data [5], • RE installation costs and fuel cost model based on the 2010 BMU pilot study [6], • Perfect foresight and hourly resolution, • Investment costs for PSP extension: 1000 €/kW (power section), 50 €/kWh (storage section), • Ratio storage energy/power for extension 3 / 5 / 7 Wh/W, efficiency: 80%, service life: 60 years, • Mixed interest rate on capital of 4%. In comparison with the ETG study, in the new study the investment costs for pumped storage and the interest rate on capital have been adopted to more realistic values. The analyses have been limited to Germany, as it was done in the ETG study, for the sake of simplification, because the focus is on the contribution of pumped storage to supply reliable available capacity. This is predominantly defined nationally and not Europe-wide in the current political context. However, in reality, scheduling takes place within the European electricity market (EEM). The shared peak load within the EEM is below the sum of the national peak loads. As a consequence, overcapacities are bound to develop if the nations involved ensure reliable available capacity by thermal power plants only. Thermal peak- load power plants with low efficiency or high variable costs would inevitably not be used and would 3 be unlikely to generate any profit contributions. In contrast to thermal peak-load power plants, PSP would also be used within the EEM and could consequently generate additional profit contributions [2]. 2007 was chosen as the reference year for meteorological conditions for several reasons. Firstly, 2007 was a good wind year with a positive long-term average compared to 2006, 2009 and 2010. Secondly, 2007 featured some extreme weather events such as storms, but also some longer calm periods. For these reasons, the chosen reference year is well-suited as a conservative assumption for questions about storage requirements for the provision of reliable available capacity [2]. Fig. 1 shows the methodological sequence of the study. As a first step, the expected residual load (the residual load is essentially the load minus RE production and must-run power plants) which has to be covered by flexible thermal power plants and PSPs was calculated. Next, assessment of cost- effective expansion of storage capacity was performed. The potential contribution of PSP to reliable available capacity was calculated based on PSP expansion and the existing fleet of PSPs. Then the necessary power of the gas fuelled power plants according to the ETG study was reduced according to the determined contribution of the PSPs. Finally, an operation and scheduling analysis for an entire year considering the complete conventional and PSP fleet was performed in order to assess the costs and CO 2 emissions for the examined scenarios. Fig. 1: Overview of the methodology sequence 4 4 Assessment of cost -effective expansion of storage capacity The graphs in Fig. 2 show the link between hours at full load and capacity expansion by PSP for the scenarios with an RE share of 60% and 80% according to the ETG study [3]. An average of 1,000 hours at full load in turbine mode was assumed as a constraint for an economically viable expansion. This is a typical calculation value which does not correspond to actual hours of operation.