Project Area A: Carnot Batteries in the energy markets (2nd funding period)

Agent-based Inverse Analysis of Market Potentials for Carnot Batteries considering Uncertain Energy System Pathways (AIM for Carnot)

Building on the results of the first funding period, the second phase will enhance the agent-based simulation model to investigate additional applications and use cases for the Carnot Battery (CB) while keeping the philosophy of inverse modelling. The already developed methodological frameworks will be further refined and extended to support the investigations of individual perspectives and incentives to invest in as well as to operate CBs. A key aspect of the project is the potential to capture additional value through capacity remunerations in future energy markets, as results from the first phase indicate that short-term market revenues may be limited. This additional potential is of high interest because future energy markets are expected to exhibit increased variability and complexity due to the ongoing expansion of renewable generation. The promising economic potential offered by Capacity Renumeration Mechanisms (CRMs) is therefore essential for guiding both the design and deployment strategies of the technology. The inverse methodology must be adapted to this framework. Furthermore, the project seeks to enhance the technical representation of CBs. A more detailed modelling framework tailored to behind-the-meter use cases enables comprehensive depiction of the battery’s operational potential and allows for exploration of multi-sector applications. This not only improves the technical fidelity of the model but also provides insights into the battery’s operational behaviour and a clearer understanding of its technical constraints. Finally, the project advances the framework developed in the first funding period for assessing risk structures from an investor’s perspective. Whereas the initial phase focused primarily on mean-reverting and path-dependent uncertainties, the new project will extend this framework to material supply risks and their potential implications for investor decision-making. Accounting for a broad spectrum of uncertainties is critical not only for the identification of relevant use cases but also for understanding the economic viability and risk profiles of CB applications. This risk assessment is expected to provide robust insights that can guide investment, deployment, and policy decisions under uncertain market conditions. In summary, the objectives described broaden the initial analysis. The integration of CRMs provides insights into agents’ economic incentives and how these opportunities shape investment decisions. The improved technical representation and the extended incorporation of risks complement the analysis. Therefore, the results provide innovative guidelines for the technical research areas of the Priority Programme, which is fully consistent with the inverse top-down approach.

Professor Dr. Wolf Fichtner
Karlsruher Institut für Technologie
Institut für Industriebetriebslehre und Industrielle Produktion
Lehrstuhl für Energiewirtschaft

Ruths energy storage system design methodology

In the joint project of the Institute of Thermodynamics (IFT) and the Institute of Solid State Physics (FKP), a Carnot battery (CB) based on a Ruths storage system (RSS) is investigated. The system couples two two-phase Ruths steam accumulators operated at different pressure levels via a compressor, a turbine, and a liquid pump. Through evaporation and condensation, the storage tanks provide an intrinsic thermodynamic buffer. Charging is achieved by compressing low-pressure steam and storing it in the high-pressure tank, while discharging takes place through expansion back to the low-pressure level. During the first funding period, a transient simulation model of the RSS was developed based on equilibrium assumptions and isentropic machine efficiencies and coupled to an energy system model. This enabled a systematic linkage between technical design and application scenarios. Key results include the identification of fluid-specific optima of electrical energy density, enabling targeted fluid screening, as well as the development of an inverse optimization approach to determine economic viability thresholds for CBs within the energy system. In particular, decentralized behind-the-meter (BTM) applications at sites with a high share of wind energy were identified as advantageous. For RSS, pressure vessel costs were found to be the dominant cost component, strongly scaling with the maximum operating pressure. For further analysis, an inverse-iterative methodology was developed that couples detailed thermodynamic modeling with energy system optimization. In this approach, technical performance parameters such as energy capacity, efficiency, and self-discharge are determined through detailed simulation and passed to the energy system optimization, which returns an optimized system design and operating strategy. This process is repeated iteratively until convergence is achieved. In the second funding period, the added value of a coupled provision of electricity, steam, and heat will be systematically investigated, and suitable industrial BTM applications will be identified. To this end, the RSS model will be extended to represent different operating modes, the map-based selection and design of compressors and expanders, and the use of fluid mixtures. The influence of kinetic effects will be validated experimentally. The nonlinear behavior of the RSS – arising from pressure-dependent state changes and further intensified by non-equilibrium effects, machine characteristic curves, and the use of fluid mixtures – is explicitly accounted for in the energy system optimization. In particular, the economic potential of deep discharge operation as a safety reserve to cover extreme load peaks will be investigated. The central project outcome will be a methodology for the optimal design of RSS based on inverse-iterative optimization, which is transferable to other CB concepts.

Professor Dr.-Ing. Markus Richter
Professor Dr.-Ing. Stephan Kabelac
Gottfried Wilhelm Leibniz Universität Hannover
Fakultät für Maschinenbau
Institut für Thermodynamik (IFT)

Dr. Raphael Niepelt
Gottfried Wilhelm Leibniz Universität Hannover
Institut für Festkörperphysik

Multi-Objective Optimisation for the Inverse Analysis of Design Requirements for Carnot Batteries from an Energy System Perspective (MOIn Carnot)

Energy storage is crucial for transitioning to sustainable energy systems. Many existing technologies, however, face challenges in terms of limited expansion potentials, requirements of critical materials, or the dependency on specific geological formations. Carnot Batteries (CBs) offer a promising alternative, yet their market competitiveness and role in future energy systems remain uncertain due to ongoing technological development and evolving market conditions. This research aims to bridge the gap between energy system modelling (ESM) and technology development, specifically for CBs. Recent works within the priority programme 2403 have made progress in this area. A multi-objective inverse (MOIn) methodology for ESM has been developed within research area A of the priority programme to analyse the requirements and opportunities of CBs from the perspective of energy systems and markets. MOIn turns highly uncertain quantities of technologies under development, such as cost or efficiency, which are typically input parameters for ESMs, into optimisation variables. The application of the MOIn methodology to the Central Western European (CWE) market area shows that CBs face challenges in achieving economic competitiveness in wholesale power markets, which is confirmed by further studies from research area A. Altogether, recent studies, including our own, suggests future research should focus on considering additional drivers for CB deployment, such as material supply risk. Moreover, future work should study behind-the-meter (BTM) applications of CBs and heat integration. The objective of this project is therefore to further improve and develop the inverse method initiated in the first funding period. On the one hand, we will extend the MOIn method to another system-level objective (material supply risk). On the other hand, we will develop a novel method for inverse modelling to generate alternatives (MGA) in order to invert multiple technology parameters into optimisation variables. This will allow to explore the near-optimal solution space for alternatives with different, yet still competitive, techno-economic parameter configurations. These new methods will be demonstrated to generate new insights on development requirements and market potentials for CBs. The implications of considering material supply risk will be studied for large-scale energy systems, reassessing previous findings. The inverse MGA method will be applied to a small-scale BTM system with coupled power and (<40°C) heat supply. Finally, this project seeks to deepen existing and establish new ways of collaboration between energy system modellers and technology development research within and beyond the priority programme’s research areas B and C.

Professor Dr. Valentin Bertsch
Ruhr-Universität Bochum
Fakultät für Maschinenbau
Lehrstuhl für Energiesysteme und Energiewirtschaft