Thermo-economically optimal design = optimal molecule + optimal process + optimal equipment.

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Higher shares of renewable energy increase the need for electricity storage. A promising storage technology is Pumped‐Thermal Electricity Storage (PTES): PTES systems transform electricity into heat using a heat pump (HP) and reconvert the heat into electricity using a heat engine. Since both HPs and heat engines require working fluids, maximum performance requires the optimal combination of PTES process and working fluids. Herein this work, the thermo‐economic potential of an Organic Rankine Cycle (ORC)‐based PTES system is analyzed by simultaneously designing both the PTES process and the working fluids used in the HP and the ORC. To rigorously explore the molecular design space, the 1‐stage Continuous‐Molecular Targeting ‐ Computer‐Aided Molecular Design method is employed. Detailed models for costing and sizing of the equipment allow for a thermo‐economic design of the PTES. The computer‐aided molecular design formulation integrates the working fluids as degrees of freedom into the process optimization. For the investigated ORC‐based PTES system with an input power of 60 MW, the optimal process and working fluids minimize the specific investment cost to SIC = 929  € kWh out − 1 . The analysis of cost drivers shows that with decreasing compressor cost, the investigated ORC‐based PTES system can become a competitive storage technology.

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To achieve the climate goals of the Paris Agreement, efficient use of energy is critical. Still, approximately 30% (31.9 EJ) of the energy input to global industry is lost as waste heat, with 28% as so-called low-temperature waste heat between 60 and 120 °C. [1] Therefore, using low-temperature waste heat offers an opportunity to develop the potential of waste heat and thereby reduce global greenhouse gas emissions.Technologies to utilize low-temperature waste heat can be divided into three categories: 1) passive heat recovery (e.g., heat exchangers); 2) heat transformation (e.g., heat pumps); and 3) power production (e.g., organic Rankine cycles (ORCs)). [2] Among these technologies, power-production technologies have the advantage that electrical power has a higher energy quality than heat. Thus, power production from lowtemperature waste heat is a promising target.For power production from low-temperature waste heat, the ORC can be considered as state-of-the-art technology. [3] The advantages of ORCs include the use of standard components, often known from the well-researched Rankine cycle, and the possibility of using working fluids perfectly tailored for a specific application. [4] Despite the advantages, today's ORCs are often unprofitable for converting low-temperature heat due to their system complexity and low thermal efficiencies. [4,5] Rahimi et al. [6] have recently reviewed three alternative technologies for power production from low-temperature waste heat: 1) thermo-osmotic energy conversion (TOEC); 2) thermally regenerative electrochemical cycle (TREC); and 3) thermally regenerative battery (TRB).TOEC are turbine-based systems that exploit a static pressure difference between a high-pressure reservoir at ambient temperature and a low-pressure reservoir at heat source temperature. [6] TOEC directly integrates heat by vaporizing water through a vapor-permeable membrane from the low-pressure to the high-pressure reservoir. [7] The TREC is an electrochemical cell that exploits a temperaturedependent redox couple. [6] The temperature dependence allows

The performance of many chemical and energy conversion processes depends on the choice of the molecules used, e.g. as solvents or working fluids. To capture the complex relations between the properties of the molecules used and the process conditions, the selection of suitable molecules should be directly integrated into process design. Solving the resulting challenging integrated design problem is enabled by the Continous-Molecular Targeting-Computer-Aided Molecular Design (CoMT-CAMD) approach. Here, the combinatorial complexity of the molecular decisions is avoided by relaxing molecular parameters in a physically-based thermodynamic model. So far, implementations of CoMT-CAMD were based on procedural programming languages. This impedes reusability and the investigation of process variants as well as the design of complex processes. In order to overcome these shortcomings, we implement the CoMT-CAMD approach based on objectoriented process modeling and thus enable the integrated process and molecular design with Modelica. The resulting approach is demonstrated for the design of a process and the working fluid for a geothermal Organic Rankine Cycle application.