The SWS‑SYS project investigated advanced concepts for electricity‑to‑heat‑to‑electricity (SWS) storage, focusing on Carnot‑batteries, conventional heat‑storage plants, and hybrid configurations that combine concentrated solar power (CSP) with Carnot storage. The technical work was organised into five application programmes (AP1.1–AP1.5) and a programme on interface definition for a modular simulation tool (AP2). In AP1.1 the team developed detailed component models for the heat‑storage medium, the heat‑pump unit, and the power conversion system. These models were coupled to a system‑level simulation that evaluated the performance of a full Carnot‑battery cycle. The results showed that a high‑temperature thermal energy storage (HT‑TES) with a temperature range of 450 °C to 104 °C can reach a round‑trip efficiency of 48 %, while a low‑temperature TES (LT‑TES) operating between 46 °C and –82 °C achieved 27 %. The simulations also quantified the mass‑flow rates required for charging and discharging: for example, a charging stream of 1 408 kg s⁻¹ and a discharging stream of 469 kg s⁻¹ were needed for a 450 °C system. In AP1.2 the project extended the modelling to a full heat‑storage plant, including the design of the storage vessel, the heat‑pump, and the power block. Annual yield calculations demonstrated that a plant with a 4‑stage HT‑TES and a 4‑stage LT‑TES could deliver a net electrical output of 6.4 % of the input energy, with a thermal utilisation factor of 85.6 %. AP1.3 explored a simplified Carnot‑battery that omits the heat‑pump and uses direct ohmic heating for charging. The resulting system achieved a lower round‑trip efficiency of 27 % but offered a faster response time, making it suitable for short‑term dispatch. AP1.4 presented a conventional heat‑storage plant that uses a single‑stage heat‑pump and a large storage tank. The model predicted a thermal efficiency of 52 % for the high‑temperature stage and 42 % for the low‑temperature stage, with a total storage capacity of 22 m³. AP1.5 investigated hybrid CSP‑Carnot systems. By integrating a parabolic‑trough CSP field with a Carnot‑battery, the hybrid configuration achieved a reference thermal efficiency (RTE) of 50 % and a reference thermal utilisation (RTU) of 50 % for a 625 °C system, outperforming the standalone Carnot‑battery by 10 % in annual energy yield. The modular simulation tool developed in AP2 defined a set of interfaces for heat and material streams, allowing component models from different partners to be assembled into a coherent system model. The tool’s architecture supports the rapid evaluation of new configurations and the comparison of alternative storage media.

The project was carried out by a consortium of academic research institutions and industry partners, coordinated by the project lead. The collaboration combined expertise in thermodynamics, materials science, and power electronics, enabling the development of realistic component models and system‑level simulations. The SWS‑SYS initiative was funded by the German Federal Ministry of Education and Research, and the project ran over a period of three years, culminating in a comprehensive final report that documents the technical findings and the simulation framework.