<p>The rapid expansion of renewable energy technologies, particularly photovoltaic systems, has led to sustained annual growth rates on the order of several tens of percent. This dynamic development is expected to fundamentally transform the structure and operation of the energy sector. One promising approach to mitigating the challenges associated with increasing shares of intermittent energy sources is the implementation of high-temperature thermal energy storage systems. The objective of this study was to develop a rapid and experimentally efficient method for determining the thermal conductivity of insulating materials suitable for high-temperature thermal energy storage systems. The investigation focused on two primary material categories: thermal insulation materials designed for elevated temperature operation and materials intended for thermal energy storage. A key contribution of this work is the development of a rapid and experimentally efficient method for determining the thermal conductivity coefficient of solid materials. The proposed technique is based on controlled heating to a steady thermal regime, enabling evaluation of thermal conductivity within a non-negligible reduction of measurement time compared to conventional steady-state approaches (e.g., guarded hot plate). The method requires minimal sample preparation and is well-suited for comparative screening of candidate materials under identical experimental conditions. This measurement approach was applied to a series of insulation material samples, allowing for consistent and reproducible assessment of their thermophysical properties. The results demonstrate that, from the perspective of maximizing retained thermal energy in the form of sensible heat and enthalpy, the most advantageous solution involves the use of insulation materials characterized by a minimal thermal conductivity coefficient in combination with a low thermal diffusivity. Such a combination effectively slows heat transfer and temperature equalization between the storage medium and the surrounding insulation, thereby preserving the usable thermal potential of the storage system for extended periods. In addition, the study indicates that targeted material modifications offer viable pathways for simultaneously enhancing thermal insulation performance and mechanical properties, highlighting the potential for further optimization of materials for high-temperature energy storage applications.</p>