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High pressure autoclave testing (HPAT) to estimate the service life of PERT geosynthetic barriers as part of Pit thermal energy storage systems
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In response to the challenges posed by man-made climate change, Pit Thermal Energy Storage (PTES) systems offer a promising solution to store solar thermal energy, or surplus energy, e.g. from industrial processes, helping reduce CO2 emissions and supporting the transition towards a sustainable energy sector. A key component of these systems is the use of geomembranes for lining the pit structure and as floating covers, which prevent the stored hot water leaks out and possible groundwater as well rainwater enter the storage, typically heated to temperatures reaching 90 °C. However, the prolonged exposure to such elevated temperatures presents significant challenges to the long-term durability of these materials, particularly in terms of thermo-oxidative degradation considering the exposure to hot liquid on one surface. To estimate the service life, HPAT is employed to simulate the extreme conditions as they prevail in PTES applications. This study presents the use of HPAT to accelerate the thermo-oxidative degradation of several PERT materials by immersing samples in water and subjecting it to elevated temperatures and additionally to a highly oxidative environment. By varying test parameters, i.e. test temperature (85 - 95 °C) and oxygen partial pressure (5 - 41 bar), and by evaluating quality-determining properties, e.g. mechanical properties, during the ageing period, the service life can be estimated with the help of a 3D evaluation method. The test results provide valuable insights into the material’s resistance to thermo-oxidative degradation, mechanical properties, and estimated service life when exposed to the harsh conditions found in PTES systems. These findings are critical for optimizing material selection, enhancing the sustainability of PTES, and ensuring the long-term performance of the thermal storage system. By utilizing HPAT, the study aims to contribute to the development of more resilient materials used for extreme conditions as they prevail in PTES applications and thus improving the overall efficiency and environmental impact.