Thermal Energy Stored for Month in New Material

Global emissions must be reduced by 60% before 2050 to avoid 2 degrees of global warming. However, energy consumption is doubling in the next 40 years due to an increasing world population and economic growth. The amount of solar power in winter drops by 90%. Solar energy could provide a larger share of global power if there was a way to store all of the worlds energy usage for months. The development of solar energy can potentially meet the growing requirements for a global energy system beyond fossil fuels, but necessitates new scalable technologies for solar energy storage. Thermal energy can be used for a broad range of applications such as domestic heating, industrial process heating and in thermal power processes. One promising way to store solar thermal energy is so-called molecular solar thermal (MOST) energy storage systems, where a photoswitchable molecule absorbs sunlight and undergoes a chemical isomerization to a metastable high energy species. Here we present an optimized MOST system (providing a high energy density of up to 0.4 MJ kg−1), which can store solar energy for a month at room temperature and release the thermochemical energy “on demand” in a closed energy storage cycle. In addition to a full photophysical characterization, solar energy capture of the present system is experimentally demonstrated by flowing the MOST system through an outdoor solar collector (≈900 cm2 irradiated area). Moreover, catalyst systems were identified and integrated into an energy extraction device leading to high temperature gradients of up to 63 °C (83 °C measured temperature) with a short temperature ramp time of only a few minutes. The underlying step-by-step mechanism of the catalytic reaction is modelled in detail using quantum chemistry calculations, successfully rationalizing the experimental observations. Energy Environmental Science – Macroscopic heat release in a molecular solar thermal energy storage system

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