Thermo-optical performance of molecular solar thermal energy storage films

Zakariaa Refaa,Anna Hofmann,Marcial Fernandez Castro,Jessica O Hernandez,Zhihang Wang,Helen Hölzel,Jens Wenzel Andreasen,Kasper Moth-Poulsen,Angela Sasic Kalagasidis

doi:10.1016/j.apenergy.2022.118541

Zakariaa Refaa, Anna Hofmann + Show 7 more

Open Access

https://doi.org/10.1016/j.apenergy.2022.118541

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Abstract

Due to their potential for solar energy harvesting and storage, molecular solar thermal energy storage (MOST) materials are receiving wide attention from both the research community and the public. MOST materials absorb photons and convert their energy to chemical energy, which is contained within the bonds of the MOST molecules. Depending on the molecular structure, these materials can store up to 1 MJ/kg, at ambient temperature and with storage times ranging from minutes to several years. This work is the first to thoroughly investigate the potential of MOST materials for the development of energy saving windows. To this end, the MOST molecules are integrated into thin, optically transparent films, which store solar energy during the daytime and release heat at a later point in time. A combined experimental and modeling approach is used to verify the system's basic functionality and identify key parameters. Multi-physics modeling and simulation were conducted to evaluate the interaction of MOST films with light, both monochromatic and the entire solar spectrum, as well as the corresponding dynamic energy storage. The model was experimentally verified by studying the optical response of thin MOST films containing norbornadiene derivatives as a functional system. We found that the MOST films act as excellent UV shield and can store up to 0.37 kWh/m2 for optimized MOST molecules. Further, this model allowed us to screen various material parameters and develop guidelines on how to optimize the performance of MOST window films.

Highlights

Heating and cooling in buildings and industry account for half of the EU’s energy consumption [1]
Our goal is to study the performance of the molecular solar thermal energy storage (MOST) coatings for energy savings and provide a detailed model that describes the physical effects of these coatings upon exposure to sunlight
The multi-physical modeling and simulations were conducted to evaluate the interaction of MOST films with light, studying their optical proper ties, as well as the dynamic energy storage

Summary

Introduction

Heating and cooling in buildings and industry account for half of the EU’s energy consumption [1]. The earlier requires the development of efficient energy storage systems, which bridge the intermittency of renewable energy production The latter can be addressed by improving the insulation of building, in particular of windows, which are responsible for a large share of all heat losses and heat gains in buildings [2,3]. Smart windows can adjust their optical properties in response to solar irradiation and/or outdoor conditions, passively or actively They have the potential to improve the en ergy efficiency of buildings and the indoor environment. Several solu tions were developed to upgrade windows with new functions to increase the energy savings of buildings [4,5,6] These solutions range from simple tinted glass to active dynamic coatings [6]. Several works attempted to evaluate the performance [4,6]

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