Abstract
Thermal energy storage systems using phase change materials (PCMs) as latent heat storage are one of the main challenges at European level in improving the performances and efficiency of concentrated solar power energy generation due to their high energy density. PCM with high working temperatures in the temperature range 300–500 °C are required for these purposes. However their use is still limited due to the problems raised by the corrosion of the majority of high temperature PCMs and lower thermal transfer properties. Micro-encapsulation was proposed as one method to overcome these problems. Different micro-encapsulation methods proposed in the literature are presented and discussed. An original process for the micro-encapsulation of potassium nitrate as PCM in inorganic zinc oxide shells based on a solvothermal method followed by spray drying to produce microcapsules with controlled phase composition and distribution is proposed and their transformation temperatures and enthalpies measured by differential scanning calorimetry are presented.
Highlights
Due to the advantages offered by latent heat thermal energy storage, such as low temperature variation during charging and discharging cycles, small unit size, high storage density, relatively constant heat transfer fluid (HTF) temperature during the discharge process and versatility, the use of phase change materials (PCMs) as energy storage materials is growing in many different applications
Micro-encapsulation of high temperature PCMs is a key process in reducing corrosion and improving thermal stability but problems related to thermal stability, mechanical resistance due to volume change during thermal cycling and compatibility between PCMs and encapsulation materials must be overcome
Thermal energy systems (TES) developed using these technologies are classified in three groups: i) sensible heat storage that is based on storing thermal energy by heating or cooling a liquid or solid storage medium, with water being the cheapest option; ii) latent heat storage using phase change materials (PCMs); and iii) thermo-chemical storage (TCS) using chemical reactions to store and release thermal energy
Summary
Due to the advantages offered by latent heat thermal energy storage, such as low temperature variation during charging and discharging cycles, small unit size, high storage density, relatively constant heat transfer fluid (HTF) temperature during the discharge process and versatility, the use of PCMs as energy storage materials is growing in many different applications. PCMs with melting temperatures between 300 and 500 °C are needed in the storage of the heat obtained from high temperature concentrated solar thermal power plants. Micro-encapsulation of high temperature PCMs is a key process in reducing corrosion and improving thermal stability but problems related to thermal stability, mechanical resistance due to volume change during thermal cycling and compatibility between PCMs and encapsulation materials must be overcome
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