**Preface to "Phase Change Materials: Design and Applications"**

In recent years, science and technology have revolutionized our way of life, improving well-being and comfort for all mankind. The discovery of new materials with unique features at macro- and nano-scales has played a significant part in this advancement. The possibility of producing materials able to perform different functions and of responding to external stimuli will undoubtedly be an extremely important research area in the near future.

There is increasingly intensive research on the development of energy storage technologies due to the increased energy needs of contemporary societies. Global energy consumption, together with greenhouse gasses and CO<sup>2</sup> emissions, is increasing at a very fast pace due to rapid global economic growth, global population growth and the human dependence on energy-consuming appliances. This increment in global energy consumption has specific environmental implications that pose serious challenges to the environment and human health. Moreover, increased global energy consumption results in the reduction in the availability of traditional energy resources, such as coal, oil and natural gas. Therefore, there is an urgent need for the development of new systems based on the conversion and storage of sustainable and clean energy.

An effective way to increase energy systems' efficiency is through the use of latent heat thermal energy storage because of its high energy density in comparison to sensible heat storage systems. Phase change materials (PCMs) are one of the key components for the development of advanced sustainable solutions in renewable energy and engineering systems. PCMs are able to either store or release large amounts of energy, while their temperature is changed slightly or kept constant. PCMs have the ability to accumulate and store lots of energy. The high storage potential of PCMs can be realized when their phase is changed.

In order to update the field of renewable energy and engineering systems with the use of PCMs, a Special Issue entitled "Phase Change Materials: Design and Applications" is introduced. This book gathers and reviews the ten contributions (nine articles and one review), with authors from Europe, Asia and America, accepted for publication in the aforementioned Special Issue of *Applied Sciences*. This book aims to attract all researchers working in this research field, and collects new findings and recent advances in the development, synthesis, structure–activity relationships, and future applications of PCMs.

> **Ioannis Kartsonakis** *Editor*
