**Preface to "Alternative Energy Systems in Buildings"**

Energy conservation through energy efficiency in buildings has acquired prime importance all over the world. The four main aspects of energy efficiency in a building include, first and foremost, the nearly zero energy passive building design before actual construction; secondly, the usage of low energy building materials during its construction; thirdly, the use of energy efficient equipments for low operational energy requirement; and lastly, the integration of renewable energy technologies for various applications. This Special Issue, published in the Energies journal, includes five contributions from across the world, including a wide range of applications, such as desiccant-assisted air conditioning systems, novel prototype design for building-integrated wind turbines, photovoltaic–wind hybrid plants integrated into an urban environment, and solar energy harvesting technologies for building integration and distributed energy generation. Finally, we wish to express our deep gratitude to all the authors and reviewers who have significantly contributed to this Special Issue. Our sincere thanks also go to the editorial team of MDPI and Energies for giving us the opportunity to publish this book, and for helping in all possible ways, especially Ms Wu, for her precious support and availability.
