According to the goals of Europe's green deal missions, the continent strives for becoming carbon neutral by 2050. Since buildings are a major contributor to the overall consumption of energy, improving their energy efficiency can be a key to a more sustainable and greener Europe. On the way towards zero-emission buildings, several challenges have to be met: In modern energy systems, several energy sources have to be orchestrated to maintain a high security of supply, to guarantee a healthy environment for the building users, and both by using a minimum of conventional energy. Further, the modern building also hosts the electric filling station for one or several electric vehicles, requiring a significant amount of electrical power. Since the components of the building energy systems are integrating more and more sensors and embedded systems, buildings are becoming networked cyber-physical energy systems -- especially larger objects like airports, shopping malls or office buildings.