Increasing consumption of energy derived from fossil fuels while has caused rapid economic growth in different communities, due to pollutant emission and its consequences, has faced the world with risky changes as well. Limitation of this non-renewable sources cased that energy consumption optimization policy become the governments work programs outline. On the other hand, growth of science and technology in the world has led to transformation of the commonly used methods of energy consumption, and discovering new energy sources has caused a major evolution in development of human societies. In this regard, the relatively simple technology, not polluting the environment etc. are the reasons that make the necessity of using solar energy more and more evident. Since most of the energy is consumed in buildings, functional identification of optimization systems in buildings is essential. The present study aimed to introduce, evaluate, and set priorities for use of energy systems in buildings. To this aim, first, all systems were identified and their fields of application were specified. Then, in a comparative study, the priorities for use of the systems and their application were examined in building sector. Key words : energy, solar system, active systems, passive systems.