The objective of this paper is to propose a modeling of the renewable energy applications for uninterruptible power supply (UPS) based on compressed air energy storage system (CAES). The system is composite technology, which composes of energy storage system and electric power supply system. The energy will transfer from the renewable energy resource to the CAES system drives the air compressor engine to produce high-pressure compressed air to be stored in a vessel. CAES is used on demand or used in during the peak periods to generate power by air motor coupling with generator. The generator is directly connected with grid connected converter, which is used to invert from AC-DC-AC in order to connect with the power line and control the power quality. This paper will only focus on the thermodynamic analysis and simulation to obtain the behavior and performance of these system for helpful in system designing. The proposed system can use to the back up power system and peak shaping for the energy management applications.