The renewable energy such as wind or solar power plays an important role in a modern power system. Due to low reliability of renewable energy source, uncertainty in a system is increasing. There are many models proposed for managing systems with renewable energy. However, these models are complicated and not computationally efficient when applied to large scale problems. In this work, we propose a stochastic model which incorporates uncertainty in renewable energy. A two-stage recourse model is used for our stochastic model with finite scenarios. Additionally, we increase a spinning reserve power of the system by adding a reserve from renewable energy. The additional reserve is computed from the expected value of renewable energy serving the system. Moreover we propose an analysis process to determine a suitable spinning reserve level once the renewable energy introduced to a conventional power system.