A novel renewable energy intermittency modeland a new midterm dynamic simulation tool in power systems are developed for examining dynamic behavior along the load curve for different combinations of the system operation reserves and renewable portfolio standard (RPS) rates. The system’s import limits are considered. It is concluded that ignoring intermittency and governor effects is an inadequate method to assess intermittency impact. The intermittencymidterm dynamic impact must be studied. For the studied system, the instability is expected to be about 25 %RPS with current reserves. Besides, the most vulnerable peak hour toinstability is the afternoon peak hour when solar begins to drop off. This article stimulates further dynamic intermittencystudies on the issues caused by renewable intermittency.The studies on the issues caused by renewable intermittency have not been revealed because of inadequate/incomprehensive study methodologies so that effective,mitigative solutions can be developed to guarantee the reliability of power grid when incorporating higher RPS if highoperation reserves are impractical.