Cloud applications are deployed in remote data center. A fast growth of demand for cloud based services result into establishment of enormous data centers consuming high amount of electrical power. So, energy conservation is a major concern in cloud computing system. It can also bring several important benefits; one of the important reasons is low utilization of computing resources. At the same time, many real time applications have been deployed in clouds. Most of the algorithms schedule the tasks according to their average-case execution times and do not consider task execution times with probability distributions in the real-world.