In this paper, we address the problem of workload scheduling in data centers, while considering the greenness of the power sources. We prove that finding a feasible solution for the problem is NP-hard. Therefore, we develop an LP-based approximation algorithm to solve the problem in polynomial time. The proposed algorithm provides strong approximation bounds on the constraints and the objective of the problem. We conduct an extensive experimental analysis to evaluate the performance of the proposed algorithm using real world data.