Energy conservation is a dynamic topic of research in High Performance Computing and Cluster Computing. Poweraware computing for heterogeneous world-wide Grid is a new track of research. In this work, we study and evaluate the impact of the heterogeneity of the nodes of a computing platform on the energy consumption. We propose to take advantage of this heterogeneity in order to save energy with no significant loss of performance by using Dynamic Voltage Scaling (DVS) in a distributed eigensolver. We show that using DVS only during the slack-time does not penalize the performances but it does not provide significant energy savings. If DVS is applied to all the execution, we get important global and local energy savings (respectively up to 9% and 20%) without a significant rise of the wall-clock times.