While an extensive set of research projects deal with the issue of power-saving for battery-based electronic devices, few have an interest in permanently-plugged Large-Scale Experimental Distributed Systems (LSEDS). However, a rapid study shows that each computer, member of a distributed system platform, consumes a substantial quantity of power, especially when those resources are idle. Today, given the number of processing resources involved in large-scale computing infrastructures, we are convinced that we can save a lot of electric power by proposing and applying "green policies". Introduced in this article, those policies propose to alternatively switch computer nodes On and Off in a clever way. Based on the analysis of some experimental large-scale system's usage, we propose a resource-reservation infrastructure which takes the energy issue into account. We validate our infrastructure on the large-scale experimental Grid'5000 platform and present the energy gains obtained.