Today, Web search is a frequent action in the everyday life of many people. To perform it on a large scale, Web companies need energy-hungry data center, which raise environmental and economical challenges. For these reasons, Green Information Retrieval promotes energy and energy-cost awareness in contemporary Web search engines. In this document, we propose to further the research on Green Information Retrieval, which is still at its early stage. Moreover, we illustrate our first results in evaluating and improving the energy efficiency of search servers.