This paper presents a state of the art and an analysis of existing works dedicated to persuasive technologies for energy consumption. Thanks to a systematic analysis, a set of concepts of persuasion has been identified and organized into a six dimensional design space. In particular, the concept of persuasion function is identified and defined. Six persuasion functions are identified: Mirror, Explain, Recommend, What-if, What-for, Suggest-and-Adjust. This design space is used to characterize the works considered in this state of the art.