Controlling energy consumption is a serious environmental issue due to global warming and pollution. Public policies are developed in this context. One such policy is the nudge, a form of policy aimed at changing individual behaviors without using financial incentives nor orders, for example by providing information to individuals so as to conduct behaviors in the direction desired by the policymaker. Interestingly ``private nudges'' can be imagined for companies. Many economists and psychologists have studied the impact of nudges on households' pro-environmental behaviors. Yet, studies focusing on nudging employees' energy use are rare. The objective of our paper is precisely to explore this issue, both from a theoretical point of view (with the help of an Agency model where peer pressure is introduced), and an empirical point of view with the help of a field experiment. Using a difference-in-difference methodology, the effects of three nudges on employees' energy conservation are tested. The first nudge, ``moral appeal'', stresses the responsible use of energy regarding environmental stakes. The second one, ``social comparison'', informs employees on the energy consumption of other firms participating in the experiment. Finally, the third nudge, ``stickers'', alerts employees about good energy conservation practices. The field experiment was conducted at 47 French companies's sites. Our results stress the complementarity of these nudges. When implemented alone, the three nudges have no significant effects on energy consumption. However, when the moral appeal and social comparison nudges are combined with the stickers one, they become effective.