This paper describes a field study to investigate whether and to what extent individuals conserve more electricity if they have the opportunity to signal their behavior to others in the online community. Moreover, the study intends to reveal how positive social sanctions (e.g., publicly rewarding people who reduce their energy consumption) and negative social sanctions (e.g., publicly warning people who increase their consumption) cause individuals to alter both their energy demand and their time dedicated to the online community. We discuss related work on identity disclosure in online communities, on promoting sustainable behavior with information systems, and on economic theory explaining the effects of prosocial motives on behavior. The study will be conducted as field experiment using an energy efficiency portal developed by us and operated by an Austrian utility company that currently facilitates 9,899 active users out of which 1,400 will be randomly selected as study participants.