The energy efficiency of network elements is becoming more prominent, with growing concern for Internet power consumption and heat dissipation in datacenters and communications closets. Previous work has looked at energy efficient wireless topologies, network nodes, routers, and protocols. In considering a fresh redesign of the Internet datacenter for energy efficiency, we believe that energy efficient encodings are worthy of study. In this work, we re-examine the choice of Ethernet encoding, develop an associated energy model, evaluate current encodings, propose new encodings, and identify the desirable features of future encodings. We found that simpler encodings are more energy efficient, with power savings of around 20% for the best encoding. Our work represents a first step in re-examining the established assumptions and practices of the PHY level of the network stack with respect to energy.