This paper gives the insights of energy efficiency of sector coded transmission (SCT) protocol for cognitive radio networks. SCT is a cluster head rotation based protocol used for cooperative spectrum sensing in cognitive radio networks. A modified transmission and reception radio model based on SCT is proposed for cognitive radio networks. Further the paper evaluates the effect of number of users, sectors and hierarchy levels on energy efficiency in SCT protocol. The frame structure for sending secondary users spectrum sensing decision data is also proposed in this work.