Wi-Fi has become a ubiquitous wireless technology in a short period of time. Each one of us has wireless gadgets competing for the Wi-Fi bandwidth. In contrast to this, studies show that the legacy technologies' spectrum like the TV spectrum was found to be unoccupied 90% of the time. Cognitive Radio (CR) Technology is the riposte to this paradoxical situation. A CR is an intelligent radio which scans the radio spectrum for free channels and uses them to its own advantage. CRs coordinate among themselves using cooperative spectrum sensing schemes to sense the spectrum efficiently. Not much is known about their energy efficiency. To study this, we develop an energy model and perform an energy efficiency analysis of two basic/generic cooperative sensing schemes distributed and centralized, for the ad hoc WLAN scenario. We further propose corresponding modified versions for these two schemes where only a fraction of secondary nodes scan in each sensing cycle as opposed to all the nodes and show the amount of energy savings over their generic counterparts.