Energy efficiency is a critical issue in wireless networks, not only due to the technological limitations on energy supplies, but also due to the environmental impact caused by the information and communication technologies. This work discusses performance tradeoffs related to the energy efficiency, providing insightful results on the intricate relationship between system parameters. We propose a new parametrization to study a network in which users with different priorities to access the network resources can interfere and cooperate among themselves. A non-cooperative model is analyzed under three different spectrum sharing schemes, and we discuss important tradeoffs between energy efficiency and throughput, and between energy efficiency and the spectrum sensing accuracy. We also propose a cooperative model, in which a low-priority user relays packets for the high-priority user as repayment for interference. The energy-throughput tradeoff is analyzed in the case of cooperation, both in the case of half-duplex and full-duplex relays with different degrees of self-interference cancellation.