In this paper, adaptive Power allocation(PA) on the source and relay is investigated to maximize Energy efficiency(EE) for OFDM-based Opportunistic regenerative relay links(O2RL). We derive EE function from O2 RL model by appropriate definition of variables to represent source/relay PA, Subcarrier transmission mode selection(STMS), and circuit power consumptions elegantly.Theoretical analysis demonstrates that EE function for O2 RL is strictly quasi-concave with respect to the overall transmit power. Exploiting the quasi-concavity property of the EE function, an EE-oriented optimal PA iterative method for O2 RL is proposed which used the bisection method to speed up the search of the optimum. Simulation results demonstrate that the O2 RL is more energyefficient than Traditional cooperative relaying strategies(TCRS), and the proposed method as compared to the Sum throughput maximization PA(STMPA) method is able to significantly improve performance in terms of system EE. In this paper, Adaptive Power allocation (PA) on the source and relay is investigated to maximize Energy efficiency (EE) for OFDM-based Opportunistic regenerative relay links (O2RL). We derive EE function from O2 RL model by appropriate definition of variables to represent source / relay PA, Subcarrier transmission mode selection (STMS), and circuit power consumptions elegantly. The theoretical analysis demonstrates that EE function for O2 RL is strictly quasi-concave with respect to the overall transmit power. Exploiting the quasi-concavity property of the EE function, an EE-oriented optimal PA iterative method for O2 RL is proposed which used the bisection method to speed up the search of the optimum. Simulation results demonstrate that the O2 RL is more energy efficient than traditional cooperative relaying strategies (TCRS), and the proposed method as compared to the sum throughput maximization PA (STMPA) method is able to significantly improve performance in terms of system EE.