In this contribution we propose a method to increase the energy efficiency of orthogonal frequency division multiplexing (OFDM)-based femtocells. This is accomplished with no impact to the current power consumption, radio frequency (RF) circuitry, link adaptation strategies, bandwidth and transmit power. The proposed technique recycles redundant resources of OFDM transmissions (e.g., guard bands and cyclic prefixes), introduced to combat frequency selectivity. We borrow the underlying idea from a technique called cognitive interference alignment (CIA). Interestingly, our novel approach does not suffer from the same issues inherent to CIA, such as synchronization at the primary receiver and channel knowledge related complications. Nevertheless, it introduces a new issue related to the interference from the OFDM signal, which prompted the adoption of an adequate linear receiver at the femtocell user equipment. Numerical findings demonstrate that spectral efficiency gains are achieved, improving the energy efficiency of the femtocell by up to 20% for the simulated scenario.