Environmental energy is becoming a feasible alternative to traditional energy sources for ultra low-power devices such as sensor nodes and smart watches. Moreover, the increas- ing need for exibility and recon gurability of such devices makes its energy management even more challenging. As a result, to e ciently exploit the potentially unlimited envi- ronmental energy, new adaptation strategies are required. In this paper we present a novel system recon guration strat- egy that exploits the intrinsic unpredictability of environ- mental energy to opportunistically recon gure the device. To assess the e ectiveness of the proposed recon guration strategy we rst perform a theoretical evaluation using sta- tistical energy pro le distribution and then we evaluate its energy e ciency on a prototype device in the presence of bursty energy pro les that we emulate using a programmable energy source.