Nanotechnology for lower grade waste heat recovery

Currently about 60% of the total US energy consumption is lost as waste heat. Significant efforts have been made to improve energy efficiency and develop heat recovery technologies. However, the effective recovery of lower grade (< 400°C) waste heat from mobile or stationary sources remains challenging. In this paper, the state of the art technologies for converting low temperature gradients directly in electric energy are reviewed and outstanding problems in the field are identified. Of the numerous emerging technologies, thermoelectrics, spin Seebeck, pyroelectrics, and electrochemical cells are selected as some of the most promising candidates for discussion.