Global demand for heating accounts for more than 50% of primary energy consumption. Thermal energy for such purposes is produced mainly by natural gas, electricity, biomass, geothermal, and solar thermal technologies. Solar energy is an abundant, but low density, resource which can be harvested with little environmental impacts. In order to achieve outputs suitable for commercial and industrial applications, optical concentrators are conventionally required to increase the temperature and efficiency of a solar thermal system's output. In this paper, we instead explore the potential for utilizing energy concentrators to boost the performance of solar thermal collectors. To determine the feasibility of this approach, engineering limitations are established for realistic energy concentrators. Our analysis reveals that maximum effective energy concentration ratios of 176 and 2208 are possible for passive and active energy concentrators, respectively. Overall, this study demonstrates the potential of this concept for solar thermal collectors and other low-grade sources of heat. (C) 2015 Elsevier Ltd. All rights reserved.