UC Berkeley

With more than 50% of the primary energy consumed worldwide currently lost as waste heat, waste-heat conversion (WHC) should be considered a promising zero-carbon source of electricity. Despite significant research on WHC, the market penetration of such technologies remains limited, in large part because the R&D community has primarily focused on the development of new WHC heat engines with limited attention given to the techno-economic aspects. As different types of WHC heat engines vary significantly in their physical origins, there is a critical need to develop a system-level techno-economic model that is relatively independent of the detailed physics and design of the engine. In this perspective, we develop a techno-economic model for WHC technologies based on the well-known endoreversible thermodynamics formulations, which results in a fairly universal model. Our results indicate that regardless of the type or efficiency, WHC heat engines are not economically viable below 100°C, which has been the focus of significant research in the literature in recent years. Under highly optimistic assumptions, such as the cost of the WHC heat engines being the same as gas turbines (∼$0.25/W) and the capacity factor of the waste heat source being 0.9, for relative device Carnot efficiency <0.2, which is typical of various WHC heat engines, WHC is economical only for temperatures above 150°C and power output in the range of 100 kW to 1 MW. We conclude this perspective by providing a future outlook on the research needed in the field of WHC heat engines for it to be techno-economically viable. We also propose that along with the temperature and amount of waste heat available from various sources, the capacity factor of the waste-heat sources must be documented.