Energy efficiency potentials: contrasting thermodynamic, technical and economic limits for organic Rankine cycles within UK industry

The laws of thermodynamics set a theoretical limit on the energy savings that can be realised in a given application. This thermodynamic potential cannot be reached in practice, and a technical potential for energy savings is defined by the performance of available technology. Only applications of the technology that are considered economic will usually be considered for installation. This economic potential will itself not be fully realised, with the actual savings that are achieved limited by further barriers. A database on surplus heat availability within UK industry was used to estimate the thermodynamic, technical, and economic potentials when converting this surplus heat to electricity using organic Rankine cycles (ORCs). Technical and economic information was based on that reported from existing installations and manufacturers. Installations economic over the target payback period totalled approximately 3.5 PJ/yr of electricity generation, primarily in the steel, chemicals and cement subsectors. However this result is sensitive to the input parameters, particularly the future price of electricity and required payback period, which are uncertain. Therefore a range of possible scenarios were investigated. The results form a basis for discussion on how to close this “gap” between the identified potentials and the savings realised in practice.