Demonstration of 10-Wp micro organic Rankine cycle generator for low-grade heat recovery

In this study, a μ-ORC (micro organic Rankine cycle) generator that produces net positive power from low-grade heat (i.e., temperature below 100 °C) was experimentally demonstrated. First, the basic performance of a 10-Wp μ-ORC prototype with a small originally developed displacement-type expander and state-of-the-art commercial DC (direct current) micro-pump was tested. The prototype μ-ORC was coupled with a DC generator to produce a net electrical power of 5 W without an external electricity supply. Finally, the components of the μ-ORC generator were packaged into a compact box to achieve a power density of 214 mW/L (volume), 293 mW/kg (weight), and 3.33 mW/cm2 (footprint), which are the best results achieved in the present study. The maximum achieved isentropic efficiencies of the expander and pump were 4.55% and 30.0%, respectively. There is much scope for further improvement of the power density. The present results suggest that a downscaled ORC generator could be used to recover the energy of widely distributed low-grade heat sources.