Direct conversion of waste heat to electricity using pyroelectric conversion

This paper presents information on how the pyroelectric effect could be applied to convert heat to electricity. Experimental results show how conversion output can be increased by properly controlling operating conditions. Pyroelectric coefficients of a thin 60/40 P(VDF-TrFE) film under high voltage were measured as a function of temperature. The extremely non-linear nature of pyroelectric coefficients was observed with respect to change in temperature. We also determined the electrical resistivity of 60/40 P(VDF-TrFE) copolymer. Subsequently, direct conversion of low-grade heat to electric power was conducted using a single 60/40 P(VDF-TrFE) film according to the Olsen cycle. Our experimental circuit directly measured pyroelectric output responding to synchronized temperature and voltage cyclings. Various operating parameters that affect pyroelectric conversion were examined in detail. The results showed that proper operating conditions are needed to ensure that the pyroelectric film reaches sufficient discharge at high temperature and also to avoid complete depolarization by overheating during the heating leg of the Olsen cycle. We determined that at least 5 MV/m of the electric field must be maintained at all times for effective pyroelectric conversion. By synchronizing temperature and voltage cyclings, we were able to achieve a net output energy density of 40J/L of copolymer per cycle under applied voltage between 600 and 1000 V and film temperature 40-70°C.