Improved Pyroelectric Energy Converter for Waste Heat Energy Harvesting Using Co-Polymer P(VDF-TrFE) and Olsen Cycle

This study is concerned with pyroelectric energy conversion to directly convert waste heat into electricity. The pyroelectric effect refers to the flow of charges to or from the surface of a material upon heating or cooling. A prototypical pyroelectric energy converter was designed, built, and tested. It performed the Olsen cycle consisting of two isothermal and two isovoltage processes in the charge-voltage diagram. Co-polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films sandwiched between metallic electrodes were used as the pyroelectric elements. Their temperature oscillation, charge, and voltage along with the overall heat input and output were measured experimentally. Then, the electrical power generated and the energy efficiency of the device were computed. The effects of channel width, frequency, and stroke length on temperature swing, heat input, and energy and power densities were investigated. Reducing the channel width and increasing the stroke length had the largest effect on device performance. A maximum energy density of 130 J/L of P(VDF-TrFE) was achieved at 0.061 Hz frequency with temperature oscillating between 69.3 and 87.6°C. Furthermore, a maximum power density of 10.7 W/L of P(VDF-TrFE) was obtained at 0.12 Hz between 70.5 and 85.3°C. In both cases, the voltages in the Olsen cycle were 923 and 1732 V imposed on a 45.7 microns thick 60/40 P(VDF-TrFE) films. To the best of our knowledge, this is the largest energy density achieved by any pyroelectric energy converter using P(VDF-TrFE). It also matches performances reported in the literature for more expensive lead zirconate stannum titanate ceramic films operated at higher temperatures between 110 and 185°C.