This study was concerned with the direct conversion of heat into electricity using pyroelectric materials. It can be divided in four different parts: (1) synthesis and characterization of novel pyroelectric materials. (2) experimental investigation of direct thermal to electrical energy conversion using the synthesized materials, (3) modeling and optimization of a prototypical pyroelectric energy converter, and (4) combination of Stirling and pyroelectric energy conversion cycles.

The first part aimed at improving the performance of 60/40 poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer for pyroelectric infrared (IR) detection and direct thermal to electrical energy conversion. Three different types of samples were prepared: commercial, purified, and porous films. Complete characterization of the thermophysical and electrical properties relevant to pyroelectric IR detection and energy conversion was performed. The figures of merit (FOMs) for IR detection were improved by 47 to 66% for purified and porous thin films compared with the commercial films. In addition, FOMs for energy harvesting indicated that the purified and porous films were attractive for thermal to electrical energy conversion as well.

The second part of the study was concerned with the direct conversion of low grade heat into electricity using pyroelectric materials. The Olsen (or Ericsson) cycle was experimentally performed on the three different types of 60/40 P(VDFTrFE) films synthesized. The commercial, purified and porous films produced a maximum energy density of 521 J/L, 426 J/L, and 188 J/L, respectively. The performance of the purified and porous films suffered from their lower electrical resistivity and electric breakdown. However, the energy densities of all films considered matched or exceeded those reported recently for ceramic and single crystal pyroelectric materials. Furthermore, the results were discussed in light of recently proposed energy harvesting FOMs.

In the third part, numerical simulations of a prototypical pyroelectric energy converter were performed by solving the two-dimensional mass, momentum, and energy equations using finite clement methods. Reducing the length of the device and/or the viscosity of the working fluid improved the energy efficiency and power density of the device by increasing the optimum operating frequency. A maximum efficiency of 5.2% at 0.5 Hz corresponding to 55.4% of the Carnot efficiency between 145 and 185°C can be achieved with commercial 1.5 cSt silicone oil as the working fluid and PZST as the pyroelectric material, corresponding to a power density of 38.4 W/L of material.

Finally, the last part attempts to experimentally combine Stirling and Olsen cycles to directly harvest waste heat into useful mechanical and electrical energy. Temperature oscillations in a Stirling engine were measured and it was determined that periodic variations in the flywheel frequency increased the temperature swing of the working fluid. However, the temperature swing was not large enough and its oscillation frequency too small for the pyroelectric material to produce electrical energy.