There is a growing and drastically underutilized abundance of energy stored on earth at small temperature difference, most familiarly in the form of low-grade waste heat. For the purpose of making use of this stockpile of energy, the direct conversion of heat to electricity is demonstrated using first-order phase transformations in lead-free BaTiO3 ferroelectrics. The thermodynamics of solid-state energy conversion using first-order phase transformations is investigated using a free-energy approach wherein the importance of the well-known Clausius-Clapeyron relation in opening up the mixed-phase region is discussed. A simple two-capacitor circuit is introduced to experimentally demonstrate the direct conversion of heat to electricity. By fluctuating the temperature by just ±5âC, current spikes of roughly 1 μA are sent back and forth across an electric load with no external battery attached. Finally, a supercritical ferroelectric Carnot cycle that would produce an energy density of 1.15 J/cm3 with a thermal efficiency of 15% is introduced, simulated, and compared with state-of-the-art pyroelectric energy-conversion methods.