Other technologies

This chapter introduces a number of technologies not covered in previous chapters that are currently at early stages of development for harvesting low-temperature waste heat, giving an overview of their operating principles and the current state-of-the-art in the field. Thermoelectrochemical cells (thermocells), which utilize redox couples dissolved in an electrolyte, are discussed first. Key developments in the areas of new redox couples, electrolytes, electrodes, and device design are summarized. Strategies to increase the Seebeck coefficient, Se, of redox electrolytes are critical to improving the efficiencies of thermocells, which are presently <5% relative to the Carnot efficiency, and the different redox couples and solvents being investigated are described. Achieving commercially viable power outputs and low $/W requires the development of thermocell arrays, and progress toward low cost and safer thermocell arrays for different applications is described. The formation of a thermally regenerative electrochemical cycle is then introduced, followed by the concepts of thermo-osmotic power generation. An overview and case studies of polygeneration systems by introducing the concept of combined water and power production (CWP) are then presented. Membrane distillation (MD) as a novel desalination technique and a thermally driven process with high potential to operate sustainably using low-grade waste heat are introduced. Furthermore the feasibility of combined power generation and water desalination utilizing an MD system is discussed. For this purpose, the fundamental theoretical modeling and experimental performance of MD power generation is presented in detail. The reported result supports the feasibility of polygeneration (simultaneous power generation and saline water desalination) using MD technology. However, the maximum overall efficiency of the CWP process utilizing the currently available membranes is only estimated at around 0.002%, which emphasizes the need for further research to develop this concept as a future sustainable water desalination technique. In the final sections of the chapter, we note the promise of polymer-based thermoelectric devices and hybrid device concepts.