Waste Heat to Power: Technologies, Current Applications, and Future Potential

Abstract

Energy consumption, environmental impact, and sustainability have risen fast through the ranks, achieving the first places in driving investments, policies, and concerns of all countries at any developmental stage. Energy transformation, though, must cope with nonunitary efficiency of devices and processes, which results in a distributed production of waste heat. A reduction of emissions, implying a conversion of waste heat to more noble forms of energy and a concurrent increase in efficiency of the same devices and processes, is of paramount importance. In view of the enthalpy content and distribution of the different sources of waste heat, low‐grade/low‐enthalpy sources below 200 °C are considered the most fertile field for research and development, with an impressive industrial growth rate. Thermodynamic cycles and thermal conversion devices based on the most relevant physical effects are herein introduced and briefly described, including both solutions that already achieved industrial maturity and less developed systems and devices whose study is still in progress. A specific focus on three application domains, selected due to their economic relevance, is done: industrial processes for the vast energy and capital availability, automotive sector for its permeation, and wearable devices for the market size. Limits and opportunities are critically discussed.

Liquid-state pyroelectric energy harvesting

“…7 Further details regarding current and new WHR/WHP technologies are provided in ref. 8 Another very popular harvesting method, particularly exploited in industrial and wearables fields, is based on the ThermoElectric (TE) effect. Of great importance in this frame are the works of Vladimir Leonov et al for the development of devices, like pulse oximeters, 9 wearable thermopiles, 10 EEG 11 or watches, 12 completely supplied by body wasted heat.…”

“…Pyroelectricity is the ability of certain materials, having specific crystalline structures, of developing a spontaneous polarization once they have undergone a temporal temperature variation, and often appears with a piezoelectric (PE) response. 8 Several PyE nanogenerators have been proposed to convert thermal energy into electricity with attention on the wearable field. 13 An overview on the state of the art is provided in Ref.…”

Heat Exchanger Assisted Exhaust Heat Recovery with Thermoelectric Generator in Heavy Vehicles

“…This is a novel concept as separate cold side heat exchanger or cooling channels are usually proposed for cooling the TE modules. [1,11] For this purpose, transformer oil is chosen as the coolant as it meets the required dielectric properties. As the electronic components are being immersed in the coolant without any kind of encapsulation transformer oil was deemed more suitable than water-based coolants.…”

“…About 30% of the combustion energy lost is in the form of waste heat through the exhaust gasses. [1] If a small amount of the energy from the waste heat is recovered, then the system efficiency of the vehicle would improve significantly. Saidur et al stated that an increase in 20% fuel efficiency can be achieved by converting 10% of waste heat into electricity.…”

Heating Homes with Servers: Workload Scheduling for Heat Reuse in Distributed Data Centers

“…District heating is seen as one of the most promising alternatives for residual heat recycling. The DCs' waste heat has the potential of replacing natural gas-based heat, bringing considerable cost savings and a lower carbon footprint to local communities [19,23].…”