Thermal energy harvesting for wireless sensor nodes with case studies

Abstract

Over the last decade, wireless computing and mobile devices have decreased in size and power requirements. These devices traditionally had significant power requirements that necessitated the use of batteries as their power source. However, as the power requirements are reducing, with wireless sensor nodes rarely exceeding 75mW, alternative means of power provision become available. One of these alternatives is the use of thermal energy harvesting from waste heat or environmental sources. This report discusses the field of thermal energy harvesting, with a particular focus on those thermal technologies that provide direct electricity as output. There are a number of technologies in this field. The general technologies discussed in this report are thermoelectric devices, such as devices utilising the Seebeck effect, thermocouples and, thermionics. Sources of thermal energy discussed include solar, the human body, vehicle exhaust systems and subsurface heating. Solar has an obvious advantage of being a very large source of energy. Cases studies are presented to show magnitudes and the daily variation of power output from Seebeck style thermoelectric devices. Overall, this report reveals that while present thermal energy harvesting technologies suffer from very low efficiencies, there are a number of promising technologies that are increasing in reliability and efficiency. This, along with a continuing decrease in power requirements on the demand side of the equation, marks thermal energy harvesting as a very promising field of research.