Micro & nanogeneration, rather than kilo & megageneration

When we refer to microgeneration, we usually mean kilo and megageneration, as opposed to giga-generation. In this review article, appearing in the first issue of the International Journal of Innovations in Energy Systems and Power, David Michael Rowe introduces a technology that generate power over a range of 15 orders of magnitude.

Abstract

A thermoelectric converter is a solid-state heat engine  in which the electron gas serves as the working fluid and converts a flow of heat into electricity. It has no  moving components, is silent, totally scalable and extremely reliable.

In the early 1960’s a requirement for autonomous long– life sources of electrical power arose from the  exploration of space, advances in medical physics, deployment of marine and terrestrial surveillance systems and the exploitation of the earth’s resources in  increasingly hostile and inaccessible locations. Thermoelectric devices employing radioactive isotopes  as a heat source (Radioisotope Powered Thermoelectric  Generators, referred to as RTGs) provided the required  electrical power. Total reliability of this technology has been demonstrated in applications such as the Voyager  space crafts with Voyager 1 passing into the  Heliosheath some 8.3 billion miles from Earth on May 24th 2006. However, employing radioisotopes as  sources of heat has remained restricted to specialised applications where the thermoelectric generator’s desirable properties listed above outweighed its  relatively low conversion efficiency (typically 5%).

The fivefold increase in the price of crude oil in 1974, accompanied by an increased awareness of environmental problems associated with global  warming, resulted in an upsurge of scientific activity to  identify and develop environmentally friendly sources of electrical power. Thermoelectric generation in applications, which employ waste heat as a heat source, is a totally green technology and when heat input is free, as with waste heat, the system’s generating power density is of greater importance than its conversion efficiency in determining the system’s economic viability. Over the past ten years or so effort has focused  on developing thermoelectric generating systems which  can recover waste heat from the human body, computer chips, automobile engines, and industrial utilities.

In this paper the basic concepts of thermoelectric generation are outlined. An overview is presented of  recent advances in the development of high performance thermoelectric materials, novel devices  and applications, both macro and micro/nano. Finally, the potential of thermoelectric recovery of waste heat   as a renewable energy source is assessed.