The National Aerospace Laboratory, Japan, has developed a thermoelectric device, which can convert heat energy into electricity with a record-high energy-conversion efficiency of 17 per cent. This break-through is expected to increase the use of thermoelectric devices, for example, using waste heat from incinerators and factories. As thermoelectric devices can produce electricity from heat, they are used by planetary explorers in situations where solar cells are not suitable. However, as devices normally have an energy-conversion efficiency of only around three to four per cent, scientists have not found many practical uses for civilian purposes. The new device excels because it is a stacked structure of three different materials, each of which converts heat energy to electricity in a different temperature range. In experiments, when one side of the device was kept at room temperature and the other side was heated to 800 deg C, the prototype was able to convert heat to electricity with 17 per cent efficiency.