A new type of thermionic generator that turns heat or light into electrical energy has been developed by researchers in Germany and the US. The new design overcomes the "space-charge problem" that has plagued previous attempts at developing practical devices. The device is about four times more efficient than previous generators and the new technology could find use in a range of applications including solar power and the harvesting of waste heat.
Thermionic generators convert heat or light into an electric current by using the temperature difference between two metallic plates that are separated by a vacuum. The "hot" plate is heated either by incident light or thermal conduction and this causes electrons to evaporate from its surface. These electrons then condense on the surface of the cold plate. This creates a charge difference between the two plates, which can drive a usable electric current.
Because they convert heat or light directly into electrical energy, thermionic generators have considerable potential for practical applications. If used in coal-fired power stations, for example, thermionic converters would, in principle, be more efficient than steam turbines. Thermionic generators could also be applied to a variety of lower-temperature applications, such as the collection of solar energy or the recycling of waste heat in car engines.
Neil Fox of the University of Bristol in the UK points out that the new generator has similarities to a planar triode design tested at the Massachusetts Institute of Technology (MIT) in the late 1950s. This previous design had suffered from energy loses caused by electron–electron collisions and scattering. "[Mannhart and colleagues] have come up with a rather neat vertical triode structure that seeks to improve on the MIT device, by incorporating beam collimating concepts similar to those used in particle accelerators," explains Fox. "The data presented...show that this magnetic triode is a significant improvement over a closed-spaced diode, but suggests that electron–electron collisions and scattering losses to the gate are still present."
The team is now working to increase the efficiency of its generator design in two ways. First, it is building high-performance converters from existing semiconductor technologies. Second, it is optimizing its electrodes through the use of new materials, especially oxides, and nanotechnology.
The work is described in the Journal of Renewable and Sustainable Energy.
Via Dr. Stefan Gruenwald, Jamie Morgan MIET BMEI