Abstract
Thermophotovoltaic (TPV) energy conversion, which uses photovoltaic (PV) cells to directly convert radiant thermal energy into electric power, has a number of important advantages for portable power generation in military applications. Since TPV is a direct energy conversion technology with no moving parts in the energy conversion system, it has the potential to provide quiet, reliable, maintenance-free electric power for thousands of hours. These systems also have the potential to be as efficient as small portable engine generators, operate on military logistic fuels, and start and operate in sub-freezing environments.
A 150 Watt thermophotovoltaic (TPV) power module has been designed, built, and tested. The technical approach taken in the design focused on optimizing the integrated performance of the primary subsystems in order to yield high energy conversion efficiency and cost effectiveness. An important aspect of the approach is the use of a narrow band fibrous emitter radiating to a bandgap matched photovoltaic array to minimize thermal and optical recuperation requirements, as well as the non-recoverable heat losses. For the prototype system, fibrous ytterbia emitters radiating in a narrow band centered at 980 nm are matched with high efficiency silicon photoconverters. The integrated system includes a dielectric stack filter for optical energy recovery and a ceramic recuperator for thermal energy recovery.
The prototype TPV system uses a rapid mix distributed fuel delivery system with controlled feeding of the fuel and heated air into a flame at the surface of the emitter. This makes it possible to operate at air preheat temperatures well above the auto-ignition temperature of the fuel thereby substantially increasing the system efficiency. The system has been operated with air preheat temperatures up to 1367 K and has produced a uniform narrow band radiation over the surface of the emitter with this approach.
The design of the system is described and test data for the system and some of the key components are presented. The results from a system model, which show the impact of various parameters on system performance, are also discussed.
