Spectral control development for thermophotovoltaics
Gallium Antimonide (GaSb) infrared photovoltaic cells are light weight whereas batteries are heavy. The specific energy in a hydrocarbon fuel is high at 12,900 W-hr per kg but a lithium ion rechargeable battery has a specific energy of only 145 W-hr per kg. A 10% efficient portable lightweight thermophotovoltaic (TPV) cylindrical generator when compared with a battery can have 6.5 times higher specific energy, operates 7 times longer, and be quickly refueled. The key is the 10% efficiency goal. This efficiency goal depends on matching the spectrum from a combustion heated ceramic IR emitter to the response band of the IR PV cell. Herein, spectral measurements are presented for a propane burner and ceramic IR emitter assembly surrounded by a fused silica glass envelope. The cylindrical IR ceramic emitter consists of an array of NiO doped MgO rods or slats. The Ni ion emission line is centered at 1.6 microns and it matches the GaSb IR response band extending out to 1.8 microns. The ceramic IR emitter is combustion heated to approximately 1200 C. The fuel and air combustion efficiency and hot gas coupling efficiency to the IR emitter are also important parameters.
Gallium Antimonide Thermophotovoltaic: Simulation and Electrical Characterization Under Different Spectral Filtration Wavelengths
Gallium Antimonide (GaSb) Thermophotovoltaic (TPV) cell is a well-known device for waste-heat harvesting technology. To date, the conversion efficiency of the GaSb TPV cell remains low due to the presence of electrical and spectral losses. In this study, a GaSb TPV cell model is developed using the Silvaco TCAD simulation software. Validation on the simulation model was performed under atmospheric (AM) 1.5 standard test condition (STC) and TPV illumination conditions. Through the validation processes, a set of GaSb physical parameters that are reliable to be used for GaSb TPV cell simulation was established. Under AM1.5 testing condition, the electrical characteristic and performance of GaSb TPV of the reference cell were obtained from an experimental characterization on commercialized devices. A deviation in fill factor and cell efficiency was found between the cell sample and simulation model under AM1.5 illumination. This is due to the presence of resistance losses in the device. Nevertheless, a percentage error of below 3% was achieved under 1200 ° C TPV spectrum. Besides, it was found that a spectral filter that cuts at 2 μm increases the cell efficiency from 11.51% to 19.10% with a power output of 1.33 W/cm2. The finding in this study demonstrates the importance of minimizing the electrical losses and the determination of an optimal filtered spectrum wavelength for developing highperformance GaSb TPV cell.
Athenian Democracy at War
Classical Athens perfected direct democracy. The plays of this ancient Greek state are still staged today. These achievements are rightly revered. Less well known is the other side of this success story. Democratic Athens completely transformed warfare and became a superpower. The Athenian armed forces were unmatched in size and professionalism. This book explores the major reasons behind this military success. It shows how democracy helped the Athenians to be better soldiers. For the first time David M. Pritchard studies, together, all four branches of the armed forces. He focuses on the background of those who fought Athens' wars and on what they thought about doing so. His book reveals the common practices that Athens used right across the armed forces and shows how Athens' pro-war culture had a big impact on civilian life. The book puts the study of Athenian democracy at war on an entirely new footing.