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.
Burner, emitter, and recuperator development for lightweight thermophotovoltaic power supply
Like batteries, thermophotovoltaic generators produce DC electricity quietly. TPV uses infrared photovoltaic cells to convert infrared radiation from a combustion heated ceramic IR emitter. However, because the specific energy in a hydrocarbon fuel like propane or butane is 12,900 Wh/kg, much larger than the specific energy of 145 Wh/kg for a Li-ion battery, TPV is very promising as a lightweight DC power supply. A portable cylindrical thermophotovoltaic (TPV) battery replacement concept has been previously described. It consists of a cylindrical TPV receiver assembly using simple diffused junction GaSb IR cells along with a novel omega recuperator and a novel doped ceramic matched IR emitter. For high energy conversion efficiency, it is very important to match the IR spectrum emitted with the IR PV receiver cells. While the GaSb IR cells have been previously demonstrated, development and demonstrations of the omega recuperator and the IR matched emitter are described for the first time here. The matched IR emitter consists of NiO doped MgO ceramic rods arrayed in a 26 mm diameter picket fence configuration. A burner, emitter, and recuperator test station is described consisting of this picket fence emitter heated at up to 1300 C by propane combustion along with an omega recuperator to preheat the combustion air. The emitted IR intensity is measured with a single GaSb test cell. Given a TPV conversion efficiency of 10%, this lightweight TPV cylinder along with 1.8 kg of fuel promises a very high specific energy of approximately 700 Wh/kg. This specific energy is 5 times higher than the specific energy for a Li-ion battery with a similar power rating making this TPV unit very lightweight. The key is the goal of 10% system efficiency. Progress towards achieving this goal is described here.
Economic potential for thermophotovoltaic electric power generation in the steel industry
A steel mill extrudes steel billets at temperatures above 1400 °C continuously 24 hours a day. The steel billets then go to cooling beds where they slowly cool down to below 1100 °C. JX Crystals Inc makes Gallium Antimonide (GaSb) thermophotovoltaic (TPV) cells that can generate over 1 W/cm2 when exposed to infrared radiant energy from glowing steel at temperatures above 1100 °C. There is a great opportunity to integrate GaSb TPV receivers into steel mill operations to generate electricity economically utilizing this now wasted radiant energy. In a recent visit to a steel mill in China producing 10 million Metric-Tons (MT) of steel a year, the operators o, the mill told us that they have 2000 m2 of glowing steel in process continuously. At 1 W per cm2, this equates to the potential to produce 20 MW o, electricity for that steel mill. In 2012, the world steel production was 1,548 million MT. So, the world wide potential for TPV electricity production could be 3.1 GW. At what cost will TPV be affordable? This application has two advantages over solar PV. The first is the high power density, a factor of 100 over solar PV modules, translating to a potential cost advantage. The second distinct advantage over solar PV is the 24 hours of operation since the sun is only available on average for 8 hours per day. One can estimate the potential value of a TPV plant ,rom the potential annual revenues. Assuming electricity at 8 cents per kWh, 1 kW of TPV electric power capacity will produce 8765x0.08 = $700 dollars per year. This implies a 3 year payback at $2.1 per W. Cost is a function of volume but should come down to below $1.5 per W at volumes above 1 MW.