Both solar cells and batteries generate quiet DC electric power. Infrared (IR) sensitive GaSb photovoltaic cells can convert energy from a combustion heated glowing ceramic IR emitter into electricity. The result is a lightweight thermophotovoltaic (TPV) battery replacement that operates day and night. We present here the design and operation of a first stand alone TPV generator. Test results on this unit have allowed us to design a scale-up hand-held 10% efficient 50 W TPV generator weighing 1.5 kg. The 50 W scale-up TPV power supply along with 1.5 kg of fuel has a projected weight specific energy density of 645 Wh/kg. This is 4 times larger than for a Li ion battery.

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.

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.

A portable cylindrical thermophotovoltaic (TPV) battery replacement is described. This small 8 cm diameter unit is designed to consume fuel at a rate of approximately 200 W and to produce 20 W of DC power. 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. With a TPV conversion efficiency of 10%, this lightweight TPV cylinder along with a fuel cylinder can have a very high specific energy of approximately 1000 Wh/kg. This specific energy is 6.5 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 10% system efficiency. An earlier design for a TPV battery replacement is also reviewed with the key differences in the recuperator, IR emitter, and TPV converter circuit enumerated. The highlighted improvements then lead to the 10% overall system efficiency.

Various types of multijunction solar cells have now been demonstrated with energy conversion efficiencies over 40%. Higher cell efficiencies are still possible. NREL, Fraunhoffer and others have announced >40% Inverted metamorphic triple-junction (IMMTJ) InGaP/GaAs/GaInAs cells. One key feature of these cells is that the lowest bandgap cell is no longer a Ge cell. The IMMTJ lowest cell bandgap now allows for a 4th junction cell either integrated or separate. Herein, it is observed that the dual focus Cassegrainian (DFC) module can be fitted with a InGaP/GaAsP/InGaAs triple junction cell at its primary focus and with a GaSb or other IR sensitive cell at its secondary focus. This can allow a straight forward rapid path to a combined cell efficiency of >44%. The potential advantages of this configuration are, first, a rapid path to a combined cell efficiency of 44%, and second, given the fact that the heat load is divided into two locations, both cells will run cooler giving a higher module efficiency.

The goal is lower cost solar electricity. Herein, two evolutional steps are described toward achieving this goal. The first step is to follow the sun with a solar tracker. Herein, a carousel tracker is described for mounting on commercial building flat rooftops in order to produce more kWh per kW relative to fixed PV modules. The second evolutionary improvement is to produce lower cost 3-sun CPV modules where two thirds of the expensive single crystal silicon material is replaced by less expensive mirror material. This paper describes the performance and durability of two prototype installations demonstrating these evolutionary innovations. In the first case, the installation and operation of 2 carousels equipped with traditional flat plate modules is described. In the second case, the operation of a carousel equipped with new 3-sun CPV modules is described. Both systems have been operating as expected for several months through the winter of 2007.

JX Crystals' 3-sun PV mirror modules have now been operating in four separate systems in the field for up to 2 years. Two post-mounted 2-axis tracking arrays of 12 modules each were installed at the Shanghai Flower Park in April of 2006. Then 672 modules were installed in a 100 kW array on N-S horizontal beam trackers at the Shanghai Flower Port in November of 2006. Finally, sets of 4 modules were installed on azimuth-tracking carousels on buildings at the Oak Ridge National Lab and at the U. of Nevada in Las Vegas in late 2007. All of these modules in each of these systems are still operating at their initial power ratings. No degradation in performance has been observed. The benefit of these 3-sun PV mirror modules is that they use 1/3 of the silicon single-crystal cell material in comparison to traditional planar modules. Since aluminum mirrors are much cheaper than high-purity single-crystal silicon-cells, these modules and systems should be much lower in cost when manufactured in high volume.

Herein, we argue that solar PV can be economical for commercial customers in the sunny Pacific Southwestern US with buildings with flat roofs.

In a series of patent applications filed between 2002 and 2005, JX Crystals Inc described a evolutionary lower-cost low-concentration planar solar photovoltaic module that uses multiple linear rows of silicon cells and standard one-sun circuit laminations incorporating glass and EVA weather proofing encapsulations. The three novel features that we described are interdependent and integrated together to yield lower cost PV modules. These 3 novel features are: (1) The use of rows of linear mirrors or linear Fresnel lenses aligned with the cell rows and concentrating the sunlight onto the cell rows. (2) The addition of a thin aluminum sheet heat spreader on the back of the circuit lamination to spread the heat away from the cell rows so that the cell operating temperature remains acceptably low. (3) The incorporation of slots in the back of the aluminum sheet heat spreader to accommodate the differences in thermal expansion between the silicon cells, the glass, and the aluminum so that the circuit interconnectivity is maintained over time. Various embodiments of this planar linear concentrator panel are shown in figures 1 to 5. Figures 1 and 2 show the original planar linear concentrator module concept from July of 2002 with either mirrors (figuremore » 1) or linear Fresnel lenses (figure 2). The idea was expanded in 2003 with the idea of an aluminum sheet heat spreader added to the back of a standard PV circuit lamination as shown in figure 3. In 2003, we also transitioned from half cells to third cells using SunPower cells as shown in figure 4. JX Crystals Inc then received funding for the 3-sun PV mirror module concept from the Shanghai Science and Technology Commission in 2003 and from the Shanghai Flower Port and the Shanghai Import and Export Trading Company in 2005. This funding led to a 800 panel pilot production run of our JX Crystals designed 3-sun module in 2006. 672 of these panels were installed in a 100 kW demonstration and an additional 24 panels were installed in a second 4 kW demonstration both at the Flower Port in Shanghai. Both of these systems were completed in 2006. Our 3-sun PV Panel concept has been described previously (see references 1, 2, & 3 available at www.jxcrystals.com under publication tab). We are now interested in bringing this potentially lower cost 3-sun technology back to the US. For any new technology, three issues need to be addressed. They are performance, durability, and cost. These topics are addressed in the next 3 sections.« less

The Cassegrainian solar concentrator module concept we shall describe here uses a primary and a dichroic secondary mirror to split the solar spectrum into two parts and direct the infrared and near visible portions of the spectrum to two separate cell locations. An efficiency of 32.9% (STC) is reported measured outdoors for a solar concentrator PV module using InGaP/GaAs dual junction (DJ) cells located at the near-visible focus at the center of the primary and GaSb infrared solar cells located behind the secondary.

The demand for solar photovoltaic cells and modules has far outstripped PV cell supply and module prices are rising. To solve this problem, JX Crystals is developing a 3-sun mirror module that uses 1/3 the cell area to triple module production at a lower cost. Our concentrator module design uses existing planar cells. We simply cut standard SunPower A300 cells into thirds. In addition, our module design uses standard circuit lamination procedures and equipment. However, we add a thin aluminum sheet at the back of the laminated circuit for heat spreading. While a standard planar module contains rows of pseudo square cells, our low concentration modules consist of rows of third-cells. We then locate linear mirrors with triangular cross sections between the cell rows. The mirror facets deflect the sun's rays down to the cell rows (patent pending). Herein, we report on the design configurations, present photographs of the test systems, and present the initial outdoor test results.

We demonstrate a 40% efficient multijunction (MJ) cell capable of being used to make a 33% efficient solar concentrator PV module using the new Cassegrainian PV module design. This very high efficiency module can then produce cost competitive solar electric power.

Over the last several years, JX Crystals has invented and systematically developed the key components for thermophotovoltaic systems. These key components include GaSb infrared sensitive cells, high power density shingle circuits, dielectric filters, and hydrocarbon-fueled radiant tube burners. Most recently, We invented and demonstrated an antireflection (AR) -coated tungsten IR emitter which when integrated with the other key components should make TPV systems with efficiencies over 10% practical. However, the use of the AR tungsten emitter requires an oxygen-free hermetic seal enclosure. During a 2003 Small Business Innovative Research (SBIR) Phase I contract, we integrated a tungsten emitter foil and a commercial SiC radiant tube burner within an emitter thermos and successfully demonstrated its operation at high temperature. We also designed a complete stand alone 500 W TPV generator. During the upcoming SBIR Phase II, we plan to implement this design in hardware.

Thermophotovoltaic (TPV) systems can be characterized by several different parameters including system electrical conversion efficiency, photovoltaic cell electric power density, infrared (IR) emitter temperature and system costs. One way of dividing TPV systems into three categories is via high (T >1400 °C), medium (T between 1400 °C and 1100 °C) and low (T < 1100 °C) IR emitter temperature. In the high T category, silicon cells can be used with porous rare earth oxide selective emitters operating at over 1400 °C. For low T emitters, cells with band gaps below 0.6 eV are being studied. These cells are typically made with ternary and quaternary compounds using MOCVD. They are being developed for space and military applications where these cells operate at temperatures of 30 °C and below. These systems can potentially have efficiencies over 15%. Diffused junction GaSb cells can be used with IR emitters in the mid-temperature range. These cells can potentially be made at low cost in high-volume production. With emitter temperatures of 1250 °C, these cells operate with power densities of 1 W cm−2. These cells can be operated at 60 °C for combined heat and power applications. Systems using these cells can have electrical conversion efficiencies well over 10%. Spectral control is another important parameter characterizing TPV system configurations. While various means of high efficiency spectral control for low- and mid-temperature systems have now been demonstrated with single-cell experiments, the frontier now lies in integrating cell arrays, heat sources and IR emitters with spectral control into complete systems.

Three new developments have now occurred, making economical TPV systems possible. The first development is 2 the diffused junction GaSb cell that responds out to 1.8 microns producing over 1 W/cm(2) electric, given a blackbody IR emitter temperature of 1250 C. This high power density along with a simple diffused junction cell makes an array cost of $0.50 per Watt possible. The second development is new IR emitters and filters that put 75% of the radiant energy in the cell convertible band. ne third development is a set of commercially available ceramic radiant tube burners that operate at up to 1250 C. Herein, we present near term and longer term spectral control designs leading to a 1.5 kW TPV generator / furnace incorporating these new features. This TPV generator / furnace is designed to replace the residential furnace for combined heat and power for the home.

Major changes in the regulation of electric and natural gas industries during recent years have forced energy companies to explore opportunities in small-size Combined Heat and Power systems. These differ fundamentally from the traditional model of central generation and delivery since small, modular electric generators can be located very close to end-users inside a building or a single house within an industrial area, combined with the production of heat and cold. In particular, interest is growing in the new technologies for sub-100kWe units, including systems based on thermophotovoltaic (TPV) technology. TPV generator tubes can be inserted into hot furnaces to generate electricity and low-grade heat. In this generator tube, a water-cooled GaSb photovoltaic converter array inside the tube faces outward toward an infrared emitter liner mounted on the inside surface of the closed-end tube. Each tube can be sized to generate several kW and a given furnace can heat several tubes. We have conducted pilot experiments on key components in order to develop the concept just described. This includes a pilot scale array tested in an electrical furnace that heat a 3" diameter alumina tube with an infrared emitting liner. Also, a silicon carbide tube with a water-cooling system was tested in a ceramic fiber lined furnace equipped with a commercial 200 kW flameless regenerative burner, simulating a TPV generator tube in such a system.

It is well known that distributed combined heat and power (CHP) systems for commercial and industrial buildings are economically desirable because they conserve energy. Here, a thermophotovoltaic (TPV) unit is described that brings CHP into the home providing both heat and electric power by replacing the typical home heating furnace with a combined TPV furnace–generator. First, the design of a 1.5 kWelectric/12.2 kWthermal TPV furnace–generator is described along with the key components that make it possible. Diffused junction GaSb cells are one of these key components. Secondly, an economic cost target is determined for this system where the cost of the photovoltaic array will be key to the economical implementation of this concept. Finally, it is argued that the GaSb cells and arrays can be manufactured at the required low cost. The cost target can be reached because the GaSb cells in the TPV furnace–generator can produce an electrical power density of 1 W cm−2 which is 100 times higher than the typical solar cell. The cost target can also be reached because the GaSb cell fabrication process parallels the silicon solar cell process where no toxic gases are used, no wafer polish is required and cast polycrystalline cells can be used.

During a recent NASA Phase 2 SBIR contract JX Crystals fabricated a batch of triple-junction voltage-matched line-focus concentrator cell circuits, which measured up to 3.4 watts of output power, over 30% AM0 efficiency, during initial flash testing. These circuits have 4 GaInP/GaAs dual junction cells on transparent GaAs assembled on top of 8 diffused junction GaSb booster cells. A novel front cell contact enables all top side bonding. Three of these circuits were flown on the NASA Lear Jet for confirming calibration in October 2001. The flight samples were then used to calibrate JXC's in-house flash tester and corrected results are reported herein.

Three new developments have now occurred making economical TPV systems possible. The first development is the diffused junction GaSb cell that responds out to 1.8 microns producing over 1 W/cm/sup 2/ electric given an IR emitter temperature of 1200 C. This high power density along with a simple diffused junction cell makes an array cost of $0.5 per Watt possible. The second development is new IR emitters and filters that put 75% of the radiant energy in the cell convertible band. The third development is a set of commercially available ceramic radiant tube burners that operate at up to 1250 C. We describe a 1.5 kW TPV generator/furnace incorporating these new features. This TPV generator/furnace is designed to replace the residential furnace for combined heat and power (CHP) for the home.

The sun's energy can be concentrated and it's spectrum divided into visible light and infrared where the visible light can be used for applications such as plant growth or building interior lighting and the IR can be converted to electricity using low bandgap GaSb photovoltaic cells. Physical Sciences Inc. (PSI) has been developing the Solar Lighting System for space based plant growth. As a result, PSI has performed outdoor testing on GaSb cells provided by JX Crystals using concentrated IR solar energy. An efficiency of 15.4% has been measured with a cell output power density of 2.21 W/cm(2). This efficiency is consistent with indoor flash test data and QE data. The efficiency can be improved to 17.3% using an improved AR coating.