Thermophotovoltaic (TPV) Cell Array Assembly Research

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The aim of this Special Notice under the ARL BAA (W911NF‐17‐S‐0003), under Grants.gov Opportunity W911NF‐17‐S‐0003‐SPECIALNOTICE‐TPV-CELL, is to fund an entity to collaborate with ARL to research Thermophotovoltaic (TPV) Cell Array assembly concepts for use on the ARL experimental test stand to produce electric output. ARL has assembled TCAs in-house in the past, but seeks entities with other approaches, more experience, and better equipment to collaborate with on this research. ARL will collaborate with the awardee on an improved design. The awardee will assemble proof of principle TCAs using TPV cells provided by ARL. The TCA will be tested by ARL on the ARL experimental test stand. ARL will then feedback the test data and work with the awardee to further improve the design. It is envisioned a few iterations of this process will lead to an optimized design to determine the limits of the TCA on overall ARL experimental test stand efficiency. The primary components of the ARL experimental test stand include a BER, TPV cell array (TCA), and Cavity. The BER is made up of a cylindrical counter flow burner with a cylindrical emitter tube covering one end of the burner with a recuperator attached to the other end of the burner. One end of the emitter is closed off with a thermally insulating lid. The outer surface of the emitter is heated to ~1100 Celsius and the burner surfaces are also at high temperatures. The TCA is made up of TPV cells mounted on heat sinks that surround the outside of the emitter. The TPV cell array and heat sinks fits inside a tubular housing with a cooling fan mounted on one end. Air from the cooling fan flows in the direction of the axis of the tubular housing through the heat sinks. The Cavity is the space between the Emitter and the TPV Cells and the Cavity design involves the interaction of the emitter surface, TPV surface, and possibly special reflectors, endcaps, and/or non-imaging optical filters. The current ARL TCA design has 108 TPV cells with each cell measuring 0.87 cm x 0.85 cm. It also includes a -circuit board with score marks to allow the circuit board to bend to create a 9 facet 180 degree semicircle. This semicircle has 54 TPV cells attached using thermally conductive epoxy. Heat sink fins are epoxied to the backside of the circuit board (see Figure 2). The axial length of the area covered by TPV cells on each facet is 53.5 mm. The distance from the surface of the TPV cells on one facet to the surface of the TPV cells on the facet 180 degrees directly across is 54.5 mm. The TPV cells can be electrically connected in various series/parallel configurations. Two circuit boards bend into a semicircle to cover the 360 degree interior of a tubular Teflon housing. The outer diameter of the fins of the current design is 87.5 mm. The outer diameter of the Teflon housing is96 mm. There is a thermocouple epoxied to the heat sink base to monitor the cell temperature. The current design has an 80 x 80 mm low power fan mounted on one opening of tubular housing with the air flowing in the direction of the axis of the tubular housing through the heat sinks. During operation of the current design on the ARL TPV Test Stand, TPV cell temperatures are controlled to less than 80 Celsius, but at the cost of more fan power which reduces the overall ARL experimental test stand efficiency. Low TPV cell temperatures are desired to ensure better TPV cell performance. Other ways to reduce the cell temperature might be improved heat sink design, integration, and attachment. Other areas of research that may be addressed include: improved circuit board design, TPV cell attachment methods; electrical connection methods and configurations; methods to reduce force air cooling required; methods to withstand high temperature and high radiation flux environments given the high emitter and burner temperatures; methods to improve view factor; methods to reduce inactive TPV cell areas; and methods to increase reflectivity for photon recycling.

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