Cold Junction Plate Optimization for the Nighttime Solar Cell TM

Abstract

The primary objective of the Nighttime Solar Cell ™ is to produce electric power at night. The cell can be used to complement daytime photovoltaic electrical energy production, or as a stan d-alone device can produce electrical power both night and day in low wattage applications. The Nighttime Solar Cell ™ op erates with a thermoelectric generator (TEG) utilizing the ambient or its surroundings as the source of thermal energy while deep spac e provides a thermal sink. The cold junctions of the TEG are insulated from the surroundings with a vacuum to improve overall effec tiveness. The Cold Junction Plate (CJP) inside the cell links the TEG's cold junctions to the thermal sink, acting as a he at spreader (HTS) to increase the heat flux from the device. The thermal model describing the operation of the cell has been enhanced to inves tigate different configurations for the HTS. For this application, the HTS utilizes radiation heat transfer to reject the waste heat to the thermal sink. A simple one dimensional model is used to investigate the effect of the HTS geometry on the cell. Typically used in high power electronic heat dissipation, here the HTS allows for a greater influence by the ther mal sink to increase cell output. Data for two -dimensional, radiatively cooled HTSs is presented, comparing cylindrical and rectangular geometries. The TEG module is modelled as a heat source in the center of the HTS. The results show that for typical N ighttime Solar Cell ™ thermal systems, square TEG modules can be modeled as cylindrical to match round heat spreaders with little loss of accuracy. The analysis also shows that the HTS thickness is favorable for using copper CJPs to increase the heat trans fer to deep space while reducing the mechanical stress on the TEGs. Also, projected performance of a prototype cell currently being built illustrates the effectiveness of high junction density modules for future cell development.