Evaluating the emissivity of pseudomorphic glass (PMG)

A flexible replacement for solar cell coverglass called Pseudomorphic Glass (PMG) has been previously characterized for relevant properties including stability under UV and particle radiation and electrical conductivity. PMG is composed of small beads of coverglass material suspended in a space grade silicone adhesive. The material has shown good environmental stability and offers several benefits for space applications. Recently, the spectral emittance of PMG was characterized and demonstrated to have superior behavior compared to conventional coverglass. This data suggests that the PMG may enable the underlying solar cell to operate at lower temperatures, and therefore increased cell efficiency. PMG configurations with different types of bead materials and silicone adhesives were selected for examination. Using measured spectral emittance data, an on-orbit model was developed to predict the temperature of the various PMG materials compared with coverglass under AM0 solar flux in a vacuum environment. The calculated temperature differences between the PMG materials and coverglass were then used to predict efficiency changes, using reported values of cell efficiency temperature coefficients. The calculations suggest that PMG coated solar cells would run ~5°C cooler than coverglass coated cells, leading to a ~0.3% absolute increase in cell efficiency. To validate this claim, an experiment was setup in which the temperature of two types of cells, one coated in coverglass and the other with PMG, were measured in response to receiving AM0 radiation at open circuit. The PMG coated cells operated at slightly lower temperatures than the coverglass coated cells.