Coatings for temperature reduction in space: a case study of solar cell covers

The temperature of an object in space in influenced by many factors, including the optical properties of the surfaces exposed to the environment. These properties can be modified by applying coatings. This paper describes a case study of such an application of thermal/optical properties control and the effects on the system that result. The example cited is the solar power panels used for satellites. The prime need for a space power system is maximum output per unit of mass. If the temperature of the array can be lowered the output will rise. Coatings on the front surface of a panel can reduce the temperature by modifying the solar absorptance and the emittance. Some coatings reflect the unwanted energy from the surface without changing the amount of usable energy that gets into the cell. Other coatings increase the ability of the panel to radiate heat and thereby remain cool. Specific examples of coatings for use on silicon (Si) and gallium arsenide (GaAs) cells will be discussed, and the quantitative gains that can be obtained will be estimated based on a thermal model of an array. The temperature reductions for such cells for various types of coating treatments (reflecting the sun in the UV, reflecting the near infrared, or increasing the far infrared emittance) and the expected increase in output form an array will be covered in these discussions. In an application where a 1% to 2% increase in output may be highly desirable, this discussion will show how 3% to 5% increases in output may be obtained.