Electrical Performance from Bifacial Illumination International Space Station Photovoltaic Array

Abstract

With the first U.S. photovoltaic array activated on the International Space Station in December 2000, on-orbit data can be compared to analytical predictions. Because of space station operational constraints, it is not always possible to point the front side of the arrays at the sun. Thus, in many cases, sunlight directly illuminates the backside of the array as well as albedo illumination on either the front or the back. During this time, appreciable power is produced because the solar cells are mounted on a thin, solar transparent substrate. It is important to present accurate predictions for both front and backside power generation for mission planning, certification of flight readiness, and on-orbit mission support. To provide a more detailed assessment of the power production capability, the authors developed a photovoltaic array electrical performance model applicable to generalized bifacial illumination conditions. We describe the space station photovoltaic array performance model and the methods used to reduce orbital performance data. Analyses were performed using SPACE, a NASA Glenn Research Center-developed computer code for the space station. Results showed an excellent comparison of on-orbit performance data and analytical results.