International Space Station Solar Array Bifacial Electrical Performance Model Developed

The first U.S. photovoltaic array (PVA) was activated on the International Space Station (ISS) in December 2000. Though normally Sun-tracking, U.S. ISS arrays are held stationary to minimize plume impingement from the space shuttle during docking and undocking, as well as during ISS assembly operations. Because of these operational constraints, it is not always possible to point the front side of the arrays at the Sun. In these cases, sunlight directly illuminates the backside of the PVA as well as albedo illumination on either the front or the back. Since the solar cells are mounted on a thin, solar transparent substrate, appreciable backside power (about one-third of the front-side power) is produced. To provide a more detailed assessment of the ISS power production capability, researchers at the NASA Glenn Research Center developed a PVA electrical performance model applicable to generalized bifacial illumination conditions. The model validation was done using on-orbit PVA performance.