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Experiment Title: Advanced Photovoltaic Experiment

Original Principal Investigator(s): Brandhorst, Henry - Invest. Role: Original, Forestieri, A.F. - Invest. Role: Original, Hickey, Mr. John R. - Invest. Role: Original, Scheiman, David - Invest. Role: Present, Brinker, Dr. David - Invest. Role: Present, Brandhorst, Henry - Invest. Role: Original, Forestieri, A.F. - Invest. Role: Original, Hickey, Mr. John R. - Invest. Role: Present, Hickey, Mr. John R. - Invest. Role: Present, Hickey, Mr. John R. - Invest. Role: Original,

The advanced photovoltaic experiment consisted of a group of three photovoltaics-related experiments for investigating a portion of the solar spectrum and the effect of the space environment on photovoltaics. The information is planned to provide correlation between space and ground testing and also to provide for more accurate performance measurement in the laboratory.

The accurate evaluation of the on-orbit performance of a solar cell intended for use in space power generation is crucial to ensuring sufficient electrical power over the lifetime of the satellite. If the conversion efficiency of a solar cell is overrated, as determined by laboratory based measurements, adequate power will not be available to meet satellite mission objectives. If underrated, more cells than necessary will be used, increasing both cost and the amount of heat which must be dissipated by the spacecraft thermal management system. An accurate determination of the space, or Air Mass Zero (AM0), performance of a solar cell is complicated by the circumstance that the efficiency of a cell for collecting a photon is a function of the wavelength of the photon. This wavelength dependent efficiency is known as the spectral response and depends on the choice of the semiconductor used for the cell, the design of the electrical junction in the cell and its anti-reflection layer. Because neither a laboratory solar simulator nor terrestrial sunlight exactly matches the spectral content of extraterrestrial sunlight, reference cells with the same spectral response of the cells under test must be calibrated in true AM0 sunlight to enable accurate measurements. This restriction creates the requirement for large numbers of reference cells, one for each unique cell design.

Over the last 35 years, the era of space photovoltaic power generation, a number of ground-based AM0 calibration techniques have been developed. These, including sounding rockets, high altitude balloons and aircraft, and mountain-top measurements, had to suffice because of limited access to space. The Long Duration Exposure Facility (LDEF) represented the first opportunity to expose a large number of solar cells directly to AM0 sunlight, record the pertinent data and safely return the cells for use in the laboratory. The timely return of the cells and flight data enabled their use as reference standards.

Photograph Classification: Prelaunch

Associated Photograph(s):
LaRC - L84-07059
KSC - KSC-384C-193.01
JSC - None
LaRC - L91-10676
KSC - KSC-390C-1840.10
JSC - None
LaRC - L90-10449
KSC - None
JSC - S32-78-090

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