Use of excess solar array power by regenerative fuel cell energy storage systems in low earth orbit

Conference · Wed Dec 31 04:00:00 EST 1997

OSTI ID:347753

Hoberecht, M A; Green, R D ^[1]

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1. National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center

Regenerative Fuel Cells (RFC`s) are a competing energy storage system technology for a number of low-earth-orbit applications. The system is comprised of an electrolyzer which utilizes solar array power to convert water into hydrogen and oxygen reactants, a fuel cell that recombines the reactants back into water and produces power during eclipse, and associated controls and reactant storage. Round-trip electrical efficiencies of RFC systems are typically lower than competing battery energy storage systems. This results in larger solar arrays for the same application, with inherent drag, mass, and cost penalties. However, the increase in solar array size can be limited, if not totally eliminated, because of the ability of RFC systems to use excess solar array power. For this paper, the International Space Station (ISS) application was chosen for evaluation and comparison of battery and RFC energy storage systems. This selection was based on the authors` familiarity with the ISS design and the availability of a detailed in-house computer model specific to the ISS electrical power system (SPACE). Combined altitude and orientation effects, seasonal variations, and beginning-of-life solar array performance were examined for individual orbits at and above specified reference points. Charging characteristics of the battery system were also investigated. The evaluation allowed a comparison of the solar array size required with the existing battery energy storage system to the projected solar array size required with a possible RFC system. The results of the examination indicated that no increase in solar array size would be necessary for the ISS if outfitted with a RFC energy storage system, in spite of the lower round-trip electrical efficiency. For orbits with a minimum of excess power, the battery energy storage system used only 73% of the available solar array power as compared to 100% usage for a RFC system. The usage by the battery system was far less for the orbits with higher amounts of excess power. In terms of solar array size, a 59% efficient RFC system thus becomes equivalent to an 80% efficient battery system. Thus, for the ISS and possibly other low-earth-orbit spacecraft, there would be little if any solar array size advantage as a result of a difference in round-trip electrical efficiency between battery and RFC energy storage systems.

• OSTI ID: 347753
• Report Number(s): CONF-970701--
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
30 DIRECT ENERGY CONVERSION
COMPARATIVE EVALUATIONS
ELECTRIC BATTERIES
ENERGY STORAGE
PHOTOVOLTAIC POWER SUPPLIES
REGENERATIVE FUEL CELLS
SIZE
SOLAR CELL ARRAYS
SPACECRAFT POWER SUPPLIES