The NASA Glenn Research Center has demonstrated the world’s first fully closed cycle hydrogen-oxygen regenerative fuel cell (RFC). The RFC is an electrochemical system that collects and stores solar energy during the day then releases that energy at night, thus making the Sun’s energy available all 24 hours. It consists of a dedicated hydrogen-oxygen fuel cell stack and an electrolyzer stack, the interconnecting plumbing and valves, cooling pumps, water transfer pumps, gas recirculation pumps, phase separators, storage tanks for oxygen (O2) and hydrogen (H2), heat exchangers, isolation valves, pressure regulators, vent and purge provisions (emergency only), instrumentation, and other components. It includes all the equipment required to(1) absorb electrical power from an outside source and store it as pressurized hydrogen and oxygen and (2) make electrical power from the stored gases, saving the product water for reuse during the next cycle. The Glenn RFC is a “brassboard” built mainly from off-the-shelf hardware components. It is used to
Construction was sponsored by the Environmental Research Aircraft and Sensor Technology (ERAST) project of the Flight Research Base Program. The ERAST charter included the development and demonstration of new technologies for unmanned aircraft that are suitable for Earth science, including RFC-equipped solar-electric aircraft with potentially unlimited endurance. Although ERAST was an aeronautics project, RFC energy storage is applicable to a wide variety of space and planetary surface missions in addition to high-altitude solar-electric flight; hence, there has been widespread interest throughout NASA to bring this technology to a flight demonstration.
Leading up to a flight demonstration are several laboratory and full-scale demonstrations of key components and subsystems, including the coordinated operation of a hydrogen-oxygen fuel cell and electrolyzer as an energy storage system in a sealed, closed-loop environment (the venue provided by this brassboard RFC).
The Glenn RFC was built up over calendar years 2002 to 2003 and was operated as an end-to-end energy storage system for the first time in September 2003. Closed-cycle operation at full power operation was first demonstrated in June 2004. Multiple back-to-back contiguous cycles at full rated power, and round-trip efficiencies to 52 percent, were demonstrated in June 2005 (see the graphs).
Electrolyzer (EZ) and fuel cell (FC) currents and voltages, reactant flows, and balances measured during a 5-day continuous run.
Long description of figure 1.
During fiscal year 2006, the system underwent numerous modifications and internal improvements aimed at reducing parasitic power, heat loss, and noise signature; increasing functionality as an unattended automated energy-storage device, and increasing in-service reliability. Unattended operation was demonstrated in June 2006.
The Glenn RFC is the first fully closed cycle RFC ever demonstrated (the entire system is sealed: nothing enters or escapes the system other than electrical power and heat). The Glenn tests have demonstrated the RFC’s potential as an energy-storage device for aerospace solar power systems such as solar electric aircraft, lunar and planetary surface installations, and system applications in any airless environment where minimum system weight is critical. Its development process has recently been slowed, but it continues on a path of risk reduction for the flight system NASA will eventually need for a manned lunar outpost.
The photograph shows the integrated equipment assembly at Glenn. The graphs on the preceding page show the electrolyser and fuel cell stack currents and voltages, reactant flows, and balances that were recorded during the June 2005, 5-day endurance run.
RFC-integrated equipment assembly, with fuel cell and electrolyser stacks shown in the foreground.
Long description of figure 2.
Find out more about research at Glenn: http://www.nasa.gov/glenn/
Glenn contact: David J. Bents, 216-433-6135, David.J.Bents@nasa.govLast updated: December 14, 2007
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