13
Tsutomu F UJIHARA 1) and Kunihisa E GUCHI 2) , Stratospheric Platforms Project Center,
E-mail: fujihara@nal.go.jp
1) and eguchi@nal.go.jp
2)
Keywords: stratospheric platform airship, regenerative fuel cells, solar cells, energy storage.
1. Introduction
An R&D program for a solar-powered stratospheric platform (SPF) airship has been promoted in NAL for future use in telecommunications and earth observations.
The airship needs a stationary flight of long duration at an altitude of 20 km and 30 m/s wind speed. For such a flight, a regenerative fuel cell
(RFC) with high energy storage capability is selected as the more promising system technology for night power supply to the airship propulsior. required for several technical problems with water management, including phase separation and non-freezing in a closed flow loop of the RFC.
Remotely-piloted and autonomous operations for the day/night power switching, design criteria for safely and efficient thermal management will also be required.
Sun
Solar cell array
Hydrogen Oxygen
3 Night line
Power transmission
Fig. 2 Solar RFC cycle mode during day/night
Energy storage vessels
Fuel cell unit for electricity generation
Electrolysis unit for H /O production
Fig. 1 Solar rechargeable power for the SPF
This paper provides an outline of a ground engineering testbed model fabricated for NAL in-house work in order to ascertain how to operate a solar RFC with fluid power and thermofluid management. The rig test results of fuel cells (FC) and electrolyte cells (EC) are also described.
2. Solar RFC power for SPF airship
A design view of the SPF airship power system is shown schematically in Fig. 1. The EC, one unit of the RFC assembly, is electrically connected to the solar cell (SC) array. As illustrated in Fig. 2, the power generated from the SC array is transmitted to the EC for H
2
/O
2 production as well as the propulsion unit during daylight hours, and at night, the H
2
/O
2
-fueled FC power is dissipated for propulsion. The power switching cycle has to be performed securely during long stratospheric flights. Solutions are
3. Ground engineering testbed model
The purpose of our ground engineering work was to establish a hardware technique for better fluid and power management in the closed flow loop, while the test data available will be reflected in a design methodology for an onboard full-scale RFC system. As depicted in the photograph in Fig. 3, the RFC testbed of 1 kW design power is comprised of the FC and EC of a proton exchange membrane (PEM) type, and storage tanks (water / H
2
/ O
2
). More details of the RFC flow diagram and specifications are presented in Fig. 2 and Table 1, respectively.
The aluminum-liner vessels with CFRP-FW
(filament wounding) are used for the H
2
and O
2 gas storage at maximum pressure of 1 MPa.
This document is provided by JAXA.

14
GO Storage Unit
(2x47L)
(4x47L)
Electrolysis Unit
(PEM 5 cells)
1kWe Fuel Cell Unit
(PEM 16 cells)
Fig.3 1kW RFC testbed model in NAL two–cycle EC/FC operation mode per day; in each cycle, power generation and H
2
/O
2
production are both performed for two hours for the simulated solar energy inputs.
Fig. 5 Performance of the design FC
Fig. 4 Closed flow diagram of RFC testbed
Table 1 1kW RFC design specification
Fig. 6 Performance of the design EC
Plotted in Figs. 5 and 6 are two sets of data showing performance characteristics as a function of electric current, determined from the results of individual rig tests of the FC and EC.
The respective test results satisfy the required design values with appropriate accuracy; the
FC-generated electric power of 1 kW or more and the EC-produced H
2
flow of 8 NL/min. In particular, the fuel flow data are coincide well with calculations, but have temperature dependent variations. The RFC testbed model is capable of providing an evaluation test in a
4. Summary
A ground-engineering RFC testbed was built in March 2002, and in the individual rig tests of the FC and EC, was found to meet the design performance requirements.
In our future work, some evaluation tests of the RFC model will run in a closed flow loop with passive control. It is expected that significant test data will become available to provide a design methodology for an onboard RFC power module of several tens of kilowatts, allowing the building of a SPF airship.
This document is provided by JAXA.