Background
Within the last two years Enable, a subsidiary of DCH Technology, has moved away from its traditional focus of stack and system development, in favour of development of design and packaging of fuel cell systems for specific applications. With this shifted focus, Enable have successfully developed fuel cells, boasting six times the power output of a conventional 'D cell' battery, and integrated these units in to prototype devices. Furthermore, Enable have accomplished the successful packaging of a fuel cell system in to a portable package 'the size of a picnic cooler'.
At the time of presenting the paper, the company were undertaking lifetime and environmental testing of their systems to 'verify product performance, determine service intervals and benchmark product lifetimes'. These studies were undertaken in conjunction with application-specific product development.
Trials and Results
Enable realised that for its fuel cells to compete with batteries in portable applications, they must meet or exceed existing customer expectations. The fuel cell units must display the ability to rapidly turn on and off as well as changing load and operating stably at any given load. As a result of this observation, response time and steady state operations have become an important area of focus for the group.
Testing has proved that all of Enables hydrogen based fuel cells exhibit response times in the order of 100 microseconds or less, when changing from a 20amp to a 70amp load. This allows the systems to comfortably meet the needs of most demanding digital applications. Furthermore, under lifecycle testing, portable fuel cells have shown the ability to rapidly transition between 12, 18 and 36ohm loads whilst maintaining stable operation after each transition.
Under a constant load, passive fuel cells were shown to have a stable output as the hydride storage unit is discharged over a period of 7hours.
Initially, the target lifetime for portable applications was set at 2,000 hours. This has since been realised and extended to 2121 hours. In addition to this, the stack tested experienced an initial 50 hours of testing. Throughout this period, stock output remained stable for both current and voltage measurements with no apparent evidence of degradation. Slight variations in output have been attributed to changes in temperature and humidity.
It is a pre-requisite of portable fuel cells to be capable of operating over a wide range of environmental conditions in order to achieve widespread market acceptance. Enable have achieved successful system operation and steady state current at 0.55 V/cell down to temperatures of 0 degrees C. Humidity and temperature have small effects on these systems in the range from 40-70 per cent relative humidity and 40-0 degrees C respectively, however, even at lower temperatures a significant amount of current flows. Enable are currently developing passive fuel cell systems that will achieve full power output at temperatures as low as 20 degrees C.
Initial portable fuel cells produced by the company were approximately 7cm in diameter, used in applications such as powering remote water quality monitoring systems. Such fuel cells have been shown to produce a constant current and voltage output over a test period of 16 hours. At present, these systems comprise of two units, however, the next generation of portable fuel cells will be single stack.
Recent developments have enabled the company to integrate passive fuel cells in to the housing of flashlights and to configure them to power a standard 12V automotive power takeoff. These new models have approximately doubled the power density of the first generation fuel cells.
In the field of fuel cell development for transportable applications, a system with 2 kilowatt peak capacity and 1.1 kilowatt ac constant output has been developed. This system is no bigger than the size of a picnic cooler.
To date, the largest transportable unit developed by Enable is a 3 kW system designed for operation by personnel without experience in fuel cells. The system is suitable to survive in a rugged transportable application for a mobile air quality monitoring equipment trailer.
Summary
Enable has developed a wide range of fuel cells that are capable of powering numerous applications. The results of trials on such systems have provided a positive response and the company shall continue development of their technologies. It will be some time before the PEM fuel cells are widely available in the industrial and consumer power markets; this time frame will however be made shorter by the continuous development work which the company undertakes.
Source: The Fuel Cell Home Proceedings Book
Edited by Marcus Nurdin