324. Fuel Cell Power Systems Weight Analysis

Paper

Abstract

This paper was presented at the Twenty-first Annual National Conference of the Society of Aeronautical Weight Engineers at Seattle, Washington, May 14-17, 1962. The weight of electrochemical fuel cell systems is an important consideration, especially if these systems are to be used as secondary power sources for space vehicles. Fuel cells appear attractive in space vehicle applications because, theoretically, they can convert chemical energy to electricity with high efficiency and good reliability under space flight environment. In this paper, fuel cell systems are weight-analyzed, and a method of estimating their weight is presented. This method is based on values of pertinent weight-influencing parameters (power, time, current density, operating voltage, and cell spacing).
The two most promising types of fuel cells for use in space appears to be hydrogen oxygen (hydrox) cells using aqueous potassium hydroxide electrolyte, and hydrox cells employing an ion-exchange membrane as the electrolyte. The following components are generally required in these systems: fuel cell generator, stored reactant and tanks, plumbing and heat exchanger, and system supports. Methods are presented for determining weight of each of these components, and these weights are summed to obtain a system weight.
The weight predication method reveals that a weight-trade must be accomplished between fuel cell generator and stored reactant to attain a minimum system weight. Minimum system weight occurs only when operating voltage is at an optimum value. A voltage optimization method is outlined and used to compute minimum system weights. These results are presented graphically as a function of power and time. Hydrox fuel cell systems are then compared to silicon solar cell systems, battery systems, and a regenerative fuel cell system on a weight basis. This comparison shows that lightweight hydrox fuel cells may compare favorably for operating times in the range from about one hour to one week.