What is a fuel cell? A fuel cell is a device that generates electricity by a chemical reaction. Anode : 2H 2 4H+ + 4e- Cathode : O2 + 4H+ + 4e- 2H2 Overall equation : 2H2 + O2 2H20 + Energy

Model Of Fuel Cell

Types of fuel cells Alkali fuel cells Molten Carbonate fuel cells Phosphoric Acid fuel cells (PAFC) Proton Exchange Membrane (PEM) Solid Oxide fuel cells (SOFC)

Fuel Cells In Space Technology For space applications energy production is cyclic NASA power system The Unitized Regenerative Fuel Cell (URFC) Applications - high altitude balloons ,high altitude solar airplanes, etc.

Unitized Regenerative Fuel Cell System Proton Exchange Membrane in URFC Energy storage system. Potential ability to store large amounts of energy URFC – Fuel Cell + Electrolyser

Energy Density Energy delivered per unit mass of storage system The Energy density is given by Ed = (Output energy/Reactant weight) Output Energy = n Vd Id td Vd = Discharge cell voltage, volts Id = Average discharge current, amps n = Number of cells in the URFC stack td = Discharge time, hours Mw = Reactant weight

Parameters Influencing Energy Density Where, R = Ideal Gas Constant = (84.78 Kg-cm3)/(cm2-gmole-k) T = Temperature in Kelvin MOPw = Maximum operating gas pressure (Kg/cm^2) f(Vd) = Id (Discharge current density in A/cm^2) Kw = 0.336*106 (cm) (Water-Tank-Figure-of-Merit) Ka = The ratio of the total cell area to stack weight=(As/w) Where , As = Total cell area W = Stack weight

Discharge Voltage And Current Density Optimization

URFCS EFFICIENCY It is defined as the ratio between output energy to the input energy with regard to charging &discharging of the system

The Solar Airplane The solar airplane is an ultra light flying wing aircraft Its surface of the wing is covered with solar cells that produce electric power Need for URFC in Solar aircraft

Schematic Diagram Of URFCS

URFC Energy Storage System Component URFC Stack Gas Storage Tanks Water Tank Condensers Regenerative Dryers Gas Regulators/ Check Valves Energy Storage System Shell

URFC Energy Storage System Operation Description Electrolysis Operation Fuel Cell Operation Electrolysis To Fuel Cell Transition Fuel Cell To Electrolysis Transition

Packaging Of URFCS

Summary Of URFCS URFCS capable of delivering 3500 watts during a 12 hour discharge period. The overall energy density is 791 w-hr/kg. Lightweight energy storage system.

Variations In URFCS Performance The Size of Water Tank: The water tank was sized to provide sufficient water storage for 3500 watts discharge power for 12 hours. The gas tank volume: The gas tank volumes were sized such that the fully charged tanks had a peak storage pressure of approximately 28.1 kg/cm2 (400psia)

URFCS Performance Parameters URFCS Stack Electrical Performance URFCS Reactant Mass/Pressure Water Vapor Management

Conclusion Energy densities as high as 800 w-h/kg are possible for URFCS based energy storage systems The longer the discharge times for the URFCS the greater the energy density possible. Over 90% of the volume could be saved from the energy storage system described in this paper.

Bibliography Journal of Power Source Fred Mitlitsky, Blake Myers, and Andrew H. Weisberg, Regenerative Fuel Cell Systems’, Energy & Fuels F. Mitlitsky, N. J. Colella, B. Myers, C. J. Anderson, “ Regenerative Fuel Cells for High Altitude Long Endurance Solar Powered Vehicles,”

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