What is a fuel cell?What is a fuel cell?

A fuel cell is a device that generates A fuel cell is a device that generates electricity by a chemical reaction. electricity by a chemical reaction.

Anode : 2H Anode : 2H 2 2 4H 4H+ +

+ 4e+ 4e--

Cathode : OCathode : O2 2 + 4H+ 4H+ + + 4e + 4e- - 2H2H2 2

Overall equation : 2HOverall equation : 2H2 2 + O+ O22 2H 2H220 0 + Energy+ Energy

Model Of Fuel CellModel Of Fuel Cell

Types of fuel cellsTypes of fuel cells

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

Fuel Cells In Space TechnologyFuel Cells In Space Technology

For space applications energy production is For space applications energy production is cyclic cyclic

NASA power system NASA power system

The Unitized Regenerative Fuel Cell (URFC) The Unitized Regenerative Fuel Cell (URFC)

Applications - high altitude balloons ,high Applications - high altitude balloons ,high altitude solar airplanes, etc.altitude solar airplanes, etc.

Unitized Regenerative Fuel Cell Unitized Regenerative Fuel Cell SystemSystem

Proton Exchange Membrane in URFCProton Exchange Membrane in URFC Energy storage system. Energy storage system. Potential ability to store large amounts of Potential ability to store large amounts of

energy energy

URFC – Fuel Cell + ElectrolyserURFC – Fuel Cell + Electrolyser

Energy DensityEnergy Density

Energy delivered per unit mass of storage system Energy delivered per unit mass of storage system

The Energy density is given by The Energy density is given by

EEd d = (Output energy/Reactant weight)= (Output energy/Reactant weight)

Output Energy = n Vd Id tdOutput Energy = n Vd Id td

VVd d = Discharge cell voltage, volts = Discharge cell voltage, volts

IIdd = Average discharge current, amps = Average discharge current, amps

n = Number of cells in the URFC stackn = Number of cells in the URFC stack

ttdd = Discharge time, hours = Discharge time, hours

MMw w = Reactant weight= Reactant weight

Parameters Influencing Energy Parameters Influencing Energy DensityDensity

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 Discharge Voltage And Current

Density OptimizationDensity Optimization

URFCS EFFICIENCYURFCS EFFICIENCY

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

The Solar AirplaneThe Solar Airplane

The solar airplane is an ultra light flying wing The solar airplane is an ultra light flying wing aircraft aircraft

Its surface of the wing is covered with solar cells Its surface of the wing is covered with solar cells that produce electric powerthat produce electric power

Need forNeed for URFCURFC in Solar aircraft in Solar aircraft

Schematic Diagram Of URFCSSchematic Diagram Of URFCS

URFC Energy Storage System URFC Energy Storage System ComponentComponent

URFC StackURFC Stack

Gas Storage TanksGas Storage Tanks

Water Tank Water Tank

Condensers Condensers

Regenerative DryersRegenerative Dryers

Gas Regulators/ Check ValvesGas Regulators/ Check Valves

Energy Storage System Shell Energy Storage System Shell

URFC Energy Storage System URFC Energy Storage System Operation DescriptionOperation Description

Electrolysis Operation Electrolysis Operation

Fuel Cell Operation Fuel Cell Operation

Electrolysis To Fuel Cell Transition Electrolysis To Fuel Cell Transition

Fuel Cell To Electrolysis Transition Fuel Cell To Electrolysis Transition

Packaging Of URFCSPackaging Of URFCS

Summary Of URFCSSummary Of URFCS

URFCS capable of delivering 3500 watts during URFCS capable of delivering 3500 watts during a 12 hour discharge period.a 12 hour discharge period.

The overall energy density is 791 w-hr/kg.The overall energy density is 791 w-hr/kg. Lightweight energy storage system.Lightweight energy storage system.

Variations In URFCS PerformanceVariations In URFCS Performance

The Size of Water Tank:The Size of Water Tank:

The water tank was sized to provide The water tank was sized to provide sufficient water storage for 3500 watts discharge sufficient water storage for 3500 watts discharge power for 12 hourspower for 12 hours..

The gas tank volume:The gas tank volume:

The gas tank volumes were sized such that The gas tank volumes were sized such that the fully charged tanks had a peak storage the fully charged tanks had a peak storage pressure of approximately 28.1 kg/cm2 (400psia) pressure of approximately 28.1 kg/cm2 (400psia)

URFCS Performance ParametersURFCS Performance Parameters

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

ConclusionConclusion

Energy densities as high as 800 w-h/kg are Energy densities as high as 800 w-h/kg are possible for URFCS based energy storage possible for URFCS based energy storage systems systems

The longer the discharge times for the URFCS The longer the discharge times for the URFCS the greater the energy density possible. the greater the energy density possible.

Over 90% of the volume could be saved from the Over 90% of the volume could be saved from the energy storage system described in this paper.energy storage system described in this paper.

BibliographyBibliography

Journal of Power SourceJournal of Power Source

Fred Mitlitsky, Blake Myers, and Andrew H. Fred Mitlitsky, Blake Myers, and Andrew H. Weisberg, Regenerative Fuel Cell Systems’, Weisberg, Regenerative Fuel Cell Systems’, Energy & FuelsEnergy & Fuels

F. Mitlitsky, N. J. Colella, B. Myers, C. J. F. Mitlitsky, N. J. Colella, B. Myers, C. J. Anderson, “ Regenerative Fuel Cells for High Anderson, “ Regenerative Fuel Cells for High Altitude Long Endurance Solar Powered Altitude Long Endurance Solar Powered Vehicles,” Vehicles,”