4Fuel Cells In Space Technology For space applications energy production is cyclicNASA power systemThe Unitized Regenerative Fuel Cell (URFC)Applications - high altitude balloons ,high altitude solar airplanes, etc.
5Unitized Regenerative Fuel Cell System Proton Exchange Membrane in URFCEnergy storage system.Potential ability to store large amounts of energyURFC – Fuel Cell + Electrolyser
6Energy Density Energy delivered per unit mass of storage system The Energy density is given byEd = (Output energy/Reactant weight)Output Energy = n Vd Id tdVd = Discharge cell voltage, voltsId = Average discharge current, ampsn = Number of cells in the URFC stacktd = Discharge time, hoursMw = Reactant weight
7Parameters Influencing Energy Density Where,R = Ideal Gas Constant = (84.78 Kg-cm3)/(cm2-gmole-k)T = Temperature in KelvinMOPw = Maximum operating gas pressure (Kg/cm^2)f(Vd) = Id (Discharge current density in A/cm^2)Kw = *106 (cm) (Water-Tank-Figure-of-Merit)Ka = The ratio of the total cell area to stack weight=(As/w)Where , As = Total cell areaW = Stack weight
8Discharge Voltage And Current Density Optimization
9URFCS EFFICIENCYIt is defined as the ratio between output energy to the input energy with regard to charging &discharging of the system
10The Solar AirplaneThe solar airplane is an ultra light flying wing aircraftIts surface of the wing is covered with solar cells that produce electric powerNeed for URFC in Solar aircraft
15Summary Of URFCSURFCS capable of delivering 3500 watts during a 12 hour discharge period.The overall energy density is 791 w-hr/kg.Lightweight energy storage system.
16Variations 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)
18ConclusionEnergy densities as high as 800 w-h/kg are possible for URFCS based energy storage systemsThe 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.
19Bibliography Journal of Power Source Fred Mitlitsky, Blake Myers, and Andrew H. Weisberg, Regenerative Fuel Cell Systems’, Energy & FuelsF. Mitlitsky, N. J. Colella, B. Myers, C. J. Anderson, “ Regenerative Fuel Cells for High Altitude Long Endurance Solar Powered Vehicles,”