L18-fuelcell5-2 - PEM Fuel Cell Performance 1 8/19/2005...

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Unformatted text preview: PEM Fuel Cell Performance 1 8/19/2005 LECTURE LECTURE LECTURE LECTURE # # # # 18 18 18 18 TOPIC TOPIC TOPIC TOPIC: P E M F u e l C e l l P e r f o r m a n c e PEM Fuel Cell Performance 2 8/19/2005 PEM Fuel Cell Performance Efficiency s The efficiency of fuel cells is often touted as one of the primary benefits of the technology s Although this is true in principle, it is important to distinguish between fuel cell stack efficiency and fuel cell system efficiency s Fuel Cell Stack Efficiency b Fuel cell stack efficiency is commonly taken to mean the actual efficiency of the electrochemical reaction s Fuel Cell System Efficiency b Fuel cell system efficiency relates to the overall performance of a fuel cell power plant PEM Fuel Cell Performance 3 8/19/2005 Efficiency s The overall efficiency of an internal combustion engine is often quoted as between 15 and 25% s These values are representative of the output efficiency at the wheels of a vehicle; efficiencies at the output of the flywheel are more typically between 30 to 35% and even higher for diesel engines s For a fuel cell power plant operating on pure hydrogen, the comparable efficiency breakdown at the output of the fly-wheel is roughly as follows: b Fuel cell efficiency: 40 to 50% b Air compression: 85% (uses 15% of gross power) b Inverter efficiency: 95% b Electric motor efficiency: 97% s Multiplying each of these values together yields an overall system efficiency of roughly 31 to 39% PEM Fuel Cell Performance PEM Fuel Cell Performance 4 8/19/2005 Efficiency s For a fuel cell system that operates using a reformer, these efficiencies are further reduced by 65 to 75% for an overall system efficiency of roughly 20 to 29% s More difficult to quantify is the effect of overall system weight s Fuel cell systems (including fuel storage) are heavier than internal combustion engine systems of comparable power and range, and therefore use more power on an ongoing basis PEM Fuel Cell Performance PEM Fuel Cell Performance 5 8/19/2005 Efficiency s Batteries have electrochemical efficiencies comparable to fuel cells s When used as an automotive power plant, battery systems also require an inverter and electric motor, although they do not require air compression, complex cooling equipment or reformer s Batteries as a means of power storage are heavier than fuel cells although this is offset somewhat by the elimination of other components PEM Fuel Cell Performance PEM Fuel Cell Performance 6 8/19/2005 Efficiency s When stepping back further, the source of fuel becomes an essential component of the overall efficiency s With an internal combustion engine, this usually involves refining hydro-carbon fuels s With a fuel cell, this involves producing hydrogen from fossil fuels or through water electrolysis, or the production of secondary fuels such as methanol for use with an on-board reformer s With a battery system, this involves a source of electrical power for charging s Analysis of these factors is complex and depends on the source fuel,...
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This note was uploaded on 09/05/2011 for the course LECTURE 101 taught by Professor Staff during the Fall '09 term at University of Florida.

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L18-fuelcell5-2 - PEM Fuel Cell Performance 1 8/19/2005...

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