Hydrogen Fuel Cells: Debunking the Hype

By Steve Auger, BlogOnSmog	Sphere: Related Content        Stumble It!
Proponents of the hydrogen economy make claims of fuel cell efficiency 2-3 times that of the internal combustion engine.  But they aren't telling the entire truth and are actually misleading the uneducated public.  The maximum theoretical fuel cell efficiency may be high (up to 83%) but what is important is not the engine efficiency but the well-to-wheel efficiency.  When you compare all aspects of generating hydrogen and conversion to electricity, the fuel cell comes up short against other green technologies.
In a previous post Hidden Smoke and Polished Mirrors  I indicated that the near-mid term future of the automobile would be dominated by plug-in hybrids while hydrogen fuel cell cars were making their final "swan song".  I would like to elaborate further on this topic by providing some rudimentary efficiency analysis for fuel cells and electric vehicles.  I limited my analysis to electric vehicles as opposed to hybrid plug-ins because much depends upon city versus highway driving and other variables.  However, my point should become clear once you see the analysis. To compare apples-to-apples and to make the analysis as simple as possible I assume that the car owner's home has an abundance of available electricity and that hydrogen is generated by electrolysis of water as opposed to extracting from natural gas.  Compressed hydrogen refilling / battery recharging is done at the home.  Thus transportation of hydrogen to the home is not required.  I also ignore the car heater and regenerative braking (requires addition of batteries for the fuel cell car).  I will also ignore the energy required to manufacture the hydrogen generation system and ignore the water usage / cost, thus giving the hydrogen option some freebees.   My analysis is an approximate "back of a napkin" type analysis.  Here is my home-to-wheel analysis : Home-to-Wheel Hydrogen Fuel Cell Efficiency Electric Vehicle Efficiency Energy Conversion 63% Losses are due to electrolysis and hydrogen compression. 85% AC/DC conversion. Energy Transfer 97% Hydrogen transfer to vehicle. 95% Battery charging. Energy Conversion 45% Conversion efficiency of hydrogen fuel cell.  Includes effect of parasitic losses. 95% Battery discharging. Drive Train 90% Losses occur between fuel cell and wheels. 90% Losses occur between battery and wheels. Total Efficiency              25%              69%   As you can see from this rough analysis, the electric vehicle is significantly more efficient from home-to-wheel than a hydrogen fuel cell vehicle.  To be fair, scientists are working at improving the efficiency of the fuel cell.  Even if the fuel cell efficiency is changed from 45% to 75% in the spreadsheet the overall home-to-wheel efficiency for the hydrogen fuel cell only rises to 41%.  I should make it clear that the previous-generation of Honda Clarity FCX only achieved a 35% fuel cell efficiency.  So car manufacturers have a long way to go to come anywhere close to the 75% efficiency that some claim is feasible. My conclusion is that the performance of hydrogen fuel cells are very much overstated - don't believe the hype about this technology.  The efficiency of the engine (or fuel cell) is only one consideration.