Are Fuel Cells Really That Efficient?
By Ulf Bossel
Ulf Bossel is at it again as he takes a critical look at the real 'well-to-wheel' efficiency of hydrogen fuel cell vehicles.
We are told that one of the major advantages of fuel cell-powered vehicles is their greater efficiency. Whereas a conventional gasoline internal combustion engine has a maximum Carnot efficiency of less than 25%, a fuel cell engine has a potential efficiency better than 30% and possibly higher. But could these calculations be based on an incorrect analysis, sort of comparing the proverbial apples to oranges?
Dr. Ulf Bossel believes so and in his recently-published four-page technical paper entitled, "Efficiency of Hydrogen Fuel Cell, Diesel-SOFC-Hybrid and Battery Electric Vehicles, he sets out to prove his case by first taking a closer look at the amount of energy it takes to make hydrogen. He argues that in order to compare the relative efficiency of hydrogen compared to other energy carrier options, including a synthetic diesel fuel (biodiesel), scientists need to base their calculations on the Higher Heating Value or HHV of all energy carriers. The use of the hydrogen's Lower Heating Value, he writes, violates the laws of physics.
"The widespread use of the Lower Heating Value LHV may be a convenient convention, but it is not supported by physics," Bossel contents."In fact, the use of the Lower Heating Value for hydrogen produced by electrolysis (and other means) violates the energy conservation principle."
By the Swiss-based scientist's calculation, a PEM fuel cell typically used in prototype fuel cell cars is, at best, 22% efficient if the hydrogen is compressed and only 17%, if its liquified. By contrast, a hypothetical diesel hybrid similar to the new Mercedes-Benz F-500 concept vehicle pictured above has a well-to-wheel efficiency of 25%. And when he looks at the efficiency of battery electric cars, he comes up with a power plant-to-wheel efficiency of 66% when regenerative braking is included.
From his perspective, battery electric cars make the most sense for local commuting, while biodiesel-fueled hybrid-electric drives make the most sense for the family vehicle if maximum energy efficiency and cutting greenhouse gas emissions are the two top priorities.
He concludes, "Statements claiming hydrogen fuel cell vehicles to be the one-and-only or the best solutions for the future transportation applications certainly need further validation."
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