Re: PEM fuel cell efficiency

DE Pauley wrote:
>
> This is only an indirect answer. MIT has a course on "Application of
> Technology" in which fuel cells are analyzed. The 'theoretical' FC
> efficiency depends on the load. In slide 9
> (http://web.mit.edu/1.149/www/lecture21/lec21slides.pdf) the efficiency
> varies from 100% at no load to 50% at full load. In slide 26 the
> 'typical' efficiency is given as 45%.

So much for MIT.

A real fuel cell, the Ballard Nexa,
does 41 percent of delta 'G' at sea level at beginning of life.
That's 39 percent of LHV.

A vehicle prime mover made of ganged Nexa cells might include
30 of them, mass 390 kg, rated aggregate power 36 kW.

Actual fuel cell vehicles use other versions with higher
specific power (more kW/kg) and therefore lower conversion efficiency.

We know it's somewhere far south of 39 percent.
That's all we know; manufacturers never tell.

(Actually, there is one other thing we know:
the longest ranges attained by internal hydrogen combustion car
prototypes in the 70s --
http://www.hydrogen.org/h2cars/overview/main01.html
-- no fuel cell car prototype has equalled or got anywhere near.)


> This probably corresponds to a
> range of load conditions encountered during driving, but I am not sure.
> A tradeoff for higher efficiency vs larger FC size would be possible.
> The optimum may be to increase the size to achieve an efficiency in the
> 60-75% range.

No chance of that. As above said, 40-percent-efficient PEM fuel cells
are way too big and heavy for cars, and the tradeoff can only
go the other way.



--- Graham Cowan, former hydrogen fan
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html --
boron as energy carrier: real-car range, nuclear cachet
.

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