Jamie: There are two reasons why low temperature PEM fuel cells would be at a disadvantage to the higher temperatures ones--phosphoric acid, molten carbonate, and solid oxide:
1. PEM cells run on hydrogen, but until the day comes that there are hydrogen pipelines all over the place, the only plausible fuel is natural gas, which must be processed (called "reforming") to extract the hydrogen within. The technique for reforming natural gas has been around for 50 years or so, and it requires the gas to be heated up to about 1800 F. The PEM cell, unfortunately, operates at about 140 F.
So a PEM cell requires equipment to heat its fuel, then more equipment to cool down the hydrogen. This equipment requires energy to operate, which must either come from burning natural gas, with the attendant pollution, or consuming some of the fuel cell's electric output, reducing the amount available for the user. Phos acid fuel cells have the same problem, although less so since they run hotter than PEM, meaning the hydrogen need not be cooled down as much.
The PAFC has another edge over PEM types in that it can live with "dirtier" (i.e., containing more carbon monoxide) hydrogen. The reforming equipment used by PEMFC and PAFC would be the similar, except the PEM would need additional equipment (and consume additional energy) to clean the hydrogen stream of the CO that would poison the PEM membrane.
All this is important from an economic view, because it is the cost of the reforming equipment, much more than the fuel cell itself, that is so expensive. PAFC's, which are the only kind commercially for sale now, probably cost its manufacturer about US$5000 per kW, although it sells them for less than that due to a government subsidy program. Probably $3500 of that cost is the reforming equipment. The reforming equipment for a PEM cell would have to cost more than that.
Higher volume might lower the costs somewhat, but reformers aren't semiconductors. Reformers require some expensive alloy steels to handle the high temperature, and various standard vessels and components already benefiting from mass market cost reduction.
Fuel cells make less sense the more they cost, especially if the efficiency is reduced because of the need to operate reforming equipment. The potential demand drops off fairly sharply once you get much above $3000 per kW. It seems likely that, even if Ballard figured out how to snap its corporate fingers and make fuel cells appear out of thin air at a cost of zero, the overall cost of the reforming equipment alone will be excessive.
This is why I say Ballard's efforts at stationary power are doomed. If, on the other hand, the company could come up with a radically different and cheaper way of getting the hydrogen out of the natural gas, then the picture would be different. Ballard, to my knowledge, has given no indication that it has anything like that.
Without naming names that get some people on this thread annoyed, I know of one fuel cell developer that uses the much higher temperature molten carbonate process. It feeds natural gas directly into the cell, where the hydrogen is extracted at its natural operating temperature, and CO has no negative impact on the materials. This approach has no need of any reforming equipment, and thus has a much better chance of eventually getting the cost down under $2000 per kW, where the potential market would be many billions of dollars annually.
2. The other reason higher heat is better is because of cogeneration. A MCFC can get around 50% in electrical efficiency, and the heat from the process, used to run a steam turbine, could add another 30%, giving a total efficiency in the 80% range.
A PEMFC only has efficiency in the low 30's% range, because of the energy needed to run the reforming equipment. Yes, there is plenty of heat used in the reforming process, but that comes from burning the natural gas. If we want heat from burning natural gas, why not just do that - who needs the fuel cell? In any event, even using that heat, the PEM's efficiency will be relatively unimpressive. |
