|
|
|
Left, Fuel cell stack for powering automobile. Right, NexaTM
portable power module, 1200 watts DC, engineered for integration into consumer products. Photos, Ballard Power Systems |
|
Bond dissociation energies.
H-H, 436 kJ/mol, H-C, 413 kJ/mol, H-O, 366 kJ/mol, O=O, 498 kJ/mol
science.uwaterloo.ca/~cchieh/cact/c120/bondel.html Fuel Cell
Chemistry:
Anode side: 2H2 => 4H+ + 4e- Cathode side: O2 + 4H+ + 4e- => 2H2O
Net reaction:
2H2 + O2 => 2H2O "This reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack.
PEMFCs operate at a fairly low temperature (about 176 degrees Fahrenheit, 80 degrees Celsius), which means they warm up quickly and don't require expensive containment structures. Constant improvements in the engineering and materials used in these cells have increased the power density to a level where a device about the size of a small piece of luggage can power a car."
http://www.howstuffworks.com/fuel-cell2.htm |
 Efficiency of converting energy from one physical system to another physical system.
Proponents proudly explain that the efficiency of fuel cells, the cornerstone of a new hydrogen based world is high. And granted it is high, upwards of 80%. And everything looks just dandy. As long as you don't count the source of the hydrogen. But they don't count that of course. Ostensibly this is not included because it isn't inside the electricity generating unit. In reality, however this energy factor isn't counted so that fuel cells will look better than what they really are, just a fancy battery. And these fancy batteries require lots of energy which has to come from somewhere and which is expended as an end product which does not re-enter a closed loop. 
"Efficiency of Fuel Cells"
Fuel-Cell-Powered Electric Car
If the fuel cell is powered with pure hydrogen, it has the potential to be up to
80-percent efficient. That is, it converts 80 percent of the energy content of the
hydrogen into electrical energy. But, as we learned in the previous section, hydrogen is difficult to store in a car. When we add a reformer to convert methanol to hydrogen, the overall efficiency drops to about 30 to 40 percent.
We still need to convert the electrical energy into mechanical work. This is accomplished by the electric motor and inverter. A reasonable number for the efficiency of the motor/inverter is about 80 percent. So we have 30- to 40-percent efficiency at converting methanol to electricity, and 80-percent efficiency converting electricity to mechanical power. That gives an overall efficiency of about 24 to 32 percent.
Gasoline-Powered Car
The efficiency of a gasoline-powered car is surprisingly low. All of the heat that comes out as exhaust or goes into the radiator is wasted energy. The engine also uses a lot of energy turning the various pumps, fans and generators that keep it going. So the overall efficiency of an automotive gas engine is about 20 percent. That is, only about 20 percent of the thermal-energy content of the gasoline is converted into mechanical work.
Battery-Powered Electric Car
The battery is about 90-percent efficient, and the electric motor/inverter is about 80-percent efficient. This gives an overall efficiency of about 72 percent.
But that is not the whole story. The electricity used to power the car had to be generated somewhere. If it was generated at a power plant that used a combustion process (rather than nuclear, hydroelectric, solar or wind), then only about 40 percent of the fuel required by the power plant was converted into electricity. The process of charging the car requires the conversion of alternating current (AC) power to direct current (DC) power. This process has an efficiency of about 90 percent.
So, if we look at the whole cycle, the efficiency of an electric car is 72 percent for the car, 40 percent for the power plant and 90 percent for charging the car. That gives an overall efficiency of 26 percent. The overall efficiency varies considerably depending on what sort of power plant is used. If the electricity for the car is generated by a hydroelectric plant for instance, then it is basically free (we didn't burn any fuel to generate it), and the efficiency of the electric car is about 65 percent.
Surprised?
Maybe you are surprised by how close these three technologies are.
This exercise points out the importance of considering the whole system, not just the car. We could even go a step further and ask what the efficiency of producing gasoline, methanol or coal is..."
howstuffworks.com/fuel-cell4.htm | 
How Fuel Cells Work:
Introduction to How Fuel Cells Work, What is a Fuel Cell? Proton Exchange Membrane, Problems with Fuel Cells, Efficiency of Fuel Cells, Other Types of Fuel Cells, Applications of Fuel Cells, Lots More Information
howstuffworks.com/fuel-cell.htm "In fuel cells, as in batteries, silent reactions produce an electric current. Unlike batteries, however, fuel
cells are almost endlessly rechargeable. The cells run on hydrogen, which reacts with oxygen from the
air in such a way that a voltage is generated between two electrodes; the reactions occur in a chemical
mediator known as an electrolyte. (Some designs consume hydrogen directly; others start with natural
gas that is converted to hydrogen before entering the cell.) Compared with conventional fossil-fuel
power sources, fuel cells are exceptionally clean and efficient. Practically their only waste product is
water; natural gas-fueled cells do produce some carbon dioxide as well, though less than would be
created if the fuel were burned..."
sciam.com/explorations/122396explorations.html Los Alamos National Laboratory: A comprehensive 32 page tutorial on Fuel Cells
education.lanl.gov/resources/fuelcells
Union of Concerned Scientists www.ucsusa
National Hydrogen Association www.ttcorp.com/nha
American Methanol Institute, www.methanol.org
Fuel Cells 2000 www.fuelcells.org
Ballard Power Systems, General Fuel Cell Information,
www.ballard.com/genfuel.asp Ballard Power Systems, Inc., headquarted in British Columbia, Canada, is a leader in the development and commercial production of various types of commercially viable fuel cell product applications. Ballard Power systems will commercially produce these fuel cell stacks. According to Ballard, "Our business involves supplying fuel cells to original equipment manufacturers
who integrate them into their products. When fuel cell products become
available consumers will be able to purchase products using Ballard fuel cells
from these original equipment manufacturers."
Frequently asked questions:
www.ballard.com/marknprod.asp
"Do all fuel cell vehicles produce zero emissions?
Fuel cell vehicle emissions vary based on the type of fuel carried onboard. Only
vehicles fuelled by an onboard supply of pure hydrogen achieve zero emissions.
Fuel cell vehicles fuelled by onboard supplies of gasoline or methanol produce
only trace amounts of smog-causing pollutants, such as oxides of nitrogen, and
greenhouse gas emissions in the range of 20 to 30 per cent less than an
equivalent internal combustion engine-powered vehicle." Ballard Power Systems
posted this question and straightforward answer at:
www.ballard.com/marknprod.asp
"When will fuel cell cars be available to the public?
Automotive companies will determine when fuel cell powered cars will be
available to the public. Auto manufacturers including DaimlerChrysler, Ford,
General Motors, Toyota and Honda have stated they plan to have fuel cell
powered cars available in 2003-2005. Ballard and XCELLSIS Fuel Cell Engines
plan to have fuel cells and fuel cell engines for automobiles ready for auto
makers to achieve their goals."
www.ballard.com/marknprod.asp
Earth Policy Institute, October 31, 2002, Fuel Cell-Powered Cars Hitting the Road Ahead of Schedule
earth-policy.org/Updates/Update19.htm Ballard: personal autos will be last to use fuel cells,
Fortune Magazine, July 14, 2003
"Whatever you may think of the long term prospects for a "hydrogen
economy", you have to admire Dr. Ballard's knowledge and integrity.
He's never tried to sell hydrogen and fuel cells as panaceas for all our energy problems. He makes no bones about where he sees the
energy to produce hydrogen as coming from: he's a strong advocate of
nuclear power.
His views of how fuel cells will appear in the market also strike me
as quite realistic. Forget about hydrogen-powered personal autos in
the near term. Fuel cells and hydrogen storage systems are still 30
times too expensive to compete with fossil fuel powered IC engines."
groups.yahoo.com/group/energyresources/message/38748
fortune.com/fortune/print/0,15935,456366,00.html
|
To look at him, President Bush seems like a reasonable man.
Why is President Bush insisting that we burn up what's left of our fossil fuel
entropic dowry as fast as possible? It infuriates any scientist worth a
hoot when he insists that it must be done -- for any reason. Non-scientists can
be excused for not knowing enough to become angry, they don't know what's going
on anyway. Here's the question we were asked, an answer for which requires one
to put on a contrarian thinking cap. If renewable energy in general and fuel
cells/hydrogen in particular is so great, why isn't the US committing in an
appropriate way this late in the game? That is to say, why is President Bush
committed so strongly to use up the fossil fuels instead of moving ahead? This is
a level four type question so the answer can not be a knee jerk response.
The knee jerk answer would be that he is stupid, an image which he cultivates
carefully. But that isn't it. Of course one may say that he has ties with the
fossil fuel industry. Wrong again. There must be something more important. We'll
leave it for you to ponder. Reading again levels three and four of ecology
understanding will give a hint. |
|
|
