Hydrogen Fuel Cell

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Permalink Reply by Cobraphx (Matt) on August 24, 2008 at 7:44pm

I totally agree that a CNG range extender is way better than a H2 or gasoline range extender. The well to wheel efficiency is pretty much the same between CNG burning hybrid and a FCV using steam reformed H2 from CNG ... see http://www.arb.ca.gov/msprog/zevprog/symposium/presentations/brooks.... Both will emit 5.5kg per KG of CNG consumed. So no reason to take on the extra cost and complexity of a hydrogen powered range extender.

But I fully agree I'd like to see range extended electric vehicle designs like the volt to use CNG instead of Gasoline.

Permalink Reply by Harvey on August 25, 2008 at 12:49am

The high density batteries are here.
Also fast recharge.

http://news-service.stanford.edu/news/2008/january9/nanowire-010908.html

About 160 miles for each 100 pounds of battery.
Replace an engine and drivetrain at about 300 pounds with a battery of 300 pounds and you get 480 miles on a single charge.
And the charge does not leak off.

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Permalink Reply by Ray Phillips on August 24, 2008 at 6:14pm

Just curious, but isn't hydrogen highly volatile? Doesn't it burn in air? The last chemistry class I had was well over 30 years ago, but I am thinking that hydrogen is much more reactive than gasoline. I do recall that the Hindenburg was filled with hydrogen when it exploded (although I am not quite old enough to have been there!) What makes hydrogen the holy grail of stored energy?

Thanks.

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Permalink Reply by Kenneth Koch on August 25, 2008 at 3:38am

"What makes hydrogen the holy grail of stored energy?"

H2 is clean, renewable and has more energy density than batteries.

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Permalink Reply by Thomas Dixon on August 24, 2008 at 6:29pm

I agree that the holy grail is to store energy as hydrogen. But it takes energy to produce hydrogen. That is where the rub comes in. But if we can produce electric power from geothermal sources we can then produce hydrogen in large quantities. Attacked is a machine that can produce the electric power you need.

Hydrogen fuel cells need to be modular. You drive up to your fueling station and they pull out your used up fuel cell and insert a charged one. Much like a large battery. When this technology becomes standardized then all fuel cells from all makers will be interchangeable. When that time comes our problems will be over.

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Permalink Reply by Cobraphx (Matt) on August 24, 2008 at 7:57pm

And why does this scheme of pulling out a depleted 50% efficient hydrogen fuel cell and replacing it better than doing the same thing with a battery that's 90-95% efficient?

Water is a more efficient energy storage mechanism that H2. Pumped Hydroelectric energy storage is 70% efficient in operation, see http://www.power-technology.com/projects/tianhuangping/.

Detailed computer analysis and model testing was carried out during the pump turbine hydraulic design stage to minimize the potential for problems such as cavitation and to ensure a turbine efficiency (neglecting head losses in the system) of 90% or better. The plant design achieved an overall cycle efficiency of 70%.

Energy stored in electrolyzed hydrogen and extracted using a fuel cell is 33% efficient (65% efficient electrolyzer, and a 50% efficient Fuel Cell). That doesn't seem like the Holy Grail to me.

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Permalink Reply by Mike Johnston on August 25, 2008 at 10:38am

Interesting numbers on efficiency that you throw around...

First off, I am not a huge fan of fuel cells myself. At least not in their current state of development and availability. However, Fuel cells are essentially batteries, just a different type than most people think of when they think "battery" (lead/acid).

As long as we are on batteries though lets stop and think about something. The lead acid battery in your car is interesting. While you are charging that battery (with 90 to 95% efficiency according to your post) the battery is also producing hydrogen gas. The only reason that batteries don't fill up with hydrogen as they charge is that a depolarizer is added to the electrolyte solution which causes the H+ and OH- ions in the solution to convert back to water. This takes nothing from the energy being delivered to the cell to charge it.

So lets say we eliminate the depolarizer and think about the reaction. In that case, the battery is storing 90 plus percent of the charge being delivered to it as potential chemical energy. But it would also be producing hydrogen gas which represents another way of storing that same energy! How is this possible? Because hydrogen is being produced as a by-product of the primary reaction in the cell and so isn't counted.

So there you have an example of a way to store energy in two ways within a single system in such a way that the potential energy of the charged battery and the hydrogen gas produced by the charging process added together equals more than 100% of the electric charge applied to the cell! Imagine that. But it is obviously true and very simple once you think outside the box just a tiny bit.

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Permalink Reply by Thomas Dixon on August 25, 2008 at 2:25pm

“And why does this scheme of pulling out a depleted 50% efficient hydrogen fuel cell and replacing it better than doing the same thing with a battery that's 90-95% efficient?”

Weight per unit of energy output is much lower for a fuel cell--?
Fuel cells don’t wear out like conventional batteries--?

Just guessing as you can see

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Permalink Reply by Mike Johnston on August 25, 2008 at 3:02pm

Why is a fuel cell only 50% efficient? Where does that figure come fro and on what is it based?

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Permalink Reply by Kenneth Koch on August 25, 2008 at 3:09pm

The best a fuel cell can do is 50% electrical energy and 50% heat. I forgot the equation. This is 3 times better than an ICE BTW.

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Permalink Reply by Mike Johnston on August 25, 2008 at 4:34pm

Um, not exactly true. Fuel cells, like electrolysis cells are subject to electrical resistance heating just like metal conductors. One aspect of my research was reducing the electrical resistance in electrolysis cells. I was able to do this to the point that I can make an electrolysis cell that is less resistive than the wire that feeds electricity to it.

The same principles should apply to a fuel cell as well. What is often described as "heat of reaction" is at least partially due to electrical resistance in both electrolysis cells and fuel cells. I am sure we could easily eliminate the heating losses in fuel cells to a great extent.

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Permalink Reply by Cobraphx (Matt) on August 25, 2008 at 5:38pm

There are plenty of references for the efficiency of Fuel Cells. Here is a good example from 2007 DOE Hydrogen Fuel Cell report

The 2006 cost of a hydrogen-fueled 80-kWe fuel cell power system at high volume production is $107/kW, compared to the 2005 target of $125/kW. For stationary systems, the 2005 target of 32% electrical efficiency at full power was met.

Most use 50% to represent what may be available in practical fuel cells in the next decade. Some info presented at CARB Hydrogen Highway Network Workshop : Why Hydrogen? . From the European Fuel Cell Forum : Efficiency of Hydrogen Fuel Cell, Diesel-SOFC-Hybrid and
Battery El...

Here's a good little page on the math behind Electrolyzers and Fuel Cells: http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/electrol.html .

Fuel Cells do have a future for sure, but I for one doubt that future is in everyone's driveway. We'll just have to see how battery technology advances in relation to fuel cell technology.

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