Posted on 08/11/2011 11:40:12 AM PDT by Freeport
While roofs across the world sport photovoltaic solar panels to convert sunlight into electricity, a Duke University engineer believes a novel hybrid system can wring even more useful energy out of the sun's rays.
Instead of systems based on standard solar panels, Duke engineer Nico Hotz proposes a hybrid option in which sunlight heats a combination of water and methanol in a maze of glass tubes on a rooftop. After two catalytic reactions, the system produces hydrogen much more efficiently than current technology without significant impurities. The resulting hydrogen can be stored and used on demand in fuel cells.
For his analysis, Hotz compared the hybrid system to three different technologies in terms of their exergetic performance. Exergy is a way of describing how much of a given quantity of energy can theoretically be converted to useful work.
"The hybrid system achieved exergetic efficiencies of 28.5 percent in the summer and 18.5 percent in the winter, compared to 5 to 15 percent for the conventional systems in the summer, and 2.5 to 5 percent in the winter," said Hotz, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering.
(Excerpt) Read more at sciencedaily.com ...
Bigger tanks equals more cost which is exactly what I said. AGAIN, I said nothing about “exotic” or “insurmountable difficulties” , those are your words.
“People store and use gasoline and propane “at home” all the time. Hydrogen will be no different when its turn rolls around.”
Propane, gasoline and NG offer such great advantages over hydrogen that hydrogen’s “turn” has been rolling around for at least the past fifty years and never arriving. I’m sure it will continue to do so for another fifty years.
With nat gas being extracted in ever-increasing amounts, and the price looking low and stable for a long time to come, I totally agree with your view.
They just finished the Rockies Express gas pipeline thru Indiana in 2009 and now they’re talking about reversing the flow to go east to west.
Is just powering a generator with methanol a big deal?
Although there is considerable worrying about C02 it really has been a boon for the greening of the globe as the poor mans fertilizer.
Nat gas really is the fuel of the future.
Given shale gas and oil coming on like gangbusters, that's probably true, but in the long run, hydrogen is as inevitable as taxes, barring some huge advance in technology. But "my" point is about the technology to safely use it. Which exists, in full, today. There may be improvements, as there always are, but if, magically, the cost to produce hydrogen dropped so that it "was" economically a better deal than fossil fuels, the technology exists now to handle it.
Many thanks, sir. Very interesting.
I don't know how long the long run is but for the foreseeable future hydrogen just isn't going to be fuel of choice. The “Hydrogen Economy” doesn’t appear to be “Home Ec.” yet.
Well, "the long run" IMO is a time frame equivalent to the span of Homo Sapiens existence on our planet. Eventually, fossil fuels are going to be depleted to the point that accessing them will be more expensive than producing hydrogen. If we maintain a high-tech civilization, we'll need an energy transport/storage medium. Of course, who knows....EEStor might turn out to be real. Or something totally unknown today.
The only drawbacks I see to hydrogen is that 1) it costs too much to produce, and 2) its energy density is relatively low. Of course 2) is mostly relevant to transport technologies....for use in the home, energy density is much less critical.
If you go to the trouble of generating hydrogen, why not generate ammonia? NH3
Ammonia has about one third of the energy density of hydrocarbons, which is extremely good.
Or why not Methan?
Sabatier won a Nobel prize in chemistry to transform hydrogen and carbon dioxide to methane using a catalyst.
Both are way easier to handle and to transport than hydrogen.
Put up some windmills or solar cells close to water, come with a truck every few weeks to pickup the ammonia/methan.
No grid needed, no need to retrofit infrastructure to hydrogen.
Of course, another conversion step reduces effency, but you save elsewhere.
But it will have to be different given the low heat value per volume of hydrogen.
A 5 gallon propane bottle has about 413,000 BTU heating value. To get the same energy out of hydrogen, compressed to 250 psi to use the same bottles, would take 113 of those same bottles. It just is not a practical fuel.
Source of data for caluclations: http://hydrogen.pnl.gov/cocoon/morf/hydrogen/site_specific/fuel_heating_calculator?canprint=false
Depends on the proposed use. What I'm basically talking about is its use as an energy storage and interconversion medium for stationary usage.
"A 5 gallon propane bottle has about 413,000 BTU heating value. To get the same energy out of hydrogen, compressed to 250 psi to use the same bottles, would take 113 of those same bottles. It just is not a practical fuel."
Yes, but for stationary use, you can easily put a 1000 gallon propane tank underground for a relatively low cost, which sort of changes the picture. For any portable use, I agree with you....unless some major breakthrough in technology appears on the scene to change the situation.
We’re in no danger of running out of hydrocarbon fuels. The oceans floors have methane galore in frozen lumps, sewage is being turned into light fuel oils and there is more coal than anyone is able to mine.
Other cheap and simple technologies haven’t been fully exploited that are available right now like solar space heating, super insulation of buildings, using ground water for heating and cooling, etc. all of which would divert hydrocarbon fuels to transportation.
Hydrogen? Not likely since while it’s technology will improve so will all these others and they have a longer way to go.
Hydrogen generation requires some other form of energy to make hydrogen. The hydrogen then has less energy than you started with at the same location. Why not just use what you started with as your energy source?
Perhaps for energy storage for something like wind or solar. But then you are talking about a rather significant amount energy storage and the efficiencies and volumes become a significant restriction like in transportation. Compressed air or water lift provide as good or better efficiencies and storage constraints.
The hydrogen works, I just see it as significantly less desirable than other options. It would be more cost for no gain.
Powering your home isn't stationary?? See discussion upthread about the NJ engineer who gets all his energy from solar hydrogen. His "one-off" system cost ~$500K, but most of that was engineering. His estimate for cost to reproduce his system was on the order of $50K. And that was years ago.
"Hydrogen generation requires some other form of energy to make hydrogen. The hydrogen then has less energy than you started with at the same location. Why not just use what you started with as your energy source?"
Because batteries are expensive for the amount of energy required to run a whole house.
"Perhaps for energy storage for something like wind or solar. But then you are talking about a rather significant amount energy storage and the efficiencies and volumes ecome a significant restriction like in transportation.
Sorry, but no. The storage volume density requirement for home power is MUCH MUCH less than for transport usage.
"Compressed air or water lift provide as good or better efficiencies and storage constraints."
Again, no. Compressed air is much less efficient (energy lost as heat during compression). And the likelihood of your house being next to a suitably tall hill for "pumped storage" is nil.
I don't believe the economics are above the options.
You need to look at the low specific gravity of hydrogen and how much waste heat is generated to compress it down to a usable volume.
I don't mean to dismiss it as unfeasible. But I do not see numbers to support it as a better option.
I do keep looking at systems like this for my personal use. I have some remote property we will be developing and I will have to extend the power line over a mile to reach it and it will not be a straight path.
But economics are the deciding factor.
Stritzki's estimate, not mine. And I haven't yet found the old article that I read that contained the info. See "patton"'s comment upthread for more recent take.
"I don't believe the economics are above the options."
????? No comprende.
"You need to look at the low specific gravity of hydrogen and how much waste heat is generated to compress it down to a usable volume.
Very little, if you use the electrolyzer to generate the pressure. Which is quite feasible in the low pressure systems I'm referring to. You may disagree that that is a "usable pressure". But I was specifically comparing to compressed air storage losses.
"I don't mean to dismiss it as unfeasible. But I do not see numbers to support it as a better option."
Compared to today's cost of fossil fuels, and with today's technology, no. But then, nothing else is either. Which is why killing off the idea of "global warming" is so important. Fortunately, Dr. Robert Spencer seems to have found the "smoking gun" scientific evidence to do so. Direct measurement of IR emission from the earth into space. One doesn't GET any more "direct" than that.
"I do keep looking at systems like this for my personal use. I have some remote property we will be developing and I will have to extend the power line over a mile to reach it and it will not be a straight path."
Take a look at the "Backwoods Home" website and/or magazine. Several really good articles about "remote energy" generation.
"But economics are the deciding factor."
Indirectly, yes. But technology will underlie any economic advances. And advances here seem to be speeding up rather than remaining constant or slowing down.
Thanks
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