Anyone who is familiar with my thinking is probably aware that my enthusiasm for solar energy has been continuously waning, particularly for PV energy, which has, in my view, a pretty profound energy/mass density problem that translates into high external costs, most of which center on toxicological issues.
The toxicology issue has failed to be noticed precisely because solar energy has failed to make a difference.
Distributed energy sucks, because by definition, all pollutants in it are distributed into the hands of people who have no idea whatsoever what they are handling. (What happened in the end to all those nickel/
cadmium batteries, and all of those mercuric oxide batteries when we were done with them?)
As far as I can tell, the chief product produced by the solar industry is
complacency, and mostly it is employed by less than "clued in" types to
pretend that their toxic, BP fueled lifestyle is really "OK" because everything will be wonderful "by 2050." Personally I find this "by 2050" crap to be an overt expression of contempt for future generations, insisting that they do what we cannot and will not do
now when we are destroying
their planet.
Shame on us.
Around here in Princeton, we have the Princeton Plasma Physics Lab - my Congressman (and an excellent
Congressman he is) Rush Holt used to be assistant director of research there. The Princeton Plasma Physics lab is devoted to trying to produce fusion energy.
It's a useless enterprise mostly - fusion energy is a pipe dream - but the fusion people have done some fundemental research on molten salt physics and chemistry, as well as neutronics, and materials science, and it is very useful to read research connected with fusion systems if one is interested in more realistic things. So I support funding for PPPL.
They have a nice nuclear science library in their facility and a very nice campus. Their scientists give nice displays and talks at local science talks for high schoolers, so they're OK in my book.
I also support funding for NREL, (the National Renewable Energy Laboratory) although I think the renewable energy business is unrealistic and is mostly hyped by Ponzi schemers, and people trying to scam money off of government grants for systems that will not last very long - something that is a terrible waste in a time of limited resources.
Not
everything that comes out of NREL is useless.
I've spent most of this weekend thinking about hydrogen cycles, that split water at
relatively low temperatures, at least when compared to the dissociation temperature of water, roughly 4000C.
I wrote two brief posts on the SI cycle, the "sulfur iodine" cycle here recently. It is the most advanced and best developed thermochemical hydrogen cycle.
There are many hundreds of hydrogen cycles however. About 90% of the papers one can read about hydrogen cycles are devoted to
nuclear hydrogen, but roughly 10% are devoted to solar thermal systems.
Hydrogen is useless in my view, as a consumer retail fuel, but as a captive intermediate to produce petroleum free fuels like the wonder fuel DME, dimethyl ether, hydrogen is quite attractive.
There are two very excellent papers of the latter type that I read this weekend.
One is:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V50-4J6WN9D-1&_user=10&_coverDate=12%2F31%2F2006&_alid=1353357911&_rdoc=1&_fmt=high&_orig=search&_cdi=5772&_sort=r&_docanchor=&view=c&_ct=7&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d2ce3fc97b4feeb3acb21326344c94cf">Solar Energy 80 (2006) 1611–1623
The other is:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V2S-4HTCTDG-1&_user=10&_coverDate=11%2F30%2F2006&_alid=1353354319&_rdoc=1&_fmt=high&_orig=search&_cdi=5710&_sort=r&_docanchor=&view=c&_ct=20&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=74add6fc61a833cc19fb4c61636d615f">Energy 31 (2006) 2805–2822
Both come out of a French renewable energy institution – how useless is that? – and both have the same principal author, Stéphane Abanades.
The second paper is a survey article entitled “Screening of water-splitting thermochemical cycles potentially attractive for hydrogen production by concentrated solar energy.” I am spectacularly uninterested in the author]s criteria for rejecting some of these cycles, but the
listing of them is very valuable. I will spend weeks probably collecting and reading the references in this paper alone.
The other paper is about the cycle I refer to in the title of this post, the cerium (IV) oxide ↔ cerium (III) oxide Hydrogen Cycles.
This two step cycle is as follows:
CeO
2 ↔ Ce
2O
3 + ½ O
2 (≈ 2000C)
Ce
2O
3 + H
2O ↔ H
2 + CeO
2 (400C - 600C)
As is always the case with hydrogen cycles, the net reaction is the disproportionation of water H
2O ↔ H
2 + ½ O
2 This is a cool cycle because it requires only one reagent, and just two reactions.
(It’s not
all that simple, but it’s a start.
Some excerpts from Abanades
Solar Energy paper:
Alternative energy carrier such as hydrogen must be developed to face problems linked to the continuous rising of oil prices and to the global warming issue due to greenhouse effect. The use of solarenergy conversion systems for the production of hydrogen, which is a promising solar fuel, solves these problems.
Water-splitting thermochemical cycles coupled to a solar energy source constitute one of the ultimate option for hydrogen production (and solar energy storage) since this pathway does not use fossil fuel (diminishing global reserves and responsible for greenhouse gas emissions). In such thermochemical processes, a fraction of the solar energy supply is stored in the chemical products with respect to the process global efficiency.
I obviously don’t agree with the solar “Rah! Rah!” stuff. I think solar energy has a land use problem and much worse from an economic standpoint, a capacity utilization problem. Any system that will be operable for just 10% to 30% of the time is more than likely a loser.
I’d have more patience for this sort of thing if these were flush times, but we have diddled around too long and we are impoverished, whether we realize it yet or not.
But the
chemistry is fun and interesting.
Like a good “solar will save us type” the author can’t avoid taking a swipe at the only
scalable greenhouse gas free form of energy that operates on a ten exajoule scale, that would be nuclear energy.
Previous studies were focused on cycles that could be compatible with a nuclear heat source at about 900oC (Beghi, 1986; Yalcin, 1989; Funk, 2001; Brown et al., 2003). Higher temperatures can be considered with solar concentrating systems (in the wide range 400–2500oC), which lowers the number ofchemical steps in the cycles, thus the irreversibilitiesassociated to products separation and transferbetween stages (Abanades et al., in press).
This is pretty funny.
Then the author describes some apparatus and then
performs the reaction. This is very, very, very cool. It, um, works, although the heater is conveniently not a
solar heater – how then could he make his graduate students and post docs work late into the night?
The hydrolysis reaction was studied in an electrically heated reactor in order to control better the operating conditions (temperature in particular).Once implemented in a global process, the hydrolyser energy input could be ensured by heat recovery from the solar reactor or from any heat exchanger used in the cycle.
If you’re talking solar one should really lose that “control” thing. A cloud drifting by can put an end to that.
5. Conclusion
The feasibility of a new thermochemical two-step cycle has been experimentally demonstrated at lab scale. This process produces hydrogen from water and solar heat, and without fossil fuel and greenhouse gas emission. The solar energy supply (heat input) is thus converted and stored into a sustainable energy carrier thanks to a two-step process. The solar activation of Ce(IV) oxide was performed under concentrated solar irradiation that permits to reach the fusion of the material over 2000 _C and its thermal reduction by releasing O2 at reduced pressure. Then, the activated Ce(III) oxide reacted completely with water to produce hydrogen. The synthesis of a chemical intermediate (reduced cerium oxide) reactive with water also allows to solve safety problems associated with hydrogen storage and transportation. The solid material stable and storable at ambient temperature (its reactivity with water is not altered with time) could be used as hydrogen tank. Heating moderately the solid oxide in presence of water could release rapidly hydrogen on demand, which makes on-board hydrogen production possible with such a system. In some cases, this chemical intermediate synthesis could permit to counteract the important problem of hydrogen storage/transport. This paper is the first demonstration of the CeO2/Ce2O3 cycle since it has never been studied before. Optimization of the high temperature solar thermal step and design of solar chemical reactor able to achieve high conversion rates are now needed for a pilot-scale process implementation.
My sarcasm notwithstanding, this is, for all its flaws, an excellent paper, and I found it a very interesting read.
Have a nice Memorial Day.
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