Self-sustaining solar reactor creates clean hydrogen fuel | Hacker News Reader

Self-sustaining solar reactor creates clean hydrogen fuel

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46 pointsukdm27 comments

http://www.udel.edu/udaily/2012/apr/solar-reactor-040312.htm...

"The reactor, which resembles a large cylinder, is comprised of layers of advanced, ultra-high temperature insulation and ceramic materials. It measures roughly 2 feet by 3 feet and weighs a hefty 1,750 pounds.

The conical geometry of the reactor’ design uses gravity to feed zinc oxide powder (the reactant) into the system through 15 hoppers.."

(From TFA) "...where it converts to a zinc vapor. At that point the vapor is reacted with water separately, which in turn produces hydrogen."

(Linked article) "During testing, light concentrated to simulate the energy of 10,000 suns will be focused down into the reactor, sending the temperature within soaring to over 3,000 degrees Fahrenheit, nearly one-third the temperature of the sun’s surface."

...

One interesting feature of the reactor is that, in theory, the zinc oxide byproduct created during the reaction will be re-usable, making the project self-sustaining."

Don't worry about the '10000 suns' requirement...

The High-Flux Solar Furnace "can nominally provide flux at 2,000 suns but, when required, can use specialized secondary optics to generate concentrations greater than 20,000 suns."

-- http://www.nrel.gov/docs/legosti/fy97/23377.pdf

This article is completely lacking any info which would allow the reader to judge how news-worthy this story is. Is this supposed to be a primary energy source (e.g., sunlight goes in, hydrogen for fueling cars comes out)? If so, what advantages does it have over existing technology? Does it have hope of being economically competitive?

It's one of many, many research projects in thermochemical hydrogen production -- the idea of splitting water using only heat (thermal decomposition), indirectly through longer chemical processes. It's been going on since at least 1977 [1], and there's 352 known thermochemical cycles for splitting water [2] (including zinc/zinc oxide), including the 14 listed [2] on wikipedia. The news today is that a grad student in Delaware built a small lab version of one of these, which he plans to run experiments with. His school media office wrote a press release for him [3], which was cloned by Physorg and written about on a few blogs.

In general, the idea (thermochemical hydrogen production) is just what you say -- heat in (solar, nuclear also researched), hydrogen out. No byproducts, as the chemical intermediates form a closed cycle.

[1] http://www.osti.gov/energycitations/product.biblio.jsp?osti_...

[2] http://en.wikipedia.org/wiki/Water_splitting

[3] http://www.udel.edu/udaily/2012/apr/solar-reactor-040312.htm...

Is thermochemical production much more efficient that say simple electrolysis of water using electricity (which could be produced by photovoltaic solar panels) without the extreme temperatures.

It's not that newsworthy:

The general idea is well known: http://en.wikipedia.org/wiki/Photocatalytic_water_splitting

This specific method is also well known: http://en.wikipedia.org/wiki/Zinc_zinc-oxide_cycle

And there are many other possible cycles: http://en.wikipedia.org/wiki/Water_splitting

At 2500c water will split into hydrogen without any help at all: http://en.wikipedia.org/wiki/High-temperature_electrolysis This reactor runs at 1600c.

This is basically a combination of the two things - use a lot of heat to make the reaction easier, and use solar catalyzed reactions to take it the rest of the way.

Sunlight, zinc oxide, and water goes in, hydrogen comes out. This is a prototype about to undergo 6 weeks of testing to answer the very question you pose about it being economically competitive. The main advantage this has? No emissions such as carbon dioxide.

Do any solar-powered generators of hydrogen produce carbon dioxide? Is the idea here that this would be a primary source of hydrogen for cars? Or is it only competitive in certain restricted applications?

"The main advantage this has? No emissions such as carbon dioxide."

Thats great, but who is going to use it if it isn't cheaper than alternatives?

The part that is missing is the energy costs of reprocessing the zinc. I didn't pay attention in chemistry 30 years ago, but I assume the zinc is reacting with the water and isn't just a catalyst. Hmm, a little googling shows:

Zn + 2 H2O → Zn(OH)2 + H2

It's supposed to be zinc oxide going in, so it probably looks more like this:

ZnO + energy → Zn + O Zn + 2 H2O → Zn(OH)2 + H2

(I know that's not balanced, but yours isn't either)

Maybe you can then get the zinc hydroxide back into oxide without too much trouble. It disassociates in water, leaving you with hydroxide and zinc ions.

Correction, there needs to be a newline there.

ZnO + energy → Zn + O

Zn + 2 H2O → Zn(OH)2 + H2

That is really cool! How long before people start hacking these in their garage?

This is a ceramic furnace as large as a washing machine, as heavy as a Honda Civic, that needs to be 6 times hotter inside than their home stove/oven/range, and the fuel (ZnO) is safe to eat in small quantities (breakfast cereal) but is toxic(?) to breathe.

I'm having trouble seeing why it would take long for a startup to start baking the clay for one of these in every home.

Zinc boils at just over 900 degrees centigrade. I guess that might make this a bit risky as a device. If, as you say, Zinc in gas form is toxic, that might be a problem.

Two by three feet and 10000 suns translates to "on a perfectly sunny day, needs a 200 by 300 feet solar collector" to produce the required heat. Actual numbers for a machine operating throughout the year will be quite a bit higher.

Speaking from experience (DIY foundry mishap involving brass), even small amounts of airborne zinc fumes are sufficient to knock a healthy adult flat on their ass for four days with superflu style symptoms.

While the goal of the project was to create a 100% renewable energy source based on sunlight, another energy source could probably be used.

This is a heat engine. Your options for renewable heat are mostly geothermal or solar.

The question is... if we connected the hydrogen to a fuel cell, is it more efficient than a steam generator?

I am skeptical. Large steam generators are very, very good.

If I was breathing 900C+ zinc gasses, I don't think its toxicity would be anywhere on my radar of concerns at the moment.

Nitpick: 3.6 times hotter than a home oven, not 6. Fahrenheit is not a linear scale, you must subtract absolute zero (about -460°F) from measurements (or convert to Kelvin) before computing ratios.

Nitpick, the modern Civics weigh about 2600-2800lbs, so it's about 70% of a Civic. Certainly the right order of magnitude though.

There's something ironic in you nit-picking about a 'modern' weight measure and then giving an answer in pounds (lbs).

2700lbs is ~1200 kg

Nitpick: kilograms aren't a measure of weight.

Lol, got me. Massive error on my part.

"Don't look into concentrated sunbeam with remaning eye."

SCNR

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