Hybrid Solar System Makes Rooftop Hydrogen

[OKIsItJustMe]

http://www.pratt.duke.edu/duke_hotz_hybrid_system

Hybrid Solar System Makes Rooftop Hydrogen

Posted August 9th, 2011

By Richard Merritt

DURHAM, N.C. – 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.

…

[WhiteTara]

1. That sounds like a cool future. nt

[d_r]

2. if our whole solar system was on a roof top

then maybe that roof was in a solar system where the whole solar system was on a roof top and that roof top was in a solar system where the whole solar system was on a roof top and wooooaaaahhhh.

[kristopher]

3. What do you think of the selection of systems for comparison?

They compared their solar methanol reformer to:

...standard photovoltaic cell which converts sunlight directly into electricity to then split water electrolytically into hydrogen and oxygen; a photocatalytic system producing hydrogen similar to Hotz's system, but simpler and not mature yet;
and
a system in which photovoltaic cells turn sunlight into electricity which is then stored in different types of batteries (with lithium ion being the most efficient)

How is it an improvement on these existing systems?

Reformer Systems
Generally, there are two different kinds of reforming: external reforming, which is carried out before the fuel reaches the fuel cell, and internal reforming, which takes place within the fuel cell stack.
External reforming could be carried out at a refinery or chemical plant and the hydrogen delivered by pipeline to filling stations. For automotive uses, on-board reformers may be used so that vehicles can use liquid fuels which are converted to hydrogen in a processor attached to the fuel cell structure. This option will of course add to the cost and complexity of the vehicle's power system. The use of hydrogen on- board reformers would allow for a less complex fuel cell system but would necessitate the introduction of hydrogen storage facilities.
...

Reforming Technologies

Steam Reforming In steam reforming, fuel is mixed with steam in the presence of a base metal catalyst to produce hydrogen and carbon monoxide. This method is the most highly developed and cost effective method for generating hydrogen and is also the most efficient, giving conversion rates of 70 to 80 per cent on a large scale.

Partial Oxidation Reforming
Partial oxidation can be used for converting methane and higher hydrocarbons but is rarely used for alcohols. This method involves the reaction of the hydrocarbon with oxygen to liberate hydrogen, and produces less hydrogen for the same amount of fuel than steam reforming. The reaction is, however, exothermic and therefore generates heat. This means that the reaction can be initiated by a simple combustion process leading to quick start up. Once the system is running it then requires little external heating. The technology is preferred where there is little access to natural gas or an abundance of oil.

Autothermal Reforming
Autothermal reforming combines the endothermic steam reforming process with the exothermic partial oxidation reaction, therefore balancing heat flow into and out of the reactor. These systems can be very productive, fast starting and compact and have been demonstrated with methanol, gasoline and natural gas. A number of auto and oil companies are also working on proprietary versions of this technology.

http://www.fuelcelltoday.com/media/pdf/education-kit/Fuel-Reforming.pdf

Also, where is the methanol going to come from? In the article it is biomethanol, but in reality the demand for liquid fuels for heavy transport and grid balancing is going to be a large enough challenge for us to meet.

[OKIsItJustMe]

4. Re: What do you think of the selection of systems for comparison?

Seems like a reasonable basis for comparison to me.

Putting it in different terms:

1. A standard solar system where the electricity is used to produce hydrogen.
2. Another method of producing hydrogen directly using sunlight.
3. Storing solar electricity in batteries of various types

[kristopher]

5. But what about existing hydrocarbon reformer technologies?

How does this change the dynamics from existing methods of producing power by running a stationary fuel cell on liquid hydrocarbons?

Isn't that the more appropriate (or at least as relevant a) comparison for judging the value of this research?

[OKIsItJustMe]

6. I guess I don’t see that

Your suggestion, I guess, is that (in essence) effectively, no (or little) energy is being recovered from the solar panels. i.e. That, it is simply a http://en.wikipedia.org/wiki/Methanol_reformer">methanol reformer.

I believe we have too little information (based on a press release) to draw that sort of conclusion.


At the very least, methanol reformers either need an external heat source (which, supposedly, in this case, is solar) or they burn some of the methanol to produce the heat.

[kristopher]

7. I see deliberate spin in the design of the comparison.

You can't comment on the way their system compares to other reformers because they didn't do a comparison with other reformers. If that is an accidental omission it speaks to incompetence, if it is deliberate, well...

You just posted another OP about the way the press screws up science reporting. That problem doesn't always start with the press.

[OKIsItJustMe]

8. I suspect it’s more likely that you just don’t like anything that suggests that hydrogen…

…might be a better way to store energy than batteries.


If the model is as flawed as you suggest, it seems odd that it would be, “named the top paper during the http://www.asmeconferences.org/ESFUELCELL2011/">ASME Energy Sustainability Fuel Cell 2011 conference in Washington, D.C.”

Perhaps the judges are simply ignorant regarding reformers, but that doesn’t seem likely.

[OKIsItJustMe]

9. Yeah, they know it’s a reformer

It was presented in the “1-10-4 Solar-driven reforming processes” session.
http://www.asmeconferences.org/ESFuelCell2011/TechnicalProgramOverview.cfm#53

ESFuelCell2011-54389 Technical Publication
Hybrid Solar System for Stationary Electric Power Generation

Authors
Nico Hotz, Duke University

Abstract
The main idea of this study is the combination of a solar-powered reformer generating hydrogen from an alcoholic biofuel with a low-temperature fuel cell to achieve a hybrid solar system for stationary electric power generation for single residential or non-residential buildings.

The main goal of this work is to combine both technologies (low-temperature fuel cells and solar power) to achieve synergies in terms of cost and energetic efficiency compared to systems based on a single energy source and energy conversion technology. Direct solar-to-electric energy conversion, such as photovoltaics, is currently not economically competitive with traditional electric power generation. Fuel cell technology using alcoholic fuel possibly generated from biomass (e.g. methanol) is not competitive in terms of costs either. The system proposed for this project consists of relatively cheap, commercially available hardware components (intermediate-temperature solar collector, pressurized gas tank, hydrogen-fed Proton Exchange Membrane (PEM) fuel cell) and benefits in terms of energetic efficiency from the cost-free supply of solar heat. The storage of liquid methanol as primary fuel in simple and safe tank requires much less space than a gas tank, e.g. for compressed hydrogen.

Additionally, the hybrid system with hydrogen as intermediate product benefits from the efficient short-term storage of a limited amount of hydrogen in a pressurized tank. This allows for the temporary storage of energy in the system avoiding the need for expensive and inefficient electric energy storage, e.g. using batteries. For electric power costumers and electric grid companies this leads to the significant advantage of a more controllable and highly flexible demand response since the stored hydrogen can be almost instantaneously converted to electric power by the fuel cell. This system configuration solves the problem of unbalanced power supply by sunlight during day and night, an intrinsic disadvantage of solar power. The proposed system can be operated without relying on power supply from the electric grid during peak hours in the early evening, as it is typical for residential buildings, when the power demand is high, but incoming solar power is already low.

Session: 1-10-4 Solar-driven reforming processes

[kristopher]

11. I actually like hydrogen

For the foreseeable future it suffers from durability, efficiency and cost issues; but I have strong hopes that in coming decades it will find an important place in the mix.

As for the paper being popular at a fuel cell conference?
Don't you think it's a pretty good snapshot of irony that that you brought that up right after dismissing reasonable questions as bias?

You wrote, "Perhaps the judges are simply ignorant regarding reformers, but that doesn't seem likely." It also doesn't seem relevant to my question, which is fairly straighforward - what is the advantage of this tech over existing reformer technologies. Since you are more of a follower of H2 tech than I am, I thought it would be relatively easy for you to explain what I was missing.

Was I wrong? Do you also fail to see any real advantage for this system?

[OKIsItJustMe]

12. I believe that what it comes down to is an efficient way of using solar heat to produce electricity

In this case, heat, provided by solar collectors is being used in a reformer to split methanol, to produce hydrogen which can be used to produce electricity.

https://share.sandia.gov/crf/crfnews.php?id=270">Past exergy analysis of reformers has indicated a need for improvement in their efficiency.


We know

1. solar thermal tends to be more energy efficient than photovoltaics
2. there’s room for improvement in the exergy of reformers

This system is taking advantage of the first, and (presumably) also the second.

Without seeing the paper itself, anything more would simply be speculation.

[Ready4Change]

10. Exactly. Methanol from where?

That's a problem with hydrogen. Many of the places were you can get it, you might be better off using it as it. Methanol is wood alcohol (the kind of alcohol that will literally blind you.) It's highly toxic, could be used as a fuel as is, or used to convert vegetable oils into biodiesel.

And while it can be sourced from renewable sources, it is much cheaper (and thus more likely) to source it from good old coal.

[OKIsItJustMe]

13. Well, it’s stated that the system uses biomethanol

Today, large scale http://en.wikipedia.org/wiki/Methanol#Production">methanol production commonly uses natural gas (i.e. methane.)

http://www.afdc.energy.gov/afdc/pdfs/mit_methanol_white_paper.pdf

…

• Analysis of the life cycle biomass-to-fuel tank energy utilization efficiency shows that methanol is better than Fischer-Tropsch diesel and methanol-to-gasoline fuels; it is significantly better than ethanol if a thermo-chemical process is used for both fuels.

…