Fw: Peeved at the pump

From: Innovatia <dennis@innovatia.com>
Date: Thu May 13 2004 - 13:38:48 EDT

Subject: Peeved at the pump

Thanks, Al Koop, for that energy article. As an engineer into power electronics, I have been sudying energy alternatives for the last few years, and this might be the occasion to say something about the prospects.

1. Solar photovoltaic (PV) panels: continuous-process "extruded" amorphous solar panel ribbons have been projected to be $0.50/W, competitive with the power grid, for at least five years. PV panels are currently running at $3.50/W at best, new. Progress here is much slower than was anticipated. For an example developer, see www.astropower.com , a leading company in continuous-process PVs. As it is, solar cells are made using semiconductor batch processing, an expensive way to make them.

2. Several different fuel cell technlogies are being developed. Hydrogen (proton exchange membrane, PEM) technology was until recently the leader, under development by www.ballard.com . A problem with PEM fuel cells, being worked on by Detroit, is that the fuel is still gasoline, which contains impurities that will easily foul a PEM "stack", the chemical-to-electric converter of the cell. A pre-conversion process is needed to filter out sulfur compounds, etc., and this is proving difficult (expensive).

Direct alcohol fuel cells (DAFCs) were stuck on a development problem that was solved a couple years ago, and now DAFCs are pulling ahead. This is particularly encouraging, as I view it, because DAFC stacks are not subject to fouling and either methanol or, preferably, the safer ethanol can be used. Ethanol is a "biofuel" and can be produced with moderately simple chemical unit operations, of fermentation and distillation of sugars. Starches require a pre-distillation step of being broken down into sugars by enzymes. Non-chemical engineers (such as the Schroeders in Colorado, including Gene Schroeder, who organized the tractorcade to Washington a few years back) have built a small commerical plant in their barn. There are grain-grower ethanol associations in the U.S. and Canada. Sugar cane is the best source and would diversify and stabilize the sugar industry, as sugar currently gluts the world markets, squeezing Belizean cane growers.

Solid oxide fuel cells are also a leading contender and seem more suited at this time for large-scale use. They also run very hot.

The best fuel cell technical site I know of is: www.benwiens.com the site of a former Ballard Energy fuel cell engineer.

3. Biofuels: besides the "ethanol economy", other plants producing large amounts of oils are under study and these organic oils are being combined with hydrocarbon geofuels - typically 20 % "bio" to 80 % "fuel") and studied. Direct-injection diesel engines have essentially no problem with these fuels once a few rubber parts are easily replaced. The 4.5 kW genset I have here at my cottage in the jungle has a Yanmar diesel engine. Similar engines have been run on discarded McDonald's frying oil for years. An enzyme transforms it into fuel directly burnable in the diesel engine.

Changing from gasoline or diesel fuel to ethanol is feasible, though ethanol's heating value (energy/kmol) is somewhat less. Photosynthesis is one of the best solar conversion processes around. Why not use it? As gas prices increase, we approach an economic crossover, especially if worldwide cane production were directed at ethanol production.

4. Solar thermal: use a solar concentrator to heat a fluid stored in an insulated tank as thermal energy. Besides nuclear and chemical (ethanol in a tank) energy, this one has the highest energy density, especially if state-change materials are used for heat storage. Then use thermal-to-electrical converters.

I am currently workng on a design for a Solar Thermal Electric System (STES) because it looks quite promising an nobody seems to be doing it. (I'm looking for a mechanical/chemical-oriented partner for this too.) Here's why it is cheaper and better than solar PV. First, storing heat in a tank is less costly and has less maintenance than storing charge in a battery bank. Second, by separating energy collection from conversion, the additional degree of freedom allows for optimizing system sizing, which reduces cost.

The thermal-to electrical converter possibilities:

1. Thermocouple stacks = thermoelectric modules (TEMs), used in Igloo-brand car coolers for example. www.hi-z.com is the leader in optimizing these for power generation. Efficiency is the issue. It is increasing but is currently around 4 %. Even so, it beats solar PV at 15 % at a system level because collecting and storing heat is relatively cheap. The TEMs are sized for desired peak power, while collector size is determined by the peak storage requirement. TEMs are relatively inefficient because thermal and electrical transfer is done by electrons diffusing through semiconductor material. It's an ugly way to move electrons.

2. Thermionic devices: I know of no commercial work but research looks promising. Ref:
arXiv:cond-mat/9801187 v1 19 Jan 1998

"Multilayer Thermionic Refrigerator and Generator", G.D. Mahan, J.O. Sofo [*], and M. Bartkowiak, Department of Physics and Astronomy, University of Tennessee, Knoxville, TN,37996-1200, and Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6030

In thermionic conversion, electron transport is ballistic instead of diffusive, and efficiency figures (which can be calculated to about 1 % accuracy on the basis of solid-state physics) are 2 to 5 times higher than thermoelectric devices. That's very encouraging, though I don't know why it hasn't attracted commercial interests yet.

3. Thermotunneling devices: place two metal plates 10 nm apart and electrons will tunnel across them. Tunneling is a quantum phenomenon that requires this close spacing. (Thermionics requires about 100 nm spacing, much easier to implement.) www.powerchips.gi is the leading company, funded by Rolls Royce, (wisely) headquartered in tax haven, Gibralter, with actual development in Canada. Using existing semiconductor processes and some novelties, prototype devices show an efficiency of 15 %. This is sufficient to obsolete the internal combustion engine. It would make ordinary solar PV obsolete too.

4. Low differential-temperature Stirling engines: The Stirling engine has been around for well over a century though fell out of use due to the unavailability of stainless steel in the 1800s. It is making a comeback and several commercial concerns are working on them. The free-piston design has one moving part. Efficiencies of 40 % or more, rivaling large steam turbines. They are essentially maintenance free. The Swedish submarine builder, Kockums, uses them in subs because they are nearly silent. At present, they are unaffordable, but mainly due to a lack of high-volume commercialization.

5. Thermophotovoltaics (TPV): An enhancement to PV, uses an optical frequency converter film in front of the PV layer to convert thermal solar to higher frequencies in the conversion range of silicon panels. This approach might keep PV competitive with solar thermal. It is in the research stage of development.

6. Wind, ocean waves, ocean thermal, geothermal, etc.: I see these as augmenting the more direct solar methods. In one of his sci-fi stories, Isaac Asimov had a whole planet running off of the temperature difference in the ground. A mine a mile deep is not at the ambient surface temperature!

In summary, there are several very promising energy developments with a 1 to 10 year time frame for mass commercialization. I see a disproportionately small amount of effort going into them relative to more of the same, such as oil exploration (without intending disrespect for Glenn Morton's efforts) and even nuclear fusion. We consequently appear to have a conditionally encouraging energy future. The alternatives result in a distributed, not necessarily centralized, approach, which is also advantageous, and rely upon an energy source that will be available for the forseeable future (and then some).

The most discouraging aspect of running out of oil to me is that oil is also used to make plastics. Nobody seems to be talking about running out of plastics, but that could also have some significant consequences. I am not enough of a chemical engineer to know whether the plastics industry could switch present processes to be fed by ethanol instead. I suspect it would require some major changes in the plastics industry. Perhaps that would result in the discovery of new kinds of ethanol-based plastics that otherwise wouldn't have been researched.

Saludos amigos/amigas,

Dennis Feucht
Received on Fri May 14 15:09:44 2004

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