Here are some general references on renewable energy:

I recommend for a good overview a recent (June 2008) "Special Report" by The Economist
magazine: http://www.economist.com/specialreports/displayStory.cfm?story_id=11565685
Note that the report is spread over  multiple web pages linked to the lead article "The Power and the Glory", under "In this Special Report" at the right side of the page.  If this reference had been available earlier I could have referred to it for some items and written less here.  Please glance at the reader comments also, some are quite informative.

DOE (Department of Energy) Energy Efficiency and Renewable Energy web site http://www.eere.energy.gov/

National Renewable Energy Laboratory in Boulder, Colorado http://www.nrel.gov/

Rocky Mountain Institute (Amory & Hunter Lovins etc.) http://www.rmi.org/

WorldWatch Institute http://www.worldwatch.org

An excellent web page on a Crested Butte resident's renewable energy efforts http://www.alisongannett.com/Alison_Gannett/Home.html

Here is a list of renewable energy sources I will discuss, as a series of tags
which will take you to the appropriate sections of the text below:

1. Energy conservation and efficiency
   
   
2. Local sources: hot water, solar buildings, photovoltaic panels, heat pumps etc.
   
   
3. Wind power, ocean power
   
   
4. Biofuels
   
   
5. Carbon Sequestration and Storage
   
   
6. Large scale photovoltaic, concentrated thermal solar, concentrated photovoltaic
   
   
7. Geothermal power with existing steam sources, Enhanced Geothermal
   
   
8. New nuclear power, including low-pollution thorium powered reactors
   
   
9. Titanium Disilicide “magic powder” production of hydrogen by sunlight
   
   
10. Appendix: Thermodynamic efficiency
    
    

I will not discuss this well known topic except to say that it will bring the single largest reduction in carbon emissions of all the methods described here, on the shortest time scale. Many gains are easy to obtain and some are already known to the general public. Perhaps the largest gain is from more efficient buildings; heating and cooling is one of the largest expenditures of energy. Other examples are compact fluorescent lights (or later, LEDs), and more efficient electric motors which have given big energy savings in China in particular. Most of us are now familiar with the issues of vehicle efficiency (especially with oil over $100!); see the Alison Gannett web page.


Local sources: hot water, solar buildings, photovoltaic panels, heat pumps etc.

My neighbor has an array of tubes on his roof to provide solar heating of water for domestic hot water and some house heating. I saw several such in China, and in some areas there these arrays are very common. It is by now well known that proper design of buildings to capture the sun's heat, perhaps storing it in “heat sinks”, can provide much or in some areas all of home heating. This could make a huge dent in carbon emissions because of the large fraction of total energy use in heating buildings. There are several such houses in the Gunnison area, for example a house on Ohio Creek road with large south-facing windows and a massive planter to store heat. Photovoltaic roof panels are now becoming popular especially in Europe; a Chinese manufacturer (Dr. Zhengrong Shi of Suntech Power Holdings) has already become a billionaire so major changes may be expected there. Solar panels in the U.S.A. are still expensive but there are several new techniques which may lower the cost a lot in the near future, from the current $0.18-$0.23 per kilowatt-hour (paying off the initial cost) to $0.05-$0.10, thus beating coal even without any subsidies. This is quoted from an encouraging recent article about new Department of Energy support for research in this area.  Heat pumps have been in use for some time; my sister-in-law has been using such a system in Ontario for many years. Heat pumps have lately been labeled “geothermal” which I find a little confusing, I would rather reserve the term for item 7. They do involve the use of buried heat exchangers to make use of a nearly constant temperature “heat sink” large mass of earth at a moderate depth. Operating on the same principle as a refrigerator or air conditioner, they provide much more heat than running the same electricity through resistor heaters; similarly heat pump air conditioning is quite efficient. Such “geothermal” installations are now being promoted by the Delta-Montrose Electric Association  http://www.dmea.com/.

Wind power, ocean power

I will not say much about wind power since it has been discussed in most news media and is rapidly being deployed already, especially in Denmark and Germany and more recently in Texas and Colorado. It is impressive that individual wind turbines are now approaching 3 megawatts capacity! China had 2.6 gigawatts (equivalent to well over a thousand turbines) installed by the end of 2006 WorldWatch report 175). An obvious problem is the “duty factor”, i.e. the wind doesn't blow all the time, but it is and will be an important component of an integrated clean electricity producing system. I know little about ocean power; engineering problems such as corrosion may be severe. A scheme involving long floating cylinders connected by mechanisms that produce electricity when the cylinders change angle is appealing and perhaps practical. Another approach is underwater turbines in tidal currents, like wind farms but using a much denser fluid. I have heard little in recent years about using the large temperature difference between surface and deep ocean water to drive heat engines, I suppose the main problem is in making very efficient heat exchangers so all the produced energy will not be used up in pumping enormous volumes of seawater.

Biofuels

Here I am somewhat skeptical. Corn ethanol appears to me to be rather a fiasco; several studies have shown there is little or no net reduction in carbon dioxide emission because of the fuel used in generating the ethanol, such as coal to run the ethanol plant and fuel for tractors. Sugar cane in Brazil may be a different situation because of the abundant production (and low cost labor!) and use of cane waste instead of coal. Most of us have heard of the catastrophic effect of the demand for corn ethanol on cattle feed prices and world food costs generally. Personally, I find it obscene to use food for motor fuel while so many starve. It's purely political, with the only valid justification being as a startup toward a more rational biofuel policy. Switchgrass (a native American perennial) requires little cultivation and is extremely productive; unfortunately the technical problems of producing alcohol or other fuel by fermentation of the cellulose have not yet been solved at least at a production level. It's a lot easier with corn or cane sugar. There are indications the problems may be solved, and there may thus be hope for some fraction of the total motor fuel in the future. One hopes this can be accomplished with the use of land unsuitable for corn and other crops, without major interference with wildlife habitat etc. Agricultural waste, wood chips etc. might also be used but do not forget that some of this needs to be returned to the land for the health of the soil! These objections do not apply to the reuse of otherwise destroyed byproducts such as cooking oil or meat garbage to produce biodiesel. In general, care should be taken in each case to calculate the total energy budget including the effect on carbon storage in soil; for example the use of palm oil for biodiesel appears to be another disaster like ethanol.

Carbon Sequestration and Storage

I have perhaps some bias against this approach, I'd say it is a complex and difficult after the fact remedy of a bad situation. It does not appear to be progressing well in this country, see this article from February 2008. It seems the coal companies are asking for more government help in development and research, and the current government is asking for more industry participation. As a result, the government “pulled the plug” on this FutureGen project. Funding was later restored in July 2008 but with a somewhat longer time scale (2013).  I don't disagree that the concept could work out. A WorldWatch report from March 19, 2008 has an excellent pro & con summary with many references. Liquid carbon dioxide is already being injected into the earth to aid in oil recovery, it doesn't seem too much of a stretch to extend the idea to keep a lot of it stored indefinitely. For another approach, it appears that reacting carbon dioxide chemically with silicate stone (see this Los Alamos web site or this Discovery Magazine article) may be much easier on a large scale than originally expected. Further references to this and some details of the CO2 separation process are in discussion of the Zero Emission Coal Alliance (ZECA) here and here; a 2000 presentation on the subject now seems rather optimistic in time scale considering current difficulties.  Science News (May 10 2008) has a very well written recent article mainly about carbon sequestration touching on many of the issues above.  More recently, see the Carbon section of the Economist report referenced at the top here.

CCS offers a hope to coal and electricity companies that existing generating stations might perhaps be retrofitted. But there are other objections to coal than carbon dioxide emission. Many of us have heard of the devastation of the Appalachian mountain region by the removal of whole mountains to get at the coal. Underground coal mining is rather dangerous although good practices (such as nearby in Colorado) have made mining in the USA much safer. Not so many have heard of some of the hazards of residues other than carbon dioxide: See the Scientific American article Coal Ash Is More Radioactive than Nuclear Waste”. (Actually this has been generally known for some time.) One should think about this when worrying about nuclear reactors (but see another approach to nuclear waste in the discussion of item 8 below). In summary, it may be that CCS will be accomplished eventually but the pace here appears too slow to do much good for the required more rapid response. A short commentary in Scientific American is mostly about this problem. Perhaps we will buy the technology from some other country that moves more rapidly.

Large scale photovoltaic, concentrated thermal solar, concentrated photovoltaic

Several large scale solar thermal energy commitments have been in the news in 2007 and 2008. An announcement was made at the end of September 2007 of commitments to develop and purchase 1500 – 2500 megawatts of AUSRA thermal solar power. On Nov. 5, Pacific Gas and Electric Company announced that it had entered into a 177 megawatt purchase agreement with AUSRA.  This is not the first let alone the only large utility scale solar commitment, for example another large one is again by PG&E to Solel for over 500 megawatts.

I will focus on AUSRA because of a number of features I find technically appealing. The plan, already proven to work using the AUSRA design at a pilot plant scale, is to focus sunlight on linear pipes and use the hot fluid thus produced to drive steam turbines and then generators. It has the advantage of only needing one-axis tracking. By contrast, the high-temperature Stirling engine design requires two-axis tracking of a hard to construct approximation to a bowl like parabolic reflector, with obviously higher construction cost. Most or all other linear pipe designs use parabolic troughs, usually molded aluminized glass. The AUSRA design uses instead many flat strips of mirror glass arrayed nearly parallel to the ground and angled to all reflect sunlight onto the collector pipe. Their intentions seems to be to use cheap flat mirrors although fewer strips could be used if they were slightly curved. (AUSRA appears to have considered this option.) This “Fresnel” design is claimed to greatly reduce the cost. (The “Fresnel” refers to Fresnel's invention in the early 19th century which made practical lighthouse lenses of molded stepped glass rather than an enormously heavy spherical surface lens.)

Another feature is low temperature operation (280° C) which of course reduces the maximum possible thermodynamic efficiency. However, it is claimed to greatly simplify other problems so as to more than make up for this inefficiency. This temperature is low enough that water can still be maintained as a liquid at high pressure, so water may be used in the linear pipes rather than oil or other higher temperature fluids plus a heat exchanger to generate steam. Lower temperature “wet”  turbines suitable for “flash” steam produced by releasing pressure on such very hot water are readily available because of the similar needs of nuclear power plants. The simplicity of a single working fluid is very appealing! The cost and maintenance of heat exchangers is completely eliminated. Other problems such as energy loss by heat radiation and corrosion are also alleviated.

Furthermore, AUSRA has proposed a low-cost means of storing energy to enable electricity generation around the clock. A large tank to contain hot water from the solar collector would solve this problem, since the water could be allowed to “flash” evaporate to drive the turbine. However the high pressure (920 psi) of 280 degree water would make such a tank or a number of smaller ones far too expensive. The proposed solution is to instead make artificial steel lined caverns deep underground; the pressure of the overlying rock would contain the steam pressure. The costs of such artificial caverns are well known, notably from the Chicago Deep Underground Storm Water system which can contain a whole city's rainwater from a storm in a network of artificial underground tunnels. With 1000 megawatts heat input for 9 hours, mostly diverted to energy storage, 20 thousand cubic meters holding 5600 Mw-hr of hot water would keep the turbogenerator running continuously at 375 MW steady heat input power. This would be a 90 foot cube, or for example a 2300 ft. long 20 ft. diameter tunnel.  For electrical output, multiply by an efficiency of 10% - 20% (Note the theoretical Carnot limit at this low temperature is about 32%.) Thus, with most of the hot water diverted to the caverns during the day, the continuous electrical power would be about 40 - 75 megawatts. Scale this up as you wish. Note there is an advantage... if the power can be spread out this way, a much smaller turbine & generator are needed for a given size of collector field. This plan has not yet been proven out but it appears to be AUSRA's ultimate goal. Again, only a single working fluid and no heat exchangers are required.

Storing energy for nighttime use as high pressure hot water is economical for AUSRA since it is already their working fluid.  But for other intermittent output renewable energy sources (wind, photovoltaic etc.) energy storage as compressed air may likely be cheaper.  The January 2008 Scientific American article  "A Grand Plan for Solar Energy"  (available on the web)  quotes costs of 3 - 4 cents for storage per kWh or 8 - 9 cents total for photovoltaic (versus the subsidized current 5 cents or so for coal).  While the volumes of underground storage are much larger than in AUSRA's plan they need not be insulated and can be natural caverns, holes left after salt mining or even sufficiently porous rock.  Natural gas is already stored this way and such compressed air storage plants have already been in use since 1978.

 What about the environmental impacts of AUSRA's scheme? Here are the “real estate requirements":  Mills et al 2004 “Design of a 240 MW_e Solar Thermal Power Plant” in Table 1 (which contains many other interesting numbers) quote about 4 million sq. meters (about a thousand acres) as the collector for a nominal 240 MW_e power plant, with some thermal storage resulting in a 0.68 capacity factor around the clock. This is for example a square 2 km or 1 ¼ mile on a side. An interesting question for use in the Southwest is whether the output condenser of the turbine is air cooled. If it is cooled by the evaporation of water, a significant amount of water will be used. An upper limit may be set by assuming all the waste heat goes to evaporate water. An example is a 1000 MW electrical output plant with at least 5000 MW solar input; 4000 MW would go to waste heat which would evaporate 57000 cubic feet in a 9 hour day. Over a whole year, this would be about 17 thousand acre feet, enough for the needs of 30 thousand households or more. Water use appears to be several times smaller if water makeup rates quoted for power plants are used, perhaps direct non- evaporation air cooling of the water is a large contribution. Nevertheless this upper limit tells us we should be worried. If air cooling is used a more costly heat exchanger is needed and efficiency will be reduced. Other environmental impacts appear minor. The working fluid is water, and common non-exotic materials are used in all the AUSRA manufacturing.

While I believe the AUSRA design will ultimately be the least expensive for large systems, some earlier designs have a head start and might be obtained more quickly.   A  "Solar Tower" power plant in Seville, Spain  was put into operation last year; it uses one of the earliest methods, a field of mirrors and a single focus,  This is one of several solar power methods expected to total  over 300 megawatts in that area by 2013.  Stirling Energy Systems is constructing a system as contracted with Southern California Edison, with first power by Jan. 2009 and 500 MW by the end of 2012 according to their 2005 announcement. It remains to be seen how the costs compare to AUSRA. The system is as mentioned before more mechanically complex but has the advantage of high temperature operation with an efficiency approaching theoretical limits, a great advantage of closed-cycle Stirling engines. (Wikipedia has a good reference on Stirling engines.) The problem of energy storage is similar to that for photovoltaic power since the electricity is generated right at the Stirling engine for an individual dish collector; the electrical energy must be stored in newer and cheaper batteries or as compressed air underground. However the Stirling engine system is very interesting for distributed electrical production rather than large scale utility production; the single Stirling Energy Systems dish power for a 37 foot diameter dish is about 25 kilowatts. Dr. Ralph Clark III (private comm.) has found that such units are available for $150,000 each currently, perhaps $50K eventually in quantity production.

Other linear systems based on parabolic troughs are also available, no doubt they will also make low cost claims. Molten salt or oil high temperature designs offer high thermodynamic efficiency, but do require heat exchangers. Another technology to watch is concentrated photovoltaic power; the sunlight is focused on small photovoltaic collectors so most of the area is covered by cheap mirrors instead of expensive silicon. Of course frying the PV units is a problem. They might be cooled (and perhaps the cooling fluid used for power or at least process heat) but they must still withstand the 10 times or more higher light flux. For such reasons these systems are to my knowledge still “experimental”. There are rumors of much improved solar cells, of reasonable efficiency (efficiency need not be really high if it is compensated by covering large areas cheaply enough) and heat resistance intrinsically or by letting infrared pass through.  However, the energy storage problem for nighttime operation has to be addressed separately. Otherwise, many of the considerations are the same as for solar thermal energy.

Geothermal power with existing steam sources, Enhanced Geothermal Energy

This will be a brief review of the general plan, as proposed in the rather comprehensive MIT report which was the basis for this topic review.  This 372 page report appears to be the definitive manual on this subject.   Geothermal energy is most commonly used now as hot water for building heating where it is readily available (Iceland, Pagosa Springs etc.) and with heat pumps between a building and a large (usually earth) “heat sink”. This is not a means of producing electricity, instead saving fossil fuel or electricity which would otherwise go to heating the building. But at some locations worldwide, enough “natural” steam is available from ground water infiltrating hot rock that commercial production of electricity succeeds, in some cases for more than a century already. Unfortunately, such places are matters of chance although new sources are currently being eagerly sought. Vast resources of energy in the form of hot rocks at 300˚ C or more lie beneath our feet, at a depth depending on location. In the West, that depth is tantalizingly small. But in general, except for a scattering of many hot springs around the landscape, the energy appears at first to be unreachable.  

Perhaps suggested by the use of “fracking” in the petro/gas industries, there have been many experiments in eight different countries over the last few years in extracting hot rock energy by drilling nearby deep holes (3 – 10 km) and cracking the solid rock (along preexisting faults) in between by the use of liquid at extremely high pressure. This is “Enhanced Geothermal Energy” as contrasted to “natural” geothermal sources. A fluid, usually water, is injected under high pressure then percolates through the cracked rock to be collected as superheated water. (The use of liquid pressurized CO2 instead appears promising, with perhaps better heat collection. Maybe this could also be used for carbon sequestration by permanently rather than temporarily shutting down spent i.e. cooled down reservoirs.) This expands into steam used to drive a turbine and generator. The difficulties include how easily the water flows (or how much pressure is needed), whether the flow is “short circuited” so the water heating is insufficient and much of the rock remains uncooled, etc. The cracks need not be closely spaced, depending on the heat conductivity of the rock, but the area exposed to the fluid must be sufficient for heat transfer; this is often a limitation. No fundamental problems have been found, and “pilot plant” operation with the generation of electric power has been achieved. What is lacking is longer term operating experience, scaling up to such a size as to be able to make reliable model predictions of the costs of massive commercial installations, and perhaps a factor 2 – 4 in flow rates by improving the techniques. Nevertheless there is an impressive array of information in the MIT Executive Summary, let alone the full report, on drilling costs, generating plant parameters, overall cost predictions etc. What about environmental costs? The heat exchange water or CO₂ circulated in the rock is of course recirculated; the question of condensing the spent steam with or without evaporative cooling was discussed above. Unless ample water is available direct air cooling will be necessary, at increased cost. Table 1.2 in the Summary estimates 2.1 km² for the above-ground “footprint” at 100 MW electrical output, and 5 km³ underground rock disrupted; the extreme depth makes groundwater problems unlikely but of course this will have to be tested. Any other environmental costs are discussed in the report and seem to be minor.  

The rock will be substantially cooled down after about 6 years in the cases planned. The intent is to shut off the extraction facility and move the turbine to a new site not far away. After a few years the rock heats up again by conduction from below and the facility can be redrilled and refractured. Thus the energy is “renewable”. This cost is included in the economic analyses. Note that the wells are more than 50% of the total capital cost (Fig. 1.8 shows details.) It is interesting that western Colorado looks like one of the biggest concentrations of greater than 250˚ C hot rock at 6.5 km depth. (See Fig. 1.4 in the Summary.) The area is indeed rich in EGS energy. Figures 1.14 – 1.16 give an overall summary of the modeling of EGS capacity and cost per kw-h versus time. You will note the capacity is expected to “take off” in the next 10 – 30 years. I am actually more optimistic provided there is some “push” by the Department of Energy and/or some brave investors. News on commitments to this promising source of energy should be closely watched.
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New nuclear power, including low-pollution thorium powered reactors

A comprehensive survey of "new" nuclear power prospects was done by a MIT study group in 2003.  It is especially interesting in that it recommends that once-through use of enriched uranium (no reprocessing) be continued, contrary to the Federal DOE plans to work toward reprocessing of spent fuel rods.  The reasons for this are explained in a mass publication in an article by Dr. Frank von Hippel in the May 2008 Scientific American.  A quick summary is that storage of spent fuel for a few years on the well guarded sites of the reactors, followed by longer term storage in "dry casks" on site after the short-lived products have decayed is the safest procedure.  Recycling such as practiced in France etc. is much more dangerous in that it separates out bomb material (plutonium) with a hazard of theft or other bold actions, and is relatively ineffective because the recycled rods are not further recycled but stored at the recycler!  Only a fraction of the offending materials (actinide elements) is "burned up".  The net effect is a "buildup" of plutonium.  Furthermore the process is expensive (government subsidized) and dangerous (safety record problems).  It only made sense while governments sought to build up stockpiles of plutonium.  There is enough natural uranium available at reasonable cost to fuel many reactors for several decades, even though only 0.7% of it (the U-235) provides the energy in conventional reactors.  In the meantime, research is under way to develop reactors which are more able to "burn up" the spent fuel rods.  The MIT group concludes that it is safest to continue current practices (and postpone Yucca mountain storage) in the meantime.  Reactor designs have been modernized to the point that safety concerns are genuinely satisfied in the minds of many; of course it will be impossible to convince quite a few people.  Chernobyl was the result of really incredible human failings in design and practice,  Some might say human beings aren't smart enough to be entrusted with nuclear power.  (I've talked to Russian physicists involved in the cleanup.)  There is a resurgence of interest in nuclear power among many including quite a few environmentalists such as myself. I hope we're smart enough to handle it!  Many agree with this statement:  Nuclear power is preferable to the effects of global warming, but renewable technologies such as wind and solar are much preferable to nuclear power.  There remains a great concern about nuclear weapons proliferation due to developing nations "I want one too" attitudes and the possibility of theft, and the general public may not be persuaded that safety and environmental problems can be solved.

It seems strange to me that relatively little attention was given in the MIT study to the use of thorium as an aid to "burning up" the waste of uranium fueled reactors, or as an independent source of nuclear energy via a number of promising schemes.  There seems to be a lack of interest in the USA; of course there is much more interest in countries with a lot of thorium such as India and Australia.  The system closest to commercial introduction appears to be that of Thorium Power, Ltd. of McLean, VA.   They offer fuel rods containing mostly thorium oxide, with more fissile material (plutonium or enriched uranium) to allow achievement of criticality in "conventional" reactors, and the thorium advantages of long lived actinide (including plutonium) burnup. (A very brief explanation is that thorium is several neutrons lighter than uranium so that the absorption in a reactor of enough neutrons to generate the long-lived "actinide" radioactive byproducts is very unlikely compared to uranium. The "burnup" of actinides already present by fission and other nuclear reactions thus wins out.)  Interest here appears to be finally increasing; the Thorium Power plan is well described in a brief article in the MIT  "Technology Review" magazine, November 2007.  It has gained the support of several Western state U.S. Senators.  I also recommend the reader comments following this article, unlike many such they are mostly informative.
 
My attention was first drawn to the subject by a letter to Physics Today complaining about the lack of interest in thorium; I looked up the work of the Nobel Prize winner Carlo Rubbia (details here ) on a novel means of producing nuclear energy.  See this Cosmos magazine article from Australia about a thorium-based reactor which requires a 1 Gev proton accelerator to keep it running; a small fraction of the produced energy is needed to run the accelerator but the reactor turns off when the accelerator is turned off.  No Chernobyls!  It also produces much less radioactive waste, in fact can be used to "burn" waste from uranium reactors.  (After about 300 years the spent fuel radioactivity is less than that of the original thorium ore!) It's quite nuclear proliferation resistant, using thorium it is essentially impossible to make a bomb (from produced U-233) because of accompanying highly radioactive decay products of U-232. But perhaps most attractive is the use of all the natural thorium, unlike uranium where only a fraction of a percent (the U-235) produces the energy, unless a proliferation-prone "breeder reactor" is used.  About 700 kg of thorium can produce the same power as 29,000 kg of natural uranium in a conventional reactor. Thorium is about three times more common than uranium, as plentiful as lead or molybdenum, and with less residual radioactivity when mined.   Thorium has the disadvantage of not sustaining a chain reaction in a reactor by itself, no matter what the configuration of moderators, unlike natural uranium let alone U-235 enriched as used for most nuclear reactors.  In the Thorium Power scheme the thorium oxide rods are supplemented by enriched uranium or plutonium which generate enough fission neutrons to bring the combination to a self-sustaining reaction.  There are also vigorous proponents of high temperature molten salt thorium breeder reactors which could ultimately use U-233 separated from such already operating reactors to bring the reactors to criticality.  U-235 or plutonium is needed at first to initiate the cycle.  There are technical problems with such hot systems, but they offer high thermodynamic efficiency and the possibility of on-site continuous chemical reprocessing of the hot liquid fuel.  The accelerator driven subcritical reactor (ADS) in the COSMOS article uses an artificial source of neutrons instead to reach criticality, so only thorium need be used and, one hopes, many of the environmental constraints might be eased. Both approaches, and a review of uranium reactors, are clearly shown in a presentation in Norway March 2007.  

Research on ADS systems and their components has been continuing slowly in several countries, mostly conceptual studies of subsystems but with some experimental work. India, with much thorium, is interested; there is considerable interest but not much funding in Australia, and there are research commitments in China, for example.  There has been some recent good news from a somewhat unexpected source: See this COSMOS article from last May. Norway is well on its way to public support of ADS reactors! The current delay appears to be mainly organizational and legal, with a lot of will to get such systems working as North Sea oil runs out. We may end up buying ADS systems from Norway a couple of decades from now.  But there are doubts.  Another article in Science is probably more favorable but it is not available on the web without a fee.

It is interesting that one of this country's major deposits of thorium is in Gunnison County, in the Powderhorn area (associated with titanium deposits which may be mined soon). It seems a pity to disrupt a wilderness with ore trucks, but “breeding” ADS systems would use much, much less material than the anxiously anticipated uranium boom resulting in hundreds of trucks carrying ore along US 50.  

I can't help but think that the ADS is much more promising than controlled nuclear fusion, which has been "ten years away" since I was a graduate student and on which billions of dollars have been spent.  It should be an option considered in somewhat longer range planning by large electric utilities; they really should encourage research efforts to bring this idea to the pilot plant stage. It would be nice to be able to buy ADS systems made in the USA but it appears the rest of the world is rapidly pulling ahead of us.

Titanium Disilicide “magic powder” production of hydrogen by sunlight

You heard it here first... a "magic powder" that when mixed with water and exposed to sunlight generates hydrogen gas! This news item comes from the "CERN Courier", the "International Journal of High Energy Physics". It was picked up from P. Ritterskamp et al in Angewandte Chemie (here is another reference and here are technical details from a coauthor's home page) and it may be years away. But fascinating; titanium disilicide, an inexpensive semiconductor, absorbs light efficiently over a broad spectrum. When mixed with water the incident sunlight energy absorbed by it splits the water, releasing hydrogen and keeping the oxygen bound to the powder. When the powder is then heated to more than 100° C it releases the oxygen and can then be reused indefinitely (it doesn't degrade like many catalysts). It's not hard to envision continuous loop processes to dry and regenerate the powder from a flat pond containing a water suspension of this powder and generating hydrogen on the spot.  It appears a concentrator isn't needed.  Auto fuel right out of the plant, and the energy storage problem solved! Sounds too good to be true, but the technical details are explained and the coauthors have patented the process and formed a company already.

Appendix: Thermodynamic efficiency

One of Napoleon’s engineers, Sadi Carnot, derived in 1824 the theoretical limits of “heat engines” such as turbines or automobiles by an elegant argument about hypothetical “ideal” engines working forward and in reverse. Note that this was well before steam engines became common! One result is an algebraic formula: maximum efficiency = (T₁ – T₂ )/(T₁ +273) where T₁ is the temperature of the inlet steam (or burned gas & air etc.) and T₂ is the “heat sink” temperature, i.e. outlet steam to a “condenser” etc., expressed in Centigrade units. (For Fahrenheit, substitute 459 for 273.) Such maximum efficiencies are approached but of course not equaled by the most modern power plants, using turbines in series etc. For example, if T₁ = 280° C and T₂ = 100°, the upper limit is 32% efficiency. There is absolutely no way this can be beaten! It means most of the energy must be dissipated to the environment in cooling the “heat sink”.