The idea of a radical new aircraft design called the blended wing body (BWB) which could greatly improve the fuel efficiency of air transport has been around for several decades. This type of aircraft completely abandons the tube and wing design which dominates commercial aviation today. Boeing and NASA have been conducting wind tunnel tests of a 13 foot wing span 6% scale model of a BWB aircraft which looks something like a manta ray. They feel that the modeling, design, and testing of this aircraft design have advanced to the stage that they can seriously propose the construction of a manned demonstrator model. Unsurprisingly the initial application intended for this aircraft design is military transport. I would not hold my breath waiting to take a ride on one of these planes, however. Even the most optimistic development scenarios would probably require several decades before this design could make a significant impact of commercial aviation.
Personally I am skeptical that a combination of highly efficient aircraft and bio jet fuel are going to make widespread jet airplane tourism a sustainable activity in the long term. However, certain high marginal return uses for air transport may continue to exist, and obviously high fuel efficiency is desirable for any such remaining applications.
Green Car Congress recently posted a story about a DOE program to fund the development of a demonstration plant for supercritical CO2 (sCO2) Brayton cycle electrical generator at the 10MW scale. Supercritical CO2 is carbon dioxide held above the critical temperature and pressure at which there is no phase transition between the liquid and gaseous states. The sCO2 Brayton cycle is an external combustion engine like the Rankine cycle steam engines that are currently used in a variety of electrical generation system (e.g. nuclear power plants, coal fired power plants, geothermal power plants, concentrating solar thermal power plants, and the secondary power cycle in a combined cycle natural gas fired power plant.). The energy community has long been interested in sCO2 power generators because they are potentially much more efficient at converting thermal energy to electrical energy than Rankine cycle generators, and because they should be inherently much more compact (The turbine for an sCO2 generator can be 30 times smaller than the turbine for a Rankine cycle plant of the same power rating.) thus leading to lower capital costs. Another advantage sCO2 Brayton cycle is that the possibility of maintaining a reasonably high thermal to electrical conversion efficiency using air cooling rather than water cooling. This feature is regarded as of special importance for solar thermal plants in desert regions where water supply issues may limit the use of water cooled generators. However, air cooling in other contexts would also help to reduce the environmental impact of thermal pollution of natural water sources by all types of generators which currently rely on water cooled cycles.
Sandia National Laboratory has already developed laboratory scale (125Kw) Brayton cycle sCO2 generators. It is hoped that the recent DOE proposal will be an intermediate step on the road to commercialization of the sCO2 Brayton cycle technology.
Science Daily recently posted an article about some Spanish scientists who have modeled a thermal energy storage system based on molten silicon at a temperature of 1410C. They refer to this system as a phase change energy storage system, implying that in the discharged state the silicon will a solid at close to the melting temperature and most of the stored energy will be used to convert the silicon the the liquid phase rather than to raise the temperature of the storage mass. Presumably the best use of such an energy storage system would be in a high concentration dual axis solar field. The thermal energy storage density would be 5 to 10 times higher than the molten salt systems currently used for energy storage in concentrated solar power (CSP) applications.
The scientists specifically model the use of thermo photovoltaic cells (TPV) as the thermal to electric power conversion technology. It is not clear to me that TPV would outperform a steam engine or a closed cycle gas turbine running off the same heat source in cost and/or conversion efficiency. It is far from clear that his idea is anything other a calculational curiosity, but at least it is a new idea in energy storage. One good thing about using silicon as an energy storage medium is that it is extremely cheap and abundant in the earth’s crust.
Salinity differences (e.g. at river mouths where fresh water mixes with salty ocean water) are a potential source of energy, although no practical method of converting the chemical potential differences to electricity have ever been developed. Chemistry World recently published an article about the development of MoS2 osmotic nano generators which set record performance levels in this obscure branch of renewable energy generation. However, even though this electricity generation method may find niche applications, it appears that the costs will still be too high to allow it to become a significant contributor to the global supply of energy.
A decade and half ago a group of scientests Calilfornia Institute of Technology (CIT) in vented a new type of fuel cell in which the proton conduction membrane of PEM fuel cells is replaced by a substance called a superprotonic solid acid. The result of this replacement is a new type of fuel cell called a solid acid fuel cell (SAF). SAF fuel cells operate at at temperature of 250C which is intermediate between PEM fuel cells (<120C) and solid oxide fuel cells (>800C). Unlike PEM fuel cells SAF cells do not require humidification and they are relatively tolerant of impurities (e.g. S and CO) which allows them to be operated using reformed hydrocarbon fuels. The 250 degree operating temperature also potentially allows the electrodes to use much lower loadings of platinum group metals in the electrodes thus leading to lower costs. On the other hand avoiding the high temperature of solid oxide fuel cells avoids some of the high costs associated with using exotic materials which can withstand high temperature operation.
However, as discussed at length in this paper the performance of state of the art SAF cells is still not good enough to allow them to complete with PEM fuel cells in most markets. SAFcell is a commercial spinoff from the CIT group, and they currently have plans to manufacture low power (100 watts or less) SAF cells for remote power and mobile power (i.e. military backpacks) applications. Apparently this is a performance niche in which the ability of the SAF cells run off reformed hydrocarbon fuels rather than highly purified hydrogen gives them an advantage over the more mature PEM fuel cells. Whether or not further advancements in this fuel cell technology will open other market niches remains to be seen.
Fossil hydrocarbons (e.g oil, natural gas, coal, etc) are used as feed stock for synthesizing a wide variety of useful compounds. Since humanity is tearing through the available feed stocks at far higher than the natural replacement rates an alternative feed stock will some day be required. One possibility is to use CO2 captured from the atmosphere. However, in order to convert CO2 into useful products it must first be reduced to carbon monoxide (CO) which is an energy intensive process. Some amount of research effort has been directed at using sunlight to drive photo catalytic reduction of CO2 to CO. Rhenium based catalysts can accomplish this feat using ultraviolet photons. However, ultraviolet light is a small component of incident sunlight so that a practical solar driven process requires a catalyst than can use the lower frequency visible components of sunlight. Chemistry World recently published an article about an Chinese/French collaboration that has succeeded in altering rhenium based catalysts so that they can catalyze the reduction of CO2 when radiated with visible light with a quantum efficiency similar to the utra-violet driven version of the same complex. Whether or not this particular organometallic complex is good enough (e.g. cheap enough, long-lived enough, efficient enough) to from the basis of a practical industrial process is not yet clear.
Chemistry World recently published an article about a new technique which achieves atomic level dispersion of palladium on a titanium oxide surface. The dispersed catalyst was 55 times more active than other palladium catalysts for a specific hydrogenation reaction. The researchers at Xiamen University in China who developed this technique are working to extent it to other noble metal catalysts (e.g. platinum). It is not immediately obvious that this development has direct implications for energy production/storage but since PEM fuel cells/electrolyzers use noble metal catalysts useful application in this field might eventually be found.
ORNL (Oak Ridge National Laboratory) has developed a plasma process for the oxidation of polymer precursors used in the production of carbon fiber which reduces processing time by a factor of 3 and reduces carbon fiber production costs by 20 to 40%. Carbon fiber is used to create extremely strong, light weight materials for a variety of applications. Lowering costs would naturally widen the field of economically viable applications for this material. ORNL has licensed this plasma oxidation process to RMX Technologies. However, RMX is itself an R&D materials science company and is unlikely to become a commercial manufacturer of carbon fiber. Instead they will develop the process further in an effort to bring it to a stage where it will be adopted by large scale producers of carbon fiber. A tip of the hat to Green Car Congress for this story
The PVTECH website recently published an article about the rapid growth in shipment of single axis trackers for for utility scale solar PV installation. These trackers can increase the solar output from solar panels by 30%. This rapid growth is being spurred in part by US government ITC (investment tax credit). Anti-government types will instantly conclude that the growth in solar tracker shipments is a pure liberal boondoggle, but the hope of the ‘government can sometimes do good types’ is that increasing competition in a profitable market will drive down tracker costs in the same was that fixed tilt system costs have been driven down dramatically in recent years.
The recent run-up in lithium prices underscores the uncertainty about the long term relation between lithium production levels and lithium price. Sodium, which is the next heavier metal in the alkali metal family is abundant and cheap compared to lithium so that the development of sodium metal battery anodes has the potential to improve the long term economic outlook for battery based energy storage.
Of course high temperature liquid sodium anodes are already in use in NGK insulators sodium sulfur (NaS) batteries. This battery technology received a serious setback in 2011 when a battery fire broke out in an energy storage facility owned by the Tokyo Electric Power Company. However, NGK has rebounded from this incident and has redesigned their batteries with a higher safety margin. They recently announced the start of operations of a 300 MWh battery facility built for Mitsubishi Electric Corporation. They also have contracts to build battery facilities in Italy and in the UAE both of which will exceed 300 MWh of energy storage capacity in their final configurations. Therefore sodium metal anodes already have some impressive energy storage achievements to their credit.
However, the solid ceramic electrolyte required for the operation of high temperature (325C) NaS batteries is expensive to manufacture. Room temperature batteries might be cheaper, plus they would open up to the door to mobility application for which the current high temperature batteries are considered inappropriate.
A research group in the Stanford University Department of Materials Science and Engineering recently published a paper paper in which they describe a room temperature sodium metal anode used with a liquid electrolyte which achieved highly reversible Na metal plating-stripping over 300 charge/discharge cycles. Of course thousands of cycles are required for real world applications and furthermore the other half of a room temperature NaS battery (the sulfur cathode) has its own set of problems which need to be solved in order to produce a commercially viable product. Prior to the publication of the Stanford paper more progress has actually been made towards designing a room temperature sulfur cathode than towards designing a sodium anode. This new research may open the door to a complete design for a room temperature NaS battery.