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.
Will light weight iron nitride transformer cores produced my a method called low temperature field assisted sintering technique (FAST) give boost to grid energy storage? A group scientist and Sandia National Laboratories apparently thinks so as shown by this
I first read about mechanical flywheels as a means of electrical energy storage more than thirty years ago when I was in graduate school. The amount of progress in practical applications during the intervening three decades has not been impressive. Steel flywheels in vacuum chambers using magnetic levitation bearings have found a market niche in uninterruptible power supplies (UPS) where the flywheels supply 10 to 15 seconds of electrical energy during a power interruption, allowing time for some other backup source (e.g. a diesel gen set) to come on line.
Flywheels made out of carbon fiber are mechanically stronger than steel flywheels and thus can spin faster and store more energy (The energy stored is proportional to square of the angular speed) and can thus provide longer time periods of energy backup in a given physical foot print. However, carbon fiber flywheels are more expensive than steel flywheels. A company called Pentadyne introduced carbon fiber flywheels into the UPS market but ultimately declared bankruptcy. A company called Beacon Power introduced carbon fiber flywheels into the power grid frequency regulation market, but they subsequently joined Pentadyne in bankruptcy. Neither of these flywheel designs is completely dead since Pentadyne was acquired by Phillips Service Industries and Beacon Power was acquired by Rockland Capital LLC. However, the long term succes of both of these enterprises is still questionable.
A new entry into the field of carbon fiber flywheels for grid energy storage is a German company called Stornetic. Interestingly Stornetic is a spin off from a company called Enrichment Technology Company (ETC) whose core technological expertise is in high speed gas centrifuges used to produce enriched uranium fuel for nuclear reactors. Apparently ETC felt that their expertise in high speed rotating machinery was a good match with flywheel energy storage.
In this brochure Stornetic states that their basic flywheel unit can deliver 22kW of power and store 3.6kWh of energy. These numbers imply 10 minutes worth of energy storage at the maximum power rating which is much longer than the 10 to 15 seconds delivered by steel flywheels in UPS system. These kind of discharge times open up the application space of grid power frequency regulation if the cost is low enough. Whether or not ETC and Stornetic can deliver carbon fiber flywheel energy at significantly lower costs than has been achieved in the past remains to be seen.
The Drexel University nano-materials group together with a group of french researchers lead by Patrice Simon of Paul Sabatier university have recently published in Science a paper describing methods for thin film carbon supercapacitors into standard silicon based micro-circuitry. The carbon is deposited on top of a silicon substrate as a titanium carbide (TiC) film. After chlorination most of the TiC film is converted into a high surface areas porous carbon film which can be used to create a micro supercapacitor. The residual TiC act as a stress buffer with the underlying Si film. Regarded a energy storage devices supercapacitors have very high power density and very long cycle life (> 1 million). However, their energy density is more than an order of magnitude lower than lithium ion batteries.
The Drexel university announcement of these new ‘energy storage on a chip’ devices is quite enthusiastic about potential micro-electronics applications, but does not really describe the application space that is being targeted. I would be extremely surprised if the energy density is high enough to compete with lithium ion batteries, but there may be lower energy requirement applications that can use this technology. The article emphasizes the fact the the carbon films are flexible and can thus be integrated into flexible circuitry. Possibly wearable electronics is one the imagined applications for this new technology.