Stanford group designs room temperature sodium metal anode with good long term cycling capability

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.

Light weight iron nitride transformer cores are produced by Sandia Labs FAST process

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
Labs announcement.

Australian company Tractile produces PV/Solar Thermal roof tiles for building integrated energy harvesting systems

The Australian company Tractile is another entrant in the solar PV / solar thermal integrated energy harvesting systems. They promise the usual advantages relative to PV only systems of shorter payback times and higher PV efficiency due to active cooling of the solar cells. They offer this advantage in the form of Solar PV / Solar thermal roofing tiles which can be integrated with non-energy harvesting tiles in a roofing installation. If you are putting on a new roof anyway the excess labor cost associated with adding solar energy harvesting will be lower than in the case of adding solar energy harvesting to an existing roof.

Blackest material created from gold nano-spheres attached to gold nano-rods may find use in solar energy harvesting

On the chemistry world website I recently read about researchers at the King Abdullah University of Science and Technology in Saudi Arabia who have created a new material containing particles in the form of a metallic nano-sphere attached to a metallic nano-rod. Dispersed in a liquid this new material is the darkest ever created, absorbing 98 to 99% of light in the wavelength range between 400 and 1400nm. The King Abdullah researchers claim that their material absorbs 26% more light than carbon nanotubes which were the previous record holder in the in the field of black materials. Among possible uses for this material that I have seen mentioned are solar cells, solar water desalination, and optical interconnects. This material in not a photovoltaic material, but it potentially has the ability to absorb light over a wide frequency range and re-emit light in a very narrow frequency band. This property could be used in conjunction with a PV material to utilize a larger portion of the solar spectrum than do current silicon solar cells.

The nano particles actually fabricated were made out of gold. I do not think that gold is necessarily required to make such a material, but this project was a research demonstration, and gold was apparently the easiest material out of which to create nano particles with the right properties. Interestingly the design of this material was inspired by the structure of the scales on the cyphochilus beetle which is an exceptionally white material, that is a material which reflects almost all of the light which shines on it. After the researchers had deciphered the structure of these scales and figured out their operating principle they realized that they could invert the structure and create an exceptionally black material.

Whether or not this discovery will lead to practical solar energy harvesting devices remains to be seen.

Aerotaxy: a possible path to relatively low cost direct band gap GaAs PV cells

This abstract of an article published in the Dec 2012 issue of  Nature describes a method of growing crystalline GaAs (gallium arsenide) nanowires in gold nano-particle aerosols at high throughput rates compared to traditional molecular beam epitaxy (MBE) or metalorganic chemical vapour deposition (MOCVD) methods of synthesis. The hope is that a high growth rate will translate to lower costs.

The company Sol Voltaics is hoping to utilize the technology in conjunction with traditional silicon solar cells produce a tandem device with higher efficiency than can be achieved using silicon by itself. GaAs is a direct band gap semiconductor which means that the probability of the absorption of an impinging photon whose energy is near the band gap is much higher than for an indirect band gap semiconductor such as silicon. This high probability of absorption means that GaAs solar cells can be very thin and still effectively absorb solar energy, whereas silicon solar cell have to be much thicker to effectively absorb all of the photons that are capable of being converted to electrical current.

The band gap of GaAs is different than that of silicon so that it absorbs a different part of the solar frequency spectrum. That fact that the GaAs film can be made very thin means that the photons of a frequency that it is not capable of using for the production of electricity can easily pass through and enter the silicon cell where the photon near the band gap of silicon can be absorbed and converted to electricity as well. The combined cell has substantially higher energy production than a silicon cell alone.

The key to the economics of such a tandem cell the the production cost of the GaAs layer. Triple junction cells with two of the junctions based on GaAs films have achieved solar conversion efficiencies in excess of 45%. However the enormous costs of producing crystalline then films of GaAs have prevented the commercialization of this technology except in specialized niche applications where low weight and small surface area is more important than cost (e.g. remote power for military application, solar power for space missions, etc).

Whether or not the cost/performance characteristics of PV cells produced by this technology can enable mainstream commercial application of GaAs remains to be seen. 

Allstom Transport and Hydrogenics form partnership to develop European fuel cell powered commuter trains

I am not really a believer in the hydrogen economy (i.e. a seamless transition from fossil fuel powered transportation to renewable hydrogen powered transportation within the context of growth based financial capitalism). However, I still follow developments in fuel cell powered transportation since a variety of mobile power application will eventually have to be weened off fossil fuel, and it is not clear that storage batteries will be effective in all of these applications.

Green Car Congress recently published a news item about a partnership between Alstom Transport and Hydrogenics to develop fuel cell powered commuter trains for the European market. Alstom Transport is a rail transport company based in France which a focus on ‘sustainable’ transportation. I put the word sustainable in quotes since what level of economic activity which is going to going to be reasonable stable on long time scales is highly uncertain, though certainly fossil fuel powered transportation cannot be included in this category. Hydrogenics is a company headquartered in Canada with manufacturing sites in Germany and Belgium which specializes in PEM fuel cell systems and in hydrogen production by electrolysis. Hydrogenics originally came into existence in 1948 as an electrolyzer company but has since added PEM fuel cells to its product line.

Whether or not the proposed system of hydrogen powered commuter trains will use hydrogen produced from Hydrogenics electrolyzers or whether the cheaper (but environmentally friendly) option of hydrogen produced from steam reforming of natural gas will be used is not clear. The announcement of this partnership talks about the delivery of several hundred engine systems and heavy duty fuel cells, but does not mention electrolyzers.

Fuels cells powered by reformed natural gas is the most likely entry point for a commercially successful entry of this technology into the transportation market. However, carbon emission point of view this option is not very attractive. Amory Lovins and others argue that a system based on fuel cells hydrogen from reformed natural gas will produce less CO2 emissions per passenger mile than transportation based natural gas powered internal combustion engines. However given the long dwell time of CO2 in the atmosphere we need to leave a significant fraction of fossil carbon reservoirs in the ground to have any impact on climate change, the economics of electrolytically produced hydrogen is still highly questionable.

This brochure on Hydrogenics PEM fuel cells for transportation application they cite an expected operation lifetime 10,000 hours. Ten thousand hours at an average speed of 30mph comes out to 300,000 miles which is pretty good durability. Fuel cell cost are dropping and reliability is rising, but hydrogen costs still stand in the way widespread adoption.

Community Finance: An Essential Element of a Wealth Sustaining Society

A reasonable standard of consumption is a prerequisite of an economic system with long term productive stability. Many people now recognize this truth, and calls for voluntary simplicity and the end of consumer society meet a positive response from many people. However, the social systems implications of a reasonable standard of consumption have not been clearly thought through, partly because social systems thinking is a difficult discipline, and partly because a strong bias in favor of certain cultural norms strongly discourages any thinking which would challenge those norms. I call this bias the Social Will. The ability of the Social Will to produce conformity of thought on key social institutions is quite powerful.

The french historian Jean Michelet in writing about the Maillotin tax rebellion (named after the mallets or Maillots that were carried by the leaders of the rebellion) under the reign of the mad king Charles VI in late fourteenth century France explains how the leaders of the rebellion demanded audiences with the Dauphin (the future Charles VII) and lectured him about how a good king should treat his faithful subjects. Michelet explains that it never crossed the minds of the rebels that they could do without kings altogether, because the religion of royalty was still in full flower. If anyone had suggested to the Maillotins the elimination of royalty, they would have rejected this advice as the ravings of a radical mad person who wanted to destroy the natural social order and bring chaos and anarchy down upon the world. The Social Will of the France of that time had ordained a hereditary monarch as an essential element of good social organization. The suffering bourgeoisie wanted a good king who would rule wisely, but the idea of replacing monarchy by some other form of government was not within the event horizon of fourteenth century France.

Similarly many people are dissatisfied with the performance of private credit markets in wake the great recession of the last decade, but the percentage of these people who recognize that fundamental structural problems exist in this system which require new forms of credit is still quite small. The Social Will of modern global society has declared private credit markets to be an eternal and perfect form. John Mavrogordato summarized this resistance to new thinking on economic organization in the following terms in his 1917 book The World in Chains: Some Aspects of War and Trade:

The distribution and exchange of commodities are necessary to the existence of the State; so necessary that it might be supposed that their regulation would be one of the primary functions of government. Proper systems of distribution and exchange correspond to the digestive processes of the body, on which depend the proper nutrition of all the parts and the real prosperity of the State as a whole; yet any comprehensive plan for their control is still regarded as the most unattainable dream of Utopia, and they are left to carry on as best they can in the interstices of private acquisitiveness.

Unless we are planning to go all the way back to neolithic villages as the fundamental social unit credit cannot be dispensed with. Any time someone proposes to spend a large amount of resources in the present in order to produce economic value over long period of time in the future (e.g. building a bridge, a university, a semiconductor manufacturing plant, a solar PV farm, a nuclear power plant etc.) someone must evaluate the likelihood that this present expenditure of resources will produce in the future a sufficiently large flow of goods and services and a small enough amount of negative externalities to justify the expense. This evaluation of the future consequences of spending on infrastructure development is the process of granting credit.

To me it seems clear that leaving this process primarily in the hands of private credit markets whose raison d’etre is to turn money into more money is inconsistent with ecologically sound economic development. The people making decisions about credit should be public servants whose purpose is to create and maintain useful infrastructure rather than to turn money into more money. These community financiers should be paid salaries for services rendered rather than making money in proportion to the amount of debt they create. This not to say that community financiers should not be concerned with monetary flows and the economic viability of the enterprises to which they grant credit. Quite the contrary. But a significant difference exists between trying to create and maintain valuable infrastructure and trying to create as much debt as you can because your personal wealth is proportional to the size of this debt.

Of course if ‘public servant’ and ‘Marxist vampire’ are inescapable identities in this context then no useful reform of the credit system can be made, and we should quit wasting our time yakking about ways to save a form of social organization which is an evolutionary dead end.

Lawrence Berkeley Laboratory Scientists Develop Low Temperature Sodium Sulfur Battery

The most widely used battery technology for multi-hour grid energy storage is NGK Insulator’s high temperature (300 to 350C) sodium sulfur (NAS) battery. The high operating temperature is required to obtain adequate mobility for the sodium ions through the solid ceramic beta-alumina electrolyte. The largest installation of such batteries is 204MWhr installation supporting a wind farm in Rokkasho Japan. This installation opened operations in 2008. The sodium sulfur chemistry is attractive from a scalability point of view since both sodium and sulfur are earth abundant elements.

High temperature operation creates safety concerns, and, in fact, a battery fire occurred on September 21, 2011 at one of NGK installation’s in Japan, leading to a shutting down of all NAS battery storage installations world wide for a long period of time. In June of 2012 NGK Insulator’s published a report describing the causes of the fire and safety enhancements which they felt provided sufficient operating margin to justify reopening their battery factory. This presentation mentions two California installations (One in San Jose and one in Vacacville) of NGK’s NAS batteries which have occurred since the safety enhancement were announced. This technology is not dead, but my sense is that enthusiasm for it has waned in spite of the enhanced safety features. These batteries are too expensive ($320/KWh) to truly revolutionize grid operations but they have found some niche markets.

From time to time I stumble upon research work exploring options to lower the operating temperature of NAS batteries. If these ideas introduce rare elements to the battery chemistry they may not have the same long term scalability as the current chemistry. For example this abstract claims that adding cesium to the liquid sodium cathode will allow the operating temperature of sodium sulfur batteries to be lowered to 150C. Unfortunately cesium is a rare element which cost about $40,000/Kg. The effect of the cesium is to enhance to wettability of the sodium on the solid beta-alumina electrolyte. Conceivably some other lower cost metal can be found which produces the same effect, but such an option awaits future research.

Recently an interesting low temperature NAS battery design has emerged from scientists (Dr. Gao Liu, Dr. Dongdong Wang, and Dr. Kehua Dai) at the Lawrence Berkeley Laboratory. They claim that this battery can operate at a temperature of 80C. This temperature is below the melting point of pure sodium (97.7C). A liquid metal anode avoids the problem of dendrite formation by solid sodium and is a key enabler of the long cycle life (4500 cycles) of current NAS batteries. Liu et al maintain this feature of the NAS battery by using an alloy of sodium and potassium which has low melting temperature. The solid beta alumina electrolyte is replaced by a solid polymer which conducts sulfur ions (rather than sodium ions) at low temperature. Their battery design also includes a new cathode which is a mixture of sulfur and a conductive polymer. Some details of the cathode and electrolyte chemistry and structure can be found in this patent

As this application for Cleantech to Market funding shows, Liu et al seem to believe that this battery architecture is not just a laboratory curiosity but has the potential to be manufacturable. I believe that the manufacture of the tubular solid ceramic electrolyte for the current high temperature version of the NAS battery is an expensive process, so that the replacement of this component by a polymer electrolyte potentially represents a significant cost savings. Some information about projected development time lines manufacturing costs for of these batteries is given in this presentation. The numbers in the presentation are probably highly speculative. Furthermore the LBL scientists themselves will probably not follow this technology to maturity but will attempt to license it to a private company. I would not hold my breath waiting for these batteries to start rolling off the assembly line in large quantities, but I am always interested in technologies which have potential long term scalability.

Silevo Produces High Efficiency Low Temperature Coefficient Silicon Solar Cell Using Thin Film Tunnel Junction Architecture on Top of an N-type Silicon Substrate

The free charge carriers in so called intrinsic semiconductors such as silicon are the result of the thermal excitation of electrons from a valence band into a conduction band. The excitation of the electron leaves behind a positively charge hole in the valance band which can also act a charge carrier. Because the free charge carriers are created by thermal excitation, the colder a semiconductor becomes the less free charge carriers are present and the electrical resistance become higher. This behavior is in contrast to metallic conductors which have free electrons in the conduction band at all temperatures and which actually have lower resistance at lower temperature because thermal lattice vibration do not interfere as much with the free motion of the conduction electrons. The density of free charge carriers in pure silicon at room temperature is low compared to metallic conductors, and the electrical resistivity is high.

The number of free charge carriers in silicon can be greatly increased by adding a small amount of another element called a dopant. Silicon has four electrons in its out shell. If the dopant atom has 5 electrons in its outer shell (e.g. phosphorous) then one of these electrons can easily be excited into the conduction band of silicon. The positively charge ionic core left behind is bound to the site the dopant atom and therefore cannot act a current carrier. Thus silicon doped with phosphorous has an excess of negative charge carriers and is therefore called an n-type semiconductor. If an atom with 3 electrons in is outer shell (e.g. boron) is added to silicon then one of the electrons in the valence band can easily become attached to the atom leaving behind a positively charge hole which can act as current carrier. The electron attached to the dopant atom is immobile and cannot act as a current carrier. Thus silicon doped with phosphorous has an excess of positive charge carriers and is therefore called a p-type semiconductor. Both of these types of doped silicon are called extrinsic semiconductors. Extrinsic semiconductors have much higher densities of free charge carrier and much lower resistivities than intrinsic semiconductors.

Pure silicon is capable of a absorbing sunlight and exciting electron/hole pairs, but no electromotive force exist which can drive the free electrons through an external circuit as an electrical current. In order to produce such a current a P-N junction is required. A P-N junction is an interface between two volumes of silicon one of which has an excess of negative charge carriers and the other of which has an excess of positive charge carriers. The most common method of producing such a junction is to take a wafer of p-type crystalline silicon (most commonly doped with boron) and exposing one surface of the wafer to phosphorous at high temperature. The phosphorous diffuses into the silicon and forms a thin layer of n-type silicon. The boundary between this layer and the bulk of the wafer is the p-n junction.

When electron/hole pairs are excited by light absorption in the vicinity of the p-n junction the electron moves to one side of the junction and the hole to the other side and they can recombine only after the electron has moved through an external circuit an back into the other side of the junction. This movement of the photo excited electrons is the source of the electrical current produced by PV cells.

Silicon PV cells can be produced starting with either p-type silicon or n-type silicon. It turns out that controlling the electrical resistivity of n-type silicon crystals is more difficult than controlling the resistivity of p-type silicon thus making n-type silicon with will controlled resistivity more expensive to produce. However PV cells utilizing n-type silicon wafers can achieve higher light to electricity conversion efficiency than PV-cells utilizing p-type wafers. P-type solar cells still dominate the market, but high efficiency n-type cells have found a niche in applications where space is at a premium so that the higher efficiency allows more energy production in a give area of rooftop.

Silevo is a player in the high efficiency n-type PV solar cell field. The typical method of producing a p-n junction in a n-type wafer to expose is one surface to boron gas at high temperature. The boron diffuses into the silicon and converts a thin layer of the wafer into a p-type semiconductor. Silevo creates an ultra thin p-type layer at one surface of the wafer not by doping but by allowing one surface of the wafer to become oxidized and then depositing thin film layers on top of the oxide. The actual physics by which by which the so-called inversion layer with a majority of p-type carriers is created is a mystery to me, but it obviously works. I believe that the high temperature boron diffusion process is fairly expensive so that Silevo’s thin film deposition process may represent a significant cost reduction.

PV cells of this type have a lower temperature coefficient of performance (% loss of efficiency per degree increase in temperature). The Silevo cells have a temperature coefficient of -0.22%/C compared to -0.45 to -0.50%/C for diffusion based solar cells. Silevo claims that this lower temperature coefficient leads to 5% to 12% increase in energy production under real world conditions. Obviously hot desert conditions will get the most benefit from the lower coefficient.

Silevo does not manufacture n-type silicon wafers itself. They are depending on general industry progress for lower costs in this aspect of the solar modules.

Silevo has garnered media attention recently because it was acquired by Solar City, a major player in the residential PV market. This attempt by Solar City to become a vertically integrated company who manufactures it own solar panels is somewhat risky, but if Silevo can really deliver a high performing low cost product the payoff could be very substantial.