Green Car Congress recently posted a story about an article in the magazine Oceanographydetailing a proposal to obtain liquid hydrocarbon fuels and protein for animal feed from large-scale industrial cultivation of marine microalgae (ICMM). Analysis indicates that coproduction of food and fuel is needed in order for algal bio-fuels to achieve production costs comparable to liquid fossil fuels. The authors argue that cultivation of marine micro algae is potentially an order of magnitude more productive (presumably per square meter of ocean cultivated) compared to biomass production on land. They further argue that the fact that salt water is used rather than fresh water can help to manage the demand on this important resource. They particularly emphasize the comparison of algal proteins to soy protein, maintaining that not only is the production more efficient but that the algal protein is potentially of higher quality. If ICMM is as efficient as projected then it may be possible to reforest marginally productive agricultural land thus leading to the removal some amount of CO2 from the atmosphere as well as helping to preserve land based bio-diversity.
Presumably intensive cultivation and harvesting of select species of marine microalgae over a large area will have negative effects on ocean bio-diversity, although this issue is not discussed in the Oceanography article. The authors do discuss the nutrient requirements of ICMM as as a sustainability issue. To achieve high productivity marine microalgae require a higher ratio of phosphorus to nitrogen compared to land based agricultural systems. The authors freely admit that the current use of rock phosphates in agricultural production is not sustainable in the long term and that nutrient recycling will have to be pursued. However, they argue that ICMM is very compatible with nutrient recycling since nearly 100% of the phosphorous in waste stream can be taken up and used by the microalgal population. This fact is in contradistinction to soil based agriculture in which nearly 80% of applied phosphorous is quickly transformed into stable forms which plants cannot utilize. Land which has undergone years of regular phosphorus applications has lots of phosphorus in it in stable forms that plants cannot digest. We may eventually be able to develop more complex system of agricultural production which utilize this phosphorus is place, but today’s highly productive (per acre and per labor hour) corn and soy bean rotations are not such a system.
My own view of the ICMM proposal is that it makes sense only if it is part of a long term plan to reduce the total human impact on the biosphere which includes other important effects in addition to green house gas emissions. We need to produce food for human beings, and if ocean farming can help us to do so with lower total impact on the biosphere then such a proposal is worth evaluating. However, if ICMM is being proposed in the context of a world of 10 billion human beings who expect constantly increasing standards of consumption (including such things as getting a large percentage of our protein from high on the food chain and frequent rapid travel over long distances) as a normal part of the operation of the economic system, then farming the ocean may just be one more step on the road to ecological disaster.
Several month’s ago Green Car Congress published a story about the development of water electrolyzer designs which do not require an ion exchange membrane separating the two half cells of the device. Since ion exchange membranes are quite expensive such designs have the potential to reduce the costs of hydrogen producing water electrolyzers. Furthermore, the researchers who published the paper in question argue that the elimination of the ion exchange membrane can relax the design constraints of MEA (Membrane Electrode Assembly) based electrolyzers and can potentially lead to design configurations which have other cost reductions in addition to the membrane manufacturing cost.
As the diagram below indicates this form of electrolyzer does indeed appear to have a very simple design. It would appear that the most costly components would be the titanium mesh electrodes impregnated with the appropriate catalysts.
The researchers used platinum nano-particles attached to the titanium mesh as catalysts. They were able to operate prototype electrolyzers in both acidic and alkaline solutions but obtained the highest electrolysis efficiency (72.5% based on the HHV of H2 at a current density of 100mA/cm2) for with alkaline electrolyte. This efficiency is comparable to that of current commercial alkaline electrolyzers such as those produced by Nel (formerly a division of Norsk Hydro). Alkaline electrolysis is economically attractive because it does not require the use of platinum group metals as catalysts.
In spite of the interesting initial results, one should not get too excited yet about this electrolyzer design entering the market place in the near future. Although the overall electrolytic efficiency of 72.5% is comparable to commercial alkaline electrolyzers an additional hydrogen loss of 10% occurs during the gas collection phase of the separation process reducing the effective efficiency to 65.3%. This loss of efficiency may not be a deal breaker since it is cost/kg that matters. Furthermore the electrolzyer in question is a non-optimized preliminary prototype and substantial optimization may be possible. The electrode current density of 100mA/cm2 is a factor of three lower than the current density of commercial alkaline electrolyzers although again similar comments to that just made about efficiency apply.
Another problem is that some amount (probably more than 1%) oxygen crosses over to the hydrogen side to the electrolysis cell and contaminates the hydrogen gas at the collection point. PEM fuel cells require less than 5 ppm V of oxygen content. Although further optimization may reduce the amount of crossover, orders of magnitude improvement seem unlikely. Nel claims that their electrolyzer systems produce H2 with less than 2ppm of O2 after purification. Whether or not a fraction of a percent O2 contamination represents a significant economic barrier to the production high purity H2 is not clear from any information that I have located so far.
In the early 1980s R. Buckminster Fuller proposed the construction of a global electricity grid as a means of transporting energy from solar and wind generators long distances over the surface of the earth. Fossil hydrocarbons such as coal, oil, and natural gas can relatively easily be transported in pipelines, train cars, and on ocean going vessels, but electricity generated from wind and sunlight cannot be transported by these methods. Such long distance electricity grids represent a very large infrastructure investment which would require unprecedented levels of international economic and political cooperation to bring to fruition.
Renewable Energy World recent published an article about representatives from Japan, China, Korea, and Russia signing a memorandum of understanding (MOU) to conduct technical and economic feasibility studies about creating an electrical grid which would allow large amounts of wind and solar energy to be transmitted between countries in the region of northeast Asia. This MOU arose out of the efforts of Masayoshi Son, a founder, chairman, and chief executive officer (CEO) of Softbank Group, a Japanese multinational telecommunications and internet corporation, who was energized by the Fukushima disaster in Japan to seek for carbon free energy alternatives to nuclear fission.
Whether or not the idea of distributing renewable energy over large geographical areas can be economically effective is not clear. High voltage DC transmission lines can transmit power of long distances with losses of 5% per 2000km and so is a feasible technology for Mongolia to southern China power transmission (The distance from Ulaan Baatar to Hong Kong is 2900km). However, a lot of physical and economic modeling will be required before anyone can be convinced to invest in such a huge transnational infrastructure project. The recent MOU is the first step down the road towards such modeling.
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.