Power Grid of the Future Saves Energy

Cars and trucks race down the highway, turn off into town, wait at traffic lights and move slowly through side streets. Electricity flows in a similar way -- from the power plant via high voltage lines to transformer substations. The flow is controlled as if by traffic lights. Cables then take the electricity into the city centre. Numerous switching points reduce the voltage, so that equipment can tap into the electricity at low voltage. Thanks to this highly complex infrastructure, the electricity customer can use all kinds of electrical devices just by switching them on.

"A reliable power supply is the key to all this, and major changes will take place in the coming years to safeguard this reliability. The transport and power networks will grow together more strongly as a result of electromobility, because electric vehicles will not only tank up on electricity but will also make their batteries available to the power grid as storage devices. Renewable energy sources will become available on a wider scale, with individual households also contributing electricity they have generated," says Professor Lothar Frey, Director of the Fraunhofer Institute for Integrated Systems and Device Technology IISB in Erlangen.

In major projects such as Desertec, solar thermal power plants in sun-rich regions of North Africa and the Middle East will in the future produce electricity for Europe. The energy will then flow to the consumer via long high-voltage power lines or undersea cables. The existing cables, systems and components need to be adapted to the future energy mix now, so that the electricity will get to the consumer as reliably and with as few losses as possible. The power electronics experts at the IISB are working on technological solutions, and are developing components for the efficient conversion of electrical energy.

For energy transmission over distances of more than 500 kilometers or for undersea cables direct current is being increasingly used. This possesses a constant voltage and only loses up to seven percent of its energy over long distances. By comparison, the loss rate for alternating current can reach 40 percent. Additional converter stations are, however, required to convert the high voltage of the direct current into the alternating current needed by the consumer.

"In cooperation with Siemens Energy we are developing high-power switches. These are necessary for transmitting the direct voltage in the power grid and are crucial for projects like Desertec. The switches have to be more reliable, more scaleable and more versatile than previous solutions in order to meet the requirements of future energy supply networks," says Dipl.-Ing. Markus Billmann from the IISB. To this end, the research scientists are using low-cost semiconductor cells which with previous switching techniques could not be used for high-voltage direct-current transmission (HVDCT).

"At each end of a HVDCT system there is a converter station," explains the research scientist."For the converters we use interruptible devices which can be operated at higher switching frequencies, resulting in smaller systems that are easier to control." A major challenge is to protect the cells from damage. Each converter station will contain about 5,000 modules, connected in series, and if more than a few of them failed at the same time and affected their neighboring modules a chain reaction could be triggered which would destroy the entire station."We have now solved this problem. With our cooperation partners we are working on tailor-made materials and components so that in future the equipment will need less energy," says Billmann.

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Manufacturing 'Made to Measure' Atomic-Scale Electrodes

Results were published in the journalNature Nanotechnology.

One of the key problems in nanotechnology is the formation of electrical contacts at an atomic scale. This demands the detailed characterisation of the current flowing through extremely small circuits– so small that their components can be individual atoms or molecules. It is precisely this miniature nature of the system, of typically nanometric dimensions (1 metro = a thousand million nanometers), where the difficulty of this yet unresolved problem arises. In particular, in unions formed by a single molecule, it has been shown that the number of individual atoms making up the contact and their positions are crucial when determining the electric current that is flowing. To date, there has been no experiment where it has been possible to control these parameters with sufficient precision.

In the research published in theNature Nanotechnologyjournal, however, these scientists have revealed and explained the changes that the electric current flowing through a molecular union (metal/molecule/metal) undergoes, depending on the area of contact uniting the molecule to the metallic electrodes. Basically, changing the number of atoms in contact with the molecule, one by one, it goes from a low state (bad contact) to another, higher one (good contact) of conduction. With bad contact the current is limited by the area of contact, while with good contact the current is limited by the intrinsic properties of the molecule.

Taking part in this collaboration project were scientists from the Donostia International Physics Center (DIPC), from the Physics of Materials Centre at the CSIC-University of the Basque Country (UPV/EHU) Mixed Centre and from the Department of the Physics of Materials at the Chemistry Faculty of the UPV/EHU.

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More Efficient Polymer Solar Cells Fabricated

"Our technology efficiently utilizes the light trapping scheme," said Sumit Chaudhary, an Iowa State assistant professor of electrical and computer engineering and an associate of the U.S. Department of Energy's Ames Laboratory."And so solar cell efficiency improved by 20 percent."

Details of the fabrication technology were recently published online by the journalAdvanced Materials.

Chaudhary said the key to improving the performance of solar cells made from flexible, lightweight and easy-to-manufacture polymers was to find a textured substrate pattern that allowed deposition of a light-absorbing layer that's uniformly thin -- even as it goes up and down flat-topped ridges that are less than a millionth of a meter high.

The result is a polymer solar cell that captures more light within those ridges -- including light that's reflected from one ridge to another, he said. The cell is also able to maintain the good electrical transport properties of a thin, uniform light-absorbing layer.

Tests indicated the research team's light-trapping cells increased power conversion efficiency by 20 percent over flat solar cells made from polymers, Chaudhary said. Tests also indicated that light captured at the red/near infrared band edge increased by 100 percent over flat cells.

Researchers working with Chaudhary on the solar cell project are Kai-Ming Ho, an Iowa State Distinguished Professor of Physics and Astronomy and an Ames Laboratory faculty scientist; Joong-Mok Park, an assistant scientist with the Ames Laboratory; and Kanwar Singh Nalwa, a graduate student in electrical and computer engineering and a student associate of the Ames Laboratory. The research was supported by the Iowa Power Fund, the Ames Laboratory and the Department of Energy's Office of Basic Energy Sciences.

The idea of boosting the performance of polymer solar cells by using a textured substrate is not a new one, Chaudhary said. The technology is commonly used in traditional, silicon-based solar cells.

But previous attempts to use textured substrates in polymer solar cells have failed because they require extra processing steps or technically challenging coating technologies. Some attempts produced a light-absorbing layer with air gaps or a too-thin layer over the ridges or a too-thick layer over the valleys. The result was a loss of charges and short circuiting at the valleys and ridges, resulting in poor solar cell performance.

But, get the substrate texture and the solution-based coating just right,"and we're getting more power out," Nalwa said.

The Iowa State University Research Foundation Inc. has filed a patent for the substrate and coating technology and is working to license the technology to solar cell manufacturers.

"This may be an old idea we're using," Chaudhary said,"but it's never before been successfully implemented in polymer solar cells."

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Methane-Powered Laptops? Materials Scientists Unveil Tiny, Low-Temperature Methane Fuel Cells

With advances in nanostructured devices, lower operating temperatures, and the use of an abundant fuel source and cheaper materials, a group of researchers led by Shriram Ramanathan at the Harvard School of Engineering and Applied Sciences (SEAS) are increasingly optimistic about the commercial viability of the technology.

Ramanathan, an expert and innovator in the development of solid-oxide fuel cells (SOFCs), says they may, in fact, soon become the go-to technology for those on the go.

Electrochemical fuel cells have long been viewed as a potential eco-friendly alternative to fossil fuels -- especially as most SOFCs leave behind little more than water as waste.

The obstacles to using SOFCs to charge laptops and phones or drive the next generation of cars and trucks have remained reliability, temperature, and cost.

Fuel cells operate by converting chemical energy (from hydrogen or a hydrocarbon fuel such as methane) into an electric current. Oxygen ions travel from the cathode through the electrolyte toward the anode, where they oxidize the fuel to produce a current of electrons back toward the cathode.

That may seem simple enough in principle, but until now, SOFCs have been more suited for the laboratory rather than the office or garage. In two studies appearing in theJournal of Power Sourcesthis month, Ramanathan's team reported several critical advances in SOFC technology that may quicken their pace to market.

In the first paper, Ramanathan's group demonstrated stable and functional all-ceramic thin-film SOFCs that do not contain any platinum.

In thin-film SOFCs, the electrolyte is reduced to a hundredth or even a thousandth of its usual scale, using densely packed layers of special ceramic films, each just nanometers in thickness. These micro-SOFCs usually incorporate platinum electrodes, but they can be expensive and unreliable.

"If you use porous metal electrodes," explains Ramanathan,"they tend to be inherently unstable over long periods of time. They start to agglomerate and create open circuits in the fuel cells."

Ramanathan's platinum-free micro-SOFC eliminates this problem, resulting in a win-win: lower cost and higher reliability.

In a second paper published this month, the team demonstrated a methane-fueled micro-SOFC operating at less than 500° Celsius, a feat that is relatively rare in the field.

Traditional SOFCs have been operating at about 800-1000°C, but such high temperatures are only practical for stationary power generation. In short, using them to power up a smartphone mid-commute is not feasible.

In recent years, materials scientists have been working to reduce the required operating temperature to about 300-500°C, a range Ramanathan calls the"sweet spot."

Moreover, when fuel cells operate at lower temperatures, material reliability is less critical -- allowing, for example, the use of less expensive ceramics and metallic interconnects -- and the start-up time can be shorter.

"Low temperature is a holy grail in this field," says Ramanathan."If you can realize high-performance solid-oxide fuel cells that operate in the 300-500°C range, you can use them in transportation vehicles and portable electronics, and with different types of fuels."

The use of methane, an abundant and cheap natural gas, in the team's SOFC was also of note. Until recently, hydrogen has been the primary fuel for SOFCs. Pure hydrogen, however, requires a greater amount of processing.

"It's expensive to make pure hydrogen," says Ramanathan,"and that severely limits the range of applications."

As methane begins to take over as the fuel of choice, the advances in temperature, reliability, and affordability should continue to reinforce each other.

"Future research at SEAS will explore new types of catalysts for methane SOFCs, with the goal of identifying affordable, earth-abundant materials that can help lower the operating temperature even further," adds Ramanathan.

Fuel cell research at SEAS is funded by the same NSF grant that enabled the"Robobees" project led by Robert J. Wood, Assistant Professor of Electrical Engineering. Wood and Ramanathan hope that micro-SOFCs will provide the tiny power source necessary to get the flying robots off the ground.

Ramanathan's co-authors on the papers were Bo Kuai Lai, a Research Associate at SEAS, and Ph.D. candidate Kian Kerman '14.

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Synthetic Breath to Test Breathalyzers

This is because the"synthetic breath" -- which helps to thoroughly test each newly developed evidential breath analyser in approval procedures at the Physikalisch-Technische Bundesanstalt (PTB) -- can now be produced even more precisely. The newly developed generator can also be used to produce gas mixtures with other components, for instance, acetone or carbon dioxide, to calibrate appropriate sensors.

Since 1998, evidential breath analyzers have been permitted for use in alcohol tests carried out by the police in road traffic. In Germany, they are an essential part of legal metrology and require a type approval from PTB before being used. For these tests, calibration gas mixtures are produced in PTB, which simulate the breath of a person who is under the influence of alcohol. The gas mixtures consist of air, water and ethanol in a precisely known composition and -- to date -- had been produced by the usual international saturation method. Here, an air stream is passed through an ethanol-water solution and enriched with ethanol and water until it is saturated. The concentration of ethanol in the gas stream is calculated via distribution coefficients which were determined empirically. In the literature, however, various values are to be found for them.

With the new generator developed at PTB, the gas mixtures can be produced in a dynamic-gravimetric way. The core of the generator is a weighing system with which the mass flows of ethanol and water are determined by the quasi-continuous weighing of the storage containers. The air is dosed via thermal mass flow controllers. The liquid components ethanol and water are injected into the carrier gas flow made of synthetic air and vaporize there completely. As the mass flows of the components are determined individually before mixing, the composition of the gas mixture can be traced directly back to the SI base unit of mass, the kilogram. The use of empirical values from the literature is, thus, no long necessary.

The measurement uncertainty of the ethanol concentration in the gas mixture of the new generator was clearly reduced in comparison to the saturation method.

In the future, the generator can also be used to produce gas mixtures with other components e.g. acetone or carbon dioxide, to calibrate other types of sensors.

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Declining Energy Quality Could Be Root Cause of Current Recession, Expert Suggests

Many economists have pointed to a bursting real estate bubble as the initial trigger for the current recession, which in turn caused global investments in U.S. real estate to turn sour and drag down the global economy. King suggests the real estate bubble burst because individuals were forced to pay a higher and higher percentage of their income for energy -- including electricity, gasoline and heating oil -- leaving less money for their home mortgages.

In economic terms, the quality of the nation's energy supply is referred to as Energy Return on Energy Investment (EROI). For example, if an oil company uses a 10th of a barrel of oil to drill, pump, transport and refine one barrel of oil, the EROI for the refined fuel is 10.

"Many economists don't think of energy as being a limiting factor to economic growth," says King, a research associate in the university's Center for International Energy and Environmental Policy."They think continual improvements in technology and efficiency have completely decoupled the two factors. My research is part of a growing body of evidence that says that's just not true. Energy still plays a big role."

In a paper published this November in the journalEnvironmental Research Letters, King introduced a new way to measure energy quality, the Energy Intensity Ratio (EIR), that is easier to calculate, highly correlated to EROI and in some ways more powerful than EROI. EIR measures how much profit is obtained by energy consumers relative to energy producers. The higher the EIR, the more economic value consumers (including businesses, governments and people) get from their energy.

When King plots EIR for various fuels every year since World War II, the graphs indicate two large declines, one before the recessions of the mid-1970s and early 1980s and the other during the 2000s, leading up to the current economic recession. There have been other recessions in the U.S. since World War II, but the longest and deepest were preceded by sustained declines in EIR for all fossil fuels.

EIR is proportional to EROI, meaning they rise and fall together, but the basic data behind the EIR calculations come out annually as opposed to every five years for EROI. EIR also gives insight into different parts of the supply chain such as at the refinery or at the gas pump, which are harder to study with EROI.

King's analysis suggests if EIR falls below a certain threshold, the economy stops growing. For example, in 1972, EIR for gasoline was 5.9 and in 2008 it was 5.5. During times of robust economic growth, such as the 1990s, EIR for gasoline was well over eight. Compare that to some estimates of EROI and EIR for corn ethanol of around one, and it's clear why corn ethanol has been widely criticized as a low quality energy source.

To get the U.S. economy growing again, King says Americans will have to produce and use energy more efficiently. That's essentially what the U.S. did after the last energy crisis by raising fuel efficiency standards for cars, increasing use of natural gas for electric power generation and developing new technologies such as Enhanced Oil Recovery to coax more oil out of the ground.

"If we aren't fundamentally changing the way we produce or consume energy now, don't expect the economy to grow as much as the past two decades," he says.

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