Posts Tagged ‘Oak Ridge National Laboratory’
Wednesday, November 12, 2014 @ 04:11 PM gHale
There are benefits for microgrids, small systems powered by renewables and energy storage devices, to break away from the main grid and working off its own island.
The benefit is microgrids can disconnect from larger utility grids and continue to provide power locally.
“If the microgrid is always connected to the main grid, what’s the point?” Department of Energy and Oak Ridge National Laboratory researcher Yan Xu asked. “If something goes wrong with the main grid, like a dramatic drop in voltage, for example, you may want to disconnect.”
The idea behind microgrids is to not only continue power to local units such as neighborhoods, hospitals or industrial parks, but also improve energy efficiency and reduce cost when connected to the main grid.
Researchers predict an energy future more like a marketplace in which utility customers with access to solar panels, battery packs, plug-in vehicles and other sources of distributed energy can compare energy prices, switch on the best deals and even sell back unused power to utility companies.
However, before interested consumers can plug into their own energy islands, researchers at facilities such as ORNL’s Distributed Energy Control and Communication (DECC) lab need to develop tools for controlling a reliable, safe and efficient microgrid.
To simulate real scenarios where energy would end up used on a microgrid, DECC houses a functional microgrid with a generation capacity of 250 kilowatts (kW) that seamlessly switches on and off the main grid.
This grid includes an energy storage system that generates 25kW of power and uses 50kW hours of energy built from second-use electric vehicle batteries, a 50kW- and a 13.5 kW-solar system and two smart inverters that serve as the grid interfaces for the distributed energy emulators. Programmable load banks that mimic equipment consuming energy on the grid can provide sudden large load changes and second-by-second energy profiles.
“A microgrid should run an automated optimization frequently, about every five to 10 minutes,” Xu said.
To optimize grid operations, microgrid generators, power flow controllers, switches and loads must end up outfitted with sensors and communication links that can provide real-time information to a central communications control.
“Microgrids are not widely deployed yet. Today, functional microgrids are in the R&D phase, and their communications are not standardized,” Xu said. “We want to standardize microgrid communications and systems so they are compatible with the main grid and each other.”
Now two years into the inception of ORNL’s microgrid project — “Complete System-Level Efficient and Interoperable Solution for Microgrid Integrated Controls,” or CSEISMIC — the microgrid test bed at DECC is functional and employs an algorithm developed at ORNL that directs automatic transition on and off ORNL’s main grid.
Xu said the next year will focus on getting the energy management system (EMS) running. The EMS will drive optimization by allowing microgrid components to fluctuate an operation based on parameters such as demand and cost.
“The EMS may, for instance, tell the PVs [solar cells] how much power to generate for the next five to 10 minutes based on the time of day and energy demand,” Xu said.
The CSEISMIC team has long-term goals of partnering with industries to conduct field demonstrations of standardized grid prototypes.
“As soon as microgrids are standardized and easy to integrate into the main grid,” Xu said, “we’ll start seeing them in areas with a high penetration of renewables and high energy prices.”
Friday, April 25, 2014 @ 11:04 AM gHale
Treating cadmium-telluride (CdTe) solar cell materials with cadmium-chloride improves their efficiency, but how that happens remained a mystery – until now.
After an atomic-scale examination of the thin-film solar cells, the light bulb has turned on and this decades-long debate about the materials’ photovoltaic efficiency increase after treatment appears solved.
A research team from led by the Department of Energy’s (DoE) Oak Ridge National Laboratory (ORNL), the University of Toledo and DoE’s National Renewable Energy Laboratory used electron microscopy and computational simulations to explore the physical origins of the unexplained treatment process.
Thin-film CdTe solar cells are a potential rival to silicon-based photovoltaic systems because of their theoretically low cost per power output and ease of fabrication. Their comparatively low historical efficiency in converting sunlight into energy, however, has limited the technology’s widespread use.
Research in the 1980s showed that treating CdTe thin films with cadmium-chloride significantly raises the cell’s efficiency, but scientists have been unable to determine the underlying causes. ORNL’s Chen Li, first author of a study on the subject, said the answer lay in investigating the material at an atomic level.
“We knew that chlorine was responsible for this magical effect, but we needed to find out where it went in the material’s structure,” Li said. “Only by understanding the structure can we understand what’s wrong in this solar cell — why the efficiency is not high enough, and how can we push it further.”
By comparing the solar cells before and after chlorine treatment, the researchers realized atom-scale grain boundaries ended up implicated in the enhanced performance. Grain boundaries are tiny defects that normally act as roadblocks to efficiency, because they inhibit carrier collection which greatly reduces the solar cell power.
Using state of the art electron microscopy techniques to study the thin films’ structure and chemical composition after treatment, the researchers found chlorine atoms replaced tellurium atoms within the grain boundaries. This atomic substitution creates local electric fields at the grain boundaries that boost the material’s photovoltaic performance instead of damaging it.
The research team’s finding, in addition to providing a long-awaited explanation, could help guide engineering of higher-efficiency CdTe solar cells. Controlling the grain boundary structure is a new direction that could help raise the cell efficiencies closer to the theoretical maximum of 32 percent light-to-energy conversion, Li said. Currently, the record CdTe cell efficiency is only 20.4 percent.
“We think that if all the grain boundaries in a thin film material could be aligned in same direction, it could improve cell efficiency even further,” Li said.
Friday, February 21, 2014 @ 09:02 AM gHale
A new suite of computer codes that closely model the behavior of neutrons in a reactor core, called neutronics, could give a more accurate way to analyze nuclear power reactors.
Technical staff at Westinghouse Electric Company, LLC, supported by the research team at the Consortium for Advanced Simulation of Light Water Reactors (CASL), used the Virtual Environment for Reactor Applications core simulator (VERA-CS) to analyze its AP1000 advanced pressurized water reactor (PWR). The testing focused on modeling the startup conditions of the AP1000 plant design.
“In our experience with VERA-CS, we have been impressed by its accuracy in reproducing past reactor startup measurements. These results give us confidence that VERA-CS can be used to anticipate the conditions that will occur during the AP1000 reactor startup operations,” said Bob Oelrich, manager of PWR Core Methods at Westinghouse. “This new modeling capability will allow designers to obtain higher-fidelity power distribution predictions in a reactor core and ultimately further improve reactor performance.”
The AP1000 reactor is an advanced reactor design with enhanced passive that builds on decades of Westinghouse’s experience with PWR design. The first eight units are currently under construction in China and the United States, and represent the first Generation III+ reactor to receive Design Certification from the U.S. Nuclear Regulatory Commission.
CASL is a U.S. Department of Energy (DoE) Innovation Hub established at Oak Ridge National Laboratory (ORNL), a part of DoE’s National Laboratory System. The consortium core partners are a strategic alliance of leaders in nuclear science and engineering from government, industry and academia.
“At CASL, we set out to improve reactor performance with predictive, science-based, simulation technology that harnesses world-class computational power,” said CASL Director Doug Kothe. “Our challenge is to advance research that will allow power uprates and increase fuel burn-up for U.S. nuclear plants. In order to do this, CASL is meeting the need for higher-fidelity, integrated tools.”
During the first generation of nuclear energy, performance and safety margins ended up at conservative levels as industry and researchers gained experience with the operation and maintenance of what was then a new and complex technology. Over the past 50 years, nuclear scientists and engineers gained a deeper understanding of the reactor processes, further characterizing nuclear reactor fuel and structure materials.
By making use of newly available computing resources, CASL’s research aims for a step increase in the improvements in reactor operations that have occurred over the last several decades.
“CASL has been using modern high-performance computing platforms such as ORNL’s Titan, working in concert with the INL Fission computer system, for modeling and simulation at significantly increased levels of detail,” said CASL Chief Computational Scientist John Turner. “However, we also recognized the need to deliver a product that is suitable for industry-sized computing platforms.”
With that understanding, CASL designed the Test Stand project to try out tools such as VERA-CS in industrial applications. CASL partner Westinghouse ended up selected as the host for the first trial run of the new VERA nuclear reactor core simulator (VERA-CS). Westinghouse chose a real-world application for VERA-CS: The reactor physics-analysis of the AP1000 PWR, which features a core design with several advanced features. Using VERA-CS to study the AP1000 provides information to further improve the characterization of advanced cores compared to traditional modeling approaches.
Westinghouse’s test run on VERA-CS focused on modeling one aspect of reactor physics called “neutronics,” which describes the behavior of neutrons in a reactor core. While neutronics is only one of VERA’s capabilities, the results provided by VERA-CS for the AP1000 PWR enhance Westinghouse’s confidence in their startup predictions and expand the validation of VERA by incorporating the latest trends in PWR core design and operational features.
The CASL team now is working on extending the suite of simulation capabilities to the entire range of operating conditions for commercial reactors, including full-power operation with fuel depletion and fuel cycle reload.
Wednesday, November 20, 2013 @ 04:11 PM gHale
By identifying fundamental forces that change plant structures during pretreatment processes used in the production of bioenergy, there may be more effective ways to convert woody plant matter into biofuels.
Pretreatment subjects plant material to extremely high temperature and pressure to break apart the protective gel of lignin and hemicellulose that surrounds sugary cellulose fibers.
“While pretreatments are used to make biomass more convertible, no pretreatment is perfect or complete,” said Department of Energy’s Oak Ridge National Laboratory’s (ORNL) Brian Davison, who was a coauthor of a research study and paper on the subject.
“Whereas the pretreatment can improve biomass digestion, it can also make a portion of the biomass more difficult to convert,” he said. “Our research provides insight into the mechanisms behind this ‘two steps forward, one step back’ process.” Also, pretreatment is the most expensive stage of biofuel production.
The team’s integration of experimental techniques including neutron scattering and X-ray analysis with supercomputer simulations revealed unexpected findings about what happens to water molecules trapped between cellulose fibers.
“As the biomass heats up, the bundle of fibers actually dehydrates — the water that’s in between the fibers gets pushed out,” said ORNL’s Paul Langan. “This is very counterintuitive because you are boiling something in water but simultaneously dehydrating it. It’s a really simple result, but it’s something no one expected.”
This process of dehydration causes the cellulose fibers to move closer together and become more crystalline, which makes them harder to break down.
In a second part of the study, the researchers analyzed the two polymers called lignin and hemicellulose that bond to form a tangled mesh around the cellulose bundles. According to the team’s experimental observations and simulations, the two polymers separate into different phases when heated during pretreatment.
“Lignin is hydrophobic so it repels water, and hemicellulose is hydrophilic, meaning it likes water,” Langan said. “Whenever you have a mixture of two polymers in water, one of which is hydrophilic and one hydrophobic, and you heat it up, they separate out into different phases.”
Understanding the role of these underlying physical factors — dehydration and phase separation — could enable scientists to engineer improved plants and pretreatment processes and ultimately bring down the costs of biofuel production.
“Our insight is that we have to find a balance which avoids cellulose dehydration but allows phase separation,” Langan said. “We know now what we have to achieve — we don’t yet know how that could be done, but we’ve provided clear and specific information to help us get there.”
Wednesday, October 30, 2013 @ 07:10 PM gHale
There could soon be new types of nuclear fuel pellets that would be safer in the event of a nuclear disaster.
New materials could end up encasing uranium-bearing fuel as an alternative to zirconium alloys, which have seen use as the outer layer of nuclear fuel pellets for the last 50 years, said a team of scientists from the University of Tennessee (UT) and Oak Ridge National Laboratory (ORNL), who will present their work at the AVS 60th International Symposium and Exhibition in Long Beach, CA.
Using sophisticated computer analyses, the UT and ORNL team identified the positive impact of several possible materials that exhibit resistance to high-temperature oxidation and failure, on reactor core evolution, thereby buying more time to cope in the event of a nuclear accident.
“At this stage there are several very intriguing options that are being explored,” said Steven J. Zinkle, the Governor’s Chair in the Department of Nuclear Engineering at the University of Tennessee and Oak Ridge National Laboratory. There is evidence that some of the new materials would reduce the oxidation by at least two orders of magnitude.
“That would be a game-changer,” he said. The materials examined include advanced steels, coated molybdenum and nuclear-grade silicon carbide composites (SiC fibers embedded in a SiC matrix).
The next step, he added, involves building actual fuel pins from these laboratory-tested materials and exposing them to irradiation inside a fission reactor. Once they perform as desired, the new fuel concepts would likely end up tested in a limited capacity in commercial reactors to then enable larger deployment possibilities.
Though it would take years before any new fuel concepts end up used commercially, given the rigorous and conservative qualification steps required, Zinkle said, these new materials may eventually replace the existing zirconium alloy cladding if they prove to be safer.
The typical core of a nuclear power plant uses the heat generated by fission of uranium and plutonium in fuel rods to heat and pressurize water. Steam then generates to drive steam turbines for electricity production. Water continuously circulates as a coolant to harness the thermal energy from the fuel and to keep the core from overheating.
The cooling pumps are a critical part of the reactor design because even when a nuclear reactor shuts down, the power it generates from radioactive decay of fission products remains at 1 percent of its peak for hours after shutdown. Given that nuclear power plants generate a staggering sum of energy under their nominal operating conditions (~4 GW of thermal energy), even one percent power levels after shutdown prove substantial. That’s why it’s essential to have cool water circulating continuously even after the shutdown occurs. Otherwise you risk overheating and ultimately melting the core – like leaving a pot boiling on the burner.
That’s basically what happened at Fukushima. On March 11, 2011, engineers at the plant managed to initially safely shut down the plant following a massive earthquake, but then a large tsunami knocked out the backup generators running the water pumps an hour later. What followed were explosions associated with hydrogen generated from the reduction of steam during high temperature oxidation of core materials, and releases of radioactive fission products. The accident displaced the local population and will take years and require a significant cost to clean-up.
Fukushima has had a profound impact on the safety culture of the industry, said Zinkle. Despite the fact that not a single U.S. nuclear power plant was unsafe or shut down in the wake of the accident, the Nuclear Regulatory Commission has issued new requirements to enhance their safety, including increasing the requirements for backup power generation on site.
Monday, August 27, 2012 @ 05:08 PM gHale
Knowing the position of missing oxygen atoms could be the key to cheaper solid oxide fuel cells with longer lifetimes.
That means new microscopy research could enable scientists to map these vacancies at an atomic scale.
Although fuel cells hold promise as an efficient energy conversion technology, they have yet to reach mainstream markets because of their high price tag and limited lifespans.
Overcoming these barriers requires a fundamental understanding of fuel cells, which produce electricity through a chemical reaction between oxygen and a fuel. As conducting oxygen ions move through the fuel cell, they travel through vacancies where oxygen atoms used to be. The distribution, arrangement and geometry of such oxygen vacancies in fuel cell materials should affect the efficiency of the overall device, researchers said.
“A big part of making a better fuel cell is to understand what the oxygen vacancies do inside the material: How fast they move, how they order, how they interact with interfaces and defects,” said Department of Energy’s Oak Ridge National Laboratory’s (ORNL) Albina Borisevich. “The question is how to study them. It’s one thing to see an atom of one type on the background of atoms of a different type. But in this case, you want to see if there are a few atoms missing. Seeing a void is much more difficult.”
ORNL scientists used scanning transmission electron microscopy to determine the distribution of oxygen vacancies in a fuel cell cathode material below the level of a single unit cell. The team verified its findings with theoretical calculations and neutron experiments at the lab’s Spallation Neutron Source.
“Even though the vacancy doesn’t generate any signal in the electron micrograph, it’s still a big disturbance in the structure,” Borisevich said. “You can see that the lattice expands where vacancies are present. So we tracked the lattice expansion around vacancies and compared it with theoretical models, and we were able to develop a calibration for this type of material.”
By providing a means to study vacancies at an atomic scale, the ORNL technique will help inform the development of improved fuel cell technologies in a systematic and deliberate fashion, in contrast to trial and error approaches.
Beyond its relevance to applications in fuel cells and information storage and logic devices, ORNL coauthor Sergei Kalinin said the team’s research is also building a bridge between two scientific communities that traditionally have had little in common.
“From my perspective, it is physics marrying electrochemistry,” Kalinin said. “The idea is that vacancies are important for energy, and vacancies are important for physics. The materials that physicists like to study are exactly the same as the materials used for fuel cells, and unless we understand how vacancies behave at interfaces, ferroic domain walls, and in thin films, we will not be able to fully appreciate the physics of these systems.”