Graduate Students 2017 Solar Nexus Annual Meeting

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Future-Proofing the Power Grid

May 1, 2017 Featured Articles, MainFeature

Boosting the Efficiency of Concentrated Solar Power Systems

Dale Karas carefully works with chemicals in a lab
Graduate student researcher Dale E. Karas qualitatively compares coated substrates to precursor nano-powders.
–C. Jose Photo

Boosting the Efficiency of Concentrated Solar Power Systems

NEXUS scientists develop new nanomaterial coatings to help absorb and reflect the sun’s rays

By Jane Palmer
May 2017

Concentrated solar power (CSP) systems represent one of two major technologies of solar power generation and provide an affordable and sustainable source of renewable energy in the state of Nevada and beyond.
Ivanpah Solar Plant

For a CSP system such as the Ivanpah Solar Plant, a mirror array collectively concentrates the Sun’s energy onto a large receiver system that operates at extremely high temperatures. –E. Marti Photo

Many CSP research design models involve a complex array of mirrors, a solar receiver and a power block. The mirrors direct and focus incident sunlight onto a solar receiver, which consists of an array of metal tubes coated with light absorbing materials. Once this solar heat is collected by the receivers a heat transfer fluid flowing along the tube transfers it to a large tank containing molten salts. This tank “contains” the thermal energy, which is then used to drive traditional steam turbines or engines that create electricity.

Due to the lower costs associated with installing CSP incorporated with energy storage systems, they can prove advantageous over the use of photovoltaic (PV) solar cells. CSP systems’ innovative new approach involves retrofitting older power plant installations that lack renewable technologies. In addition, CSP systems are easier to maintain, and, even more importantly, power can be stored in a cost-effective storage system and therefore continuously generated during nighttime conditions.
“We can store the energy harvested from the sun during the daytime,” says NEXUS scientist Dr. Jaeyun Moon of the Center for Energy Research (CER) and Energy & Environmental Materials Laboratory (EEML) at the University of Nevada, Las Vegas (UNLV). “Then we can continuously generate power from the stored energy through the nighttime or on cloudy days, during moments of solar inactivity.”
Materials science plays an important role in CSP technology. CSP systems use advanced materials on the mirror arrays and solar receiver system to optimize the reflection, concentration, and absorption of the sun’s rays. In their efforts to improve the efficiency of these systems, Moon and UNLV graduate student Dale Karas investigate various techniques devised to limit wasteful heat loss and to maximize the conversion of solar energy into thermal energy. Not only does the team’s research have implications for the field of solar energy, it also aims to significantly reduce the current water needs involved in CSP plant cooling.
“If we increase the efficiency it is another way to reduce the water usage for electricity,” Moon says. “That means we can generate more electricity by using the same amount of water.”

Microscopic Solar Receiver Coatings

Undergraduate student researcher Samuel Tam prepares samples for spectral absorptivity measurements

Undergraduate student researcher Samuel Tam prepares samples for spectral absorptivity measurements. –D. Karas Photo

The team’s goal is to create materials that will optimize the ability to absorb the sun’s rays while minimizing heat loss. To this end, Dr. Moon has investigated the use of special types of nanomaterials that are assembled at elevated temperature and vapor pressures.  Under these extreme conditions the scientists can exert precise control over the way that these materials crystalize and structure themselves.

In particular the team focuses on a special class of materials – mixed inorganic oxides – and how to modify the surfaces of the mirrors. These mixed inorganic oxides can be tailored for specific optical behavior under certain experimental conditions and they prove stable at high temperatures, a feature that allows the CSP system to function more efficiently. In their experiments the scientists have found a coating of these oxides remain stable at higher temperatures and additionally improve the light absorption of the solar receiver.
“Our research introduces optically-tailored nanomaterials that are geometrically- and chemically-tuned for energy-efficient system performance,” Dr. Moon says. “They can contribute improving overall conversion efficiency and substantially reduce costs.”

Simulating Science

In conjunction with their experimental work, the UNLV research team has also developed computer simulations to investigate the optical properties of the materials and how they respond to heat. Industry consultants with expertise in standard optical software codes support the UNLV scientists, ensuring the accuracy of the custom models and methods developed specifically for energy transport calculations. These academic partnerships are motivated by the National Photonics Initiative, a multi-scale research effort that promotes optical technology and manufacturing supporting the renewable energy infrastructure in the southwestern United States.
By combining the experimental and computational approaches, the team hopes to identify materials that can be used to increase CSP system efficiency. “Our optically-tuned nanomaterials contribute to energy-efficient technologies by boosting high-temperature thermocycles, limiting water use, and reducing environmental impacts for power generation at solar sites,” Karas says.
The completed synthesis produces solar absorber coating materials onto testable substrates

The completed synthesis produces solar absorber coating materials onto testable substrates – these mimic their deposition onto a large CSP receiver system (Left).  Scanning electron microscopy image of the absorber coating (Right) –D. Karas Photo

“The question of overall energy efficiency requires not only understanding the properties and response of materials,” Karas says. “We must be cognizant of their operation in a total CSP system workflow: Do certain precursor chemicals require a significant amount of energy to manufacture, and could this be limited in our materials? Have we thoroughly accounted for potential toxicology of the materials, to nullify any risk of health concerns or environmental damage? Could we further reduce water usage to save the required energy needed to treat water for other uses in our desert climate?”
Karas credits the collaborations within the Solar Energy-Water-Environmental Nexus program, with helping the team understand, and account for, such considerations in designing the ultimate CSP system. “We are privileged that our contributions help the growing infrastructure and personal welfare of residents here in Nevada,” Karas says.
Undergraduate student researcher Cilla Jose wins first place in a poster competition

Undergraduate student researcher Cilla Jose wins first place in a poster competition for the Southern Nevada Division of the American Chemical Society, highlighting this project in energy-efficient materials science. –E. Marti Photo

Creating the foundation for solar energy research

Jaeyun Moon headshotJaeyun Moon is one of five new faculty hires funded by the NEXUS project. The objective in supporting such positions is to develop expertise within the Nevada System of Higher Education to investigate the confluence of renewable energy, water and the environment and help further the economic development, workforce development and education relating to solar power in the state.
Each institution has committed to continuing the positions beyond the NEXUS funding, which supports the new faculty for two years. Moon began work at the University of Nevada, Las Vegas in 2014, having competed her Ph.D. in materials science and engineering from the University of California, San Diego. Moon’s NEXUS research investigates high temperature materials to improve solar power efficiency and reduce water use at solar facilities.
“New faculty stimulate growth within their institution via the development of new laboratories, which always require new graduate research assistants,” says Gayle Dana, Project Director of NEXUS. “A faculty new hire starts a chain reaction beneficial to the university and the state’s economy.”

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Nexus Notes monthly publication
May 2017

NEXUS Notes is a monthly publication of the Solar Nexus Project, which is a five-year research project funded by the National Science Foundation’s Established Program to Stimulate Competitive Research “EPSCoR” (Cooperative Agreement #IIA-1301726) focusing on the nexus of (or linkage between) solar energy generation and Nevada’s limited water resources and fragile environment.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

solarnexus.epscorspo.nevada.edu

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If you would like to know more about the NEXUS project,
please contact, Dr. Gayle Dana
Gayle.Dana@dri.edu
530-414-3170

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