Clearing up cloudy understanding on solar power plant output

Matt Lave (6112) uses pyranometers like these to measure the amount of irradiance, or available sunlight. There are four round pyranometers, capped by small glass domes, on this device. The work by Matt and Josh Stein (6112) shows that the variability of a point sensor is larger than the variability of a PV power plant. (Photo by Dino Vournas)

by Stephanie Hobby

The sun’s abundant energy presents a clean, affordable, and renewable way to keep the power on. Systems are relatively easy to install and begin working immediately. They are virtually maintenance-free and can run unassisted for decades.

But clouds are dimming industry growth: What happens when they cover part of a solar photovoltaic (PV) array and cause a dip in output, how big is the dip, and how can a utility company compensate for it?

Matt Lave (6112) has been working to understand that drawback and determine just how much clouds can affect solar power plant output.

Typically, sunlight is measured using a single irradiance point sensor, which correlates nicely to a single PV panel. But that doesn’t translate to a large PV power plant.

“If a cloud passes over, it might cover one panel, but other panels aren’t affected,” Matt says. “So if you use the single point sensor to represent the variability of the whole power plant, you will significantly overestimate the variability.”

To get a more accurate picture of how clouds affect PV power plants, Matt developed a Wavelet Variability Model, or WVM, to use data from a point sensor and scale it up to accurately represent the entire power plant. The WVM uses measurements from an irradiance point sensor, the power plant footprint — or the arrangement and number of PV modules in the plant — and the daily local cloud speed to estimate the output of a power plant.

In many cases, output measurements from the power plant aren’t available, but point sensor data is, so the WVM is useful for estimating how much energy must be stored to make up for cloud-caused fluctuations.

The variability is a concern for grid operators as unanticipated changes in PV plant output can strain the electric grid. At short timescales, measured in seconds, sharp changes in power output from a PV power plant can cause local voltage to flicker. At longer timescales, measured in minutes, producing less PV power than expected produces balancing and frequency issues, where load can exceed generation. Backup systems (such as battery storage) to mitigate the variability can substantially add to the cost of a PV power plant.

He points to Puerto Rico, where changes in power output are required to be less than 10 percent per minute. “With this tool, you can estimate how often you’ll exceed that limit, and determine how to mitigate those effects.”

Matt and Josh Stein (6112) teamed with researchers from University of California at San Diego, where Matt did graduate work, and recently published a book chapter in Solar Energy Forecasting and Resource Assessment. The chapter, “Quantifying and Simulating Solar-Plant Variability using Irradiance Data,” offers metrics to characterize and simulate the variability of solar power plant output.

This work supports the DOE SunShot vision of reducing solar costs and greatly increasing how much solar energy goes to the electric grid. By helping grid operators solve variable short-term power generation problems, Matt says utilities will be more likely to increase their solar energy portfolios.

 “Essentially, there has been something of a problem in the industry with people assuming that the point sensor’s variability represents their whole plant’s variability, and significantly overestimating the problems that would be caused by connecting PV to the electric grid. That’s something I hope to help people understand. It’s not going to be as big of a problem as it would seem from an irradiance point sensor,” Matt says.


-- Stephanie Hobby

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Agreement lets Sandia, UNM staff work side-by-side

Julia Phillips, Sandia Acting Div. 7000 VP and chief technology officer, and UNM Provost Chaouki Abdallah shake hands after signing the Inter-Institutional Visitors Agreement allowing closer research collaboration.  (Photo by Randy Montoya)

by nancy Salem

Sandia has launched a new kind of collaboration designed to strengthen research bonds between the Labs and the University of New Mexico.

“This is another sign of the close and deepening partnership between two of the pre-eminent research institutions in the state,” Acting Div. 7000 VP and Chief Technology Officer Julia Phillips said at the Jan. 17 signing of the Inter-Institutional Visitor Agreement (IVA). “It enables Sandia to provide access to unique capabilities we have to further the research agenda of UNM. And Sandia has the opportunity to engage with the fine researchers at the university — professors and students. I am delighted.”

Julia signed the agreement with UNM Provost Chaouki Abdallah, who said it will further the missions of the university and Sandia through strategic partnership. “We will leverage our respective strengths and maximize our respective resources,” he said. “New Mexico and the nation will be well served by UNM and Sandia sharing facilities, equipment, and talent. UNM appreciates the significance of this pact and Sandia’s support of our faculty and students.”

An IVA allows Sandia to work collaboratively with academic and research institutions without having to put in place a Cooperative Research & Development Agreement (CRADA), which typically requires a private industrial partner to commercialize the work, says Vic Weiss (10679), who helped negotiate the agreement. “Sometimes we just want to do research with a university, to push the frontiers of science and make discoveries,” he says. “An IVA is an instrument that lets that happen.”

 The IVA signed in January will allow UNM staff to irradiate material samples at the Annular Core Research Reactor and the Gamma Irradiation Facility in Tech Area 5. The university researchers want to predict sample response to experimental conditions like those at the Large Hadron Collider in Geneva, Switzerland, which is being upgraded. 

Matt Burger, senior manager in Nuclear Facilities and Applied Technology Dept. 1380, says UNM and Sandia will benefit from the collaborative research. “We have a large contingent of staff in Division 1000 looking at radiation effects on materials and electronics,” says Matt, who worked on the agreement with Paul Raglin (1210). “We will share data back and forth. I’m very excited about this collaboration.”

Vic says a condition of an IVA is that the research should closely align with Sandia’s mission. “We have to be trying to solve some engineering or scientific research issue that aligns with our mission and the university’s,” he says. “We want to be able to work with academic and research institutions to leverage our knowledge and expertise in trying to solve some of these more challenging scientific and engineering issues.”

Matt says the agreement will give UNM students access to facilities with capabilities beyond what is available on campus. “It provides a platform for collaborative investigation into radiation effects sciences, which is important to the organization I work for,” he says.

UNM Vice President for Research Mike Dougher said the agreement is a “big step forward because, bottom line, it is the scientist-to-scientist collaborations that are critical to our long-term collaborative success.”

“Previously when UNM and Sandia researchers wanted to collaborate, UNM had to use a project-specific contract to have Sandia staff run the experiments,” he said at the signing. “With this agreement, Sandia technical staff can collaborate directly with UNM researchers and run the experiments together.”

Julia said the IVA will be a model for potential further collaboration between Sandia and UNM. “This could be the first of many with UNM and other institutions,” she said. “It opens the door for academic research institutions to work with Sandia and push the frontiers of science.”


-- nancy Salem

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Sandia helps bring life-saving vaccines to far reaches of the world

Physical chemist Eric Coker (1815), left, looks over shipping containers developed by Santa Fe businessman Bruce McCormick, right, that safely transport and store temperature-sensitive vaccines and biopharmaceuticals. Eric helped McCormick create a solar thermal icemaker to provide cooling for the containers. They worked together through the New Mexico Small Business Assistance Program.         (Photo by Randy Montoya)

by Nancy Salem

Like people, vaccines don’t do well when it’s too hot or too cold. The life-saving biopharmaceuticals can perish if their temperature shifts a few degrees.

That fragility presents a challenge when the people who need vaccines live off the beaten path.  “The vast majority of the world’s population lives in areas where electricity and refrigeration are not reliable,” says Bruce McCormick, president of SAVSU Technologies of Santa Fe. “It is difficult to get vaccines to these areas. We’re talking several billion people.”

McCormick, an inventor, knew of the obstacles in vaccine distribution in developing countries. Vaccines and other biologic materials such as blood, tissue, genes, stem cells, and proteins are made of living organisms that degrade at warmer temperatures until no longer effective. A bigger danger is freezing. “Seventeen to 39 percent of all vaccines are exposed to freezing temperatures through improper storage, and it kills them,” he says.

With technical help from Sandia through the New Mexico Small Business Assistance Program (NMSBA), McCormick has developed a solar thermal icemaker to provide cooling for high-performance shipping containers that safely transport and store temperature-sensitive vaccines and biopharmaceuticals. Thousands of the systems are being used throughout the world, and McCormick has signed a distribution agreement for an expanded line of products.

“We are committed to extending the reach of life-saving materials for research and treatment to humans around the world,” he says.

Good intentions

Vaccines are often transported to remote places in coolers not powered by electricity or fuel, but using some form of ice. For most vaccines, the temperature must stay between 2 and 8 degrees Celsius (36 and 46 Fahrenheit).

“Inadvertent freezing is the result of good intentions,” McCormick says. “The vaccines are in a cooler going from point A to point B. Ice is the primary means of thermal storage, and the feeling is that more is better. The vaccines end up freezing.”

Transportation is hard to manage, and the range of vaccine distribution is limited by how long a cooler can maintain the proper temperature. “If you have a cooler that can keep the vaccine alive for 24 hours, that’s how long you have to load, bring it to the village, community, or health care center, and administer,” McCormick says. “As a result there are complicated logistics in moving the vaccines from, for example, a national distribution facility where they have reliable electricity to a remote clinic. But they have to get there. It’s referred to as the last mile.”

About five years ago, the Program for Applied Technology in Health (PATH), a Seattle-based non-governmental organization (NGO) that promotes new technology in the world health community, issued a challenge to industry to improve vaccine transport. McCormick had experience building insulated products and working with nanoporous materials.

He formed SAVSU (State of the Art Vaccine Storage Unit), teamed with a company that does industrial coatings, put together a prototype — and won the challenge.

“With that I needed to start working to commercialize it,” McCormick says.

A failsafe system

 His first container, the NanoQ, is a box that holds separate cases for ice and the payload, designed with super-insulating materials that allow low levels of heat transfer. It stores vaccines in hot environments for up to 10 days. A thermal buffer keeps the contents from inadvertently freezing.

The system uses ice because it goes to places where there are no special resources and water is common. “It’s simple to operate. People don’t need to be trained,” McCormick says. “We don’t want to limit the reach of the technology.”

PATH asked if the box could store medicines longer than 10 days if the ice was swapped out. Replacing the ice would require refrigeration in areas where electricity is unreliable. “Even in big cities there are power outages,” McCormick says. “The power went out for a weekend in a city in Mexico and all the vaccines in refrigerators in a district health center were destroyed. This is a fairly common occurrence around the world. You have to have power running 24/7 with no interruption when you use standard refrigeration systems.”

McCormick turned to NMSBA, which pairs entrepreneurs with scientists at Sandia and Los Alamos national laboratories. The state-funded program was established in 2000 by the New Mexico Legislature to help small businesses get technical support from the labs. It has provided $39 million in assistance to 2,195 companies in 33 counties. The help is free of charge to the business.

The challenge was to make the NanoQ a long-term storage device instead of just a transportation container. Ice would have to be made in the field. “I found information about a large solar icemaker made at Sandia in the 1980s using a refrigeration technology called adsorption,” McCormick says. “I wanted to find one of the original engineers who worked on the project.”

They had retired and the project was defunct, but through NMSBA McCormick was paired in 2011 with Sandia engineer Brian Iverson, who found an old version of the solar icemaker at the Labs. Brian took it apart, studied the design and the notes of the original team, and set about making a better one using new technology.

“Bruce needed a passively driven refrigeration system,” says Brian, now a professor at Brigham Young University. “I started digging into who had worked on the project, what the system’s components were made of, and the process by which ice is made using solar energy.”

Physical chemist Eric Coker (1815) joined the project. “Brian did the engineering and I took his recommendations and applied chemical knowledge to fill in the design gaps,” Eric says. “I researched what would be a good adsorbent and adsorbate to make it work at the scale Bruce needed. It had to be portable and completely off grid with the only inputs being sunlight and water.”

Eric and Brian delivered a workable design. The icemaker has a one-meter-square solar collection area, a condenser, and evaporator. Thermal energy is collected, and the heat drives a fluid, in this case methanol, out of a porous carbon material.

The fluid moves by gravity to the condenser where it liquefies. At night, when heat is no longer driving fluid off the carbon, the condensed liquid evaporates and the gas is absorbed back into the carbon, drawing heat from the environment. That reaction has a cooling effect that freezes water in a trough, creating from 2 to 12 pounds of ice a day.

“It needs no electricity or photovoltaic cells. It’s a refrigeration cycle,” Brian says. “Bruce did not want expensive components such as a PV cell.”

McCormick says the icemaker is key to SAVSU’s ability to offer the NanoQ to international agencies as a permanent replacement for expensive and impractical refrigeration systems. “They go together,” he says.

‘A good feeling’

McCormick says the collaboration with Eric and Brian was a high point of the SAVSU journey. “It was great,” he says. “On a personal level, it’s fun to brainstorm with people who have more knowledge than I do in the field of solar thermal energy, to be able to really explore possibilities and new ideas. You don’t always know where you’re going to land but you can create a project in a way that you’re open to exploring what seem to be interesting channels. We have the best design possible.”

McCormick has developed two other products, the CryoQ, for materials that need to be shipped at deep-frozen temperatures, and the PHD, for small-volume shipments. SAVSU products transport and store all kinds of biomaterials and other regenerative products used to treat disease.

The World Health Organization (WHO) Performance, Quality and Safety (PQS) system recently created a new specification for a 10-day storage container such as the NanoQ. Organizations such as UNICEF and the Gates Foundation that fund vaccination programs require the products to be approved by the WHO PQS.

In addition to producing the NanoQ for global health needs, SAVSU recently entered into an agreement with BioLife Solutions for distribution of the PHD and CryoQ products into the stem cell and regenerative medicine markets.

Eric, who has been at Sandia 13 years, says it was exciting to work on a project that so clearly saves lives around the world. “It’s a really good feeling,” he says. “It’s very gratifying to think the work I did could help people in Third World countries receive vaccines that are still in good shape.”

The NanoQ is being used at community health centers in Asia, Africa, and Latin America. “We’ve seen it work,” says McCormick, whose collaboration with Sandia won an NMSBA Innovation Award in 2011. “The purpose of the boxes is to assure that vaccines are available at the community level when outbreaks occur. The NanoQ coupled with the solar thermal icemaker is a game changer in how vaccines are stored and distributed in developing countries.”


-- Nancy Salem

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