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Microgrids: So Much More than Backup Energy

August 24, 2012

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While very reliable today, the U.S. electricity grid is old and has gone at least five decades without a significant technological upgrade. There are two prongs to the microgrid work at NREL: innovative research and partnering with industry.
Credit: Dennis Schroeder

Most Americans don't have to think much about energy reliability. We plug in a computer and it powers up; we flip a switch and the lights come on.

While very reliable today, the U.S. electricity grid is old and has gone at least five decades without a significant technological upgrade. The U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL) is working with industry on one solution to help maintain a secure, reliable flow of energy: microgrids.

A microgrid is a smaller power grid that can operate either by itself or connected to a larger utility grid. Microgrids can serve areas as small as a few houses, all the way up to large military installations.

"If your home was part of a microgrid, you could continue to receive power even when the utility power goes out," NREL Electrical Engineer Mariko Shirazi said. "It gives you the ability to ride through any disturbances or outages by seamlessly switching over to locally generated power."

It's important to note that a backup power system — like a diesel generator — is not the same as a microgrid. Backup generators supply power to local loads in the event of an outage, but there is usually a delay or blip when you lose power and disconnect from the utility grid before the backup kicks in. In addition, a backup system is never meant to run continuously, nor to put power into the grid. However, the reverse is true — a microgrid can serve as a backup power supply.

A microgrid senses the quality of the power flowing through the grid. In the event of an outage, it can disconnect from the grid at a moment's notice. It can also leverage solar, wind, or stored energy to supplement a dip in the current power supply. If things are running smoothly with the regional grid, a microgrid generating electricity from renewable sources can export that clean energy to the grid for everyone's use.

Just Connect and Go?

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As part of its microgrid research, NREL recently worked with the Sacramento Municipal Utility District to test microgrid-ready natural-gas generators at the Distributed Energy Resources Test Facility.
Credit: Connie Komomua

The major components of a microgrid include a source of power generation, local loads, and electrical switching gear. It might also include inverters and energy storage — all of which sounds easy enough to just connect up to get started, right?

"These technologies are in different stages of maturity; the challenge is to get them all to operate together in a stable, concerted way to accomplish the goals of efficiency, security, and energy reliability — all of which are required from a microgrid," NREL Electrical Engineer Greg Martin said.

There are two prongs to the microgrid work at NREL: innovative research and partnering with industry.

NREL works with industry to test microgrid systems by providing the experts as well as the infrastructure to support microgrid testing. The U.S. Department of Defense is also working with NREL researchers to examine using microgrids to improve base reliability. Testing includes using grid simulators, load banks, and generators, all currently at theDistributed Energy Resources Test Facility at the National Wind Technology Center near Boulder, Colorado.

"We use equipment such as a grid simulator to create a virtual electric grid to test equipment that is planned to be connected to a utility," Martin said. "We create outages, or some other kind of electrical phenomenon, to make sure the equipment operates as expected. We basically try to make stuff work while making sure it works the way it's supposed to."

"Utilities need to be shown that this technology is safe to integrate into the system and won't affect the normal operations," NREL Energy Systems Integration Director Ben Kroposki said. "One of the goals at NREL is to provide that test bed for a variety of scenarios to be run so that utilities can see that the risk is being reduced."

An example: take a 200-kilowatt microgrid in a residential area with 100 kilowatts of photovoltaics (PV) installed on homes. When all the homes are grid-connected through a local utility, those 100 kilowatts of PV are no big deal. But once the homes are disconnected from the grid, that's a high ratio of PV. Researchers work with industry to figure out which resources have to be maintained to keep the power reliability needed for critical loads. Key questions include, should the homes start shedding loads if a cloud crosses the sun and the PV power drops? Or is energy storage needed, so when a cloud comes, the power supply stays consistent?

NREL is leading the way in understanding issues in energy systems integration and helping industry work through them. The lab's research tools will get a boost when the Energy Systems Integration Facility (ESIF) is completed later this year.

Taking Research to the Next Level

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NREL is leading the way in understanding issues in energy systems integration and helping industry work through them. The lab's research tools will get a boost when the Energy Systems Integration Facility is completed later this year.
Credit: Dennis Schroeder

"ESIF is going to be like our current lab on steroids, and will expand our testing scale to 1 megawatt," Martin said. "We'll be able to test large single components like large utility-scale inverters. We'll also be able to scale up the complexity of our testing. Using the Research Electrical Distribution Bus [REDB], and hardware-in-the loop, we'll be able to connect dozens of sources and loads and be able to test their interactions with each other. Now, we collect single data points. At ESIF, we'll be able to collect high-speed, time-synchronized data at numerous points throughout the REDB."

Using a high-performance computing data center, NREL will be able to simulate entire distribution systems. When testing a microgrid system, engineers can monitor its voltages and frequencies at the point where it joins the distribution system, enabling them to simulate the effect of a microgrid on the larger utility. This is important, because being physically connected to the grid is often not practical — plus, the utility doesn't have to worry about putting an unproven technology on their system.

"Utilities see this as a growth area, and they would like to understand it," Shirazi said. "Even if they aren't implementing a microgrid themselves, they may want to understand how it works for those customers who do want to install one on a section of their distribution system. Working with NREL helps them implement this type of system without impacting their customers."

NREL's grid simulators make this testing possible without hooking up the equipment to the regional utility grid — which would be prohibitively tricky. First, researchers would need the foresight to know when voltage anomalies were going to happen, and assuming they could catch them, there would be only one chance to test equipment. With grid simulators, researchers can create voltage and frequency anomalies and see how the system behaves.

"ESIF is going to give us more research power, both in the actual electrical power but also in the ability to collect data across all points in the system," Martin said. "It will also offer really awesome visualization that will enable us to look at data coming in from different places, to look at simulations and video feeds, in a really nice, easy, big way. We're sure this visualization capability will help ignite collaborations among NREL, industry, utilities, academia, and government agencies."

"ESIF is really going to move us forward to the next generation of power systems in this country," Kroposki said. "There is consensus that our utility grid is aging and that we can get benefit out of making it more intelligent, efficient, and capable of accepting more sources of energy."

Learn more about NREL's Energy Systems Integration testing facilities.

— Heather Lammers

Posted originally by NREL. Please follow us on Twitter and "like" us on Facebook!

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Embrace of Renewables in Heartland Wows Execs

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Executive Energy Leadership Program (Energy Execs) participant Mark Dow checks out the wind turbines at the John Deere dealership in Greensburg, Kansas.
Credit: Dennis Schroeder

Seventeen executives traveled through middle America last month and came away amazed by the can-do spirit alive in the heartland, in awe of how those connected to the land overcame disaster and economic crisis to embrace renewable energy.

The 17 were members of the 2012 class of the Executive Energy Leadership Program (Energy Execs) run by the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL). Each of them — representing private business, local, state, and federal government, and nonprofits — will use the program to bring back to their workplaces an idea to enhance sustainability or build renewable energy projects. The field trip complemented classwork done at the NREL campus on the practical outgrowth of research in renewable energy and energy efficiency.

The Energy Execs traveled by bus from Denver to Lamar, in the southeast corner of Colorado, to meet with economic-development and community leaders and see one of the largest wind farms in the nation. They then rode on to Greensburg, Kansas, site of a devastating 2007 tornado — and now site of the most LEED Platinum energy-efficient buildings per capita of any town or city in the world.

"To see them embrace these technologies, to bring their care for the land and their conservation values to the newest technologies … that's pretty impressive," said Charles Allison, Jr., an associate professor in finance, energy policy, and sustainability management at the New School in New York City. "Understanding who they are goes a long way toward knowing how to integrate energy efficiency into their towns."

Old Windmills and New Wind Turbines

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Bob Emick, center, with back to camera, speaks to the Energy Execs at his ranch in Lamar, Colorado. The ranch hosts a wind farm with 98 1.5-megawatt wind turbines, powerful enough to provide electricity to tens of thousands of households. Bob's son Greg, at the right, wearing a cowboy hat, told the group that the turbines provide the family with a steady income.
Credit: Dennis Schroeder

In Lamar, the Energy Execs visited the Emick family ranch, where 98 1.5-megawatt wind turbines rotate at speeds of up to 24 rotations a minute, bringing electricity to tens of thousands of homes — and where in the blazing sun, cows find shade in the turbines' shadows. It's part of a 150-turbine wind farm that spreads from Prowers County to Bent County to the east.

"NREL approached my dad and said they wanted to put up some meteorological towers to study the wind," rancher Greg Emick earlier told a gathering of the Energy Execs, the Prowers County Economic Development organization and other policymakers from Prowers and surrounding counties. "They spent five years studying the wind, and they found that we had a really good wind resource here."

Xcel Energy got interested, and in 2003, during a six-month span of busy construction, the Colorado Green Wind Power Project built 98 turbines on Emick's land, with another 10 on nearby property. In addition to the Colorado Green Project, Lamar Light & Power generates electricity from their own two turbines.

The wind farm gives the Emick family a steady income and adds $400,000 a year to Prowers County's coffers. That "may seem insignificant, but down here that is very significant," said County Commissioner Gene Millbrand. During construction, there were 250 jobs; now there are about 20 well-paying jobs. "I don't know how our county could have survived this recession had it not been for the stimulus and the revenue we get from this wind farm."

Emick and Millbrand said there was near-universal agreement among residents that wind energy would be a good thing. Why? Well, there are the jobs and the tax revenue, and besides, said Emick, "It beats ranching."

The tour of the Emick farm provided an unexpected historic perspective when family patriarch Bob Emick presented his barn containing dozens of antique but freshly painted windmills, each a work of art in itself, adorned with the finest in 19th-century script. Another 40 of Bob Emick's windmills are on display at the American Wind Power Center in Lubbock, Texas.

"I just can't get over the irony of Mr. Emick being into those windmills, collecting them for 30 years, and the serendipity of having 98 wind turbines put on his land," said David Warner of NREL. "His own hobby and interest played out for him and his family in a very big way."

Town Embraces Its Values to Rebuild

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Energy Execs visit the barn where Bob Emick keeps his collection of vintage windmills near Lamar, Colorado. Participants said it was a pleasing irony that a rancher who has one of the nation's best collections of ancient windmills now hosts 98 modern wind turbines on his acreage.
Credit: Dennis Schroeder

Then it was on to Kansas.

Greensburg, Kansas, is about 100 miles west of Wichita, in Tornado Alley — no more so than the evening of May 4, 2007, when an EF-5 twister smashed into town, destroying 95% of the structures.

It was just one more slowly dying rural Kansas town until then, its chief attraction the Big Well, the largest hand-dug well in the nation, said Superintendent of Schools Darin Headrick.

The destruction was too much for some, who relocated, dropping Greensburg's population from about 1,400 to fewer than 1,000. But those who remained were steadfast.

At the first post-tornado town meeting a week later — attended by 500 people — a proposal to turn the town into a sustainable, tornado-safe paragon of clean energy caught fire.

As part of a DOE rebuilding team, NREL scientists, including Shanti Pless, came to town to advise on energy efficiency and the prospects for wind energy. Residents said yes to the grand vision, even though it meant months-long delays in getting back into permanent housing in the town.

At a meeting with town leaders and Energy Execs, Daniel Wallach, executive director of the nonprofit Greensburg GreenTown, said: "After this disaster, it would have been easy to say 'let's fold this whole town up.' But if we were going to survive and be a player and bring business here, we had to do this."

"Our ancestors were the original recyclers," Greensburg Mayor Bob Dixson said. "They farmed, they ranched, they didn't waste. It was so much in their nature, and it's so much common sense. Why import energy when we have abundant solar and wind resources?"

Today, Greensburg has nine LEED Platinum buildings, including the K-12 school, the city hall, the county hospital, and the biggest employer in town, the John Deere dealership. Each uses half or less of the energy of a standard building of its type. The Deere building employs skylights and natural daylight, captures and recycles water, uses geothermal heating, and draws power from its own wind turbine.

"It takes a lot of courage, when you've lost everything you had, to not just want to get back to a sense of normalcy, but to wait and do it right," Greensburg City Administrator Ed Truelove said.

Energy Execs Inspired to Take Action, Collaborate, Innovate

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Wind turbines power the Best Western Hotel in Greensburg, Kansas. Greensburg rebuilt after a devastating 2007 tornado and now has nine LEED Platinum buildings, each using half or less of the energy of standard building of its type. The LEED Platinum buildings include the K-12 school, the city hall, the county hospital, and the biggest employer in town, the John Deere dealership.
Credit: Dennis Schroeder

On the ride back to Denver, the Energy Execs reflected on what they had learned and how they can bring clean energy to their workplaces.

Raimone Roberts, an executive with a large construction company, wants to help rebuild inner-city Detroit, one energy-efficient block at a time. "I learned that simple systems can work very well, and that you need to be very clear about the vision, about showing how the project reflects community values," Roberts said. "They inspired me to not be afraid to ask questions, no matter how ludicrous, because if you ask enough questions you come up with innovations that can lead to great change."

Manisha Patel, deputy assistant director for regulatory policy at the White House Council on Environmental Quality, said: "We no longer have to change the way people think about renewable energy. The mental change has happened. What isn't there is an infrastructure that will allow renewables to truly penetrate into our delivery system around the country."

"I was awestruck by the human ingenuity and the perseverance of the human spirit, how driven people can be," Patel said. "The things I've seen make me personally want to be a better person. I'm going back and sharing these stories. I'm energized, and I want to do things."

"When you hear about American spirit and innovation, it is often just rhetoric. This trip showed me that it isn't just rhetoric. It can be real."

Keith Hay of the Colorado Public Utilities Commission said visiting Greensburg convinced him to be more ambitious with his clean energy project. "How do we take energy efficiency from the status quo to deepening it, taking it to the next level? I want to help the commission figure out how we move to more integrated solutions."

Finding Sustainability Fans Everywhere

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Kiowa County Memorial Hospital administrator Mary Sweet, front, leads the Energy Execs on a tour of the LEED Platinum hospital in Greensburg, Kansas. Today, Greensburg is the world leader in LEED Platinum buildings per capita.
Credit: Dennis Schroeder

Patrick Hamel of the Colorado Department of Public Health and Environment will redouble his efforts to win approval for a rooftop solar project for the Argo Mine in Idaho Springs, which would cut energy use by 40%. "I saw a sign in the new school that stuck with me" when touring Greensburg's new K-12 school, Hamel said. "'Your beliefs don't make you a better person, but your actions do.'"

Carol Dollard, an energy engineer at Colorado State University (CSU) who wants to build a small wind farm at a CSU cattle research center on the Eastern Plains, was impressed by "the whole green building thing in Greensburg.

"Did I see anything I hadn't seen before? No. But they just got it. They weren't content with one LEED building that could be financed with government help. They have the mentality that you should do it right every time.

"The most remarkable thing for me was the human ingenuity," said Dollard, who lives in a neighborhood recently devastated by the High Park wildfire. "It started with individuals and spread. They wanted to do what was right for them, but also what was right for their community and for the future."

Karen Hancock joined the field trip after the theater shootings in her city, Aurora, Colorado. "I had to ask, 'Aren't you just traumatized by what happened to you?'"

Greensburg residents said they did experience trauma, and some are still feeling it, Hancock said. "But they said the rebuilding of the town was a kind of green therapy that took them away from their problems. They were able to make their community better and their personal lives better out of a tragic event."

Dick Hemmingsen, director of renewable energy initiatives at the University of Minnesota, said the can-do spirit of the people in Lamar and Greensburg — and their embrace of conservation — reminded him of his own great-grandparents, who built sod huts with green roofs, using the warmth of the earth to survive.

"It's just another way to get back to the future," Hemmingsen said. "It's an inspiration to see people rolling up their sleeves to get things done that have to be done."

Learn more about Greensburg's recovery.

— Bill Scanlon

Posted originally by NREL. Please follow us on Twitter and "like" us on Facebook!

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NREL: 35 Years of Clean Energy Leadership

Thirty-five years ago, when President Jimmy Carter opened the Solar Energy Research Institute (SERI) in Golden, Colorado, gasoline cost 62 cents a gallon, and solar power about $100 a watt.

Now, in the summer of 2012, the price of gasoline at the pump is $3.89 per gallon, the installed cost of solar power about $4 a watt.

That's a six-fold increase in the cost of gasoline, and a 95% reduction in the cost of solar. And with solar and wind energy growing by about 35% a year, and biofuels burgeoning, the laboratory in Golden is more vital than ever.

After 14 years as a solar institute, SERI achieved national lab status in 1991 under President George H. W. Bush. SERI became NREL, the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory.

35 Years of Innovations, Breakthroughs, Discoveries

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NREL's 327-acre main campus got an infrastructure boost in 2006 and 2007 when projects in the pipeline were accelerated. On the right, beyond the solar panels, is the Research Support Facility, recently tagged as the top net-zero energy building in the world.
Credit: Dennis Schroeder

What a 35 years it's been.

From its start on July 5, 1977, to today, NREL has pushed the boundaries of what's possible, leading the way to a clean energy future.

Wind turbines have grown from farmhouse curiosities to multi-megawatt behemoths.

NREL scientists inaugurated the era of the super-efficient multi-junction solar cell and combined those cells with lenses that concentrate the sun's rays by 500 times to multiply the power of photovoltaics.

The laboratory worked with industrial partners to lower the price of enzymes used to refine alternative biofuels by 97%.

And NREL scientists found ways to get two electrons from a photon of light; discovered a cost-effective way to virtually eliminate wasteful reflection off a solar cell; helped engineer an economic way to place transparent solar cells in window glass; engineered ways to get biofuels and hydrogen from algae; mapped renewable energy resources in dozens of countries; came up with new standards for aerodynamic wind turbines and concentrating solar power; and set the bar higher for sustainable buildings.

NREL researchers have won 52 R&D 100 awards — the "Oscars of Invention." That places NREL among the top national labs in R&D 100 awards per employee. Just this year, NREL won two: one for the highest-efficiency solar cell, and another for a revolutionary new type of air conditioning that uses 75% less energy than typical systems and can work in any climate.

From Rented Space to the Laboratory of the Future

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NREL's National Wind Technology Center hosts giant turbines, which manufacturers throughout the world bring to the site for testing and certification.
Credit: Dennis Schroeder

From its origins in rented office space, NREL has expanded to a 327-acre campus that is a model for what a sustainable, green office park can look like.

"When I bring visitors on the site, I often tell them that when I came to SERI, this site was 300 acres of nothing but sage brush and rattlesnakes," said Stan Bull, NREL's former associate director for Science and Technology. "But look at it now."

Today, the NREL campus is a living model of sustainability, hosting hundreds of architects, planners, and lawmakers each year, along with a multitude of scientists from around the world.

It wasn't always so.

"The people who joined SERI early, who suffered through the great swings of support and inattention in the 1980s, were like monks in a monastery keeping the candle of hope and dedication burning while nobody else cared," said Art Nozik, an NREL senior research fellow emeritus whose breakthroughs on singlet fission opened the door to greater solar cell efficiency. "Today, when the awareness and importance of our mission is understood and appreciated by a large fraction of the world's population, we can be confident that we can move forward at an accelerated rate to help our society and planet to survive and flourish."

Ron Judkoff arrived in 1978, as the organization's first building energy efficiency scientist. "Back then, we were all in rented space, and when NREL built its first major building on campus, the Field Test Laboratory Building, no one thought to invite our small group of building energy efficiency scientists and engineers into the process," recalled Judkoff, who is now NREL's principal program manager for building energy research. "In fact, most of the staff and management probably thought the term 'building science' was an oxymoron."

Last month, Construction Digital, a monthly online magazine, named NREL's Research Support Facility (RSF) — a 326,000-square-foot building housing 1,300 employees — the top net-zero energy building in the world. "Net zero" means the building uses no more fossil-fuel-based energy in a year than it makes up for in on-site renewable energy. In all, the RSF has received more than 30 awards for sustainable design and construction.

Now, with several buildings that have achieved lofty LEED (Leadership in Energy and Environmental Design) status, the technologies developed by NREL and its industrial partners are found on the campus and in the world market. The "SolarWall" transpired collector, light louvers, electrochromic and thermochromic windows, thermal storage walls, and NREL's Open Studio software tools that simplify optimal energy design, are getting friendly receptions in the marketplace.

"I expect the awards to keep coming, and our campus to serve as a shining example of energy efficiency throughout the world for many years to come," Judkoff said.

Origins Traced to 1970s Oil Embargo

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The sun hits the commemorative medallion on the floor of NREL's Science and Technology Facility (S&TF) at solar noon on July 5, 2012. The medallion was placed in the S&TF in 2006 to commemorate the anniversary of the lab in 1977, and the day in 1991 when President George H.W. Bush elevated the institute to National Lab Status.
Photo by Dennis Schroeder / NREL

SERI was approved by Congress and championed by President Carter in large part because of the oil embargo that pushed the price of gasoline from about 36 cents a gallon in 1972 to 62 cents in 1977.

From a focus on solar energy, NREL has grown to also include cutting-edge breakthrough research in wind, biofuels, energy efficiency, transportation, and geothermal energy.

Walt Musial was hired in 1988 as a testing engineer at a time when many of the U.S. wind power companies were going bankrupt because of canceled tax credits.

"The industry was moving to Europe, and NREL's National Wind Technology Center [NWTC] was one of the last safe havens where good-quality research was being done to explore big problems still facing the technology," Musial recalled.

NREL's wind center became the go-to site for companies, both foreign and domestic, to test their turbines and blades in the wind blowing down from the foothills of the Rocky Mountains and in the NWTC's dynamometer.

Not Just a Research Lab, but a Factor in the Marketplace

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Two scientists work on a project to enhance the efficiency of thin-film solar cells at NREL's Process Development and Integration Laboratory, which helps private companies boost the performance of their cells and modules.
Credit: Dennis Schroeder

In its early years, SERI/NREL was a research lab that didn't involve itself in the realities of the marketplace. That changed in the early 1990s as NREL reached out to industry to help turn science into technology, working with the private sector to ramp up and bring renewable energy and energy efficiency to market.

Many of today's top solar companies percolated their ideas in the DOE Incubator program run at NREL.

NREL has been issued 262 patents and has agreements with 305 industry partners, 64 universities, and 33 not-for-profit organizations. It currently has 116 Cooperative Research and Development Agreements (CRADAs) with industry.

An International Reach; a Helping Hand in Disasters

NREL's reach spreads across five continents — from wind and solar studies in Indonesia to biofuel-powered vehicles in Antarctica.

NREL's Roger Taylor and Dick DeBlasio recall that in the wake of the Earth Summit in Rio de Janeiro in 1992, they implemented the first stage of what later became a Brazilian national program to deploy solar and small wind power systems in communities without electricity in rural Brazil. "Luz para Todus" (Light for All) became a multi-year rural electrification program after the installation of more than 100 lighting, water pumping, and health clinic systems. "Our work in Brazil was very rewarding and fun," said DeBlasio, a chief engineer. "I started here in May of 1978, but it seems like yesterday."

NREL scientists and engineers have helped rebuild communities devastated by hurricanes, floods and tornadoes — showing how to bring sustainable energy and architecture to cities and towns, from tornado-ravaged Greensburg, Kansas, to New Orleans, flooded in the wake of Hurricane Katrina.

Renewable Energy's Growth Has Exploded

In the 35 years that NREL has led the way to a clean energy future, renewable energy has exploded:

• Installed renewable energy tripled between 2000 and 2009 in the United States and globally.
• While renewable energy comprised 2% of all new electrical capacity installations in the United States in 2002, by 2009 renewable energy comprised 55% of all new installations.
• Installed wind energy capacity increased by a factor of 14 between 2000 and 2009 in the United States.
• The weighted average price of wind power in the United States fell to 4.4 cents per kilowatt hour, making it cost competitive with fossil fuels.
• The United States leads the world in wind energy capacity at more than 35 gigawatts.

Just in the past decade, solar energy generation quadrupled in the United States. The annual growth rate of installed solar photovoltaic electricity capacity was 39%, while wind energy capacity grew by 34% a year.

Bull recalls the early days as "a mixture of wild-eyed hopes and utter disappointment," as the lab at first grew rapidly, then "declined precipitously overnight" when half the staff was laid off. Now, more than 2,000 people are employed at NREL.

"SERI/NREL has been and I think always will be a special place because the staffers have such a deep-seated dedication and commitment to the vision and mission," Bull said. "Just the name NREL is an incredible 'door opener' both nationally and internationally. It's almost frightening at times the impact the name alone has on acceptance in the world of energy."

Learn more about NREL's 35 years of innovation.

— Bill Scanlon

Posted originally by NREL. Please follow us on Twitter and "like" us on Facebook!

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Thermal Scout Finds Trouble at Solar Plants

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At SkyFuel Inc.'s testing facility in Arvada, Colorado, NREL Engineer Allison Gray drives a pickup truck equipped with Thermal Scout, a device that teams a GPS unit on the roof with an infrared camera in the pickup bed. NREL colleague Benjamin Ihas checks the readings on a laptop to the right of the driver's seat.
Credit: Dennis Schroeder

At a 20-megawatt concentrating solar power (CSP) plant, some 10,000 mirrors reflect sunlight onto 10,000 receiver tubes, each of which must operate efficiently to get the maximum impact from the sun.

Yet, operators don't have a good sense for which among the 10,000 tubes may have an air leak, or a hydrogen leak, or have been shattered by a flung rock. The best they can do is look at the entire output and roughly guess that if the plant seems to be operating, say, 4% under capacity, it may have about 400 bad tubes.

The only alternative is to laboriously check each tube by hand, an odyssey that can take months.

Now, the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL) has available for license a device called Thermal Scout that can identify and analyze bad receiver tubes as fast as a car or truck can rumble down the rows of mirrors at a CSP plant.

Thermal Scout combines a global positioning system (GPS) on the roof of a car, an infrared camera in the back seat, and some sophisticated software that tracks and analyzes in real time. All the driver has to do is push a couple of buttons, then drive in a very straight line down the rows while Thermal Scout does all the rest of the work.

For the 40 multi-megawatt CSP plants in the world today — and the 28 new ones slated to be built by 2014 —Thermal Scout could mean turning a months-long task into a two-day sprint.

Need for Rapid Detection Device Spurred Invention

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The infrared camera used in Thermal Scout can identify and analyze bad receiver tubes at the speed at which a truck can rumble down the rows of mirrors at a CSP plant.
Credit: Dennis Schroeder

NREL Senior Engineer Tim Wendelin started working on the concept a decade ago when leaders in the parabolic trough industry explained to him the importance of being able to characterize the performance of their receivers in the field.

Wendelin combined an infrared camera with a precise GPS unit and software to produce a device that provided shortcuts to the old, labor-intensive method of checking each tube manually. But it was still cumbersome.

He credits his NREL colleagues Allison Gray and Benjamin Ihas with bringing real-time analytics and user-friendliness to the device, which they dubbed "Thermal Scout" in 2011.

"They brought it into the 21st century," Wendelin said. "Now, it is so smooth and easy to use."

At a CSP plant, the sun strikes mirrors that heat up a fluid that turns water into steam to turn turbines that generate electricity for homes and buildings. The heating fluid is enclosed in a black-coated stainless-steel tube — the receiver. The receiver is surrounded by a glass tube and a vacuum that minimizes thermal loss. The infrared camera in Thermal Scout focuses on that glass tube.

The GPS device ensures that even with slowdowns or potholes, the camera captures the image of that glass tube as the vehicle wheels down the row of receivers.

The tube-shaped receivers are typically about 4 meters — or 13 feet — long and about 70 millimeters — or 3 inches — wide. In a typical CSP plant, there might be 100 receivers in a row, and some 100 or 200 rows.

"The beauty of Thermal Scout is that it's used in a consistent geometry," Wendelin said. "The receivers are all in rows, and it can snap a shot of each one of them."

Receivers are designed to last for decades, but something as simple as a rock sent flying by a passing vehicle can compromise the tubes and let in outside air. Or, the thermal fluid that passes through the tube can degrade over time, causing a buildup of hydrogen between the steel tube and the glass. Earlier generations of receivers weren't built quite as well and may have shorter lifetimes compared to today's receivers.

Thermal Scout is User-Friendly

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NREL Senior Engineer Tim Wendelin, right, started working on the concept of Thermal Scout a decade ago to try to characterize the performance of the receivers in a CSP plant. NREL engineers Benjamin Ihas, left, and Allison Gray, center, enhanced the concept and made it user friendly.
Credit: Dennis Schroeder

Thermal Scout users start with NREL-developed software that asks them to define the row geometry and specify the number of rows, something they only need to do once. Users also need to input the temperature of the fluid as it enters a row of receivers and its (higher) temperature when it reaches the end of the row.

Armed with that information, the infrared camera — with the help of the GPS — knows when to snap to capture thermal images of each receiver.

The GPS device is on top of the car, the infrared camera mounted on a tripod in the back seat.

The driver clicks "Start Test," the software fine-tunes the camera to get the right focus, and the driver starts moving.

Thermal Scout can operate well at 25 mph, but most plants have a 10-mph speed limit to keep road dust from landing on the mirrors or receivers.

If a passenger is interested, he or she can watch a video on the left side of the screen and still images on the right. At the bottom is a real-time plot of the average of the peak temperatures.

"The software will find the highest peak temperature, which in our case is always the receiver tube," Ihas said. "It can take 100 slices and run a statistical analysis to make sure there are no strange artifacts giving a false reading."

For example, if the camera captures a metal joint or the sun's reflection on the bottom of the tube, eliciting a temperature way above the norm, that anomaly is filtered out of the equation.

Later, when plant operators analyze the data, they can see, for example, that receiver 35 in row 12 showed some higher temperatures. They can retrieve the images from that specific receiver and verify — or not — that the tube is indeed malfunctioning or running a little warmer.

Device Helps Operators Determine When to Replace Receivers

Enlarge image

Thermal Scout's data acquisition interface. The left screen is a video image with the mirrors in blue and the tube in lighter blue. On the right is a still shot with the tube in orange. Below, a series of dots shows which tubes are at an elevated temperature. Data can be read in real time or saved to be analyzed later.
Credit: Dennis Schroeder

The latest enhancement of Thermal Scout is built-in data analysis, which has been streamlined and made intuitive for users. 

Click for a row report in Thermal Scout, and a Web page is generated that can be shared with anyone at the plant. Click to "acquire one image," and that image can be examined in detail, now or later.

Another click, and a complete data analysis for a row, a series of rows, or the entire plant appears on the screen.

"Thermal Scout can very quickly identify a hot receiver, including the row, the number, the glass temperature, and where to find it," Ihas said.

Every line of pixels is a line of data, Gray, an NREL engineer, noted. And NREL can help troubleshoot problems remotely.

Of course, it's up to plant operators to decide when to replace the problematic receivers — when a few are bad, or when dozens or hundreds are bad. A row of receivers can be shut down overnight, and a few replaced by the time the sun rises the next morning. Still, it's a laborious job, so the plant uses its own discretion on what failure rate warrants replacement of receivers.

A recent test of a five-year-old plant found that about 5% of the receivers were performing poorly or starting to waver, Ihas said.

"Thermal Scout would likely be used every two years or so at a large CSP plant, unless something happened to the output that warranted more frequent checks," Gray said.

"There's probably a threshold where they would say, 'We need to address this; we need to replace some receivers,'" Wendelin added.

Florida Power and Light, which installed early-generation CSP receivers, used an early version of Thermal Scout several years ago to quickly assess their tubes and determined that it made the most fiscal sense to replace them all. "They never would have been able to make that determination without Thermal Scout," Wendelin said.

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