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
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.