Tracking systems are already innovative. They track the sun rather than keeping solar panels in a fixed position. Many single-axis trackers claim at least a 25% performance gain over fixed-tilt systems, and developers still think there is room for improvement. A number of brands are exploring ways to improve backtracking (adjusting panel orientation to limit row-to-row shading at various times of the day) and accept more diffused light when cloud cover may prevent a direct sunlight path to the panels. These small tweaks would only increase energy gain by another few percentage points, but every bit is a bonus for traditional tracking companies and their customers.
“It’s nice to see innovation coming out of a company that [makes a sophisticated racking system],” said Dustin Shively, director of engineering at Clēnera, a U.S. solar developer that has installed many tracking systems. “It would be easy for them to say they want to make a modest margin and that’s enough. But it’s always, ‘How can we make things better and how can we optimize?'”
Shively is specifically referencing NEXTracker, a decentralized tracker manufacturer that holds the largest share of the global tracking market. The company released its TrueCapture self-adjusting tracker control system in July 2017 that claims another 2 to 6% energy gain through continuous optimization of individual rows of panels in response to site features and weather conditions. Clēnera was one of the first large-scale solar developers to implement the new technology on its tracking installations.
“The single-axis tracker algorithm has been unchanged since the 1990s. You know where the sun rises and what tracking profile you should have,” Shively said. “NEXTracker thought it was better to manipulate each row instead of using one profile across the whole site. Let’s move rows independently to avoid shading on rolling terrain. With diffused light scenarios, when it’s cloudy, you don’t want to point at the sun, you want to point flat. It’s not an obvious solution, but it turned out to be true. That’s another method [NEXTracker] employed to change the single-axis algorithm to make more energy.”
NEXTracker is not the first company to test out different backtracking algorithms to adapt to uneven terrains, but it was the first to make a big play into capturing more diffused light. Greg Beardsworth, director of product management at NEXTracker, said finding ways to squeeze out more energy during low-light conditions was an interesting task.
“You’ve got cloud cover or haze or even pollution—enough of your irradiance is scattered and there’s not a direct beam coming from the sun,” he said. “On a perfectly overcast day with no sun peeking through, your best energy production would be perfectly flat, so the panel sees as much of the sky as possible for diffused light.”
NEXTracker’s TrueCapture system’s ability to recognize low light conditions and adjust panels to a better angle will even prove beneficial to thin-film projects, which already perform better than c-Si in low light. A small “computer” is connected at each row and wirelessly links with the tracking site’s main controller. Since each of NEXTracker’s rows are self-powered by one motor, they can act independently and adjust as needed. TrueCapture is currently being used on new projects and can be added to older projects too.
“It’s really exciting to come in with basically a software layer and a few extra instruments for detecting the diffused light conditions and be able to get this additional energy value out of existing sites,” Beardsworth said.
Array Technologies is also trying to adjust its trackers for more diffused-light capture. The company recently released SmarTrack, its own tracking technology that utilizes a machine-learning algorithm to monitor and optimize backtracking positions that will be available for retrofit and new installation in early 2019. Optical sensors will allow Array trackers to adjust for optimal diffused light angles.
Even though Array’s centralized tracking configuration (with multiple rows linked to one motor) will prevent individual rows from acting independently of each other, company reps said moving many rows in unison according to sunlight and weather conditions is an efficient method on large-scale projects.
“Array’s centralized design maximizes efficiency by monitoring and reacting to real-world conditions on the block level,” said Array Technologies reps in an email to Solar Power World. “By monitoring the production of an entire motor block and moving it as a whole, we are able to determine the optimum settings without constant readjustment to individual rows.”
The larger focus of SmarTrack—and also NEXTracker’s TrueCapture and Spanish tracking manufacturer Soltec’s TeamTrack—is to improve traditional backtracking methods. Backtracking adjusts a row’s angle so adjacent row shading in early morning and late afternoon hours won’t significantly decrease energy harvest. This increase of power at the beginning and end of each day widens the “shoulders” of the power production curve.
“The logic that backtracking has followed since the beginning of time is it assumes all the rows are in the same slope and perfectly flat. There’s no undulation or slope difference between the rows,” Beardsworth said. “When you make that assumption, yeah, backtracking works as advertised.
“Now the real world, we’re building sites on more diverse locations and geography. It’s not just the flat desert Southwest anymore,” Beardsworth continued. “One of the fastest-growing geographic markets has been the Southeast and those sites tend to have more undulation in topography. It’s not cost-effective, practical or environmentally sensitive to level the land to make it perfectly flat. So we’re seeing this row-to-row height variation as a much bigger factor now.”
These new technologies allow each row of a project to have its own unique backtracking algorithm based on the topography of neighboring rows. Site-specific, row-by-row backtracking behavior broadens those power production shoulders even more.
Soltec also uses “asymmetric backtracking” to adjust to rolling terrains with sensors to control the response to cloud-cover, snow-cover, flood levels and wind speeds. Its TeamTrack control system takes advantage of its independent tracking tables to position each one according to predicted shadow projections.
“This control considers all the slopes in the terrain to avoid all the shadows and maximize energy generation,” said José Alfonso Teruel, R&D manager for Soltec. “We achieve this by using a central solution that has information of the whole plant and calculates how each tracker’s angular position is affecting the rest. This solution is adjustable and once it’s configured it doesn’t need more operations for the whole life of the plant, behaving according to the shadow projection calculations and NREL’s sun position algorithms.”
Tracking algorithm updates will also help with the increasing demand for bifacial modules on trackers. Soltec has been testing bifacial modules with its trackers in many configurations and scenarios to find the best backtracking algorithms for the new modules.
“The first tests reveal that the different backtracking variations are very dependent on the albedo, but for most of the cases, it’s more convenient to optimize the front capture,” Teruel said. “We will have more conclusive data during the following months.”
NEXTracker also believes its TrueCapture system complements bifacial modules on trackers.
“We have a forward view that has a lot of the bifacial market share growing, especially on trackers,” Beardsworth said. “You can take your gain from bifacial, which, depending on site conditions, could be anywhere from 5 to 10% added energy and take the TrueCapture gains of 4 to 6%—you can be getting close to 20% more annual production than a standard tracking power plant from a year ago.”
These various tracking algorithm updates haven’t made a significant impact on project development—yet. Maybe one day rows will be positioned closer together since backtracking can be more precise, and more rows can fit on a site. Until then, NEXTracker said it’s happy that projects are getting financed with TrueCapture gains built-in to energy estimates. Developers like Clēnera are pleased to offer system owners these additional savings.
“We’re not making big design changes due to TrueCapture,” Shively said. “Everything [gained] is an upside—being able to see more energy.”