DNV has begun installing what it calls the largest bifacial solar panel test facility in the world, at Davis, California, with the goal of benchmarking brand variations in the market to facilitate widespread adoption. The $250,000 project recently won a $200,000 grant from the US Department of Energy.
The test site will house 1,500-volt bifacial panel arrays from as many manufacturers as are willing to cooperate, says Tara Doyle, the head of Business Development & Project Management at DNV GL, based in Berkeley. The tests will focus on 1,500 volt panels rather than lower voltage panels, since 1,500 volts is expected to become the norm in the solar industry soon.
The string arrays will include single-axis trackers as well as fixed-tilt mounting systems, placed over two different ground cover materials to measure the difference in energy yield provided by albedo, or reflected light.
The tests will include 50 kilowatts of four types of panels — Trina, Hanwha, Longi and Astronergy, and all types of panels will be tested on a NEXTracker tracker, initially. Once a second type of tracker is used, as is being considered, the size of the field bed could resemble a utility-scale test installation, DNV says.
The solar panels will first undergo indoor characterization of the modules, including flash testing, which determines the maximum albedo value that the panels could yield under perfect field conditions. In the market today, bifacial panels are only yielding a 10% to 15% energy boost, despite the potential for up to about a 90% bifacial factor gain, as manufacturers report it.
This is because there are a large number of variables in the available positioning of the panels on different sorts of mounting equipment. Once the top three or four variables have been studied and optimized, the bifacial boost is expected to reach 25% or more, according to experts in Germany.
“What we are trying to do is correlate the bifacial factor to the module output in the field; then we can see if the bifacial factor from manufacturers can be a predictor of the bifacial gain in the field,” says Doyle. Data at the site will be recorded as soon as the panels go live, and DNV expects to produce an interim report by September 2019, followed by a more formal report after one year of data is collected. “We’re also aiming to compare expected energy output from energy simulation models to the field data we are collecting as part of our study. In a nutshell, we’re seeing which models predict bifacial gains most accurately,” she says.
The data from the DNV tests will be used not only to help design more efficient solar projects, but also secure financing at lower costs since risk will be reduced as a result of the performance benchmarking.
“One concern with bifacial panels is that there is a wide range of manufacturer claims for the bifacial factor, so bankers and other financiers don’t know which data to believe,” says Tristan Erion-Lorico, the head of PV Module Business, Laboratory Services for DNV. “Our aim is a large set of bankable data that can be reported anonymously,” he says.
Apart from peak performance testing, DNV also will consider panel reliability, looking at different design factors such as glass-on-glass which could have potential issues with damp heat and humidity freeze, Erion-Lorico notes.
“We do respect the other ongoing bifacial studies that might be looking at one manufacturer’s module and a number of different trackers, or one tracker manufacturer with a number of different modules,” says Erion-Lorico “There also are plans for testing over a number of different albedos, so all these studies will complement each other,” he says.
DNV will share the data publicly with anonymity for the panel manufacturers, unless the manufacturer chooses to have its name included with the data. With the presence of DOE funding in the DNV project, the public sharing of data is expected to be widespread. One of the problems solar project developers have in choosing which panels to use with which tracker is that data sets are generally proprietary, they are based on widely varying field variables, and they are not publicly shared.
“Once our data and other data is released next year, more bifacial installations will take place in the market. Then real field data from these installs will start coming in during 2019,” reckons Erion-Lorico.
NV GL delivers testing and advisory services to the energy value chain including renewables and energy management. Their expertise spans onshore and offshore wind power, solar, conventional generation, transmission and distribution, smart grids, and sustainable energy use, as well as energy markets and regulations.