Californian testing organization PV Evolution Labs has worked with tracker manufacturer Nextracker on a white paper seeking to quantify the solar power yield gains offered by bifacial panels mounted on single-axis trackers. PV Evolution chief executive Jenya Meydbray has said: “Bifacial PV technology represents the single largest LCOE [levelized cost of energy] improvement opportunity since the introduction of trackers.”
That bifacial plus single-axis trackers equals yield gains is not in doubt but the industry has nevertheless struggled to turn that knowledge into bankable yield assumptions to date. Meydbray says that stumbling block has held up wider deployment of the combination.
The CEO's assertion was borne out almost immediately, with publication of the yield gain study swiftly followed by Nextracker signing a deal with engineering, procurement and construction company Shanghai Electric to provide more than 1 GW of its NX Horizon products for the fifth phase of the huge Mohammed bin Rashid Al Maktoum Solar Park, in Dubai.
The fifth phase of the eventual 2.8 GW solar field, previously described as a 900 MW slice of generation capacity, was reported yesterday as having a 1 GW scale, in a press release issued by Nextracker, which is part of electronics contract manufacturer Flex. The Nextracker statement gave a completion date of 2023, which would mark finalization of the last phase of the gargantuan project commissioned by the Dubai Electricity & Water Authority. The authority says it has plans to expand the field to 5 GW, by 2030.
“We are tremendously honored to partner with Shanghai Electric Power Generation Group to help deliver the best performance outcomes for the Dubai Electric & Water Authority,” said Nextracker CEO Dan Shugar. “Shanghai Electric is one of the leading high-tech companies in China, with over one hundred years of manufacturing legacy, and we are deeply privileged to be chosen for our technology. We look forward to exploring many ways to collaborate and partner in the future.”
The white paper produced by Nextracker predicted yield gains of 5-7% in low albedo (20%) conditions, such as panels mounted above grass, gravel or sand. The gains available would rise to 10-12% on a high albedo (50%) site, such as on snow or white fabric, according to the tracker company.
The manufacturer tested two-in-portrait (2P) panel orientation, with vertical panels either side of the torque tube, as well as 1P set-ups – with each vertical panel above the tube – and claimed the latter offered an albedo-dependent gain of 0.6-1.2%. The paper's authors attributed the difference mainly to a favorable rear-side, ground view factor. “The ratio of the array height above grade to the array width, or wingspan, is significantly higher for the 1P tracker than for the 2 P tracker,” the white paper reads.
The results from the Nextracker testbed in Fremont, California were compared with data from the sites used by PV Evolution Labs, in Davis, California, and by the U.S. National Renewable Energy Laboratory, in Golden, Colorado. The paper's authors stated Nextracker's testing methodologies ensured the company's results could be reasonably compared with the other two sites, with deviation across the locations of 3% in high albedo conditions and 1% in low albedo. “Insofar as consistency breeds confidence, the general agreements between these field-measured bifacial gains – under both high and low albedo conditions, as well as across multiple test facilities and states – is encouraging,” stated the paper.
Nextracker compared bifacial gains as DC-side energy yield improvements in mono and bifacial modules. The tracker manufacturer made a point of comparing equivalent bifacial and monofacial modules, insofar as they shared the same manufacturer and cell technology, architecture and cell stringing. The Nextracker test site, which included modules from three manufacturers, featured five rows of 1P trackers and four of 2P orientations, all of which were interior rows, to exclude any outer-row exaggeration of bifaciality returns.
Modules were flash-tested on the front and rear sides to determine installed power ratings per installed capacity and the actual bifaciality coefficient. The devices were also selected to achieve the lowest string-level power mismatch to avoid losses.
Nextracker stressed the figures were confined to its NX Horizon tracker, as the architecture of that product minimizes structural shading losses and rear-side mismatch loss factor, compared to other systems. The manufacturer said the NX Horizon offered a structure shading factor of 12.3%, compared to 20% with a rival product. The reported mismatch loss factor was 3.5% for Nextracker, versus 8.8% for the undisclosed competitor product. The NX Horizon offers 1.02-1.67% higher DC-side bifacial gains than its competitors, according to Nextracker.
The company modeled the test conditions using PVsyst and found the software's predictions “reasonably good.” During three months of high-albedo values generated by white fabric, Nextracker measured a 12.5% bifacial gain, compared to the 11.2% predicted by PVsyst. In the low-albedo environment, field measurements recorded 5.9% gains – higher than the 5.5% prediction.
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