Published on January 15th, 2019 | by Charles W. Thurston0
Nextracker Rolls Bifacial Solar Dice For 750 Megawatts
January 15th, 2019 by Charles W. Thurston
NEXTracker is currently involved in close to 750 megawatts of new bifacial solar tracker projects, following recent bank approval of the first utility-scale project with bifacial panels on its single-axis NX Horizon, says Dan Shugar, the founder of the company.
This first array is the 160 megawatt Southern Oak Solar project, in Mitchell County, GA, approved on January 10 and being developed by Invenergy. It will include LONGi panels and NEXTracker’s TrueCapture orientation control system.
The combination of the two technologies means the array could produce an energy yield of 20% or more than an install on a fixed mount, monofacial panel array, NEXTracker suggests. The specific bifacial boost for this project is dependent on multiple factors including insolation levels, ground reflection albedo, and weather.
Renewable Energy Systems will construct the Southern Oak Solar project, which is expected to come on line by 2019. CoBank, a national association of rural banks, acted as sole lender, issuing bank, collateral agent and administrative agent for the deal.
Georgia Power announced a power purchase agreement for Georgia Power to buy all the energy and environmental attributes from Southern Oak Solar through 2049. This agreement is part of the utility’s Renewable Energy Development Initiative (REDI), which is designed to advance the growth of renewable energy goals across the state of Georgia.
“Southern Oak Solar is a significant transaction with leading utility Georgia Power, and it is also our largest solar project to date, firmly establishing Invenergy as a leading developer of utility scale solar projects,” said Invenergy’s President Jim Murphy.
LONGi bifacial cells lead the market. Hi-MO3, launched in 2018, is a next generation bifacial module built with monocrystalline half-cut cells. As of August 2018, LONGi R&D has exceeded 23% front-side efficiency of its bifacial PERC cell, while rear-side efficiency reached 18% and bifaciality surpassed 82%; these benchmarks are all industry-leading milestones, the company reports.
“The development pace of the efficiency of the bifacial cell is amazing. So far, mass production efficiency of bifacial cell has exceeded 22%, increasing up to 0.2% every six months while bifaciality has remained above 75%,” said Lv Jun, the vice president of LONGi Solar.
The NX Horizon was designed with bifacial panels in mind, says Shugar. One key feature of the single-portrait table of the NX design that optimizes bifacial performance is the 1.5 meter distance from the ground to the torque tube. Two-In-Portrait tables are typically 2.4 meters high, so less reflected ground light is captured.
The trackers are designed to enhance rear-side irradiance and are compatible with such as modules featuring half-cut cells and center busbar architectures. The design also includes an increased distance between the PV panel and the round torque tubes, so back-side shadowing is minimal. Added clearance to the tubes ensures that in the case of center junction-box modules, no contact occurs, even in severe wind conditions. The rails also include a center gap to enable DC cable management and time-efficient installation, the company says.
In a test of bifacial panels on NX Horizon trackers in the southwest desert, the single-axis gain over fixed tilt was 22%, the bifacial panel boost was 11% over monofacial, and the TrueCapture or light sensing algorithm control gain was 3.5% for a total yield gain of 36.5% over a fixed-tilt monofacial installation, NEXTracker reported in a June presentation.
The desert test conditions for the NX Horizon included an albedo of 38%, a ground cover ratio of 35%, and a bifacial flash test factor of 85%. The compared fixed-tilt array used the same panels, was fixed at 25% and had a ground cover ratio of 65%, the company said.
While bifacial boost is typically found in the field to be in the 10% to 15% range thus far, research shows that the boost could readily double, if enough critical factors are understood and planned for in tracker design and configuration. That rise may take time. “A 25% to 35% bifacial boost would require extraordinary conditions,” says Shugar.
Invenergy and its affiliated companies have successfully developed more than 21.8 gigawatts of projects that are in operation, construction or contracted, including wind, solar, and natural gas power generation and advanced energy storage projects.
Independent engineering firm DNV-GL recognized LONGi solar as a “Top Performer” in its PV module reliability Scorecard 2018. LONGi solar has also ranked as the most financially stable PV manufacturer in Asia and second worldwide.