pv magazine test: October 2021 Results
By George Touloupas
This article was originally published in pv magazine – December 2021 edition. Learn more about the pv magazine test here.
pv magazine test involves a range of indoor tests, as well as an outdoor performance test in Gsolar’s test facility in Xi’an, China. Some of these tests are standard in the industry, while others are innovative and provide data on important module quality and performance issues.
October 2021 Test Results Explained
As detailed in the previous issue, the pv magazine test rooftop PV installation was reconfigured to ensure more accurate tracking of the high-power, high-current modules using microinverters. George Touloupas, Senior Director of Technology and Quality at CEA, discusses additional modifications to accommodate high currents on the rooftop, and presents the first results from the newly configured array.
By October 18, replacement and reconfiguration of the microinverters had been completed, and since then module performance has been tracked, except for three days of mandated power cuts. During this period, we observed some energy yield anomalies for the high current modules, the root cause of which is the difference in resistive losses for the DC cable between modules with widely differing currents. As the DC cable loss is proportional to the square of the module current, these differences in losses for 15 m of 2.5 mm² DC cable can reach up to 24 W, between a G12 (210 mm wafer) and a M6 (166 mm) module, and 6 W between a M10 (182 mm) module and a M6 one. Increasing the cable cross section to 4 mm² will narrow this to 15 W and 4 W, respectively, but we still consider this to be wide, as the power of a G12 module will be in the range of 550 W to 660 W. In PV plants, the modules are connected in long, high-voltage strings (typically 1,500 V), so the percentage of the resistive losses over the total string power is much lower than for an individual module.
We have therefore decided to change the cables to the bigger 4 mm², and at the same time develop a method of applying a correction factor to the output of high-current modules to account for the difference in resistive losses that may otherwise distort the energy yield comparisons in favor of modules using smaller wafers. The modifications were completed in mid-November and the results will be presented later. This month, we only present the data for low-current modules, with higher current products (M10 and G12) to be added in the next issue.
Bifacial Boost
Table 1: Bifacial boost - October 2021
The average bifacial boost is 7.8% for October 2021. Bifacial boost is defined as the extra energy yield of the bifacial products compared to the average energy yield of all monofacial mono PERC products. The right-hand side of Table 2 below shows the comparison between different PV module technologies for October 2021. Bifacial modules are steadily performing above all the other technologies, with monofacial mono modules having the lowest yield. [Read: LCOE of Monofacial vs Bifacial Modules: Are Bifacials Worth the Extra Cost?]
Table 2: Energy yield ranking - October 2021
Daily Temperature and Irradiance Data
Figure 1: Daily meteo station data - October 2021
Total Energy Yield
Figure 2: Total energy yield - October 2021
Relative Yield of Different Technologies
Figure 3: Relative yield of different technologies – October 2021
Notes on the Energy Yield Measurements
The energy yield comparison among various technologies, including bifacial boost, will be analyzed using products installed after the beginning of 2019.
The energy yield is given in Wh/Wp and calculated by dividing the energy produced by the module by the Pmax at STC of the module. This Pmax is the maximum STC power after a process of stabilization.
The results are grouped in categories, per module type.
The bifacial boost depends on many parameters: the bifaciality factor, the installation geometry, the albedo of the ground, the sun angle and diffuse irradiance. The ground in this case is gray gravel.
George Touloupas is CEA’s Senior Director, Technology and Quality
Test Cooperation
pv magazine test is a cooperative effort involving pv magazine, APsystems, CEA, and Gsolar. All testing procedures are carried out at Gsolar’s test laboratory in Xi’an, China. CEA supervises these tests and designed both the indoor and outdoor testing procedures.