Pilot project with China Electric Institute (CEI) verifies the power generation performance of monofacial and bifacial PERC modules in Sanya and Turpan

The China Electric Institute (hereinafter referred to as CEI) has compared the outdoor power generation performance of the then emerging mono-crystalline PERC and polycrystalline modules in 2016-2017. The 1-year monitoring data of two real-life fields in Sanya, Hainan (humid and hot marine environment) and Turpan,

Xinjiang (dry and hot environment), shows that the PERC module had an excellent performance in terms of both power generation and anti-degradation (the first-year yield gain of a PERC module is 3-4%). For details, please refer to “Analysis Of Which Module Has Higher Power Generation By Pilot Project Data”, “Comprehensive Degradation Performance of Mono-crystalline PERC In Practical Application” and “Power Generation Performance of Mono-crystalline PERC module”.

Bifacial PERC modules were first launched in China in 2017 and were widely used in 2018. In order to further verify the power generation performance of monofacial and bifacial PERC modules in harsh environments, in 2018 the CEI mounted monocrystalline PERC modules, polycrystalline modules and polycrystalline PERC bifacial modules in their Hainan and Turpan test fields and conducted energy yield tests over a year. Pictures of the pilot projects and comparison data are as follows:

The monofacial and bifacial PERC modules for the pilot project were provided by LONGi, and the polycrystalline modules were from two Tier 1 manufacturers. The power of the modules was retested by the CEI before 2mounting samples, with power generation data measured from the DC side and the results used to calculate the power generation per watt.

In this test, the LONGi monofacial PERC module continued its excellent power generation performance, as on previous occasions, its power exceeding that of the polycrystalline module. In the Sanya test field, the average power generation per watt of the LONGi monofacial PERC module was 4.7% higher than that of polycrystalline module ① and 4.1% higher than that of polycrystalline module ②. In the Turpan test field, the average power generation per watt of the LONGi monofacial PERC module was 3.7% higher than that of polycrystalline module
① and 4.9% higher than that of polycrystalline module ②

For the bifacial PERC module, the yield gain relative to the monofacial PERC module under two different albedo conditions was tested in two fields. In the Sanya test field, with a ground type of white paint with high albedo, the average rear side gain was 18.5% during July to November 2018. Tested on cement ground, the average rear side gain was 8.6% during November 2018 to May 2019. In the Turpan test field, the average rear side gain was 20.1% under surface conditions of white paint from June to October 2018. Replacing the ground material with gravel, the average bifacial gain was 7.0% from November 2018 to June 2019.

The yield gain of the bifacial modules was shown to be higher in summer than in winter throughout the year; for a sunny day, the power generation gain is represented by a U-shaped curve that is higher in the morning and evening than at noon. The figure below shows the power generation of monofacial and bifacial PERC modules in the Sanya test field on April 29, 2019:

The yield gain of the bifacial module is derived from the irradiation received on its rear side. In order to investigate the uniformity of the light received on the rear side of the module, six measuring points were taken on the back of the module to monitor irradiation. The position of each measuring point is shown in the figure below

The irradiance for each point on the rear side in typically clear weather is shown in the figure below. The irradiance of different positions is relatively high at noon and relatively low in the morning and evening. The higher the position, the higher the irradiance.

In terms of the test results in Turpan, we focused on the working current of the module under high irradiation conditions, calculating the total inclined irradiation and string current for each month. The results in July 2018 and June 2019 are shown in the figure below. Turpan is an area with abundant light resources. The maximum daily irradiation is usually about 1,000W / m2, and there are few days with poor irradiation.

Detailed analysis shows that optimal daily irradiation was not more than 1,100W / m2 in sunny weather (such as August 24, 2018). The highest annual irradiation occurred in cloudy weather (July 4, 2018). The instantaneous irradiation was close to 1,300W / m2. The enhancement effect of reflection from clouds on irradiation is usually very short.

Conclusion: in the one-year real-life field test conducted by CEI in Sanya, Hainan (humid and hot marine environment) and Turpan, Xinjiang (dry and hot environment), the LONGi monofacial PERC module maintained its power generation advantage over the polycrystalline module, with a power generation gain of 4- 5%; the newly added LONGi bifacial PERC module demonstrated a stable and reliable power generation gain compared with the monofacial module. The yield gain with white paint is about 20% and that with cement and gravel is about 8%. The case study analyzes the irradiance at different positions on the rear side, the annual irradiance and the working current, which can provide valuable reference for the application of bifacial modules in power station systems.