Empirical Data From the China Electric Institute (Cei) Verifies the Power Generation Performance of LONGi’s Bifacial Half-Cell Module at Its Pilot Project in Qionghai, Hainan

PVTIME - It is generally recognized that
half-cell technology reduces the working current of a cell string, thereby also
reducing the internal loss of a PV module and improving the module’s power by
more than one gear. Compared with a full cell module, half-cell technology
reduces the hotspot and working temperatures of the module, significantly
improving power generation performance and reliability and offering better
power generation performance under shadow or uneven irradiation conditions.

The analysis of
the impact of half-cell technology on the power generation of modules is mainly
seen in the early research papers of the Fraunhofer Institute and ISC, but
rarely in the power generation analysis of commercial modules. In order to
better study the impact of half-cell technology on module power
generation,  LONGi and the China Electrical Research Institute
(hereinafter referred to as "CEI") jointly conducted a one-year
empirical study in Qionghai, Hainan.

The demonstration
power station was officially put into operation in June 2019. This article will
analyze the power generation data for more than half a year.

1. Test Plan

The demonstration
power station is equipped with monocrystalline and bifacial full-cell modules,
monocrystalline and bifacial half-cell modules and purchased polycrystalline
half-cell modules (PERC technology is adopted). All modules are retested by the
CEI in order to use the actual power for single Wp power generation
calculation. The details are as follows:

2. Power
Generation Advantages of Monocrystalline PERC over Polycrystalline PERC and
Power Generation Gains of Bifacial Modules

First of all, the
power generation difference between monocrystalline and polycrystalline (PERC
Monofacial) half-cell modules: in the 9-month statistical period, the power
generation gain of a monocrystalline half-cell module is about 3.72%, which
shows that the monocrystalline module maintains the advantages of low
irradiance performance and power temperature coefficient when compared with a
polycrystalline module. The power generation gain increases month on month. On
the one hand, the advantage of winter irradiation is more obvious than that of
low and weak light. On the other hand, it should be related to the excellent
anti-LID performance of the LONGi module.

As shown in the
figure above, the power generation gain of a monocrystalline half-cell bifacial
module under cement surface conditions is 15.3%, compared with that of a
monocrystalline half-cell module over a period of 9 months, with the gain
meeting expectations.

3. Analysis of the Influence of Half-Cell Technology
on Power Generation of a Bifacial Module

Due to half-cell technology having the characteristics of reducing
internal current transmission loss of a module, the higher the irradiation, the
higher the cell string current, and the more the power generation loss is
reduced by half-cell technology. As shown in the figure below, the average
power generation gain of a half-cell bifacial module is 2.8%, compared with
that of a full-cell equivalent, which obviously reflects the characteristics of
high-power generation gain in a month with good irradiation and low power
generation gain in one with poor irradiation. The power generation gain in each
month is positive. In addition to irradiation, the higher temperature is also
positively related to the power generation gain of the half-cell module, the
following figure listing the monthly historical temperatures of Qionghai city
as a reference.

It can be seen
from the statistics of a single month (October 2019) that the power generation
of the half-cell bifacial module is weaker than that of the full-cell module
due to irradiation differences on October 8 and 31, but power generation gains
on all other days are positive, gains being generally positive related to the
daily power generation.

In order to further study the effect of irradiation, we also compared the
power generation data of the single day of October 12. It can be seen that the
power generation of the half-cell bifacial and the full cell bifacial module is
about 370W / m2 (corresponding to the ambient temperature of 27.2 °
C). Considering the irradiation gain and bifacial ratio of the rear side, the
critical point of irradiation is about 400W / m2. When the
irradiation is lower, the whole cell module has higher power generation
capacity. The power generation capacity of the half-cell module is relatively
high when the irradiation is over 1000W / m2, the power generation
advantage of the half chip module being 5%.

The empirical data
for the Qionghai half-cell module from the CEI once again confirms the power
generation gain of the LONGi monocrystalline module relative to the
polycrystalline module and the bifacial gain brought by the bifacial half-cell
module. Compared with the bifacial full cell module, the half-cell equivalent
has an obvious power generation advantage in a high irradiation environment,
and it is clear that the critical irradiation value is about 400W / m2. The
high current of the monocrystalline PERC cell and the working current gain
brought by the light on the rear side of the bifacial cell make bifacial PERC
technology very suitable for combination with half-cell technology, which
brings multiple improvements in power capacity, power generation and reliability.

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