TwinPeak Technology Whitepaper
REC Solar Pte. Ltd.
Tuas South Avenue
Singapore
Singapore
Tel: +
www.recgroup.com
NE- - .
What advantages do four bus bars offer?
The use of four bus bars to a cell, as shown in figure , decreases the
distance between them. This proximity means electrons have less
far to travel to reach the ribbon, vastly improving the flow and the
reliability performance of the panel. This reduced distance lowers
the resistance in the cell, increasing current; in turn, this allows finger
width to be reduced, exposing more cell surface area to light and
generating more current, as well as keeping the fill factor high. The
reduction in cell resistance seen through adding a fourth bus bar
improves cell efficiency by over . per cell and adds Wp per panel.
During the stringent qualification performed by REC, a major
improvement in the test performance of the four bus bar panels has
been seen, especially in the thermal cycling and mechnical load tests.
This is aributed to the lower cross section of the ribbon permied by
the smaller size, which creates less stress on the cell.
What advantages does a split junction box offer?
A standard junction box is generally a single plastic housing which
contains three bypass diodes and connection options to enable the
panel to be connected to the rest of the system. The term ‘split junction
box’ describes where these functions are split into three smaller boxes,
one per internal string, with one bypass diode each (fig. ).
The major advantage of this is to enable the new cell layout seen in the
REC TwinPeak Series. Use of the split junction box principle uses one
less cross-connector than a standard panel, which reduces internal
panel resistance and saves space. This extra space can then be used
to give a larger gap between cells, increasing internal reflection of
light onto the cell surface and subsequently increasing light capture.
Tests have also shown a reduction of between and °C in heat
build up behind the three new boxes compared to the single box on
a standard panel. The cooler temperatures achieved help increase
panel reliability and produces a power gain of around Wp per panel.
In the REC TwinPeak Series, the junction box will be in the center of
the panel and the cable lengths will be same as today.
What advantages does PERC technology offer?
Although PERC technology cannot be seen in the cells and makes no
difference to the visual appearance of the panel, it offers a major boost
to overall production. PERC technology is an additional step which
REC has introduced to the cell production process. Based on a change
in the design of the rear of the cell, a special dielectric PERC layer is
coated on the backside of the cell and the aluminum metallization
layer, providing contact to the silicon wafer only through laser-made
microscopic holes (fig. ).
The addition of the PERC layer enables increased capture of light
falling on the cell surface increasing the overall performance and
efficiency. PERC technology works by reflecting back into the body
of the cell any wavelengths of light that have passed through without
generating electrons. This minimizes the recombination of atoms at the
aluminum metallization layer, reducing the heat generated in the cell,
allowing it to work more efficiently. Through this, the cell will also be
able to absorb more infrared light (wavelengths of between and
nm), increasing production in low light conditions and improving
overall energy yield (fig. ).
A second way in which PERC technology contributes to increased
yield is by the passivation of the back of the cell. This means that any
electrons generated near the boom of the cell are less likely to be lost
to the aluminum metallization layer. Unaracted by the mealization,
they can rise back through the cell structure, reaching the interface
between the base and emier, contributing to cell current (fig. ).
The overall benefit of PERC technology to the output of the panels is
to add Wp higher power at Standard Test Conditions.
How will the consumer benefit from the technology in
the new panel?
Through the combination of these technologies into one new solar
panel, the REC TwinPeak Series has enabled a power increase of
around Wp per panel. This has been achieved through reducing
resistance at both cell and panel levels, exposure of more cell area to
sunlight and increasing the amount of light absorbed. Together, these
technology enablers ensure that the REC TwinPeak Series provides a
higher energy yield throughout the day when compared to standard
panels, and a higher energy yield, means a higher rate of return on a
solar installation.
Furthermore, the increase in power per m of the REC TwinPeak Series
will shi REC’s wa class production upwards, helping customers
reduce overall balance of system costs compared to standard panels
over the same surface area. This is of particular importance to the C&I
and residential market segments and allows customers to generate as
much energy out of their installation as possible, based on the cost-
effective position provided by the polysilicon platform. These benefits
are of course in addition to REC’s industry-leading product quality, the
fact that REC’s panel production is PID free, and the reliability of
a strong and established European brand.
REC is a leading global provider of solar energy solutions. With more than years of experience, we offer sustainable,
high performing products, services and investments for the solar industry. Together with our partners, we create
value by providing solutions that beer meet the world’s growing energy needs. REC is headquartered in Norway and
listed on the Oslo Stock Exchange (ticker: RECSOL). Our , employees worldwide generated revenues of USD
million in .
Fig : A cross-section of a cell showing the ‘reflective’ properties of PERC technology
Light is returned
back into the body
of the cell
The rear of the cell is passivated,
preventing electrons formed at
the back from being lost through
absorption in the aluminum
metallization layer
Dielectric
PERC layer
Small metal
contacts
Aluminum
metallization
CONVENTIONAL CELL PERC CELL
Fig. : The simplified structure of a conventional solar cell (l) compared to a cell with
PERC technology (r)
CONVENTIONAL CELL PERC CELL
Dielectric
PERC layer
Small metal
contacts
Base layer (silicon wafer) Base layer (silicon wafer)
Emier layerEmier layer
Aluminium metallization Aluminium metallization