N-Peak Technology Whitepaper
What advantages do half-cut cells offer?
As can be seen in fig. , the mono cells of the REC N-Peak are cut into
two equal rectangular pieces. Halving the cell reduces internal current
by , which cuts resistance and therefore also power loss. As power
loss is proportional to the square of the current, the power loss in the
complete module is reduced by a factor of four.
Reducing power loss in a half-cut cell produces a higher fill factor - an
indicator of cell quality. Modules with a higher fill factor have a lower
series resistance meaning reduced loss of current internally in the cell.
In turn, this produces higher cell efficiency giving higher energy yields,
especially at times of high irradiance.
Fig : An REC N-Peak n-type mono half-cut cell, showing bus bars and the darker, uniform
aesthetic of a mono cell, with its distinctive rounded corners
What benefits do five bus bars bring to the product?
Five bus bars on a cell decreases the distance that electrons travel to
reach the ribbon, decreasing internal stress as there is less congestion
along the electron’s path, improving flow and reliability of the module.
With this, resistance in the cell is lowered, so cell current increases.
Stringent accelerated testing has been carried out on N-Peak cells
which have demonstrated a major improvement in the thermal cycling
performance with five bus bars, meaning that thanks to the improved
electron flow, the cells are less stressed by heat and therefore more
efficient and durable.
What are the advantages of PERT technology?
In , REC was the first module manufacturer to introduce
Passivated Emier Rear Cell technology (PERC) to mass production on
multisilicon cells. PERC is fundamentally an additional layer at the rear
of the cell with many tiny holes punched into it to allow an electrical
connection between the bulk and the back side. This reduces electron
recombination and also reflects certain wavelengths back through the
cell to give a second chance at being captured. Equally, the reduction
in metalization on the rear side of the cell enhanced the operating
temperature of the cell, keeping it lower for higher efficiency.
Using its vast experience and know-how in the use of rearside cell
passivation with PERC, REC was able to develop this technology for
n-type mono cells, where the rear of the cell is now totally diffused, i.e., it
has no tiny holes. This passivation layer is known as Passivated Emier
Rear Cell Totally Diffused (PERT) and acts like a barrier layer across the
complete area of the cell, separating the two negatively charged layers,
preventing recombination of electrons at the rear (passivation), keeping
heat generation low and allowing the cell to operate more efficiently
while giving high and stabilized conversion efficiencies.
To back this up, third party testing has shown that the REC N-Peak
Series has an NMOT value (Normal Module Operating Temperature)
of a market-leading °C and a temperature coefficient, the by
which a module loses power generation capacity for every °C rise in
temperature, is also reduced to an impressive ./°C.
What advantages does a split junction box offer?
The use of a three-part split junction box is key to enabling the ‘twin’
section cell layout seen in REC N-Peak Series modules. Spliing the
junction box into smaller parts uses less metallization, again reducing
resistance in the module and saving space. In turn, this then allows a
slightly larger gap between cells increasing the internal reflection of
light that does not land directly on a cell and therefore the likelihood
that it is captured and can contribute to energy generation.
Power loss = R x I, where R is the resistance and I is the current
With three smaller boxes used, there is a reduction of between and
°C in heat build up compared to a standard module. This keeps the
cells cooler, increasing cell absorption efficiency, module reliability and
overall output.
The use of the split junction box on the rear (fig. ) is also the key factor
which enables the module to be split into two ‘twin cell sections’ of
half-cut cells connected in parallel (fig. ). With this layout design, the
module can continue to produce energy, even when one part of the
module, or the string, is shaded. What this means, is that rather than
the shading causing a bypass diode to be activated and a cell string
the complete length of the module being circumvented, bringing the
complete string capacity down with it, instead only half the length of
a module is bypassed, enabling at least of the module to continue
contributing to the module’s higher overall energy yield.
What advantages does REC’s new frame design offer?
Although thinner in height at only mm, the new frame structure of
the REC N-Peak Series in fact offers more strength and robustness
than standard products. A three year development project enabled
the use of two support bars on the rear for the first time on a -cell
module, increasing its load-bearing strength dramatically.
Fig : Rear view of the REC N-Peak module with support bars and split junction box
The two support bars across the rear prevent the glass and laminate
from bending as far as it would otherwise under heavy load. The
reduced deflection means the cells are less susceptible to damage,
increasing their durability and long-term reliability as the chance of
breakage and deformation is greatly reduced. Testing has shown that
the support bars truly limit module deflection and deformation, with
less than degradation aer mechanical load testing. Indeed, the
support bars add so much extra strength that the module can even
withstand downward loads of up to Pa.
Conclusion:
The use of mono n-type technology in the REC N-Peak Series pushes
module power, efficiency, and wa classes, ever higher. With their
higher purity levels, mono cells are more efficient at turning sunlight
into energy with the subsequent addition of n-type technology boosting
cell efficiency even more. An improved temperature performance due
to PERT helps protects the cells from overheating helping achieve
even higher efficiency and with no boron present in the cell bulk, there
is no occurrence of LID; the benefit for customers being no immediate
power drop upon first exposure to sunlight. The result of all of this is
higher energy yield for customers.
However, the initial power level of a solar module is not the only critical
feature, but also the performance over its entire lifetime. It is here that
the REC N-Peak Series excels the new frame design provides additional
robustness, affording increased protection to the high performance cells
over a longer period of time.
With cell level technology enabling increased energy generation and the
stronger frame design ensuring that power is preserved over decades,
the REC N-Peak Series is supported by a warranty of maximum
degradation in year one and . degradation in years , leading to
a final value of aer years, making it the ideal solar module for
high energy generation over its entire working lifetime.
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