Alpha Series Technology
No LID
Light Induced Degradation (LID) is a phenomenon seen in many
crystalline cell technologies, where a solar panel irrecoverably loses
power capacity during its initial phase of exposure to sunlight. This is
caused by the combination of boron and oxygen in the cell. Through
the use of n-type monocrystalline cells as a base, the REC Alpha Series
avoids this as these elements are kept separate in the cell and not
given a chance to combine. This means the REC Alpha shows no sign
of permanent loss of power immediately aer installation and the
customer will receive the power levels paid for.
High resistance against microcracks through HJT
A panel has to endure a lot of different weather conditions during its
lifetime. Heavy loads on the front side through snow, dynamic stress
from wind and daily temperature variations all put the panel under high
pressure. Under such conditions, the fragile cells in a conventional panel
can develop microcracks, potentially leading to a reduction in overall
performance. Independent testing by the University of Central Florida
(UCF) has shown that the reduced thermal and mechanical stress on the
cell during production leads to beer build quality and a high resistance to
such defects.
No direct contact with metallization
In conventional cells, the cell metallization is in direct contact with
silicon. This metal-silicon contact acts as recombination trap for
electrons and holes generated by light, reducing the efficiency of the
solar cell. However, an HJT cell employs a transparent conductive oxide
layer (TCO) deposited on top of the doped amorphous silicon, which
prevents direct contact between the contacts and the silicon, meaning
the ohmic losses seen in a conventional cell can be reduced.
As the TCO layers are conductive, there is less need for the high
amounts of silver paste found in conventional cells, which frees up
more HJT cell surface area for increased light capture.
Leading temperature coefficient
Through the use of HJT cells, the REC Alpha’s temperature ratings
are greatly improved. The REC Alpha Series demonstrates a market-
leading temperature coefficient - this is an indication of the percentage
loss in power for every °C rise above °C - and means continued high
efficiency performance even at higher operating temperatures.
Fig : Temperature ratings of standard panels compared to REC Alpha panels
Temperature ratings of panels: Standard Alpha
Temperature coefficient of P
MAX
: . /°C . /°C
Temperature coefficient of V
OC
:
. /°C . /°C
Temperature coefficient of I
SC
: . /°C . /°C
What is REC’s advanced cell connection technology?
The REC Alpha Series uses a specially-developed foil and wire
combination to create the contacts between the cell and the
metallization. This is a far less invasive process than the high
temperature soldering found on a conventional cell, protecting the
integrity of an HJT cell for beer quality while reducing the overall lead
content of the panel by .
Fig : Advanced low temperature connection joining two half-cut cells
Eric Schneller et al, PV Magazine Webinar, ., Fewer microcracks thanks to HIT
technology?,
www.pv-magazine.com/webinars/fewer-microcracks-thanks-to-hit-technology
To create the bond between wires and cell, the wires are first placed
on the foil, before the foil is placed on the cell (fig. ). The foil will act
as an extra protective layer against leakage and mechanical stress. The
foil is then lightly heated to ensure it stays in position during further
manufacturing stages. Once the panel reaches lamination, the outer
layer of the wires melts to form a fully mature bond to the cell. This
results in improved aesthetics as the wires are only / of the width of
the ribbons used on conventional cell connections.
What are the benefits of the REC Alpha’s advanced low
temperature connection technology?
One of the key advantages of the REC Alpha Series’s advanced cell
connection technology is that the number of manufacturing process steps
is far fewer than used to make conventional cells. Additionally, the Alpha’s
cells require only relatively low temperatures of ~°C compared to a
conventional cell where temperatures of up to °C or more are required.
Improved build quality
In a conventional panel, the ribbons need to be soldered to the cell
busbars with very high temperatures, creating high thermal stress
between the different materials. The advanced cell connection
technology is solder-free, so has no need to heat the cells so intensely
in production. The elimination of cell soldering produces a cell with far
fewer weak points, greatly reducing the chance of hotspots and other
defects occuring. and the lower temperatures used greatly reduce
the risk of damage caused by the difference in thermal coefficents
between materials, e.g., tin/lead solder mix and the silicon. By not
heating the cell in the same invasive way, there is a much reduced
chance of defects occuring in the cell structure which would otherwise
create internal resistance and reduce power.
When looked at practically, a conventional cell, based on halfcut
technology with ribbons and only solder points per ribbon has
soldering points per cell and cell solder points in total.
This makes the cells more susceptible to micro-cracks through the
regular appliance of heat and pressure. The REC Alpha’s advanced cell
connections however, see the wires directly applied to the cell surface,
meaning that no bus bars need to be printed on the cell, reducing
coverage of the cell surface. It also eliminates the cell soldering
process completely, i.e., there are zero ( solder points on the cell, and
only soldering points in the entire panel.
Improved current flow and reduced power loss
REC’s advanced low temperature connection technology is also about
reducing ohmic (resistance) losses in the panel. Reduced losses mean
more power, and higher energy yields. Testing has shown that an
increase in the number of wires to (from five busbars) provides the
best balance between reducing internal resistance and cell coverage to
achieve the most power. As a result the REC Alpha has over cell to
wire connection points per cell resulting in nearly . connections
in a full panel. This reduces the distance for current to travel and vastly
improves current flow (less ‘congestion’), for reduced power loss.
Increased efficiency through round wires
A further advantage of wires compared to conventional bus bars is that
their round shape increases reflection of sunlight onto the cell (fig. ). As
a result the cell can produce more energy resulting in a higher efficiency.
Fig : Illustration showing increased sunlight reflection of round wires compared to ribbons
How does REC guarantee the quality of cell connections?
As the advanced low temperature connection technology was a
proprietary development by REC and Meyer Burger, REC has been fully
involved at all development and testing stages.
Sunlight
Ribbon Wire
Cell