Technology

A redesign of the backside of the cells to improve the capture of light falling on the surface compared to standard diffusion technologies.

This is done by applying a dielectric layer made of aluminum oxide to the back of the cells that reflects the light passing through it without being converted into light, thus getting a second chance for the reflected light.
Besides this also passivation layers and antireflection layers out of silicon nitride are applied, as a result, the PERC solar cells achieve higher efficiencies (21-22% eff. rates for monocrystalline cells) and the Levelized cost of Energy (LCOE) becomes much more competitive.

Combining the advantages of crystalline silicon (c-Si) cells with the superior passivation characteristics and good light absorption of amorphous silicon (a-Si) make cells with extremely high-efficiency rate (23-25%), outstanding temperature coefficient, and remarkable behavior under low light conditions.

Production is done by applying thin layers of doped and intrinsic amorphous silicon together with transparent, conductive oxide layers (TCO) made usually of indium tin oxide (ITO) on both sides of an n-type monocrystalline silicon wafer, this also results in consisting performance for the long term without LID (light-induced degradation) effect that occurs in p-type solar wafers and PID (potential-induced degradation) which is avoided by the extremely conductive TCP coating on both of the sides of the cells.

Similar metallization pattern as in the front side of the cell but with possible slightly thicker dielectric coating and different color the rear side of a bifacial cell has no full area contact as in the case of the aluminum back surface.

Bifacial modules require a transparent back sheet or glass at the rear side and a more optimized placement for the junction box.

The light intensity in the back of the module is typically 10-40% than the front (depends on the installation) which provides a typical increase in module power of 10-20%.

A typical solar cell consists of thin Ag fingers that collect the cell current and transfer it to the thicker busbars (usually 4 to 5) which are subsequently connected to the module ribbons.

Increasing the number of busbars to 9-12 in multi busbars metallization pattern reduces the current per ribbon and shorter the distance the current has to travel to them and thus reduces the resistive losses in both parts of the process.

By reducing the resistance of the cell thinner contact fingers can be used which lower the production costs.

In addition to that, the cell is more resistant to after production cracking due to higher busbars usage.

In opposition to typical solar panels with glass only in the front and back sheet in the back, the glass-glass design has glass instead of in the back making it much more sustainable and with a lower yearly degradation rate.
This reflects among others in higher manufacturer warranty (30 years in oppose to standard 25 years) and more suitable to harsh environments conditions such as high humidity, high temperatures, and sandy environment
This design is usually 20% heavier than the back sheet counterparts although they don’t require aluminum frames and should be considered in case of limited loading capacity.
The frames version is more suitable for floating projects and tracking systems as they give the highest resistance against severe mechanical stress.

Some panels are now using cells that are cut in half instead of full square/pseudo-square cells and gaining a higher efficiency rate by lowering the resistivity losses as each cell yield half of the normal current.
Since resistive losses scale with the square of the current and linear with the resistance, this reduces the resistive power losses in the strings by 75%.
An additional advantage of half-cut cells is that they are better with shading losses due to the way they are internally wired between them in the panel.
The cutting process is done at the end of the solar cell manufacturing process allowing minimum changes in the production line but a possible additional investment will be needed in the modules manufacturing line with regards to tabber-stringer equipment that can handle half-cut cells

Solar panels shingling is made by cutting the solar cells into smaller strips along the busbars and directly interconnect them by placing them onto each other like roof tiles.
This results in higher density and efficiency rate, aesthetic appearance, lower currents which results in potential lower resistive losses and less vulnerability to mechanical and environmental stresses.
Production is more complex compared to standard modules due to the cutting, placing, and interconnecting process which results in higher prices among others.
Highly used in BIPV (Building Integrated photovoltaic) due to the much uniform appearance compared to conventional modules.