What are the advantages of CIS technology compared with silicon technology?

The CIS technology offered by Solar Frontier delivers higher specific energy yields (kWh/kWp) than other technologies. The main reasons for this are:

  • Good low light behavior in diffused light and with low irradiation angles
  • High shadow tolerance
  • High temperature stability
  • Light Soaking Effect

In short: the ideal module for use in real life conditions.

It should also be noted that the modules are manufactured without the use of any toxic materials such as lead or cadmium, as is confirmed by the RoHS certificate (see topic Environmental Aspects).

CIS technology also stands apart from other technologies because of its simpler manufacturing process, which consumes less energy and raw materials. And last but not least, we have only just begun to explore the full capabilities of CIS technology. There is still significant potential for enhancing efficiency much more quickly and simply. In contrast, the rapid advances in polysilicon technology are largely in the past, any further developments will probably be relatively gradual.

Please explain the Light Soaking Effect.

The buffer layer in the CIS module by Solar Frontier is responsible for the Light Soaking Effect. This layer is a component of the CIS thin film and ensures that the charge is transported more easily between the photoactive layer and the transparent contact (TCO) on the front of the module. Initially, this buffer layer forms an energy barrier, which makes the flow of electrons more difficult. Excited by the photons in the sunlight, the first electrons begin moving and neutralize the faulty areas which at first still remain in the boundary areas between the layers. This causes the energy barrier to shrink, electrons can flow more easily, and the serial resistance is lowered. Consequently the flow of energy increases and the module functions more efficiently. Unlike classic CIS, one of the remarkable features of the Solar Frontier technology is that toxic cadmium is replaced with zinc. Not only is this less harmful to the environment, it is also essential for creating the Light Soaking Effect. As a result, the properties of the buffer layer are improved and the module output increases. This effect is the result of years of intensive work by our research and development department.

How quickly does the Light Soaking Effect take effect?

The Light Soaking Effect starts as soon as the module is exposed to sunlight for the first time. Saturation is typically reached after about 50 to 60 hours of sunlight.

What is meant by better low light behavior or low angles of incidence?

The energy spectrum of sunlight varies according to the Air Mass (AM) factor. The air mass factor is a measurement of the path sunlight has to take as it travels through the Earth's atmosphere: AM = 1 stands for perpendicular incidence on the Earth's surface (midday at the equator), and AM > 1 stands for lower angles of incidence (sunrise or sunset). Although the absolute energy density of the radiated sunlight falls as the AM becomes larger, at the same time the energy shifts toward longer wavelengths (as evidenced in the red sky in the morning and evening). 

Since the Solar Frontier CIS modules are more sensitive than other technologies to this light at longer wavelengths, and even into the infrared range, the relative quantity of energy recovered at these times is significantly higher.

But the behavior of the modules using CIS technology is also more favorable than with c-Si modules in diffuse light conditions (also referred to as blue, low light) such as occur in full daylight when the sky is unclear, cloudy, foggy etc. This means that the spectral range of sunlight with shorter wavelengths and greater energy density can also be converted into energy more effectively by CIS modules than by silicon modules.

What does high shadow tolerance mean?

The cell structure of CIS modules is completely different from that of c-Si modules. The reasons for this are rooted in the technology and manufacturing processes: The narrow CIS cells run parallel to each other for the entire length of the module, whereas c-Si cells are typically square with a side length of 15 cm. In both cases, the cells are connected in series. If defined shadow conditions are to be expected in a given project (e.g., horizontal shadows in the morning and evening on a shed roof or free field), energy production can be optimized accordingly: The CIS modules in this case must be installed so that the cells are at right angles to the cast of the shadow, that is to say vertically (portrait alignment) in the shed roof example. If X% of a module or module array is in shadow, energy production is still retained at a level of (100-X)%.

What is "aurora"?

The "aurora effect" is a term used to describe the appearance of a mild, whitish haze on the CIS buffer layer. This is caused by our use of zinc instead of cadmium in this layer. Because of the manufacturing process, it may occur in <2% of manufactured modules, and is visually undesirable in only a very few of these cases. It is not a sign of any deterioration and has no effect whatever on the performance of the module. Moreover, aurora is only discernible when viewed at close range and from certain viewing angles.

Why are bypass diodes used in Solar Frontier modules when they are not used in CdTe modules?

Bypass diodes prevent an entire string from stopping production in the event that a single module is defective or completely overshadowed.

How do CIS-based modules perform compared with monocrystalline modules?

A meaningful comparison of the two module technologies can only be made, if at all, in terms of the highest specific yield generated by a module, that is to say the kWh/kWp; that is to say with regard to the better performance ratio. Monocrystalline silicon modules usually have the highest efficiency ratings or the highest output figures. However, these are measured under standard test conditions, which practically never exist as such in real life. A much more realistic comparison is the output capability of the modules under non-ideal conditions that predominate for reasons related to the weather or the systems themselves. These include: Non-ideal roof orientations (facing West, East or even North), non-ideal roof angle (too flat, too steep, curved), shading caused by chimney stacks, trees, terrain features; unfavorable angle of incidence of sunlight over the course of a day or year, low light, diffused light.

Solar Frontier CIS modules have been developed to provide the best possible outputs, that is to say the highest yields measured as kWh per kWp, under these less than perfect conditions as well. The result is optimum energy generation under all light conditions, including those that are not ideal. You can find more information and real comparative yield data in the area entitled CIS vs. other technologies on our homepage.

Do the Solar Frontier PowerModules undergo potential-induced degradation?

No. PID is associated with a reduction in module output caused by large differences in voltage between the module and the frame, as a result of which the material becomes more conductive, and leakage currents can occur within the module. There are a number of possible causes for this degradation. However, none of them can occur with our PowerModules due to the technological principles of their production, the CIS technology itself and the chemicals they contain. 

Is the output of the CIS PowerModules impaired by snail trails?

Snail trails are a phenomenon that can only exist on crystalline silicon modules. There are three different types of snail trail: discoloration of the silver-(Ag) paste at right angles across the c-Si cell, discoloration along the edge of the cell (formation of a "frame"), and discolorations emanating from the cell connections (also called "fingerprints"). Due to the chemical composition of Solar Frontier CIS modules and the technological differences between these and c-Si modules, it can be guaranteed that snail trails will not occur on Solar Frontier modules.