Why are solar panels available in black and blue?

Many news outlets and PV-related articles frequently use the term 'blue ocean of solar panels' to depict the sweeping sea of panels found in massive solar farms.

But since the majority of solar panels we encounter every day are black, how come these articles keep using 'blue' to describe them?

The reason is that solar panels actually come in both black and blue. Typically, the panels that appear black are monocrystalline, whereas the blue ones are polycrystalline.

• Blue Solar Panels: The internal cells are made of polycrystalline silicon, which is produced using a casting process. This results in multiple silicon crystals of varying sizes inside, with grain boundaries existing between them. Light scatters at these grain boundaries. Additionally, the silicon nitride anti-reflective coating commonly used during manufacturing creates an interference effect for specific wavelengths (such as blue light). These two factors combined give polycrystalline panels their characteristic grainy appearance, typically showing up as light blue, blue-gray, or indigo. Polycrystalline panels represent an earlier technological path in photovoltaics.

• Black Solar Panels: The internal cells are made of monocrystalline silicon, which is grown using the Czochralski method. This results in a highly complete and ordered crystal structure with neatly arranged atoms. Such a structure ensures an extremely low light reflectance on the surface (typically below 3%-5%), allowing most visible light to be absorbed. Combined with advancements in cell texturing technology, the optimization of silicon nitride film thickness, and improvements in photovoltaic glass coating technology, monocrystalline solar modules present a uniform deep black appearance. Monocrystalline panels have been the mainstream photovoltaic technology path since 2019.

Apart from the difference in color, these two types of solar panels also vary significantly in efficiency. Blue solar panels, which are polycrystalline modules representing earlier photovoltaic technology, typically have a power generation efficiency of below 18% (with cell sizes of 166mm or smaller). In contrast, current black monocrystalline modules generally achieve efficiencies exceeding 23% (utilizing larger cell sizes such as 166mm, 182mm, 183mm, or 210mm).

You can simply distinguish whether a solar panel uses monocrystalline or polycrystalline technology by its color. However, this method relies on the color of the panel's front side. Due to the lack of a textured surface, the back side of bifacial monocrystalline modules still appears blue.