Debunking Myths About Polycrystalline Solar Panels

Solar energy is becoming increasingly popular, which gives rise to various myths about the types of solar panels, especially polycrystalline ones. Two common misconceptions are that polycrystalline panels perform better in cloudy weather, i.e. in low light conditions and that their multi-directional crystals are more effective at absorbing light from different angles. Let’s deal with these myths based on scientific evidence.

Myth 1: Increased efficiency in cloudy weather

It is widely believed that polycrystalline panels are more efficient in cloudy conditions compared to monocrystalline panels. However, scientific evidence suggests otherwise. Research in a scientific journal from Oxford Academic’Clean Energy‘ (Volume 6, Issue 1, February 2022, Pages 165–177) showed that

The differences in efficiency between these types of panels are negligible in low light conditions, but monocrystalline panels showed greater efficiency in all experiments.

Effect of crystal structure
In our previous article you can familiarize yourself with the differences between poly- and monocrystalline solar modules.
The efficiency of solar panels in converting sunlight into electricity is primarily determined by their crystalline structure. Monocrystalline panels, whose solar cells are made from a single crystal, are usually more efficient due to the smoother flow of electrons, i.e. silicon structure defects are minimal. In its turn, polycrystalline panelsconsisting of several fused silicon crystals, have slightly lower efficiency. Cloudy conditions reduce available sunlight and affect both types of panels equally, and there is no data to support the benefit of polycrystalline panels in such conditions.

Effect of light intensity
The intensity of sunlight on a cloudy day can differ significantly from a clear day. In central Russia, as in other temperate climatic zones, this difference can be quite significant. On a clear summer day in temperate latitudes, solar radiation can reach approximately 900 – 1000 W/m².

On cloudy days, the intensity of sunlight decreases depending on the degree of cloudiness. On heavily cloudy days, the intensity can decrease to 100-200 W/m², which is about 5-10 times less than on clear days. These are approximate values ​​and may vary depending on many factors including geographic location, cloud type and other atmospheric conditions.

Volt-ampere characteristics
The graph below shows the dependence of the current-voltage characteristic (volt-ampere characteristic) of a solar panel depending on the intensity of solar radiation using the example of a solar power of 450 W. It can be seen that as the intensity of sunlight decreases, the current generated by the solar panel mainly decreases and, to a lesser extent, the voltage generated. So on a clear sunny day, with a solar radiation intensity of 1000 W/m², the short-circuit current Isc ~ 11 A, and the open-circuit voltage Uхх ~ 42 V. With a radiation intensity of 200 W/m², Isc ~ 2.5 A, Uхх ~ 38 V. Thus Thus, when the light intensity decreases by 5 times, the generated energy decreases by more than 5 times, because As the current decreases, the voltage at the panel’s maximum power point also decreases. This behavior is typical for both poly- and monocrystalline solar panels.

Influence of solar radiation intensity on the type of current-voltage characteristic

Myth 2: Improved light absorption due to crystal orientation in semi-crystalline solar panels

This myth is based on the assumption that the unique structure of polycrystalline solar panels, consisting of many silicon crystals fused together, allows them to more efficiently absorb light from different angles compared to monocrystalline panels, which use a single continuous crystal.

The main flaw in this myth is a misunderstanding of how solar panels absorb light and convert it into electricity. The efficiency of a solar panel is determined by its ability to convert photons from sunlight into electrical current. This process depends more on the quality of the semiconductor material and the design of the cell itself, rather than on the direction or angle of incidence of the light.

People often think of the crystals in a polycrystalline solar cell as something like protruding crystals, as in the figure below, which can absorb light from everyone efficiently, because the rays hit them perpendicularly.

What do people think a polycrystalline solar cell looks like?

However, in polycrystalline panels, the boundaries between individual crystals can create additional obstacles to the movement of electrons, which slightly reduces their efficiency compared to monocrystalline panels. These internal boundaries do not improve light absorption; rather, they can create regions where electrons become stuck or recombine without reaching the junction and generating electrical current.

Additionally, modern solar panels, regardless of type, typically feature anti-reflective or anti-glare coatings and are optimized for maximum light absorption. These coatings are designed to minimize light loss due to reflection and are effective regardless of the type of crystalline structure of the solar cells in the panel.

What a polycrystalline solar cell actually looks like

Conclusion

Myths about the superior efficiency of polycrystalline solar panels in cloudy weather and improved light absorption due to crystal orientation have no scientific basis. The efficiency of absorbing light and converting it into electricity depends on many factors, including the quality of the semiconductor material, cell design, anti-reflection coating and overall panel design, rather than the orientation of the chips. This is supported by a number of scientific studies in the field of photovoltaics, demonstrating that the key aspects of the efficiency of solar panels are their physical and chemical properties, and not simply the orientation of the crystals within them.