In real-time situations, solar panels may not always get direct sunlight from the sun. For instance, where there is shade / covered by other buildings and also when it is cloudy/rainy the production output might get affected.
So, solar panels perform at their best level when direct sunlight hits them. To understand how the performance gets affected in terms of indirect sunlight first we need to understand how radiation from the sun reached the earth's atmosphere. The amount of radiation reaching the earth's atmosphere is less than what is in outer space. Once they hit the atmosphere these light rays are categorized as
Global Horizontal Irradiance (GHI)The total amount of direct sunlight hitting perpendicular to the surface of the solar panels.
- Diffuse Horizontal Irradiance (DHI)
DHI does not have a direct path from the sun. It gets scattered by particles in the air, and clouds and hits the solar panels after getting reflected.
- Global Tilted Irradiance (GTI)
GTI refers to irradiation on a tilted surface. The solar panels are mounted at a particular angle and the sunlight hits these panels.
- Albedo
Albedo refers to the solar irradiation reflected from the ground.
Solar panels produce power by a combination of the above-mentioned direct and indirect irradiation inputs. So, if there is no direct irradiation, then the panels will still produce power but there will be a drop in the performance of the panels. When considering shade, solar panels will generate less power output as they are not in their optimum conditions. These factors impact the amount of shading the longer the solar panels are under shade there will be less optimum output. Sunlight and shade are wary throughout the day so in general, the optimum production will vary throughout the day. Different types of clouds do have an impact on the power output. Do Solar Panels Work on Cloudy Days? the article describes the different types of cloud sources and how it affects the electricity production of the panels.
In recent years newer technology has been introduced into the market that is designed to reduce the impact of partial shade. These cells are known as half-cut cells. Compared to the traditional standard silicon cells each whole solar cell is cut into half making them half-cut cells, this, in turn, increases the number of cells in a solar panel and improves the performance and durability of the module. These half-cut cells have in total of 120 and 144 half-cut cells. With these half-cut cells, there will be a reduced resistive loss and increased power output. Figure 1 shows the different cell dimensions used in the past according to the ITRPV, half-cut and quarter cut cells will dominate the
Figure 1: Different cell dimensions.
So in terms of shading, when you have two strings in parallel when there is shading on the lower side of that panel, the current will be lowered but these shaded cells can be completely isolated while the top part (unshaded cells) will be producing full power.
The kind of inverter installed will also play an important factor. For example, if a string inverter is used in the system then shading in one panel will significantly affect the power output for the entire solar array. On the other hand, using microinverters /DC optimizers will not affect the entire solar array. As each microinverter is connected to every solar panel in the array this is will not affect the power output. Shade on a single panel will only cause a small drop in the power production.
If you want to know more about the basic types of solar inverters available in the market, this article will give you the basic information you need to know.
Shortly, solar panels work best in direct sunlight but in a residential area is it not always possible for the solar panels to be under direct sunlight in that case, they will work perfectly fine but they won’t be as efficient.