From Morning Sun to Indoor LED Light: Uncovering How Light Intensity Inspires Green Energy from Photovoltaic Cells

With the popularization of renewable energy, solar cells have gradually become one of the most important sources of green energy. However, many people may not be aware that the power generation efficiency and power generation of solar cells are affected by a variety of factors, the most important of which is the light conditions. So, how do light conditions affect the power generated by solar cells? Today, we will popularize this topic.

1. light intensity and power generation
Light intensity, simply put, is the radiant power of sunlight per unit area. For solar cells, the higher the light intensity, the more energy received by the solar cell, the higher its output power. Therefore, on sunny days with strong sunlight, the power generated by solar cells is usually higher.
The power generation capacity of a photovoltaic cell is usually measured under standard test conditions at a light intensity of 1000 W/m², which is the standard value used in laboratories to simulate sunny day light. When the light intensity increases, the photovoltaic current in the solar cell increases, which in turn increases the output power; conversely, if the light intensity decreases, for example on cloudy days or during sunset hours, the power generated by the cell decreases significantly.
Light intensity varies over the course of the day. Beginning in the early morning, the sun gradually rises, the light intensity also increases gradually; at noon, the light intensity reaches its highest value; in the afternoon, as the sun gradually sinks in the west, the light intensity gradually weakened until the sunset disappears completely. This change in sunlight intensity directly affects the solar cell power generation in a day.

2. Light angle and power generation efficiency
The angle of light will also have a great impact on the power generation of solar cells. When sunlight is incident vertically on the surface of the solar cell, the photovoltaic cell can absorb the most light energy, and thus the highest power generation; and when the sunlight is oblique, part of the light will be reflected, the light energy absorbed by the battery is reduced, and the power generation is correspondingly reduced.
In order to maximize the power generation efficiency of the cells, many solar systems are equipped with sun tracking devices that automatically adjust the angle of the PV cells according to the position of the sun to maintain the optimal angle of incidence. This technology has been effective in increasing the overall power generation of PV cells.

3. The impact of light duration on power generation
Light duration is also an important factor that affects the power generation of solar cells. The longer the light hours in a day, the more total electricity a solar cell can generate. This is why at high latitudes, solar cells generate relatively less electricity due to short winter light hours, while in areas with long light hours, the amount of electricity generated throughout the year is higher.
In addition to this, seasonal changes also affect the light hours. For example, in summer, when days are longer, solar cells are able to generate electricity for a longer period of time; whereas in winter, when days are shorter, the time and total amount of electricity generated will naturally decrease.

4. Climatic conditions and photovoltaic performance
Climatic conditions can likewise have a significant impact on the power generated by solar cells. Under cloudy and hazy conditions, the sun's rays are blocked by clouds or suspended particles, leading to a reduction in the amount of light energy received by the PV cell, and the power generated will be significantly reduced. In addition, rain and snow can also affect the absorption of light by PV panels, reducing the power generation performance of the cells.
Interestingly, the performance of PV cells does not only depend on the strength of the sunlight, sometimes too strong sunlight may not be a good thing. For example, the power generation efficiency of solar cells tends to decrease under high temperature conditions because the increased temperature increases the resistance inside the cell, which leads to lower power generation. This is why, in some areas, people keep their PV modules cooler by using cooling systems to increase their power generation efficiency.

5. Effect of spectral composition
Sunlight consists of photons of different wavelengths, known as the spectrum. Solar cells absorb different wavelengths of light differently, and variations in spectral composition can also have an impact on the power generated by solar cells. In general, PV cells have the highest absorption efficiency for visible light and relatively low absorption for ultraviolet and infrared light. Therefore, the power generation performance of PV cells is better when there is more visible light component in the spectrum.
When the skies are cloudy, or in the early morning and evening, the spectrum of sunlight changes, with a decrease in the visible component and an increase in the infrared component, and the power generation efficiency of the PV cell decreases in this case as well. In order to improve the spectral response of photovoltaic cells, some research has been devoted to the development of materials capable of absorbing a wider range of the sun's spectrum, such as chalcogenides, which have shown better light-absorbing properties under laboratory conditions.

6. AM 1.5 G Test Standard
In the testing of photovoltaic cells, it is common to use AM 1.5 G as the standard spectral condition. AM stands for Air Mass, and AM 1.5 means that the path of the sun's rays through the atmosphere is one and a half times longer than the sun's direct vertical path through the atmosphere. AM 1.5 G is a standard widely used worldwide and represents the spectral condition of the sun's rays passing through the atmosphere and on the earth's surface on a clear day, which corresponds to a light intensity of about 1000 W/m². AM 1.5 G is a globally used standard that represents the spectral conditions produced by light passing through the atmosphere and onto the Earth's surface on a clear day, and corresponds to a light intensity of approximately 1000 W/m² and a luminous intensity of approximately 100,000 Lux.
The use of AM 1.5 G ensures that the test conditions in the laboratory are as close as possible to the actual conditions in order to accurately assess the performance of the solar cells in everyday environments.

7. Indoor light standards and intensity
There are also national standards for indoor light intensity. For example, according to China's relevant national standards (e.g., Building Lighting Design Standard GB 50033-2013), indoor spaces for different purposes have different light requirements. Generally speaking, the illuminance level for an ordinary office environment should be around 300-500 Lux, while the illuminance standard for a school classroom is higher, usually above 500 Lux.
For indoor light intensity per square meter, when converted to power, it is usually between 5-15 W/m², depending on the actual type of light source and light efficiency. This light intensity is far below the standard for outdoor sunlight, but is sufficient for daily activities and lighting indoors.

8. Environmental factors affecting light conditions
In addition to the factors mentioned above, shading by pollutants such as dust, bird droppings, leaves, etc. can also affect the light conditions of the PV cells, thus reducing the power generated. These obstructions will prevent part of the sunlight to reach the surface of the photovoltaic cell, the formation of the so-called “hot spot effect”, that is, the temperature of the blocked cell increases, not only reduces the efficiency, but also may cause damage to the cell.
To prevent this, PV cells need to be cleaned regularly to ensure that the surface remains clean and to maximize light absorption. For some areas located in areas with a lot of sand and dust or frequent bird activity, installing a self-cleaning coating or setting up a cleaning system are both more effective solutions.