You have installed solar panels, but are worried that in cloudy weather photovoltaics will not generate electricity. So it is reasonable to ask: does photovoltaics work without the sun?
Solar energy is one of the energies of the future. Because it is clean, sustainable and endlessly available. However, this form of energy generation also brings problems with it. After all, the sun doesn’t always shine when you need electricity. But what actually happens when the sky is cloudy? Does photovoltaics work without the sun? Or can no electricity be generated at all? We will clarify these questions in this article.
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What is photovoltaics?
The origin of the name photovoltaics can be found in Greek. The syllable “Phos” stands for light, or more precisely for sunlight, and “Volt” refers to the electrical voltage.
The term therefore refers to the generation of electricity from sunlight, or more precisely from high-energy light waves. It should not be confused with solar thermal energy, which is also often referred to as solar power. This is because no electricity is generated here, but “only” service water is heated.
How does photovoltaics work?
Unlike solar thermal energy, which relies on long-wave infrared radiation, a PV system uses high-energy, short-wave ultraviolet light rays to generate electricity. But how exactly do photovoltaic systems work? The solar system is made up of semiconductors.
Widely used are silicon semiconductors, which are assembled to form the visible collector modules. These semiconductors are composed of different layers that react to the incident light radiation.
The substances embedded in these layers are excited, causing the molecules to vibrate. Through the emission and absorption of electrons, a current of electrons is ultimately generated – energy flows. This process takes place countless times in each module.
By means of rectifiers and inverters, the voltage is then transformed so that it can be fed into the power grid and used.
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Sunlight – the engine of solar energy
In order to generate electricity from solar energy through the photovoltaic process, the sun is indispensable. More precisely, it is its rays that transport the necessary energy. In order to excite the molecules in the semiconductor, the energy of the sun’s rays is required.
It is expressed in the oscillations with which the light beam travels. Short-wave rays, i.e. ultraviolet light, are particularly energetic.
A short wave amplitude means a high frequency and thus a high energy content. But longer-wavelength light can also be harnessed via the semiconductor, albeit with a lower yield.
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Direct versus diffuse radiation
Sunlight consists of a mixture of different types of radiation. Direct radiation travels in a straight line from its origin to the solar collector. Indirect or diffuse rays, on the other hand, are refracted and redirected by clouds, fog, or other disturbances in the atmosphere.
They reach their destination in a roundabout way and therefore arrive at the collector on completely different and unpredictable paths and angles.
In figures, this means that the complete solar radiation hitting the earth carries about 1340 watts per square meter of surface.
If you take into account factors such as scattering or adsorption of rays, you are left with about 120 watts of usable energy per square feet. In USA and Europe, however, only about 50 percent of this energy comes from direct radiation.
The other half of this energy is diffuse, i.e. non-targeted, light radiation that travels through the atmosphere.
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Does photovoltaics work without the sun?
The question of whether photovoltaics will work without the sun is a legitimate one. However, one thing should be made clear in advance: No solar system can function entirely without sunlight. This is because when the sun’s rays are absent, there is simply no electrical voltage.
Therefore, the question should rather be: Can a system function and generate electricity without direct sunlight?
The answer is yes. Because in addition to direct radiation, a certain amount of diffuse light is always present and thus also involved in electricity generation. Even if these rays can be used less effectively, they still contribute their share to the electricity generated.
What power is available without the sun?
On sunny days, the proportion of rays that directly hit the solar system is around 75 percent. Only 25 percent of the exposure is diffuse. On cloudy days without sun, on the other hand, the proportion of diffuse radiation is around 92 percent.
Accordingly, an equally large proportion of the (admittedly lower) energy yield on sunless days is generated via precisely this diffuse solar radiation.
For your solar system, this simply means that it will perform and generate electricity even without direct solar irradiation on the collectors. Various conclusions can be drawn from this’, which we will discuss in more detail in the following sections.
Solar energy despite clouds and fog
Due to the usability of diffuse radiation, your photovoltaic system can produce power even without direct irradiation from the sun. This means that you can expect an almost year-round yield of electrical energy. This increases the performance and thus the profitability of your PV system.
If you include the gains from diffuse light in the payback calculation, the duration until cost recovery decreases. Your solar system becomes more economical.
This effect is often neglected in such profitability calculations, but it practically contributes to the overall success.
Photovoltaics without sun – yield possibilities for worse locations
This explains why even supposedly unfavorable locations can sometimes be worthwhile for the installation of a solar system. Although a lower yield must be expected in these locations, it is more constant.
Thus, large areas facing away from the sun can also provide yields when set up economically and contribute their share to the overall success of a larger interconnected system.
Even without the sun, the PV system produces yields!
Solar power is environmentally friendly and efficient. And that even if the necessary sun rays are missing. Photovoltaics completely without sun – unfortunately, this is not possible. But the high proportion of diffuse radiation makes a PV system worthwhile even when the sun is not visible.
This means that during clouds, fog and other times without intensive sunlight, a solar system continues to generate electrical energy diligently.
This opens up new possibilities and puts the profitability and practical possibilities in a whole new light.