The PV yield is lower when the sky is cloudy than when the sun is shining directly. However, the solar cells in the solar modules generate solar energy even when the sun is shining less. In this guide, you will find out what influence clouds and shade have on photovoltaics.
First things first
PV system in cloudy conditions
A PV system also works when it is cloudy. When the sky is overcast, it achieves 10 to 25% of the yield when the sun is shining.
Photovoltaics without sun
Photovoltaics do not work without the sun. Therefore, no electricity is produced at night. Moonlight is not enough for this.
solar system in the shade
Solar also works in the shade. The yield is then up to 90% lower than usual. Therefore, avoid permanent shading.
Diffuse light
Photovoltaics do not need direct sunlight to function. It can also absorb diffuse light.
Does photovoltaics work without sunlight and in the shade?
Solar systems also work without direct sunlight and in the shade. However, the solar yield then drops to about 10 to 25% of its normal output. The amount of available light counts for solar power production and this is available even without sun.
Contrary to popular belief, a solar system does not necessarily produce the most solar power in hot weather with lots of sunshine. Then the solar modules overheat and their performance can up to 25% This is why the technical data for solar modules states 25°C as the optimal temperature for power generation.
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What is the yield of a photovoltaic system without sun and when the sky is overcast?
On dark days with overcast skies and no sun, global radiation is about 200 W per square meterThis results in a yield of 0.15 to 0.30 kW per kWpA solar system with an output of 5 kWp generates under such conditions about 1000 watts.
Global radiation is the portion of solar energy that actually reaches the earth's surface. It consists of direct radiation and diffuse radiation.
The difference:
- Direct radiation: Sun rays that hit the ground directly.
- Diffuse radiation: Sun rays refracted onto the earth's surface.
On sunny days, diffuse radiation is about 25%When the sky is overcast, diffuse radiation increases to about 92% and the photovoltaic system produces less electricity.
| nominal power of the PV system | yield without clouds | yield under medium cloud cover | yield in heavy cloud cover |
| 6 kWp | 6,000 kWh | 3,600 kWh | 1,200 kWh |
| 7 kWp | 7,000 kWh | 4,200 kWh | 1,400 kWh |
| 8 kWp | 8,000 kWh | 4,800 kWh | 1,600 kWh |
| 9 kWp | 9,000 kWh | 5,400 kWh | 1,800 kWh |
| 10 kWp | 10,000 kWh | 6,000 kWh | 2,000 kWh |
| 11 kWp | 11,000 kWh | 6,600 kWh | 2,200 kWh |
What happens if the PV system is partially shaded?
If the PV system is partially shaded, the bypass diodes in the solar modules switch off this part and redirect the current. Bypass diodes divide the module into three parts and protect the module. However, bypass diodes have a limited lifespan and fail under constant load, which leads to considerable damage.
| shading of the PV system | PV power |
| 5 PV modules without shading | 100% |
| partial shading, 1 module | 80% |
| partial shading, 2 modules | 60% |
| partial shading, 3 modules | 40% |
| partial shading, 4 modules | 20% |
| full shading | 0% |
To be on the safe side or in the case of permanent partial shading, PV optimizers or micro inverters are recommended.
Does a PV system work when it is cloudy?
A PV system works even when there is less solar radiation when it is cloudy. Under ideal weather conditions, solar radiation in Germany is between 800 and 1,200 W/m². When there is light cloud cover, solar radiation drops to 400 and 800 W/m². When there is heavy cloud cover, global radiation is only 200 W/m².
A PV system continues to generate a yield of 10 to 25 %because global radiation is made up of direct and diffuse radiation. Direct radiation refers to the sun's rays that hit the ground directly. Diffuse radiation refers to the sun's rays that are refracted on the ground.
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Does photovoltaics work completely without sun?
Photovoltaics do not work without the sun. Therefore, no energy is generated at night. This is because there is no absorbable sunlight available. The moonlight is not enough to activate the solar modules. Therefore, they become inactive and no longer produce electricity during the night.
But photovoltaics also works without electricity generation if the PV system is equipped with a electricity storage The power storage unit stores excess solar power during the day instead of feeding it into the public power grid. The stored solar energy is used when there is no sun.
How much electricity does a PV system produce in winter?
Only 30 to 35 percent of the annual average yield of a photovoltaic system is achieved in winter. The reason for this is the lower radiation output the sun and the higher average amount of diffuse light due to cloud cover. On a midsummer day, up to 20 times more solar energy can reach the earth than on a cloudy winter day.
| solar radiation | No clouds | Light to moderate cloud cover | Cloudy / foggy |
| Summer | 600 to 1000 W / m² | 300 to 600 W / m² | 100 to 300 W / m² |
| winter | 300 to 500 W / m² | 150 to 300 W / m² | 50 to 150 W / m² |
Conclusion: Does solar also work in the shade?
Photovoltaic systems also produced without sun and in shade Energy. The solar cells absorb the photons contained in the diffuse radiation and use them to produce solar power. However, the performance of the PV system in the shade is up to 90% worse than in direct sunlight.
But good yields can also be achieved in partial shading. PV optimizers and module inverters can significantly increase the performance of your solar system under such conditions.
In order to achieve the highest possible efficiency of the solar modules, appropriate analyses, simulations and forecasts should be carried out during the planning phase of a PV system. Therefore, trust in experienced and certified solar installers.
