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How do solar panels work on cloudy days and at night?

Solar panels can use direct and indirect sunlight to generate electricity, so even if the light is partially blocked by dense clouds or rain, they can continue to function. This means that solar panels can still generate electricity on cloudy days.

However, solar panels are not efficient on cloudy days, and at night, they generate very little electricity. But this does not mean that solar customers will cut off power after bad weather or dark. Solar cell storage and net metering ensure continuous access to electricity.

More clouds means that the efficiency of your solar panels will decrease. For solar panels made of silicone (the most common material used to make solar cells so far), a 20%-30% shade of the module can cause a 30%-40% reduction in power output.

Solar panels convert sunlight into direct current (DC), most of which is converted to alternating current (AC) to power electronic devices in the home. On unusually clear days, when your solar system generates more energy than needed, the excess energy can be stored in the battery or returned to the utility grid.

This is where the net metering comes in. These plans are designed to provide solar system owners with credits for the excess electricity they generate, and then they can use this electricity when their system generates less energy due to cloudy weather. Net metering laws may vary depending on your state, and many utility companies will provide them voluntarily or in accordance with local legislation.

Solar panels are less efficient on cloudy days, but a persistently cloudy climate does not mean that your property is not suitable for solar energy. In fact, some of the most popular solar areas are also some of the most cloudy.

For example, the total number of solar photovoltaic systems installed in Portland, Oregon in 2020 will rank 21st in the United States. Seattle, Washington, with more rainfall, ranked 26th. The combination of long summers with mild temperatures and longer cloudy seasons is beneficial to these cities, as overheating is another factor in reducing solar output.

Rainwater can help keep solar panels running efficiently by washing away dust and dirt. A study found that the accumulation of dust on the surface of photovoltaic solar panels can reduce efficiency by as much as 50%.

A study in the Journal of Renewable and Sustainable Energy in 2020 proposed a new method for estimating the amount of sunlight available for solar power plants, because the current subjective characteristics of cloudiness are the use of terms such as “cloudy” or “partially cloudy”. It is not an accurate measurement.

This new method, called Spectral Cloud Optical Property Estimation (SCOPE), estimates three characteristics of clouds and determines the amount of sunlight reaching the surface of the earth in order to more accurately predict cloud cover: cloud top height, cloud thickness, and cloud optical length.

SCOPE can be used to provide reliable real-time estimates of cloud optical properties at intervals of 5 minutes to achieve more accurate solar predictions.

Although solar panels do not produce energy when it is dark outside, they can still power your home during this time due to stored energy reserves and net metering. However, this is not always the case, because early solar systems cannot obtain solar energy at night, which means that once the sun goes down, solar energy cannot be used. The research and progress of energy storage and backup battery systems have created more opportunities for the solar industry for large companies and residential owners.

Even now, breakthroughs in solar energy are happening all the time. For example, researchers at the University of California, Davis are working on radiant solar cells that can heat and absorb energy from the cold night sky, just like traditional solar cells absorb the light of the hot sun during the day. Such nighttime photovoltaic cells may continue to generate electricity without relying on storing excess energy in solar cells or the grid (most of which use fossil fuels). According to this research, the prototype that has been manufactured for the project can generate 50 watts of electricity per square meter, which is about 25% of the electricity that traditional solar panels can generate during the day.

Another study by the University of British Columbia found that, interestingly, the application of E. coli can help improve the efficiency of solar panels on cloudy days. The researchers used bacteria’s natural ability to convert sunlight into energy and coated organic materials with metal nanoparticles before introducing it into the electrodes. The project is still in the experimental stage, but if this material can be successfully marketed and widely used, it may compete with traditional solar panel systems.