Do solar panels work on cloudy days? The truth about using solar panels on cloudy days

f you’re new to solar, one of the first things you might wonder is, "Do solar panels work on cloudy days?" A perfectly reasonable question considering their main job is collecting sunlight and converting solar irradiance into electricity.

Do solar panels work on cloudy days?

It may be surprising to some, but solar panels actually do work on overcast days. Even though PV cells perform better when exposed to direct sunlight, they can also well function under indirect radiation, albeit with less efficiency. Let us explore this process in a little more detail.

How does the solar system operate on cloudy days?

To better understand how solar panels work on cloudy days, let’s briefly go over their basic operating principle. A solar cell – the smallest operation unit of a solar panel – is usually made of two layers of semi-conducting material, most commonly silicon. One of these layers is doped with phosphorous and another with boron, which gives them opposite charges. At the junction of positively and negatively charged layers an electromagnetic field is created.

When the sun's rays hit the surface of the cell, photons (the smallest particles of light) knock electrons inside it loose from their standard positions and the electric field pushes them from the n-p junction. The movement of these electrons creates the flow of electricity, which is transferred further by the wiring.

So, we found that solar panels generate electricity by absorbing photons. But what happens when the clouds block a part of the light emitted by the sun? Cloud cover reduces the intensity of solar irradiance hitting the Earth, but a significant number of photons still reach its surface, and thus can be absorbed by the solar cells. Thus, cloudy skies don’t mean your solar system won’t generate electricity, it’ll just be somewhat less efficient.

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Efficiency drop of solar panels on cloudy days

Unfortunately, on cloudy days your solar panels will produce less power compared to their normal output. The loss in output will largely depend on the thickness of the cloud coverage. Scattered and sparse clouds would result in a drop in energy production of around 10-15%, while fully overcast skies can lead to a 70-90% decrease in performance.

But sometimes clouds can even slightly increase the output from solar panels. PV cells can absorb not only direct but also reflected light, which means they can simultaneously collect both direct sunlight and the light reflected from the clouds. As a result, solar panels on cloudy days can get more irradiance and thus produce more electricity than they could on a sunny day.

Does fog reduce solar system efficiency?

Another question that prospective solar buyers tend to ask is, do PV panels generate electricity on foggy days? Fog blocks sunlight in a similar manner to clouds, which means less of it eventually reaches the panels. But then again, a decrease in energy production depends on fog density. Generally, even in a thick fog solar systems can work with about 50% efficiency. Besides, fog usually dissipates before midday, so it causes less trouble than clouds for solar operation.

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How does rain affect solar system performance?

The rain itself won’t hinder the efficiency of solar panels. In fact, it will help them work better: the rainwater will wash away dirt and debris and thus improve their performance. The real problem here is the density of the cloud cover associated with rainy weather. Dark and thick rain clouds are likely to block a great deal of sunlight from hitting the solar panels.

What solar panels work best on cloudy days?

There are no specific solar panels that are designed to better handle cloudy days; however, the type of solar technology does matter. Monocrystalline solar cells are manufactured from a high-quality single piece of silicon - this structure enables electrons to move freely within the cell. This makes monocrystalline modules more efficient and helps them work better in lowlight conditions.

If you have a fair amount of cloudy days in your area, it may make sense to simply add more panels to your solar system. But in case your rooftop space is limited, the best solution will be to choose the most efficient solar modules on the market.

How to ensure a sufficient power supply when my solar system underproduces?

Insufficient power supply during cloudy days is a common concern among solar customers. To minimize the impact of overcast conditions on solar PV performance, you have to install your system with the right orientation and at the optimal angle. This greatly affects the amount of sunlight solar cells will be able to capture.

Underproduction is not an issue for grid-tied solar systems with net metering, as on cloudy days their owners can simply pull electricity from the local utility grid without financial loss.

And finally, homeowners who would like to avoid any electricity shortages during gloomy days should consider pairing their solar system with battery storage. With a solar battery, you will be able to keep any extra energy your PV system generates on sunny days and use it later when your panels underperform due to cloudy weather.

Key takeaways

Solar panels normally lose some percentage of their output on cloudy days. The scale of efficiency drop will mostly depend on the density of the cloud coverage: scattered translucent clouds allow more photons to pass through them and reach solar cells, while thick rainy clouds block the sunlight almost completely resulting in a significant drop in solar production.

However, you can minimize the negative impact of overcast weather by buying more efficient solar panels and choosing the best installation angle. In addition to this, to balance the underperformance of the solar system during lowlight hours you can pull energy from the grid if your solar system is tied to it or take energy from the battery if you have one.  

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