How Do Solar Panels Work on Cloudy Days and at Night?

Solar panels under the night sky
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Solar panels can use both direct and indirect sunlight in order to generate power, so they will continue to function even when the light is partially blocked by dense clouds or rain. That means solar panels will still generate electricity on cloudy days.

However, solar panels are not as efficient on cloudy days, and at night, they generate very little power. But that doesn't mean solar customers go without power on bad weather days or after dark. Solar battery storage and net metering ensure consistent access to electricity.

How Do Solar Panels Work on Cloudy Days?

More clouds mean that your solar panels will work less efficiently. When it comes to solar panels made with silicone (by far the most common material used to manufacture solar cells), a 20%-30% shading of the module can result in a 30%-40% reduction in the power output.

Solar panels convert sunlight to direct current (DC) electricity, most of which is inverted into alternating current (AC) to power electronics in the home. On exceptionally sunny days when your solar system produces more energy than is needed, the excess power can be stored in batteries or return to the public utility power grid.

This is where net metering comes in. These programs are designed to give solar system owners credit for the excess power they generate, which they can then draw on when their system is producing less energy due to cloudy weather. Net metering laws may vary depending on your state, and many utility companies will offer them either voluntarily or due to local legislation.

Do Solar Panels Make Sense in Cloudy Climates?

Solar panels are less efficient on cloudy days, but a consistently cloudy climate doesn’t mean that your property isn’t well-suited for solar. In fact, some of the most popular regions for solar power are also some of the most overcast.

For example, Portland, Oregon ranked 21st in the U.S. for the total number of solar PV systems installed in 2020. The even rainier Seattle, Washington, ranked 26th. The combination of long summer days and mild temperatures with a longer season of gloomy days works out in these cities’ favor, since excess heat is another factor that reduces solar output.

Rain and Solar Panels

Rain may help keep solar panels running efficiently by washing off dust and dirt. One study found that the accumulation of dust on the surface of photovoltaic solar panels can reduce efficiency by up to 50%.

Solar Power Forecasting

A 2020 Journal of Renewable and Sustainable Energy study proposed a new method for estimating the amount of sunlight available for solar power plants, since cloud cover is currently characterized subjectively using terms like “cloudy” or “partly cloudy” rather than exact measurements.

The new method, known as Spectral Cloud Optical Property Estimation (SCOPE), estimated three properties of clouds and determines the amount of sunlight reaching the Earth’s surface in order to give more accurate predictions for 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 both day and night at 5-minute intervals, which allows for more precise solar forecasting.

How Do Solar Panels Work at Night?

Solar panels at night
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While solar panels do not produce energy when it's dark outside, they will still be able to power your home during these times thanks to stored energy reserves and net metering. This wasn’t always the case, however, as earlier solar energy systems that couldn’t access the sun’s energy at nighttime meant that solar power was unavailable once the sun went down. Research and advancements in energy storage and battery backup systems have created more opportunities for the solar energy industry for both larger companies and residential homeowners.

Even now, breakthroughs in solar energy are happening all the time. For instance, researchers at the University of California Davis are working on thermoradiative solar cells that would heat up and draw energy from the cold night sky, just as traditional solar cells absorb light from the hot sun during the day. This nighttime photovoltaic cell could potentially keep generating power continuously without needing to rely on storing excess energy in solar batteries or on power grids (most of which run on fossil fuels). According to the study, the prototypes already made for the project can produce 50 watts of electricity per square meter, which is about 25% of what traditional solar panels are able to generate during the day.

Another study from the University of British Columbia found that the application of E. coli bacteria, interestingly enough, could help improve solar panel efficiency on cloudy days. Researchers took advantage of the bacteria’s natural ability to convert sunlight into energy by coating the organic material with metallic nano-particles before introducing it into an electrode. The project is still in its experimental phase, but has the potential to compete with conventional solar panel systems if they’re able to successfully market the material for widespread use.

Considering the Pros and Cons

Whether or not solar panels are worth it comes down to the individual consumer. Going solar will inflict higher short-term costs when it comes to installation, but could prove itself to be a smart investment if it lowers your electricity costs and carbon footprint. Although, cost may become less of a defining factor in the future, at least according to the National Renewable Energy Laboratory (NREL), a government-funded lab that studies solar cell technology in the United States.

NREL is tasked with analyzing the total costs associated with installing solar panels for residential, commercial, and utility-scale systems, and has found that both hard costs (the costs of the physical solar cell hardware itself) and soft costs (aspects like labor or government permits) have both decreased significantly since 2010. Total residential rooftop solar costs, which were previously the highest of the three categories, more than halved between 2010 and 2020. 

Considering states like Oregon and Washington that have a thriving solar panel industry despite their cloudier climates, it is absolutely possible to operate on solar energy even if you live in a region with cooler temperatures or overcast weather. If you’re not able to invest in solar storage batteries for your own solar system, it’s a good idea to look into net metering programs with your local electricity company to help offset the costs.

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