Do solar panels work on cloudy days?

Key Takeaways:

• Solar panels lose about 23% to 67% of power output on cloudy days.

• High clouds affect solar panels less and “cloud lensing” can even boost sunlight.

• Low-angle solar panels or panels that face multiple directions are better at harnessing energy on overcast days.

You might love the idea of going solar except for one thing: most of the time, the sky above your house is gray. Many people wonder if solar panels are effective in regions with frequent cloud cover. The answer is yes, solar panels work on cloudy days, though their efficiency is affected. Understanding how clouds impact solar is important to maximizing your solar investment or even deciding that solar isn't worth it for you.

Do solar panels work on cloudy days?

Yes, solar panels do generate electricity on cloudy days, although at a reduced capacity. Cloud cover affects the amount of sunlight reaching the panels and reduces output by anywhere from 23% to 67% of their maximum potential, according to a University of Port Harcourt study. However, that’s not the whole story.

Some solar owners have seen they actually get more total power on a cloudy day than on a sunny one. This can be because clouds spread out the sun’s rays making them diffuse. If you have a solar panel section on a north-facing roof, this section will get more energy on a cloudy day than on a sunny one.

Also, the tilt of your panels affects things. Flatter panels can absorb more energy from an overcast sky during earlier and later parts of the day than more angled ones.

The bottom line is that cloudy days reduce solar panel output for most people but not in all cases.

How solar panels generate power

Let’s take a step back and review how solar panels work. Solar panels convert sunlight into electricity through photovoltaic (PV) cells. These cells, typically made of silicon, generate an electrical current when sunlight hits them and excites electrons inside. This photovoltaic effect produces direct current (DC) electricity.

An inverter then transforms this DC power into alternating current (AC), which is what your home or business can use. You can only use solar energy when it’s generated. You can store extra energy in a battery backup or feed it back into the grid.

Since the photovoltaic effect uses sunlight, solar panels naturally produce less electricity under clouds, at night, or during the winter months.

The effect of clouds on solar panels

There’s no getting around the fact that cloud cover reduces solar energy reaching the earth. However, high clouds let more energy through. You might not be able to tell whether you have more high or low clouds in your area, but it makes a big difference to your solar panels. Fog can also cut power, but how much your panels suffer depends on other conditions.

An interesting phenomenon called cloud lensing actually boosts the sun’s power through a cloud. This happens when ice crystals in high clouds act like a giant magnifying glass and focus the sun’s rays.

Cloud optical thickness (COT) also affects solar panel output:

• Thin clouds (COT < 3): 20 to 40% output retention.

• Moderate clouds (COT 3–6): 10 to 25% output.

• Thick overcast (COT > 10): Under 10% output, nearing zero during thunderstorms.

Dense cumulus clouds really reduce output, while high cirrus clouds allow better sunlight penetration. Stratus clouds reduce output moderately while multiple cloud layers compound the effect. The short answer to how clouds affect solar panels: it depends.

Direct vs. diffuse light

Solar panels utilize both direct sunlight and diffuse light. Direct sunlight provides the highest energy output, but PV cells can also harness diffuse light scattered by clouds and the atmosphere. This means you get energy from solar panels in a wide range of climates. Modern panels also use advanced materials that capture multiple light wavelengths, which boosts performance in suboptimal conditions.

Can rain or cool temperatures help solar panels?

Rain and cool temperatures can actually enhance solar panel performance. Rain washes away dust, dirt, and pollen, improving light absorption. Cool temperatures are also good for energy generation, as solar panels operate best below 77°F (25°C). 

Above this temperature, efficiency decreases because heat affects how electrons behave in the PV cells. Since cloudy days often bring cooler temperatures, this can offset losses from reduced light. So, a cooler and cloudy climate isn’t all bad for solar.

Maximizing solar output on cloudy days

To maximize solar output in cloudy conditions, consider the following strategies:

• High-efficiency monocrystalline panels: These panels capture diffuse light more effectively due to their crystalline silicon structure. Monocrystalline panels with backside mirrors or bifacial panels can capture even more diffuse light. However, bifacial panels are best for commercial or industrial applications.

• Optimal orientation and tracking systems: Fixed-tilt systems in cloudy regions benefit from lower tilt angles (15°–30°) to maximize exposure to diffuse sky radiance. You can also use a solar tracking system with a ground-mounted installation to maintain the right angle throughout the day.

• Energy storage and grid integration: Lithium-ion batteries store surplus energy for use during cloudy periods or at night. Net metering policies allow you to "bank" excess energy with the grid and use it during cloudy days.

• Regular maintenance: Keep panels clean and free of debris to let them perform at their best.

• Efficient inverters: Having a high-quality solar inverter lets you get the most out of your solar panels.

Electricity cost matters more than clouds

Just because you live in a cloudy area like Portland or Seattle doesn’t mean you shouldn’t get solar panels. The cost of electricity is a huge factor in solar panel savings independent of weather. You could live in a cloudy place with great solar potential because of a high electric bill.

High electricity rates amplify your solar savings, while low electricity costs reduce potential savings and lengthen the payback period. This payback period is the time to recoup your solar investment.

Even in less sunny areas, rising electricity rates can make solar an economically viable option that gives you long-term cost stability. While cloudy days can put a damper on energy production, electricity costs dictate the monetary value of that energy. So don’t be afraid to explore solar in less optimal climates.

Wrapping up: Effects of clouds on solar panels

Solar panels provide a reliable source of energy even in cloudy conditions. Clouds can reduce output by 23% to 67%, but this isn’t the only factor that affects your decision to get solar panels. Consider your energy usage and local regulations along with the environmental benefits of solar.

Clouds and solar panels: FAQ

Below are a few frequently asked questions about how clouds affect solar energy.

How efficient are solar panels on a cloudy day?

On cloudy days, efficiency drops for the average solar panel. Light cloud cover may yield about 23% of normal output, while overcast conditions can reduce production by 67%. Systems with north-facing panels and flatter panels can generate energy from overcast days better.

Do solar panels work with moonlight?

No, solar panels do not effectively work with moonlight. Moonlight is reflected sunlight and is far too weak to generate a usable amount of electricity through photovoltaic cells. A standard flashlight can be 1,000 times brighter than moonlight.

How much will a 100-watt solar panel output on a cloudy day?

A 100-watt solar panel on a cloudy day will produce significantly less than its rated output. Expect roughly 43 to 77 watts, depending on cloud density. Heavy overcast saps energy more while lighter cloud cover might not affect output much.

Do solar panels work if it's not sunny?

Yes, solar panels work if it's not sunny. They can use diffuse sunlight, which penetrates cloud cover to generate electricity. However, the output is reduced compared to sunny conditions. But even without direct sunlight, solar panels can still convert ambient light into energy.