Do Solar Panels Work In Cloudy Weather?

When you’re thinking about installing solar panels you must understand how they perform in cloudy weather.

Solar panels are amazing when the sun is high in the sky, but power production drops considerably when the sun isn’t shining.

Solar power performance in cloudy weather is an essential factor to consider if:

• You live in an area prone to cloudy conditions
• Your climate brings a lot of cloudy weather in the short winter days
• You’re looking for an energy system for off-grid living

Depending on the type of cloud, and the time of year, the energy produced by solar panels could be as low as 2% of their usual power output (link takes you to a study). But that’s the worst case scenario.

An average power generation figure is closer to 10% – 25% but this is only a rough estimate and actual power generation will vary based on your local conditions and the specific setup of your solar system.

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In My Experience

I’ve used solar power as the main energy generation system for my off-grid home since 2010.

On cloudy days in the depths of winter, our solar energy system doesn’t produce much power.

But in the summer, a cloudy day isn’t a problem at all (unless a dark thunderstorm rolls in). We use power as normal and still fully charge our battery bank.

On light to moderately cloudy days in late spring, summer, and early fall, you’ll get good power generation. On a cloudy day in the middle of summer, you’ll even get as much as 70% of your normal power production.

But on winter days with heavy cloud, you’ll get next to nothing.

If you’re installing grid-tied solar, you’ll still have the main power grid to fall back on, so cloudy days are an inconvenience, but not a major concern.

Just make sure you honestly appraise your weather conditions and do a full cost benefit analysis before you take the plunge.

But if you’re planning an off-grid solar installation, cloudy winter days can be a big problem. You’ll either need an oversized system capable of charging a large battery bank, or you’ll need a generator for backup power.

Of course, the other option is to structure your household so you can scrape by on minimal power when the sun isn’t shining.

For my household, minimal power means running a very efficient chest freezer, a water pump, a few lights, and a laptop.

How Do Solar Panels Work? The Basics

Solar panels capture sunlight and convert it into electricity we can use to power the electrical appliances and devices in our homes.

1. Solar Cells: Solar panels are built from a series of individual solar cells. Each solar cell contains a silicon semiconductor which absorbs photons (tiny particles of energy without mass travelling at the speed of light).
2. Electric Current Generation: The photons energize the electrons in the semiconductor material. The energized electrons flow through the semiconductor creating an electric current.
3. Electrical Conductors: Within the solar panel, metal electrical conductors capture the flow of electrons and create an electrical circuit. This allows the generated electricity to be harnessed.
4. Direct Current Generation: The electricity produced by solar panel is in the form of direct current (DC). The same type of electricity that batteries provide.
5. Inverter Conversion: Most consumer electrical appliances use alternating current (AC). Before we can use the electricity generated by our solar panels an inverter has to convert the current from DC to AC.
6. Utility or Appliance Usage: Once converted to AC, the electricity can power appliances, lighting, and other electrical devices.

Do Solar Panels Work In Cloudy Weather?

You’ll get some energy from solar panels on cloudy days but the power output will be lower than when direct sunlight is hitting the panels.

Solar panels work best on sunny days, and generate the most electricity when sunlight is hitting the panels, but they don’t need direct sunlight to produce power. Solar panels can still produce power from the diffused light on a cloudy day.

As I’m writing this, it’s early November, it’s a gloomy overcast morning, I’m using power in the house and my solar panels are charging my battery bank.

This is what it looks like outdoors. Pretty cloudy!

Now, if the cloud clover looked like that in December or January when the sun is very low in the sky, my system wouldn’t produce enough power to charge my batteries at all. My battery bank would be supplying power to compensate for the low solar power production.

If you’re going to live off grid, one way to ensure you get enough power on cloudy days is to oversize your system, but extra solar panels and increased battery capacity add to the cost of the system.

It may be more cost effective to use a backup generator instead of installing a larger solar system. A generator gives you plenty of on-demand power on cloudy days as long as you’ve got the fuel to run it.

An oversized solar power system on the other hand will still struggle to produce a useful amount of power on very cloudy, winter days, although the extra battery capacity will provide more stored power.

The Impact Of Weather On Solar Energy Production

Weather conditions have a significant impact on the amount of solar energy your panels produce. While sunny days are ideal for maximum output, what happens when the sky is overcast, or when it’s raining?

Weather Conditions and Solar Energy Production

• Sunny Days: High power production due to abundant direct sunlight.
• Partly Cloudy Days: Moderate power production as some direct sunlight still reaches the panels.
• Overcast Days: Lowest power production as most of the sunlight is diffused or blocked by the clouds.
• Rainy Days: Power output depends on cloud cover. During heavy rain with thick cloud cover, power output will be very low.

Solar Panel Output In Different Cloud Conditions

• Light Blanket Cloud Cover/Patchy cloud: Solar panels can produce 50-70% of their maximum output.
• Medium Cloud Cover: Output drops to around 30-50% of the maximum.
• Heavy Cloud Cover: Solar panels might only produce 10-20% of their maximum output (and much less in winter).

How Different Types Of Clouds Block Sunlight

Different types of cloud will have different effects on your solar power production.

Cirrus Clouds

Cirrus clouds are high altitude clouds with a feathery appearance. These clouds are the highest and thinnest of all cloud types. They won’t have much impact on solar power generation.

Cirrostratus Clouds

Most often seen in winter, cirrostratus clouds are another high altitude cloud. These clouds often cover the sky and may be several thousand feet thick. Luckily this cloud is fairly transparent and doesn’t block all of the sunlight. You can even see the sun through the cloud layer. When you see these clouds, a change in the weather is on the way (rain or snow).

Cirrocumulus Clouds

Cirrocumulus clouds look like long rows of cloud or multiple small puffs closely packed together. They remind me of the furrows in a plowed field. Sunlight easily passes through these high altitude clouds and won’t have an enormous effect on solar power generation. These clouds are often seen in winter and indicate fair weather.

Altocumulus Clouds

Altocumulus clouds are the most common type of mid-level cloud. Puffy in appearance and with some parts darker than others, they often appear in clumps or layers. These clouds don’t blanket the sky so some sunlight will get through to your solar panels. These clouds indicate fair weather.

Altostratus Clouds

Altostratus clouds form gray sheets or layers, often covering the entire sky. The layers can be thin enough to let sunlight through and you sometimes see the sun faintly behind them. These mid-level clouds will block a significant amount of sunlight and their presence indicates rain or snow.

Nimbostratus Clouds

Nimbostratus clouds blanket the sky with a thick layer of dark cloud and block out most of the sunlight. These mid-level clouds often produce long lasting rain or snow showers.

Cumulus Clouds

The big, fluffy, white cumulus clouds that look like giant cotton balls floating across a blue sky, won’t have much impact on solar power generation at all. You’ll see a mild drop in power production as the cloud passes in front of the sun, then 3 or 4 minutes later, when it’s passed by, you’re back to full sunlight hitting the panels until the next cloud drifts overhead. These low-level clouds are seen during periods of nice weather.

Stratus Clouds

Stratus clouds are another type of low-level cloud that blanket the sky. They’re not as dark as nimbostratus clouds and some sunlight will still get through. These clouds usually indicate a dry but gloomy day.

Cumulonimbus Clouds

Low-level cumulonimbus clouds are huge clouds that rise high into the sky. Formed on hot days when warm, wet air rises, these thunderstorm clouds are a signal that heavy rain, or hail (sometimes a tornado) is on the way. When you see these clouds heading your way, you can be sure your power production will be severely limited until the storm passes.

Stratocumulus Clouds

Stratocumulus clouds are another type of low-level cloud heralding stormy weather ahead. These patchy clouds are white or grey and some sunlight will get through the gaps in the cloud. When you see these clouds, a storm could be inbound.

How Much Energy Can Solar Panels Produce in Cloudy Weather?

The amount of energy that solar panels can produce in cloudy weather depends on several factors including the thickness and type of clouds, the type and efficiency of the solar panels, their orientation and angle relative to the sun, and the season.

Factors Affecting Solar Panel Output in Cloudy Weather

Cloud Thickness and Type
Thicker clouds block more sunlight than thinner ones. Other types of clouds let more light pass through.

Solar Panel Type and Efficiency
Some types of solar panels are better at capturing diffused light than others.

Panel Orientation and Angle
Panels that are properly oriented and angled will capture more light on cloudy days. If you’re going off-grid, a ground mounted system is better than a roof installation.

Why A Ground Mounted Solar Panel System Is Better Than A Roof Mounted System

A ground mounted solar array gives you a lot more flexibility than a roof mounted system. You aren’t limited by your roof size or the direction your roof pitch faces.

With a ground mounted system, you can adjust the angle of your solar panels for optimum efficiency in the winter and the summer.

In the winter, in the northern hemisphere, solar panels capture more light when they’re set at a steeper angle, in the summer they work best at a shallow angle.

The best angle for your solar panels depends on your latitude as well as the season.

With a roof mounted system, your panels will be fixed at one angle which is usually the angle of your roof.

Ground mounted solar panels can also work with a motorized tracker which moves your array throughout the day as the sun moves across the sky.

Solar panels in a fixed position facing south, miss much of the early morning sun from the east and the late afternoon/evening sun from the west.

With a motorized tracker, the array turns to capture the most sunlight throughout the day.

If you want to get the most energy from your solar panels in cloudy weather, being able to set them at the optimum angle will help you squeeze as much energy from your system as possible.

Ground mounted solar panels are also easier to keep clean. A layer of dust or frost on your panels reduces their efficiency, and if you’ve got snow buildup, you won’t get any power at all unless you sweep the snow off the panels.

Researchers at UC San Diego reported a 7.4% drop in solar panel efficiency over a 5 month drought period when there wasn’t any rain to remove the dust buildup.

That’s a lot of power to lose day in, day out because of dirty panels, and it’s a significant power loss in cloudy weather.

Our solar panels are ground mounted. We use a mop to clean them when they’re dusty, and a soft broom to clear away snow.

Solar Panel Technological Advancements For Cloudy Weather

New types of solar panels claim to be more efficient in cloudy conditions.

Bifacial solar panels (intended for ground mounting) capture sunlight hitting the front of the panel as well as extra light reflected onto the back of the panel from the ground.

The extra light hitting the panels will produce slightly more power on cloudy days.

Thin-film solar panels are another new technology showing better performance in low-light conditions and cloudy climates.

Tips for Maximizing Solar Panel Efficiency in Cloudy Weather

Even in cloudy weather, there are ways to maximize the efficiency of your solar panels. Here are some tips:

1. Proper Installation: Ensure your solar panels are installed at the optimal angle and direction to capture the maximum amount of sunlight throughout the day.
2. Regular Cleaning: Dust, leaves, snow, and bird poop on your solar panels block sunlight which reduces their efficiency. Regular cleaning helps maintain their performance.
3. Use a Solar Battery Bank: A solar battery bank stores excess power produced on sunny days for use during cloudy days or at night.

Cleaning is really only suitable for a ground mounted system. It’s quick and easy to do it yourself as needed.

There’s little point cleaning roof mounted panels yourself or hiring a service to clean them for you.

• Messing around on your roof is dangerous!
• The cost of a cleaning service usually outweighs the value of the potential power gain.

Battery Storage For Cloudy Weather

One of the main components of most solar power systems for off-grid living, is the battery storage system. Batteries aren’t essential, though.

Some people get by without batteries, choosing to use a backup generator for power at night and during cloudy weather.

Given the cost of deep cycle solar batteries, and their short lifespan (5 – 7 years), choosing to use a generator instead of batteries is an understandable choice. And a generator will produce full power no matter the time of day or level of cloud cover.

(Being able to plug power tools into a generator is also handy).

Choosing The Right Solar Battery

When you’re designing your battery storage, you’ll need to consider several factors:

1. Capacity & Power: The battery’s capacity tells you how much electricity it can store, while its power rating indicates how much electricity it can deliver at once.
2. Depth of Discharge (DoD): Most batteries need to retain some charge at all times to ensure a long lifespan. The DoD indicates how much of the battery’s capacity can be used. Lead acid batteries for example shouldn’t be discharged below 50%.
3. Round-Trip Efficiency: This is the amount of energy that can be used as a percentage of the amount of energy it took to store it. Basically it’s how much power is lost in the storage process. Lithium-ion batteries have the highest round-trip efficiency (but they can explode or catch on fire).
4. Battery Life & Warranty: Over time, even with proper maintenance, batteries degrade and hold less charge. And some batteries turn out to have manufacturing defects. Consider both the battery’s lifespan and the warranty offered by the manufacturer. Cheap batteries are never a good investment. Rolls and Trojan are brands I’ve used and been happy with.

Maximizing Your Battery’s Efficiency 

To get the most out of your solar battery, keep the following tips in mind:

1. Proper Sizing: Make sure your battery bank has enough capacity to store sufficient energy for your needs. Batteries are expensive, so don’t waste money on more battery storage than you need.
2. Regular Maintenance: Check your batteries regularly to ensure they’re in good working condition and replace if necessary. Lead acid batteries need topping up with distilled water on a regular basis. Equalize your batteries on the schedule specified by the manufacturer.
3. Smart Energy Use: Be mindful of your energy use, especially during cloudy periods. Try to use less energy when your solar panels are producing less power.

Image Credits:

(1) Cirrus Clouds Photo Copyright: University Corporation for Atmospheric Research (UCAR). Licensed under (CC BY-NC 4.0) via OpenSky. 

(2) Cirrostratus Clouds Photo Copyright: University Corporation for Atmospheric Research (UCAR) by Carlye Calvin. Licensed under (CC BY-NC 4.0) via OpenSky.

(3) Cirrocumulus Clouds Photo Copyright: University Corporation for Atmospheric Research (UCAR) by Carlye Calvin. Licensed under (CC BY-NC 4.0) via OpenSky.

(4) Altocumulus Clouds Photo Copyright: Vitaium, CC BY-SA 4.0, via Wikimedia Commons

(5) Altostratus Clouds Photo Copyright: University Corporation for Atmospheric Research (UCAR). Licensed under (CC BY-NC 4.0) via OpenSky.

(6) Nimbostratus Clouds Photo Ccopyright: Famartin, CC BY-SA 4.0, via Wikimedia Commons

(7) Cumulus Clouds Photo Copyright: Lance Vanlewen, CC BY-SA 4.0, via Wikimedia Commons

(8) Stratus Clouds Photo Copyright: Famartin, CC BY-SA 4.0, via Wikimedia Commons

(9) Cumulonimbus Clouds Photo Copyright: Adityamadhav83, CC BY-SA 3.0, via Wikimedia Commons

(10) Stratocumulus Clouds Photo Copyright: Indrajit Das, CC BY-SA 4.0, via Wikimedia Commons