Do Solar Panels Work On Cloudy Days? (Efficiency Report)

Many people mistakenly believe that solar panels only work on clear sunny days when this is not the case at all. They are designed to still produce electricity regardless of the weather conditions using the available solar energy on the day.

Solar panels work on cloudy days as they don’t require direct sunlight to generate electricity; they will not produce electricity when the weather is cloudy or rainy. The level of solar radiation received and absorbed during inclement weather will be less.

The key elements of this discussion are :

  • How solar panels function to create electricity
  • Why direct sunlight is best for solar panels
  • The effect of weather conditions on electricity generation from solar panels
  • How the seasons can affect solar panel efficiency
  • What other factors influence solar panels & power generation

Let’s explore these in more detail to understand how solar panels work when the sun is not shining.

Solar panels covered partially by clouds

How Do Solar Panels Work?

Solar panels create electricity by using the sun’s radiation to split off electrons in the photovoltaic cells found inside the silicon panels. This creates a flow of electrons through the panel resulting in an electric current.

Solar panels are composed of silicon panels with PV cells inside them. When sunlight hits them, energy in the light in the form of photons is absorbed, and the photons release electrons that are then absorbed through bus bars on the side of the panel and transmitted through wires as DC electric current.

Using boron and phosphorous to create positively charged and negatively charged semiconductors, the different charges create an electric field between them, allowing the electrons to become an electric current.

As the electrons hit the metal plates, they are converted into a current and transmitted by wires to the inverter, which converts the DC to AC, then used to power the home.

Since sunlight carries photons all the time, there are still photons present in sunlight on cloudy days, and this is how solar panels can still generate electricity when there is no direct sunlight.

When there is bad weather and little to no sunlight, or it is nighttime, the panels cannot produce electricity, and this is where the ability to store that energy and then use it is utilized.

Storing Energy In A PV System

If the PV system has storage capacity in batteries, the current is also used to charge the batteries using excess energy generated during the day.

  • For example, if the house has a 10kW PV system and only 6kW is utilized, the remaining 4kW would be diverted to the batteries for storage.

The batteries are used to supply power at night when the sun has gone down or during days when solar radiation levels are not sufficient to deliver the required load to the home. The DC from the batteries is then directed to the inverter and converted into AC for use in the home.

To understand how solar panels can work on cloudy days, we need to look at the level of solar radiation received during clear sunny days and how that level would drop on cloudy days.

Now that we know how solar panels work, we can look at cloudy days’ effect on generating capacity.

Why Solar Panels Work Best In Direct Sunlight

The energy received in direct sunlight provides optimum electrical generation capacity for solar panels, and during the peak sunlight hours, they produce the most electricity.

This is why the orientation and angle of the solar panels on your roof are critical.

During peak hours of direct sunlight, the photovoltaic cells in the panels receive the maximum light levels as the sun moves across the horizon and solar radiation levels decrease.

This principle also applies across the seasons. However, solar panels produce electricity in peak sunlight hours of winter as well, and it’s only when the weather conditions worsen that the levels of generation drop.

Regardless of whether it’s spring or mid-winter, if direct sunlight hits the solar panels, they will be operating at optimum levels to generate electricity.

Solar panel on a house roof

How Do Weather Conditions Affect Solar Panels?

As weather conditions worsen and become cloudy or rainy, the clouds block off sunlight, reducing the available intensity of sunlight reaching the solar panels. The denser the cloud cover, the less sunlight reaches the panels.

Depending on the density of the cloud cover, the efficiency of the solar panels can be reduced by as much as 70% or more, leaving the levels of electricity production very low and resulting in reduced power capacity to the home.

Where there are no batteries to stabilize the supply, the PV system may revert to using supplied AC power. If there is no supplied power, the system may be unable to maintain all the appliances in the home.

How Much Less Power Do Solar Panels Produce On Cloudy Days?

Your solar panels would produce between 10% and 25% less electricity on partly cloudy days than on days with direct sunlight.

Where the cloud cover is more severe, your solar panels would only produce about 10%-30% of their capacity, and this can, of course, negatively impact the power supply to your home.

To check whether your PV system is producing power, look outside and see whether shadows are cast, and if there are, then there is light enough for your PV panels to generate electricity.

Would Solar Panels Work In Rain Or Snow?

With rain and light snow, the cloud cover may not be heavy enough to eliminate all sunlight from hitting the solar panels and allowing them to generate electricity.

With more intense rain and snow, this would depend on the level of cloud cover involved.

Heavy snow could severely limit the panels’ level of sunlight. If the snowfall is consistent or you have blizzard conditions, this would curtail the ability of the solar panels to generate electricity.

Rain is good for your panels as it cleans off the accumulated dirt and dust found on the glass, increasing their efficiency, especially if you haven’t cleaned them in a while.

Snow has another potential effect on solar panels as it can accumulate on the surface of the panels and block sunlight from reaching the PV cells and stop electricity generation until it melts off or is cleaned.

The same would apply with consistent rain as this could also reduce the ability of the panels to generate electricity as they could keep layers of dirt and dust on the surface and reduce the levels of light coming in.

Does Electricity Generation Fluctuate With The Seasons?

Due to the changes in the sun’s position in winter and summer, there is a difference in the generation output of solar panels in winter and summer.

Splitting the year into two sections between March 21st (the Vernal Equinox) and September 21st (The Autumnal Equinox), there is a quantitative difference in generational capacity on solar panels.

On average, the summer months from September 21st to March 21st produce around 65% of the annual solar energy output, while the winter months accounted for the other 35%. Of course, these figured may vary depending on your summer and winter weather conditions.

Why Solar Panels Produce Less Electricity During Winter?

There are three reasons that your panels produce less electricity during winter, and these same reasons would have some bearing as to why they produce less electricity on cloudy days.

The days are shorter during winter. This means lower levels and duration of sunlight during winter and coupled with inclement weather, would further reduce the sunlight levels reaching your panels.

In winter, the sun is lower in the sky, reducing the level of light reaching the panels even at midday when the sun is at its peak.

The typically more cloudy and overcast days that winters bring along with shorter days and the sun’s lower position in the sky compound the effect of reduced electricity production.

Can Cloudy Days Increase Your Energy Costs?

The impact of reduced electricity production on your electricity costs would be negligible as the effect of cloudy days is factored into your system’s design.

When calculating your energy requirements, the designers of your system would work on the total annual energy requirements based on the annual consumption data extracted from your utility bills.

Using this as a guide, they would design a system that delivers more capacity during the spring and summer and builds up additional kilowatt-hours within the utility. This will see you through the months with lower sunlight levels.

Also, with the roof panels, the amount of space you have available would often be effectively optimized to deliver more from your panels to accommodate the cloudy days when sunlight is not at its maximum.

Having said this, persistent cloudy conditions could deplete batteries and electricity production over days or weeks.

With severe snowstorms seen across the US in recent years that continued for several days, these conditions could drain batteries and stop electricity production due to the continued lack of adequate sunlight.

If your system is grid-tied, then if you have poor weather, you can switch back to the grid supply until your energy generation system is back online. This would potentially cost you some money, but it may not if you have net metering.

Net metering is where you feed electricity back into the grid and gain credits from the utility supplier. Then, if you need to access power when your PV system hasn’t generated enough power, you can offset your usage against credits on your account.

Do Solar Panels Work Better In Hot Or Cold Conditions?

Believe it or not, the colder temperatures make solar panels more efficient than warmer weather.

Electrons are more active during colder weather, and this increased activity allows them to produce more electricity as the panels absorb more sunlight.

The higher the temperature, the lower the voltage produced, and for every degree above 77°F, the panel loses 1% of its efficiency. For every one degree below 77°F, the panel efficiency increases by 1%.

This is the case with most electronic devices, and your solar panels are no different.

With this in mind, you may think that if cloudy days are cooler, the solar panels will work better, but this is not the case as the yardstick is still the level of sunlight that reaches the panels that provide the best results.

How Cloudy Days Can Cause A Production Spike?

Under certain conditions, cloudy days can cause your electricity production to spike due to sudden increases in solar radiation intensity caused by the clouds!

As strange as that may seem, it is true. If you take a magnifying glass and focus the sun’s rays on wood or paper, the material will start to smolder or even burn. This is due to the heat being increased as it’s magnified.

Certain clouds passing in front of the sun create the same effect and can briefly but significantly boost the intensity of the light reaching your panels.

Water in the clouds acts as a magnifying glass for the sun’s rays, called the ‘edge of cloud’ effect. Cumulus clouds have that light, fluffy texture and the edges of those clouds have a ‘mist’ of water vapor that creates this effect.

What Are Other Elements That Affect Solar Panel Efficiency?

Clouds have the biggest impact on blocking sunlight to solar panels, but other things can also affect electricity generation.

When assessing your roof, you need to consider which direction the roof is facing as north-facing is optimal as it would get the most amount of sunlight throughout the year.

While not every house may face north, you can use ground-mounted solar panels that do face north to bolster the roof installation.

Another consideration is the trees around your home. While they won’t block the same levels of light as cloudy days would, the shadows they cast on your panels could well affect the generational capacity, and you may need to trim them down a bit to eliminate the effect of shadow.

Lastly, the type of inverter you use on the panels also affects system performance.

String inverters are the most common, and this is where all the panels are linked to a single inverter. If anyone’s panel is in the shade, then the whole system only operates on the power of the weakest panel.

Micro-inverters are installed on every panel, and if one is shaded by cloud, then only that panel’s output is diminished; the rest run at optimum.

Power optimizers mix both string and micro-inverters, negating the effect of shade from trees or clouds on the panel’s production capacity.

While micro-inverters and power optimizers are more expensive than string inverters, they provide optimal electrical production – even on cloudy days!

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