Solar panels still work on cloudy days

However, solar output typically decreases significantly in cloudy conditions. Determining the impact overcast conditions have on the output of solar panels is difficult; as there are many different types of clouds.

It is a long-maintained theory that solar panels can still produce between 10 – 25% of their rated output in cloudy conditions. However, this applies a very broad brush to a range of different cloudy conditions and does not account for the difference in weather conditions at different geographic locations.

In all likelihood, rooftop solar panels will produce more than 10 – 25% of their output in cloudy conditions, as this estimate relates to low-level cloud cover.

What are cloudy conditions?

The main difficulty in determining the effect of output due to cloudy weather is that there are all sorts of different cloud types. The Bureau of Meteorology has come up with a list of 10 main cloud type classifications:

Ten different cloud types:

So now we have a classification for the cloud types, but what effect does each have on solar output?

Studies on the effect of clouds on solar output

A study conducted by monitoring firm Solar Analytics on the effect of clouds on solar found diminished rates of output for different types of cloud. Using real-time monitoring of solar systems located in Adelaide, Brisbane, Melbourne and Sydney, the study concluded that different cloud levels decreased output at the following rates:

• High level cloud: Solar output largely unaffected
• Overcast conditions: 50% reduction in output
• Low-level dark cloud: Solar output reduces by 70 – 90%

The study is useful in that it shows the impact on production by high-level, overcast and low-level cloud cover, but it is hard to classify the clouds, and quantify the cloud density and strength.

Study concludes cloud cover impact is impossible to measure!

A study on the effect of cloudiness on the production of electricity by photovoltaic panels by the Tomas Bata University in Zlín in the Czech Republic found that ‘it is impossible to determine the effect of different types of clouds on electricity production of photovoltaic panels’.

The study, based on the 10 main cloud types, was able to distinguish between high, medium and low cloud cover but was unable to ‘determine the strength of cloud cover, type and density of clouds, which are in various heights’.

Analysis of cloud studies

The studies indicate that it is very difficult to definitively determine the impact clouds have on solar output. Though, the Solar Analytics study points to higher output figures than what has previously been considered the norm.

Self-monitoring

If you already have solar panels and a smart monitor, monitoring the output of your system in different cloud conditions is best way to assess the impact of cloudy weather on production. The data will be specific to your location and install, and far more accurate than any predictions.

Calculating solar exposure at your location

Our solar calculator uses historical data that measures global solar irradiance recorded at your location based on your roof direction and tilt. Global solar irradiance is the made up of both direct solar irradiance and diffuse solar irradiance.

The use of historical data means that our calculator computes the solar potential at your property in both sunny and cloudy conditions.

How solar panels generate power when it is cloudy

We know that solar panels work by converting sunlight into electricity, but how do they work when it is cloudy?

Diffuse solar exposure

Diffuse solar exposure is the energy that falls on a surface from all parts of the sky except for the direct beam of the sun (direct solar). It is the diffuse solar exposure that allows solar panels to generate electricity when it is cloudy.

Winter production

Do solar panels work in winter? Yes, they do, and Australian conditions are well suited to generating solar power. However, panel output reduces fairly significantly during the winter season due to the lower number of sunshine hours and increase in cloudy conditions.

Solar production varies by season, but winter produces the lowest output in Australia. By way of comparison, winter performance is typically 41% - 73% less than in summer.

Tips for maximising solar on cloudy days

There are a number of smaller measures that can be undertaken to achieve year-round better solar output, in particular, on cloudy days.

Installing a solar battery

In middle or heavy cloud conditions, it’s still possible to use solar power effectively by drawing from a home battery. Solar batteries can store energy for later use. During cloudy conditions, this energy can be deployed for use throughout the home saving you the need to buy electricity from the grid.

While solar panels do not generate electricity at night, a panel and battery system can still allow you to use solar power.

Buying good components

Good quality equipment performs better in low-light and cloudy conditions. As a rule, better panels can generate more electricity in less than ideal conditions.

Keep your panels clean

Solar panels that are clean and free from debris, perform better than those that aren’t. While often the increase in output is fairly minor, it nonetheless helps the panels to perform better in cloudy conditions.

Avoid panel obstruction

Trees or other objects that block the path of the sun to rooftop panels will reduce output. If trees can be trimmed to avoid shading panels, this will ensure maximum light reaches the panels when it is sunny and cloudy.

Don’t let clouds put you off!

The upshot is solar panels work in cloudy conditions, albeit not as effectively. If you are deciding whether or not to invest in solar, you shouldn’t be put off by cloudy conditions in your location. Solar panels are a worthwhile investment in all locations in Australia.