Solar panel production can vary significantly based on weather conditions. For example, production can be 20-30% higher on a sunny day than the predicted average output. On a rainy and overcast day, it can be as low as 10% of potential production in severe thunderstorms or 20-30% on average.
A solar panel system's size and the use of battery storage can help ensure a consistent electricity supply on rainy days. Speaking with a qualified local supplier or installer is recommended to find the right solar panel system and battery storage solution.
By how much will my solar panel production decrease on a rainy day?
You might wonder what the difference is in solar production when it is cloudless and sunny versus when it’s overcast or even a rainy day.
Firstly, to get an overall idea of what a particular sized solar system can produce in a specific location, you can go on to the output calculator on our website, enter your postcode and system size, and the calculator will give you an expected output yearly and monthly solar system generation output in kWh.
Many of you who have purchased a residential or commercial solar system will have been supplied with an annual system output estimate via the installation company.
The system output is calculated using the sunlight hours for the year in a particular area and relying on close-by weather station data from the past decade to estimate a yearly average.
These estimates also extend to monthly output estimates, but naturally, one cannot predict the likely solar output precisely for a specific date, so these are general estimates only. Nevertheless, over time they are usually quite accurate.
To clarify, just because every 1st of April was rainy in Townsville in the last five years, for example, doesn’t mean the following 1st of April will be rainy. So, the likely predictions of solar output rely on a mix of variable weather conditions, from bright and sunny to overcast and rainy.
Solar Output Calculator
So if you are after the most likely output for your system month by month – try our output calculator.
If this calculator tells you that in March in Brisbane, your 6.6 kW size system will generate, on average, 30.4 kWh, how much of this predicted output will it produce on a very sunny versus a rainy day?
In my experience, watching the performance of many systems via detailed monitoring software such as Solar Analytics, on a sunny day, you would expect to add another 20 to 30% to this 30kWh number, meaning on a clear sky, below 25 degrees day, you could generate as much as 40-plus kWh.
Contrasting this on a rainy and overcast day, system production reduces to as little as 10% of potential output in a severe thunderstorm with dark clouds. Still, usually, 20-30% of the predicted average output is what will be achieved.
In numbers, this means instead of producing 40kWh plus on a sunny day, as per the sample above, one will potentially have to contend with an overall production of around 10kWh on a rainy and cloudy day.
I have put a 30 kWh system on our premises, and in summer, we sometimes produce close to 160 kWh. On a rainy and overcast day, the solar PV system will still generate a minimum of 30 to 40 kWh, which is usually enough to run the premises. If one needs more electricity on days like this, this is where a battery comes into its own.
If you have a large solar system and 30 kWh production on a rainy day is not sufficient to cover your needs, with a large battery bank, you can then release the stored renewable energy, which was harvested on a sunny day, for your extra electricity needs on a rainy day. Please go and check out our battery-related FAQs.