If you are investigating solar energy, you may remember one of the first practical questions you considered when thinking about solar energy as a realistic source of renewable power, even if you were not thinking about solar energy in particular. These questions are practical ones, such as asking what efficiency rate a solar cell would provide you with when raining outside. In fact, a raincloud will denote clouds, less sunlight, as well as shorter sun hours.

The simple answer is that solar panels actually lose efficiency during a rainstorm but do not shut down. Sometimes, rain can even be beneficial for improved performance. The reasons for this are not so simple and require a look at where solar power actually comes from, what happens during a rainstorm affecting sunlight, and actual data.

How Solar Panels Function in Non-Ideal Weather Conditions

Solar panels work on light, not heat. This is more important than many people realize. Photons in sunlight are turned by photovoltaic cells into an electric current. Direct sunlight is more effective, but diffused sunlight, sunlight reflected by clouds, still has energy.

Rainy days are characterized by high cloud coverage. This will lower the amount of solar energy reaching the surface of the solar panel. Clouds will not shield all lights. In fact, clouds scatter lights. These are weakened lights, but they are still capable of arousing the cells. Hence, it can be inferred that the solar panel will still produce energy when it is raining.

Another aspect that is often overlooked is that of temperature. Solar panels perform marginally better in lower temperatures. Rain has a precipitation effect on temperature that reduces it to some extent. So, there is an effect on production but not on cessation.

What Efficiency Looks Like on a Rainy Day

There is no single efficiency number that can be generalized across all rainy days. This is because the amount of production is dependent on the intensity of the rainfall, the thickness of the clouds, the time of day, the orientation of the panels, and the system that is in use. However, there are well-documented guidelines on the levels of performance.

When there is cloudy rain, the performance of solar cells could range between 30% to 60% of their performance under clear skies. However, under heavy rain with high cloud formations, their performance could go down to 10% to 25%. Though in rare cases, their performance could go down to zero under cloudy rain, but this does not happen in daylight.

The United States Department of Energy’s publication 5 Ways to Get Sunshine on a Cloudy Day states that solar cells are meant to harness both direct solar rays and diffused sunlight; this explains why solar power continues to be generated even if sunlight is obstructed by clouds. Solar power is effective in rainy locations because of this aspect.

Rainfall Intensity and its Effects

Light Rain and Overcast Skies

During the days when there is light rain and the rain is falling steadily, the clouds may be less thick. The scattered sunbeams will be relatively stronger, and the efficiency of the solar panels may be enhanced. Most systems will continue to provide a significant part of the daily output.

Heavy Rain and Storm Conditions

During rainfallstorms, the amount of irradiance gets reduced as the clouds are thick. The efficiency decreases are more evident, and the power output will be able to meet only a portion of the demand. However, this condition lasts only during the duration of the rainfallstorm.

Short Rain Events vs. All-Day Rain

Short rains may not have much effect on energy received during a day. A network could lose some production during rainfall but compensate for that during brighter times before or after. Rain throughout the day leads to lower totals, but modern networks are designed with yearly totals in mind, not peak totals during a day.

Solar Energy Forecasting in Rainy Weather

Accuracy in forecasting is very important to ensure grid stability and planning. Cloudy and rainy conditions affect the output variability, though it is not unpredictable. Advanced forecasting techniques can account for factors like cloud conditions, rainfall, and existing track record to forecast output.

The research named Solar power forecasting under different weather conditions, published by the National Institutes of Health through NCBI, illustrates the potential to accurately predict power production by sunlight even in rainy and cloudy conditions since fluctuations associated with rain can be effectively taken into consideration. The study has confirmed the hypothesis that rain has a meaningful, instead of random, impact on electricity production.

What this means in effect is that utilities, as well as property owners, can make plans for rainy days without considering the possibility of intermittent solar energy.

Can Rain Affect Solar Panels?

Rain will not damage solar panels. Panels are designed to be water, humidity, and temperature-resistant. Most panels are exposed to conditions much harsher than rain, for instance, strong storms and wind.

Indeed, there are times when rain becomes quite helpful. Cleaning of dust and other particles that settle on solar panel surfaces occurs naturally when it rains. This may increase production efficiency in some cases to produce slightly higher amounts of power compared to before when production started.

However, in areas that always receive rain, this capacity to clean by itself could work to ease maintenance requirements compared to regions which are always dry and dusty, requiring cleaning by hand.

Efficiency of Solar Panels in a Year Period

In evaluating solar energy, one must not put too much emphasis on individual rainy days. The solar systems are sized on average production for a year or so. Sunny days normally compensate for the cloudy ones.

In many climates, the periods of rainfall can occur around the time of maximum daylight hours or maximum sun angle, thus offsetting losses. In many places with high rainfall, for instance Northern Europe or the Pacific Northwest, solar power can still be an economic option because of its steadiness.

This is why installation evaluations emphasize long-term irradiance patterns rather than weather patterns. This is because a couple of low-output days will not impact the long-term functionality of the system.

Common Misconceptions about Rain And Solar Power

One of the myths is that solar panels cannot function during rain. This is not true. They work as long as there is light.

Another misunderstanding is that high rainfall is not suitable for solar energy. Actually, a large number of solar-performing regions have rainfall. The important thing is the total yearly sunshine and not a cloudless day.

Finally, it is also assumed that the effect of rainfall is always negative in terms of reduction in system efficacy. Even though it is true that the intensity of solar radiation is affected by rainfall, it is also true that it has an indirect positive effect of cooling and cleaning the panels.

Practical Recommendations for Homeowners and Businesses

If you are looking at solar and are concerned about rainy days, here are a few real-world considerations to bring things back down to earth.

Firstly, you can forecast a reduced production capacity when it is raining, but you are not to produce zero power. This is because your energy system is still working throughout the day.

Second, it was decided to focus on the annual yield of energy rather than what happens within an average daily cycle. This is how solar power installations are sized and how they are measured.

Third, it’s necessary to acknowledge the potential ability of rain to minimize maintenance and assist panels in performing effectively when the weather clears.

Finally, if your power consumption is important to you even in adverse weather, you can also use solar power together with batteries where excess energy is stored during sunny days and later utilized in rainy days.

But how efficient is that solar panel on rainy days? Not as efficient as on sunny days, but certainly not inefficient either. Rain and cloud patterns decrease sunlight intensity and result in less production, but still allow for energy production from diffused light. Rain, in particular, has actually been shown to increase solar panel productivity in many cases.

When it comes to solar power, what you have to be aware of is that you have to look at it from the long-term average instead of from a weather perspective. The thing is that if you want a sure-fire answer, you have to go through the solar power data prevalent in your region. By that measure, you would be taking the rains into consideration.