What Are The Best Months For Solar Energy Production In The USA?

The summer months in the USA are when the most energy is generated from solar power, but the months preceding summer and winter also provide significant energy generation.

The best months for solar generation are from March through to September. The optimum months are May to August when the sun is at its highest point in the sky,  the atmospheric conditions are ideal, and the days are longer to provide more available solar energy and sunlight.

Considering the months where the maximum solar energy is generated, we also need to determine where the weather conditions offer the best all-around power generation in the USA. It may not be where you think!

The Best Months For Solar Energy Production In The USA

What Is The Seasonal Solar Energy Generation Curve?

As each season cycles, solar energy generation levels fluctuate accordingly, so the most energy generation is achieved between the vernal equinoxes from March 21 to September 21.

This period is where the weather is the least obnoxious for the most part. While there will be rain, light snow, and other atmospheric disruptions, for the most part, the weather is agreeable to good production capacity.

However, there is an interesting paradox that is worth discussing here. In the USA, you would think the most solar energy is generated in hot, dry areas like Arizona, but this isn’t the case at all.

What Is The Optimum Operating Temperature For Solar Panels?

Solar panel vs different weather

When solar panels are tested, they are tested under Standard Test Conditions which defines the optimum temperature for maximum efficiency as 77℉ as this is the average temperature of the optimum solar hours between Spring and Autumn.

While solar panels can operate in much warmer temperatures, the higher the temperature, the less efficient the solar panels will become. This is because they, too, are electronic devices and prefer a more temperate climate to perform properly.

Take your mobile phone or laptop; for example, they function a lot better when the temperatures are more moderate than if they are melting the tar on the road outside, and this is because when the electrons in the device are heated, they become ‘excited’ and this makes them less efficient in absorbing and conducting electricity. This phenomenon occurs in solar panels as well.

Consider this, would you rather run a marathon when the outside temperature is in the high 80’s or 90’s vs. the mid to low 70’s? Well, your solar panels feel the same way; every degree above 77 degrees Fahrenheit will decrease the solar panel’s efficiency, and every degree below that will increase it accordingly.

How Much Less Energy Do Solar Panels Produce Above 77℉?

Solar panels

As a general rule and based on the average manufacturer’s specs, most solar panels have a temperature coefficient of between 0.2% and 0.5% per degree Celsius, so for every one degree celsius above or below the optimum, the panel has a temperature coefficient will lose around 0.2%-0.5% inefficiency.

To convert that to Fahrenheit, use the following example:

At 83℉ or 28°C, which is 6℉ above the 77℉ optimum, the loss of generating capacity would be around 1,1%. If we take a 320W panel and apply that, we would lose about 4W at that temperature.

If you have 10 or 12 panels of this size operating, that could be a loss of 48W while the temperature is above the 77℉ mark and more if the temperature continues to rise.

The same principle applies to temperatures below 77℉ as this will improve the generational capacity as the temperature drops.

With this in mind, you may be surprised to learn that because of this, a solar panel array on a roof in Minnesota will generate more energy for the homeowner than that same array on a roof in Arizona would!

Arizona Vs. Minnesota For Solar Panel Efficiency 

Solar panels Arizona Vs. Minnesota

As it turns out, the more temperate regions in the USA are far better for optimal energy generation from solar panels. This is because the daytime temperatures all hover around that 77℉ mark or lower for most of the year.

Even as the weather cools toward winter and warms during spring, the daytime atmospheric conditions are ideal for solar panels to produce electricity. This is why many homeowners opt to install solar panels during winter and reap the benefits from spring to fall!

This is not to say that solar panel arrays in Arizona don’t generate electricity efficiently. Still, their optimum months would be when it’s cooler there and not during the very hot peak summer periods.

Arizona’s lowest temperatures of around 44℉ (low) to  71℉ (high) occur in winter and spring temperatures average around 55℉ peaking 90℉ and summer starts around 77℉ and peaks at 107℉.

In Minnesota, the average daily temperature from May 22 to September 17 is around the 71℉ mark, with the peak temperature in July at 83℉. So for most of the optimum periods of solar energy production, the same 320W panel would be producing more energy consistently and more efficiently than in Arizona.

The Temperature Coefficient Consideration 

Temperature Coefficient

As with any project requiring an energy load assessment, you need to consider the local climate conditions as part of that assessment. The average weather conditions play an essential role in the specifications of the solar panels.

When looking at solar panels, please enquire about the temperature coefficient rating on the different brands and panel sizes as the closer that coefficient is to zero, the less its efficiency will be affected by the temperature fluctuations.

Do some research to have a good idea of the peak months and average daytime temperatures in your area. When you choose the panels for your system, they will function at optimum generation efficiency, which means a consistent and reliable power source for your home or business.


The best months for solar energy generation in the USA are March and September. Still, PV systems in those areas will be more efficient when the average temperatures are moderate.

That doesn’t mean that your PV system will let you down if you live in a hotter area. It just means that people who live in the colder areas have a small reason that living where they are is better!

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