The Earth is in constant motion, and its motion complicates how the Sun’s light reaches the surface of the planet. This light impacts our everyday lives, and in our modern world, we have an increased appreciation for the Sun as we consider all the benefits of solar energy. 

When you’re thinking about going solar, how the Sun interacts with the Earth matters. The mechanics of this interaction come into play when we consider daily peak sun hours. 

Peak sun hours have an important role in a solar system’s energy production. Though there are 8 to 12 hours of sunlight in a day, the daily peak sun hours are those when solar radiation is at its highest—which means your solar energy production will also be at its peak. Understanding the daily peak sunlight and how your solar panels will experience it can be an important factor in the decision to make the switch. Let’s dive into what you need to know and how you can determine your daily peak sun hours.

Solar Basics

The Earth rotates on its axis once every 24 hours, creating day and night. The length of each day and night is in constant fluctuation, depending on your proximity to the equator. The Earth also orbits around the Sun once every 365.25 days and tilts on its axis to bring about the seasons as different parts of the planet receive more or less direct sunlight at different times of the year. 

Every location on Earth receives some amount of solar light, radiation, or energy at least part of the year. The specific amount of solar energy reaching a specific location on the Earth’s surface—like the solar panels on your roof—varies based on certain conditions, ranging from physical location, time of day, time of season, local weather, and local landscape.

Depending on these variables, the surface of the Earth receives the Sun’s light at different angles throughout the day. Sunlight can hit at 0 degrees (just above the horizon) to 90 degrees (directly overhead). When the Sun is directly overhead, solar panels receive the maximum amount of light and energy. The more angled the Sun’s rays are and the longer the distance the light travels through the atmosphere, the weaker the light and energy are when they reach your solar panels or Earth’s surface. With the Earth’s round shape and tilted axis, this effect becomes more pronounced the farther away you are from the equator. This is why polar regions never receive sunlight directly overhead and experience periods of no sunlight or no darkness.

Solar Noon

Solar noon is the moment the Sun passes a specific location’s meridian and reaches its highest position in the sky—and it’s when solar panels can receive the greatest amount of the Sun’s energy. In most cases, solar noon does not align with the 12 o’clock noon of the clock.

When you’re trying to determine your daily peak sunlight hours, knowing solar noon is important because your peak hours will be on either side of this high point in the day.

All About the Tilt

The 23.5 degree tilt in the Earth’s axis of rotation contributes to the amount of solar energy the Earth receives at any given location. It’s because of the tilt we experience longer daylight hours in the northern hemisphere from the spring (vernal) equinox to the fall (autumnal) equinox. In the southern hemisphere, the effect is the opposite. Days and nights stay a constant 12 hours long on the equinoxes, which occur each year on or around March 22 and September 22. 

The U.S., which largely occupies the middle latitudes of the northern hemisphere, receives more solar energy in the summer because the days are longer and the Sun is nearly overhead. In the winter, the daylight periods are shorter and the Sun’s light is much more angled, allowing less energy to be received at the surface and collected by solar panels. 

This tilt of the Earth makes your location a critical factor in determining your daily peak sunlight hours, and it’s also why your peak hours will vary over the course of the year.

Diffusion

As sunlight passes through Earth’s atmosphere, some of it is absorbed, diffused, or reflected by elements in the air before it can reach the surface, impacting how much energy solar panels can absorb. This diffusion can be caused by air molecules, water molecules, clouds, smoke, dust, pollution, and volcanic ash. The presence of these elements, and their density in the air, impacts the intensity of the solar radiation your location can receive. According to the U.S. Department of Energy, when solar radiation reaches the Earth’s surface without being diffused it’s known as “direct beam radiation”; however, atmospheric conditions can reduce this radiation by 10% on clear, dry days and up to 100% on foggy, hazy, and cloudy days.

This diffusion effect is another factor to consider when calculating daily peak sunlight hours. It can change your top hours for energy production on a daily, or even hourly, basis.

Peak Sunlight Hours

Energy production for solar panel systems is measured by kilowatt-hours per square meter (kWh/m2). Under ideal conditions, a peak sunlight hour is defined as the hour of the day in which the sunlight’s intensity is near an average of 1,000 kWh/m2. Generally, the optimal period for solar panels to receive the maximum energy from the Sun is between 10 a.m. and 4 p.m., but this period can vary widely based on all the factors mentioned previously. 

For example, if you live in Nevada, a state with some of the highest peak sunlight hours, you can capture more of the Sun’s energy with fewer solar panels. If you live in one of the lowest peak sunlight hour states, like Michigan, additional solar panels will likely be necessary but you can still produce the amount of electricity your household consumes.

Calculating Peak Sunlight Hours

There are several resources you can use online to get a general calculation for your specific location. The National Renewable Energy Laboratory (NREL) created the PVWatts Calculator, which offers the available photovoltaic energy production based on your physical address. Once you have an understanding of the daily peak sun hours in your location, our article How Many Solar Panels Do You Need? walks you through a simple calculation to determine how many solar panels you will need. 

More general calculations of ranges of peak sun hours are available by state from a number of resources, including this one from Solar Reviews. For maps of the Sun’s energy at different times of the year, check out NREL’s Solar Resource Maps and Data.

Non-Peak Sun Hours

When the Sun isn’t shining or your local conditions aren’t optimal for solar energy production, it’s natural to wonder if your solar panels can still generate electricity. The fact is solar panels continue to capture energy even if conditions aren’t optimal. On cloudy days, solar panels still generate 10-25% of their normal power output, and in areas where large cloud cover is expected solar systems are designed with more panels to accommodate the local conditions.

Local Setup

The ideal home application for a solar power system is a roof pitched at 45 degrees and facing the southern sky. Not all locations are going to have this ideal setting, so this is where Blue Raven Solar experts step in to examine your geographic location and home to design a custom solar energy system. They’ll determine the best placement, the ideal number of solar panels appropriate for your electricity needs, and consider the other factors to maximize the power production of your rooftop system—including peak sun hours.

Understanding how the Sun works relative to your location on the planet and at different times of the day or year is important when considering the switch to solar. If you are ready to begin harnessing the power of the Sun for your home, contact us today.