How Are Fluctuations In Solar Energy Supply And Demand Related To The Weather Time Of Day And Time Of Year?

Solar energy is energy from the sun that is converted into thermal or electrical energy. It is a renewable energy source that can help reduce reliance on fossil fuels and mitigate climate change ( The amount of solar energy that reaches the Earth’s surface in one hour is more than the global energy consumption for an entire year ( Solar power does not generate pollution or waste, making it a clean and sustainable energy alternative ( As solar technology continues to improve in efficiency and decline in cost, it has emerged as an important renewable energy source for the future.

Solar Irradiance

Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation. It is measured in watts per square meter (W/m2) (1). The solar irradiance that reaches the Earth’s atmosphere is approximately 1,366 watts per square meter on average, but it varies by about 6.9% throughout the year due to the Earth’s elliptical orbit around the Sun and other factors (2).

The solar irradiance received at any location on the Earth’s surface varies minute-to-minute due to changing weather conditions. It also varies predictably throughout the day with the rising and setting of the Sun. Solar irradiance peaks at solar noon when the Sun is at its highest point in the sky and is lowest at dawn/dusk when sunlight travels through more of the Earth’s atmosphere (3).

Seasonally, solar irradiance fluctuates because of the tilt of the Earth’s axis of rotation. When the Southern Hemisphere is tilted towards the Sun during its summer months, the solar irradiance is more direct and therefore greater than in the winter months when the Northern Hemisphere is tilted away.

Factors Affecting Solar Irradiance

Solar irradiance, or the power per unit area received from the Sun in the form of electromagnetic radiation, varies throughout the day and across seasons due to several factors. The main factors that affect solar irradiance are:

Time of Day

The time of day has a significant impact on solar irradiance. Irradiance is lowest in the early morning and evening hours when the sun is low on the horizon. It reaches its peak at solar noon when the sun is at its highest point in the sky. This is because the sunlight has the shortest path through the atmosphere at noon.

Seasonal Variation

Solar irradiance varies across seasons, with the highest irradiance occurring on the summer solstice in June and the lowest on the winter solstice in December. This seasonal variation is caused by the tilt of the Earth’s axis of rotation relative to its orbit around the sun. The sun takes a higher path through the sky during the summer months, resulting in more direct sunlight and higher irradiance.

Weather Conditions

Cloud cover has a significant impact on solar irradiance, as clouds reflect and absorb sunlight before it reaches the Earth’s surface. Clear sky days will experience higher irradiance than cloudy days. Precipitation like rain and snow also scatter and reflect sunlight, reducing surface irradiance. Atmospheric aerosols and pollution can reduce irradiance through absorption and scattering as well.

Peak Sun Hours

Peak sun hours refer to the number of hours in a day when solar irradiance is at its maximum – typically 1000 W/m2 or greater (1). This is the maximum amount of solar energy available per square meter per day. The number of peak sun hours varies significantly by location and season.

In the continental United States, the southwest region experiences the most peak sun hours. States like Arizona, Nevada, New Mexico, and California average 5-7 peak sun hours per day annually. The southeast region experiences the fewest peak sun hours, with states like Louisiana, Alabama, and Florida averaging 4-6 hours annually (2).

Peak sun hours also fluctuate by season. Most of the continental US experiences peak sun in the summer months of June-August with an average of 6-8 hours. Winter months of December-February have the fewest peak sun hours, averaging 2-4 hours for most regions (3).

Knowing the peak sun hours for a location helps determine the potential solar energy available and size solar arrays accordingly. Tracking peak sun hours by season also helps better align solar supply with energy demand.

Electricity Demand Fluctuations

There are significant daily and seasonal fluctuations in electricity demand, largely driven by weather conditions. In the summer, electricity demand peaks during the afternoon and early evening hours when air conditioning use is highest. According to the U.S. Energy Information Administration, the use of air conditioning accounts for over 10% of household electricity consumption. Demand dips overnight when businesses close and household activities decline (Factors affecting electricity prices).

During winter, electricity demand peaks in the mornings and evenings when lighting, heating, and appliance use in homes is high. Heating accounts for over 15% of household electricity usage annually. Demand declines during warmer afternoon hours. The seasonal swing in heating and cooling needs leads to higher electricity demand in summer and winter compared to spring and fall (What Causes My Energy Consumption to Fluctuate?).

Beyond temperature, factors like cloud cover, humidity, and wind speed also influence electricity demand. Cloudy days increase lighting demand. Higher humidity increases air conditioning usage. Extreme hot or cold weather can strain the grid as demand surges.

Aligning Supply and Demand

The intermittent nature of solar energy creates challenges in aligning supply and demand. Solar irradiance varies throughout the day and year, with peak production occurring midday and in the summer months. However, electricity demand peaks in the evenings and mornings when solar production is low (Energy5). This mismatch between solar energy supply and electricity demand complicates grid integration.

Solutions exist to better align solar supply and demand. Energy storage systems, like batteries, can store excess daytime solar generation for use during peak evening hours (Energy5). Sophisticated forecasting models help predict weather conditions and energy demand, allowing grid operators to plan supply and storage needs in advance. Ultimately, aligning solar supply and demand requires coordination between solar generators, storage providers, and grid operators.

Geographical Considerations

Solar potential varies dramatically by location based on latitude and climatic conditions. According to data from the National Renewable Energy Laboratory, the American Southwest has the highest solar potential in the United States with states like Arizona, Nevada, New Mexico, and California averaging 5 to 7 kWh/m2/day of solar irradiance.[1] This makes these regions ideal for large-scale solar power generation. The Southeast also has reasonably good solar potential. However, New England and Pacific Northwest regions have lower solar irradiance averaging 3 to 4 kWh/m2/day.

To take advantage of solar power, grid infrastructure upgrades are needed to handle the intermittent nature of solar generation. Large, modern transmission lines are required to move solar power from sunny regions like the desert Southwest to major population centers. Battery storage solutions can also help match solar supply with electricity demand. Texas, California, and other states are making major investments into transmission and storage to enable large-scale solar adoption.[2]

Future Outlook

The future of solar energy is very promising, with projections showing massive growth in solar energy production and capacity. According to the Solar Futures Study by the National Renewable Energy Laboratory (NREL), solar energy could account for up to 45% of U.S. electricity generation by 2050.

Global installed solar PV capacity is projected to reach over 4,000 GW by 2030, up from only about 600 GW at the end of 2019, according to the International Energy Agency (IEA). This is driven by continued cost declines and strong policy support.

There are also ongoing innovations to help address the intermittency of solar energy generation and better align supply with demand. Some key developments include improved solar forecasting, time-of-use pricing to incentivize peak solar production, wider deployment of energy storage solutions like batteries, and increased grid flexibility.

Smart inverters that can dynamically control solar system output are also helping smooth out fluctuations in solar production. Overall, the future is very bright for solar to play a major role in powering the world in a sustainable manner.


There are several ways consumers, utilities, and governments can address solar variability and align supply with demand:

  • Consumers can shift discretionary electricity usage to times when solar production is highest, such as midday. This includes running appliances like dishwashers and clothes dryers when the sun is out.
  • Utilities can incentivize consumers to shift usage with time-of-use electricity pricing that charges less at peak solar production times. Smart meters enable this differential pricing.
  • Utilities can invest in energy storage like batteries to store excess solar energy when production is high for later use when production drops. Pumped hydro and compressed air storage are other large-scale options.
  • Utilities can expand and modernize electricity grids to balance supply and demand over larger regions, smoothing out local variability.
  • Governments can fund research into better solar forecasting to help utilities predict variability and schedule other power sources accordingly.
  • Governments can streamline permitting and interconnection processes to accelerate solar+storage deployments to align with renewables growth.
  • Governments can modify building codes to make homes and businesses “solar ready” for easy distributed solar and storage additions.
  • Governments can implement policies like renewable portfolio standards, carbon pricing, and tax credits to incentivize solar adoption and products that address variability.

With smart strategies and technologies, the variability of solar supply can be balanced with flexible demand to enable continued solar energy growth (


Balancing solar energy supply with energy demand is crucial for utilizing solar power efficiently. Solar irradiance fluctuates throughout the day and year due to the sun’s position and weather conditions. These fluctuations lead to variable solar energy generation. Meanwhile, electricity demand also fluctuates based on the time of day, day of week, and season. There are often mismatches between solar supply and energy demand. To maximize solar power benefits, supply and demand should be aligned as much as possible. This may involve implementing demand response measures, energy storage solutions, and time-of-use rate structures. Overall, being aware of solar irradiance patterns and electricity demand profiles enables grid operators and consumers to better integrate solar into the energy mix. Careful alignment of solar supply and energy demand will be increasingly important as solar generation expands in the future.

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