How Much Solar Energy Hits The Earth?

Solar energy refers to the light and heat that comes from the sun. Understanding how much solar energy reaches the Earth is important because solar energy has the potential to provide a significant portion of the world’s energy needs in an environmentally sustainable way. However, harnessing solar energy can be challenging due to the vast scale and variability involved.

This article examines the Sun’s massive energy output, how a tiny fraction of that energy is intercepted by the Earth, variability factors that affect the amount we receive, the potential of solar across the globe, challenges that need to be overcome, and recent advancements that are making solar more viable. By the end, you’ll have a solid understanding of Earth’s solar income and the promise and difficulties in leveraging the Sun to power our future.

Table of Contents

The Sun’s Energy Output

The total energy output from the sun is enormous. The sun produces energy through nuclear fusion reactions in its core, converting hydrogen to helium and releasing energy in the process. The rate at which energy is generated in the sun’s core is described as the solar luminosity. According to research, the current solar luminosity is approximately 3.86×10^26 watts. This is an immense amount of power, equivalent to nearly a billion times the energy consumption of humanity.

The sun converts around 4 million tonnes of matter into energy every second via fusion reactions. This vast energy output arises from the incredible pressures and temperatures in the sun’s core, reaching 15 million degrees Celsius. It is the sheer scale and mass of the sun, over 330,000 times the mass of Earth, that allows such high energy production to be sustained.

While enormous, the sun’s energy output does vary slightly over time. As the sun ages and condenses over billions of years, models predict that the solar luminosity will gradually increase. But in general, the energy pouring out of the sun remains relatively stable, maintaining the conditions for life as we know it here on Earth.

Energy Spread Over Vast Space

The sun emanates a tremendous amount of energy every second. However, this energy spreads out over vast distances in space resulting in a small amount of energy actually reaching Earth . Specifically, the amount of solar irradiance per unit area decreases with the square of the distance from the sun as described by the inverse square law (1). This fundamental law of physics states that the intensity of radiation from a point source is inversely proportional to the square of the distance from the source. Here’s how that determines how much solar energy hits Earth and other planets (1):

The sun radiates F watts of energy per unit area at the surface. At a distance R away from the sun, the energy per unit area is now (F/R^2) watts per square meter. Since Earth orbits at a distance of about 150 million kilometers from the sun, the amount of solar energy reaching Earth is about 1400 watts per square meter.

(1) https://www.jpl.nasa.gov/edu/pdfs/juno_solar_power_tm_worksheet_teacher.pdf

Solar Irradiance

Solar irradiance is a measure of the amount of solar power or energy from the sun that reaches a given area over a certain time period, typically measured as power per unit area. It is measured in watts per square meter (W/m2) and represents the intensity of sunlight hitting the Earth’s atmosphere. The solar constant, the amount of solar irradiance measured above the atmosphere, has an average value of approximately 1,360 W/m2 (according to Wikipedia). This value fluctuates slightly due to changes in solar activity and the Earth’s orbit.

Solar irradiance is highest at the equator, where the sunlight strikes perpendicular to the Earth’s surface, and lowest at the poles. The irradiation absorbed at the Earth’s surface depends on location, time of day, season, local landscape and weather. Solar irradiance drives Earth’s climate system and provides the energy that powers photosynthesis in plants and other phototrophs.

Effects of Atmosphere

As sunlight passes through the atmosphere, it interacts with molecules and particles that absorb and scatter the radiation, reducing the amount of solar energy that reaches Earth’s surface. According to the Physical Geography website, around 30% of incoming solar radiation is reflected back to space or absorbed by atmospheric gases, clouds, and particles. The primary atmospheric components that impact solar radiation are:

Absorption – Gases like water vapor, carbon dioxide, and ozone absorb specific wavelengths of solar radiation through electronic or vibrational transitions.
Scattering – Small particles like air molecules and aerosols scatter light in all directions, diffusing direct beam radiation.
Reflection – Clouds reflect a significant portion of radiation back to space, with higher albedo clouds reflecting more.

After accounting for atmospheric effects, the PVEducation website indicates that around 1000 W/m2 of solar radiation reaches the Earth’s surface on a clear day. The actual amount varies based on latitude, time of day, season, cloud cover, and local climate and geography.

Variability

The amount of solar energy that reaches Earth’s atmosphere is not constant. The Sun’s energy output changes over different timescales ranging from seconds to billions of years (NASA, n.d.).

The amount of solar radiation changes throughout the day as the Earth rotates. It also varies between seasons, with the highest solar output hitting the Northern Hemisphere in the summer and the Southern Hemisphere in the winter. The 11-year solar cycle causes the amount of solar activity like sunspots and solar flares to wax and wane over this period. Changes in solar output correlate to small changes in global temperature on Earth (Wikipedia, n.d.).

Variations in the Sun’s irradiance over long timescales are caused by changes in convection, magnetic activity cycles, and sunspot cycles. Changes in solar activity can impact the amount of cosmic rays entering the atmosphere and the amount of cloud cover on Earth. Overall, studies show that solar variability has played a role in climate change over millennia, but the effect is relatively small compared to human-caused factors in recent decades (Academic Oxford University Press, 2002).

Global Solar Potential

According to a report by PricewaterhouseCoopers, the amount of solar energy reaching the Earth’s surface in just one hour is equal to the total energy consumption of all humanity in an entire year (1). To put that in perspective, the total solar energy potential hitting the Earth annually is 89,300 terawatts – over 6,000 times more energy than the population currently uses. Capturing just 0.1% of that solar potential would be enough to satisfy humanity’s energy needs. While global solar potential is clearly immense compared to our energy usage, there are challenges to harnessing it on a large scale.

(1) https://www.pwc.com/gx/en/sustainability/assets/earths-solar-potential.pdf

Challenges

While solar energy offers many benefits, there are also challenges related to capturing and storing the sun’s energy. Two of the biggest difficulties are the high costs of energy storage and intermittency issues.

Solar panels can only generate electricity when the sun is shining. But energy demand continues 24/7. This mismatch requires storage systems like batteries to stockpile excess solar electricity for use at night. Unfortunately, storage technologies are still expensive. Large-scale batteries can cost millions of dollars to install and maintain.

Intermittency also causes problems for grid stability. Solar output fluctuates based on weather and time of day. Cloud cover alone can cause solar generation to rapidly spike up and down. Managing these variable flows is complex, often requiring backup power sources.

More work is needed to bring down storage costs and better integrate solar into the overall energy system. But these challenges are not insurmountable. With continued research and policy support, solar has the potential to play a major role in the world’s energy mix.

Latest Advancements

Solar technology continues to rapidly advance as researchers explore new materials and designs to improve efficiency and lower costs. Some of the most promising recent innovations include:

Perovskite solar cells, made from inexpensive materials, have seen remarkable leaps in efficiency from 3.8% in 2009 to over 25% today. Commercial perovskite panels may be available within 5 years. According to Nature, perovskites have great potential but still face challenges with stability.

Tandem or multi-junction solar cells use multiple stacked photovoltaic layers to absorb light at different wavelengths, achieving efficiencies over 35%. However, production costs are still high. SolarReviews notes this is an exciting area of ongoing research.

Thin, lightweight, and flexible solar panels enable new applications on vehicles, buildings, clothing, and more. Companies like Tesla are integrating solar into roof shingles. Organic solar cells made from carbon-based materials also offer flexibility and low costs.

While silicon panels dominate today, solar farms and rooftops of the future may contain a diverse mix of technologies tailored to different needs. Continued innovation will make solar more efficient, affordable and ubiquitous across society.

Conclusion

In conclusion, the amount of solar energy that hits the Earth each year is enormous. The total solar irradiance at the top of the atmosphere is around 1,361 watts per square meter. Of this, about 30% is reflected back into space by the atmosphere, clouds and surface. The remaining energy that is absorbed is roughly 35,000 times greater than the total energy consumption of humankind each year.

Solar energy has great potential to help meet the world’s growing energy needs in a sustainable way, but there are still challenges around efficiency, storage and infrastructure that need to be addressed through ongoing research and development. As solar technology continues to improve, we can expect it to play an increasingly significant role in powering our homes, businesses and transportation.

Understanding the full potential of solar energy hitting the Earth, and how much can realistically be captured, is an important part of planning our energy future and transitioning to renewable sources. With continued innovation and investment, solar power will help pave the way to a cleaner, greener planet.