From sunlight to solar parks: The meteorology behind solar power

You’ve probably heard us say that we believe it’s essential for everyone on our team to think like a short-term power trader. But what might be less obvious is that we also have a dedicated team of in-house expert meteorologists. They don’t just provide the most accurate inputs for our forecasts; they also ensure that our power forecasts and traders are deeply grounded in atmospheric science.

By sharing these insights, we want to give you a glimpse into the level of detail we incorporate into our decision-making – where precision, science, and trading expertise come together to stay ahead in the market.

All energy is solar energy

Beneath spring sunshine’s gentle warmth lies an extraordinary story. Deep inside the Sun, billions of hydrogen atoms collide and fuse into helium, releasing immense energy in a process that has powered our solar system for over four billion years. This nuclear reaction generates an astonishing 3.8 x 10²⁶ watts of energy – enough to meet Earth’s energy demand for millions of years in just one hour.

This energy travels the 150-million-kilometer distance between the Sun and Earth in a little over eight minutes. When it arrives, it does more than illuminate our skies. In fact, solar radiation fuels nearly every energy system on our planet: it drives atmospheric circulation, creating winds that spin turbines; it evaporates water, feeding the hydrological cycle and hydropower; and, of course, it directly powers solar panels, converting photons into electricity.

In this article, we explore the meteorology of solar radiation and its role in solar power forecasting – how energy from the Sun reaches the Earth, impacts solar panels, and is predicted using advanced weather models.

How the Sun’s energy travels through space

We begin with the basics. Energy moves through the universe in three fundamental ways:

• Conduction – This is the transfer of energy through direct contact between atoms or molecules. Imagine heating one end of a metal bar with a lighter. Over time, the heat spreads along the bar as energetic atoms transfer their energy to neighboring atoms.
• Convection – This occurs in liquids and gases when warmer, less dense material rises while cooler, denser material sinks, creating circulation patterns. On Earth, sunlight warms the surface, which then heats the air above it. This warm air rises, creating convection currents that drive wind patterns and weather systems.
• Radiation – Unlike conduction and convection, radiation does not require a medium to transfer energy. Instead, energy is emitted as electromagnetic waves, which can even happen in a vacuum.

The latter is how the Sun’s energy travels across space to reach Earth. Without radiation, sunlight would never reach us, and life as we know it wouldn’t exist.

Source: World Atlas

What happens once solar radiation reaches Earth

Once solar radiation reaches our planet, it interacts with the atmosphere, clouds, and surface, influencing climate patterns, weather, and the amount of solar power available for electricity generation.

From a fundamental perspective, when solar energy encounters particles in the atmosphere, it can interact in several ways:

Absorption and emission

Molecules and particles in the atmosphere absorb specific wavelengths of solar radiation, causing electrons to move to higher energy levels. This absorbed energy is later converted into heat, warming the atmosphere and influencing weather patterns.

The excited electrons return to lower energy states, emitting energy in the form of radiation. This process contributes to the greenhouse effect, as gases like water vapor and carbon dioxide absorb and re-emit infrared radiation.

Source: Azizi, Mahdi & Talatahari, Siamak & Giaralis, Agathoklis. (2021). Optimization of Engineering Design Problems Using Atomic Orbital Search Algorithm. IEEE Access. PP. 1-1. 10.1109/ACCESS.2021.3096726

The principle governing emission is the Stefan-Boltzmann law, which states that every object with a temperature above absolute zero (0 K, – 273°C) emits thermal radiation. The total energy radiated per unit surface area of a black body is proportional to the fourth power of its absolute temperature (T)

Fun fact: The human body, with an average skin temperature of around 33°C (306 K), emits approximately 160 W of thermal radiation, comparable to that of an old-school incandescent light bulb.

Scattering (or why the sky is blue)

Before energy is absorbed, it can be scattered, meaning its direction is changed without being fully absorbed by the particle.

One of the most fascinating effects is Rayleigh scattering, which answers the question, ‘Why is the sky blue?’. Small molecules in the atmosphere scatter shorter (blue) wavelengths of sunlight more than longer (red) wavelengths.

During the day, when the Sun is high in the sky, its light travels through a shorter path in the atmosphere. Shorter wavelengths, like blue light, are scattered more strongly by air molecules, making the sky appear blue. When the Sun is low on the horizon, its light travels through a greater thickness of the atmosphere, scattering away the shorter blue wavelengths. The remaining light is dominated by longer wavelengths, such as red and orange, creating the warm hues of sunrise and sunset.

The energy budget

Now, let’s take a closer look at the interactions in our atmosphere by introducing the energy budget. This concept refers to the balance between the energy that reaches Earth from the Sun and the energy that flows from Earth back into space.

Solar and thermal radiation

Below, we reference diagrams illustrating the global mean energy budget under all-sky conditions – which include clouds – and clear-sky conditions. Solar and thermal radiation are part of the same continuous energy cycle, but they differ in their origin and wavelength:

• Solar radiation – also known as shortwave radiation – comes directly from the Sun. This includes visible light, ultraviolet (UV), and near-infrared (NIR) radiation.
• Thermal radiation – also called longwave radiation – is emitted by Earth and the atmosphere. This is dictated by the Stefan-Boltzmann law mentioned above.

Earth’s energy balance is a dynamic system influenced by both solar and thermal radiation. Here is how it works in simplified terms:

• On average, 340 W/m² of solar radiation reaches the top of Earth’s atmosphere.
• Some of this radiation is reflected back into space by clouds, aerosols, and the Earth’s surface.
• The remainder is absorbed by the atmosphere and surface, warming the planet.
• The atmosphere, surface, and clouds emit thermal radiation, which helps regulate Earth’s temperature by contributing to the greenhouse effect.

Source: Wild et al. (2019). The cloud-free global energy balance and inferred cloud radiative effects: an assessment based on direct observations and climate models. Climate Dynamics, 52. https://doi.org/10.1007/s00382-018-4413-y.

What does this all mean for solar power? For solar energy production, only shortwave radiation matters. Solar panels are designed to capture and convert shortwave radiation into electricity.

Additional processes

If, like us, you’re passionate about climate change, two additional processes are worth mentioning:

• Evaporation: A significant portion of absorbed solar energy is used to transform water from liquid to vapor.
• Sensible heat transfer: Some of the energy warms the air directly, causing changes in temperature in air masses.

Forests play a major role in energy absorption and transfer, as they capture solar radiation and gradually release heat. Deforestation disrupts this balance, reducing evaporation and increasing sensible heat. This leads to hotter, drier conditions and changes in local and global energy balances.

Solar irradiance in NWP models

Taking a step further towards forecasting solar power production, it’s essential to understand how solar irradiance is handled in Numerical Weather Prediction (NWP) models.

To recap, NWP models simulate the atmosphere and oceans by solving physical equations (e.g., the flow of fluids) and return predictions for hundreds of meteorological variables, ranging from the sea to the upper atmosphere.

In the case of solar, NWPs model the path of shortwave and longwave radiation as it interacts with the Earth’s atmosphere. This includes absorption, emission, and scattering and ultimately determines how much solar energy reaches the surface. In essence, these models create a mathematical representation of what happens to every W/m² of incoming solar radiation from the top of the atmosphere to the ground.

Cloud cover is one of the biggest challenges in solar power forecasting. Depending on their thickness, altitude, and composition, clouds can scatter, absorb, or reflect solar energy, affecting how much radiation reaches the surface. Aerosols (e.g., dust, pollution, and sea salt) also affect solar radiation absorption and scattering. For solar power traders, these fluctuations can directly impact market positions and profitability.

Different NWP models approach these problems using parameterizations, which is a mathematical approximation of how radiation moves through the atmosphere at scales too small for the model to resolve directly. For instance, the European Centre for Medium-Range Weather Forecasts (ECMWF) uses a radiation scheme that accounts for gas, aerosol, and cloud interactions.

Notably, solar radiation is a very computationally intensive aspect of weather forecasting, requiring massive processing power to precisely model the complex interactions between the Sun and Earth’s atmosphere.

This field is constantly evolving as researchers refine radiation models and integrate new data sources. For more on these developments, also read our piece on the different types of weather models.

Scratching the surface

The interactions between the Sun and Earth’s atmosphere are far more complex than what we’ve covered here. For one, the energy that reaches the surface is anything but uniform. Due to the Earth’s curvature, solar radiation is more concentrated near the equator and weaker at higher latitudes. Seasons also play a role. Because the Earth’s axis is slightly tilted, different parts of the planet receive varying amounts of sunlight throughout the year.

Another crucial factor is the angle at which sunlight reaches the surface. When the Sun is directly overhead, its rays strike the surface perpendicularly, delivering more energy per square meter. When the Sun is lower in the sky, its rays hit at an angle, spreading the same amount of energy over a larger area. For solar panels, this means that positioning significantly affects energy capture and conversion.

Accurately forecasting solar power production for large-scale solar parks thus requires the understanding of numerous atmospheric variables. This is where our meteorologists make a difference. They help us translate complex weather data into actionable forecasts that optimize solar power trading in short-term energy markets.

If you’re interested in the latest methods to predict solar generation for trading on short-term markets, also check out our previous article on forecasting solar power production with AI.