Explained: Solar Position Algorithm For Solar Radiation Applications

Explained: Solar Position Algorithm For Solar Radiation Applications


Explained: Solar Position Algorithm For Solar Radiation Applications

Representational image. Credit: Canva

The design of solar energy systems, the development of solar tracking technologies, and the forecasting of solar radiation all make extensive use of the Solar Position Algorithm. These applications can forecast solar energy production, estimate solar radiation levels at certain places, and optimize the installation and performance of solar panels by precisely calculating the sun’s position.


Algorithms for calculating the sun’s position in the sky at a given location, time, and date are known as solar position algorithms. The “Solar Position Algorithm” (SPA), created by the National Renewable Energy Laboratory (NREL) in the United States, is one popular solar position algorithm. The solar zenith angle, solar azimuth angle, and solar elevation angle may all be calculated precisely using the SPA algorithm.

The date, time, and coordinates of the location of interest are only a few of the variables that the SPA algorithm considers. The position of the sun is calculated using trigonometric calculations and astronomical models.


To determine the sun’s precise location, the SPA considers several factors. The date, time, latitude, and longitude of the observer’s position on Earth are among these factors. The azimuth angle and the zenith angle are two crucial pieces of information that the algorithm delivers by taking these variables into account.


The azimuth angle depicts the sun’s position concerning the observer’s horizontal axis. It is expressed in degrees, where 0° represents north, 90° represents east, 180° represents south, and 270° represents west. For optimal exposure to sunlight, solar panels or solar tracking systems can be oriented using this angle.

On the other hand, the zenith angle depicts the sun’s location concerning the observer in a vertical orientation. It is calculated from the zenith (direct overhead) of the observer to the location of the sun. The sun is overhead when the zenith angle is zero degrees, and it is on the horizon when the zenith angle is ninety degrees. When determining how much solar energy is reaching the surface of the Earth, the zenith angle is beneficial.

The SPA performs a series of procedures to find the sun. To start, the specified date is converted into a Julian Day, which is a continuous count of days going back to January 1, 4713 BC. The Julian Century, which reflects the number of centuries since January 1, 2000, is then calculated. These conversions offer a consistent chronology for precise computations.

The program then calculates the Earth’s latitude and longitude from its heliocentric position using the Julian Century. These numbers represent where the Earth is about the Sun. The procedure determines the sun’s geocentric right ascension and declination using the Earth’s heliocentric coordinates. These numbers specify the sun’s position with the reference frame of the Earth.

The algorithm then calculates the local hour angle, which is the angle between the observer’s meridian and the sun’s meridian at the specified time, using the observer’s latitude and longitude. The azimuth and zenith angles can only be determined with the help of this information. The method determines the azimuth and zenith angles of the sun after receiving the local hour angle and its declination. The sun’s exact location in the sky at the given place and time is determined by these values.

The algorithm then adjusts atmospheric refraction. This adjustment ensures that the sun is positioned correctly by taking into account how light bends as it travels through the atmosphere of the Earth.

Importance of Solar Position Algorithms:

Algorithms for calculating the position of the sun in the sky use data such as date, time, and geographic coordinates. The solar zenith angle, solar azimuth angle, and solar elevation angle are all provided by these methods. Several solar radiation applications, including the following, depend on precise estimations of the sun’s position:

Solar Energy System Design: Accurate understanding of the sun’s location enables solar panels to be angled and oriented in a way that maximizes their exposure to light and energy-generating capacity.

Solar Tracking Systems may change the position of solar panels in real time using solar position algorithms, ensuring that they are constantly facing the sun for maximum energy absorption.

Solar Resource Assessment: Accurate solar position calculations help evaluate the potential of solar resources at a given place by identifying the presence and strength of solar radiation. For project planning, site selection, and energy yield predictions, this information is essential.


Solar position algorithms are essential for solar radiation applications because they make it possible to calculate the sun’s exact location in the sky. These algorithms help with effective solar energy system design, solar tracking, and solar resource assessment by precisely determining the sun’s zenith, azimuth, and elevation angles. Solar position algorithms are used to improve the functionality, energy effectiveness, and financial viability of solar energy installations, promoting the wide adoption of clean and sustainable solar energy.

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