The Sun’s Position

Source: Griffith Observatory

Understanding Solar Position Calculation

When it comes to orienting photovoltaic modules to maximize solar energy absorption, understanding the sun’s position throughout the day is crucial. Two key angles, the azimuth angle, and the elevation angle, play a significant role in this calculation.

Local Solar Time vs. Local Time

Local Solar Time (LST) refers to the time when the sun is highest in the sky, while Local Time (LT) can vary due to factors like the Earth’s orbit eccentricity and human adjustments such as time zones and daylight saving time.

Local Standard Time Meridian (LSTM)

The Local Standard Time Meridian (LSTM) acts as a reference meridian for a specific time zone, similar to the Prime Meridian for Greenwich Mean Time. It is calculated based on the difference between Local Time (LT) and Greenwich Mean Time (GMT).

Equation of Time (EoT)

The Equation of Time (EoT) corrects for the Earth’s orbit eccentricity and axial tilt. It is calculated based on the number of days since the start of the year and is used to adjust the solar time.

Time Correction Factor (TC)

The Time Correction Factor accounts for variations in Local Solar Time within a time zone due to longitude differences and incorporates the Equation of Time. The Earth’s rotation of 1° every 4 minutes influences this correction factor.

Hour Angle (HRA) and Declination

The Hour Angle converts Local Solar Time into angular degrees the sun moves across the sky. The Declination angle, based on the number of days since the start of the year, is also a key factor in determining the sun’s position.

Elevation and Azimuth

The elevation angle (α) and azimuth angle are crucial in calculating the sun’s position. The elevation angle is determined by the latitude, declination angle, and Hour Angle, while the azimuth angle considers the declination, latitude, and Hour Angle as well.

Understanding these angles and factors is essential for optimizing the positioning of photovoltaic modules to harness solar energy efficiently throughout the day.

Source: Shutterstock