How solar zenith and azimuth impact panel efficiency

What do solar zenith and solar azimuth mean?

Solar zenith definition: Solar zenith refers to the point in the sky where the sun is directly above a location on Earth. At this point, the sun is at its highest point for the day, typically occurring around solar noon. At solar zenith, the altitude angle (or elevation angle) is at its maximum value.

You can see on the ground when the sun is at its solar zenith, as shadows will be at their smallest. This is because the sun is exactly at zenith with a zenith angle of 0 degrees, so shadows are being cast directly downwards rather than at an angle. The elevation angle is equal to 90 degrees when the sun is at zenith. The zenith angle is calculated using the position of the sun and the zenith point. The minimum zenith angle occurs at solar noon, while the elevation angle is at its maximum.

Solar azimuth definition: The solar azimuth is the direction along the horizon where the sun is located. It is measured in degrees from the North in a clockwise direction. So, while solar zenith refers to the sun’s altitude, solar azimuth refers to its horizontal position. The solar azimuth helps you determine the sun’s position in relation to the North. The elevation angle (or altitude angle) is measured from the horizon and varies throughout the day. Historically, sailors used the sun’s azimuth and elevation along with tools like sextants to determine their position at sea.

For example, if the sun is directly East, the solar azimuth is 90 degrees. If the sun is directly South, the solar azimuth is 180 degrees. At sunrise and sunset, the elevation angle is zero, and these times are important reference points for solar position calculations. Sunset times are used to determine the duration of sunlight and the variation in solar angles throughout the day. The optimal tilt angle is typically calculated to make the panel surface as perpendicular as possible to the sun’s rays at solar noon, based on latitude and season.

Why are solar zenith and azimuth important for solar design?

Understanding solar zenith and azimuth is crucial for optimizing a solar PV plant. PV modules work best when the sun’s rays are perpendicular to their surface, so engineers need to position panels in a way that maximizes the amount of time the sun is perpendicular. The main interest is in maximizing the elevation angle of the sun at solar noon, which depends on the location's latitude and the time of year. This can be done by using the solar zenith and azimuth to plot the sun’s trajectory across the land, giving a solid idea of where you should place panels. The maximum elevation angle of the sun occurs at the summer solstice, which is important for PV system design.

You should use solar azimuth to determine panel orientation. Because most of the sun’s energy travels in a straight line, panels must be directly facing the sun for as long as possible throughout the day. Solar noon is the time of day when the sun is highest in the sky and lies due south (or due north in the Southern Hemisphere), corresponding to a specific azimuth value depending on latitude. Solar noon is the central point along the solar azimuth. This means that if the panel’s orientation aligns with solar noon, it can absorb sunlight throughout the day. Once the panel is positioned according to azimuth, the panel should be tilted to best reflect the solar zenith. The optimal panel orientation varies across different locations and regions, and regional differences in solar angles must be considered.

Solar azimuth and solar zenith are used in RatedPower to map out the far shading, or horizon effect. This will show the reduction in sunlight caused by obstructions in the surrounding landscape, such as mountains or buildings. Any objects along the horizon that interrupt the sun’s rays will reduce the amount of energy a solar panel can collect and should be avoided whenever possible. Evaluating the far shading effect can reveal whether your chosen location is suitable for a solar plant.

This can be difficult with generic information, which is why RatedPower allows users to upload a horizon file featuring data specific to their location for a more accurate estimation. The values of solar angles and irradiation are site-specific and must be analyzed for each location.

What is a horizon file, and how do you customize and upload it to the RatedPower software?

RatedPower has a powerful tool called the Horizon Importer, which allows you to upload a customized horizon file. The horizon file contains the information we need as a set of points in degrees, including the azimuth angle and solar zenith. This allows RatedPower software to use your exact information to estimate far shading losses for your site accurately, rather than relying on generic data.

Uploading your horizon file is simple. Under the Horizon tab, you will see a button that allows you to upload your horizon file in a .csv or .hor format. If your horizon file is not accepted, there is also a generic template in RatedPower to fill out the relevant data points. The software will then provide a graphic showing the far shading of your location and help you position your panels for maximum energy collection.