For solar installers, to increase the solar system performance, it's important to not only select high-performing solar panels, but to also consider shading analysis, to avoid or reduce the shading issues on rooftop on grid solar system or ground on grid solar system.
Solar installers can use this method to accurately predict on how, shadows from trees, terrain, nearby structures, and solar panel rows, to impact the power output of a PV system throughout the day and seasons.
Most rooftop on grid solar system can not avoid from shading due to the limited space on given rooftops, the flat rooftop solar system has higher shading rate than tilt rooftop solar system, with concerns on how to reduce the shading loses becomes the million dollar question. On the other hand, ground on grid solar system can avoid most of the outside shadings factors, more concerns coming from solar panel array shadings with inside.
01 Using Latitude To Calculate Solar Elevation Angle
Solar elevation angle, a geographical term, refers to the angle between the direction of incidence of sunlight and the ground level at a certain point on the earth.
When calculating the shadow occlusion of photovoltaic modules, the data of the solar altitude angle at 12 noon on the winter solstice is often used, and if the solar altitude angle data at 12 noon on the local winter solstice is not easy to find, it can be calculated by the local latitude.
On the winter solstice, the sun directly hits the Tropic of Capricorn (23°26′ S or 23.43° S), and the solar altitude angle at noon is calculated by the formula H=90°-|α-β|, α is the local geographic latitude, and the β is the Tropic of Capricorn latitude (i.e., at the noon, solar altitude angle = 90°-|local geographic latitude - the latitude of the direct sun point at this time|) Note: North latitude is positive, and south latitude is negative.
For example, if the latitude of Beijing is about 40°N, then the solar altitude angle on the winter solstice in Beijing is H=90-|40-(-23.43)|=26.57°.
For example, if the latitude of Xiamen is about 24.5°N, then the solar altitude angle of Xiamen on the winter solstice is H=90-|24.5-(-23.43)|=42.07°
02 Calculation Of The Distance Between The Obstacle And The Solar Panel.
When there is an obstacle in front of the solar panel, if the obstacle is high enough, it will cause shading to the solar panel and affect its power generation efficiency.
The minimum distance of the fixed solar panels to be blocked by obstacles:
D'=H×cotα×cosγ
D'-The minimum distance (mm) of the solar panel without being shaded by obstacles, and this distance is the minimum distance between the obstacle and the solar panel on the projection line of the horizontal plane, as shown in the following schematic diagram;
H-The vertical distance between the highest point of the obstacle and the lowest point of the solar panel sunlight receiving surface (mm);
β - Installation inclination angle of solar panel (°);
γ - Installation azimuth of solar panel (°);
α-Sun altitude angle (°), taken at 12 noon on the winter solstice day of the project site.
03 Calculation Of Shading Between Solar Panel Array
When solar panels are fixed in rows, the front row of solar panels may cause shading to the rear row of solar panels, in order to avoid this situation, the shading calculation should be carried out during the design to ensure that there is enough distance between the two rows to avoid the front row of solar panels from casting shading to the rear row of solar panels, PV system on rooftop with rooftop solar mounting rack would be clearly facing more complicated shading situations than PV system on the ground with ground solar mounting rack.
The minimum distance at which a fixedly arranged solar panels is obscured by a front row of solar panels:
D'=H×cotα×cosγ
D'-The minimum distance (mm) of the solar panel without being shaded by front row of solar panels, and this distance is the minimum distance between the Solar panel rows on the projection line of the horizontal plane, as shown in the following schematic diagram;
H-The vertical distance between the highest point of the front row and the lowest point of the solar panel sunlight receiving surface at the back row (mm);
β - Installation inclination angle of solar panel (°);
γ - Installation azimuth of solar panel (°);
α-Sun altitude angle (°), taken at 12 noon on the winter solstice day of the project site.
This analysis is typically facilitated by solar design software and on-site evaluations to ensure strategic panel placement and optimal system configuration, ultimately leading to greater efficiency. By taking into account potential shading conditions, property owners can make the most of their solar energy investment. But in some cases, the installer has to take into consideration that to avoid shading might cause lower land utilization ratio, and limited the total solar system installation capacity. More installation capacity or Higher system efficiency, that is the question.
