Simulation Metric : Point-in-time Sunlight Hours Simulation
Location : Pittsburgh
Performance Objective(s) : Understanding different sun positions and analysing shadow ranges
Analysis Period : 20th March, 21st June, 22nd September, 21st December, 9:00am - 3:00pm
Understanding the sunpath is essential for proper design and location of solar photovoltaic collectors or modules in the early phase. It also helps understand shadowing in the process of PV design. The solstices and equinoxes were simulated and then evaluated in order to evaluate the number of daylight hours, shadows of surrounding elements and the date and time of the highest and lowest altitude of the sun on these days. Excessive shading may affect landscaping, result in higher energy bills, and lessen the enjoyability of backyards.
Pseudo script for Sunpath Diagram and shadow ranges
This simulation requires the location data including the latitude and the longitude, the plane of the site to be analysed, and the analysis period. The shadow range meshes and sun path diagrams are both made using DIVA.
Shadow Analysis Perspective View
Shadow analysis Top View
Spring Equinox: March 20th
During the spring, the sun is directly over the equator, making the sun appear higher than it actually is in the northern hemisphere. Pittsburgh experiences almost equal hours of day and night due to this. The shadow ranges are cast towards the east end of the site, and mostly affect the southern end of the house. The maximum sun angle is about 49 degrees and causes shadow ranges along the E-W orientation of the site.
Summer Solstice: June 21st
During the summer solstice, the sun is high above the ground and almost directly overhead to the surface of the earth in Pittsburgh. The sun’s rays almost directly hit the Tropic of Cancer in the Northern hemisphere, and the sun travels the farthest along the sky, making it the longest day of the year. On this day, the building will receive the longest number of continuous daylight hours from 8AM-6PM. The summer solstice is the day when the sun is at its highest point in the sky at 72.28 degrees at 12 PM.
Autumn Equinox: September 21st
The autumn equinox in the northern hemisphere is when the sun is at a lower angle than in the summer, with the sun being a little over the horizon in the south. This is because the sun is directly over the equator. The south face of the house is bound to receive a good amount of sunlight on this day. The shadow ranges on this day are cast larger and along the E-W axis of the site making it somewhat more shaded. The days and nights appear to have an equal distribution of twelve hours each on the autumnal equinox because the sun appears to be above the horizon, though it is not.
Winter Solstice: December 21st
The winter solstice saw that the sun was very low on the horizon in the South for most of the day. This is because Pittsburgh is located in the northern hemisphere, and in winters, the sun’s rays hit almost perpendicular to the Tropic of Capricorn. This is the shortest day of the year with daylight hours from 8AM-4PM and is when the least amount of sunlight is received. The shadow ranges cast by the greenery around are very evident and extend over most of the house for most of the day. However, the trees around the house shed much of their foliage causing some part of the southern face to receive some sunlight. The sun angle is lowest on the winter solstice, which is 25.90 degrees.
Solar Elevation vs Solar Azimuth
The graph above compares the solar elevation during the summer and winter solstices and the equinoxes which reconfirms the sun position being highest during summer solstice, lowest during winter solstice and the equinoxes have solar angles equal to each other.
Sun Path diagrams with sun angles for solstices and equinoxes