Solar Position

1. Solar Position

2. Sun’s movement through the day/year is a critical environmental factor that needs to be understood to design a high performance building • Planned correctly, you can take advantage of the sun’s path • Natural daylighting • Passive heating • Photovoltaic energy generation • Natural ventilation

3. Altitude – vertical angle the sun makes with the ground plane Azimuth – horizontal angle between the sun and true north (-180 degrees, 180 degrees, positive in a clockwise direction from north) Solar Position

4. Sun’s path varies throughout the year • Summer – sun is high and rises/sets north of east-west (northern hemisphere) • south of east-west (southern hemisphere) • Rises much earlier and sets much later in the summer than the winter • To plan for the extreme heat in the summer study the summer solstice • Sun is at its highest noon altitude Seasonal Variations/Important Dates

5. Winter sun is low in the sky Rises/sets south of east-west (northern hemisphere) Rises/sets north of east-west (southern hemisphere) To study extremes of winter look at the sun’s path during winter solstice, sun is at its lowest noon altitude Seasonal Variations/Important Dates

6. To study more average positions look at the sun’s path on the spring and autumn equinoxes, sun rises and sets due east-west Altitude of the noon sun at the equinox is determined by the latitude of the site Rule of thumb for optimum angle of solar panels is the latitude of the site, rays are most perpendicular to the panel for most of the year Seasonal Variations/Important Dates

7. Study particular days • Solstices: extreme of the sun’s position • Equinoxes: average sun position • Study different seasons: • Winter studies – How to maximize sun to passively heat the building • Summer studies – How to minimize sun to passively cool the building Tips/Rules of Thumb

8. Dates to Remember

9. Morning – try to capture the sun’s energy to warm up spaces when the sun is low in the sky, need to protect against glare Noon – Strongest and highest in the sky. Avoid hot midday sun to reduce cooling loads. May want to capture the sun for passive solar heating/energy generation Afternoon – Prevent overheating/glare Occupancy hours – Think about when the building is used most Look at some specific times of day

10. Used to read solar azimuth and altitude throughout the day Like a photograph of the sky, looking straight up towards the zenith with a 180 fish-eye lens Paths of the sun at different times of the year can be projected onto this flattened hemisphere Stereographic Sun Path Diagrams

13. Used to read solar azimuth and altitude Azimuth lines- angle lines run around the edge of the diagram Altitude lines – represented as concentric circular dotted lines that run from the center out Date lines – Start on the eastern side of the graph and run to the west. Represent the path of the sun on one particular day of the year Hour lines/analemma – shown as figure 8 lines that intersect the date lines and represent the position of the sun at a specific hour. Intersection between date and hour gives the suns position How to read stereographic sun path diagrams

14. Locate the required hour line on the diagram Locate the required date line (solid lines are Jan-June and dotted July-Dec Find the intersection point of hour and date lines (solid with solid, dotted with dotted) Draw a line from the very center of the diagram through the intersection point to the perimeter Read the azimuth angle take clockwise from the north Trace a concentric circle around from the intersection point to the vertical north axis, displays altitude angle Interpolate between concentric circle lines to find altitude Gives suns position as defined by azimuth and altitude Reading the Sun Position