Tilt and azimuth
The sunlight that reaches the earth is strongest when it strikes a surface perpendicularly or a 90° angle, yet the position of the sun in the sky varies through the day and through the year for every location. This means that to capture as much sunlight as possible and mazimize production, a PV module must be properly positioned. There are two important ways in which a PV module can be positioned relative to the sun:
- Direction relative to the cardinal directions (North, East, South, West).
- Angle relative to the surface of the earth.
Understanding the ideal orientation and angle requires a basic understanding of the earth's movements.
Movements of the earth
The earth is at all times rotating around its own axis (completing a full rotation approximately every 24 hours) and orbiting around the sun (completing a full orbit appxoimately every 365 days).
Daily rotation
The earth completes a full revolution around its own axis approximately every 24 hours. This causes the strength of the sun to vary throughout the day as it arcs through the sky, rising in the East and setting in the West. The strength of the sun's rays peak when it is at the top of its arc between East and West at around 12:00.
The Earth rotates around its own axis once each day. One side of the earth is always in the dark.
Yearly orbit
The yearly orbit of the earth around the sun accounts for the variation in the strength of the sun in different areas between the seasons. The earth's axis is at an angle, roughly 23.5°, which creates seasonal variation as the angle of the sun's rays striking any location on earth varies depending upon the position of the earth in its orbit around the sun. This also has an effect on the number of hours of light that a location receives each day, which becomes more pronounced moving further away from the equator. June 21 in the Southern hemisphere is the shortest day of the year and December 21 is the longest day of the year. The opposite is true in the Northern hemisphere.
The Earth orbits the sun in a nearly perfect circle once each year. The angle of the axis of the earth does not vary as it moves around the sun each year. (1) December 21st. (2) March 20th (3) June 21st (4) September 20th
Left: June 21 - The Northern hemisphere is tilted towards the sun and therefore receives more direct sunlight and has more daylight each day than the Southern hemisphere. Right: December 21 - The Southern hemisphere is tilted towards the sun and therefore recevies more direct sunlight and has more daylight each day than the Northern hemisphere.
Orientation
The most important window for PV system production is between 9:00 and 15:00. At 9:00 the sun is rising in the East and gaining strength. At around 12:00 the sun is reaching the peak if its arc in the sky between East and West. In the Southern hemisphere, the position of the sun in the sky is due North at this point. In the Northern hemisphere it is due South. At 15:00 the sun is beginning to fall towards the West and is losing strength. To maximize the amount of sunlight that an a PV module captures, it is ideal to if it is pointed due North (0°)in the Southern hemisphere and due South (180°) in the Northern hemisphere as this enables the PV module to capture the maximum amount of sunlight as the sun arcs from East to West. Additionally if the PV module is properly facing either of these directions it it will be able to take maximum advantage of the sun's rays when it is at its strongest.
Southern hemisphere: A PV module on a fixed mounting structure will maximize yearly production by facing directly towards the North:
June 21, 9:00 in Quelimane, Mozambique (17°S): The sun rises in the East.
June 21, 15:00 in Quelimane, Mozambique (17°S): The sun descends in the West.
Northern hemisphere: A PV module on a fixed mounting sturcture will maximize yearly production by facing directly towards the South:
Dec 21, 9:00 in Oaxaca, Mexico (17°N): The sun rises in the East.
Dec 21, 15:00 in Oaxaca, Mexico (17° N): The sun descends in the West.
The earth makes a complete rotation about its own axis approximately every 24 hours. As the earth rotates the sun moves through the sky each day, rising in the East and setting in the West.
The earth rotates around the sun in a nearly perfect circle one time every 365 days. Better color/image simulator for graphics https://ccnmtl.github.io/astro-simulations/sun-motion-simulator/#
Original https://astro.unl.edu/naap/motion3/animations/sunmotions.html
