Once you have determined a good site location for your solar panels, it is necessary to ensure that there will be no obstructions to the sun’s light throughout the year.

The sun tracks across the sky the whole year ‘round, but its track changes significantly throughout the year. Therefore, the site survey must take into account the sun’s position at different times of the year.

There are always two days of the year when the day is exactly 12 hours long. These days are termed “solar equinoxes” and fall on the 21 ^st of March and the 21 ^st of September. This is when the sun rises directly from the equator’s east and sets in its west. Six hours after sunrise, or “solar noon,” as it is called, the sun’s angle is (90° - the local latitude).

In the Northern Hemisphere, the 21 ^st of June is recorded as the longest day of the year, a day known as the “summer solstice,” while the 21 ^st of December is recorded as the shortest day of the year, a day known as the “winter solstice.” (Note that the winter solstice does not always fall on the 21 ^st. This date should be checked annually if it is significant to your plans.)

A great tool to analyze the Sun's path for your location is available at Sun Eath Tools.

During summer solstice, the sun is angled 23.5° higher than when it is at the equinox. During winter solstice, its angle is 23.5° lower. These phenomena are caused by the earth’s tilt and are related to Earth’s orbit around the sun. Summer solstice occurs in the Northern Hemisphere when the North Pole tilts towards the sun; the Pole tilts away from the sun at the time of winter solstice.