Last spring I took a class called Energy and Sustainability, with professor Lonnie gamble, and learned how to capture the most of the sun’s energy and turn it into electricity, by placing solar panels at optimal angles, in the correct direction.

Optimal direction and angles for solar panel placement is determined by the sun’s position in the sky at different times of the year.  In the northern hemisphere (where we are), the sun is highest in the sky in the summer, and lowest in the winter; it rises in the east and sets in the west, in the southern sky.

Based on these facts, Lonnie suggest that static solar panels (those without trackers, that do not move) be placed at an angle equal to the degree of the latitude where they are installed, minus 15 degrees in the summer, plus 15 degrees in the winter; they will need to face south, toward the sun.

During the summer, the northern hemisphere is tilted towards the sun; meaning the sun is higher, and also in the sky for more hours than it is in the winter.    Because the sun is highest in the sky in summer, the panels needs to lay flatter (top tilted further north) to catch the most sunlight; thus the minus 15 degree angle.  The opposite is true for winter; when the sun is lowest in the sky, and closer to the horizon, the angle of the panels will need to be increased (top tilted more towards south) to catch the most sunlight.  (See picture below for an understanding of panel angles).

The Khare’s house, located in Fairfield Iowa is located at a latitude of 41 degrees.  So, the optimal summer angle for static solar panels would be 26 degrees (41-15), and the winter angle would be 56 degrees (41 +15).

The following explanation may give you a better understanding of how latitude determines how much light falls onto a location during different times of the year (and also why adding or subtracting 15 degrees to a panel angle will prove beneficial):

As the Earth orbits around the sun, the sun “moves” between the Tropic of Cancer on the Summer Solstice (June 21) to the Tropic of Capricorn on the Winter Solstice (Dec 21). The Tropic of Cancer is the circle of latitude on the Earth that marks the most northerly position at which the sun appears directly overhead, and the Tropic of Capricorn is the circle of latitude that marks the most southerly position at which the sun is overhead.

The positions of these circles of latitude–Tropic of Cancer at 23.5 N and  Tropic of Capricorn at 23.5 S–are dictated by the tilt of the Earth’s axis, which is 23.5 degrees,  relative to the Earth’s orbital plane around the sun. *The “top” of the Earth’s Axis is the North Pole, and the “bottom” is at the South Pole.

The “movement” of the sun throughout the sky during the day, is due to the earth rotating around it’s axis (one full rotation equals 24 hours).  The changing of the seasons throughout the year is due to the Earth orbiting around the sun (one full orbit equals 365 days).

The sun is highest in the Northern hemisphere’s sky on June 21–when it is 90 degrees above the Tropic of Cancer, which has a latitude of 23.5 degrees.  In order to determine how many degrees the sun is above your particular latitude on June 21, you subtract the difference of your latitude and the latitude of the Tropic of Cancer from the 90 degree angle of the sun.  This is what the equation looks like for Fairfiled, IA:  90 – (41-23.5) = 72.5

To determine the angle of the sun above your latitude at Winter Solstice, you would take the angle of the sun at Summer Solstice (in this case 72.5) and subtract 47; this (23.5 X 2) is the difference in maximum height of the sun for any location on the Earth over a one year period.

As the Earth orbits the sun, and the sun “moves” from the Tropic of Cancer to the the Tropic of Capricorn, its position and angle changes a little every day; this is why determining the angle of your solar panels by subtracting 15 degrees from you latitude in the summer and adding 15 in the winter is a good idea.  This 15 degree angle is a sort of average that allows for catching most of the available solar energy on any give day while only having to change the angle of your panels twice a year.

For the absolute maximum solar gain, you would use a solar tracker, which would allow the panels to shift their angles throughout the day, following to the movement of the sun.


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