Tracking the Sun
by Lincoln Kraeuter
(Jensen Beach, FL, USA)
This blog will describe a solar tracking mechanism which can be used for large paraboloids or conical horns. The chefs of India requested a solar oven which delivers 1000 watts. What is the diameter of a paraboloid which delivers 1000 watts? 1000 watts = 1100 watts/ square meter x .75 x area in square meters where .75 is the reflection efficiency of aluminum foil. Then using the equation: area = pi x radius squared yields: 1.212/ pi = radius squared = .386 taking the square root gives: .621 or a diameter of 1.24 meters. This is a fairly large paraboloid and rather awkward to adjust to the transiting sun. A system of pipes and bearings would help. There are three requirements which must be satisfied to track the energy of the sun. DAILY AXIS of ROTATION First: the paraboloid must rotate on an axis that parallels the axis of the rotating earth. That is, an axis that points to the north star and the southern cross. One can use a magnetic compass to approximate the north south line on the surface of the earth. But, when you see the north star it is not on the surface of the earth. It is at an angle above the surface. This angle is equal to the latitude of the stove/oven site. For example: the island of Hispaniola is roughly at 20 degrees N Lat. Therefore,the north south axis is pointed 20 degrees upward to the north star. South Sudan is roughly 8 degrees N Lat. Tilt the daily axis 8 degrees upward to the north star. Second: The seasonal change in the transit of the sun is caused by the tilt of the earth's axis to the orbit around the sun. The earth's axis still points to the north star. An imaginary line drawn from the center of the sun to the center of the earth traces out lines of latitude, approximately. As the seasons change from winter to summer, this line shifts from the tropic of Capricorn, 23.45 S Lat. through the equator, and then to the tropic of cancer 23.45 N Lat. As seen from the earth, the noon day angle of the sun changes 23.45 plus 23.45 equals 46.90 degrees. This change is in south to north direction, taking one half a year. It then cycles back 46.90 degrees to winter. The paraboloid horn must be tilted 46.9 degrees in a north south direction to maintain a stationary focus. This is done by drilling eight or more bearing holes in the beams supporting the solar collector. when the focus moves approximately 7 degrees north or south the bearings must be reset. Continued under the title: Tracking the Sun
Thank you Lincoln for your hard work and effort to help us understand how an efficient tracking system can work.
I am sure there are those who visit this site that will find this helpful.