Glazed collectors: i.e. evacuated tubes and flat plate collectors - the single one factor that effects the collectors efficiency is most is the Angle of Incidence of sunlight to the flat glass or curved glass cylinders. Typically in the best low iron glass at perfect orientation to the sun - only 90% of the sunlight gets through the glass while at least 10% gets reflected off the surface. No matter how efficient the absorber is in capturing the solar thermal energy - if only 90% get through - then 90% insolation x 90% efficiency means at a theoretically best is 81% efficient collector under optimal conditions. Evacuated tubes have an obvious distinct disadvantage to a flat surface - as the plane rotates away from the south. On east or west facing roofs, the back side of the tube curvature will typically be greater than a 40 degree angle of incidence from September 21st to March 21st above 40 degrees latitude. Rotating the absorber in the tube will not change the angle of incidence to the glass. In the summertime above 40 degree latitude the morning and/or afternoon sun will be north of a south facing absorber in the glass tube. IT IS IMPOSSIBLE for a tubular surface that covers the same area TO CAPTURE AS MUCH SUNLIGHT AS A FLAT SURFACE - as much of the surface on one side will always be curved AWAY from the sun. Even at direct 0 orientation at solar noon to a flat plate or evacuated tube facing south only the 10 o'clock to 2 o' clock position on a tube is in excellent orientation to the sun. TOTAL NONSENSE IS TUBULAR PEOPLE CLAIMING THE TUBES TRACK THE SUN! Please take a geometry class! PLEASE NOTE THIS IS TRUE FOR SOLAR ELECTRIC OR SOLAR THERMAL COLLECTORS THE ANGLE OF INCIDENCE TO THE GLASS IS CRITICAL. NOTE TO FOLLOW - IT IS ILLEGAL TO TO PUT ANNEALED GLASS ON A ROOF. Only tempered glass can legally be put on a roof. Gator tom
Tom Lane Energy Conservation Services 6120 SW 13th ST, Gainesville, FL 32608 (352) 377-8866 F (352) 338-0056 Give Your Sun A Job <http://www.ecs-solar.com/>
FLAT PLATE OR EVECUATED TUBES.docx
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