The Roof-Top Tracker
A Brief History
First there was a solar panel, then someone figured out a way to make it follow the sun as it “moved” across the sky. Solar panels absorb more energy when they stare directly at the sun. Then someone else kept adding more solar panels to the gadget that followed the sun. Then came the wind…
As the moving arrays got bigger, the pivot bearings, motors, shafts, gearboxes, shock absorbers and structures got ever bigger to carry the weight and to withstand the buffeting winds. Afternoon prevailing Westerlies will catch the broad face of the array and try to send the whole thing into the next county.
A New Configuration
The Linear Module is a new shape, which means it can be made into a different kind of tracker. Long narrow modules linked together like Venetian blinds can be made to follow the sun. Lying close to the rooftop the entire assembly lives in that place we call the boundary layer where the force of the wind is small. The narrow aspect of the modules gives very little leverage to what wind there is.
As a result, the pivot bearings, motors, shafts etc. are quite small and inexpensive. This means that by reconfiguring a good idea we can make a less expensive better idea. This is how the Roof-Top Tracker evolved.
There are some other interesting advantages to this new configuration:
Hidden from View
Solar panels are somewhat hard to disguise. If placed at an optimal fixed angle on the roof, they catch the eye and often not favorably. Flat roof adobe-style houses are very popular in sunny arid climates. These houses are particularly challenging because the array must stand above the normal roofline. Typically, they have parapets (short walls) around the edges of the roof, usually at least a foot high. Modules lying flat on the roof are completely disguised but far from an angle that offers optimal year-round performance. The Roof-Top Tracker can hide below the parapets yet offer variable tilt angles to get optimum performance.
Conventional modules decrease their output when one cell is shaded. As the sun goes down multiple adjacent tracking arrays will shade the neighboring arrays to the east. As soon as the shadow covers just one string of cells on one of the modules in the array, the entire series circuit of modules believes it has been shaded. That’s the nature of series circuits. The electrical output drops significantly and abruptly.
An array of Linear Modules shading one another late in the afternoon experiences a different behavior. Because there is only one linear string of cells in each module, the encroaching shade decreases the electrical output in a slow but continuous manner. This means that more sunshine is converted to electricity each day for every dollar invested in solar cells.
The Roof-Top Tracker is made of numerous strong, stiff but lightweight elements. Each piece is handled easily and safely by one or two people. It is designed to be assembled quickly and easily on the roof. No cranes required and no scary wind-sail problems.
The Roof-Top Tracker is not available yet. Production is scheduled to begin in mid 2008.
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Copyright Solar Automation, Inc. 2007