Algorithm Positions Solar Trackers, Movie Stars March 30, 2011
Math and programming experts at a federal laboratory took an
algorithm used to track the stars and rewrote its code to
precisely follow the sun, even taking into consideration the
vagaries of the occasional leap second. Now, the algorithm and
its software are helping solar power manufacturers build more
precise trackers, orchards to keep their apples spotless and
movie makers to keep the shadows off movie stars. The Solar
Position Algorithm (SPA) was developed at the U.S. Department of
Energy's National Renewable Energy Laboratory to calculate the
sun's position with unmatched low uncertainty of +/- 0.0003
degrees at vertex, in the period of years from -2000 to 6000 (or
2001 B.C. until just short of 4,000 years from now). That's more
than 30 times more precise than the uncertainty levels for all
other algorithms used in solar energy applications, which claim
no better than +/- 0.01 degrees, and are only valid for a
maximum of 50 years. And those u