These 2 each of 3$ applications are useful.
1. Sun Seeker - This is an application for showing the azimuth and elevation of the sun, for any location and any day of the year. It includes a view of the sun path as looking through the camera, so one can view the trees, power lines and other rooftops. It us useful in evaluation of the sun shading. <http://www.ozpda.com/sunseeker_iphone.php
2. HM Tracker - This application allows you to key in the tracking array size and elevation form the ground. It evaluates the resulting wind load forces on the structural components. It even suggests the sizes of the steel components - post,torsion tube, vertical and horizontal beams and purlins. In so far as Houston code requires that the array withstand 120 MPH winds, the application could serve as an aid in the mechanical design. <http://www.heliomasters.com/