Predicting the impact of panel orientation and tracking on PV daily energy harvest

The benefits of taking solar radiation data measurements over extended periods of months or years include 1. predicting the expected daily harvest at potential solar farm sites, and 2. determining if existing PV installations are working properly for the given solar conditions. If radiation measurements are separated into two components, i.e., sky without the beam of the sun, and the beam of the sun, then the incident solar power on a flat surface with any azimuth and tilt can be estimated with reasonable accuracy. This paper shows daily harvest estimates made from twelve months of solar radiation measurements at a desert site in West Texas near the town of Toyah, latitude 31°. The key findings are. The best all-year fixed tilt angle for a south-facing panel is 30° (i.e., the “use latitude tilt” rule). Fixed tilt adjustments at equinoxes to 10° and 50° adds 5% to the annual daily energy harvest. South-facing, single-axis tracking with 25° fixed-tilt provides 31% more annual energy than a 30° fixed mount. Double-axis tracking provides 38% more annual energy than a 30° fixed mount. Double-axis tracking is only marginally better than single-axis tracking (i.e., annual energy increase of 38% compared to 31%).