Quick Answer: For Houston, the daily watt-hour output is increased, on average, by 30%.
Caveat: But tracking has additional costs and maintrenance, compared to a fixed array. Why not just install 30% more panels and forget tracking? Trackers can maximize the energy harvested when the demand is high.Such as when the peaking generators are turned on.
Details: The National Renewable Energy Lab website has a calculator, in which one chooses the location of the array, and the method of tracking. Choose the location, ad the tracker type (Fixed,1 axis tracking and 2 axis tracking)