Sun Time or Solar Time is the time of the day when the sun is producing the most energy on a particular location. The best time for producing solar electricity is between the hours of 9am and 3pm. At these times, the solar collector or module will be collecting the most energy and transferring it back to the system through the inverter.
It is imperative that during the hours of 9am and 3pm there is no shading of the solar modules in order to capture the most sunlight possible. Shading can occur from neighboring trees and building structures and can be detrimental to a solar systems efficiency.
There are multiple other factors which affect system performance such as array azimuth and tilt angle, but having a properly placed array with no shading during Sun Time is a must.
If you are planning to set up a PV system in your home, then you should plan and properly position your system in order to harvest the maximum possible solar energy and deliver as many kilowatt hours back into your system.