REM takes the data from the solar thermal or photovoltaic input screens and runs them through the solar processor in the calculation engine.   The solar processor determine the utilizabile solar available based on the selected weather site and the system specifications.  The utilizable solar is used to calculate the amount of energy available for water and space heating or for power generation.  For solar thermal systems, REM will simply deduct the utilizable solar for hot water from the hot water load and determine energy consumption for hot water.  REM does not report the amount of solar utilization - that can be determine by the difference in hot water load from a no solar system and the design system.