This work has the objective to evaluate and validate the performance of a system that has already been implemented, but in a study stage, of a pre-heating system for diesel motors engines on a thermoelectric power plant named Gera Maranhão through use of solar thermal energy with real time in loco monitoring, measurement and calculations. Five independently and evenly distributed subsystem are responsible to pre-heat one diesel motor engine Wartsila20V32 with 8.73MW, with a total solar incident surface area of 1000 square meters, with 500 solar panels installed. A meteorological station, with global radiation and ambient temperature sensors were installed to measure and collect climate conditions to study and analyze the potential net energy through eficiency calculations.