This document discusses thermal losses in solar central receivers. It provides background on concentrated solar power and central receiver systems. The main types of receivers - external and cavity - are described. The main sources of thermal loss are identified as radiation, convection, and absorption. A mathematical model is presented to calculate net power based on absorbed, radiation, and convection losses. Simulation results are presented for a receiver in Jodhpur, India across varying solar flux levels. Convection losses are most affected by flux and weather. Radiation losses rise with increased temperature difference. The receiver maintains 78-82% efficiency as total losses rise with higher flux.