The key to improving solar module efficiency is to mitigate the losses during carries’ generation, transportation and recombination process and cell to module process. These losses can be classified into optical, thermal and electrical mechanisms, such as the mismatch between energy of incident photo and band gap of semiconductor material, radiation emitted to the environment and structural defects and impurities. Photovoltaic effect refers to conversing solar energy to chemical potential energy and to electricity finally. This paper aims to analyse and quantify the losses and thermal sources generated during this whole conversion process. A comprehensive model which combines the experimental performance parameters and microscopic operation mechanisms is developed, to calculate the optical and electrical losses, heat source generation and ultimate power output efficiency of the solar module under actual operating condition. The results show that, for a real silicon solar module with conversion efficiency at 18.50%, about 66.01% solar energy is lost in carries generation, with remaining 2.29% and 10.91% in transport and recombination process, respectively. Also, about 2.3% of incident energy is lost from cell to module process. Those losses, approximately 62.92%, are transformed into thermal source, which rises the cell temperature. Besides, almost 18.58% of total energy leaves the cell due to multilayer reflection. Furthermore, some suggestions are provided in the end to control losses and improve module performance.