This paper aims, to investigate the shunts in multi-crystalline (m-c) Si solar cells by lock-in infrared thermography (LIT) technique and to study their effect on the cell performance by PSpice simulations. LIT provided useful information about the location and nature of shunts which was used in the simulation. Based on the shunt location and shunt resistance of the cell obtained experimentally from the I-V characteristic of the cell, shunt resistance at the shunted region have been estimated by simulation using the distributed diode model approach of solar cell by fitting. Based on these values of shunts, simulation has been performed to obtain the information about the deterioration in cells performance caused by the shunts. This type of simulation is useful to study different types and severity of shunts at different locations of cells. Solar cells which have been used in this study show a power reduction in the range of 3% to 15% due the shunts. This reduction was more severe for the shunt which was on the bus-bar compared to the edges.