In this paper, a 2D numerical simulation of a solar chimney with a top V cap was performed to evaluate the induced air flow degradation. Dimensions including the width of the cap and the cap offset from the top of chimney are specified as key parameters. Meanwhile, height and width of the chimney are fixed. The numerical model was confirmed to be accurate compared to the published data. The results showed that reducing the offset and increasing the width reduces airflow through the chimney. The effect of offset on chimney intake air is significant. When considering the addition of the top V cap, the airflow is reduced by about 20% compared to the chimney without a cap. This is because the cap forms three primary vortices including one vortex below the cap and two ones above the cap. The vortex under the cap in the direction from the absorber plate to the glass cover increases the air flow out of chimney at the side of the glass cover. The region with great turbulent kinetic energy forms at upper side of the cap. The air flow correlation as a function of the heat flux to the absorber plate, cap offset and cap width have been developed with errors of less than 2.5%.