Besides meeting the ever increasing energy demand, renewable energy source can play a critical role in reducing global carbon emissions and the pace of investment on such renewable energy has greatly increased as the cost of technologies fall and efficiency continues to rise. However, the benefits of re-newables go beyond reducing carbon emissions and mostly relates to crises in fossil energy. The solar chimney is a novel technology which has proved capable of generating electrical energy from the sun and atmospheric air. However, it's implementation has been involved with many challenges. In the present study, thermal performances of solar chimneys are assessed experimentally for some different experimental setups. Experimental setups that are employed in this study have two distinct features in comparison with other setups that have been used in the prior arts: 1. Setups are indoor, in contrary to conventional outdoor setups, the environmental parameters can be entirely controlled in this study and steady state condition can be reached. 2. Both setups are capable of measuring thermal performance of the collector in addition to performance of solar chimney. Setups differ in geometry to investigate effects of geometry on overall performance of solar chimneys. It is demonstrated in this study that the thermal and hydraulic performances of common form of solar chimneys are not adequate and low thermal performance of collectors is one of the important reasons of poor power generation of solar chimneys. It is found that by changing shape of the collector from circular to an innovative square shape, Nusselt number (Nu), air flow velocity and convective heat transfer coefficient (h) increases 1225%, 245% and 603% respectively. Finally, the reasons for poor performance of common solar chimneys are comprehensively discussed. (c) 2020 Elsevier Ltd. All rights reserved.