The researchers' main target in this work is to demonstrate the performance of small-scale (5-45 kW) axial and radial compressed air turbines which are able to operate at specific boundary conditions. These boundary conditions were chosen to be compatible with a small-scale solar powered Brayton cycle. The evaluation is dependent on the turbines' efficiency, compactness and output power. Firstly, preliminary design work was completed in order to figure out the turbines' shapes and find initial information about the impact of various factors on their efficiency values and output powers. Factors considered were: inlet pressure, inlet temperature, pressure ratio, rotational speed and the mass flow rate. Their performance during the off design conditions was also recorded. Subsequently, three-dimensional computational fluid dynamics modelling was completed for each turbine and at every single studied case in order to study in depth the effect of other factors and have accurate results. The results show that the radial turbine is superior when the main concern is working with low mass flow rate. On the other hand, the axial turbine is more desirable when the low rotational speed is of interest. The cycle results showed that an improvement in the cycle's thermal efficiency ranging from 6% to 12% can be achieved with a turbine efficiency increase from 80% to 90% respectively for fixed cycle boundary conditions. Finally, two different data sets from the previous experimental work have been used to examine the accuracy of the current work and the outcomes were highly accurate. (C) 2016 Elsevier Ltd. All rights reserved.