Externally fired gas turbines represent one of the investigated solutions for the electrical production starting from heat at relatively high temperatures, such as from biomass combustion or high concentration solar power. This solution is particularly attractive for small and micro-scale plants, because they do not require many auxiliary components such as condensers, circulation pumps and so on, thereby showing a large potential for cost reduction. A further cost reduction may be obtained by converting automotive turbochargers into stationary powerplants. This paper tries to focus some issues, which need to be well discussed, such as the capability of extracting mechanical power from a turbocharger. Particularly, the proposed solution relies in a free turbine working in parallel to the main shaft instead than in series. The paper shows the modelling of the system in the AMESim environment and the results from the use of different thermodynamic parameters and turbocharger models. Gross efficiencies between 8 and 17% were found for plant sizes between 2 and 15 kW of mechanical power.