One of the crucial issues limiting development of highly efficient vertical axis wind turbines, which might be an interesting alternative for current market leading horizontal axis technology, is availability of reliable and efficient low-speed generators. Among the most different generator constructions, the axial flux coreless units offer greater efficiency and relatively robust construction. Although, more efficient, axial flux constructions still require heat management as to not decrease the efficiency benefits as well as protect the integrity of the unit itself. With high powered generators and engines heat management is typically approached by inclusion of an active cooling systems, such solutions are not economically viable for a micro and low powered generator units. The paper presents the development and validation of a coupled numerical model of a coreless axial flux generator with permanent magnets. The proposed model integrates Computational Fluid Dynamics (CFD), electromagnetic field analysis, and heat transfer simulations in order to simulate the generator’s operational behaviour under various working conditions. The coupling of these simulations provided a comprehensive representation of the generator operation and allowed the evaluation of the influence of thermal conditions on electromagnetic performance. Validation of the numerical model predicting capabilities has been performed by comparison to analogous experimental data, obtained from tests conducted on a dedicated experimental rig.