Distributed generation is nowadays regarded as the future of energy production. In this work, two engineering energy systems have been studied, namely horizontal axis wind turbines (HAWT) and an innovative heat exchanger for recuperated and externally fired gas turbines. The two topics share the final target, which is power production in a distributed generation perspective. The aforementioned two energy systems have been studied with a similar scientific and technical approach: after an initial review about the background, a modeling tool has been specifically developed for each topic. The models have been then validated against experimental data, taken from the literature (HAWT) or directly from an in-house built test bench (immersed particles heat exchange). Once the confidence of the models had been assessed, they have been employed to optimize the energy systems, particularly with regards to some of their geometrical features. In both cases, the study allowed et to obtain some possible design improvements of the systems, et to enhance the engineering knowledge of them. The analyses conducted may be useful to graduate students in Mechanical Engineering and energy professionals.