The focus of this work was to evaluate the thermal performance of a cogeneration system used to produce power and dry aromatic herbs. The waste heat from the exhaust gases of the diesel engine was recovered to heat air using a thermosyphon heat exchanger. The heated air was employed in a convective tray dryer in order to dry Origanum vulgare, Mentha spicata, and Ocimum basilicum. The experiments were carried out at full load in a stationary compression ignition engine coupled to a generator. The maximum global energy efficiency of the cogeneration system was 40.14%, and the effectiveness of the heat exchanger achieved 39%.