An electrical energy generation system can include a housing, an electrical generator supported by the housing, a turbine operatively connected to the electrical generator, and a hollow frustum positioned in the housing and spaced apart from the turbine. The frustum can be configured to receive airflow via a lower opening and to direct the airflow toward the turbine with increased velocity. Another electrical energy generation system can include an electrical generator, a turbine operatively connected to the electrical generator, and an enclosed passageway configured to increase a speed of an airflow from an artificial source toward the turbine. The enclosed passageway can be positioned to support the turbine. The systems can include one or more baffle elements to straighten the airflow along a direction aligned with a rotational axis of the turbine. Electrical energy generation systems harvest waste or exhaust air from rooftop vent or fan assemblies.