A hybrid air-cooled condenser system. The system may be provided by converting one among the many air-cooled condensers or condenser bays of a conventional condenser system to an evaporative cooler or condenser. The evaporative condenser may be plumbed in the condenser system to be in series in the vapor path with, upstream or downstream of, the air-cooled condensers. In one embodiment, the working fluid flows from an output or discharge header of the air-cooled section or assembly of the hybrid condensing system to an inlet of the evaporatively cooled section, e.g., to one or more evaporative coolers or condensers. In one modeled geothermal power plant, the condensing load on the air-cooled section was reduced by 50 percent when compared to a fully air-cooled condenser system. The condenser arrangement may be used to improve summer time performance of geothermal power plants.
 The United States Government has rights in this invention under Contract No. DE-AC36-08GO28308 between the United States Department of Energy and the Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory.