This part I of the study presents the thermoeconomic optimization formulations of three new trigeneration systems using organic Rankine cycle (ORC): SOFC-trigeneration, biomass-trigeneration, and solar-trigeneration systems. A thermoeconomic modeling is employed using the specific exergy costing (SPECO) method while the optimization performed using the Powell's method to minimize the product cost of trigeneration (combined, cooling, heating, and power). The results help in understanding how to apply the thermoeconomic modeling and thermoeconomic optimization to a trigeneration system. (C) 2013 Elsevier Ltd. All rights reserved.