SUMMARY A simple thermoeconomic analysis is performed for a seasonal latent heat storage system for heating a greenhouse. The system consists of three units that are a set of 18 packed-bed solar air heaters, a latent heat storage tank with 6000 kg of technical grade paraffin wax as phase-changing material, and a greenhouse of 180 m 2 . The cost rate balance for the output of a unit is used to estimate the specific cost of exergy for a yearly operation. Based on the cost rate of exergy, fixed capital investment, operating cost, and economic data, approximate cash-flow diagrams have been prepared. The systems feasibility depends on the cost rate of exergy, operating cost, internal interest rate, and rate of taxation strongly. A cash-flow diagram based on exergy considerations may enhance the impact of thermoeconomic analysis in feasibility studies of thermal systems. Copyright # 2006 John Wiley & Sons, Ltd.