In a previous paper, the performance of the humidification-dehurnidification (HD) desalination process was optimized through mathematical programming. In this paper, by adding a solar system to the model, the total solar HD system is optimized. The main purpose of this optimization is the reduction of fresh water production costs. By using special operational and geographical constraints the model can be used for any region to determine optimum operation point of system. Results show that solution obtained by cost objective function has a cost 7-28% lower than other objective functions. Also recycling, in spite of the increase of productivity and decrease of specific thermal energy consumption of the HD process, increases the cost of production.