The cost of biodiesel production as a renewable source is always an obstacle in industry. In order to overcome this problem, another renewable source, solar collector was used to investigate and optimize the transesterification reaction of rapeseed oil for methyl ester production. Three main factors, which include catalyst (NaOH) concentration, reaction temperature and time, were varied according to a central composite design. The yield of methyl ester as the first response was determined by using NMR method. The second response was the commercial cost of production. In order to reduce fossil energy consumption for electric power as a main part of cost, the solar collector was used to provide heat. The results based on response surface method showed that the best conditions for producing biodiesel in the constant molar ratio of 1:6 oil:methanol were the temperature of 60 C, NaOH concentration of 0.3% wt/ wt and reaction time of 60 min. In these optimum conditions, the yield of methyl ester and the cost of production for one-liter biodiesel were 78.6% and 0.706$, respectively. Also, some chemical and physical properties of biodiesel were compared with those of petro-diesel fuel and biodiesel production without solar collector has been done for achieving price differences. (C) 2017 Elsevier Ltd. All rights reserved.