Making solar thermal systems less expensive, often results in a lower system efficiency. However, the cost-benefit ratio is relevant from the perspective of the consumer. The complex impact of component-related and system-related design parameters on the economics of a complete system makes the evaluation and economical optimization difficult. Therefore, a complete simulation environment has been developed, which can automatically optimize solar-thermal systems, including collector and system parameters. The main collector module consists of a one-dimensional thermal model that was validated with a commercial solar collector. The efficiency curve and the production cost were calculated as a function of several design and construction parameters. The collector module was linked to the commercial software Polysun®, so that parametric studies can be performed with minimal effort. Optimization problems can be solved by using the Matlab® optimization toolbox. The simulation environment was used for sensitivity studies and optimization problems in order to analyze the impact of collector design-parameters with respect to system cost, system yield and economic values. We will demonstrate how a collector can be optimized and how the ideal system parameters like collector number and storage volume can be easily calculated. Finally, we will show how the optimizer is used for a given system in order to find ideal values for the absorber-sheet thickness and the number of pipes. Due to the holistic approach, the application of this tool set can be used for collector development as well as for system planning.