To investigate the influence of the collector costs on the cost/benefit ratio and the dimensioning of the system, the specific collector price was gradually reduced to 70% of the base case. Such a reduction could be realistic with improved materials and/or production processes. All other parameters match the base case. Figure 3 (a) shows that the less expensive collectors lead to higher primary energy saving, due primarily to an enlargement of the absolute collector area in the optimal system configuration. In opposition to the enlargement of collector area the storage device capacity almost stays constant within the examined range of collector costs, which means that the specific storage volume decreases. Selected results of the best configurations for the respective collector costs are listed in Table 1.