Investment determinants on residential photovoltaic (PV) in Germany were measured via questionnaire. The survey covered social influences in terms of injunctive and descriptive norms, and economic, ecological and autarkic motives for the investment. Descriptive norms were more relevant for the investment decisions than injunctive norms, but both were considerably less important than all of the other three investment motives. Additionally, we observed the actual distribution of PV systems in the

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... participants' living area; we gathered the observation data on PV distribution from governmental databases. We found survey data on descriptive and objective norms and observation data to be unrelated. These findings indicate that multiple approaches are necessary to assess the relevance of social influences reliably.