The presented work offers an improved planning tool as a response to the demand for active and passive solar architecture. An integral solution is presented for the design of solar assisted heating systems and decentralized electricity production using photovoltaics (PV) on building roof-tops and facades. The tools are applicable in the early stage of architectural planning and the underlying simulation is consistently usable throughout all further steps. In particular, this solution offers a number of sensible approximations at the beginning of the planning process and allows refining the input data at a later stage. The two software programs Lesosai and Polysun form the basis for the project. In a first step, a software interface is created which provides access to the simulation kernel of Polysun through the graphical user interface of Lesosai. Consequently, the architects do not have to install and learn to handle additional software next to Lesosai. Furthermore, no data has to be entered twice and the consistency of all simulation results is guaranteed by the software package. In a second project step, Lesosai’s front-end is optimized with respect to the architects’ needs.