We have evaluated savings and costs for the energy-strategy 2050 of the city of St.Gallen, which pursues a significant reduction in the consumption of fossils, a reduction to 2 tonnes CO2 emissions per person, zero nuclear power share in its energy mix. By the end of the year 2016, we will have developed a tool, which allows to quantify the costs for implementing transition paths in line with prespecified energy strategy. In particular, we would like to stress this modelling will allow also for analyses of important scenarios, regarding the dynamics of energy prices and interest rate term structure.