In this paper we combine a fairly complex system dynamics model of the Nord Pool power market with stochastic price models from financial economics. The idea is to combine the fundemantal relationships of a system dynamics model, with a good representation of stochasticity from stochastic price models. The purpose is to provide long-term price prognoses for investment decisions as an alternative to the current approach of using scenarios for long-term prices generated by fundamental, partial equilibrium models. Our paper describes a case study at Agder Energi, a Norwegian utility operating in the Nord Pool market.