Growth of «new» market economies is associated with rapid expansion of knowledge capital. It leads to the emergence of knowledge-based economies. As the literature broadly uses international cross-section samples to study the role of knowledge capital, we tried to recapitulate on the results of this research. However, our main aim was to show how they can be applied to analyse the growth of single economies and develop scenarios for the next 20 to 30 years. Extended production functions with endogenous TFP determined by knowledge capital generate potential output that may considerably differ from effective output. This calls for constructing complete models, addressing both final demand and total supplies. Their suggested structure is presented using the annual long-term macro-econometric models W8D of Polish economy.