This paper deals with the problem of defining efficient portfolios of electricity production assets using the Portfolio Theory, that is to say, by applying the return-risk analysis not to a single asset (e.g. a power station, a wind farm, a combined cycle gas plant), but to the set of technologies operating in a territory at a definite time. First of all, we study to what extent this methodological approach can be implemented to solve the problem of defining efficient sets of power production technologies, considering the fact that the Portfolio Theory was initially proposed in the field of financial investment. We focus on the main concepts of this framework (return, risk and diversification) and its uses in the energy mix context. Second, the evolution of the Spanish generation mix during the ten year period 2001-2010 is analysed according to two different variables: capacity and produced energy. Furthermore, we pay attention to the Spanish Government 2020 energy planning and compare it with several scenarios suggested using different patterns observed during 2001-2010 period. Finally, the most important conclusions are drawn and some lines of future research are proposed.

Fernando de Llano Paz Et Al (2012). The Problem of Determining the Energy Mix: from the Portfolio Theory to the Reality of Energy Planning in the Spanish Case, European Research Studies Journal Volume XV Issue 4, 3-30