Assessment of calculation methods for Primary Energy Factors. Case study of Swedish electricity mix

Abstract

The use of the concept of "primary energy" is present in all types of regulations at both European and national level, so that all aspects related to the reduction of energy use and energy efficiency measures speak in terms of primary energy and Primary Energy Factors, necessary for its conversion. The existing consensus on the use of the term is not such in terms of the methodology for calculating the Primary Energy Factors to be adopted, which is the reason for the search for a methodology that acquires the status of global and standard. Using an analytical methodology, this study will analyze and compare the main methods used by agencies and institutions: the Physical Energy Content Method and the Partial Substitution Method, together with another less widely used method, the Exergy Method. The three calculation methodologies will be applied to the case study of the Swedish electricity production mix. The main objective of this thesis is to analyze the advantages and disadvantages of those methodologies, as well as discuss the difficulties of defining some variables such as efficiencies and system boundaries. The results obtained in this study demonstrate the complexity of trying to analyze a system as complex as the energy consumption of a country based on the calculation of a single number or Primary Energy Factor. The system boundaries affect the results. At the same time, the use of the Physical Energy Content Method is discarded because it incurs thermodynamic discrepancies. On the other hand, the use of the Partial Substitution Method and Exergy Method is encouraged, since they reflect more accurately the primary energy consumption, as long as the values of efficiencies that they use are clearly defined and referenced. However, there is a more widespread use of the Physical Energy Content Method in the institutions since the other methods present the great difficulty of establishing a consensus on the energy and exergy efficiencies values adopted. The complexity of choosing a calculation methodology is not only due to the choice of efficiencies but other factors, such as system boundaries, also influence the final results and they have to be reflected in some way. Therefore, it is difficult to decide on a single solution and future studies on other indicators and variables affecting primary energy usage are needed, for instance, CO2 emissions associated with generation technologies.