This paper brings together several contemporary topics in energy systems aiming to provide a literature review based reflection on how several interrelated energy systems can contribute together to a more sustainable world. Some directions are discussed, such as the improvement of the energy efficiency and environmental performance of the systems, the development of new technologies, the increase of the use of renewable energy sources, the promotion of holistic and multidisciplinary studies, and the implementation of new management rules and "eco-friendly and sustainable" oriented policies at different scales. The interrelations of the diverse energy systems are also discussed in order to address their main social-economic-environmental impacts. The subjects covered include the assessment of the electricity market and its main players (demand, supply, distribution), the evaluation of some urban systems (buildings, transportation, commuting), the analysis of the implementation of renewable energy cooperatives, the discussion of the diffusion of the electric vehicle and the importance of new bioenergy systems. This paper also presents relevant research carried out in the framework of both the Energy for Sustainability Initiative of the University of Coimbra and the Sustainable Energy Systems focus area of the MIT-Portugal Program. To conclude, several research topics that should be addressed in the near future are proposed.

EU ETS impacts on stock market returns of Spanish power sector. Long-run positive effect of EU ETS on market returns is found only in Phase II. No short-run effects were found. EUA price effect is company-specific. a r t i c l e i n f o b s t r a c tEuropean Union carbon emissions allowances (EUA) price fluctuations can affect electricity companies' stock market values as these oscillations may change firms' profitability and thus investors' decisions. This outcome can differ not only contingent on the EU ETS Phase, but also on firms' generation mix. Moreover, stock markets may react differently to EUA increases in comparison to decreases, thus asymmetrically.By using daily data from January 2008 to July 2014, this article analyses long-run equilibrium relations and short-run interactions between the aggregated electricity industry stock market returns and EUA price changes. Moreover, we test if the relationship between EUA price variations and electricity stock returns is asymmetric and if the carbon price effect and the asymmetry are power firm-specific.Adding to earlier studies, we initially provide an inspection of the individual impact of EU ETS Phase II and on-going Phase III; followed by a comparative analysis between power firms which core activity relies on renewable energy sources and those whose sources are fundamentally non-renewable ones.A statistically significant positive long-run impact of EU ETS on the aggregated power sector stock market return is found concerning Phase II and works asymmetrically. Moreover, evidence is provided demonstrating that asymmetry and EUA effects are power firm-specific.

Assess determinants on market splitting behaviour of Iberian electricity markets. Logit and non-parametric models to express market splitting probability response. Explanatory variables: wind, hydro, thermal and nuclear power; ATC and demand. Results: increase of market splitting probability with higher availability of low marginal cost electricity. Coordination policies governing both interconnections and renewables deployment. a b s t r a c tThis paper aims to assess the main determinants on the market splitting behaviour of the Iberian electricity spot markets. Iberia stands as an ideal case-study, where the high level deployment of wind power is observed, together with the implementation of the market splitting arrangement between the Portuguese and the Spanish spot electricity markets.Logit and non-parametric models are used to express the probability response for market splitting of day-ahead spot electricity prices as a function of the explanatory variables representing the main technologies in the generation mix: wind, hydro, thermal and nuclear power, together with the available transfer capacity and electricity demand. Logit models give preliminary indications about market splitting behaviour, and then, notwithstanding the demanding computational challenge, a non-parametric model is applied in order to overcome the limitations of the former models.Results show an increase of market splitting probability with higher wind power generation or, more generally, with higher availability of low marginal cost electricity such as nuclear power generation.The European interconnection capacity target of 10% of the peak demand of the smallest interconnected market might be insufficient to maintain electricity market integration. Therefore, pro-active coordination policies, governing both interconnections and renewables deployment, should be further developed.