Abstract
European energy strategy towards decarbonization, and its practical implementations in the different EU countries, will imply a continuous increase of variable (non-dispatchable) renewable energy (VRE), like wind and solar PV generation. This increasing VRE along with the progressive closing of current greenhouse gas (GHG) emitting plants, will decrease the net demand (inflexible demand minus non-dispatchable generation), reducing the amount of dispatchable generation needed to face both low VRE periods and larger net demand ramps. These problems need to be assessed to anticipate possible mismatches between net demand values and ramps, and the available resources with generation and ramping capabilities, so that the security and quality of supply is guaranteed. In case of expected risk, regulatory mechanisms, such as new market clearing rules or incentives to new flexibility sources or to new generation and storage technologies, could be required. This paper looks at the possible evolution of the Portuguese power system focusing on the net demand ramp problem. The historical and expected evolution of the hourly ramps of the net demand are analyzed considering different scenarios of high wind and solar PV penetration, according to different degrees of convergence to the EU energy strategic objectives.

Abstract
This paper aims to model collaborative behaviours related to distributed generation investments in a residential neighbourhood, by means of Cooperative Game Theory (CGT). The main objective is to analyse the economic impact of the installation of photovoltaic solar panels and batteries, and the assessment of the potential energy savings due to the cooperation among residential households. In this regard, both the purchase of needed energy from the grid and the sale of the spare energy from the households' self-generation to the grid are considered. The comparison between cooperative and non-cooperative behaviours in the investments and energy management decisions is analysed based on the Shapley value, a cost sharing method from CGT, concluding that cooperation among prosumers to share energy in a residential energy community is in general more efficient than prosumers making individual decisions.

Abstract
The increasing penetration of Distributed Energy Resources is changing the energy system by empowering consumers with the capacity to generate the electrical energy they need and sell its excess. This trend follows the EU strategy towards increasing competition and flexibility on the electricity market, as well as pushing the role of customers, expanding their rights and their involvement in energy communities (ECMs). Peer-to-Peer (P2P) energy markets appear as one of the possible solutions to accomplish these goals by providing direct energy trading between peers. Although P2P are being extensively addressed in the literature (e.g., market structures and platforms, experimental projects), few works offer a broad perspective of the different aspects involved in the actual implementation of these structures, as well as the real benefits that this type of markets can have for the players and for the system itself. This paper reviews business models related with ECMs and P2P markets, and the system benefits and main regulatory issues.

Abstract
Many Generation Expansion Problems (GEP) models have been proposed in the literature based on agent-based equilibria or cost-minimization, integrated in bilevel or single-level models. In the simplest (and unrealistic) single-level cost minimization GEP with only the balance constraint, it can be proved that optimal generation investments are recovered through the system marginal cost, meaning that the Net Present Value (NPV) is 0. However, in more complex representations with additional constraints (such as technical or minimum capacity system constraints) non-profitable investments might occur, i.e., their NPV can go below 0. The aim of this work is to provide insights on how introducing complexity into GEP models affects the investments with and without imposing positive NPV as new constraints. The non-linearities in the NPV formulation are solved with a novel iterative algorithm. The main conclusion from the case studies is that the cost minimization GEP model forcing positive NPV can help to better represent the behavior of energy market players and simulate oligopolistic energy markets without explicitly representing profit maximization.

Abstract
The circular economy contrasts with the traditional linear economy since it presents a sustainable way both to produce goods and services and to contribute to the development of economies. This paper aims to contribute to a better knowledge of the efficiency of resources productivity, a common indicator to compare how circular economies are, through the estimation of the main determinants for the circular economy in Europe. A systematic analysis and comparison of the performance of all the European Union countries was performed to get further insight into their root causes and to help designing future policies towards a more circular European Union economy. With this purpose, a set of determinant factors for a circular economy in Europe were analysed, under the period between 2000 and 2016. A cluster analysis was applied and complemented with three econometric estimation methods: panel unit root tests, panel cointegration tests and vector autoregression model. The main findings allowed to cluster European countries into three different groups according to the growth rate of their resources productivity and to explain them according to the selected exploratory factors. Special efforts were made to explain the highest productivity growth group, as a way to find relevant drivers towards sustainable productivity growths.

Abstract
Power systems will face important structural changes in the near future due to the empowerment of consumers, who may resort on self-consumption, and reduce their purchases of electricity from the grid. The avoided costs of purchasing energy, as compared to the investment costs of installing their own self-generation capacity, could be one of the drivers of the consumers' decision making. The system expansion will therefore result from the interaction of the traditional market agents, maximizing their profits by investing in and operating centralized generation assets, and the new active consumers, minimizing their expenses while meeting their energy needs. This paper presents a Nash equilibrium model that considers centralized and behind-the-meter distributed generation expansion, by representing the operation and investments decisions of both types of agents with their own conceptually different strategies. To simplify the resolution, the equilibrium model is transformed into an equivalent minimization problem from its Karush-Kuhn-Tucker conditions. The model application to Spain-like system case example allows to assess the impact of the network access-tariff (whether being mainly volumetric-based or power-based) and the impact of the big industrial market power on the generation expansion, for the time horizon 2019-2037.