José Villar

Abstract
The increasing penetration of renewable electricity generation is complicating the bidding and estimating processes of electricity prices, partly due to the shift of the overall cost sensitivity from operation (fuel) costs to investment costs. However, cost minimization models for capacity expansion are frequently based on the principle that, for a perfectly adapted system allowing non-served energy, marginal remuneration allows overall operation and investments costs recovery. In addition, these models are usually formulated as finite-horizon problems when they should be the-oretically solved for infinite horizons under the assumption of companies’ infinite lifespan, but infinite horizon cannot be dealt with mathematical programming since it requires finite sets. Previous approaches have tried to overcome this drawback with finite horizon models that tend asymptoti-cally to the original infinite ones and, in many cases, the investment costs are annualized based on the plants’ lifespan, sometimes including a cost residual value. This paper proposes a novel approach with a finite horizon that guarantees the investment costs’ recovery. It is also able to obtain the marginal electricity costs of the original infinite horizon model, without the need for residual values or non-served energy. This new approach is especially suited for long-term electricity pricing with investments in renewable assets when non-served demand is banned or when no explicit capacity remuneration mechanisms are considered. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

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. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

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. © 2020 Elsevier B.V.

Abstract

Abstract
This paper proposes a near to real-time local market to provide reactive power to the transmission system operator (TSO), using the resources connected to a distribution grid managed by a distribution system operator (DSO). The TSO publishes a requested reactive power profile at the TSO-DSO interface for each time-interval of the next delivery period, so that market agents (managing resources of the distribution grid) can prepare and send their bids accordingly. DSO resources are the first to be mobilized, and the remaining residual reactive power is supplied by the reactive power flexibility offered in the local reactive market. Complex bids (with non-curtailability conditions) are supported to provide flexible ways of bidding fewer flexible assets (such as capacitor banks). An alternating current (AC) optimal power flow (OPF) is used to clear the bids by maximizing the social welfare to supply the TSO required reactive power profile, subject to the DSO grid constraints. A rolling window mechanism allows a continuous dispatching of reactive power, and the possibility of adapting assigned schedules to real time constraints. A simplified TSO-DSO cost assignment of the flexible reactive power used is proposed to share for settlement purposes.