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Artículos en revistas Numerical models of transmission-constrained electricity markets are used to inform regulatory decisions. How robust are their results? Three research groups used the same data set for the northwest Europe power market as input for their models. Under competitive conditions, the results coincide, but in the Cournot case, the predicted prices differed significantly. The Cournot equilibria are highly sensitive to assumptions about market design (whether timing of generation and transmission decisions is sequential or integrated) and expectations of generators regarding how their decisions affect transmission prices and fringe generation. These sensitivities are qualitatively similar to those predicted by a simple two-node model. info:eu-repo/semantics/publishedVersion

Abstract In the field of innovative power sources, photovoltaic are playing an important role as new clean energy generators. The performances being dependent on instantaneous weather condition, photovoltaic sources are usually equipped with an auxiliary energy storage device. There are applications where the opportunity to couple the photovoltaic source with ultracapacitor can be taken into account. The aim of the paper is to study the performances of a hybrid system constituted by photovoltaic and ultracapacitor sources. In particular, the paper deals with the study of the ultracapacitor rate design for photovoltaic systems feeding pulsing loads. The results of the study, which can also be referred to temporary unfavourable weather conditions, have been validated by experimental data. In the final part of the paper, some considerations on economical implications about the dimensioning of a photovoltaic–ultracapacitor systems are drawn.

Abstract In the last years, electric vehicles (EVs) are getting significant consideration as an environmental-sustainable and cost-effective alternative over conventional vehicles with internal combustion engines (ICEs), for the mitigation of the dependence from fossil fuels and for reduction of Green-House Gasses (GHGs) emission. However, many challenges are still ongoing to their large scale implementation. Among them, the negative impact on the electrical grid operation in case of an uncoordinated contemporary charging of a huge number of EVs. In the recent literature different solutions are proposed for handling the peak demand of EVs and the related problems. One answer is offered by the implementation of EV charging strategies, through aggregation agents, for containing the impact on the grid, guaranteeing the quality of the service. The implementation of a real charging strategy is strictly related to a deployment of smart-grid technologies, such as smart meters, Information and Communication Technologies (ICTs) and energy storage systems (ESSs). In particular ESSs are playing a fundamental role in the general smart grid paradigm, and can become fundamental for the integration in the new power systems of EV fast charging stations of the last generation: in this case the storage can have peak shaving and power quality functions and also to make the charge time shorter. In the present paper, an overview on the different types of EVs charging stations, in reference to the present international European standards, and on the storage technologies for the integration of EV charging stations in smart grid is reported. Then a real implementation of EVs fast charging station equipped with an ESS is deeply described. The system is a prototype, designed, implemented and now available at ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) labs. A wide experimental activity has been performed on the prototype system in order to test its functionalities in the integration in a smart grid available at the same ENEA lab, including a smart metering system. The integration has been possible thanks to the use of a customized communication protocol, developed by the researchers and here described. The results of the experimental tests show that the system has a good performance in the implementation of peak shaving functions, in respect of the main distribution grid, making the prototype like a network nearly zero-impact system.

Abstract The organic Rankine cycle (ORC) has been growing in importance as a technology for producing electricity from low temperature waste and renewable heat sources. In small-scale applications, the most used working fluid has been HFC-245fa, although this is being substituted for low GWP alternatives. A new HCFO working fluid, HCFO-1224yd(Z), has appeared as a possible alternative for HFC-245fa. In this study, this alternative working fluid is analysed and, finally, the working fluid is experimentally tested as drop-in alternative in a commercial ORC system. The main purpose is to determine the feasibility of using HCFO-1224yd(Z) as a drop-in replacement for HFC-245fa in a real facility that was initially designed to operate with HFC-245fa. The results show how the use of HCFO-1224yd(Z) offers power output that ranges from 7.5% to 17.4% lower than that provided by HFC-245fa. Although HFC-245fa offers higher power output, the results show that HCFO-1224yd(Z) offers up to 7.7% higher cycle net efficiency; this is due to the higher input thermal rate required by HFC-245fa. Finally, HCFO-1224yd(Z) has been stated as a suitable alternative to HFC-245fa as a drop-in replacement in a small-scale, low-temperature ORC, which increases its attractiveness for heat source with higher temperatures.

Domestic heating represents the most dominant energy function in Dutch households nowadays. Using district heat from CHP (combined heat and power) by means of a NGCC (natural gas-fired combined cycle) plants is generally acknowledged as an effective option to reduce primary energy consumption for heating. However, methods to calculate energy savings from CHP differ widely. This paper compares a number of different methods, including the method from the EU CHP Directive, to estimate primary energy savings in comparison with the typically used domestic gas-fired condensing boiler. Real hourly CHP plant performance data is used. An estimation of the CO2 mitigation cost of delivering district heat to Dutch dwellings is made. We find that supplying dwellings with district heat from an NGCC-CHP saves energy, regardless of the calculation method and for a rather wide range of reference efficiencies. CO2 mitigation costs are acceptable from a social perspective (at discount rates up to 4%, excluding fuel taxes) and negative from a private perspective (at discount rates up to 10%, including fuel taxes).

AbstractAlthough canopy height has long been a focus of interest in ecology, it has remained difficult to study at large spatial scales. Recently, satellite‐borne LiDAR equipment produced the first systematic high resolution maps of vegetation height worldwide. Here we show that this new resource reveals three marked modes in tropical canopy height ~40, ~12, and ~2 m corresponding to forest, savanna, and treeless landscapes. The distribution of these modes is consistent with the often hypothesized forest‐savanna bistability and suggests that both states can be stable in areas with a mean annual precipitation between ~1,500 and ~2,000 mm. Although the canopy height states correspond largely to the much discussed tree cover states, there are differences, too. For instance, there are places with savanna‐like sparse tree cover that have a forest‐like high canopy, suggesting that rather than true savanna, those are thinned relicts of forest. This illustrates how complementary sets of remotely sensed indicators may provide increasingly sophisticated ways to study ecological phenomena at a global scale.

Abstract In this paper the Selective Modal Analysis (SMA) method is used for reproducing the eigenvalues involved in subsynchronous control interactions (SSCI) between DFIG-based wind farms and series compensated transmission lines. The SMA method provides a reduced system matrix containing a desired part of the eigenstructure of a system without computing the eigenvalues and eigenvectors of the full system. The key concept for obtaining such reduced matrix resides in an appropriate identification of a subset of state variables and eigenvalues of the system. The intrinsic problems in identifying the corresponding subset for analyzing the SSCI phenomenon are explored and illustrated using a simplified radial system. In addition, a systematic approach for obtaining a subset with minimum dimension is proposed. The methodology consists in a two-phase iterative procedure that reduces the computational load and promotes the convergence of the SMA method to the desired eigenstructure. The proposed algorithm is validated on a relative large power system derived from a practical network.

Abstract In the Swiss canton of Geneva, an energy efficiency portfolio has been operated since 2009. In contrast, such programs have been in place for more than 40 years in the US. There are numerous lessons to be learnt from their experience. We have therefore conducted a comparative analysis including Geneva and 11 leading states in the US, with the objective to identify explanatory factors for the success of energy efficiency programs. First, we compared total investment in energy efficiency programs between 2006 and 2015 and public policies related to energy efficiency in each state. Second, we analyzed the levelized cost of saved energy (LCSE) of the programs from the perspective of program administrators. Our cost-effectiveness analysis showed that the program investment scale has been strongly influenced by i) the existence of public mandates, which require program administrators to set ambitious targets and maximize their investment in cost-effective energy efficiency measures, ii) financial instruments that ensure program expenditure to be recovered, and iii) complementary funding from other programs. Moreover, learning and accumulated experience of the program administrators allow to reduce the LCSE. We conclude that the combination of financial instruments with public mandates can ensure a high level of effectiveness.