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This paper focuses on the combined use of geographical information systems and multi-criteria decision methods when developing a decision support model in order to determine the most favourable sites for the installation of wind turbines on a regional scale. This study differs from others in three ways: (1) it analyses two distinct scenarios (depending on whether major or minor constraints, as defined in the existing literature, are applied); (2) the area under study, Cadiz, already has an extensive network of wind-generating facilities; and (3) this study analyses at length areas where installation is not suitable. The methodology is proven to be a valid and appropriate tool for identifying potential areas for wind-energy facilities on a regional scale for both planners and investors. The model is proved to be useful for planning and evaluating phases: for example, it helps to outline criteria which can be used to define sectors where the number of suitable areas for wind-energy facilities can be increased, as well as locations where repowering might be a suitable alternative.

Abstract This paper presents a control strategy for sun trackers which adapts continuously to different sources of error, avoiding the necessity of any kind of calibration by analyzing the produced electric power to sense the position of the Sun. The proposed strategy is able to meet the strict specifications for HCPV sun trackers despite of mechanical uncertainties (misalignments in the structure itself, misalignment of the solar modules with respect to the wing, etc.) and installation uncertainties (misalignments of the platform with respect to geographical north). Experimental results with an industrial-grade solar tracker showing the validity of the proposed control strategy under sunny and moderate cloudy conditions, as well as with different installation precisions by un-calibrating the system on purpose are exposed.

Profitability studies are needed to establish the potential pathways required for viable biomethane production in the Brandenburg region of Germany. This work study the profitability of a potential biomethane production plant in the eastern German region of Brandenburg, through a specific practical scenario with data collected from a regional biogas plant located in Alteno (Schradenbiogas GmbH & Co. KG). Several parameters with potential economic influence such as distance of the production point to the grid, waste utilization percentage, and investment, were analyzed. The results illustrate a negative overall net present value with the scenario of no governmental investment, even when considering trading the CO2 obtained throughout the process. Subsidies needed to reach profitability varied with distance from 13.5 €/MWh to 19.3 €/MWh. For a fixed distance of 15 kms, the importance of percentage of waste utilization was examined. Only 100% of waste utilization and 75% of waste utilization would reach profitability under a reasonable subsidies scheme (16.3 and 18.8 €/MWh respectively). Concerning the importance of investment, a subsidized investment of at least 70% is demanded for positive net present values. Besides, the sensitivity analysis remarks the energy consumption of the biogas upgrading stage, the electricity price, and the energy consumption of biogas production as major parameters to be tackled for the successful implementation of biogas upgrading plants. The results here obtained invite to ponder about potential strategies to further improve the economic viability of this kind of renewable projects. In this line, using the CO2 separated to produce added-value chemicals can be an interesting alternative.

Abstract Rational function-based models have proved to be very efficient for accurate frequency-dependent modeling of power system components. These models are able to characterize the components terminal behaviours (analysing the admittance matrix) for nodal analysis. This provides a fast convergence and inherent stability to the solution routine of the model. This work presents a general framework for interfacing the dynamic phasor method to the rational models. That would be promising for the electromagnetic transient analysis (under harmonic distortion), in the frequency domain. Therefore, Y-element rational pole-residue models (employing the vector fitting method) are developed. Moreover, the pole-residue model is converted into the state-space representation. Next, the dynamic harmonic approach (in the frequency domain) is employed for harmonic analysis. It is shown that the order of state-space system can become a major concern for frequency-dependent networks analysis. Therefore, to generate a reduced-order model, the balanced realization theory is applied. Moreover, (for the sake of simplicity and efficiency) the trapezoidal integration rule is employed to discretise the state-space equations. For validation of the modelling, it is applied on three test case studies and results of these studies are compared with their time-domain analysis results.

Abstract Herein a novel path is analysed for its economic viability to synergize the production of biomethane and dimethyl ether from biogas. We conduct a profitability analysis based on the discounted cash flow method. The results revealed an unprofitable process with high cost/revenues ratios. Profitable scenarios would be reached by setting prohibitive DME prices (1983–5566 €/t) or very high feed-in tariffs subsidies (95.22 €/MWh in the best case scenario). From the cost reduction side, the analysis revealed the need of reducing investment costs. For this purpose, we propose a percentage of investment as incentive scheme. Although the size increase benefits cost/revenues ratio, only the 1000 m3/h biogas plant size will reach profitability if 90% of the investment is subsidized. A sensitivity analysis to check the influence of some important economical parameters is also included. Overall this study evidences the big challenge that our society faces in the way towards a circular economy.

This paper presents a wind resource assessment in Venezuela using an efficient combination of spatial interpolation and orographic correction for wind mapping. Mesoscale modelling offers a relatively accurate means to model meteorological conditions by solving the continuity and momentum equations. However, this approach is both time and computationally demanding. The methodology used in this work offers a computationally inexpensive solution by combining both a simple geo-statistical Kriging method to interpolate horizontal wind speed and an orographic correction to account for changes on terrain elevation. Hourly observations of wind speed and direction for 34 masts recorded during the period 2005–2009 have been analysed in order to define a statistical model of wind resources. The resulting method, which includes an exploratory statistical analysis of the wind data, is a computationally economical alternative to mesoscale modelling. Simulations results include equivalent mean wind speeds and wind power maps which have been created to a height of 50, 80 and 120 m above the ground based on a horizontal resolution of 15×15 km. Results show that the greatest wind energy resources are located in the coastal area of Venezuela with a potential for offshore applications. Preliminary findings provide a very positive evidence for offshore exploitation of wind power. Results also suggest that wind energy resources for commercial use (utility-scale) are available in northern Venezuela, additionally; they suggest excellent conditions for wind power production for micro-scale applications, both on- and off-grid.

This paper presents a simple, fast, and efficient method for determining the maximum loading point (MLP) and the voltage stability security margin of electric power systems. The proposed method is based on nonlinear programming techniques. The MLP is accurately obtained after a few load change steps. The computational procedure involves two kinds of load changes. Initially, load increases toward the MLP are defined for minimizing an objective function based on sensitivities. In case an overestimated load increase drives the system outside the feasible (stable) operating region, another very simple optimization-based procedure aimed to minimize the power mismatches determines the load adjustment (curtailment) to pull the system back onto the feasibility boundary. Simulation results for small test to large realistic systems are shown to validate the proposed method.

Abstract This work presents an experimental investigation on the preferential accumulation of liquid water in the channels of a multiple serpentine PEMFC with 50 cm 2 active area. Neutron imaging was used for visualizing the liquid water distribution during the cell operation for a wide range of operating conditions. Liquid water accumulation in the cathode channels was observed for most of the operating conditions, with a preferential accumulation in certain channels of the flow field. A statistical analysis was performed in order to determine the main characteristics of this accumulation (i.e. channel number and degree of accumulation). As cathode channels were positioned in vertical direction, it was found that gravity effects had an important influence in the accumulation, as well as the relative position of the channel with respect to the inlet and outlet locations. The gas flow direction had also a major impact on the water accumulation within the channels, with significantly more water accumulated in channels with upwards gas flow.