• Energy Research
• engineering and technology close
• CO close

The constraint solving techniques are the mechanisms that ensure all transactions in a competitive electricity market can be achieved without violation of operating limits. It becomes a very important issue in a competitive electricity market, because an improper handling of these can segment the electrical market and will have a significant impact on the ability to exercise market power. The main purpose of this paper is to develop a methodology to solve the power system constraints (both in normal operation and after contingencies) that arise after the daily energy market has been cleared. All this based on a competitive market environment, increasing and decreasing the generation of connected units, and connecting offline ones, all within different time scenarios.

Abstract Phosphate removal from wastewater and the correspondent sustainable technologies are urgent issues to solve since phosphorous causes eutrophication of water sources. The effect of heat treatment on the mixture eggshell (ES), rich in calcium carbonate, with fiber palm (F), rich in carbonaceous material for phosphate removal is here reported focusing on the effects of temperature and F/ES ratio. The gases obtained from the F pyrolysis process help to improve the Ca(OH)2 formation. In samples with a ES/F ratio of 1/10 (ESF-1:10) the CaCO3 is mainly transformed into Ca(OH)2 (83 %) at 600 °C instead of 800 °C. The obtained solids were employed for phosphate removal from aqueous solutions and characterized before and after P removal. The ESF-1:10 sample pyrolyzed at 600 °C exhibited the best adsorption performance (48.3 %) at 2 h while ES showed 6.5 % at the same experimental conditions. The pseudo-second-order model kinetic and Langmuir model isotherm provided better-fitting models for the adsorption behavior of P. The adsorption capacity using Langmuir model was 72.0 mg g−1, and the pseudo-second-order kinetic model assumes that the removal process of adsorbate is controlled by chemical adsorption. These results show that the Ca(OH)2 is responsible for the phosphate removal by ligand exchange followed by precipitation mechanism leading to the formation of apatite.

Utilizando un enfoque variacional, hemos investigado los efectos del campo magnético, la posición de las impurezas y las concentraciones de nitrógeno e indio sobre la energía de unión de las impurezas en un pozo cuántico de Ga1−xIn x N y As1−y/GaAs. Nuestros cálculos han revelado la dependencia de la unión de impurezas en el campo magnético aplicado, la posición de las impurezas y las concentraciones de nitrógeno e indio. En utilisant une approche variationnelle, nous avons étudié les effets du champ magnétique, de la position des impuretés et des concentrations d'azote et d'indium sur l'énergie de liaison des impuretés dans un puits quantique Ga1−xIn x N y As1−y/GaAs. Nos calculs ont révélé la dépendance de la liaison des impuretés sur le champ magnétique appliqué, la position des impuretés et les concentrations d'azote et d'indium. Using a variational approach, we have investigated the effects of the magnetic field, the impurity position, and the nitrogen and indium concentrations on impurity binding energy in a Ga1−xIn x N y As1−y/GaAs quantum well. Our calculations have revealed the dependence of impurity binding on the applied magnetic field, the impurity position, and the nitrogen and indium concentrations. باستخدام نهج متغير، قمنا بالتحقيق في تأثيرات المجال المغناطيسي، وموضع الشوائب، وتركيزات النيتروجين والإنديوم على طاقة ربط الشوائب في بئر Ga1 − xIn x N y As1 −y/GaAs الكمومي. كشفت حساباتنا عن اعتماد الشوائب الملزمة على المجال المغناطيسي المطبق، وموضع الشوائب، وتركيزات النيتروجين والإنديوم.

AbstractIn this commentary we critically discuss the suitability of payments for ecosystem services and the most important challenges they face. While such instruments can play a role in improving environmental governance, we argue that over‐reliance on payments as win‐win solutions might lead to ineffective outcomes, similar to earlier experience with integrated conservation and development projects. Our objective is to raise awareness, particularly among policy makers and practitioners, about the limitations of such instruments and to encourage a dialogue about the policy contexts in which they might be appropriate.

Rapid urbanization has resulted in often unplanned increases in population, and food demand in cities. Historically, hinterlands to these cities have acted as breadbaskets producing food to the urban residents. Accordingly, a large amount of available freshwater has been needed to support these croplands. However, the rapid expansion of cities in developing countries has significantly changed both the croplands around cities and the water demand. It is thus important to quantitatively investigate the water-food nexus of cities related to the changing hinterland agriculture. Water footprint is an indicator reflecting the human impact on water. In this study, we quantified both the blue and green water footprint of major crop products in Suzhou city, China using a bottom-up accounting method. A novel decomposition analysis was carried out with a Logarithmic Mean Divisia Index (LMDI) method to study the driving forces that changed the water footprint during the period 2001-2010. The drivers were designed to reflect the factors related to farmland, such as yield and crop area. This is different from previous decomposition analyses, which focused on economic factors such as GDP. The results show that the crop water footprint of Suzhou city has seen a general decreasing trend between 2001 and 2010. The decomposition analysis showed that the decline of crop area was the main driver that decreased the crop water footprint, followed by the virtual water content (water consumption per unit of production). In contrast the changes of crop combination and yield contributed to an increase in the crop water footprint. Although the shrink of urban croplands decreased the water footprint of crop products. Cities’ increasing demand for food will increase the crop water footprint of consumption. This will increase the dependence of cities on external water footprint of crop products (water embodied in imported crops), which may impact upon food security in cities in the long term.

The hybrid system is analyzed and optimized to produce electric energy in Non-Interconnected Zones in the Colombian Caribbean region, contributing both to the improvement in the reduction of greenhouse gas emissions and to the rational use of energy. A comparative analysis of the performance of these systems was carried using a dynamic model in real wind and solar data. The model is integrated by a Southwest Wind Power Inc. wind turbine. AIR 403, a proton exchange fuel cell (PEM), an electrolyze, a solar panel and a charge regulator based on PID controllers to manipulate oxygen and hydrogen flows in the cell. The transient responses of the cell voltage, current, and power were obtained for the demand of 200 W for changes in solar radiation and wind speed for all days of the year 2013 in the Ernesto Cortissoz airport, Puerto Bolívar, Alfonso Lopez airport and Simon Bolívar airport, by regulating the flow of hydrogen and oxygen into the fuel cell. The maximum contribution of power generation from the fuel cell was presented for the Simon Bolívar airport in November with a value of 158,358W (9.45%). A multi-objective design optimization under a Pareto front is presented for each place studied to minimize the Levelized Cost of Energy and CO2 emission, where the objective variables are the number of panel and stack in the PV system and PEM.  

The thermoelectric effect allows the direct conversion of thermal energy into electrical energy without the need for moving parts and its applications are endless, with only the availability of a temperature gradient. Combustion vehicles generate energy losses of up to 62% and it is estimated that efficiency with thermoelectric generators can be increased by up to 8%. In this work we propose a system of waste heat from exhaust gases from the thermoelectric effect. A computational model was developed using the finite element method. Based on the simulations, a set of curves of electrical variables can be made as a function of temperature. There is a good correlation between the model and datasheet data. Based on the modeled system, it was possible to evaluate a generation system with the generation of up to 120W with 5.8% efficiency, representing an increase of up to 3% in overall efficiency.