The world’s population continues to grow at a high rate, such that today’s population is twice that of 1960, and is projected to increase further to 9 billion by 2050. This situation has brought about a situation in which the percentage of the global energy used in cities is increasing considerably. Biomass is a resource that is present in a variety of different materials: wood, sawdust, straw, seed waste, manure, paper waste, household waste, wastewater, etc. Biomass resources have traditionally been used, and their use is becoming increasingly important due to their economic potential, as there are significant annual volumes of agricultural production, whose by-products can be used as a source of energy and are even being promoted as so-called energy crops, specifically for this purpose. The main objective of this work was to analyze the state of research and trends in biomass for renewable energy from 1978 to 2018 to help the research community understand the current situation and future trends, as well as the situation of countries in the international context, all of which provides basic information to facilitate decision-making by those responsible for scientific policy. The main countries that are investigating the subject of biomass as a renewable energy, as measured by scientific production, are the United States, followed by China, India, Germany and Italy. The most productive institutions in this field are the Chinese Academy of Sciences, followed by the National Renewable Energy Laboratory, Danmarks Tekniske Universitet and the Ministry of Education in China. This study also identifies communities based on the keywords of the publications obtained from a bibliographic search. Six communities or clusters were found. The two most important are focused on obtaining liquid fuels from biomass. Finally, based on the collaboration between countries and biomass research, eight clusters were observed. All this is centered on three countries belonging to different clusters: USA, India and the UK.

The peanut (Arachys hypogaea) is a plant of the Fabaceae family (legumes), as are chickpeas, lentils, beans, and peas. It is originally from South America and is used mainly for culinary purposes, in confectionery products, or as a nut as well as for the production of biscuits, breads, sweets, cereals, and salads. Also, due to its high percentage of fat, peanuts are used for industrialized products such as oils, flours, inks, creams, lipsticks, etc. According to the Food and Agriculture Organization (FAO) statistical yearbook in 2016, the production of peanuts was 43,982,066 t, produced in 27,660,802 hectares. Peanuts are grown mainly in Asia, with a global production rate of 65.3%, followed by Africa with 26.2%, the Americas with 8.4%, and Oceania with 0.1%. The peanut industry is one of the main generators of agroindustrial waste (shells). This residual biomass (25–30% of the total weight) has a high energy content that is worth exploring. The main objectives of this study are, firstly, to evaluate the energy parameters of peanut shells as a possible solid biofuel applied as an energy source in residential and industrial heating installations. Secondly, different models are analysed to estimate the higher heating value (HHV) for biomass proposed by different scientists and to determine which most accurately fits the determination of this value for peanut shells. Thirdly, we evaluate the reduction in global CO2 emissions that would result from the use of peanut shells as biofuel. The obtained HHV of peanut shells (18.547 MJ/kg) is higher than other biomass sources evaluated, such as olive stones (17.884 MJ/kg) or almond shells (18.200 MJ/kg), and similar to other sources of biomass used at present for home and industrial heating applications. Different prediction models of the HHV value proposed by scientists for different types of biomass have been analysed and the one that best fits the calculation for the peanut shell has been determined. The CO2 reduction that would result from the use of peanut shells as an energy source has been evaluated in all production countries, obtaining values above 0.5 ‰ of their total emissions.

This study aims to highlight the contribution made by different international institutions in the field of urban generation of renewable energy, as a key element to achieve sustainability. This has been possible through the use of the Scopus Elsevier database, and the application of bibliometric techniques through which the articles content published from 1977 to 2017 has been analysed. The results shown by Scopus (e.g., journal articles and conferences proceedings) have been taken into account for further analysis by using the following search pattern (TITLE-ABS-KEY ({Renewable energy} AND ({urban} OR ({cit*})). In order to carry out this study, key features of the publications have been taken into consideration, such as type of document, language, thematic area, type of publication, and keywords. As far as keywords are concerned, renewable energy, sustainability, sustainable development, urban areas, city, and energy efficiency, have been the most frequently used. The results found have been broken down both geographically and by institution, showing that China, the United States, the United Kingdom, Italy, Germany and India are the main research countries and Chinese Academy of Sciences, Ministry of Education China and Tsinghua University the major contributing institutes. With regard to the categories, Energy, Environmental Sciences, and Engineering are positioned as the most active categories. The scientific community agrees that the study of the renewable energy generation in cities is of vital importance to achieve more sustainable cities, and for the welfare of a growing urban population. Moreover, this is in line with the energy policies adopted by most of developed countries in order to mitigate climate change effects.

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This study analyzes the numerical convergence and processing time required by several classical and new solution methods proposed in the literature to solve the power-flow problem (PF) in direct-current (DC) networks considering radial and mesh topologies. Three classical numerical methods were studied: Gauss–Jacobi, Gauss–Seidel, and Newton–Raphson. In addition, two unconventional methods were selected. They are iterative and allow solving the DC PF in radial and mesh configurations. The first method uses a Taylor series expansion and a set of decoupling equations to linearize around the desired operating point. The second method manipulates the set of non-linear equations of the DC PF to transform it into a conventional fixed-point form. Moreover, this method is used to develop a successive approximation methodology. For the particular case of radial topology, three methods based on triangular matrix formulation, graph theory, and scanning algorithms were analyzed. The main objective of this study was to identify the methods with the best performance in terms of quality of solution (i.e., numerical convergence) and processing time to solve the DC power flow in mesh and radial distribution networks. We aimed at offering to the reader a set of PF methodologies to analyze electrical DC grids. The PF performance of the analyzed solution methods was evaluated through six test feeders; all of them were employed in prior studies for the same application. The simulation results show the adequate performance of the power-flow methods reviewed in this study, and they permit the selection of the best solution method for radial and mesh structures.

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Universities around the world should be at the forefront of energy-saving and efficiency processes, seeking to be at the same level or preferably higher than the rest of society, and seeking the goal of 20% renewable energy by 2020. Sustainability practices have been carried out by several universities. In Mexico, the National Autonomous University of Mexico (UNAM) is a leader in this subject; in fact, the newest National School of Higher Studies - Juriquilla (ENES-J) that belongs to UNAM, located in the city of Queretaro (Mexico), is involved in its sustainability plan, with one of its main objectives being to save electric energy. UNAM has some campuses outside of Mexico City, and one of them is the National School of Higher Studies Juriquilla (ENES-J) in the state of Queretaro, where there is the Orthotics and Prosthetics Laboratory (OPL), in which has been installed a Computer Numerical Control (CNC) machine type Haas Automation model UMC-750, which has 5-axis and is an effective means to reduce the number of setups and increase accuracy for multi-sided and complex parts. This machine will be used to design, build, and assess human prosthesis. This study aimed to contribute to sustainability policies at the ENES-J from UNAM, implementing a solar photovoltaic system (PVS) to deliver electricity to the grid and contribute to reducing the electricity load at the Orthotics and Prosthetics Laboratory (OPL), as well to propose new research lines to support the sustainability policies in universities, and also proposing a financial analysis. To achieve this, in an area of 96.7 m2, 50 solar panels type mono-Si Advance Power API-M330 with an efficiency of 17.83% and a capacity factor of 20.4% will be installed and will provide 17.25 kW of power and 345 kWh of energy. The financial analysis shows the initial costs of 46,575 USD/kW, operation and maintenance (O&M) costs (savings) of 569 USD/kW-year, a monthly electricity export rate of 0.10 USD/kWh, electricity exported to the grid of 21.5 MWh, and an electricity export revenue of 2,145 USD. To assess the environmental balance with this PVS at ENES-J, an analysis of greenhouse gases (GHG) is carried out by using the RETScreen software. In this analysis, a GHG emission factor of 0.45 tCO2/MWh was found, as well as a savings of 12,089 USD per year.

Global energy consumption has increased the emission of greenhouse gases (GHG), these being the main cause of global warming. Within renewable energies, bioenergy has undergone a great development in recent years. This is due to its carbon neutral balance and the fact that bioenergy can be obtained from a range of biomass resources, including residues from forestry, agricultural or livestock industries, the rapid rotation of forest plantations, the development of energy crops, organic matter from urban solid waste, and other sources of organic waste from agro-food industries. Processing factories that use loquats to make products such as liqueurs and jams generate large amounts of waste mainly in the form of skin and stones or seeds. These wastes are disposed of and sent to landfills without making environmentally sustainable use of them. The University of Almeria Sports Centre is made up of indoor spaces in which different sports can be practiced: sports centre pavilion (central court and two lateral courts), rocodrome, fitness room, cycle inner room, and indoor swimming pool. At present, the indoor swimming pool of the University of Almeria (UAL) has two fuel oil boilers, with a nominal power of 267 kW. The main objective of this study is to propose an energetic analysis to determine, on the one hand, the energetic properties of the loquat seed and, on the other hand, to evaluate its suitability to be used as a solid biofuel to feed the boilers of the heated swimming pool of the University of Almeria (Spain), highlighting the significant energy and environmental savings obtained. Results show that the higher calorific value of loquat seed (17.205 MJ/kg), is like other industrial wastes such as wheat straw, or pistachio shell, which demonstrates the energy potential of this residual biomass. In addition, the change of the fuel oil boiler to a biomass (loquat seed) boiler in the UAL's indoor swimming pool means a reduction of 147,973.8 kg of CO 2 in emissions into the atmosphere and an annual saving of 35,739.5 €, which means a saving of 72.78% with respect to the previous fuel oil installation. A sensitivity analysis shows that fuel cost of base case is the variable with the most sensitivity changing the initial cost and net present value (NPV).