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Poultry litter (PL) gasification was experimentally investigated using a lab-scale bubbling fluidised bed reactor. Characterisation of the gasification process was performed in terms of yields and compositions of both gas and tar, lower calorific value (LCV) of the product gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Experiments were carried out at different temperatures (700-750 °C) and equivalence ratios (ERs). The effect of gasifier temperature at a constant ER of 0.21 shows that an increase in temperature improved the gasification process performance whilst the total tar content decreased, implying that higher temperature enhances the conversion of biomass to product gas. The total gas yield increased from 0.93 to 1.24 N2-free m3/kgfeedstock-daf, LCV increased from 3.38 MJ/m3 to 4.2 MJ/m3, while the tar content was reduced by 24% (5.6-4.25 gtar/kgfeedstock-daf). The detailed analyses of tar compositions reveal that styrene and xylenes were the most abundant compounds in the secondary tar group. Moreover, naphthalene and 1, 2-methyl naphthalene were the dominant compounds found in tertiary polycyclic aromatic hydrocarbons (PAH) and alkyl tertiary groups, respectively. Furthermore, at the highest tested temperature of 750 °C and ER of 0.25, bed agglomeration took place causing the shutdown of the gasifier. The defluidisation of the bed occurred due to the high ash content of PL comprising of low melting temperature alkali compounds. The results obtained from this study showed the performance and potential challenges associated with gasifying PL in a fluidised bed reactor for the combined heat and power production at farm level.

This paper proposes an effective dc voltage and power-sharing control structure for multiterminal dc (MTDC) grids based on an optimal power flow (OPF) procedure and voltage-droop control implemented in the different hierarchical layers. In the proposed approach, an OPF algorithm is executed at the secondary control level of the MTDC grid to find the optimal reference values for the dc voltages and active power of the voltage-regulating converters. Then, at the primary control level, the voltage-droop characteristics of the voltage-regulating converters are tuned based upon the OPF results. In this control structure, the optimally-tuned voltage-droop controllers lead to the optimal operation of the MTDC grid. In case of variation in load or generation of the grid, a new stable operating point is achieved based on the voltage-droop characteristics. Then by executing a new OPF, the voltage-droop characteristics are returned for optimal operation of the MTDC grid after the load or generation variations. This paper also considers the integration of frequency support loop in the proposed control framework in case of connection of weak ac grids. The simulations performed on a study case inspired by the CIGRE B4 dc grid test system demonstrate the efficient grid performance under the proposed control strategy. Peer Reviewed

Conventional energy resources are not climate sustainable. Currently, engineers and scientists are looking for sustainable energy solutions influenced by climate change. A wide variety of sustainable natural energy resources are available, but they require technical solutions for their implementation. The general trend in energy research is based on renewable resources, amongst which solar energy stands out, being the most mature and widely accepted. In this paper, the current state of the sustainable energy system has been analysed. The main purpose is to provide additional context to assess future scenarios. The study of past contributions allows sustainability planning and increasing the welfare of future society. The aim is to highlight global trends in research on sustainable solar energy from 1995 to 2020 through a bibliometric analysis of 4260 publications. According to their linkages, the analysed articles are distributed in nine clusters: Sustainability assessment, Sustainable energy solutions, Environmental payback time analysis, Sustainability of solar energy in different scenarios, Environmental sustainability, Solar energy applications, Sustainable energy optimisation, Energy transition and Energy and sustainable scenarios. The most repeated keywords are Sustainability, Renewable energy, and Solar energy. Energy research and the exploration of new renewable solar resources are still necessary to meet sustainable energy’s future challenges.

In this paper we investigate the prospects for the large-scale use of low-emission energy technologies in Africa. Many African countries have recently experienced substantial economic growth and aim at fulfilling much of the energy needs associated with continuing along paths of economic expansion by exploiting their large domestic potentials of renewable forms of energy. Important benefits of the abundant renewable energy resources in Africa are that they allow for stimulating economic development, increasing energy access and alleviating poverty, while simultaneously avoiding emissions of greenhouse gases. In this study we analyse what the likely energy demand in Africa could be until 2050, and inspect multiple scenarios for the concomitant levels of greenhouse gas emissions and emission intensities. We use the TIAM-ECN model for our study, which enawbbles detailed energy systems research through a technology-rich cost-minimisation procedure. The results from our analysis fully support an Africa-led effort to substantially enhance the use of the continent's renewable energy potential. But they suggest that the current aim of achieving 300 GW of additional renewable electricity generation capacity by 2030 is perhaps unrealistic, even given high GDP and population growth: we find figures that are close to half this level. On the other hand, we find evidence for leap-frogging opportunities, by which renewable energy options rather than fossil fuels could constitute the cost-optimal solution to fulfil most of Africa's growing energy requirements. An important benefit of leap-frogging is that it avoids an ultimately expensive fossil fuels lock-in that would fix the carbon footprint of the continent until at least the middle of the century.

Solar tracking is an efficient strategy to increase the radiative capture of photovoltaic collectors. Within the multiple efforts made in recent decades to improve the production of these facilities, various works have studied solutions to optimize the number of rotation axes (single or dual rotation axes), the degree of collector coverage, the distances between trackers, the geometric arrangement of trackers or the minimization of shading between collectors. However, although in this type of installation it is common to find collectors with geometric shapes other than rectangles, no studies on the influence of the shape of the collectors on the radiative incidence are found in the literature. In this connection, the present work systematically addresses the study of incident solar radiation in photovoltaic installations with dual-axis trackers with collectors of different geometric shapes. By means of the exhaustive study, the conclusion is drawn that, for dual-axis photovoltaic installations with an optimal tracking strategy, the main variables that influence the annual radiative incidence are the spacing between collectors, the coverage ratio (GCR), and the collector surface, while the type of arrangement of collectors and the shape of these do not show predictive values.