It is important to examine in detail how the distribution of academic research topics related to renewable energy is structured and which topics are likely to receive new attention in the future in order for scientists to contribute to the development of renewable energy. This study uses an advanced probabilistic topic modeling to statistically examine the temporal changes of renewable energy topics by using academic abstracts from 2010−2019 and explores the properties of the topics from the perspective of future signs such as weak signals. As a result, in strong signals, methods for optimally integrating renewable energy into the power grid are paid great attention. In weak signals, interest in large-capacity energy storage systems such as hydrogen, supercapacitors, and compressed air energy storage showed a high rate of increase. In not-strong-but-well-known signals, comprehensive topics have been included, such as renewable energy potential, barriers, and policies. The approach of t... [more]

Wind energy and wind power forecast errors have a direct impact on operational decision problems involved in the integration of this form of energy into the electricity system. As the relationship between wind and the generated power is highly nonlinear and time-varying, and given the increasing number of available forecasting techniques, it is possible to use alternative models to obtain more than one prediction for the same hour and forecast horizon. To increase forecast accuracy, it is possible to combine the different predictions to obtain a better one or to dynamically select the best one in each time period. Hybrid alternatives based on combining a few selected forecasts can be considered when the number of models is large. One of the most popular ways to combine forecasts is to estimate the coefficients of each prediction model based on its past forecast errors. As an alternative, we propose using multivariate reduction techniques and Markov chain models to combine forecasts. Th... [more]

The wood processing industry produces a significant amount of wood waste. Biomass valorization through pyrolysis has the potential to increase the added value of wood wastes. Pyrolysis is an important thermochemical process that can produce solid, liquid, and gas products. This paper aims to review the pyrolysis of wood wastes from Indonesia, including teak wood (Tectona grandis), meranti (Shorea sp.), sengon (Paraserianthes falcataria (L) Nielsen), and rubberwood (Hevea brasiliensis). The review is based on an in-depth study of reliable literatures, statistical data from government agencies, and direct field observations. The results showed that pyrolysis could be a suitable process to increase the added value of wood waste. Currently, slow pyrolysis is the most feasible for Indonesia, with the main product of charcoal. The efficiency of the slow pyrolysis process can be increased by harvesting also liquid and gaseous products. The use of the main product of pyrolysis in the form of c... [more]

To improve access to affordable, reliable and sustainable energy in rural areas of the global south, off-grid systems using renewable generation and energy storage are often proposed. However, solution design is often technology-driven, with insufficient consideration of social and cultural contexts. This leads to a risk of unintended consequences and inappropriate systems that do not meet local needs. To address this problem, this paper describes the application of a capabilities-led approach to understanding a community’s multi-dimensional energy poverty and assessing their needs as they see them, in order to better design suitable technological interventions. Data were collected in Tlamacazapa, Mexico, through site visits and focus groups with men and women. These revealed the ways in which constrained energy services undermined essential capabilities, including relating to health, safety, relationships and earning a living, and highlighted the specific ways in which improved energy... [more]

This paper presents the possibilities of adapting active mines to generate green energy after their closure using their resources and/or infrastructure. For this purpose, firstly, the temporal horizon of selected mines in Poland was determined, its basic assumption being the analysis of the current state. In the research, 18 mining plants operating within 12 mines in the Upper Silesian Coal Basin (USCB) were analyzed. The analyzed mines belong to three of the five largest hard coal producers in Poland, and the main object of exploitation is hard coal of energy types. Severe restrictions or even abandonment of further investments in the development of the coal mining industry were taken into consideration (regarding the construction of new shafts or the development of new exploitation levels). When determining the temporal horizon, the challenges that hamper the exploitation based at the levels of natural hazards and depth of exploitation in each mine were considered. Secondly, the crit... [more]

This article presents a comparative analysis for the design considerations for a solar power generation transformer. One of the main existing problems in transformer manufacturing is in the renewable energy field, specifically the solar power generation, where the transformer connected to the inverter is operated under a certain harmonic content and operating conditions. The operating conditions of the transformer connected to the inverter are particularly unknown for each solar power plant; thus, the transformer will be subject to a particular harmonic content, which is defined by the inverter of the solar power plant. First, the fundamental calculations for solar power plant transformer and the proposed methodology for the design calculation of the distribution pad-mounted three phase transformer are presented. Then, a design study case is described where a distribution transformer and an inverter of a particular solar power plant are used for the analysis. Next, the transformer unde... [more]

This article presents a high-performance lead-free piezoelectric energy harvester (LPEH) system for magnetic field. It based on a Ba0.85Ca0.15Ti0.90Zr0.10O3 + CuO 0.3 wt% (BCTZC0.3) composite was fabricated by sintering at 1450 °C. The BCTZC0.3 composite, which has an enhanced high energy conversion constant (d33×g33), shows improved piezoelectric power-generation performance when compared with conventional piezoelectric energy harvesters. The BCTZC0.3-based LPEH produces instantaneous maximum power of 8.2 mW and an energy density of 107.9 mW/cm3 in a weak magnetic field of 250 μT. This system can be used to charge a capacitor and operate a wireless sensor network (WSN) system to provide temperature sensing and radio-frequency (RF) transmission in a 250 μT magnetic field. The proposed LPEH is a promising green-energy device for potentially self-powering WSN systems when applied.

With recent technology advances and price drop, battery energy storage systems (BESSs) are considered as a promising storage technology in power systems. In this paper, a stochastic BESS planning model is introduced, which determines optimal capacity and durations of BESSs to co-locate utility-scale solar photovoltaic (PV) systems in a high-voltage power system under the uncertainties of renewable resources and electric load. The optimization model minimizing total costs aims to obtain at least 20% electric energy from renewable sources, while satisfying all the physical constraints. Furthermore, two-stage stochastic programming is applied to formulate mathematical optimization problem to find out optimal durations and capacity of BESSs. In scheduling BESSs, chronology needs to be considered to represent temporal changes of BESS states; therefore, a scenario generation method to generate random sample paths with 1-h time step is adopted to explicitly represent uncertainty and temporal... [more]

This paper presents the first systematic comparison between south-facing monofacial and bifacial photovoltaic (PV) modules, as well as between south-facing bifacial and vertical east-west facing bifacial PV modules in Alaska. The state’s solar industry, driven by the high price of energy and dropping equipment costs, is quickly growing. The challenges posed by extreme sun angles in Alaska’s northern regions also present opportunities for unique system designs. Annual bifacial gains of 21% were observed between side by side south-facing monofacial and bifacial modules. Vertical east-west bifacial modules had virtually the same annual production as south-facing latitude tilt bifacial modules, but with different energy production profiles.

Recently, biomass application as a renewable energy source is increasing worldwide. However, its availability differs in dependence on the location and climate, therefore, agricultural residues as cow dung (CD) are being considered to supply heat and/or power installation. This paper aims at a wide evaluation of CD fuel properties and its prospect to apply in the form of pellets to direct combustion installations. Therefore, the proximate, ultimate composition and calorific value were analyzed, then pelletization and combustion tests were performed, and the ash characteristics were tested. It was found that CD is a promising source of bioenergy in terms of LHV (16.34 MJ·kg−1), carbon (44.24%), and fixed carbon (18.33%) content. During pelletization, CD showed high compaction properties and at a moisture content of 18%,and the received pellets’ bulk density reached ca. 470 kg·m−3 with kinetic durability of 98.7%. While combustion, in a fixed grate 25 kW boiler, high emissions of CO, SO2... [more]

The prevailing need for a more sustainable management of natural resources depends not only on the decisions made by governments and the will of the population, but also on the knowledge of the role of energy in our society and the relevance of preserving natural resources. In this sense, critical work is being done to instill key concepts—such as the circular economy and sustainable energy—in higher education institutions. In this way, it is expected that future professionals and managers will be aware of the importance of energy optimization, and will learn a series of computational methods that can support the decision-making process. In the context of higher education, this paper reviews the main trends and challenges related to the concepts of circular economy and sustainable energy. Besides, we analyze the role of simulation and serious games as a learning tool for the aforementioned concepts. Finally, the paper provides insights and discusses open research opportunities regardin... [more]

In this study, the Flow-Induced Vibration (FIV) of pivoted cylinders (at a distance) is numerically investigated as a potential source of energy harvesting. In particular, we investigate the effect of pivot point placement, arm length, and natural frequency on the FIV performance of six different cross sections in the Reynolds number of around 1000. All sections have similar mass, area, and moment of inertia to eliminate non-geometrical effects on the performance. Classical studies show that the synchronization phenomenon (lock-in) occurs when the vortex formation frequency is close enough to the body’s natural frequency. Due to the configuration of the cylinder in this research (pivoted eccentrically), the natural frequency is also a function of the flow velocity as well as the geometrical specifications of the system. The simulation is done for the arm lengths between −3D and +3D for all cross sections. Results show that maximum output power is principally influenced more by the pivo... [more]

The development of a complete system of indicators and a composite sustainable energy index could prove useful to evaluate both the state of the art and the progress of national energy towards sustainable development. However, in the case of energy sustainability, a knowledge gap arises due to incomplete coverage and lack of systematic focus on sustainability components. The objective of our research is to obtain Sustainable Energy Development Aggregated Index to rank the EU Member States on the path to sustainable energy. We propose a set of indicators related to sustainable development in energy policy in the EU-28, grouped in three dimensions: social, economic and environmental and apply the standardized sums method in order to obtain the dimensional and aggregated indexes. The countries on the podium are Denmark, The Netherlands and Austria. The worst-performing countries (with index values below the first quartile) are Estonia, Malta, Slovakia, Poland, Greece, Cyprus and Bulgaria.... [more]

Due to the stochastic nature of the source, wind turbines operate under non-stationary conditions and the extracted power depends non-trivially on ambient conditions and working parameters. It is therefore difficult to establish a normal behavior model for monitoring the performance of a wind turbine and the most employed approach is to be driven by data. The power curve of a wind turbine is the relation between the wind intensity and the extracted power and is widely employed for monitoring wind turbine performance. On the grounds of the above considerations, a recent trend regarding wind turbine power curve analysis consists of the incorporation of the main working parameters (as, for example, the rotor speed or the blade pitch) as input variables of a multivariate regression whose target is the power. In this study, a method for multivariate wind turbine power curve analysis is proposed: it is based on sequential features selection, which employs Support Vector Regression with Gauss... [more]

An integrated energy system interconnects multiple energies and presents a potential for economics improvement and energy sustainability, which has attracted extensive attention. However, due to the obvious volatility of energy demands, most existing integrated energy systems cannot operate in a totally self-sufficient way but interact with the upper grid frequently. With the increasingly urgent demand for energy saving and emissions reduction, renewable resources have occupied a larger and larger proportion in energy system, and at last they may be dominant in the future. Unlike conventional fossil fuel generation, the renewable resources are less controllable and flexible. To ease the pressure and guarantee the upper grid security, a more independent integrated energy system is required. Driven by that, this paper firstly reviews the optimal strategies considering both independence and benefit from perspectives of individual efforts and union efforts. Firstly, the general optimizatio... [more]

Electrification of powertrain systems offers numerous advantages in the global trend in vehicular applications. A wide range of energy sources and zero-emission propulsion in the tank to wheel significantly add to electric vehicles’ (EV) attractiveness. This paper presents analyses of the energy balance between micro-photovoltaic (PV) installation and small electric vehicle in real conditions. It is based on monitoring PV panel’s energy production and car electricity consumption. The methodology included energy data from real household PV installation (the most common renewable energy source in Poland), electric vehicle energy consumption during real driving conditions, and drivetrain operating parameters, all collected over a period of one year by indirect measuring. A correlation between energy produced by the micro-PV installation and small electric car energy consumption was described. In the Winter, small electric car energy consumption amounted to 14.9 kWh per 100 km and was 14%... [more]

Tidal energy is one of the major sources of renewable energy. To accelerate the development of tidal energy, improved designs of Tidal Current Turbine (TCT) are necessary. The effect of tower on performance and wake of TCT is investigated using Computational Fluid Dynamics (CFD) simulations. Transient analysis with transient rotor stator frame change model and shear stress transport turbulence model are utilized in ANSYS CFX. An experimentally validated numerical model with full scale tidal turbine with a blockage ratio of 14.27% and Tip Speed Ratio (TSR) 4.87 is used to simulate the effect of different tower diameters on performance and wake. The effect of different tower diameters is quantified in terms of coefficient of performance (CP). Coefficient of performance for a 3.5 m tower diameter is 0.472 which is followed by 3, 2.5 and 2 m with coefficients of performance of 0.476, 0.478 and 0.476 respectively. Similarly, the coefficient of thrust (CT) on the rotor for 3.5 m tower diamet... [more]

The COVID-19 pandemic represents not just a global health crisis, but may signal the beginning of a new era of economic activity, the potential consequences of which we currently do not fully understand. In this context, the mid-to-long-range impacts of the pandemic on the energy sector have been studied extensively in the last few months. Despite these efforts, the pandemic still raises many open questions concerning the long-term operation and planning of power systems. For instance, how will the pandemic affect the integration of renewable energy sources? Should current power system expansion plans change in light of the COVID-19 pandemic? What new tools should be provided to support system operators during global health crises? It is the purpose of this paper to better understand the many aspects of these open questions by reviewing the relevant recent literature and by analyzing measured data. We point out the main challenges that the pandemic introduced by presenting patterns of... [more]

In this research, a technoeconomic comparison of energy efficiency options for energy districts located in different climatic areas (Naples, Italy and Fayoum, Egypt) is presented. A dynamic simulation model based on TRNSYS is developed to evaluate the different energy efficiency options, which includes different buildings of conceived districts. The TRNSYS model is integrated with the plug-in Google SketchUp TRNSYS3d to estimate the thermal load of the buildings and the temporal variation. The model considers the unsteady state energy balance and includes all the features of the building’s envelope. For the considered climatic zones and for the different energy efficiency measures, primary energy savings, pay back periods and reduced CO2 emissions are evaluated. The proposed energy efficiency options include a district heating system for hot water supply, air-to-air conventional heat pumps for both cooling and space heating of the buildings and the integration of photovoltaic and solar... [more]

Connecting a large number of distributed sources to the medium and low voltage grid poses many problems. The most important of these are the voltage changes inside the network, what can be observed when the power flow from these sources towards the HV/MV (High Voltage/Medium Voltage) transformer station. In particular, if the power consumption in nodes of the MV network is small and the distance between the place of installation of the source and the substation is large, increases and changes in voltage may be dangerous for the insulation of the network and burdensome for the consumers connected to it. The solution most frequently used to control voltage increases is the appropriate setting of the controller that affects the on-load tap changer of the MV/HV or even MV/LV (Medium Voltage/Low Voltage) transformer. It is also possible to regulate the reactive power of the sources and, of course, to limit their generated active power (curtailment of generation). The development of energy s... [more]

This century registers a significant expansion in the wind power market. However, the vast majority of these investments are concentrated in large wind turbines. The century begins with an installed capacity of about 20 GW, which reaches 650 GW in 2019. On the other hand, it is important to highlight that small wind turbines have not followed this virtuous path, a fact that is evident in Brazil’s reality. In this context, the article aims at evaluating the current situation of the wind energy market for Small Wind Turbines in Brazil (SWT) and its future perspectives, identifying the main characteristics of the sector, its challenges, and opportunities. It is an exploratory−explanatory research study that investigates the theme, generating knowledge that turns to practical application, as it seeks answers to solve local interests. This methodological approach provides objective evidence that the production of knowledge about the use of SWT in Brazil still remains embryonic, shaded by th... [more]

The energy sector and electricity generation in particular, is responsible for a great share of the global greenhouse gas (GHG) emissions. World electricity generation is still largely based on the burning of fossil fuels. However, Brazil has already a very low electricity carbon intensity due to the country’s large hydropower capacity. In countries with low grid carbon intensities such as Brazil, the investment in photovoltaic solar systems (PVSS) even if it is cost-effective, might become challenging as any new generation competes essentially against other renewable generation and the carbon offset is not a key driver for investment anymore. This study builds further upon that case to examine if national renewable energy incentives could actually lead to an increase of global net carbon emissions from the installation of PVSS in countries with a low grid carbon intensity. The study presents a life cycle analysis (LCA) of ten photovoltaic systems representative of the different operat... [more]

Increasing the energy efficiency of residential and non-residential buildings is a crucial point towards the development of the sustainable cities of the future. To reach such a goal, the commonly employed intervention measures (for instance, on facades and glass) are not sufficient and efforts in reaching a fully renewable energy generation are mandatory. In this context, this paper discusses the applicability of a system with solar and biomass as the main energy sources in different climates for heating, cooling, domestic hot water and electricity generation in office buildings. The energy system includes solar thermal collectors with thermoelectric generators, a biomass boiler, a reversible heat pump/organic Rankine cycle and an adsorption chiller. The results showed that the system can operate with a share of renewables higher than 70% for all energy needs, with up to 80% of the overall energy demand supplied only by solar and biomass sources even in the northern locations.

In this study we aimed to determine the extent to which changes in the share of renewable energy sources, their structural complex, and the level of energy security in Eastern Europe, Caucasus and Central Asia (EECCA) countries in the medium- and long-term are interconnected. The study was performed through modeling and determination of the structural characteristics of energy security in the countries. The methodology of the approach to modeling was based on solving the problem of nonlinear optimization by selecting a certain scenario. For the study, the data of EECCA countries were used. The ability of EECCA countries to benefit from long-term indirect and induced advantages of the transformation period depends on the extent to which their domestic supply chains facilitate the deployment of energy transformation and induced economic activity. This study provides an opportunity to assess the degree of influence of renewable energy sources on the level of energy security of countries i... [more]

This research tackles effective and functional management practices in energy consumption using advanced technological solutions to mitigate unexpected events. This study specifically focuses on the recent COVID-19 pandemic that led to a reduction in energy consumption and therefore meddled with the project management’s status quo for the energy sources. Moreover, this research analyzes the role of information and communication technology (ICT) solutions in energy management before and after the recent coronavirus pandemic turmoil. This study also examined the role and place of sustainable energy resources in the effective management of energy consumption during the COVID-19 pandemic. The main purpose of this research is to demonstrate how the recent coronavirus pandemic affected energy consumption and energy prices in many countries and how it paved the way for the new ICT in managing energy consumption. This study elaborated a model to show how these changes evolved in selected Europ... [more]