The high utilization of renewable energy to manage climate change and provide green energy requires short-term photovoltaic (PV) power forecasting. In this paper, a novel forecasting strategy that combines a convolutional neural network (CNN) and a salp swarm algorithm (SSA) is proposed to forecast PV power output. First, the historical PV power data and associated weather information are classified into five weather types, such as rainy, heavy cloudy, cloudy, light cloudy and sunny. The CNN classification is then used to determine the prediction for the next day’s weather type. Five models of CNN regression are established to accommodate the prediction for different weather types. Each CNN regression is optimized using a salp swarm algorithm (SSA) to tune the best parameter. To evaluate the performance of the proposed method, comparisons were made to the SSA based support vector machine (SVM-SSA) and long short-term memory neural network (LSTM-SSA) methods. The proposed method was tes... [more]

This paper presents the wind energy potential and wind characteristics for 25 wind sites in Eritrea, based on wind data from the years 2000−2005. The studied sites are distributed all over Eritrea, but can roughly be divided into three regions: coastal region, western lowlands, and central highlands. The coastal region sites have the highest potential for wind power. An uncertainty, due to extrapolating the wind speed from the 10-m measurements, should be noted. The year to year variations are typically small and, for the sites deemed as suitable for wind power, the seasonal variations are most prominent in the coastal region with a peak during the period November−March. Moreover, Weibull parameters, prevailing wind direction, and wind power density recalculated for 100 m above ground are presented for all 25 sites. Comparing the results to values from the web-based, large-scale dataset, the Global Wind Atlas (GWA), both mean wind speed and wind power density are typically higher for t... [more]

In Poland, various solar collector systems are used; among them, the most popular are flat plate collectors (FPCs) and evacuated tube collectors (ETCs). The work presents two installations located at a distance of 80 km apart, working in similar external conditions. One of them contains 120 flat plate collectors and works for the preparation of hot water in a swimming pool building; the second one consists of 32 evacuated tube collectors with a heat pipe and supports the preparation of domestic hot water for a multi-family house. During the comparison of the two quite large solar installations, it was confirmed that the use of evacuated tube solar collectors shows a much better solar energy productivity than flat plate collectors for the absorber area. Higher heat solar gains (by 7.9%) were also observed in the case of the gross collector area. The advantages of evacuated tube collectors are observed mainly during colder periods, which allows for a steadier thermal energy production.

Slaughterhouse waste management is an important technological, economic, and environmental challenge. Recently, more and more attention has been paid to the possibility of obtaining biogas from waste generated by slaughterhouses. The aim of the paper was to examine the effect of an emulsifier addition in the form of a carboxymethyl cellulose solution to create animal waste fermentation media based on the quantity and quality of the generated biogas. The adopted research goal was achieved based on a laboratory experiment of methane fermenting poultry processing waste. The waste was divided into two fractions: soft (tissue) and hard (bone). A fat emulsifier in a concentration of 1%, 2.5%, 5%, and 10% of fresh weight of the substrate was added to each substrate sample made from the above fractions. The emulsifier used was a 55% carboxymethyl cellulose solution, since this emulsifier is most commonly used in food production. The experiment was conducted in order to determine how the additi... [more]

The Ukrainian energy sector is one of the most inflexible energy sectors in the world as a result of the almost complete depreciation of the equipment of the main sources of power supply: nuclear, thermal, and hydropower. In connection with existing problems, there is a need to develop and use new energy-saving technologies based on renewable energy sources. In this proposed research, a regression model of renewable energy growth in the energy sector of Ukraine was developed. The studied literature reveals that the independent use of individual functioning elements of renewable energy sources function as the primary power source that is not an optimal solution for stable energy supply. This study proposes the use of hybrid renewable energy systems, namely a combination of two or more renewable energy sources that will help each other to achieve higher energy efficiency, accelerate the growth of renewable energy in the share of the Ukrainian energy sector and/or improve functioning with... [more]

The Ukrainian energy sector is one of the most inflexible energy sectors in the world as a result of the almost complete depreciation of the equipment of the main sources of power supply: nuclear, thermal, and hydropower. In connection with existing problems, there is a need to develop and use new energy-saving technologies based on renewable energy sources. In this proposed research, a regression model of renewable energy growth in the energy sector of Ukraine was developed. The studied literature reveals that the independent use of individual functioning elements of renewable energy sources function as the primary power source that is not an optimal solution for stable energy supply. This study proposes the use of hybrid renewable energy systems, namely a combination of two or more renewable energy sources that will help each other to achieve higher energy efficiency, accelerate the growth of renewable energy in the share of the Ukrainian energy sector and/or improve functioning with... [more]

Salinity gradient resource presents an essential role for power generated in the process of pressure-retarded osmosis (PRO). Researchers proposed several designs for coupling the PRO process with the desalination plants, particularly reverse osmosis technology for low-cost desalination but there is no study available yet on the utilization of the concentrated brine reject from a thermal desalination plant. This study evaluates the feasibility of power generation in the PRO process using thermal plant brine reject-tertiary sewage effluent (TSE) salinity gradient resource. Power generation in the PRO process was determined for several commercially available FO membranes. Water flux in Oasys Forward Osmosis membrane was more than 31 L/m2h while the average water flux in the Oasys module was 17 L/m2h. The specific power generation was higher in the thin film composite (TFC) membranes compared to the cellulose triacetate (CTA) membranes. The specific power generation for the Oasys membrane... [more]

This paper aims at the optimal designing of a stand-alone microgrid (PV/wind/battery/diesel) system, which can be utilized to meet the demand load requirements of a small residential area in Kasuga City, Fukuoka. The simulation part is developed to estimate the electrical power generated by each component, taking into account the variation of the weather parameters, such as wind, solar irradiation, and ambient temperature. The optimal system design is then based on the Particle Swarm Optimization (PSO) method to find the optimal configuration of the proposed system, using the least-cost perspective approach.

The energy management system is executed in microgrids for optimal integration of distributed energy resources (DERs) into the power distribution grids. To this end, various strategies have been more focused on cost reduction, whereas effectively both economic and technical indices/factors have to be considered simultaneously. Therefore, in this paper, a two-layer optimization model is proposed to minimize the operation costs, voltage fluctuations, and power losses of smart microgrids. In the outer-layer, the size and capacity of DERs including renewable energy sources (RES), electric vehicles (EV) charging stations and energy storage systems (ESS), are obtained simultaneously. The inner-layer corresponds to the scheduled operation of EVs and ESSs using an integrated coordination model (ICM). The ICM is a fuzzy interface that has been adopted to address the multi-objectivity of the cost function developed based on hourly demand response, state of charges of EVs and ESS, and electricity... [more]

Renewable energy sources (RESs) play an indispensable role in sustainable advancement by reducing greenhouse gas (GHG) emissions. Nevertheless, due to the shortcomings of RESs, an energy mix with RESs is required to support the baseload and to avoid the effects of RES variability. Fossil fuel-based thermal generators (FFTGs), like diesel generators, have been used with RESs to support the baseload. However, using FFTGs with RESs is not a good option to reduce GHG emissions. Hence, the small-scale nuclear power plant (NPPs), such as the micro-modular reactor (MMR), have become a modern alternative to FFTGs. In this paper, the authors have investigated five different hybrid energy systems (HES) with combined heat and power (CHP), named ‘conventional small-scale fossil fuel-based thermal energy system,’ ‘small-scale stand-alone RESs-based energy system,’ ‘conventional small-scale fossil fuel-based thermal and RESs-based HES,’ ‘small-scale stand-alone nuclear energy system,’ and ‘nuclear-r... [more]

The article discusses the planning of wind energy development in the West Pomeranian Region after the introduction of the Act "On investments in wind farms" as of 20 May 2016. The purpose of the article is to provide the forecast of the region’s wind energy development in 2019−2030 by taking into account current legal regulations in Poland. The article proposes an original, optimizing multi-criteria wind energy development model for the studied region, exploring various types of technologies that may appear in the system, taking into account recent legal and political changes in the field of renewable energy regulation in Poland. The results of the optimization model show that the currently passed Act "On investments in wind farms" in Poland actually stopped the development of wind energy in the region. On the other hand, in accordance with the objectives of the adopted draft of the Polish energy policy until 2040, it is expected that the share of renewable energy in electricity produc... [more]

In this study, a methodology was suggested for wind and solar energy investment plans through linear optimization model for the countries with an energy-based current deficit problem. The originality of the study is that it is a renewable energy investment model based on the functioning of the balance of payments for current deficit reduction, which has not previously been encountered in the literature. While creating the model, without causing external economic imbalance, certain parameters were taken into consideration such as profit transfers for the foreign direct investments, interest payments for the domestic investments, import rates for the wind and solar energy systems, energy electric power production values, electric power load balance, electricity transmission infrastructure, CO2 emission, future electric power demand projection, and import source rates in the electric power production. It was proven that the model, for the 2019−2030 period in Turkey, not only is an opportu... [more]

Despite the rapid development of photovoltaic (PV) industry, direct current (DC) fault arc remains a major threat to the safety of PV system and personnel. While extensive research on DC fault arc has been conducted, little attention has been paid to the long-time interactions between the PV system and DC arc. In this paper, a simulation system with an arc model and PV system model is built to overcome the inconvenience of the fault-arc experiments and understand the mechanism of these interactions. For this purpose, the characteristics of the series DC arc in a small grid-connected PV system are first investigated under uniform irradiance. Then, by comparing with different arc models, the Habedank model is selected to simulate the fault arc and a method to determine its parameters under DC arc condition is proposed. The trends of simulated arc waveforms are consistent with the measured data, whose fitting degree in adjusted R-squared is between 0.946 and 0.956. Finally, a phenomenon o... [more]

Nowadays, many buildings are equipped with various energy sources. The challenge is how to efficiently utilize their energy production. This includes decreasing the share and costs of external energy—usually electrical energy delivered from the grid. The following study presents a qualitative approach with a combined control to solve the problem. The approach is demonstrated using a simulated residential building equipped with a hybrid energy system: a thermal energy storage combined with an electrical heater, a geothermal heat pump and a solar thermal collector. Consequently, the share of renewable energy was increased and, conversely, costs of the external energy from grid decreased by 12.2%. The results were based on a qualitative approach and the algorithm which predicts the need of energy of the building over the next 6 h with the aid of weather forecasting. This approach included a storage tank of 300 L. The energy costs can be further decreased 7.7% by increasing thermal storage... [more]

Energy access remains a challenge for many countries, as recognized by sustainable development goal 7 of the United Nations Development Programme. Although the Myanmar government has set a target of 100% electrification by 2030, less than half of the households are currently connected to the national grid. To expedite electrification, decentralized approaches should be considered. Mini-grids are an effective alternative that can fill the gap between a solar home system and the national grid; however, many of the existing mini-grids in Myanmar are powered by diesel generators. Diesel fuel is significantly more expensive in rural areas than in urban areas due to high transportation costs. Although mini-grids powered by solar photovoltaics and batteries are cost-competitive with diesel generators, the deployment of renewable energy-based mini-grids is slow. In this study, we analyzed the barriers to mini-grid deployment and prioritized the barriers. We conducted a questionnaire survey wit... [more]

The main problem explored in this study is how Taiwan and other countries meet the challenges of the United Nations Sustainable Development Goals regarding energy transition by using legal instruments or policy bundles. This study adopts textual analysis and legal policy analysis as its main form of research methodology, and the theory of energy justice, as well as principles of energy management, to correlate with the Sustainable Development Goals. Furthermore, this study aims to construct an analysis structure for national energy transition and to analyze the current situation within Taiwan’s electricity sector reforms, while providing evidence of the national experience of electrical industry reforms as an international reference. This study also compares the differences between the seventh Sustainable Development Goal relationship and national energy transitions in Taiwan and Japan, based on the similar initiative of the revised Electricity Act with the policy bundle. This study sp... [more]

The National Center for Atmospheric Research (NCAR) recently updated the comprehensive wind power forecasting system in collaboration with Xcel Energy addressing users’ needs and requirements by enhancing and expanding integration between numerical weather prediction and machine-learning methods. While the original system was designed with the primary focus on day-ahead power prediction in support of power trading, the enhanced system provides short-term forecasting for unit commitment and economic dispatch, uncertainty quantification in wind speed prediction with probabilistic forecasting, and prediction of extreme events such as icing. Furthermore, the empirical power conversion machine-learning algorithms now use a quantile approach to data quality control that has improved the accuracy of the methods. Forecast uncertainty is quantified using an analog ensemble approach. Two methods of providing short-range ramp forecasts are blended: the variational doppler radar analysis system an... [more]

Denmark, Germany, and Finland are countries that have emerged as technology leaders in key renewable energy fields—wind energy, solar power, and bioenergy. In this article, we dig into the policy trajectories of these countries and concentrate particularly on a phenomenon that is common for them all—the long-term commitment to promoting particular renewable energy (RE) technologies. Analyzing commitment, its causes and its consequences, can be considered important, as earlier findings show that long-term, consistent policy signals are a key for policy success. In this article, we point out that this ‘sticking’ to a RE technology has emerged and manifested in multiple ways in the case countries. Examples include relying on existing cultural capacities when navigating energy policy direction, strategically promoting scaling of technology markets to root new energy practices in society and developing energy policies as an extension of existing socio-technical structures. In order to under... [more]

The underground air tunnel system shows promising potentials for reducing energy consumption of buildings and for improving indoor thermal comfort, whereas the existing dynamic models using the computational fluid dynamic (CFD) method show computational complexity and are user-unfriendly for parametrical analysis. In this study, a dynamic numerical model was developed with the on-site experimental calibration. Compared to the traditional CFD method with high computational complexity, the mathematical model on the MATLAB/SIMULINK platform is time-saving in terms of the real-time thermal performance prediction. The experimental validation results indicated that the maximum absolute relative deviation was 3.18% between the model-driven results and the data from the on-site experiments. Parametrical analysis results indicated that, with the increase of the tube length, the outlet temperature decreases with an increase of the cooling capacity whereas the increasing/decreasing magnitude slow... [more]

Studies on the environmental, social, and governance (ESG) index have become increasingly important since the ESG index offers attractive characteristics, such as environmental friendliness. Scholars and institutional investors are evaluating if investment in the ESG index can positively change current portfolios. It is crucial that institutional investors seek related assets to diversify their investments when such investors create funds in the renewable energy sector, which is highly related to environmental issues. The ESG index has proven to be a good investment choice, but we are not aware of its performance when combined with renewable energy securities. To uncover this nature, we investigate the dependence structure of the ESG index and four renewable energy indices with constant and time-varying copula models and evaluate the potential performance of using different ratios of the ESG index in the portfolio. Criteria such as risk-adjusted return, standard deviation, and conditio... [more]

This paper addresses economic aspects of heat savings in the context of strategic heat planning. The analysis uses the city of Aalborg, Denmark, as a case where municipalisation through a recent acquisition of a coal-fired cogeneration of heat and power (CHP) plant has made an update of a municipal strategic energy plan necessary. Combining datasets on buildings and insulation techniques with economic methods, we investigate how the local district heating tariff can be adapted to improve the conditions for heat savings and support the transition to lower supply temperatures in line with the requirements of future fourth generation district heating systems. The paper concludes that implementing a fully variable heat tariff scheme improves the financial incentive for heat savings, while also making the system development less vulnerable to fluctuations and shortages in capital markets. The paper supplements existing literature on heat savings with novelty in its approach and in its syste... [more]

The growing share of renewable energy makes the optimization of power flows in power system models computationally more complicated, due to the widely distributed weather-dependent electricity generation. This article evaluates two methods to reduce the temporal complexity of a power transmission grid model with storage expansion planning. The goal of the reduction techniques is to accelerate the computation of the linear optimal power flow of the grid model. This is achieved by choosing a small number of representative time periods to represent one whole year. To select representative time periods, a hierarchical clustering is used to aggregate either adjacent hours chronologically or independently distributed coupling days into clusters of time series. The aggregation efficiency is evaluated by means of the error of the objective value and the computational time reduction. Further, both the influence of the network size and the efficiency of parallel computation in the optimization p... [more]

Solar heat, already captured by vast asphalt fields in urban areas, is potentially a huge energy resource. The vertical soil temperature profile, i.e., low enthalpy geothermal energy, reveals how efficiently the irradiation is absorbed or radiated back to the atmosphere. Measured solar irradiation, heat flux on the asphalt surface and temperature distribution over a range of depths describe the thermal energy from an asphalt surface down to 10 m depth. In this study, those variables were studied by long-term measurements in an open-air platform in Finland. To compensate the nighttime heat loss, the accumulated heat on the surface should be harvested during the sunny daytime periods. A cumulative heat flux over one year from asphalt to the ground was 70% of the cumulative solar irradiance measured during the same period. However, due to the nighttime heat losses, the net heat flux during 5 day period was only 18% of the irradiance in spring, and was negative during autumn, when the soil... [more]

Planning the operation scheduling with optimization heuristic algorithms allows microgrids to have a convenient tool. The developments done in this study attain this scheduling taking into account the impact of energy storage useful life in the microgrid operation. The scheduling solutions, proposed for the answer of an optimization problem, are obtained by using a metaheuristic algorithm called Differential Evolutionary Particle Swarm Optimization (DEEPSO). Thanks to the optimization that is conducted in this study, it is possible to formulate dispatches of the existent microgrid (MG) by always looking for the ideal dispatch that implies a lower cost and provides a greater viability to any project related to renewable energy, electric vehicles and energy storage. These advances oblige the battery manufacturers to start looking for more powerful batteries, with lower costs and longer useful life. In this way, this paper proposes a scheduling tool considering the energy storage useful l... [more]

Although improving the hydrodynamic performance is a key objective in the design of ocean-powered devices, there are some factors that affect the efficiency of the device during its operation. In this study, the impacts of a wide range of surface roughness as a tribological parameter on stream flow around a hydro turbine and its power loss are studied. A comprehensive program of 3D Computational Fluid Dynamics (CFD) modeling, as well as an expansive range of experiments were carried out on a Darrieus Hydro (DH) turbine in order to measure reduction in hydrodynamic performance due to surface roughness. The results show that surface roughness of turbine blades plays an important role in the hydrodynamics of the flow around the turbine. The surface roughness increases turbulence and decreases the active fluid energy that is required for rotating the turbine, thereby reducing the performance of the turbine. The extent of the negative impact of surface roughness on the drag coefficient, pre... [more]