This study evaluated the energy saving potential of renewable energy generation systems based on integrated solar energy in an urban environment. The solar city concept was implemented using photovoltaic (PV) and solar thermal systems. As a case study, the Sejong national pilot smart city in South Korea was selected to evaluate the renewable energy penetration rate. For evaluating the proposed renewable energy systems, the electrical and thermal loads of the smart city were estimated using field measurement data. Then, the renewable energy penetration rate of the city was evaluated. The HomerPro software was used to analyze the PV generation and operating energy consumption of the natural gas (NG) generator with a district heating network. The thermal load-supporting potential of the solar thermal system was estimated using the TRNSYS software. The results showed that the proposed urban integrated renewable energy system could meet over 30% of the renewable energy penetration rate and... [more]

Photovoltaic (PV) generation is potentially uncertain. Probabilistic PV generation forecasting methods have been proposed with prediction intervals (PIs) to evaluate the uncertainty quantitively. However, few studies have applied PIs to geographically distributed PVs in a specific area. In this study, a two-step probabilistic forecast scheme is proposed for geographically distributed PV generation forecasting. Each step of the proposed scheme adopts ensemble forecasting based on three different machine-learning methods. When individual PV generation is forecasted, the proposed scheme utilizes surrounding PVs’ past data to train the ensemble forecasting model. In this case study, the proposed scheme was compared with conventional non-multistep forecasting. The proposed scheme improved the reliability of the PIs and deterministic PV forecasting results through 30 days of continuous operation with real data in Japan.

Due to the significant reduction in water droplet size caused by the strong air-water interaction in the spray nozzle, air-mist spray is one of the promising technologies for achieving high-rate heat transfer. This study numerically analyzed air-mist spray produced by a flat-fan atomizer using three-dimensional computational fluid dynamics simulations, and a multivariable linear regression was used to develop a correlation to predict the heat transfer coefficient using the casting operating conditions such as air-pressure, water flow rate, casting speed, and standoff distance. A four-step simulation approach was used to simulate the air-mist spray cooling capturing the turbulence and mixing of the two fluids in the nozzle, droplet formation, droplet transport and impingement heat transfer. Validations were made on the droplet size and on the VOF-DPM model which were in good agreement with experimental results. A 33% increase in air pressure increases the lumped HTC by 3.09 ± 2.07% depe... [more]

The transformation of the energy sector towards an increased share of renewable energy sources in the energy mix requires attention in the area of electricity storage. Renewable energy sources (photovoltaics or wind energy) are marked by the intermittency of electricity production and require the construction of energy storage to adapt the energy supply to the demand, providing greater stability. The authors focused on verifying the solution of gravitational energy storage in existing shafts of hard coal mines in Poland. The issue is significant for Poland, as a country with an extensive mining infrastructure, which is searching for new scientific and practical solutions to utilize disused mining shafts for new purposes. In the analysis, the focus was on one shaft located within the Upper Silesian Coal Basin (Górnośląskie Zagłębie Węglowe), maintained for the drainage of the neighboring deposit. The article presents the calculation of energy that can be stored and an analysis of the ef... [more]

Microalgae are considered to be potentially attractive feedstocks for biodiesel production, mainly due to their fast growth rate and high oil content accumulated in their cells. In this study, the suitability for biofuel production was tested for Chlorella vulgaris, Chlorella fusca, Oocystis submarina, and Monoraphidium strain. The effect of nutrient limitation on microalgae biomass growth, lipid accumulation, ash content, fatty acid profile, and selected physico-chemical parameters of algal biodiesel were analysed. The study was carried out in vertical tubular photobioreactors of 100 L capacity. The highest biomass content at 100% medium dose was found for Monoraphidium 525 ± 29 mg·L−1. A 50% reduction of nutrients in the culture medium decreased the biomass content by 23% for O. submarina, 19% for Monoraphidium, 13% for C. vulgaris and 9% for C. fusca strain. Nutrient limitation increased lipid production and reduced ash content in microalgal cells. The highest values were observed f... [more]

In the process of the electrification of the vehicle industry, an important issue is to adapt production to new technological solutions and to achieve a break-even point in the production costs of an electric vehicle in the short term compared to its traditional counterparts. By the end of 2020, 10 million electric cars were sold worldwide. In today’s globalized and crisis market realities, it is very difficult for state authorities to build a competitive advantage. Based on the concept of M.E. Porter, generating competitiveness does not take place at the macroeconomic, but at the mezzoeconomic level. The key purposes of this review paper are threefold: firstly, to identify the infrastructure for the production of electric cars (market size, resources) in some major Asian countries, including Indonesia; secondly, to identify the importance of FDI for Indonesia and the essence of their relations with China, and thirdly, to investigate whether Indonesia is able to build a competitive adv... [more]

In a sudden load increasing process (SLIP), the hydroelectric generating system (HGS) experiences a severe vibration response due to the sudden change of the hydraulic-mechanical-electric parameters (HMEPs). The instability of HGS limits the ability of sudden load increase, and its flexibility and reliability are reduced. Thus, in this study, a new transient nonlinear coupling model of HGS is proposed, which couples the hydro-turbine governing system (HTGS) and the hydro-turbine generator shafting system (HGSS) with the hydraulic-mechanical-electric coupling force, rotating speed, flow rate, hydro-turbine torque, electromagnetic torque, and guide vane opening. By using numerical simulation, the influences of different HMEPs on the vibration characteristics of HGS in SLIP are analyzed. The result shows that, compared with stable operating conditions, the vibration amplitude of HGS increases sharply in SLIP. The increase of the sudden load increasing amount, blade exit flow angle, mass e... [more]

The utilization of air conditioning in public and private buildings is continuously increasing globally and is one of the major factors fueling the growth of the global electricity demand. The higher utilization of renewable energy sources and the transition of the electricity-generating industry to renewable energy sources requires significant energy storage in order to avoid supply−demand mismatches. This storage-regeneration process entails dissipation, which leads to higher energy generation loads. Both the energy generation and the required storage may be reduced using thermal energy storage to provide domestic comfort in buildings. The development and utilization of thermal storage, achieved by chilled water, in a community of two thousand buildings located in the North Texas region are proven to have profound and beneficial effects on the necessary infrastructure to make this community independent of the grid and self-sufficient with renewable energy. The simulations show that b... [more]

Considering loads when optimizing wind-farm layouts or designing farm-control strategies is important, but the computational cost of using high-fidelity wake models in the loop can be prohibitively high. Using simpler models that consider only the spatial variation of turbulence statistics is a tempting alternative, but the accuracy of these models with respect to the aeroelastic response is not well understood. This paper therefore highlights the effect of replacing wake meandering with spatially varying statistics (“profile functions”) in the inflow to a downstream turbine. Profile functions at different downstream and lateral locations are extracted from a large-eddy simulation with an upstream turbine and compared with two lower-fidelity models: one that prescribes both the mean and standard deviation of the turbulence and one that prescribes only the mean. The aeroelastic response of an NREL 5 MW wind turbine is simulated with the three different wake-model fidelities, and various... [more]

To expand the airfoil database and realize the reverse digital airfoil design, this paper proposes a new sectional expression function of wind turbine airfoil based on the Joukowski transformation and derives the function equation for the novel airfoil. Compared with the existing airfoil function, the new airfoil function can adjust the parameter values to control the relative thickness, relative thickness position, relative camber, and relative camber position of the airfoil. Taking the common airfoil (NACA63-212) as an example, the existing airfoil is fitted according to the expected direction. The maximum fitting deviation is 1.22135×10-3, better than the four existing methods for airfoil shape fitting, which demonstrates well the practicability and accuracy of this method. It also shows that changing the parameter values can generate a new airfoil to enrich the airfoil database. Therefore, the proposed method broadens the ideas for airfoil design and method research.

This article has been developed to assess the economic feasibility of a rooftop photovoltaic installation of industrial self-consumption. Numerical models that enable an interested person to obtain the main expected parameters will be generated, with those models being the article’s main contribution to the field. To do this, a calculation methodology will be developed through which the reader, knowing the location of the facility and dimensions of the roof, will be able to calculate the maximum installable power, the main parameters related to production, the cost of the installation, and the LCOE of the plant. The use of actual costs will be facilitated in case they are known. Still, it will remain possible to apply the major equipment costs (modules, inverter, and structure) considered throughout the article. This developed calculation methodology will also allow a quick comparison of the forecasts of production, CAPEX, and LCOE of plants designed with different inclinations and dif... [more]

Ammonia is gaining popularity around the world due to its advantages as an energy vector over other zero-carbon fuels and has the potential to be a key component for deep decarbonisation of energy systems. However, little is known about public attitudes and concerns about the technology, one of the factors that will determine its successful implementation. This research examined public perception of green ammonia technologies through online surveys conducted in Mexico (n = 563) and the UK (n = 357). The results suggest that most of the participants in the two countries support the development of these technologies, with men being more likely to show support than women. Participants in Mexico and the UK had both negative and neutral associations of ammonia as a chemical, but overall perceptions of green ammonia were surprisingly positive. A multiple regression analysis indicates that support for this technology is highly dependent on the way participants perceive the benefits and the ri... [more]

Connections to world markets facilitate local markets developments to support more efficient capital allocation and greater investment and growth opportunities. Under the framework of cross-market rebalancing theory, in this study, we aim to systematically examine the market connections among world financial, energy, renewable energy and European carbon markets by measuring the return spillovers from 2008 to 2021. We find that the renewable energy market is more closely connected to the world financial and energy markets in the sense of the return transmission, while the carbon market is less connected to them. However, due to improved market regulations and determinations related to fighting climate change, the connections between the carbon market and other markets have gradually intensified. Plotting the return spillover indexes, we observe that strong return spillovers from the renewable energy market to other markets occurred when large investment plans were announced. Regarding t... [more]

Efficient and flexible operation is essential for competitiveness in the energy market. However, the CO2 emissions of conventional power plants have become an increasingly significant environmental dilemma. In this study, the optimization of a steam power process of an IGCC was carried out, which improved the overall performance of the plant. CCPP with a subcritical HRSG was modelled using EBSILON Professional. The numerical results of the model were validated by measurements for three different load cases (100, 80, and 60%). The results are in agreement with the measured data, with deviations of less than 5% for each case. Based on the model validation, the model was modified for the use of syngas as feed and the integration of heat into an IGCC process. The integration was optimized with respect to the performance of the CCPP by varying the extraction points, adjusting the steam parameters of the extractions and modifying the steam cycle. For the 100% load case, a steam turbine power... [more]

The paper presents the results of experimental research on pool boiling heat transfer of dielectric liquid FC-72. Measurements were made at atmospheric pressure on open surfaces with microchannels. Heat transfer surfaces, in the form of parallel milled microchannels, were made of copper. The rectangular cross-sectional microchannels were 0.2 to 0.5 mm deep and 0.2 to 0.4 mm wide. The surfaces, compared to a smooth flat surface, provided a five-fold increase in the heat transfer coefficient and a two-fold increase in the critical heat flux. The article analyses the influence of the width and height of the microchannel on the heat transfer process. The maximum heat flux was 271.7 kW/m2, and the highest heat transfer coefficient obtained was 25 kW/m2K. Furthermore, the experimental results were compared with selected correlations for the nucleate pool boiling.

This article discusses the atomization of composite liquid fuels. A large group of injectors is considered. A comparative analysis of the atomization characteristics (droplet sizes and velocities, jet opening angles) and the influence of the fuel characteristics (density, viscosity, component composition) and the process parameters (the ratio of the fuel−air mass flow rates, the features of the jet formation) has been carried out. Finally, the most effective types of injectors, which provide for the necessary characteristics of fuel atomization for its combustion, have been determined. The most favorable conditions for the applicability of each type of atomization have been formulated. Possible mechanisms of secondary fragmentation of droplets of composite fuels have been analyzed: those resulting from mutual collisions of droplets in the flux and from the interaction with a solid surface as well as those resulting from thermal overheating in the presence of a phase boundary or a large... [more]

One of the key aspects of vehicle-to-grid technology (V2G) is the analysis of uncertainty in electric vehicle user behavior. Correct estimation of the amount of available energy from electric vehicles that are expected to provide ancillary services to the electricity system operator or to secure the end user’s demand is essential to design these services in an appropriate way. Therefore, it is necessary to analyze the probabilities of V2G service performance for different scenarios. This paper presents the author’s approach to determining the values of V2G service provision probabilities using survey data. It was found that estimating these values using simulation and forecasting tools makes sense when the coefficients resulting from survey responses are used as initial data. Thus, the paper also presents the results of the surveys that were conducted. As the results from the simulations show, the values of the probabilities of V2G services are not high, which should induce future oper... [more]

Concerning the problem of wanting the performance of heat engines used in the automotive, aeronautics, and aerospace industries, researchers and engineers are working on various possibilities for improving combustion efficiency, including the reduction of gases such as CO, NOx, and SOx. Such improvements would also help reduce greenhouse gases. For this, research and development has focused on one factor that has a significant impact on the performance of these engines: the phenomenon of cavitation. In fact, most high-performance heat engines are fitted with a high-speed fuel supply system. These high speeds lead to the formation of the phenomenon of cavitation generating instabilities in the flow and subsequently causing disturbances in the combustion process and in the efficiency of the engine. In this review article, it is a question of making a state-of-the-art review on the various studies which have dealt with the characterization of the phenomenon of cavitation and addressing th... [more]

It is well known that the output power from small wind turbines (SWTs) fluctuates noticeably more when compared to that from other types of dispersed generators, such as residential photovoltaic (PV) power generation systems. Thus, the degradation of voltage quality, such as flicker emissions, when numerous SWTs are installed in a low-voltage distribution system is a particular concern. Nevertheless, practical examples of flicker emissions from small wind power facilities have not been made public. This paper aims to clarify the characteristics of flicker emissions by SWTs and their severity. The measurement results at the two selected sites indicate that the flicker emissions solely caused by variable-speed SWTs with a total power rating of ~20 kW are notably lower than the upper limit, and they are at their highest when the mean total output power is approximately 3/4 of the total power rating of small wind power facilities.

The massive expansion of Distributed Energy Resources and schedulable loads have forced a variation of generation, transmission, and final usage of electricity towards the paradigm of Smart Communities microgrids and of Renewable Energy Communities. In the paper, the use of multiple DC microgrids for residential applications, i.e., the nanogrids, in order to compose and create a renewable energy community, is hypothesized. The DC Bus Signaling distributed control strategy for the power management of each individual nanogrid is applied to satisfy the power flow requests sent from an aggregator. It is important to underline that this is an adaptive control strategy, i.e., it is used when the nanogrid provides a service to the aggregator and when not. In addition, the value of the DC bus voltage of each nanogrid is communicated to the aggregator. In this way, the aggregator is aware of the regulation capacity that each nanogrid can provide and which flexible resources are used to provide... [more]

The aim of this study is to verify the reliability of NOx emissions measured using Smart Emissions Measurement System (SEMS) equipment in comparison with the NOx emissions measured using certified Portable Emissions Measurement System (PEMS) equipment. The SEMS equipment is simple system, and it is less expensive than the PEMS equipment, as it comprises an On-Board Diagnostics (OBD) signal from the test vehicle and a NOx sensor. The SEMS equipment based on low-cost sensors has an advantage of building big data, but there are insufficient previous studies comparing of NOx emissions with certified the PEMS equipment. Therefore, this study is important in verifying the suitability of the SEMS equipment by comparing the NOx emissions measured by the various test modes and RDE using the two types of equipment. To analyze the correlation between the PEMS and SEMS equipment, the advanced diesel vehicle was equipped with the two types of equipment to simultaneously measure NOx emissions. After... [more]

As the wind power market grows rapidly, the importance of technology for real-time monitoring and diagnosis of wind turbines is increasing. However, most of the developed technologies and research mainly focus on large horizontal-axis wind turbines, and research conducted on small- and medium-sized wind turbines is rare. In this study, a novel low-cost and real-time health monitoring and diagnosis system for the small H-type Darrieus vertical axis wind turbine is proposed. Turbine operating conditions were classified into parked/idle and power production. In the case of the power production condition, abnormality diagnosis was performed using key monitoring parameters, including vibration, fundamental frequency, the bending stress of the tower and generator vibration. The turbine abnormalities were diagnosed in two stages by applying the alert and alarm limits, determined by referring to international standards and material properties and the long-term measurement data together.

Plastics are one of the basic construction materials with a wide range of various applications. One of their disadvantages is the problem of managing the waste they generate. Chemical recycling offers the possibility of liquefying polymeric waste and using it as fuel components. Existing technologies giving good quality products are expensive. The HT technology developed and described by the authors is cheaper and enables a high quality product to be obtained. The authors have shown that the quality of the received fuel components is influenced not only by the polymer waste processing technology, but also by the feedstock composition. The presented thermolysis technology not only enables more advanced recycling, but also gives the possibility of partial improvement of the product quality. A product with the best physico-chemical properties was obtained from a blend of PE:PP:PS used in the ratio 60:30:10. It was proved that diesel and petrol blends composed of a 5% v/v share of petrol a... [more]

Due to the constant trend of building wind turbine sets and photovoltaic cells, the so-called renewable energy sources, it is important to develop a mathematical model that will allow us to analyse the economic viability of their operation. By using this model, multivariate calculations should be carried out and developed in the form of universal nomograms that will allow us to estimate this viability almost on an immediate basis. In this paper, such a model for the unit cost of electricity production from renewable energy sources is presented. It is based on a continuous-time Net Present Value notation. The multi-variant calculations performed with it take into account different subsidy levels and operating time of the renewable energy sources. The paper presents values of unit costs of electricity production from renewable energy sources and values of maximum subsidies for this production. It turns out that subsidies are necessary for renewable energy sources to exist on the energy m... [more]

In alcohol distilleries, the amount of distillery stillage generated can be up to 15 times larger than the amount of alcohol produced. The stillage has high concentrations of organics and nitrogen, a low pH, and a dark brown color. Currently, stillage is mainly used for soil fertilization. For this purpose, it requires thickening and is used seasonally, which creates storage problems and transport costs. To reduce environmental pollution, physicochemical and biological processes have been employed for the treatment of distillery stillage. However, according to bioeconomy principles, the stillage should be transformed into value-added products. Therefore, this review paper focuses on methods of stillage processing that enable energy recovery. Due to its high content of organic compounds, stillage is often used as a raw material for biogas production. Accordingly, anaerobic digestion of stillage is discussed, including an overview of the bioreactors used and the effects of operational pa... [more]