Increased demand for food production, influenced by the constant growth of population, resulted in the agricultural production systems that are more energy and economy intensive. The aim of this study was to evaluate the energetic and economic efficiency of sugar beet and wheat production. Attention was given to the fertilizer usage and its share in energy consumption since it can amount to 50%. Data show that energy input in wheat production was 5.84 MJ·kg−1 and in sugar beet it was 0.93 MJ·kg−1. The highest share of energy input both in wheat and sugar beet was observed for fertilizers, 52.45% and 46.70%, respectively. Economic analysis has shown that wheat production is a low profitable production with a net return of only 20.69 USD·ha−1, in comparison with sugar beet production with a net return of 513.53 USD·ha−1. Costs related to the fertilizer use prevailed in total variable and total production costs. Economic analysis has also shown that the benefit-to-cost ratio was higher in... [more]

The widespread availability of wind turbine operation data has considerably boosted the research and the applications for wind turbine monitoring. It is well established that a systematic misalignment of the wind turbine nacelle with respect to the wind direction has a remarkable impact in terms of down-performance, because the extracted power is in first approximation proportional to the cosine cube of the yaw angle. Nevertheless, due to the fact that in the wind farm practice the wind field facing the rotor is estimated through anemometers placed behind the rotor, it is challenging to robustly detect systematic yaw errors without the use of additional upwind sensory systems. Nevertheless, this objective is valuable because it involves the use of data that are available to wind farm practitioners at zero cost. On these grounds, the present work is a two-steps test case discussion. At first, a new method for systematic yaw error detection through operation data analysis is presented an... [more]

Underground pumped-storage hydropower (UPSH) is a promising technology to manage the electricity production in flat regions. UPSH plants consist of an underground and surface reservoirs. The energy is stored by pumping water from the underground to the surface reservoir and is produced by discharging water from the surface to the underground reservoir. The underground reservoir can be drilled, but a more efficient alternative, considered here, consists in using an abandoned mine. Given that mines are rarely waterproofed, there are concerns about the consequences (on the efficiency and the environment) of water exchanges between the underground reservoir and the surrounding medium. This work investigates numerically such water exchanges and their consequences. Numerical models are based on a real abandoned mine located in Belgium (Martelange slate mine) that is considered as a potential site to construct an UPSH plant. The model integrates the geometrical complexity of the mine, adopts... [more]

We assemble a multiscale physical model of gas production in a mudrock (shale). We then tested our model on 45 horizontal gas wells in the Barnett with 12−15 years on production. When properly used, our model may enable shale companies to gain operational insights into how to complete a particular well in a particular shale. Macrofractures, microfractures, and nanopores form a multiscale system that controls gas flow in mudrocks. Near a horizontal well, hydraulic fracturing creates fractures at many scales and increases permeability of the source rock. We model the physical properties of the fracture network embedded in the Stimulated Reservoir Volume (SRV) with a fractal of dimension D < 2 . This fracture network interacts with the poorly connected nanopores in the organic matrix that are the source of almost all produced gas. In the practically impermeable mudrock, the known volumes of fracturing water and proppant must create an equal volume of fractures at all scales. The... [more]

Nowadays, research on electric vehicles is increasing because they have the potential to decrease greenhouse-gas emissions dramatically in the transport sector. For these types of vehicles, the battery is one of the main components. The traction system needs a cell series connection to fulfill the energy requirements. Nevertheless, batteries differ from each other due to a normal dispersion in their capacity, internal resistance, and self-discharge rate. This paper presents a novel battery equalizer circuit using an RC-based topology to equalize two adjacent cells of a battery pack. It has the advantage of merging a resistor-based equalizer, a capacitor-based equalizer, and an RC-based equalizer in one circuit. In this way, it is possible to limit the current stress in the components of the circuit. The proposed method increases the equalization time by 35% for a threshold current of 4 A. However, it is possible design the system for another threshold current. Finally, the complexity o... [more]

The frequent outbreak of cyanobacteria bloom results in an urgent need for the resource utilization of cyanobacteria. However, the development of routine thermal treatment (i.e., gasification and pyrolysis) is hindered by the issue of high moisture content. In order to minimize the dewatering requirement, this study investigated the chemical looping co-gasification of the cyanobacteria/coal mixture. The results showed that the residual moisture of cyanobacteria not only could serve as the gasifying agent of coal, but also presented a better gasification effect than the injecting steam. Meanwhile, blending cyanobacteria also improved the performance of coal chemical looping gasification in terms of the syngas quality, gasification rate, and carbon conversion efficiency. Cyanobacteria pyrolysis supplied abundant hydrocarbons and hydrogen-rich gases. The highest syngas yield of 1.26 Nm3/kg was obtained in the mixture fuel of 46 wt.% cyanobacteria and 54 wt.% coal under a 0.3 oxygen carrie... [more]

Renewable energy shares in electricity markets are increasing and therefore also require an increase in flexibility options. Conventional electricity price modelling with optimisation models in thermally dominated markets is not appropriate in markets with high shares of renewable energies and storages because price structures are not adequately represented. Previous research has already identified the impact of uncertainty in renewable energy feed-in on investment and dispatch decisions. However, we are not aware of any work that investigates the influence of uncertainties on price structures by means of optimisation models. Appropriate modelling of electricity price structures is important for investment and policy decisions. We have investigated the influence of uncertainty concerning water inflow by applying a second stage stochastic dual dynamic programming approach in a linear optimisation model using Norway as an example. We found that the influence of uncertainty concerning wat... [more]

Crucial oil reservoirs are located in naturally fractured carbonate formations and are currently reaching a mature phase of production. Hence, a cost-effective enhanced oil recovery (EOR) method is needed to achieve a satisfactory recovery factor. The paper focuses on an experimental investigation of the efficiency of water alternating sour and high-nitrogen (~85% N2) natural gas injection (WAG) in mixed-wetted carbonates that are crucial reservoir rocks for Polish oil fields. The foam-assisted water alternating gas method (FAWAG) was also tested. Both were compared with continuous water injection (CWI) and continuous gas injection (CGI). A series of coreflooding experiments were conducted within reservoir conditions (T = 126 ℃, P = 270 bar) on composite cores, and each consisted of four reservoir dolomite core plugs and was saturated with the original reservoir fluids. In turn, some of the experiments were conducted on artificially fractured cores to evaluate the impact of fractures o... [more]

The traditional security-constrained optimal power flow (SCOPF) model under the classical N-1 criterion is implemented in the power industry to ensure the secure operation of a power system. However, with increasing uncertainties from renewable energy sources (RES) and loads, the existing SCOPF model has difficulty meeting the practical requirements of the industry. This paper proposed a novel chance-constrained preventive SCOPF model that considers the uncertainty of power injections, including RES and load, and contingency probability. The chance constraint is used to constrain the overall line flow within the limits with high probabilistic guarantees and to significantly reduce the constraint scales. The cumulant and Johnson systems were combined to accurately approximate the cumulative distribution functions, which is important in solving chance-constrained optimization problems. The simulation results show that the model proposed in this paper can achieve better performance than t... [more]

This paper analyzes the drivers behind the changes of the Aggregate Carbon Intensity (ACI) of Latin America and the Caribbean (LAC) power sector in five periods between 1990 and 2017. Since 1990 the carbon intensity of the world has been reduced almost 8.8% whereas the carbon intensity of LAC countries only decreased 0.8%. Even though by 2017 the regional carbon intensity is very similar to the one observed by 1990, this index has showed high variability, mainly in the last three years when the ACI of LAC fell from 285 gCO2/kWh in 2015 to 257.7 gCO2/kWh. To understand what happened with the evolution of the carbon intensity in the region, in this paper a Logarithmic Mean Divisia for Index Decomposition Analysis (IDA-LMDI) is carried out to identify the accelerating and attenuating drivers of the ACI behavior along five periods. The proposal outperforms existing studies previously applied to LAC based upon a single period of analysis. Key contributions are introduced by considering the... [more]

Borehole thermal energy storage (BTES) systems facilitate the subsurface seasonal storage of thermal energy on district heating scales. These systems’ performances are strongly dependent on operational conditions like temperature levels or hydraulic circuitry. Preliminary numerical system simulations improve comprehension of the storage performance and its interdependencies with other system components, but require both accurate and computationally efficient models. This study presents a toolbox for the simulation of borehole thermal energy storage systems in Modelica. The storage model is divided into a borehole heat exchanger (BHE), a local, and a global sub-model. For each sub-model, different modeling approaches can be deployed. To assess the overall performance of the model, two studies are carried out: One compares the model results to those of 3D finite element method (FEM) models to investigate the model’s validity over a large range of parameters. In a second study, the accura... [more]

Disproportionation and phase separation are big issues that occur under extreme pressure and temperature conditions during hydrogen compressor cycles, which makes metal hydrides inactive and reduces compression efficiency. It is important to identify boundary conditions to avoid such unwanted phase separation. However, no investigation related to this problem has been carried out so far. Thus we propose a method to investigate the critical temperature and pressure condition for the alloy degradation during the hydrogen compressor cycle. The V20Ti32Cr48 alloy was chosen as a model system for the purpose. The influence of two important parameters (i.e., hydrogen content and temperature) was investigated individually. The disproportionation of V20Ti32Cr48 alloy during the hydrogen compressor cycle test occurred at temperatures higher than 200 °C and 75% H2 content of the total capacity at the initial condition. A clear and obvious boundary condition between disproportionation and keeping... [more]

The bioethanol sector is an extremely complex set of actors, technologies and market structures, influenced simultaneously by different natural, economic, social and political processes. That is why it lends itself to the application of system dynamics modelling. In last five years a relatively high level of experience and knowledge has accumulated related to the application of computer-aided system modelling for the analysis and forecasting of the bioethanol sector. The goal of the current paper is to offer a systematic review of the application of system dynamics models in order to better understand the structure, conduct and performance of the bioethanol sector. Our method has been the preferred reporting items for systematic reviews and meta-analyses (PRISMA), based on English-language materials published between 2015 and 2020. The results highlight that system dynamic models have become more and more complex, but as a consequence of the improvement in information technology and st... [more]

Double-oxide Mn3O4-Co3O4 nanoparticles were synthesized and anchored on multiwalled carbon nanotubes (MWCNTs) via a single-step solvothermal method. The largest specific area (99.82 m2g−1) of the catalyst was confirmed via a nitrogen adsorption isotherm. Furthermore, the uniform coating of the Mn3O4-Co3O4 nanoparticles on the surface of the MWCNTs was observed via scanning electron microscopy and transmission electron microscopy; the uniform coating provided an effective transport pathway during the electrocatalytic activities. The rotating disk electrode and rotating ring disk electrode measurements indicated that the electron transfer number was 3.96 and the evolution of H2O2 was 2%. In addition, the Mn3O4-Co3O4/MWCNT catalyst did not undergo urea poisoning and remained stable in an alkaline solution. Conversely, commercial Pt/C could not withstand urea poisoning for long. The performance cell achieved a power density of 0.4226 mW cm−2 at 50 °C. Therefore, Mn3O4-Co3O4/MWCNT is an eff... [more]

For a wind turbine to extract as much energy as possible from the wind, blade geometry optimization to maximize the aerodynamic performance is important. Blade design optimization includes linearizing the blade chord and twist distribution for practical manufacturing. As blade linearization changes the blade geometry, it also affects the aerodynamic performance and load characteristics of the wind turbine rotor. Therefore, it is necessary to understand the effects of the design parameters used in linearization. In this study, the effects of these parameters on the aerodynamic performance of a wind turbine blade were examined. In addition, an optimization algorithm for linearization and an objective function that applies multiple tip speed ratios to optimize the aerodynamic efficiency were developed. The analysis revealed that increasing the chord length and chord profile slope improves the aerodynamic efficiency at low wind speeds but lowers it at high wind speeds, and that the twist p... [more]

Rapeseed oil press cake (RPC) is an abundantly available and renewable agricultural waste material for the production of fuels or chemicals. In this study, the rates of carbon dioxide gasification of rapeseed oil press cake char were measured by thermogravimetric analysis measurements performed at various temperatures (800−900 °C) and CO2 mole fractions (0.10−1.00). The char was obtained by slow pyrolysis, where the dried RPC was decomposed at a temperature range of 1000 °C to obtain char free of impurities that can affect the measurements. The random pore model appeared to be suitable for describing the effect of conversion on the reaction rate. The temperature, CO2, and concentration dependence of the reaction rate were given by the Arrhenius equation and a power law (nth order) correlation. The kinetic parameters based on the experimental data were determined by a two-step estimation procedure. For the experimental conditions employed in this study, the parameters E and n were 222.1... [more]

In the present experimental study, nucleate pool boiling heat transfer measurements of two high-flux tubes (sample A and sample B) were conducted at atmospheric pressure with HFE-7200 as the working fluid. Both high-flux tubes were made from a sintered Cu-Ni (high-flux) alloy powder. The porous high-flux surface was coated inside the test tube and it is tested within the heat flux ranging from 2.6 to 86 kW/m2. The major difference between sample A and sample B was the coating thickness, where sample B (0.6 mm) was much larger than that of sample A (0.07 mm). Both tubes showed about three times enhancement in heat transfer coefficient (HTC) when compared to plain tube. Even though sample B contained a higher HTC than sample A, it also revealed a faster level-off phenomenon regarding the HTC vs. wall superheat. The major parameter which characterizes the boiling performance of high-flux tube was the ratio of coating thickness to pore diameter which also yielded different trends upon HTC... [more]

A significant amount of conventional power plants in the European power system is anticipated to be replaced by solar and wind power in the future. This may require alternative sources for inertia support. The purpose of the paper is to learn about the consequences on the frequency deviation after a fault in the European power system when more wind and solar are introduced and when wind is considered as a possible provider of inertia. This study quantifies the expected maximum requirement for additional inertia in the future European power system up to 2050. Furthermore, we investigated the possibility of wind power to meet this additional need by providing emulated inertia. The European power system of the EU-28 countries has been clustered to the five synchronous grids, UCTE, Nordic, UK, Baltic and Irish. The future European energy mix is simulated considering twelve different scenarios. Production units are dispatched according to their expected environmental impacts, which closely... [more]

The process of pyrolysis of beet pulp, a by-product after the extraction of raw sugar from sugar beet, with the addition of defecation lime was studied in a thermobalance coupled with a mass spectrometer. The beet pulp pyrolysis process took place completely at 600 °C, and the resulting char, tar and gas were characterized by higher heating values of 23.9, 21.6 and 7.77 MJ/kg, respectively. The addition of the defecation lime to beet pulp caused both an increase in the char production yield and a decrease in the tar production yield. At the same time, the higher heating value of char and tar decreased along with the increase of defecation lime added to the sample. The deconvolution of derivative thermogravimetric (DTG) curves allowed us to identify the basic components of beet pulp, for which the activation energy by isoconversion method was calculated. The 20 wt.% addition of defecation lime caused an increase of the activation energy by about 18%. Further increase in the defecation l... [more]

The complexity of a smart grid with a high share of renewable energy resources introduces several issues in testing power equipment and controls. In this context, real-time simulation and Hardware in the Loop (HIL) techniques can tackle these problems that are typical for power system testing. However, implementing a convoluted HIL setup in a single infrastructure can be physically impossible or can increase the time required to test a smart grid application in detail. This paper introduces the Joint Test Facility for Smart Energy Networks with Distributed Energy Resources (JaNDER) that allows users to exchange data in real-time between two or more infrastructures. This tool enables the integration of infrastructures, exploiting the synergies between them, and creating a virtual infrastructure that can perform more experiments using a combination of the resources installed in each infrastructure. In particular, JaNDER can extend a HIL setup. In order to validate this new testing concep... [more]

The durability and performance of electrochemical energy converters, such as fuel cells and electrolysers, are not only dependent on the properties and the quality of the used materials. They strongly depend on the operational conditions. Variations in external parameters, such as flow, pressure, temperature and, obviously, load, can lead to significant local changes in current density, even local transients. Segmented cell technology was developed with the purpose to gain insight into the local operational conditions in electrochemical cells during operation. The operando measurement of the local current density and temperature distribution allows effective improvement of operation conditions, mitigation of potentially critical events and assessment of the performance of new materials. The segmented cell, which can replace a regular bipolar plate in the current state of the technology, can be used as a monitoring tool and for targeted developments. This article gives an overview of th... [more]

Wind power variations at two heights (the surface level and turbine hub level) were investigated at 20 locations in the shelf seas of India using hourly fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalyses of the global climate (ERA5) data covering the last 40 years (1979 to 2018). The interannual and seasonal variability in wind power was studied. The wind power density, the exceedance probability of power density and the exploitable wind resources were examined. In the Indian shelf seas, the annual mean wind power density at 10 m above mean sea level varies from 82 to 353 W/m2. Wind power density at 110.8 m is 20% to 40% higher than at 10 m above mean sea level. The study shows that the shelf seas have an abundance of wind power, with wind speeds over 3 m/s during 90% of the time at locations 1 to 3, 12 and 13, with a high occurrence of exploitable wind energy above 0.7 × 103 kWh/m2. Among the locations studied, the most power-rich area w... [more]

Electric vehicles (EVs) are being increasingly adopted because of global concerns about petroleum dependence and greenhouse gas emissions. However, their limited driving range results in increased charging demands with a stochastic characteristic in real-world situations, and the charging demands should be attributed toward charging stations in time-varying road networks. To this end, this study proposes guidance strategies to provide efficient choice for charging stations and corresponding routes, and it includes the time-varying characteristic of road networks in problem formulation. Specifically, we propose two route guidance strategies from different perspectives based on the charging demand information. The first strategy focuses on the effects of the number of EVs on the charging stations’ operation, and the reachable charging stations with the fewest vehicles are selected as the heuristic suggested ones. The other strategy considers the travel cost of individual drivers and sele... [more]

Further increases in the number of photovoltaic installations in industry and residential buildings will require technologically and economically flexible energy storage solutions. Some countries utilize net-metering strategies, which use national networks as “virtual batteries.” Despite the financial attractiveness, net-metering faces many technological and economical challenges. It could also lead to the negative tendencies in prosumer behavior, such as a decrease in motivation for the self-consumption of photovoltaic (PV)-generated electricity. Batteries, which are installed on the prosumer’s premises, could be a solution in a particular case. However, the price for battery-based storage solutions is currently sufficiently unattractive for the average prosumer. This paper aimed to present a comparison of the economic and energy related aspects between net-metering and batteries for a single case study by considering the Lithuanian context. The net present value, degree of self-suffi... [more]

The article examines the introduction of solar-combi systems in large-size sports facilities. The examined solar-combi systems consist of solar collectors, a biomass heater and thermal storage tanks. In a sense, they constitute hybrid thermal power plants. The full mathematical background is presented on the operation of such systems, along with a proposed operation algorithm, aiming at the maximization of the captured solar radiation. A case study is implemented for the coverage of the thermal energy needs for hot water production and swimming pools heating, met in the Pancretan Stadium, Crete, Greece. In this way, the article aims to indicate the technical and economic prerequisites that can guarantee the feasibility of the examined systems, highlighting the significant potential contribution of such systems towards the realization of energy transition plans from fossil fuels to renewables. The economic feasibility of the introduced system is based on the avoiding diesel oil and elec... [more]