Surface lignite mines of the Balkan Peninsula face growing pressure due to the CO2 emissions reduction initiatives, rapidly increasing renewable-power capacity, and cheap natural gas. In this frame, the development of a modern mine land rehabilitation strategy is considered as a prerequisite for mitigating the social and economic impacts for the local communities. In the case of western Macedonia lignite mines, these prospects are investigated based on a PEST (political, economic, social, technological) analysis of seven alternative land uses. Urban (industrial) development, green houses, and industrial heritage parks are considered as the most appropriate land uses for mitigating the socioeconomic impacts due to the loss of employments. For the land uses occupying large areas (i.e., agriculture, forestry, livestock farming, and photovoltaic parks), an optimisation algorithm is proposed for determining the mix of land uses that maximise revenue, equity, and natural conservation and min... [more]

An experimental study has been conducted to provide a characterization of the transformations that particle size distributions and the number density of soot particles can encounter along the exhaust line of a modern EURO VI compliant heavy-duty engine, fueled with compressed natural gas. Being aware of the particles history in the exhausts can be of utmost importance to understand soot formation and oxidation dynamics, so that, new strategies for further reducing these emissions can be formulated and present and future regulations met. To this purpose, particle samples were collected from several points along the exhaust pipe, namely upstream and downstream of each device the exhaust gases interact with. The engine was turbocharged and equipped with a two-stage after-treatment system. The measurements were carried out in steady conditions while the engine operated in stoichiometric conditions. Particle emissions were measured using a fast-response particle size spectrometer (DMS500) s... [more]

The worldwide investment in renewable energy sources is leading to the formation of local energy communities in which users can trade electric energy locally. Regulations and the required enablers for effective transactions in this new context are currently being designed. Hence, the development of software tools to support local transactions is still at an early stage and faces the challenge of constant updates to the data models and business rules. The present paper proposes a novel approach for the development of software tools to solve auction-based local electricity markets, considering the special needs of local energy communities. The proposed approach considers constrained bids that can increase the effectiveness of distributed generation use. The proposed method takes advantage of semantic web technologies, in order to provide models with the required dynamism to overcome the issues related to the constant changes in data and business models. Using such techniques allows the s... [more]

In this study, a new multi-use offshore tension leg platform (TLP) was designed for wave energy production through an embedded wave energy converter (EWEC) system. The proposed EWEC system consists of four built-in tuned liquid column dampers for absorbing the hull motion energy and eight Wells turbines as the power take-off devices. A multifold nonlinear analytical model of this multibody system was developed considering the hydrodynamics of the TLP-EWEC system during large motions and the aerohydrodynamics of the chamber-turbine groups. A comprehensive assessment, including an evaluation of motion responses and preliminary generating capacity, was performed for different wave-load directions using the numerical time integration method. The results indicated that the multi-use platform can generate a considerable amount of turbine power for the offshore platform energy mix as well as serve for offshore oil and gas production in the target oil fields. Such additional benefits and profi... [more]

The main objective of the present work is to provide a comprehensive picture of the wind conditions in the Spanish continental nearshore considering a state-of-the-art wind dataset. In order to do this, the ERA5 wind data, covering the 20-year time interval from 1999 to 2018, was processed and evaluated. ERA stands for ’ECMWF Re-Analysis’ and refers to a series of research projects at ECMWF (European Centre for Medium-Range Weather Forecasts) which produced various datasets. In addition to the analysis of the wind resources (reported for a 100 m height), the performances of several wind turbines, ranging from 3 to 9.5 MW, were evaluated. From the analysis of the spatial maps it was observed that the Northern part of this region presents significant wind resources, the mean wind speed values exceeding 9 m/s in some locations. On the other hand, in regard to the Southern sector, more energetic conditions are visible close to the Strait of Gibraltar and to the Gulf of Lion. Nevertheless,... [more]

Environmental issues are nowadays of great importance. In particular air and water quality should be kept at as high levels as possible. Energy conversion systems and devices which are applied for converting the chemical energy contained in different fuels into heat, electricity and cold in the industry and housing are sources of different gases and solid particle emissions. Medical data show PM2.5 dust in particular is highly dangerous for human health. Therefore, limiting the number of low-quality fuel combustion processes is a key issue of modern energy policy. Statistical data show that domestic heating systems account for a large share of the total emissions of PM2.5 and PM10 dust. For example in Poland in 2017, the share of households in the total annual emissions of PM2.5 dust was equal to ca. 35.8%, while the share of PM2.5 emission in industry (i.e., power generating plants, industrial power plants and technologies) was equal to only 23.6%. A possible way of solving this probl... [more]

A RhxSy/C catalyst with high mass-specific electrochemical surface area (ECSA/mass), high hydrogen oxidation reaction (HOR)/hydrogen evolution reaction (HER) activity, and high Nafion® ionomer-affinity was synthesized and evaluated. A new sulfur source, Na2S instead of (NH4)2S2O3, was applied to prepare the rhodium sulfide precursor Rh2S3 that resulted in a RhxSy catalyst with higher HOR/HER catalytic activity after thermal treatment. The higher activity was attributed to the higher quantity formation of the more active phase Rh3S4, in addition to the other active Rh17S15 phase, in the RhxSy catalyst. Using this new sulfur source, carbon substrate functionalization, and the mass-transfer-controlled nanoparticle growth process, the average particle size of this catalyst was reduced from 13.5 nm to 3.2 nm, and its ECSA/mass was increased from 9.3 m2/g-Rh to 43.0 m2/g-Rh. Finally, by applying the Baeyer−Villiger and ester hydrolysis process to convert the Nafion® ionomer-unfriendly ketone... [more]

To address the large temperature difference in the air heater (AH) inlet of a traditional exhaust heat utilization system and energy grade mismatch problems during the heat and mass transfer processes, this study proposed a new multi-level waste heat cascade utilization system. Based on a principle of “temperature-to-port and cascade utilization”, this system uses the boiler side high-temperature flue gas and low-temperature air, and the turbine side high-temperature feed water and low-temperature condensate water, to conduct cross heat exchange according to the energy grade matching principle. Combined with a typical 1000 MW coal-fired unit, the heat transfer characteristics and energy-saving benefits of the new system were analyzed. The results showed that the new system has excellent performance: the heat rate decreased by 91 kJ/kWh, coal consumption decreased by 3.3 g/kWh, and power generation efficiency increased to 49.39%.

The presence and evolution of static power converters in electric grids are growing on a daily basis. Starting from the most used voltage source converter (VSC), passing through the use of multilevel converters, the most recent configuration is the so-called modular multilevel converter (MMC). Because of its intrinsic advantages, it is used not only in high-voltage systems but also in low- and medium-voltage ones to interface renewable energy sources such as photovoltaic (PV) panels. Several configurations and maximum power point tracker (MPPT) algorithms have been proposed and analyzed for MMC-PV-based systems. However, when using distributed MPPTs, partial shading conditions cause a problem. The PV panel can be directly connected to the MMC using its dc link or submodule. Based on this configuration, this paper proposes a novel control strategy that tracks both the ac grid current and ac circulating current for a single-phase low-voltage system to obtain the maximum power under any i... [more]

A novel analytical method was developed for analysis of efficiency at maximum power of a hybrid cycle combining electrochemical and Otto engines. The analysis is based on the low-dissipation model, which relates energy dissipation with energy transfer rate. Efficiency at maximum power of a hybrid engine operating between two reservoirs of chemical potentials is evaluated. The engine is composed of an electrochemical device that transforms chemical potential to electrical work of an Otto engine that uses the heat generated in the electrochemical device and its exhaust effluent for mechanical work production. The results show that efficiency at maximum power of the hybrid cycle is identical to the efficiency at maximum power of an electrochemical engine alone; however, the power is the product of the electrochemical engine power and the compression ratio of the Otto engine. Partial mass transition by the electrochemical device from the high to the low chemical potential is also examined.... [more]

We analyze energy use efficiency of manufacturing industries in US manufacturing over five decades from 1960 to 2011. We apply a 4-component stochastic frontier model, which allows disentangling efficiency into a short- and long-term efficiency as well as accounting for industry heterogeneity. The data come from NBER-CES Manufacturing Industry Database. We find that relative to decade-specific frontiers, the overall efficiency of manufacturing industries, which is a product of transient and persistent efficiencies has deteriorated greatly in the 1970s and rebounded only in the 2000s. The industries are very efficient in the short-term and this has not changed over five decades. The high level of overall inefficiency is almost completely due to the structural inefficiency which can be explained by what is referred to as the “energy paradox”. Finally, higher energy-intensive industries perform worse in terms of energy use efficiency than their low energy-intensity counterparts.

Biomass is the fourth largest energy source in the world; it is easy to store and can be converted into various kinds of renewable energies. The biomass cogeneration system is an important way to utilize biomass energy, especially in northern China. At present, there are many problems in biomass power plants in China, such as high latent heat loss of chimney and cooling towers, low power generation efficiency, and thermal efficiency. In order to solve this problem, this paper introduces low vacuum circulating water heating technology in the biomass cogeneration system, and expounds the differences between China and Western countries in biomass power plants. Based on this background, the technology is redesigned and reformed to make it more suitable for the biomass fuel varieties in the power plant location, and realize the localization of technology and the expansion of scale. The application of this improved technology in China’s biomass cogeneration project is analyzed. Based on the... [more]

Device engineering with proper material integration into perovskite solar cells (PSCs) would extend their durability provided a special care is spent to retain interface integrity during use. In this paper, we propose a method to preserve the perovskite (PSK) surface from solvent-mediated modification and damage that can occur during the deposition of a top contact and furtherly during operation. Our scheme used a hole transporting layer-free top-contact made of Carbon (mostly graphite) to the side of hole extraction. We demonstrated that the PSK/graphite interface benefits from applying a vacuum-curing step after contact deposition that allowed mitigating the loss in efficiency of the solar devices, as well as a full recovery of the electrical performances after device storage in dry nitrogen and dark conditions. The device durability compared to reference devices was tested over 90 days. Conductive atomic force microscopy (CAFM) disclosed an improved surface capability to hole exchan... [more]

The profitability of domestic battery energy storage systems has been poor and this is the main barrier to their general use. It is possible to increase profitability by using multiple control targets. Market price-based electricity contracts and power-based distribution tariffs alongside storage of surplus photovoltaic energy make it possible to have multiple control targets in domestic use. The battery control system needs accurate load forecasting so that its capacity can be utilized in an optimally economical way. This study shows how the accuracy of short-term load forecasting affects cost savings by using batteries. The study was conducted by simulating actual customers’ load profiles with batteries utilized for different control targets. The results of the study show that knowledge of customers’ load profiles (i.e., when high and low peaks happen) is more important that actual forecast accuracy, as measured by error criteria. In many cases, the load forecast based on customers’... [more]

Crop yields are important items in the economic performance and the environmental impacts of second-generation biofuels. Since they strongly depend on crop management and pedoclimatic conditions, it is important to compare candidate feedstocks to select the most appropriate crops in a given context. Agro-ecosystem models offer a prime route to benchmark crops, but have been little tested from this perspective thus far. Here, we tested whether an agro-ecosystem model (CERES-EGC) was specific enough to capture the differences between miscanthus and switchgrass in northern Europe. The model was compared to field observations obtained in seven long-term trials in France and the UK, involving different fertilizer input rates and harvesting dates. At the calibration site (Estrées-Mons), the mean deviations between simulated and observed crop biomass yields for miscanthus varied between −0.3 t DM ha−1 and 4.2 t DM ha−1. For switchgrass, simulated yields were within 1.0 t DM ha−1 of the experi... [more]

In this work, the analysis of a hybrid LiBr/H2O absorption-cooling and flash-desalination system, using solar thermal energy as heat source, is presented. An absorption open-cycle with three pressure levels is used in combination with a single-stage flash-desalination process to use the coolant as product water, resulting in an increase in cooling and desalination efficiency. For the application, a 20-room coastal hotel complex in San Felipe, Baja California, Mexico, is taken as a case study and the sizing of the solar collection and storage system is carried out for the operation of the proposed hybrid system, during the summer operative period. The operational dynamics during the week with the highest ambient temperatures are presented. The dimensioning of the solar collector’s area and the energy storage resulted in a collection area of 620 m2 with 30 m3, respectively, reaching a solar fraction of 69%. The absorption-cooling subprocess showed an increase of 13.88% in the average coe... [more]

The Li4Ti5O12/C composites were prepared by a hydrothermal method with in situ carbon addition. The influence of the morphology and content of various carbon materials (conductive carbon black, mesoporous carbon G_157M, and carbon replicas) on the electrochemical performance of the Li4Ti5O12/C composites was investigated. The obtained composites were characterized using X-ray diffraction, scanning electron microsopy, high-resolution transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, and N2 sorption-desorption isotherms. Morphology of the Li4Ti5O12/C composites depends on the carbon matrix used, while both morphology and the amount of carbon material have a great impact on the rate capability and cycling stability of the obtained composites. At low current densities, the Li4Ti5O12/C composite with 5 wt.% G_157M exhibits the highest discharge capacity, while at high charge-discharge rates, the Li4Ti5O12/carbon black composites show the best electrochemical... [more]

With the development of the convergence of IT and automotive technology, platoon-based driving systems are getting more attention and how to disseminate messages in the platoon is an important issue. In this paper, to enhance the energy efficiency and traffic throughput (e.g., average velocity) while meeting transmission deadlines, we propose an energy efficient message dissemination scheme (EMDS) in platoon-based driving systems, which also provides proper power control and relay selection. To find out the optimal policy to balance the probability of successful message dissemination and transmission power cost in EMDS, we formulate a Markov decision process (MDP) problem that considers the velocity of the vehicles in the platoon. To evaluate the performance of EMDS, we analyze the outage probability, the average velocity, and the expected power consumption using the discrete-time Markov chain (DTMC) model. Evaluation results demonstrate EMDS with the optimal policy improves the averag... [more]

A series of functionalized ferrocene derivatives carrying electron-donor and electron-withdrawing (hetero)aromatic substituents has been designed as potential alternative electrolyte redox couples for dye-sensitized solar cells (DSSC). The compounds have been synthesized and fully characterized in their optical and electrochemical properties. A general synthetic approach that implies the use of a microwave assisted Suzuki coupling has been developed to access a significative number of compounds. The presence of different electron-rich and electron-poor substituents provided fine tuning of optical properties and energy levels. HOMO and LUMO energy values showed that the substitution of one or two cyclopentadienyl rings of ferrocene can be successfully exploited to increase the maximum attainable voltage from a standard DSSC device using TiO2 as a semiconductor, opening the way to highly efficient, non-toxic, and cheap redox shuttles to be employed in solar energy technologies.

Thermal conversion of ash-rich fuels in fluidized bed systems is often associated with extensive operation problems caused by the high amount of reactive inorganics. This paper investigates the behavior of wheat straw lignin—a potential renewable fuel for dual fluidized bed gasification. The formation of coherent ash residues and its impact on the operation performance has been investigated and was supported by thermochemical equilibrium calculations in FactSage 7.3. The formation of those ash residues, and their subsequent accumulation on the surface of the fluidized bed, causes temperature and pressure fluctuations, which negatively influence the steady-state operation of the fluidized bed process. This paper presents a detailed characterization of the coherent ash residues, which consists mostly of silica and partially molten alkali silicates. Furthermore, the paper gives insights into the formation of these ash residues, dependent on the fuel pretreatment (pelletizing) of the wheat... [more]

A comprehensive analysis of combustion behaviour during cold, intermediately cold, warm and hot start stages of a diesel engine are presented. Experiments were conducted at 1500 rpm and 2000 rpm, and the discretisation of engine warm up into stages was facilitated by designing a custom drive cycle. Advanced injection timing, observed during the cold start period, led to longer ignition delay, shorter combustion duration, higher peak pressure and a higher peak apparent heat release rate (AHRR). The peak pressure was ~30% and 20% and the AHRR was ~2 to 5% and ±1% higher at 1500 rpm and 2000 rpm, respectively, during cold start, compared to the intermediate cold start. A retarded injection strategy during the intermediate cold start phase led to shorter ignition delay, longer combustion duration, lower peak pressure and lower peak AHRR. At 2000 rpm, an exceptional combustion behaviour led to a ~27% reduction in the AHRR at 25% load. Longer ignition delays and shorter combustion durations... [more]

Conditioning of lignocellulosic hydrolysates with sulfur oxyanions, such as dithionite, is one of the most potent methods to improve the fermentability by counteracting effects of inhibitory by-products generated during hydrothermal pretreatment under acidic conditions. The effects of pH, treatment temperature, and dithionite dosage were explored in experiments with softwood hydrolysates, sodium dithionite, and Saccharomyces cerevisiae yeast. Treatments with dithionite at pH 5.5 or 8.5 gave similar results with regard to ethanol productivity and yield on initial glucose, and both were always at least ~20% higher than for treatment at pH 2.5. Experiments in the dithionite concentration range 5.0−12.5 mM and the temperature range 23−110 °C indicated that treatment at around 75 °C and using intermediate dithionite dosage was the best option (p ≤ 0.05). The investigation indicates that selection of the optimal temperature and dithionite dosage offers great benefits for the efficient fermen... [more]

Monopiles supporting offshore wind turbines can experience permanent non-recoverable rotations (or displacements) during their lifetime due to the cyclic nature of hydrodynamic and aerodynamic loading exerted on them. Recent studies in the literature have demonstrated that conventional cyclic p−y curves recommended in different codes of practice (API-RP-2GEO and DNVGL-RP-C212) may not capture the effects of long-term cyclic loads as they are independent of the loading profile and the number of applied cycles. Several published methodologies based on laboratory scaled model tests (on sands) exist to determine the effect of cyclic lateral loads on the long-term behaviour of piles. The tests vary in terms of the pile behaviour (rigid or flexible pile), number of applied loading cycles, and the load profile (one-way or two-way loading). The best-fit curves provided by these tests offer practical and cost-efficient methods to quantify the accumulated rotations when compared to Finite Elemen... [more]

Combined heat and power systems dedicated to micro-scale applications are currently increasing in popularity. The use of such systems is beneficial from the standpoint of increasing the usage of renewable energy, increasing energy efficiency and reducing CO2 emissions into the atmosphere. This paper shows two examples of prototypical micro-cogeneration systems powered by biomass. In the first, smaller one, electricity is generated in thermoelectric generators using heat from the wood-fired stove. The second one is equipped with a 100 kWt batch boiler and operates according to a modified Rankine cycle. The energy and ecological analysis were conducted and discussed, including selected aspects of heat and power generation and gaseous pollutant emission. Measurements were performed using a dedicated control and measurement station with a PLC controller. As was shown, thermoelectric generators operated respectively with the power of 22.5 We in the case of the air-cooled unit and 31.2 We in... [more]

Boil-off gas (BOG) disposal in liquefied natural gas (LNG) tankers has long been considered inevitable owing to the constant vaporization of the LNG in the storage tanks, but results in energy waste and environmental pollution. To address these challenges, we developed a re-liquification system that can condense the BOG and return it to the storage tank. The re-liquification system was modeled, and a case study was conducted to evaluate the viability of the system. The energy waste, which was quantified by tonnes of oil equivalent (TOE), greenhouse-gas emissions in tonnes of carbon dioxide (TCO2), and cost reduction in millions of U.S. dollars (MUSD), was evaluated for five different tanker cruising speeds. The re-liquification system significantly reduced the average TOE, TCO2, and cost by up to 9120.40 TOE/year, 19,474.33 TCO2/year, and 1.9765 MUSD/year, respectively, for five different tanker speeds with multi-stage compression.