Article investigates the issue of terms of trade in energy products. The goal of this paper is to check how the terms of trade in energy fluctuate. The analysis is carried out on the example of Poland as a country which offers an interesting energy imports and exports structure. The time horizon covers the period from 2005–2015 and is extended to give the broader picture of the phenomenon wherever possible. In the research, the author uses the barter terms of trade concept. The paper has been organized in four sections. The study opens with introductory remarks presenting Polish energy situation, which is followed by a description of the terms of trade concept on the grounds of international economics. The results of the research are discussed in section three which ends with a summary and conclusions. The last part includes an additional description of study constraints and suggestions the next research steps. The statistical data used in the paper comes from national databases of the Polish Central Statistical Office and international sources such as the Organisation for Economic Cooperation and Development. Additional information on energy prices was derived from recognized branch sources such as BP Statistical Review of World Energy.

The article presents the results of the analysis of straw obtained from ripening wheat, which was subjected to four water soaking cycles in demineralized water. The soaking was carried out under laboratory conditions at 20°C. As a result, part of mineral matter, including a significant amount of alkaline sodium and potassium salts and substances containing sulfur and phosphorus, was washed out. The process of soaking has a great impact on the chemical composition of ash obtained from water-treated straw, which increased its acidity. The Na2O content in the analyzed ash has decreased by 78%, while the K2O content has decreased by 60%. In turn, the content of water-insoluble, acid-forming SiO2 has increased by 80%. As a consequence, a positive change in the values of indices, on the basis of which the tendency of straw to slagging and deposit formation during the combustion and gasification processes is assessed, has been observed. Already after the second water soaking cycle it became apparent, based on the AI alkali index, that the examined fuel should not cause difficulties resulting from the increased intensity of use of the boiler during the combustion process. Meanwhile, the value of the BAI bed agglomeration index was considered to be safe, indicating a low possibility of bed agglomeration during the combustion or fluidized bed gasification, after the third water soaking cycle. The third of the analyzed indices, the Fu fouling index, did not indicate any tendency to deposit formation during the combustion; however, four water soaking cycles reduced its initial value by 80%. The last of the analyzed indexes, the SR, slag viscosity index did not change its value during the experiment, which, both for the raw straw and after subsequent soaking cycles, indicated that the fuel should have a low tendency to accumulate slag during the combustion process.

The Energy Law of April 10, 1997 initiated changes in the energy market in Poland. Actions taken on the basis of this law were aimed at the modernization and development of the power sector. Organizational and legal changes causing the development of distributed generation, thus increasing the level of market competition have been introduced. The care for high quality of customer service, including the protection of vulnerable customers, environmental protection, growing share of renewable energy and emission reduction requirements have become a reality. It seems, therefore, that it is necessary for the Polish energy sector to undergo permanent modernization, to develop the production and industrial infrastructure and to develop modern conventional technologies by way of implementing innovations in the field of energy companies. The author of the paper argues that it is indispensable to make a broadly understood transfer of knowledge and technology to the energy sector on the basis of a knowledge-based economy. This also applies to energy clusters, which currently constitute a platform for cooperation: entrepreneurs, scientific-research units, and public authorities. The functioning of these entities is an important catalyst for the transfer of knowledge and technologies. Their regional nature boosts competitiveness of the involved enterprises, and is a natural way of transferring knowledge to the energy market.

The article presents the question of solidarity in relation to the energy policy of the European Union. This topic seems particularly important in the context of the crisis of the European integration process, which includes, in particular, economic problems, the migration crisis and the withdrawal of the United Kingdom from the European Union (Brexit). The issue of solidarity was analyzed from the legal and formal, institutional, and functional and relational points of view. The aim of the article is to show to what extent the theoretical assumptions, resulting from the provisions of European law on the solidarity, correspond with the actions of the Member States in the energy sector. The practice of the integration process indicates that the particular national economic interests in the energy sector are more important for the Member States than working towards European solidarity. Meanwhile, without a sense of responsibility for the pan-European interest, it is not possible to effectively implement the EU’s energy policy. The European Commission – as the guardian of the treaties – confronts the Member States with ambitious challenges to be undertaken “in the spirit of solidarity”. In the verbal sphere, this is supported by by capitals of the individual countries, but in practice, the actions taken divide the Member States into opposing camps instead of building a sense of the European energy community. This applies in particular to such issues as: the management of the energy union, investments in the gas sector (e.g. Nord Stream I and Nord Stream II), and the position towards third countries – suppliers of energy raw materials to the EU (in particular towards the Russian Federation). Different views on the above problems make it extremely difficult for Member States to take action “in the spirit of energy solidarity”. Thus, the energy problem becomes another reason for the weakening of European unity.

Gasification technology is often seen as a synonym for the clean and efficient processing of solid fuels into combustible gas containing mainly carbon monoxide and hydrogen, the two basic components of synthesis gas. First and foremost, the facts that gas may be cleaned and that a mixture with any composition may be prepared in a relatively easy and inexpensive manner influence the possibility of using gas produced in the energy and chemical industries. In the energy industry, gas may be used directly to generate heat and electricity in the systems of a steam power plant or in combined cycle systems. It is also possible to effectively separate CO2 from the system. However, in chemistry, synthesis gas may be used to produce hydrogen, methanol, synthetic gasolines, and other chemical products. The raw material for gasification is full-quality pulverized coal, but a possibility of processing low-quality sludges, combustible fractions separated from municipal waste as well as industrial waste also exists. Despite such a wide application of technology and undoubted advantages thereof, making investment decisions is still subject to high uncertainty. The paper presents the main technological applications of gasification and analyzes the economic effectiveness thereof. In this context, significant challanges for the industrial implementation of this technology are discussed

The sustainable management of energy production and consumption is one of the main challenges of the 21st century. This results from the threats to the natural environment, including the negative impact of the energy sector on the climate, the limited resources of fossil fuels, as well as the unstability of renewable energy sources – despite the development of technologies for obtaining energy from the: sun, wind, water, etc. In this situation, the efficiency of energy management, both on the micro (dispersed energy) and macro (power system) scale, may be improved by innovative technological solutions enabling energy storage. Their effective implementation enables energy storage during periods of overproduction and its use in the case of energy shortages. These challenges cannot be overestimated. Modern science needs to solve various technological issues in the field of storage, organizational problems of enterprises producing electricity and heat, or issues related to the functioning of energy markets. The article presents the specificity of the operation of a combined heat and power plant with a heat accumulator in the electricity market while taking the parameters affected by uncertainty into account. It was pointed out that the analysis of the risk associated with energy prices and weather conditions is an important element of the decision-making process and management of a heat and power plant equipped with a cold water heat accumulator. The complexity of the issues and the number of variables to be analyzed at a given time are the reason for the use of advanced forecasting methods. The stochastic modeling methods are considered as interesting tools that allow forecasting the operation of an installation with a heat accumulator while taking the influence of numerous variables into account. The analysis has shown that the combined use of Monte Carlo simulations and forecasting using the geometric Brownian motion enables the quantification of the risk of the CHP plant’s operation and the impact of using the energy store on solving uncertainties. The applied methodology can be used at the design stage of systems with energy storage and enables carrying out the risk analysis in the already existing systems; this will allow their efficiency to be improved. The introduction of additional parameters of the planned investments to the analysis will allow the maximum use of energy storage systems in both industrial and dispersed power generation.

The second decade of the 21st century is a period of intense development of various types of energy storage other than pumped-storage hydroelectricity. Battery and thermal storage systems are particularly rapidly developing ones. The observed phenomenon is a result of a key megatrend, i.e. the development of intermittent renewable energy sources (IRES) (wind power, photovoltaics). The development of RES, mainly in the form of distributed generation, combined with the dynamic development of electric mobility, results in the need to stabilize the grid frequency and voltage and calls for new solutions in order to ensure the security of energy supplies. High maturity, appropriate technical parameters, and increasingly better economic parameters of lithium battery technology (including lithium-ion batteries) result in a rapid increase of the installed capacity of this type of energy storage. The abovementioned phenomena helped to raise the question about the prospects for the development of electricity storage in the world and in Poland in the 2030 horizon. The estimated worldwide battery energy storage capacity in 2030 is ca. 51.1 GW, while in the case of Poland it is approximately 410.6 MW.

The aim of the paper is to draw attention to risks and challenges faced by the national grid infrastructure both in the area of transmission and distribution. The study presents the characteristics of the network grid in the area of transmission and distribution. The threats concerning the transmission and distribution infrastructure were also discussed. Both the national transmission and the distribution grids are adapted to presently occurring typical conditions of the demand on electricity and to the execution of internal tasks in normal states, but they may pose a potential threat to the security of the energy supplies. In the context of the forecasted future growth of the electricity demand, the insufficient capacity of the National Power System in domestic sources and sources available through interconnections, the uneven distribution of sources and customers with the lack of adequate grid transmission capacity, the necessity to improve the quality and reliability of energy supply to end users and to intensively develop renewable energy sources, the current grid infrastructure in the area of transmission and distribution will be insufficient. It will be necessary to expand and modernize the 400 and 220 kV transmission grid, the 110 kV distribution grid, in large urban agglomerations in particular, the MV distribution grid in rural areas in particular, and to implement investments aimed at increasing the export and import capacities of the National Power System. The paper presents challenges faced by transmission and distribution system operators. They mainly concern the field of investments and the area related to the preparation and implementation of investments in the grid. These challenges result from national legislation which is inappropriate and imposes many legal and administrative barriers substantially limiting the speed and effectiveness of the investment process.

Until the early 1990s, the domestic power industry was a natural monopoly. This was caused by the specificity of the operation of the electricity transmission and distribution sub sectors, technical challenges of coordinating the operation of generating units and transmission networks, requirements regarding long-term forecasting of the industry development, and returns to scale. In view of the above, the objective of the presented paper is to assess the economic situation of energy companies operating in a competitive electricity market. The article analyses the main areas of activity of the energy companies, i.e.: the areas of production, transmission, distribution, and sales. In addition, the market shares of the various energy companies, in terms of generating capacity and the amount of the energy produced, were analyzed. Furthermore, the technical and economic situation of enterprises operating in the power sector was also subjected to analysis. The mentioned analysis has revealed that the profit received from the main activity of the enterprises (i.e. the sale of electricity) has decreased in recent years. What is more, the energy sector must adapt to legal and regulatory changes related to the intensification of the decarbonization policy pursued by the European Commission. Therefore, national energy should focus on developing skills in the areas of innovation, such as: electro mobility, energy storage, energy management, etc.

The dynamic development of wind power in recent years has generated the demand for production forecasting tools in wind farms. The data obtained from mathematical models is useful both for wind farm owners and distribution and transmission system operators. The predictions of production allow the wind farm operator to control the operation of the turbine in real time or plan future repairs and maintenance work in the long run. In turn, the results of the forecasting model allow the transmission system operator to plan the operation of the power system and to decide whether to reduce the load of conventional power plants or to start the reserve units.

The presented article is a review of the currently applied methods of wind power generation forecasting. Due to the nature of the input data, physical and statistical methods are distinguished. The physical approach is based on the use of data related to atmospheric conditions, terrain, and wind farm characteristics. It is usually based on numerical weather prediction models (NWP). In turn, the statistical approach uses historical data sets to determine the dependence of output variables on input parameters. However, the most favorable, from the point of view of the quality of the results, are models that use hybrid approaches. Determining the best model turns out to be a complicated task, because its usefulness depends on many factors. The applied model may be highly accurate under given conditions, but it may be completely unsuitable for another wind farm.

This article presents a hybrid control system for a group of mobile robots. The components of this system are the supervisory controller(s), employing a discrete, event-driven model of concurrent robot processes, and robot motion controllers, employing a continuous time model with event-switched modes. The missions of the robots are specified by a sequence of to-be visited points, and the developed methodology ensures in a formal way their correct accomplishment.

In this article, an engineering/physical dynamic system including losses is analyzed inrelation to the stability from an engineer’s/physicist’s point of view. Firstly, conditions for a Hamiltonian to be an energy function, time independent or not, is explained herein. To analyze stability of engineering system, Lyapunov-like energy function, called residual energy function is used. The residual function may contain, apart from external energies, negative losses as well. This function includes the sum of potential and kinetic energies, which are special forms and ready-made (weak) Lyapunov functions, and loss of energies (positive and/or negative) of a system described in different forms using tensorial variables. As the Lypunov function, residual energy function is defined as Hamiltonian energy function plus loss of energies and then associated weak and strong stability are proved through the first time-derivative of residual energy function. It is demonstrated how the stability analysis can be performed using the residual energy functions in different formulations and in generalized motion space when available. This novel approach is applied to RLC circuit, AC equivalent circuit of Gunn diode oscillator for autonomous, and a coupled (electromechanical) example for nonautonomous case. In the nonautonomous case, the stability criteria can not be proven for one type of formulation, however, it can be proven in the other type formulation.

The designing of transmultiplexer systems relies on determining filters for the transmitter and receiver sides of multicarrier communication system. The perfect reconstruction conditions lead to the bilinear equations for FIR filter coefficients. Generally there is no way of finding all possible solutions. This paper describes methods of finding a large family of solutions. Particular attention is devoted to obtaining algorithms useful in fixed-point arithmetic needed to design the integer filters. As a result, the systems perform perfect reconstruction of signals. Additionally, a simple method is presented to transform any transmultiplexer into an unlimited number of different transmultiplexers. Finally, two examples of integer filters that meet perfect reconstruction conditions are shown. The first illustrates a FIR filter which does not require multiplications. The frequency properties of filters and signals are discussed for the second example.

A novel 4-D chaotic hyperjerk system with four quadratic nonlinearities is presented in this work. It is interesting that the hyperjerk system has no equilibrium. A chaotic attractor is said to be a hidden attractor when its basin of attraction has no intersection with small neighborhoods of equilibrium points of the system. Thus, our new non-equilibrium hyperjerk system possesses a hidden attractor. Chaos in the system has been observed in phase portraits and verified by positive Lyapunov exponents. Adaptive backstepping controller is designed for the global chaos control of the non-equilibrium hyperjerk system with a hidden attractor. An electronic circuit for realizing the non-equilibrium hyperjerk system is also introduced, which validates the theoretical chaotic model of the hyperjerk system with a hidden chaotic attractor.

The minimum energy control problem for the positive descriptor discrete-time linear systems with bounded inputs by the use of Weierstrass-Kronecker decomposition is formulated and solved. Necessary and sufficient conditions for the positivity and reachability of descriptor discrete-time linear systems are given. Conditions for the existence of solution and procedure for computation of optimal input and the minimal value of the performance index is proposed and illustrated by a numerical example.

The motion planning problem consists in finding a control function which drives the system to a desired point. The motion planning algorithm derived with an endogenous configuration space approach assumes that the motion takes place in an arbitrary chosen time horizon. This work introduces a modification to the motion planning algorithm which allows to reach the destination point in time, which is shorter than the assumed time horizon. The algorithm derivation relies on the endogenous configuration space approach and the continuation (homotopy) method. To achieve the earlier destination reaching a new formulation of the task map and the task Jacobian are introduced. The efficiency of the new algorithm is depicted with simulation results.

The paper presents a simple, systematic and novel graphical method which uses computer graphics for prediction of limit cycles in two dimensional multivariable nonlinear system having rectangular hysteresis and backlash type nonlinearities. It also explores the avoidance of such self-sustained oscillations by determining the stability boundary of the system. The stability boundary is obtained using simple Routh Hurwitz criterion and the incremental input describing function, developed from harmonic balance concept. This may be useful in interconnected power system which utilizes governor control. If the avoidance of limit cycle or a safer operating zone is not possible, the quenching of such oscillations may be done by using the signal stabilization technique which is also described. The synchronization boundary is laid down in the forcing signal amplitudes plane using digital simulation. Results of digital simulations illustrate accuracy of the method for 2×2 systems.

The study involved using the liquid-solid compound casting process to fabricate a lightweight ZE41/AlSi12 bimetallic material. ZE41 melt heated to 660 oC was poured onto a solid AlSi12 insert placed in a steel mold. The mold with the insert inside was preheated to 300 oC. The microstructure of the bonding zone between the alloys was examined using optical microscopy and scanning electron microscopy. The chemical composition was determined through linear and point analyses with an energy-dispersive X-ray spectroscope (EDS). The bonding zone between the magnesium and aluminum alloys was about 250 μm thick. The results indicate that the microstructure of the bonding zone changes throughout its thickness. The structural constituents of the bonding zone are: a thin layer of a solid solution of Al and Zn in Mg and particles of Mg-Zn-RE intermetallic phases (adjacent to the ZE41 alloy), a eutectic region (Mg17(Al,Zn)12 intermetallic phase and a solid solution of Al and Zn in Mg), a thin region containing fine, white particles, probably Al-RE intermetallic phases, a region with Mg2Si particles distributed over the eutectic matrix, and a region with Mg2Si particles distributed over the Mg-Al intermetallic phases matrix (adjacent to the AlSi12 alloy). The microstructural analysis performed in the length direction reveals that, for the process parameters tested, the bonding zone forming between the alloys was continuous. Low porosity was observed locally near the ZE41 alloy. The shear strength of the AZ91/AlSi17 joint varied from 51.3 to 56.1 MPa.

A method for manufacturing of Al-Si alloy (EN AC-44200) matrix composite materials reinforced with MAX type phases in Ti-Al-C systems was developed. The MAX phases were synthesized using the Self-propagating High-Temperature Synthesis (SHS) method in its microwave assisted mode to allow Ti2AlC and Ti3AlC2 to be created in the form of spatial structures with open porosity. Obtained structures were subjected to the squeeze casting infiltration in order to create a composite material. Microstructures of the produced materials were observed by the means of optical and SEM microscopies. The applied infiltration process allows forming of homogeneous materials with a negligible residual porosity. The obtained composite materials possess no visible defects or discontinuities in the structure, which could fundamentally deteriorate their performance and mechanical properties. The produced composites, together with the reference sample of a sole matrix material, were subjected to mechanical properties tests: nanohardness or hardness (HV) and instrumental modulus of longitudinal elasticity (EIT).

Inconel 713C is a nickel-based casting alloy characterised by improved heat and creep resistance [1]. It is used e.g. in aircraft engine components, mainly in the form of precision castings. Precision casting enables very good reproduction of complex shapes. However, due to major differences in casting wall thickness and the resultant differences in rigidity, defects can form in precision castings. The most common defects in precision castings are shrinkage porosities and microcracks. Inconel 713C is considered to be a difficult-to-weld or even non-weldable alloy. However, the need to repair precision castings requires attempts to develop technologies for their remelting and pad welding which could be used in industrial practice. This article presents the results of tests consisting in TIG pad welding of defects identified in precision castings intended for the aircraft industry. It was found that the main reason behind failed attempts at repairing precision castings by welding technologies was hot cracking in the fusion zone. Such cracks form as a result of the partial melting of intercrystalline regions along the fusion line. The deformations occurring during the crystallization of the melting-affected zone (fusion zone + partially melted zone + heat affected zone) or pad weld lead to the rupture of the intercrystalline liquid film. Hot cracks form within the so-called high-temperature brittleness range (HTBR) of the alloy. Another type of cracks that was identified were ductility dip cracks (DDC), whose formation is related to the partial melting of carbides.

The paper presents relationships between the degree of structure fineness and feeding quality of the Al – 20 wt.% Zn (Al-20 Zn) alloy cast into a mould made from sand containing silica quartz as a matrix and bentonite as a binder, and its damping coefficient of the ultrasound wave at frequency of 1 MHz. The structure of the examined alloy was grain refined by the addition of the refining Al-3 wt.% Ti – 0.15 wt.%C (TiCAl) master alloy. The macrostructure analysis of the initial alloy without the addition of Ti and the alloy doped with 50-100 ppm Ti as well as results of damping experiments showed that the structure of the modified alloy is significantly refined. At the same time, its damping coefficient decreases by about 20-25%; however, it still belongs to the so called high-damping alloys. Additionally, it was found that despite of using high purity metals Al and Zn (minimum 99,99% purity), differences in the damping coefficient for samples cut from upper and bottom parts of the vertically cast rolls were observed. These differences are connected with the insufficient feeding process leading to shrinkage porosity as well as gases present in metal charges which are responsible for bubbles of gas-porosity.

The article deals with the influence of chemical composition of martensitic stainless steel for castings GXCrNi13-4 (the 1.4317 material) on mechanical properties and structure of as cast steel after heat treatment. Properties of these martensitic stainless steel are heavily influenced by chemical composition and structure of the material after heat treatment. Structure of these steels after quenching is formed with martensite and residual austenite. When tempering the steel the carbon content in martensite is reduced and gently deposited carbides occur. The way of heat treatment has a major impact on structure of martensitic steels with low carbon content and thus on strength, hardness and elongation to fracture of these steels. Chemical composition of the melt has been treated to the desired composition of the lower, middle and upper bounds of the nickel content in the steel within the limits allowed by the standard. Test blocks were gradually cast from the melt. The influence of the nickel equivalent value on structure and properties of the 1.4317 steel was determined from results of mechanical tests.

The Upper Greensand Formation, mostly capped by the Chalk, crops out on the edges of a broad, dissected

plateau in Devon, west Dorset and south Somerset and has an almost continuous outcrop that runs from the Isle

of Purbeck to the Vale of Wardour in south Wiltshire. The Formation is well exposed in cliffs in east Devon and

the Isle of Purbeck, but is poorly exposed inland. It comprises sandstones and calcarenites with laterally and

stratigraphically variable amounts of carbonate cement, glauconite and chert. The sedimentology and palaeon-

tology indicate deposition in marginal marine-shelf environments that were at times subject to strong tidal and

wave-generated currents. The formation of the Upper Greensand successions in the region was influenced by

penecontemporaneous movements on major fault zones, some of which are sited over E-W trending Variscan

thrusts in the basement rocks and, locally, on minor faults. Comparison of the principal sedimentary breaks in

the succession with the sequence boundaries derived from world-wide sea-level curves suggests that local tec-

tonic events mask the effects of any eustatic changes in sea level. The preserved fauna is unevenly distributed,

both laterally and stratigraphically. Bivalves, gastropods and echinoids are common at some horizons but are

not age-diagnostic. Ammonites are common at a few stratigraphically narrowly defined horizons, but are rare

or absent throughout most of the succession. As a result, the age of parts of the succession is still poorly known