Poland

Electromobility is a growing technology for land transport constituting an important element of the concept of sustainable economic development. The article presents selected research results concerning one of the segments of this market-vehicles powered by hydrogen fuel cells. The subject of the research was to gain extensive knowledge on the economic factors influencing the future purchasing decisions of the demand side in relation to this category of vehicles. The research was based on a numerical experiment. For this purpose a comparative analysis of purchase prices in relation to the TCO of the vehicle after 3–5 years of use was performed. The research included selected models that are powered by both conventional and alternative fuels. The use of this method will allow to assess the real costs associated with the hydrogen vehicle. The authors emphasize the important role of economic factors in the form of the TCO index for the development of this market. The experimental approach may be helpful in understanding the essence of economic relations that affect the development of the electro-mobility market and the market demand for hydrogen fuel cell-powered vehicles in Poland.

This study advances several methods to evaluate the operation of a hydrogen generator plant. The model developed helps customize plants that contain multiple generators of varying powers using a decision module which determines the most efficient plant load distribution. Evaluation indices to assess individual devices within the plant are proposed and system flexibility maximizes the amount of renewable energy stored. Three case studies examined the variable load distribution of an electrolysis system connected to a 40 MW wind farm for energy storage purposes and incorporated a “night-valley” operational strategy. These methods facilitate the selection of the proper plant configuration and provide estimates for individual device effectiveness within the system.

The purpose of this work is the literature review in the field of hydrogen storage in solid sorbents. The best solid sorbents for hydrogen storage were selected with the possibility of synthesis them from coal fly ash. In addition the on-board hydrogen storage analysis was carried out. The review method consists of two parts. The first part based on research questions included types of the best sorbents for hydrogen storage the possibility to obtain them from coal fly ash and practical use in hydrogen storage system on-board. The second part was the selection of publications from The Web of Science and Elsevier Scopus databases and the analysis as well as available reports on the websites at this scope. After searching the relevant articles in the databases abstracts were analysed in terms of the questions asked. The links between references and research were checked. The search procedure was repeated several times. Finally articles with high Impact Factor index published by authors recognized on a global scale were selected for the presented review. The collected information proved that carbon materials are suited to hydrogen storage because of their high porosity large specific surface area and thermal stability. Besides solid sorbents such as zeolites metal-organic frameworks activated carbons or zeolite template carbons can be obtained from coal fly ash. Thanks to silicon aluminium and unburned carbon content fly ash is a good material for the synthesis of hydrogen sorbents. Under cryogenic conditions and high pressure it is possible to adsorb as much as 8.5 wt% of hydrogen. Although the Department of Energy (DOE) requirements for the hydrogen storage system on-board vehicles are not met the review of scientific publications shows that research in this area is developing and better parameters are being obtained.

Blending hydrogen into the natural gas infrastructure is becoming a very promising practice to increase the exploitation of renewable energy sources which can be used to produce “green” hydrogen. Several research projects and field experiments are currently aimed at evaluating the risks associated with utilization of the gas blend in end-use devices such as the gas meters. In this paper the authors present the results of experiments aimed at assessing the effect of hydrogen injection in terms of the durability of domestic gas meters. To this end 105 gas meters of different measurement capabilities and manufacturers both brand-new and withdrawn from service were investigated in terms of accuracy drift after durability cycles of 5000 and 10000 h with H2NG mixtures and H2 concentrations of 10% and 15%. The obtained results show that there is no metrologically significant or statistically significant influence of hydrogen content on changes in gas meter indication errors after subjecting the meters to durability testing with a maximum of 15% H2 content over 10000 h. A metrologically significant influence of the long-term operation of the gas meters was confirmed but it should not be made dependent on the hydrogen content in the gas. No safety problems related to the loss of external tightness were observed for either the new or 10-year-old gas meters.

There can be observed global interest in waste pyrolysis technology due to low costs and availability of raw materials. At the same time there is a literature gap in forecasting environmental effects of thermal waste treatment installations. In the article was modelled the chemical composition of pyrolysis gas with main focus on the problem in terms of environmental hazards. Not only RDF fuel was analysed but also selected waste fractions included in its composition. This approach provided comprehensive knowledge about the chemical composition of gaseous pyrolysis products which is important from the point of view of the heterogeneity of RDF fuel. The main goal of this article was to focus on the utilitarian aspect of the obtained calculation results. Final results can be the basis for estimating ecological effects both for existing and newly designed installations.

Pyrolysis process was modelled using Ansys Chemkin-Pro software. The investigation of the process were carried out for five different temperatures (700 750 800 850 and 900 °C). As an output the mole fraction of H2 H₂O CH₄ C₂H₂C₂H₄ C₃H₆ C₃H₈ CO CO₂ HCl and H₂S were presented. Additionally the reaction pathways for selected material were presented.

Based on obtained results it was established that the residence time did not influenced on the concentration of products contrary to temperature. The chemical composition of pyrolytic gas is closely related to wastes origin. The application of Chemkin-Pro allowed the calculation of formation for each products at different temperatures and formulation of hypotheses on the reaction pathways involved during pyrolysis process. Further based on the obtained results confirmed the possibilities of using pyrolysis gas from RDF as a substitute for natural gas in energy consumption sectors. Optimization of the process can be conducted with low financial outlays and reliable results by using calculation tools. Moreover it can be predicted negative impact of obtained products on the future installation.

Efficient hydrogen emission from ethanol with disperse graphene foam particles by using a continuous wave infrared laser diode is reported. The products of ethanol dissociation - hydrogen methane and carbon oxide were measured using mass spectrometry. It was found that the most efficient generation of hydrogen was observed when graphene particles were irradiated by a focused laser beam proceeded at the surface of ethanol solution. The process was assisted by intense white light emission resulting from the laser induced multiphoton ionization of graphene combined with the simultaneous emission of hot electrons. The hot electron emission enables the efficient dissociation of ethanol molecules located close to the solution surface with graphene foam particles.

A polyethylene (PE) liner is the basic element in high-pressure type 4 composite vessels designed for hydrogen or compressed natural gas (CNG) storage systems. Liner defects may result in the elimination of the whole vessel from use which is very expensive both at the manufacturing and exploitation stage. The goal is therefore the development of efficient non-destructive testing (NDT) methods to test a liner immediately after its manufacturing before applying a composite reinforcement. It should be noted that the current regulations codes and standards (RC&S) do not specify liner testing methods after manufacturing. It was considered especially important to find a way of locating and assessing the size of air bubbles and inclusions and the field of deformations in liner walls. It was also expected that these methods would be easily applicable to mass-produced liners. The paper proposes the use of three optical methods namely visual inspection digital image correlation (DIC) and optical fiber sensing based on Bragg gratings (FBG). Deformation measurements are validated with finite element analysis (FEA). The tested object was a prototype of a hydrogen liner for high-pressure storage (700 bar). The mentioned optical methods were used to identify defects and measure deformations.

Body-centered cubic (BCC) alloys are considered as promising materials for hydrogen storage with high theoretical storage capacity (H/M ratio of 2). Nonetheless they often suffer from sluggish kinetics of hydrogen absorption and high hydrogen desorption temperature. Carbon materials are efficient hydrogenation catalysts however their influence on the hydrogen storage properties of BCC alloy has not been comprehensively studied. Therefore in this paper composites obtained by milling of carbon catalysts (carbon nanotubes mesoporous carbon carbon nanofibers diamond powder graphite fullerene) and BCC alloy (Ti1.5V0.5) were extensively studied in the non-hydrogenated and hydrogenated state. The structure and microstructure of the obtained materials were studied by scanning and transmission electron microscopes X-ray diffraction (XRD) and Raman spectroscopy. XRD and Raman measurements showed that BCC alloy and carbon structures were in most cases intact after the composite synthesis. The hydrogenation/dehydrogenation studies showed that all of the used carbon catalysts significantly improve the hydrogenation kinetics reduce the activation energy of the dehydrogenation process and decrease the dehydrogenation temperature (by nearly 100 K). The superior kinetic properties were measured for the composite with 5 wt % of fullerene that absorbs 3.3 wt % of hydrogen within 1 min at room temperature.

The presented research focuses on an optimization design of a catalyst distribution inside a small-scale methane/steam reforming reactor. A genetic algorithm was used for the multiobjective optimization which included the search for an optimum of methane conversion rate and a minimum of the difference between highest and lowest temperatures in the reactor. For the sake of computational time the maximal number of the segment with different catalyst densities was set to be thirty in this study. During the entire optimization process every part of the reactor could be filled either with a catalyst material or non-catalytic metallic foam. In both cases the porosity and pore size was also specified. The impact of the porosity and pore size on the active reaction surface and permeability was incorporated using graph theory and three-dimensional digital material representation. Calculations start with the generation of a random set of possible reactors each with a different catalyst distribution. The algorithm calls reforming simulation over each of the reactors and after obtaining concentration and temperature fields the algorithms calculated fitness function. The properties of the best reactors are combined to generate a new population of solutions. The procedure is repeated and after meeting the coverage criteria the optimal catalyst distribution was proposed. The paper is summarized with the optimal catalyst distribution for the given size and working conditions of the system.

Transport is one of the key sectors of the European economy. However the intensive development of transport caused negative effects in the form of an increase in the emission of harmful substances. The particularly dramatic situation took place in the V4 countries. This made it necessary to implement solutions reducing emissions in transport including passenger transport. Such activities can be implemented in the field of implementation of low-emission and zero-emission vehicles for use. That is why the European Union and the governments of the Visegrad Group countries have developed numerous recommendations communications laws and strategies that order carriers to implement low- and zero-emission mobility. Therefore transport organizers and communication operators faced the choice of the type of buses. From an economic point of view each entrepreneur is guided by the economic efficiency of the vehicles used. Hence the main aim of the article was to conduct an economic evaluation of the operational efficiency of ecological vehicles. As more than 70% of vehicles in use in the European Union are still diesel driven the economic efficiency assessment was also made for vehicles with traditional diesel drive. To conduct the research the method of calculating the total cost of ownership of vehicles in operation was used. As a result of the research it was found that electric buses are the cheapest in the entire period of use (15 years) and then those powered by CNG. On the other hand the cost of using hydrogen buses is the highest. This is due to the high purchase prices of these vehicles. However the EU as well as the governments of individual countries support enterprises and communication operators by offering them financing for investments. The impact of the forecasted fuel and energy prices and the planned inflation on operating costs was also examined. In this case the analyses showed that the forecasted changes in fuel and energy prices as well as the expected inflation will significantly affect the costs of vehicle operation and the economic efficiency of using various types of drives. These changes will have a positive impact on the implementation of zero-emission vehicles into exploitation. Based on the analyses it was found that in 2035 hydrogen buses will have the lowest operating costs.

Hydrogen is an explosive gas which could create extremely hazardous conditions when released into an enclosure. Full-scale experiments of hydrogen release and dispersion in the confined space were conducted. The experiments were performed for hydrogen release outflow of 63 × 10−3 m3/s through a single nozzle and multi-point release way optionally. It was found that the hydrogen dispersion in an enclosure strongly depends on the gas release way. Significantly higher hydrogen stratification is observed in a single nozzle release than in the case of the multi-point release when the gas concentration becomes more uniform in the entire enclosure volume. The experimental results were confirmed on the basis of Froud number analysis. The CFD simulations realized with the FDS code by NIST allowed visualization of the experimental hydrogen dispersion phenomenon and confirmed that the varied distribution of hydrogen did not affect the effectiveness of the accidental mechanical ventilation system applied in the tested room.

Issues related to the reduction of the environmental impact of means of road transport by the use of electric motors powered by Proton Exchange Membrane (PEM) fuel cells are presented in this article. The overall functional characteristics of electric vehicles are presented as well as the essence of the operation of a fuel cell. On the basis of analyzing the energy conversion process significant advantages of electric drive are demonstrated especially in vehicles for urban and suburban applications. Moreover the analyzed literature indicated problems of controlling and maintaining fuel cell power caused by its highest dynamic and possible efficiency. This control was related to the variable load conditions of the fuel cell vehicle (FCV) engine. The relationship with the conventional dependencies in the field of vehicle dynamics is demonstrated. The final part of the study is related to the historical outline and examples of already operating fuel cell systems using hydrogen as an energy source for energy conversion to power propulsion vehicle’s engines. In conclusion the necessity to conduct research in the field of methods for controlling the power of fuel cells that enable their effective adaptation to the temporary load resulting from the conditions of vehicle motion is indicated.

Steam methane (CH4–H2O) reforming in the presence of a catalyst usually nickel is the most common technology for generating synthesis gas as a feedstock in chemical synthesis and a source of pure H2 and CO. What is essential from the perspective of further gas use is the parameter describing a ratio of equilibrium concentration of hydrogen to carbon monoxide (/ = 2/). The parameter is determined by operating temperature and the initial ratio of steam concentration to methane = 2 0 /4 0 . In this paper the author presents a thermodynamic analysis of the effect of green hydrogen addition to a fuel mixture on the steam methane reforming process of gaseous phase (CH4/H2)–H2O. The thermodynamic analysis of conversion of hydrogen-enriched methane (CH4/H2)–H2O has been performed using parametric equation formalism allowing for determining the equilibrium composition of the process in progress. A thermodynamic condition of carbon precipitation in methane reforming (CH4/H2) with the gaseous phase of H2O has been interpreted. The ranges of substrate concentrations creating carbon deposition for temperature T = 1000 K have been determined based on the technologies used. The results obtained can serve as a model basis for describing the properties of steam reforming of methane and hydrogen mixture (CH4/H2)– H2O.

The hydrogen economy is one of the possible directions of development for the European Union economy which in the perspective of 2050 can ensure climate neutrality for the member states. The use of hydrogen in the economy on a larger scale requires the creation of a storage system. Due to the necessary volumes the best sites for storage are geological structures (salt caverns oil and gas deposits or aquifers). This article presents an analysis of prospects for large-scale underground hydrogen storage in geological structures. The political conditions for the implementation of the hydrogen economy in the EU Member States were analysed. The European Commission in its documents (e.g. Green Deal) indicates hydrogen as one of the important elements enabling the implementation of a climate-neutral economy. From the perspective of 2050 the analysis of changes and the forecast of energy consumption in the EU indicate an increase in electricity consumption. The expected increase in the production of energy from renewable sources may contribute to an increase in the production of hydrogen and its role in the economy. From the perspective of 2050 discussed gas should replace natural gas in the chemical metallurgical and transport industries. In the longer term the same process will also be observed in the aviation and maritime sectors. Growing charges for CO2 emissions will also contribute to the development of underground hydrogen storage technology. Geological conditions especially wide-spread aquifers and salt deposits allow the development of underground hydrogen storage in Europe.

The state of environmental pollution brought about as a result of the modern civilization has been monitored in the interests of the environment and human health since the seventies of the last century. Ensuring the energy security is one of the most basic existential requirements for a functional civilized society. The growing civilizational needs caused by broadly understood development generate demand for the production of all kinds of goods in all sectors of the economy as well as world-wide information transfer. The current energy demand is mostly covered using fossil fuels such as coal oil and natural gas. Some of the energy demand is covered by the energy generated in nuclear reactions and a small part of it comes from renewable energy sources. Energy derived from fossil fuels is inevitably associated with fuel oxidation processes. These processes in addition to generating heat are responsible for the emission of harmful compounds to the atmosphere: carbon monoxide carbon dioxide nitrogen oxides hydrocarbons and particulate matter. These pollutants pose a serious threat to the people as well as the environment in which they live. Due to the large share of fossil fuel energy generation in the process of combustion it becomes necessary to seek other means of obtaining the so-called "clean energy". Fuel cells may have a very high potential in this respect. Their development has enabled attempts to use them in all modes of transport. An important factor in the development of fuel cells is their relatively high efficiency and the coinciding strictening of the emission norms from internal combustion engines used to power maritime transport. Therefore the aim of this article has been to assess the potential of fuel cells as a main source of propulsion power source. A review of the designs of fuel cell systems and their use was performed. The article summarizes the assessment of the potential role of fuel cells as a power source of maritime transport.

Depleting fossil fuel resources and anthropogenic climate changes are the reasons for the intensive development of new sustainable technologies based on renewable energy sources. One of the most promising strategies is the utilization of hydrogen as an energy vector. However the limiting issue for large-scale commercialization of hydrogen technologies is a safe efficient and economical method of gas storage. In industrial practice hydrogen compression and liquefaction are currently applied; however due to the required high pressure (30–70 MPa) and low temperature (−253 ◦C) both these methods are intensively energy consuming. Chemical hydrogen storage is a promising alternative as it offers safe storage of hydrogen-rich compounds under ambient conditions. Although many compounds serving as hydrogen carriers are considered some of them do not have realistic perspectives for large-scale commercialization. In this review the three most technologically advanced hydrogen carriers—dimethyl ether methanol and dibenzyltoluene—are discussed and compared. Their potential for industrial application in relation to the energy storage transport and mobility sectors is analyzed taking into account technological and environmental aspects.

The COVID pandemic has caused a major exodus of passengers who chose urban and suburban transport. In many countries especially in the European Union there is a tendency to choose individual means of transport causing damage to the environment and contributing significantly to greenhouse gas emissions. One method to promote urban transport is replacing bus fleets with newer ones thus making public transport more attractive and reducing the emission of harmful exhaust fume components into the atmosphere. The aim of this study was to show a methodology for calculating CO2e for bus fleets. When determining CO2e the principal greenhouse gases such as CO2 CH4 and N2O are usually considered. However CO emissions also have indirect effects on climate through enhanced levels of tropospheric O3 and increased lifetime of CH4; therefore CO2 CH4 N2O and CO emissions were determined for CO2e emission calculations. Two bus fleet variant scenarios were analysed; the first non-investment variant assumed passenger transport using the old fleet without any P&R parking zones. The second scenario was based on the current state which includes the purchase of new low-emission buses and the construction of P&R infrastructure. The calculations were performed using the COPERT emission model with real data from 52 buses running on 13 lines. For the analysed case study of the Rzeszow agglomeration and neighbouring communes implementing the urban and suburban transport modernisation project resulted in a reduction in estimated CO2e emissions of about 450 t. The methodology presented which also considers the impact of CO emissions on the greenhouse effect is a new element of the study that has not been presented in previous works and may serve as a model for other areas in the field of greenhouse gas emission analyses. The future research scope includes investigation of other fuels and powertrain supplies such as hydrogen and hybrid vehicles.

Hydrogen-based technologies are among the most promising solutions to fulfill the zero-emission scenario and ensure the energy independence of many countries. Hydrogen is considered a green energy carrier which can be utilized in the energy transport and chemical sectors. However efficient and safe large-scale hydrogen storage is still challenging. The most frequently used hydrogen storage solutions in industry i.e. compression and liquefaction are highly energy-consuming. Underground hydrogen storage is considered the most economical and safe option for large-scale utilization at various time scales. Among underground geological formations salt caverns are the most promising for hydrogen storage due to their suitable physicochemical and mechanical properties that ensure safe and efficient storage even at high pressures. In this paper recent advances in underground storage with a particular emphasis on salt cavern utilization in Europe are presented. The initial experience in hydrogen storage in underground reservoirs was discussed and the potential for worldwide commercialization of this technology was analyzed. In Poland salt deposits from the north-west and central regions (e.g. Rogóźno Damasławek Łeba) are considered possible formations for hydrogen storage. The Gubin area is also promising where 25 salt caverns with a total capacity of 1600 million Nm3 can be constructed.

One of the strategic goals of developed countries is to significantly increase the share of renewable energy sources in electricity generation. However the process may be hindered by e.g. the storage and transport of energy from renewable sources. The European Union countries see the development of the hydrogen economy as an opportunity to overcome this barrier. Therefore since 2020 the European Union has been implementing a hydrogen strategy that will increase the share of hydrogen in the European energy mix from the current 2 percent to up to 13–14 percent by 2050. In 2021 following the example of other European countries the Polish government adopted the Polish Hydrogen Strategy until 2030 with an outlook until 2040 (PHS). However the implementation of the strategy requires significant capital expenditure and infrastructure modernisation which gives rise to question as to whether Poland is likely to achieve the goals set out in the Polish Hydrogen Strategy and European Green Deal. The subject of the research is an analysis of the sources of financing for the PHS against the background of solutions implemented by the EU countries and a SWOT/TOWS analysis on the hydrogen economy in Poland. The overall result of the SWOT/TOWS analysis shows the advantage of strengths and related opportunities. This allows for a positive assessment of the prospects for the hydrogen economy in Poland. Poland should continue its efforts to take advantage of the external factors (O/S) such as EU support an increased price competitiveness of hydrogen and the emergence of a competitive cross-border hydrogen market in Europe. At the same time the Polish authorities should not forget about the weaknesses and threats that may inhibit the development of the domestic hydrogen market. It is necessary to modernise the infrastructure; increase the share of renewable energy sources in hydrogen production; increase R&D expenditure and in particular to complete the negotiations related to the adoption of the Fit for 55 package.

In this study four energy storage systems (Power-to-Gas-to-Power) were analysed that allow electrolysis products to be fully utilized immediately after they are produced. For each option the electrolysis process was supplied with electricity from a wind farm during the off-peak demand periods. In the first two variants the produced hydrogen was directed to a natural gas pipeline while the third and fourth options assumed the use of hydrogen for synthetic natural gas production. All four variants assumed the use of a gas expander powered by high-temperature exhaust gases generated during gas combustion. In the first two options gas was supplied from a natural gas network while synthetic natural gas produced during methanation was used in the other two options. A characteristic feature of all systems was the combustion of gaseous fuels within a ballast-free oxidant atmosphere without nitrogen which is the fundamental component of air in conventional systems. The fifth variant was a reference for the systems equipped with gas expanders and assumed the use of fuel cells for power generation. To evaluate the individual variants the energy storage efficiency was defined and determined and the calculated overall efficiency ranged from 17.08 to 23.79% which may be comparable to fuel cells.

Hydrogen is an environmentally friendly biofuel which if widely used could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost‐effective methods of production and storage. So far hydrogen has been produced using thermochemical methods (such as gasification pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation) with conventional fuels waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency can rapidly build biomass and possess other beneficial properties which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies.

Dark fermentation is a promising method to produce hydrogen from lignocellulosic biomass. This study assessed the influence of temperature phosphate buffer concentration and substrate concentration on direct hydrogen production form cellulose using response surface methodology. Mixed bacterial culture was successfully enriched on cellulose and used as an inoculum for hydrogen production. The model indicated that the highest cumulative hydrogen production (CHP) of 2.14 L H₂/Lmedium could be obtained at 13.5 gcellulose/L 79.5 mM buffer and 32.6 °C. However hydrogen yield is then only 0.58 mol H₂/molhexose due to low substrate conversion efficiency (SCE). Simultaneous optimization of CHP and SCE with desirability function approach resulted in the H₂ yield of 2.71 ± 0.1 mol H2/molhexose and 93.8 ± 1.8% SCE at 3.35 gcellulose/L 69 mM buffer and 32.9 °C. Phosphate concentration above 80 mM decreased H₂ production but had positive effect on cellulose consumption. The bacterial community analysis showed that Ruminiclostridium papyrosolvens was responsible for cellulose hydrolysis. Lachnoclostridium sp. was positively correlated with ethanol production at high phosphate buffer concentration while Caproiciproducens sp. with caproate production at low buffer concentration. The obtained results opens the possibility of simultaneous hydrogen and caproate production from cellulosic substrates.

The use of hydrogen exists in various sectors in Poland and Germany. Hydrogen can be used in industry transport decarbonisation of the Polish steel industry and as one of the low-emission alternatives to the existing coal applications in this sector. Limiting climate change requires efforts on a global scale from all countries of the world. Significant economic benefits will be realized by stimulating the development of new technologies to deal with climate change. The scenarios show an increasing demand for industrial hydrogen in the future. The key is to replace gray hydrogen with green and to convert industrial processes which will create additional hydrogen demand. The condition for the development of a green hydrogen economy is access to adequate installed capacity in renewable energy. Germany will become the leading market in the era of energy transformation in the coming years. The implementation of the hydrogen assumptions in Poland is possible to a greater extent by the efforts of entrepreneurs

The European steel industry is experiencing new challenges related to the market situation and climate policy. Experience from the period of pandemic restrictions and the effects of Russia’s armed invasion of Ukraine has given many countries a basis for including steel along with raw materials (coke iron ore electricity) in economic security products (CRMA). Steel is needed for economic infrastructure and construction development as well as a material for other industries (without steel factories will not produce cars machinery ships washing machines etc.). In 2022 steelmakers faced a deepening energy crisis and economic slowdown. The market situation prompted steelmakers to impose restrictions on production volumes (worldwide production fell by 4% compared to the previous year). Despite the difficult economic situation of the steel industry (production in EU countries fell by 11% in 2022 compared to the previous year) the EU is strengthening its industrial decarbonisation policy (“Fit for 55”). The decarbonisation of steel production is set to accelerate by 2050. To sharply reduce carbon emissions steel mills need new steelmaking technologies. The largest global steelmakers are already investing in new technologies that will use green hydrogen (produced from renewable energy sources). Reducing iron ore with hydrogen plasma will drastically reduce CO2 emissions (steel production using hydrogen could emit up to 95% less CO2 than the current BF + BOF blast furnace + basic oxygen furnace integrated method). Investments in new technologies must be tailored to the steel industry. A net zero strategy (deep decarbonisation goal) may have different scenarios in different EU countries. The purpose of this paper was to introduce the conditions for investing in low-carbon steelmaking technologies in the Polish steel market and to develop (based on expert opinion) scenarios for the decarbonisation of the Polish steel industry.

The energy sector is nowadays facing new challenges mainly in the form of a massive shifting towards renewable energy sources as an alternative to fossil fuels and a diffusion of the distributed generation paradigm which involves the application of small-scale energy generation systems. In this scenario systems adopting one or more renewable energy sources and capable of producing several forms of energy along with some useful substances such as fresh water and hydrogen are a particularly interesting solution. A hybrid polygeneration system based on renewable energy sources can overcome operation problems regarding energy systems where only one energy source is used (solar wind biomass) and allows one to use an all-in-one integrated systems in order to match the different loads of a utility. From the point of view of scientific literature medium and large-scale systems are the most investigated; nevertheless more and more attention has also started to be given to small-scale layouts and applications. The growing diffusion of distributed generation applications along with the interest in multipurpose energy systems based on renewables and capable of matching different energy demands create the necessity of developing an overview on the topic of small-scale hybrid and polygeneration systems. Therefore this paper provides a comprehensive review of the technology operation performance and economical aspects of hybrid and polygeneration renewable energy systems in small-scale applications. In particular the review presents the technologies used for energy generation from renewables and the ones that may be adopted for energy storage. A significant focus is also given to the adoption of renewable energy sources in hybrid and polygeneration systems designs/modeling approaches and tools and main methodologies of assessment. The review shows that investigations on the proposed topic have significant potential for expansion from the point of view of system configuration hybridization and applications.