The application of renewable energy sources poses the problems connected with output volatility. In order to decrease this effect the energy storage technologies can be applied, particularly fuel cells connected with hydrogen storage. In this paper the application of SOFC system for a household in Poland is proposed. Economic and technical analysis is performed. It was found that the proposed installation is profitable after 25 years of operation when compared with conventional solution - heat pumps and gas-fired boilers.

Finite fossil fuel resources, as well as the instability of renewable energy production, make the sustainable management of energy production and consumption some of the key challenges of the 21st century. It also involves threats to the state of the natural environment, among others due to the negative impact of energy on the climate. In such a situation, one of the methods of improving the efficiency of energy management – both on the micro (dispersed energy) and macro (power system) scale, may be innovative technological solutions that enable energy storage. Their effective implementation will allow it to be collected during periods of overproduction and to be used in situations of scarcity. These challenges cannot be overestimated - modern science has a challenge to solve various types of problems related to storage, including the technology used or the control/ /management of energy storage. Heat storage technologies, on which research works are carried out regarding both storage based on a medium such as water, as well as storage using thermochemical transformations or phase-change materials. They give a wide range of applications and improve the efficiency of energy systems on both the macro and micro scale. Of course, the technological properties and economic parameters have an impact on the application of the chosen technology. The article presents a comparison of storage parameters or heat storage methods based on different materials with specification of their work parameters or operating costs.

Dr. Krzysztof Fic of the Poznań University of Technology discusses energy storage, aesthetic medicine’s quest for immortality, and how much time goes into being a scientist.

The paper describes factors influencing the development of electricity storage technologies.

The results of the energy analysis of the electric energy storage system in the form of hydrogen are

presented. The analyzed system consists of an electrolyzer, a hydrogen container, a compressor, and

a PEMFC fuel cell with an ion-exchange polymer membrane. The power curves of an electrolyzer

and a fuel cell were determined. The analysis took the own needs of the system into account, i.e. the

power needed to compress the produced hydrogen and the power of the air compressor supplying

air to the cathode channels of the fuel cell stack. The characteristics describing the dependence

of the efficiency of the energy storage system in the form of hydrogen as a function of load were

determined. The costs of electricity storage as a function of storage capacity were determined. The

energy aspects of energy accumulation in lithium-ion cells were briefly characterized and described.

The efficiency of the charge/discharge cycle of lithium-ion batteries has been determined. The

graph of discharge of the lithium-ion battery depending on the current value was presented. The key

parameters of battery operation, i.e. the Depth of Discharge (DoD) and the State of Charge (SoC),

were determined. Based on the average market prices of the available lithium-ion batteries for the

storage of energy from photovoltaic cells, unit costs of electrochemical energy storage as a function

of the DoD parameter were determined.

The aim of this document is to present the topic of modeling district heating systems in order to enable optimization of their operation, with special focus on thermal energy storage in the pipelines. Two mathematical models for simulation of transient behavior of district heating networks have been described, and their results have been compared in a case study. The operational optimization in a DH system, especially if this system is supplied from a combined heat and power plant, is a difficult and complicated task. Finding a global financial optimum requires considering long periods of time and including thermal energy storage possibilities into consideration. One of the most interesting options for thermal energy storage is utilization of thermal inertia of the network itself. This approach requires no additional investment, while providing significant possibilities for heat load shifting. It is not feasible to use full topological models of the networks, comprising thousands of substations and network sections, for the purpose of operational optimization with thermal energy storage, because such models require long calculation times. In order to optimize planned thermal energy storage actions, it is necessary to model the transient behavior of the network in a very simple way – allowing for fast and reliable calculations. Two approaches to building such models have been presented. Both have been tested by comparing the results of simulation of the behavior of the same network. The characteristic features, advantages and disadvantages of both kinds of models have been identified. The results can prove useful for district heating system operators in the near future.

Department of Electrical Drive and Industrial Equipment University of Science and Technology (AGH) The article describes the method of determining mechanical losses and electromagnetic motor torque on the example of a flywheel energy storage system utilizing BLDC motor. The description of the test stand contains: the topology of power factor correction boost rectifier, an inverter supplying the BLDC motor, and the measuring system. The detailed experimental results are included in the paper.

This paper discusses selected problems regarding a high-frequency improved current-fed quasi-Z-source inverter (iCFqZSI) designed and built with SiC power devices. At first, new, modified topology of the impedance network is presented. As the structure is derived from the series connection of two networks, the voltage stress across the SiC diodes and the inductors is reduced by a factor of two. Therefore, the SiC MOSFETs may be switched with frequencies above 100 kHz and volume and weight of the passive components is decreased. Furthermore, additional leg with two SiC MOSFETs working as a bidirectional switch is added to limit the current stress during the short-through states. In order to verify the performance of the proposed solution a 6 kVA laboratory model was designed to connect a 400 V DC source (battery) and a 3£400 V grid. According to presented simulations and experimental results high-frequency iCFqZSI is bidirectional – it may act as an inverter, but also as a rectifier. Performed measurements show correct operation at switching frequency of 100 kHz, high quality of the input and output waveforms is observed. The additional leg increases efficiency by up to 0.6% – peak value is 97.8%.

The article presents the analysis of the simulation test results for three variants of the power electronics used as interface between the power network and superconducting magnetic energy storage (SMES) with the following parameters: power of 250 kW, current of 500 A DC and voltage of 500 V DC. Three interface topologies were analyzed: two-level AC-DC and DC-DC converters; three-level systems and mixed systems combining a three-level active rectifier and a two-level DC-DC converter. The following criteria were considered: input and output current and voltage distortions, determined as THDi and THDu, power losses in power electronics components; cost of the semiconductor components for each topology and total cost of the interface. Results of the analysis showed that for high-power low-voltage and high-current power electronics systems, the most advantageous solution from a technical and economical perspective is a two-level interface configuration in relation to both AC-DC and DC-DC converters.

The aim of the investigation presented in this work was to realise complex calculations of a new, combined water-steam system with peak-load hydrogen turbine to be applied in nuclear units with gas-cooled reactors. The system’s characteristic feature is the presence of two heat sources: a nuclear steam generator; and a hydrogen-oxygen combustion chamber. The main idea is to create a system capable to operate in two modes, with one or two heat sources, which leads to a significant output change. The investigation included also the overall efficiency of conversion of the nuclear energy, assumed the heat needed for producing hydrogen and oxygen comes from such a source. This part of the work included an analysis of the rationality of hydrogen production and utilisation. An additional aim of the research was to determine the optimal solution regarding the system performance and the capability of its technical realisation. The obtained results are promising: the system performance is very high, and its operating parameters are technically realisable in today’s conditions. In addition, it enables an emission-free, dispatchable electricity generation during the daytime demand peak.

This paper proposes four different cost-effective configurations of a hybrid energy storage system (HESS) in an electric city bus. A comparison is presented between a battery powered bus (battery bus) and supercapacitor powered bus in two configurations in terms of initial and operational costs. The lithium iron phosphate (LFP) battery type was used in the battery bus and three of the hybrids. In the first hybrid the battery module was the same size as in the battery bus, in the second it was half the size and in the third it was one third the size. The fourth hybrid used a lithium nickel manganese cobalt oxide (NMC) battery type with the same energy as the LFP battery module in the battery bus. The model of LFP battery degradation is used in the calculation of its lifetime range and operational costs. For the NMC battery and supercapacitor, the manufacturers’ data have been adopted. The results show that it is profitable to use HESS in an electric city bus from both the producer and consumer point of view. The reduction of battery size and added supercapacitor module generates up to a 36% reduction of the initial energy storage system (ESS) price and up to a 29% reduction of operational costs when compared to the battery ESS. By using an NMC battery type in HESS, it is possible to reduce operational costs by up to 50% compared to an LFP battery ESS.

Increasing the share of energy production from renewable sources (RES) plays a key role in the sustainable and more competitive development of the energy sector. Among the renewable energy sources, the greatest increase can be observed in the case of solar and wind power generation. It should be noted that RES are an increasingly important elements of the power systems and that their share in energy production will continue to rise. On the other hand the development of variable generation sources (wind and solar energy) poses a serious challenge for power systems as operators of unconventional power plants are unable to provide information about the forecasted production level and the energy generated in a given period is sometimes higher than the demand for energy in all of the power systems. Therefore, with the development of RES, a considerable amount of the generated energy is wasted. The solution is energy storage, which makes it possible to improve the management of power systems. The objective of this article is to present the concept of electricity storage in the form of the chemical energy of hydrogen (Power to Gas) in order to improve the functioning of the power system in Poland. The expected growth in the installed capacity of wind power plants will result in more periods in which excess energy will be produced. In order to avoid wasting large amounts of energy, the introduction of storage systems is necessary. An analysis of the development of wind power plants demonstrates that the Power to Gas concept can be developed in Poland, as indicated by the estimated installed capacity and the potential amount of energy to be generated. In view of the above, the excess electricity will be available for storage in the form of chemical energy of hydrogen, which

The optimal energy management (OEM) in a stand-alone microgrid (SMG) is a challenging job because of uncertain and intermittent behavior of clean energy sources (CESs) such as a photovoltaic (PV), wind turbine (WT). This paper presents the effective role of battery energy storage (BES) in optimal scheduling of generation sources to fulfill the load demand in an SMG under the intermittency of theWT and PV power. The OEM is performed by minimizing the operational cost of the SMG for the chosen moderate weather profile using an artificial bee colony algorithm (ABC) in four different cases, i.e. without the BES and with the BES having a various level of initial capacity. The results show the efficient role of the BES in keeping the reliability of the SMG with the reduction in carbon-emissions and uncertainty of the CES power. Also, prove that the ABC provides better cost values compared to particle swarm optimization (PSO) and a genetic algorithm (GA). Further, the robustness of system reliability using the BES is tested for the mean data of the considered weather profile.

The article presents the current state of the CNG market used as an alternative fuel for car engines. Attention was paid to European Union directives requirements and the current state of the directives’ fulfillment. The economic aspect of CNG usage was analyzed and the approximate costs of driving 10,000 km on different fuels in the last four years were presented. The PtG process which uses electric energy (hydrogen production) and carbon dioxide captured from the flue gas for the production of synthetic methane were discussed. The scheme of the SNG plant with the indication of its most important components was presented, and attention was paid to the mutual complementation of PtG technologies with carbon dioxide capture technology. The benefits of synthetic methane production are presented and the use of compressed natural gas to power engines in vehicles has been described. First, the focus was on the single-fuel use of CNG in bus and truck engines, paying particular attention to the ecological aspect of the implemented solutions. It has been shown that the use of compressed natural gas will reduce almost 100% of the particulates emission from the combustion process. The advantages and disadvantages of the alternative fuel supply are given. Next, the aspect of dual-fuel use in diesel engines was analyzed on the example of a smaller engine. The degree of reduction of harmful compounds emission from the combustion process is shown. Finally, attention was paid to the possible scale effect, referring to the number of motor vehicles in Poland.

In this article, the contribution of renewable energy sources (RES) to the worldwide electricity production was analyzed. The scale of development and the importance of RES in the global economy as well as the issues and challenges related to variability of these sources were studied. In addition, the chemical conversion of excess energy to renewable methanol has been presented. The European Union regulations and targets for the years 2020 and 2030 concerning greenhouse gases reduction were taken into consideration. These EU restrictions exact the further development of renewable energy sources, in particular, the improvement of their efficiency which is closely related to economics. Moreover, as a part of this work, energy storage were described as one of the ways to increase the competitiveness of renewable energy sources with respect to conventional energy. A method for the conversion of carbon dioxide separated from high-carbon industries with hydrogen obtained by the over-production of green energy were described. The use of methanol in the chemical industry and global market have been reviewed and thus an increasing demand was observed. Additionally, the application of renewable methanol as fuels, in pure form and after a conversion of methanol to dimethyl ether and fatty acid methyl esters has been discussed. Hence, the necessity of modifying car engines in order to use pure methanol and its combination with petrol also was analyzed.