VOLUME 16 / Issue 4 Revija Journal of Energy Technology (JET) je indeksirana v bazah INSPEC© in Proquest’s Technology Research Database. The Journal of Energy Technology (JET) is indexed and abstracted in database INSPEC© and Proquest’s Technology Research Database. JOURNAL OF ENERGY TECHNOLOGY Ustanovitelj / FOUNDER Fakulteta za energetiko, UNIVERZA V MARIBORU / FACULTY OF ENERGY TECHNOLOGY, UNIVERSITY OF MARIBOR Izdajatelj / PUBLISHER Fakulteta za energetiko, UNIVERZA V MARIBORU / FACULTY OF ENERGY TECHNOLOGY, UNIVERSITY OF MARIBOR Glavni in odgovorni urednik / EDITOR-IN-CHIEF Jurij AVSEC Souredniki / CO-EDITORS Bruno CVIKL Miralem HADŽISELIMOVIC Gorazd HREN Zdravko PRAUNSEIS Sebastijan SEME Bojan ŠTUMBERGER Janez USENIK Peter VIRTIC Ivan ŽAGAR Uredniško izdajateljski svet / PUBLISHING & EDITORIAL COUNCIL Dr. Anton BERGANT, Litostroj Power d.d., Slovenia Prof. dr. Marinko BARUKCIC, Josip Juraj Strossmayer University of Osijek, Croatia Prof. dr. Goga CVETKOVSKI, Ss. Cyril and Methodius University in Skopje, Macedonia Prof. dr. Nenad CVETKOVIC, University of Nis, Serbia Prof. ddr. Denis ĐONLAGIC, University of Maribor, Slovenia Doc. dr. Brigita FERCEC, University of Maribor, Slovenia Prof. dr. Željko HEDERIC, Josip Juraj Strossmayer University of Osijek, Croatia Prof. dr. Marko JESENIK, University of Maribor, Slovenia Prof. dr. Ivan Aleksander KODELI, Jožef Stefan Institute, Slovenia Prof. dr. Rebeka KOVACIC LUKMAN, University of Maribor, Slovenia Prof. dr. Milan MARCIC, University of Maribor, Slovenia Prof. dr. Igor MEDVED, Slovak University of Technology in Bratislava, Slovakia Prof. dr. Matej MENCINGER, University of Maribor, Slovenia Prof. dr. Greg NATERER, Memorial University of Newfoundland, Canada Prof. dr. Enrico NOBILE, University of Trieste, Italia Prof. dr. Urška LAVRENCIC ŠTANGAR, University of Ljubljana, Slovenia Izr. prof. dr. Luka SNOJ, Jožef Stefan Institute, Slovenia Prof. Simon ŠPACAPAN, University of Maribor, Slovenia Prof. dr. Gorazd ŠTUMBERGER, University of Maribor, Slovenia Prof. dr. Anton TRNIK, Constantine the Philosopher University in Nitra, Slovakia Prof. dr. Zdravko VIRAG, University of Zagreb, Croatia Prof. dr. Mykhailo ZAGIRNYAK, Kremenchuk Mykhailo Ostrohradskyi National University, Ukraine Prof. dr. Marija ŽIVIC, Josip Juraj Strossmayer University of Osijek, Croatia Tehnicni urednik / TECHNICAL EDITOR Sonja KRAJNC Tehnicna podpora / TECHNICAL SUPPORT Tamara BRECKO BOGOVCIC Izhajanje revije / PUBLISHING Revija izhaja štirikrat letno v nakladi 100 izvodov. Clanki so dostopni na spletni strani revije - www.fe.um.si/si/jet.html / The journal is published four times a year. Articles are available at the journal’s home page - www.fe.um.si/en/jet.html. Cena posameznega izvoda revije (brez DDV) / Price per issue (VAT not included in price): 50,00 EUR. Informacije o narocninah / Subscription information: http://www.fe.um.si/en/jet/subscriptions.html Lektoriranje / LANGUAGE EDITING Shelagh MARGARET HEDGES (EN), AMIDAS d.o.o. (SLO) Oblikovanje in tisk / DESIGN AND PRINT Tiskarna Saje d.o.o. Naslovna fotografija / COVER PHOTOGRAPH Jurij AVSEC Oblikovanje znaka revije / JOURNAL AND LOGO DESIGN Andrej PREDIN Ustanovni urednik / FOUNDING EDITOR Andrej PREDIN Izdajanje revije JET financno podpira Javna agencija za raziskovalno dejavnost Republike Slovenije iz sredstev državnega proracuna iz naslova razpisa za sofinanciranje domacih znanstvenih periodicnih publikacij / The Journal of Energy Technology is co-financed by the Slovenian Research Agency. Spoštovani bralci revije Journal of energy technology (JET) Vse od zacetkov cloveštva so bili ogrevanje bivališc, kurjenje in toplotna obdelava hrane izjemnega pomena. Tudi v današnjem casu cloveštvo porabi velik del energije za ogrevanje in hlajenje. Ceprav so sistemi ogrevanja zelo napredovali in se je mocno izboljšal izkoristek naprav, ljudje še vedno porabimo približno 50 % vse energije za ogrevanje. Ogrevanje v svetu še vedno vecinoma poteka s pomocjo fosilnih goriv. Približno polovica energije se porabi za industrijsko ogrevanje, preostala polovica pa za ogrevanje stavb, sanitarne vode, kuhanje in potrebe po toploti v kmetijstvu. Vecino toplotne energije še vedno pridobimo s pomocjo zgorevanja fosilnih goriv. Procesi ogrevanja prispevajo približno 40 % vseh emisij ogljikovega dioksida. Glede na svetovno ekološko situacijo mislim, da je skrajni cas za intenzivno uporabo obnovljivih virov v mnogo vecji meri. Tudi procesi soproizvodnje toplote in elektricne energije ter uporabe toplotnih crpalk bi morali prispevati k precejšnjemu zmanjšanju emisij toplogrednih plinov. Z intenzivno uporabo vodikovih tehnologij bi lahko veliko prispevali tudi k izboljšanju ekološke situacije … Vsem bralcem želim zanimivo branje nove številke revije JET in upam, da bo vsak našel kaj zanimivega. Jurij AVSEC odgovorni urednik revije JET Dear Readers of the Journal of Energy Technology (JET) Since the beginning of mankind the heating of dwellings, burning and thermal processing of food have been of the utmost importance. Even today, humanity uses a large part of energy for heating and cooling. Despite the fact that heating systems have advanced greatly, and the efficiency of devices has improved greatly, people still use approximately 50% of all energy for heating in the world. Heating in the world is still done mainly with the help of fossil fuels. About half of the energy is used for industrial heating, and the remaining half for heating buildings, sanitary water, cooking and heat needs in agriculture. The majority of thermal energy is still obtained by burning fossil fuels. Heating processes contribute about 40% of all carbon dioxide emissions. Considering the global ecological situation, I think that the time has come for the intensive use of renewable resources to a much greater extent. The processes of co-production of heat and electricity and the use of heat pumps should also contribute to a substantial reduction of greenhouse gas emissions. Furthermore, with the intensive use of hydrogen technologies, we could make a substantial contribution to improving the ecological situation... I wish all readers an interesting reading of the new issue of JET magazine, and I hope that everyone will find something interesting . Jurij AVSEC Editor-in-chief of JET Table of Contents Kazalo Analytical estimation of the thermal stability of HTS magnets during sudden discharge Analiticna ocena toplotne stabilnosti HTS-magnetov med nenadnim praznenjem Takanobu Mato, So Noguchi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Charging stations connected to street light power systems Polnilne postaje prikljucene na elektroenergetski sistem ulicne razsvetljave Peter Janiga . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Inflationary elevated energy prices as main factor of fuelling economically viable electricity production in EU fossil fuel based thermal power plants Inflacijsko povišane cene energije kot glavni faktor pospeševanja ekonomsko upravicene proizvodnje elektricne energije v EU fosilno gorivnih termoelektrarnah Martin Bricl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model Analiticna ocena optimalnega nagiba PV panela na podlagi modela proucevanja soncnega sevanja pri jasnem nebu Elena Golubovska, Biljana Citkuseva Dimitrovska, Roman Golubovski . . . . . . . . . . . . . . . . . . . 41 SWOT analysis of hydrogen economy Ekonomija vodika s SWOT-analizo Dominik Oravec, Florinda F. Martins, Frantisek Janicek, Miroslava Farkas Smitkova . . . . . . . . 54 Instructions for authors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63 JET Volume 16 (2023) p.p. 11-17 Issue 4, 2023 Type of article: 1.01 http://www.fe.um.si/si/jet.htm ANALYTICAL ESTIMATION OF THE THERMAL STABILITY OF HTS MAGNETS DURING SUDDEN DISCHARGE ANALITICNA OCENA TOPLOTNE STABILNOSTI HTS-MAGNETOV MED NENADNIM PRAZNENJEM Takanobu MatoR1R 1 Corresponding author: Mr. Takanobu Mato, Hokkaido University, Information Science and Technology, Kita 14, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0814, Japan, Tel.: +81-11-706-7670, E-mail address: mato@em.ist.hokudai.ac.jp So Noguchi22 Hokkaido University, Department, Information Science and Technology, Kita 14, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0814, Japan Keywords: HTS magnets, no-insulation technique, thermal stability, analytical expression Abstract Since the advent of 2nd-generation high-temperature superconducting (HTS) tapes, which show great features on critical temperature, critical current density, and critical magnetic field, many researchers have been trying to generate ultra-high magnetic fields using HTS coils. One more promising technology is a no-insulation (NI) winding technique. This technique suppresses the possibility of thermal runaway and burning-out of HTS coils drastically. The interest in compact nuclear fusion magnets wound with HTS conductors has been increasing rapidly during the last five years. The simulation of such magnets larger than MRI/NMR HTS magnets takes an unfeasibly long time. Therefore, we present a simple expression of the coil temperature rise under a simple assumption derived from the simple coil model, to investigate the stability of large-scale magnets. The method’s advantages are simplicity, versatility, and nearly no computation, enabling a time reduction in the first-cut design. Povzetek Od pojava superprevodnih trakov druge generacije, ki delujejo pri visokih temperaturah (HTS) in ki izkazujejo izjemne znacilnosti v smislu kriticne temperature, gostote kriticnega toka in kriticnega magnetnega polja, si številni raziskovalci prizadevajo za generiranje ultravisokih magnetnih polj z uporabo HTS-tuljav. Obetavna tehnologija na tem podrocju je tehnika navijanja brez izolacije (NI). Ta pristop znatno zmanjša tveganje za termicni preboj in izgorevanje HTS-tuljav. V zadnjih petih letih opažamo vecje zanimanje za kompaktne magnete jedrske fuzije, ki so naviti s HTS-prevodniki. Simulacija takih magnetov, vecjih od HTS-magnetov, uporabljenih v MRI-/NMR-napravah, zahteva neizvedljivo dolg cas. Zato v tem clanku predstavljamo preprost izraz za opis dviga temperature tuljave, ki temelji na preprosti predpostavki, izpeljani iz osnovnega modela tuljave, s ciljem raziskovanja stabilnosti magnetov velikih dimenzij. Glavne prednosti predlagane metode so njena preprostost, univerzalnost in minimalna potreba po racunskih operacijah, kar omogoca skrajšanje casa zacetnega nacrtovanja. , Takanobu Mato, So Noguchi JET Volume 16 (2023) p.p. Issue 4, 2023 1 INTRODUCTION Towards the future of nuclear fusion power, our group is trying to establish a way to simulate and evaluate the thermal stability of superconducting magnets to generate ultra-high magnetic fields. Superconducting magnets wound with high-temperature superconductors (HTS), especially Rare-Earth Barium Copper Oxide (REBCO) [1], are considerably promising for the magnetic confinement of plasma. HTS tapes, such as REBCO-coated conductors, can maintain superconductivity in high magnetic fields (> 20 T). In 2011, Hahn et al. proposed a no-insulation (NI) winding technique for HTS pancake coils [2], where there is no insulation between the winding turns. The NI winding technique improves the thermal stability of HTS pancake coils greatly, solving the long-lasting thermal instability for high magnetic field generation [3], [4]. The mechanism of the high thermal stability is explained as follows [5]: a hot spot, which potentially causes a thermal runaway, appears in an NI HTS coil. The operating current can flow into the adjacent turns through the turn-to-turn contact surfaces, avoiding the hot spot. The consequent Joule heat dissipation is less than the case of a conventionally turn-insulated HTS coil. As a matter of fact, a metal-insulation winding technique, which is categorized as one of the no-insulation winding techniques, was adopted to generate 20 T for a nuclear fusion coil at MIT [6]. The electromagnetic, thermal, and mechanical behaviors of NI HTS coils are complicated, and the simulation takes a long time, even to evaluate the thermal stability [7]. Furthermore, a fine simulation of such a large-scale NI HTS magnet is complex. Several researches and developments have been made on NI HTS magnet simulation methods; however, a fast and easy way to evaluate thermal stability is still necessary as a fundamental step of thermal stability designs. This paper proposes a simple analytical expression of NI HTS coil temperature. It is useful in the first-cut conceptual design. The formulation is given in the paper, and an arbitrary NI REBCO coil was investigated with different parameters. The maximum temperatures reached were checked as a function of the radial turn-to-turn resistance. For such a large magnet, a cooling effect is not negligible due to the long time constant. The timescale of heat dissipation and cooling effect is also discussed in the paper. The proposed expression for thermal evaluation enables the parameter survey as well. This helps clarify the thermal stability boundary, which will be addressed in the future. 2 MODEL AND FORMULATION 2.1 Circuit Model Fig. 1 shows an electrically equivalent circuit of an NI HTS magnet. The NI HTS coils are stacked and connected in series, forming the NI HTS magnet. The NI HTS magnet has the self-inductance The introduction mentions that each NI HTS coil has a radial current path through the turn-to- turn contact surfaces. The resistance in the radial direction is expressed as a radial resistance connected in parallel with the magnet inductance . The current source is not shown in the equivalent circuit, because only the cases of sudden discharge tests are evaluated (mentioned later). . Analytical estimation of the thermal stability of HTS magnets during sudden discharge Figure 1: Electrically equivalent circuit of an NI HTS magnet 2.2 Formulation of Coil Temperature From the above-shown electrically equivalent circuit model, we derived the current and temperature of the NI HTS magnet, considering the cooling effect. Here, the NI HTS magnet was assumed to be disconnected from a power source as the worst scenario, commonly called a sudden discharge test. The magnet is immersed in a coolant such as liquid helium. The magnet current during discharging decays exponentially; the following Equation expresses it: 3 ANALYTICAL RESULTS The current and temperature transitions of large-scale NI HTS magnets were investigated in this Section. Table 1 shows the magnet specifications. The magnet generates approximately 10 T at the magnet center. It was assumed that the magnet was immersed in liquid helium, and the heat could only move through the magnet surfaces in contact with the liquid helium. The heat is transferred according to Newton’s law of cooling. The heat transfer coefficient was also assumed constant at 100 W/(m2·K) [8]. The current profiles after the power shutdown at t = 0 s are shown in Fig. 2 in the cases of radial resistances 10, 50, and 100 µO as a design parameter. The magnet current decays exponentially, and the time constant shortens as the high radial resistance. The magnet is heated with the Joule heat by the current passing through the radial current. Fig. 3 shows the magnet temperature in the three cases of different radial resistances. The temperature increases rapidly, and reaches a maximum after the power shutdown due to the cooling. In the case of radial resistance 100 µO, the maximum temperature is 172 K. It is noted that the lower the resistance is, the lower is the reached maximum temperature. This is because a low resistance results in a long time constant, i.e., a long time for energy dissipation and sufficient cooling. Table 1: Magnet specifications Parameter Value inner diameter [m] 0.50 outer diameter [m] 1.0 height [m] 0.3 magnet inductance [mH] 70 mass density [kg/m3] 9000 specific heat [J/(kg·K)] 100 heat transfer coefficient [W/(m2·K)] 100 magnetic energy [MJ] 56 initial current [kA] 40 operating temperature [K] 4.2 Takanobu Mato, So Noguchi JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the thermal stability of HTS magnets during sudden discharge Figure 2: Coil current of an NI HTS coil with different radial resistance by Equation (2.1) Figure 3: Temperature of an NI HTS coil with different radial resistance by Equation (2.4) Next, the maximum reached temperatures were investigated as a function of the radial resistances. The result is shown in Fig. 4. The maximum temperature increased monotonically and saturated at ~352 K. In the thermal stability view of NI HTS magnets, the increased temperature should be within 300 K to prevent coil performance degradation [8]. The reference line is also drawn in the Figure. When the radial resistance is beyond 1 mO, the increased temperature exceeds 300 K. The electrical time constant is also shown in Fig. 4. It is evident that the low resistance led to the long electrical time constant, and the consequent temperature rise was low. Figure 4: Reached temperature of HTS magnet as a function of radial resistance It is shown that the balance of the timescale of energy dissipation and cooling affects the thermal stability significantly . Now, we introduced the ratio of the electrical time constant to the thermal time constant, , as below: (3.1) The ratio computed as a function of the radial resistance is shown in Fig. 5. Here, it is noted that the thermal time constant remained constant at 614 s. The ratio increased linearly as the electrical time constant decreased. The high ratio means the heat dissipation occurred within a short time so as not to cool the magnet effectively. It is shown that the ratio is one at around 0.1 mO. Whereas the ratio is ~100 at 10 mO; i.e., the cooling effect is 1/100 times better from the viewpoint of Joule heat dissipation. Around the region of = 100, the reached maximum temperature is fully saturated in Fig. 4. In such a large-scale NI REBCO magnet with a long time constant, the radial resistance plays a significant role in thermal stability, and must be designed meticulously. 4 CONCLUSIONS In the paper, we have proposed the simple stability-evaluation expression of no-insulation (NI) high-temperature superconducting (HTS) magnets. The formulation is shown of the magnet temperature during sudden discharging. It can be used to evaluate the thermal stability of large-scale NI HTS magnets. Several parameter surveys were also conducted using the proposed formula. The results showed that the radial resistance should be low to suppress the high temperature rise by enabling long Joule heat dissipation, whereas the time constant is long. Optimizing the radial resistance is needed [9], [10]. Further analysis is ongoing using the proposed formula. References [1] M. Wu et al.: Superconductivity at 93 K in a new mixed-phase Yb-Ba-Cu-O compound system at ambient pressure, Phys. Rev. Lett, Vol. 5, Iss. 9, p.p. 908-910, 1987 [2] S. Hahn et al.: HTS pancake coils without turn-to-turn insulation, IEEE Trans. Appl. Supercond, Vol. 21, Iss. 3, p.p. 1592-1595, 2011 [3] S. Hahn et al.: 45.5-Tesla direct-current magnetic field generated with a high-temperature superconducting magnet, nature, Vol. 570, p.p. 496-499, 2019 [4] J. LIu et al.: World record 32.35-tesla direct-current magnetic field generated with whole superconductor magnet, Supercond. Sci. Technol, Vol. 33, Iss. 3, Art. no. 03LT01, 2020 [5] A. Ikeda et al.: Transient behaviors of no-insulation REBCO pancake coil during local normal-state transition, IEEE Trans. Appl. Supercond, Vol. 26, Iss. 4, 2016 [6] D. Chandler et al.: MIT-designed project achieves major advance toward fusion energy, MIT news, available at https://news.mit.edu/2021/MIT-CFS-major-advance-toward-fusion-energy-0908, 2021 [7] S. Noguchi et al.: A newly developed screening current simulation method for REBCO pancake coils based on extension of PEEC model, Supercond. Sci. Technol, Vol. 35, Iss. 4, Art. no. 04400, 2020 [8] Y. Iwasa et al.: Case studies in superconducting magnets: design and operational issues, Springer: New York, 2009 [9] Y. Suetomi et al.: Quench and self-protecting behavior of an intra-layer no-insulation (LNI) REBCO coil at 31.4 T, Supercond. Sci. Technol, Vol. 34, Iss. 6, Art. no. 064003, 2021 [10] S. Noguchi et al.: A simple protection evaluation method for no-insulation REBCO pancake coils during local normal-state transition, Supercond. Sci. Technol, Vol. 32, Iss. 4, Art. no. 045001, 2019 Takanobu Mato, So Noguchi JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the thermal stability of HTS magnets during sudden discharge JET Volume 16 (2023) p.p. 18-28 Issue 4, 2023 Type of article: 1.01 http://www.fe.um.si/si/jet.htm CHARGING STATIONS CONNECTED TO STREET LIGHT POWER SYSTEMS POLNILNE POSTAJE PRIKLJUCENE NA ELEKTROENERGETSKI SISTEM ULICNE RAZSVETLJAVE Peter JanigaR1R 1 Corresponding author: Assoc. Prof., Peter Janiga, Slovak University of Technology in Bratislava, Faculty of Electrical Engineering and Information Technology, Ilkovicova 3, 84104 Bratislava, Tel.: +421 2 6029 1811, E-mail address: peter.janiga@stuba.sk Keywords: street lighting, public lighting, charger, charging station, power quality, electric vehicle, lamp, luminaire Abstract Street light grids are dense and compact networks in all cities. They power the luminaires and elements of smart cities. Recently, they have also been used to power chargers for electric vehicles. The article analyses how charging stations can be connected to public lighting networks, and gives knowledge about connecting the charger and optimising operations to increase the power delivered to vehicles. Initial installations show that the combination of luminaires, public lighting networks and chargers shows specific characteristics. The aim of the paper is to provide knowledge about the implementation of chargers in street light grids. The last part of the paper presents the results a case study, which is focused on voltage drops and limits for installing charging stations. Povzetek Elektroenergetski sistemi za ulicno razsvetljavo so gosta in kompaktna omrežja v vseh mestih. Napajajo svetila in elemente pametnih mest. V zadnjem casu se uporabljajo tudi za napajanje polnilnic elektricnih vozil. Clanek analizira, kako lahko polnilne postaje prikljucimo na omrežja javne razsvetljave, podaja znanja o priklopu polnilnika in optimizaciji delovanja za povecanje moci, ki se pretaka v vozila. Zacetne inštalacije kažejo, da kombinacija svetilk, omrežij javne razsvetljave in polnilnic kaže specificne znacilnosti. Namen prispevka je podati znanje o implementaciji polnilnic v omrežja javne razsvetljave. Zadnji del prispevka predstavlja rezultate študije primera, ki se osredotoca na padce napetosti in omejitev za namestitev polnilnih postaj. 1 INTRODUCTION Street light grids (SLG) are the main parts of cities and municipalities. They are on all the streets. They are a network that covers the entire city and allows smart city elements to be powered. A specific feature of an SLG is that the main appliance (luminaire) is switched on only at night. These properties create possibilities for the use of SLG to power charging stations for electric vehicles. There are already several projects in the world, but there is not enough experience and information on how to build and operate these common networks [9]. Charging modes In relation to the method of connecting the vehicle to the power network, the EN 61851-1 [1] Standard defines four possible connection modes. • Mode 1 - In this case, a standardised socket with a nominal current value not exceeding 16A is used to connect to the AC supply voltage network. It can be a single-phase socket with a nominal voltage of 230V, or a three-phase socket with a nominal voltage of 400V, in both cases with a protective earth conductor. • Mode 2 - In this case, a standardised socket with a rated current value not exceeding 32A is used to connect to the AC supply voltage network. It can be a single-phase socket with a nominal voltage of 230V, or a three-phase socket with a nominal voltage of 400V, in both cases with a protective earth conductor. The difference from mode 1, in addition to the rated current, is the need to use a charge control circuit with separate electrical protection in this case. The circuit is integrated directly into the control box of the charging cable, which must be at a distance of 0.3m from the plug, or directly on it. • Mode 3 - Is charging through a device reserved only for charging electric vehicles. The device is connected permanently to the AC power supply. It is necessary to use a charging control circuit that communicates with the device (charging station) during the entire charging period. • Mode 4 - In the first three modes charging was carried out using the vehicle’s on-board charger. The fourth mode uses a charger located outside the vehicle’s deck to connect the vehicle to the power network. The charger can be powered from an AC or DC network. However, the standard is to be powered by an AC current, which must be converted to a DC current in a charging station outside the vehicle. Even in this case, communication is necessary, where the charging control circuit communicates with the public charging station during the entire charging period. The method of charging electric vehicles and their integration into the distribution grid can have a significant impact on the energy system. In the case of high-power charging at fast-charging stations with high capacity, managing substantial amounts of electrical energy simultaneously may necessitate adjustments in the distribution grid. Peak load management is crucial, as the current collective surge in charging can create peak loads on the grid. Implementing an intelligent charging infrastructure that can optimise charging based on the current state of the grid is essential. The development of technologies and strategies for electric vehicle charging plays a crucial role in the pursuit of a sustainable and efficient integration into the energy system. 2 METHODS The calculation methodology is based on the definition of boundary conditions such as operating charging stations in general and existing public lighting networks. The charging stations are divided into AC and DC. This division determines the output power of the charger. Charging stations with an AC current are typically slower than DC stations [8]. Charging with an AC current can be divided into two groups: slow charging with a power of up to 3.7kW, and accelerated charging with a power of 3.7kW to 22kW. When charging with a DC current, we are talking about fast and ultra-fast charging. Fast DC charging is considered to be charging with a power of up to 100kW, while the power of fast charging stations is usually not less than 50kW. Ultra-fast DC charging is charging with a power of more than 100kW. 2.1 Connecting the stations to the street light grids Although the implementation of charging stations in the SLG is a relatively new topic, there are already several ways to connect and control the station [2]. However, everything depends on the possibilities and current capacity reserves of the SLG, because public lighting is always a primary functionality that cannot be influenced negatively by other additional appliances. 2.2 Implementation of a charging station on a pole Connecting the charging station to a public lighting pole can be done in two ways. The first of them is the connection of a charging station in the form of a wall box to an existing pole. The second is the integration of the charging station directly into the public lighting pole. This solution is better for networks with reconstructed poles, where it is expected to replace the original poles with new ones. This solution is not visually disturbing, and the public lighting pole looks the same as ordinary poles, except that it contains a charging connector. The third solution is to place the charging station in a separate column. This solution is suitable if there is no pole near or for parking spaces. However, there must be a public lighting cable nearby to power the charging station. From the point of view of installation, this solution is suitable for more extensive renovations, where cable lines are also replaced. Figure 1: Charging station integrated to the pole (right), charging station in the form of a wall box (middle), charging station in a separate column In all cases, as with all public AC charging stations, the Type 2 connectors defined in EN 61851-1 are used as standard. 2.3 Electrical connection of the charging station From the point of view of connecting the power line, there are several ways to implement charging stations in the SLG. The first of them is the connection of the charging station to the power line that is common to public lighting. In this case, intelligent control is necessary, that corrects the maximum power of the charging station based on the current state of the network, so as not to limit the public lighting function. Depending on the possibilities of the network, different capacities of charging stations can be used, up to charging stations with a power of 22kW when supplied from three phases. Figure 2: Connection of the charging station to the power line common with the power supply of the SLG The second option is to connect the charging station to only one phase of the three-phase system. This phase is reserved for the power supply of the charger and other appliances (e.g. smart city appliances). In this case, public lighting luminaires are powered from the remaining two phases of the three-phase system. A disadvantage with this connection is the unbalanced load on the phase system and a lower charging power for the user, which is around 7kW (for 230 V). Figure 3: Connecting the charging station to the reserved one phase of the three-phase system Another option is the use of two independent three-phase power lines. One is used exclusively to power the public lighting network, and the other to power charging stations or other additional appliances. This method is advantageous to realise only in case of complex reconstructions of SLG, where old power lines are replaced with new ones. The advantage is that the maximum charging power is always available. It is given by the maximum current carrying capacity of the branch and the used charging stations. The power of the charging stations is independent of the lights. This, of course, applies if the power line of the public lighting switchboard is sized for the maximum charging power of the lamps and charging stations in the branches. Figure 4: Charging station powered from a separate power line A specific case of the previous option is the connection of an SLG line and a line for charging stations at their ends. This creates a two-side power supply system, which can have a positive effect, for example, to reduce voltage drops, but this system requires luminaires with remote switching on the system. 2.4 Voltage drop The design of an SLG requires taking care of voltage drop, because it has long distance of power line. The same holds for the implementation of charging stations, but the power load is higher. There is no general Standard that defines the maximum value of the voltage drop in the SLG. The EN 50160 [4] Standard defines a specific voltage deviation of ± 10%, which, at a nominal voltage of 230 V, is in the range of 207 V to 253 V. However, this Standard is only for distribution grids, and defines the SLG voltage only at the power supply point. In Slovakia, the STN 332130 [3] Standard defines the maximum voltage drops for building a lighting installation. Due to the similar indoor appliances and public lighting, it is used in practice as an approximate problem in the calculation of voltage drops in the public lighting network. According to this Standard, the voltage drop in the SLG does not exceed 4% of the nominal voltage from the switchboard to the appliances. 2.5 Calculation of voltage drop There are several ways to calculate voltage drops. In the calculations, a simplification is used so that the entire load is at the end of the line. This simplification represents the worst possible situation. For the following calculations, relation (2.1) is from STN 332130, which is for three-phase circuits. This is adjusted to relation (2.2), because the goal of the calculation is to determine the maximum lengths of the power lines by using standard cable cross-sections and a maximum voltage drop of 4% of the nominal voltage value. Charging stations connected to street light power systems Peter Janiga JET Volume 16 (2023) p.p. Issue 4, 2023 Charging stations connected to street light power systems Peter Janiga JET Volume 16 (2023) p.p. Issue 4, 2023 Charging stations connected to street light power systems Figure 5: Dependence between maximum current and length of line for 4% voltage drop and variable cables. Copper (CYKY) and aluminium (AYKY) Peter Janiga JET Volume 16 (2023) p.p. Issue 4, 2023 In the graph, the CYKY-J 4x10 means a cable with a copper core with 4 ,where 3 wires are for phases, and one is for PEN (neutral N together with protective earth PE). The cross-section is 10 square millimetres 3 RESULTS The case study deals with several variants of connecting charging stations to the public lighting network. It determines how far from the SLG switchboard the charging stations can be connected, or how many can be placed in a branch with different cable lines, and the voltage drop is no higher than 4% of the nominal voltage. In this case study, all variants were based on the complex formula (3.1) to calculate the voltage drop. It takes into account the distribution of the current load Ii in the chosen distances of the branch li, based on the sum of the current moments. In Tab. 1 and Tab. 2 are the maximum lengths of cable lines from the switchboard, where the charging station can be placed, and the voltage drop has not exceeded the Standard requirements (4%). For the first variants the powering is from one phase according to Fig. 6. Table 1: Maximal length of line – variant 1 One charger 3.7kW (1x16A, 230V) connected to one phase without luminaires Wire CU 4x10 CU 4x16 CU 4x25 CU 4x35 AL 4x16 AL 4x25 AL 4x35 AL 4x50 Max. length of line (m) 190 304 474 664 188 293 411 587 Table 2: Maximal length of line – variant 1 One charger 7.4kW (1x32A, 230V) connected to one phase without luminaires Wire CU 4x10 CU 4x16 CU 4x25 CU 4x35 AL 4x16 AL 4x25 AL 4x35 AL 4x50 Max. length of line (m) 95 152 237 332 94 147 205 293 In this case the charger uses different phase like luminaires. The current in the phase is independent on the luminaires`operation. The length for a 7.4kW charger is shorter, equivalent to the power. The third variant is powered according to Fig. 7. In this case there are luminaires with an input power of 50 W every 25 metres for a typical situation [7]. The charger and luminaires are connected to all three phases. In this case, we try to simulate the operation with luminaires. The length is calculated only for one charger with full power. Charging stations connected to street light power systems Peter Janiga JET Volume 16 (2023) p.p. Issue 4, 2023 Table 4: Maximal length of line – variant 4 One charger 22kW (3x32 A) connected to three phases with luminaires every 25m, with the charger connected in the middle of the line Wire CU 4x10 CU 4x16 CU 4x25 CU 4x35 AL 4x16 AL 4x25 AL 4x35 AL 4x50 Distance to charger (m) 47 74,5 116,5 163 46,5 72 101 143,5 Max. length of line (m) 925 1225 1525 1825 925 1225 1450 1750 4 DISCUSION Comparing the second and third variants, we see that the distance difference when using the power line is minimal. So, in the model example, it does not make a significant difference whether the charging station is powered from a dedicated phase that does not power the lights, or is powered from a phase that powers the lights in addition to the charging station. The reason is that the power consumption of luminaires is significantly less than the consumption of the charger. A more significant difference can occur if the consumption of the lights is comparable to the power input of the charger (e.g. old luminaires with high consumption). The aim of the fourth variant is to show that the maximum length of the power lines is increasing significantly when the charging station is moved from the end of the branch (variant 3) to half the distance (variant 4). Because the charging station is an appliance with a significantly higher power consumption compared to modern LED luminaires, the total lengths of the branches in variant 4 are, in some cases, up to 10 times larger than in the case of variant 3. Dependence between the number of chargers and the distance from the switchboard In terms of load, a 7.4kW charging station connected to one phase is equivalent to a 22kW charger connected to three phases. In both cases, the power per phase is the same. Tab. 5 shows how many chargers can be installed at distances of 50, 100, 200 and 300 metres from the switchboard. The consumption of luminaires is not taken into account. In residential areas, the consumption of LED lamps is significantly less than the consumption of the charging station [5]. The closer the charging stations are to the switchboardthe more there can be. Cross-sections CU10 and AL16 are not suitable for maximum load (7.4kW one phase or 22kW three phase) and have limited options for powering the light. If it were necessary to install charging stations at distances greater than 200 metres, it would be worth considering the use of even larger cable conductor cross-sections than those shown in Tab 5. Charging stations connected to street light power systems Table 5: Number of chargers without luminaires Maximum number of chargers (7.4kW one phase or 22kW three phase) without luminaires Wire CU 4x10 CU 4x16 CU 4x25 CU 4x35 AL 4x16 AL 4x25 AL 4x35 AL 4x50 50m from switchboard 1 3 4 5 1 2 3 4 100m from switchboard 0 1 2 3 0 1 2 2 200m from switchboard 0 0 1 1 0 0 1 1 300m from switchboard 0 0 0 1 0 0 0 0 There is a possibility to increase the number of charging stations in the branch and increase the sum of installed power of the charging stations, but this requires intelligent control, that redistributes the available current capacity for the charging stations [6]. During simultaneous charging of electric vehicles from several charging stations in the branch, it is necessary to limit their output power, so that the current capacity of the branch is not exceeded. The last example is the consideration of a 500m long branch. This branch contains luminaires every 25m. The connection is implemented as in Fig. 7. The first charging station is located at a distance of 25m and each subsequent 25m further. Table 6: Number of chargers for a 500m line Number of 22kW chargers in a 500m line with 100W luminaires every 25m. The chargers are connected in distance of 25, 50, 100, 150m Wire CU 4x10 CU 4x16 CU 4x25 CU 4x35 AL 4x16 AL 4x25 AL 4x35 AL 4x50 Number of chargers 2 2 3 4 2 2 3 4 Tab 6 shows how many chargers can be connected to a 500m line. When the chargers are every 25m, which means every pole, there can be only 2 to 4 chargers, but relatively close to the switchboard (25m to 100m). The result is that the charger is not easy to connect at a long distance from the switchboard on an existing SLG. 5 CONCLUSION Currently, there are several professional and scientific articles focused on charging stations. However, the charging stations associated with the SLG operation are addressed minimally. The goal was to provide comprehensive information about charging station operation and implementation methods. It can be connected to existing networks, as well as newly built ones. The electrical connection can be single-phase or multi-phase. The choice of a suitable solution depends on the chargers used, and also the method of operation of the SLG. This paper provides a description of the theoretical level, and a case study focused on the issue of the distance between the charging stations and the switchboard (or power supply point). Because charging stations have a significant consumption compared to luminaires, inappropriate placement and connection of the charging station can shorten the power line. The calculations consider the nominal power of the charging stations. By using charge management (reducing the input power of the charger), the number of installed chargers increases, but, on the other hand, the charging time increases. As part of research on this topic the authors have carried out several measurements. The results were processed step by step, and will be published in the following publications. The aim of these measurements will be for providing a base to the theoretical level and showing the risks and potential of SLG in connection with charging stations. ACKNOWLEDGMENT This paper is supported by the agency VEGA MŠVVaŠ SR under Grant No.: VEGA1/0390/23. References [1] EN 61851-1 Electric vehicle conductive charging system. Part 1: General requirements [2] EN 62196-1 Plugs, socket-outlets, vehicle connectors and vehicle inlets - Conductive charging of electric vehicles - Part 1: General requirements [3] STN 33 2130 Electric engineering regulations. Internal electric distribution lines [4] EN 50160 Voltage characteristics of electricity supplied by public electricity networks [5] T. Novak, J. Sumpich, J. Vanus,K. Sokansky, R. Gono, J. Latal, P. Valicek: A model for predicting energy savings attainable by using lighting systems dimmable to a constant illuminance, (2020) Lecture Notes in Electrical Engineering, 554, pp. 860 – 869 DOI: 10.1007/978-3-030-14907-9_83 [6] L. Kuncicky, T. Novak, K. Sokansky, Z. Slanina: Road Lighting Control Options, (2019) Proceedings of 44th WILGA Symposium on Photonics Applications and Web Engineering, Wilga, POLAND, MAY 26-JUN 02, 2019, DOI: 10.1117/12.2536886 [7] J. Škoda and M. Motycka: Lighting Design Using Ray Tracing, 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4), 2018, pp. 1-5, doi: 10.1109/LUMENV.2018.8521111. [8] C. Suarez and W. Martinez: Fast and Ultra-Fast Charging for Battery Electric Vehicles – A Review, 2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019, pp. 569-575, doi: 10.1109/ECCE.2019.8912594. [9] T. Chen et al.: A Review on Electric Vehicle Charging Infrastructure Development in the UK, in Journal of Modern Power Systems and Clean Energy, vol. 8, no. 2, pp. 193-205, March 2020, doi: 10.35833/MPCE.2018.000374. Peter Janiga JET Volume 16 (2023) p.p. Issue 4, 2023 JET Volume 16 (2023) p.p. 29-40 Issue 4, 2023 Type of article: 1.01 http://www.fe.um.si/si/jet.htm INFLATIONARY ELEVATED ENERGY PRICES AS THE MAIN FACTOR OF FUELLING ECONOMICALLY VIABLE ELECTRICITY PRODUCTION IN EU FOSSIL FUELS BASED THERMAL POWER PLANTS INFLACIJSKO POVIŠANE CENE ENERGIJE KOT GLAVNI FAKTOR POSPEŠEVANJA EKONOMSKO UPRAVICENE PROIZVODNJE ELEKTRICNE ENERGIJE V EU FOSILNO GORIVNIH TERMOELEKTRARNAH Martin BriclR1R1 Corresponding author: dr. Martin Bricl, mag.inž.str., E-mail address: martin.bricl@student. um.si Keywords: electricity production, elevated energy prices, fossil fuels, economically viable energy production, thermal power plants Abstract The inflation in the last two years has driven the prices of the materials, goods as well as energy significantly higher. With steep increased inflation from month to month in the last two years, the overall inflation peaked at 9.2%, and core inflation at 6.2% in 2022 for the Eurozone area. This elevated prices are troubling the markets, industry and households, making the everyday business much more difficult for them than it was in pre-inflationary times. Also, additional geopolitical changes happened in the last two years (the war in Ukraine) which impacted the energy supply from the east significantly , primarily lowering the inflow of Russian gas to the European states to almost zero and banning the Russian crude from the international markets. This demanding condition on the energy market, as well as the very narrow time frame for building up a sufficient supply of energy for the winter of 2022 resulted in rather unexpectedly favourable conditions for energy generation (electricity or heat) from still operating coal based thermal power plants, which, in some way, is unacceptable, since we are exiting the coal based thermal power plants in EU actively, and trying to substitute them with renewables & alternatives. However, the aforementioned international markets stress test revealed that abandoning the fossil fuels from our everyday life will not be that easy, as we thought a decade ago. Povzetek Inflacija je v zadnjih dveh letih bistveno dvignila cene surovin, blaga in energije. Z mocno narašcajoco inflacijo iz meseca v mesec v zadnjih dveh letih je skupna inflacija leta 2022 za obmocje evra dosegla najvišjo vrednost pri 9,2 %, osnovna inflacija pa pri 6,2 %. Te povišane cene povzrocajo težave trgom, industriji in gospodinjstvom, ki jim otežujejo vsakdanje poslovanje. V zadnjih dveh letih so se zgodile tudi dodatne geopoliticne spremembe (vojna v Ukrajini), ki so mocno vplivale na oskrbo z energijo z vzhoda, predvsem so zmanjšale dotok ruskega plina v evropske države na skoraj nic in privedle do prepovedi izvoza ruske surove nafte na mednarodne trge. Te zahtevne razmere na energetskem trgu in zelo ozek casovni okvir za vzpostavitev zadostne zaloge energije za zimo 2022, so povzrocile precej nepricakovano ugodne razmere za proizvodnjo energije (elektrike ali toplotne) iz še delujocih termoelektrarn na premog, kar je nesprejemljivo, saj EU aktivno opušca proizvodno elektricne energije iz termoelektrarne na premog in jih poskušamo nadomestiti z obnovljivimi viri in alternativami. Vendar pa je že omenjeni stresni test mednarodnih trgov pokazal, da opustitev fosilnih goriv iz našega vsakdana ne bo tako preprosta, kot smo mislili pred desetletjem. 1 INTRODUCTION The changed conditions on the international markets are the main driver for the completely new outlook with regard to the energy production in the Eurozone area. With closed pipelines for gas from Russia towards Europe and limited Russian crude purchases due to international sanctions, the European Union was, in early 2022, in a tough position regarding the supply of electricity & heat for the domestic markets. With searching for an alternative supplier of the gas from Africa, the Americas and the Middle East, the EU started, or intensified, already operational production from its coal fired thermal power plants, in order to supply a crucial part of the electricity for the domestic market during the winter of 2022. The unexpected inflation emerged during that same time, being only transitional phenomena according to the reassurances of the FED and ECB. Nevertheless, that was not the case, as core inflation peaked at 9.2% and 6.2% correspondingly. This was a surprise for us all, and also for the market regulators who admitted their mistake at the time. The combination of both occurrences resulted in completely new market conditions with elevated prices overall, that made it possible for the thermal power plant to operate within green numbers for them, despite higher fuel, operation, maintenance and carbon dioxide allowances costs. Moreover, even the oil based thermal power plants operated in green numbers, which was a surprise for the energy market, since we are all working actively on the green transition, shifting our energy production from fossil fuels towards renewables and alternatives. 2 CHANGED MARKET CONDITIONS 2.1 Spike in coal spot prices As described in the introduction, the changed market condition contributed to the situation, where there was enough of a price elevation for the fossil fuel based thermal power plants to operate within the profitable area for them. With the price of electricity, also the price of fuel and operation & maintenance costs increased significantly. Below, in Figure 1, the spot price for the Newcastle coal is shown, where the spike in the price is seen [1] during the period of 2020 – 2023, which was driven mainly by the inflation pressures on the spot price, as well as very high demand for the particular coal, since thermal power plants were getting into the process of start-up. Newcastle coal is thermal coal exported out of the port of Newcastle (FOB) in New South Wales, Australia. It is the price benchmark for the seaborne thermal coal in the Asia-Pacific region, and is exported worldwide as primary fuel for the thermal power plants. Figure 1: The movement for the Newcastle Coal spot price. Note the spike in the spot price during 2020 to 2023. The spike was fuelled because of elevated inflation during this time, as well as the elevated demand for the coal, since the thermal power plants were backing the grid electricity consumption due to low production from gas powered power plants. From Figure 1 we can observe that the spot price of Newcastle coal increased from its low price of 51,95 € per metric tonne to 433,70 € per metric tonne, meaning that the purchase price of the primary fuel for the operating power plant went up by a factor of 8,3. Consistent with the measures from the central banks to slow and lower the inflation is also the decrease of the Newcastle coal spot price, where normalization of the price took place in the first two quartiles of 2023. Nevertheless, the elevated purchase prices for the coal persisted for almost two years, making the operators of the thermal power plants look very closely for the changes in coal spot prices, to secure the most advantageous price when ordering coal. 2.2 Higher maintenance and operational costs The operational costs of the conventional thermal power plants have risen significantly, due to the higher costs of the fuel and carbon emission allowances, which two present the main reason for the higher operational cost of the thermal power plants. However, also significant is the increase of the cost of the human labour. Due to inflationary pressures on the wages, the average personal income within the European Union increased by 4.4% in 2022, resulting in additional increases in operational costs. In Figure 2, the Eurostat labour cost levels [2] are presented on the EU map. Figure 2: The cost of labour within the EU. The densest orange colour marked countries have the highest labour cost within the EU. The labour cost ranges from 7,1 €/hour as the lowest average value to 53,4 €/hour as the highest average value (compensation of employees, plus taxes, minus subsidies). The average labour cost is averaged across all sectors of the industry, and is not only focused on the energy production sector. From Figure 2 we can observe that Iceland, the Netherlands, Denmark & Norway have the highest labour costs. The source: https://ec.europa.eu/eurostat/databrowser/view/LC_LCI_LEV/default/map?lang=en&category=labour.lc.lcan. 2.3 Price of carbon emission allowances Carbon emission allowances are also an additional cost to the end price of the electricity producers from the fossil fuels. The price of carbon emission allowances dictates the market, and it is dependent on the asking - offer performance of demand. Within the European Union the European Commission is releasing the carbon emission allowances (coupons) as well, as it is also the regulator for that particular market. In Figure 3, the price movement for the carbon emission allowances [3] is presented for the time period from 2010 to 2023. From the price movement in the presented graph we see that it is independent of the current international market conditions, since it is regulated as a cap-and-trade market. The rise in the price is achieved by limiting the number of issued and available allowances in every session of releasing the new allowances by the regulator. The spot price of the carbon emission allowances in phase 4 ETS has been fluctuating (after the significant rise of the price) in the area between 70 US dollars – 100 US dollars for a metric ton of emitted carbon dioxide into the atmosphere. The elevated prices of the carbon emission allowances are putting significant pressure on the operational costs of the thermal power plants, making it very difficult for them to operate economically positively. Nevertheless, the high electricity prices on the market were allowing the thermal power plants to operate economically positively within the two-year time period, despite the mechanisms in place to exit the coal-based electricity production gradually in the EU and G-20 countries. The EU regulators are in the process of discussion as to whether the governments across the EU shall also implement the carbon emission taxation for households – the suggested taxation could include additional taxes on the fuel for the transportation & heating of the households. That should give an additional boost to the green transition within the EU, but the regulators were quickly reminded that a lot of people could not afford this kind of additional expenses in the shape of new taxation, since the last overall inflation data for June 2023 is remaining at a high 5,5%, weakening the purchase power of the average European household from month to month. Because of that, there is not likely to be pressure from the EU regulators for the aforementioned taxation for now. 3 CRUCIAL ROLE OF THERMAL POWER PLANTS 3.1 Changed energy market conditions After the first price elevation the normalisation of electricity price was performed, mainly because of the cap regulated electricity price, decided by the governments. Gradually, the cap on the electricity prices is expected to be removed. However, the prices of electricity can stay elevated or can even rise further. The reason for that is the EU`s significant increase investment in renewables during the latest energy crisis as a response to the shrinking gas and crude oil imports from Russia. Due to the significant increase of electricity production from renewables, the instability of the grid is rising, making the distribution planning of grid operators even more difficult. That is resulting in a new way for how to adapt to the current energy market conditions, enforcing the electricity end users to change when to save and when to use electricity. 3.2 Thermal power plants crucial for energy supply In autumn 2022 it became evident that the shrinking supply of the Russian gas and crude would not cover the winter energy needs of Europe. Therefore, the safety plan of putting big thermal power plants [4] back in operation was launched, as presented in figure 4. Consequently, the thermal power plants went from stand-by mode to full operation, resulting in high domestic coal demand. Thermal power plants supplied the electricity as well as needed heat to consumers and end-users, enabling them to save stored gas and oil for later. Figure 4: Largest coal fired thermal power plants in the EU as of 2021. Since some nuclear power plants in the EU, particularly in France, were in regular maintenance shut down procedure during that time, the coal fired thermal power plants backed Europe’s electricity network and prevented it from collapse. From that aspect, the coal fired thermal power plants had a crucial role in energy supply, as well as stabilising the distribution network, proving once again that they are very important for our energy supply, and that they should stay in the energy mix for the foreseeable future. 4 COAL AS AN ECONOMICALLY VIABLE FUEL 4.1 Price of electricity as the positive impact factor The electricity price averaged from the lowest position in February, 128,78 €/MWh to 469,35€/MWh in August 2022, making more than 3 times higher prices during the summer months. The high peak of the electricity sale price has, consequently, boosted the thermal power plant operation into the economically positive area, despite elevated fuel and carbon emission allowances costs. The average monthly electricity wholesale prices in the EU are presented in Figure 5 [5]. Figure 5: Average monthly electricity wholesale price in the EU in 2022, €/MWh. The high electricity prices have caused the needed action from the governments in order to determine the price cap for households & industry to maintain the normal electricity prices. That action was crucial to keep the industry in good shape and not exposed to the high energy prices too much. The cap also enabled the households to cope through the winter, when the energy usage is higher, especially in the cooler parts of Europe. 4.2 Elevated costs of fuel & carbon emission allowances The prices of the coal have been elevated during 2022, mainly as the result of the lower imports of gas and crude from Russia. Some EU countries decided that it was best to start the thermal power plants for the time being, and to wait for the situation to be stabilised on the energy market. The applicable input factors for the thermal power plant operation evaluation are presented in Table 4.1 below. Table 4.1: Main applicable input factors for the calculation of the economic performance for an example thermal power plant. Input Factor Quantity Unit Peak Coal Price 433,70 €/t Carbon Emission Allowances 100,00 €/t Boiler Fuel Consumption 6,30 kg/s Generated CO2 Emission 0,87 kg/kWh Operation & Maintenance 43 € / kWh installed 4.3 Thermal power plant economic performance As aforementioned, a thermal power plant with an installed capacity of 119 MWe has consumed through the year 2022 altogether 199,221.00 tons of coal. Taking into consideration the assumed average coal price of 433,70 €/t, the total expenditure for fuelling the thermal power plant with coal throughout the year is accounted for at 86,402,199.70 € as presented in Figure 6. Figure 6: Produced electricity from a thermal power plant & carbon emissions to the atmosphere. Figure 7 is presenting the costs versus monthly expenses for operating the thermal power plant during the 2022 period. The red bars represent the expenses and the green bars the positive net electricity sale by the price that the market dictated. From the Figure it is obvious that the third quarter of 2022 was the most profitable for the thermal power plant operators. Figure 7: Costs versus Electricity Sale Performance for a thermal power plant during the 2022 period. Figure 8 presents the negative and positive operating months for the thermal power plants and their net monthly result. From the Figure we can see that, for 5 months out of 12 months in the year, the operation of the thermal power plants was positive. Especially positive was the third quarter of the year 2022. The net profit of the observed case was 9.94 million € on a yearly basis. Figure 8: Economic profitability performance of a thermal power plant during the 2022 time period. 5 EXITING THE INFLATION & ENTERING THE RECESSION ERA 5.1 Transitory versus lasting phenomena The starting inflation, being labelled as a transitory one, was present through the major part of 2021. With the beginning of 2022 it was more than obvious that inflationary pressures were starting to accelerate the inflation itself, consequently lifting the core inflation well above 5%. At that point the central banks and other regulators were forced to react to the situation, mainly by lifting the bank rates, but also with some other actions, such as, for example, capping the energy prices, in order to retain the price control across the energy market. Figure 9 below shows the rising of the bank interest rates due to the hard inflation environment [6]. Figure 9: Rising of the ECB rates during 2022 & 2023 due to inflationary pressures. The source: https://tradingeconomics.com/euro-area/interest-rate. 5.2 The future aspect of inflation presence The current elevated interest rates are keeping the prices of material costs as well as other services relatively high. The ask – demand ration has not been restored fully. Therefore, some inflationary pressures are still present, despite raising the interest rates. There are forecasts that, by the end of the year 2023, some additional interest rates raising will be put in place, leading the current market situation towards a stricter monetary policy, with the intention to lower the overall and core inflation to the desired levels by around 2% on a yearly basis. Big efforts by the regulators are in place to avoid a recession at the end of the rates` hikes. Instead of that, a so-called soft landing is expected, meaning that the markets and economy overall will be able to survive the transitionary time of increased interest rates, without shrinking itself and consequently falling into a recession. From the aspect of the raw materials` price movement, the strict monetary policy is expected to slower the ask – demand ratio, leading to the normalisation of the prices. It is crucial to secure the stable prices of the energy sources (derivates) before the winter 2023 – 2024, since another price spike of the derivates would mean relatively high pressures on the economies of the EU, which are already facing additional problems, such are broken supply chains, elevated cost of the raw materials, and, as aforementioned, elevated costs of the energy. As expected, the recession possibility is increasing further with the less positive market data feedback. Should the current situation continue, an overall recession in the EU economy is imminent, meaning that the conditions for the viable thermal power plant operation will end, mainly because of slower activity of the production industries that will, consequently, consume less energy as a result of the lower goods demand from the market and end customers. 6 CONCLUSIONS The demanding period of the last few years showed us that, although the green transition is in progress, the dependence on fossil fuels is still very much present in our everyday life. The regulators and decision makers shall establish the system in which the green transition decisions have support – social as well as economical. Returning to the usage of the fossil fuels shall be as crucial backup only in a case of demanding electrical network conditions and when the imminent stabilisation of the network is required. In the last two years the combination of geopolitical and economic factors helped to establish the environment in which the existing thermal power plants with a high CO2 emission factor were able to operate economically viably, which is in contradiction of the green transition policies. The regulators of the electricity production and distribution shall subsidise the green electricity production, so that it would have economical advantage in comparison with the price of electricity produced in conventional power plants. References [1] Trading economics: The movement of Newcastle Spot Price [online], https://tradingeconomics.com/commodity/coal (2.8.2023) [2] Eurostat: Labour cost within the EU [online], https://ec.europa.eu/eurostat/databrowser/view/LC_LCI_LEV/default/map?lang=en&category=labour.lc.lcan (7.8.2023) [3] Statista: The movement of spot price for carbon emission allowances [online], https://www.statista.com/statistics/1322214/carbon-prices-european-union-emission-trading-scheme/ (15.8.2023) [4] Statista: Largest coal fired thermal power plants in EU [online], https://www.statista.com/statistics/1264199/largest-operational-coal-power-plants-by-capacity-in-the-eu-27/ (18.8.2023) [5] Eurostat: Average monthly electricity wholesale price in EU in 2022 [online], https://www.statista.com/statistics/1322214/carbon-prices-european-union-emission-trading-scheme/ (20.8.2023) [6] Trading economics: Rising of ECB rates during 2022 & 2023 [online], https://tradingeconomics.com/euro-area/interest-rate (22.8.2023) Nomenclature EU European Union FED Federal Reserve Board ECB European Central Bank FOB Freight on Board US United States ETS Emission Trade System CO2 Carbon dioxide MWe Megawatt electric MWh Megawatt hour kWh Kilowatt hour t Tonne kg Kilogram s Second % Percentage € Euro Martin Bricl JET Volume 16 (2023) p.p. Issue 4, 2023 Inflationary elevated energy prices as main factor of fuelling economically viable electricity production in EU fossil fuel based thermal power plants Martin Bricl JET Volume 16 (2023) p.p. Issue 4, 2023 Inflationary elevated energy prices as main factor of fuelling economically viable electricity production in EU fossil fuel based thermal power plants Martin Bricl JET Volume 16 (2023) p.p. Issue 4, 2023 Inflationary elevated energy prices as main factor of fuelling economically viable electricity production in EU fossil fuel based thermal power plants Martin Bricl JET Volume 16 (2023) p.p. Issue 4, 2023 Inflationary elevated energy prices as main factor of fuelling economically viable electricity production in EU fossil fuel based thermal power plants Martin Bricl JET Volume 16 (2023) p.p. Issue 4, 2023 Inflationary elevated energy prices as main factor of fuelling economically viable electricity production in EU fossil fuel based thermal power plants Martin Bricl JET Volume 16 (2023) p.p. Issue 4, 2023 JET Volume 16 (2023) p.p. 41-53 Issue 4, 2023 Type of article: 1.01 http://www.fe.um.si/si/jet.htm ANALYTICAL ESTIMATION OF THE OPTIMAL PV PANEL TILT BASED ON A CLEAR-SKY IRRADIANCE MODEL ANALITICNA OCENA OPTIMALNEGA NAGIBA PV PANELA NA PODLAGI MODELA PROUCEVANJA SONCNEGA SEVANJA PRI JASNEM NEBU Elena Golubovska1R Corresponding author: Prof. Dr, Roman Golubovski, UKIM, FNSM, Arhimedova bb, Skopje, N.Macedonia, Tel.: +389 70 206 459, E-mail address: roman@pmf.ukim.mk 1 University Ss. Cyril and Methodius, Faculty of Computer Science and Engineering, Skopje, N.Macedonia 2 University Goce Delcev, Faculty of Electrical Engineering, Shtip, N.Macedonia 3 University Ss. Cyril and Methodius, Faculty of Natural Sciences and Mathematics, Skopje, N.Macedonia 1, Biljana Citkuseva Dimitrovska2, Roman Golubovski3R Keywords: PV panel tilt, optimal PV panel inclination, PV conversion efficiency, sun position model, clear-sky solar irradiance model Abstract PV panel tilt and sun tracking are crucial aspects of PV conversion efficiency. We propose an analytical methodology for estimation of the optimal PV panel tilt based on calculation of the sun`s position and the application of a clear-sky solar irradiance model. Our methodology outputs three angles referencing a geolocation and the moment of interest: the incidence angle q, the sun altitude a and the sun azimuth z. The irradiance model estimates the solar irradiation at a geolocation that can be used for PV conversion estimation based on specified tilt ß. The moment PV power is used for calculation of the daily energy production, and the optimal ß is identified in the tilt range of 0° to 90°. Seasonal division of the year is performed, and optimal seasonal tilt is estimated based on the maximally produced seasonal energy, tested with every corresponding ß. The methodology is tested on four typical seasonal models - 12 months, 4 three-month quarters, 2 half-year seasons and a single optimal annual fixed ß The preliminary simulations produced promising results consistent with the practical engineering implementations. Povzetek Nagib PV-panela in sledenje soncu sta kljucna vidika ucinkovitosti PV-pretvorbe. Predlagamo analiticno metodologijo za oceno optimalnega nagiba fotonapetostne plošce na podlagi izracuna položaja sonca in uporabe modela soncnega sevanja pri jasnem nebu. Naša metodologija prikaže tri kote, ki se nanašajo na geolokacijo in trenutek opazovanja: vpadni kot q, višinski kot sonca a in azimut sonca z. Model obsevanja ocenjuje soncno sevanje na geolokaciji, ki se lahko uporabi za oceno pretvorbe PV na podlagi dolocenega nagiba ß. To je trenutek, ko se PV moc uporabi za izracun dnevne proizvodnje energije, optimalni ß pa se doloci v obmocju nagiba od 0° do 90°. Izvede se sezonska delitev leta in optimalni sezonski nagib se oceni na podlagi najvecje proizvedene sezonske energije, testirane z vsakim ustreznim ß Metodologija je preizkušena na štirih tipicnih sezonskih modelih - 12 mesecih, štirih trimesecnih kvartalih, dveh polletnih sezonah in enem optimalnem letnem fiksnem ß. Predhodne simulacije dajejo obetavne rezultate, skladne s prakticnimi inženirskimi izvedbami. 1 INTRODUCTION Renewable energies are subject to continuous research for their sustainability, contrary to the depletive and hazardous properties of fossil fuels and nuclear fission. Solar energy is obviously the most sustainable form, independent of other circumstances, until it reaches the atmosphere and is degraded acceptably while propagating through it. Solar irradiation is used efficiently by photovoltaic (PV) conversion, which is the cheapest electrical energy production technology compared to the rest. PV technologies are also affordable at the household level, making them globally popular today. The widespread market sustains a growing PV production industry that increases the PV conversion efficiency continuously and lowers the market costs. However, besides the improved material performances, planners of PV plants also tackle installation efficiency issues for maximizing energy production against lower costs. Among other things, they aim for optimal latitude (L) placement, as well as optimal panel tilt (ß) for the sun`s incidence angle (q) closest to the possible zenith, and longer possible under daylight. The incidence angle q can be maintained optimally by horizontal azimuth tracking, but the panel azimuth is usually fixed towards local noon (1200h). The panel tilt optimization is subject to vertical inclination adjustment strategies, ranging from fixed tilt throughout the year to daily tracking (involving the use of computers equipped with sensors and actuators, introducing additional costs such as hardware, cabling, maintenance and energy consumption), depending on the economic circumstances. This paper proposes an analytical methodology for estimation of the optimal PV panel tilt based on the estimated sun position defined by the incidence angle q, the sun`s altitude a and its azimuth z, and application of a clear-sky solar irradiance model. The sun's location is determined [1] against a specified geolocation for a specified date and time. The solar irradiance model [2], unlike efforts estimating locally arrived irradiation based on statistical meteorological data or measurement-based modelling [3] - [15], calculates the maximal possible incoming solar irradiation that can be used for PV conversion estimation considering the latitude placement and sun`s position, as well as the panel tilt ß. This allows for momentary power estimation and possible energy production over a specified period. The methodology allows tracking optimal ß on a daily basis (the daily fixed tilt for which maximal daily energy can be produced), or for arbitrary defined seasons (the fixed tilt for which maximal seasonal energy can be produced). This approach is tested on four typical seasonal models - 12 months, 4 three-month quarters, 2 half-year seasons, and a single optimal annual fixed ß. 2 SUN POSITION MODEL The current sun position model calculates the incidence angle q that the sun`s rays fall under at a specific geolocation (latitude and longitude) in a specific moment of the year (date and time), being the angle between the sun`s ray falling on that location and its perpendicular vertical line, as well as the seasonal sun altitude a and the daily azimuth z. In order to calculate these three essential angles, additional specifics regarding the earth's rotations need to be considered. Figure 1 shows the earth's annual (365.25 days) rotation around the sun, as well as the fixed declination d of the earth's axis (23.45°), which oscillates with respect to the sun, producing on earth a solar declination angle between ± 23.45° depending on the moment in the year. Figure 1: Annual motion of the earth around the sun There are four fiducial dates during the year - 21 Jan (the summer solstice), which is the longest (summer) day in the northern hemisphere; 21 Dec (the winter solstice), which is the shortest (winter) day in the northern hemisphere; and 21 Mar and 21 Sep (the two equinoxes) with equal duration of their day and night. The daily declination d for day N (of the 365 in a year) according to ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) can be calculated with the expression 2.1. Elena Golubovska, Biljana Citkuseva Dimitrovska and Roman Golubovski JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model Elena Golubovska, Biljana Citkuseva Dimitrovska and Roman Golubovski JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model Elena Golubovska, Biljana Citkuseva Dimitrovska and Roman Golubovski JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model Elena Golubovska, Biljana Citkuseva Dimitrovska and Roman Golubovski JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model JET Volume 16 (2023) p.p. Issue 4, 2023 Elena Golubovska, Biljana Citkuseva Dimitrovska and Roman Golubovski Figure 6: Annual latitude curves of the monthly optimized tilt Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model 6 CONCLUSION Solar energy is an abundant source of sustainable green energy, yet delicate from a harvesting perspective, due to the blocking properties of the unpredictable atmospheric conditions (vapor and particles), as well as the solar incidence angle on which the PV conversion efficiency depends. Furthermore, the more directly (perpendicular to the sun`s rays) the PV panels are exposed, the more heated they become, which, in turn, lowers the PV conversion efficiency. Continuous automated tracking (at least for the optimal tilt, and preferably for the optimal azimuth too) is usually a significant expense, so efforts are made to maximize energy harvesting based on the optimal "seasonal" fixed tilt, with latitude being the fundamental parameter and "season" being a sequence of days with no significant change in energy conversion if the tilt is optimized daily. The problem of optimal fixed tilt calculation is recognized by the engineering community, and enormous effort is made worldwide to define such an analytical model for optimal tilting without expensive tracking or time-consuming measurements, which can be depicted in lots of published papers, like [3] - [15]. Some approaches use statistical meteorological data as a basis to determine the geometrical circumstances under which the panel had its optimal tilt for maximal efficiency. Others use regression over measured data under known weather circumstances to model the analytical expression for optimal tilt calculation, which, on the other hand, introduces some "off latitude" deviation in the results. Some of the authors consider the context's parameters, that have a significant impact on the measurements, like vapor, microparticles and pollution, which influence the local atmosphere over the panels. Interestingly, very few consider the operational heat, which lowers the PV conversion efficiency. If not addressed properly with cooling, it does coerce the model off the latitude value. Especially significant we find the work of Ogundimu @ al [14], providing a comprehensive overview of the contributions of previously published models proposing methodologies for optimal tilting at specific latitudes, providing correcting parameters that those scholars have calculated based on direct measurements or local (historical) statistical meteorological data. We believe that these approaches based on measured data or meteorological information do not always consider all circumstances influencing the resulting PV conversion efficiency, leading to those latitude corrections. Our proposed concept for analytical estimation of the optimal PV panel tilt, based on the su`sn position and clear-sky irradiance models, provides a reliable and consistent methodology for daily tracking and arbitrary seasonal tilt optimization under ideal atmospheric conditions, as Nakamura @ al [15] support by their experimental setup. This approach is not burdened by costly and time-consuming measurements, heavy meteorological data statistics, or regression modeling. The algorithm is precise and easy to implement, thus providing an affordable and straight-forward-to-use tool for that purpose. If significant, local atmospheric conditions could be considered in the irradiance model, which would be one of the next development steps. References [1] S. A. Kalogirou: Solar Energy Engineering Process and Systems, Elsevier, 2009 [2] J. A. Duffie, W. A. Beckman: Solar Engineering of Thermal Processes, John Wiley and Sons, 2013 [3] E.D. Mehleri, P.L. Zervas, H. Sarimveis, J.A. Palyvos, N.C. Markatos: Determination of the optimal tilt angle and orientation for solar photovoltaic arrays, Renewable Energy, Elsevi­er, Vol. 35, Iss. 11, pp. 2468-2475, 2010 [4] R. Tang, T. Wu: Optimal tilt-angles for solar collectors used in China, Applied Energy, Else­vier, Vol. 79, Iss. 3, pp. 239-248, 2004 [5] M. Yakup, A. Q. Malik: Optimum tilt angle and orientation for solar collector in Brunei Darussalam, Renewable Energy, Elsevier, Vol. 24, Iss. 2, pp. 223-234, 2001 [6] Y. B. Gebremedhen: Determination of Optimum Fixed and Adjustable Tilt Angles for Solar Collectors by Using Typical Meteorological Year data for Turkey, International Journal of Renewable Energy Research, Vol. 4, Iss. 4, pp. 924-928, 2014 [7] E. A. Handoyoa, D. Ichsania, Prabowoa: The optimal tilt angle of a solar collector, Inter­national Conference on Sustainable Energy Engineering and Application 2012, Elsevier, Energy Procedia 32, pp. 166-175, 2013 [8] A. Rouholamini, H. Pourgharibshahi, R. Fadaeinedjad, G. Moschopoulos: Optimal Tilt Angle Determination of Photovoltaic Panels and Comparing of their Mathematical Model Predictions to Experimental Data in Kerman, IEEE Canadian Conference Of Electrical And Computer Engineering 2013 [9] A. K. Abdelaal, A. El-Fergany: Estimation of optimal tilt angles for photovoltaic panels in Egypt with experimental verifications, Sci Rep 13:3268, 2023 [10[ E. Gonzalez-Gonzalez, J. Martín-Jimenez, M. Saanchez-Aparicio, S. D. Pozo, S. Laguela: Evaluating the standards for solar PV installations in the Iberian Peninsula: Analysis of tilt angles and determination of solar climate zones, Sustainable Energy Technologies and Assessments, Elsevier, Vol. 49, No. 101684, 2022 [11] A. U. Obiwulu, N. Erusiafe, M. A. Olopade, S. C. Nwokolo: Modeling and estimation of the optimal tilt angle, maximum incident solar radiation, and global radiation index of the photovoltaic system, Helyion, Elsevier, Vol. 8, 2022 [12] M. A. M. Ramli, H. R. E. H. Bouchekara, M. S. Shahriar, A. H. Milyani, M. Rawa: Maximi­zation of Solar Radiation on PV Panels With Optimal Intervals and Tilt Angle: Case Study of Yanbu, Saudi Arabia, Frontiers in Energy Research, Vol. 9:753998, 2021 [13] G. Hailu, A. S. Fung: Optimum Tilt Angle and Orientation of Photovoltaic Thermal System for Application in Greater Toronto Area, Canada, Sustainability, Vol. 11, No. 22, 2019 [14] E. O. Ogundimu, E. T. Akinlabi, C. A. Mgbemene: Maximizing the Output Power Harvest of a PV Panel: A Critical Review, Journal of Physics: Conference Series, Vol. 1378, Iss. 3, 2019 [15] H. Nakamura, T. Yamada, T. Sugiura, K. Sakuta, K. Kurokawa: Data analysis on solar irradi­ance and performance characteristics of solar modules with a test facility of various tilted angles and directions, Solar Energy Materials & Solar Cells, Elsevier, Vol. 67, Iss. 1-4, pp. 591-600, 2001 [16] M. Iqbal: An Introduction to Solar Radiation, Academic Press Toronto, 1983 [17] J. W. Spencer:Fourier series representation of the position of the sun, Search, Vol. 2, Iss. 5, p.172, 1971 [18] H. C. Hottel: A Simple Model for Estimating the Transmittance of Direct Solar Radiation through Clear Atmospheres, Solar Energy, Vol. 18, Iss. 2, pp. 129-134, 1976 Elena Golubovska, Biljana Citkuseva Dimitrovska and Roman Golubovski JET Volume 16 (2023) p.p. Issue 4, 2023 Analytical estimation of the optimal PV panel tilt based on a clear-sky irradiance model JET Volume 16 (2023) p.p. 54-62 Issue 4, 2023 Type of article: 1.01 http://www.fe.um.si/si/jet.htm SWOT ANALYSIS OF HYDROGEN ECONOMY EKONOMIJA VODIKA S SWOT-ANALIZO Dominik Oravec1, Florinda F. Martins2, Frantisek Janicek3, Miroslava Farkas SmitkovaR1R1 Corresponding author: Assoc. Prof. Miroslava F. Smitkova, Institute of Power and Applied Electrical Engineering, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, Ilkovicova 3, 812 19, Bratislava, Slovak Republic Tel.: +421 2 602 91 , E-mail address: miroslava.smitkova@ stuba.sk 1,3 Institute of Power and Applied Electrical Engineering, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, Ilkovicova 3, 812 19, Bratislava, Slovak Republic 2 School of Engineering (Instituto Superior de Engenharia do Porto), Polytechnic of Porto (P.Porto), Porto, Portugal Keywords: Energy accumulation, energy, greenhouse gas, hydrogen, hydrogen economy Abstract The paper deals with the types of hydrogen production, methods for its storage and transport, and possibilities of the end use of hydrogen. The basics of the hydrogen economy are described briefly, and then the SWOT analysis is performed of the hydrogen economy. The strengths, weaknesses, opportunities, and threats of the hydrogen economy are summarized in the SWOT analysis. The biggest problems and threats, with the possibilities of solving those problems, are summarized based on that analysis. The SWOT analysis considers aspects of the hydrogen economy e.g. energy demands, financial difficulty, safety, and awareness about hydrogen. The Conclusions involve suggestions on how to avoid the above-mentioned awareness, and how to increase hydrogen utilization. Povzetek Prispevek obravnava vrste pridobivanja vodika, nacine njegovega skladišcenja in transporta ter možnosti koncne uporabe vodika. Na kratko so opisane osnove ekonomije vodika, nato pa je opravljena SWOT-analiza ekonomije vodika. Prednosti, slabosti, priložnosti in nevarnosti vodikovega gospodarstva so povzete v SWOT-analizi. Na podlagi te analize so povzeti najvecji problemi in nevarnosti z možnostmi reševanja teh problemov. SWOT-analiza upošteva vidike vodikovega gospodarstva, npr. energetske zahteve, financne težave, varnost in ozavešcenost o vodiku. Sklepi vkljucujejo predloge, kako se izogniti zgoraj omenjenemu zavedanju in kako povecati izkoristek vodika. 1 INTRODUCTION Nowadays, industrially developed countries are using energy mainly from fossil fuels, which are not infinite resources. That is causing faster development in energy resources and possibilities of accumulation energy. The main alternative sources are renewable energy resources with low negative impact on the environment. Renewable resources are difficult to predict in terms of production. This causes the necessity to accumulate energy during high energy production. Current ways for energy accumulation are, e.g., pumped-storage hydroelectricity or batteries. Hydrogen represents another way to accumulate energy. The hydrogen economy deals with issues around the accumulation of energy in hydrogen form, e.g. from renewable sources or fossil fuels. There is an effort to find the best ways for the production, storage, transport, and end use of hydrogen. 2 HYDROGEN PRODUCTION Production of hydrogen is a process where there is a splitting chemical bond of water which produces separated hydrogen and oxygen. We divide the hydrogen in the color spectrum. Every color depends on the method of production, see Table 1. Each color corresponds to a different extraction process. Nevertheless, the steam reforming of fossil fuels creates the most greenhouse gases. It is the most used method of hydrogen production. Selected methods of hydrogen production are described in Table 2. Table 1: Color marking of hydrogen Color Method of production Gray hydrogen Hydrogen is produced by the steam reforming of fossil fuels. Nowadays, it is the most used method of hydrogen production. This method doesn’t use capture devices. Brown/Black hydrogen The process of hydrogen production is using black or brown coal. It has the worst impact on the environment. Blue hydrogen Hydrogen is produced by the steam reforming of fossil fuels with capture devices. The reduction of greenhouse gases is around 90 %. Pink hydrogen Hydrogen is produced through electrolysis, using a high temperature from nuclear reactors. It can also be referred to as red or purple hydrogen. Turquoise hydrogen A process called methane pyrolysis is used. In the future, it may be valued as a low-emission hydrogen. It depends if the process is powered by renewable sources. Yellow hydrogen It is a new phase. The electrolysis uses solar energy. White hydrogen Geological hydrogen is found in underground deposits and created by fracking. There is no strategy for how to use this hydrogen. Green hydrogen The energy for electrolysis comes from renewable sources like photovoltaic panels or wind turbines. Table 2: Hydrogen production method Method of production Brief description of production Electrolysis The chemical bond of water is split by an electric current. Thermochemical cycles An endothermic process where energy from nuclear or solar sources is used for the thermal splitting of water. Steam reforming of natural gas The endothermic reaction of natural gas and water vapor. Water vapor has a temperature around 750 – 900 °C. This process creates hydrogen, carbon monoxide, and a smaller amount of carbon dioxide. Nowadays, mainly fossil fuels are used for hydrogen production, which amount is around 96% of the total production. Electrolysis of water covers the rest, just 4%, see Figure 1. Figure 1: Division of hydrogen production 3 HYDROGEN STORAGE Hydrogen can be stored in different forms, and every form has specific energy demands. Options for storage are hydrogen in gas form, liquid hydrogen and hydrids, where the hydrogen is bound to different alloys. SWOT analysis of hydrogen economy Dominik Oravec, Florinda F. Martins, Frantisek Janicek, Miroslava F. Smitkova JET Volume 16 (2023) p.p. Issue 4, 2023 Obrázok, na ktorom je text, diagram, rad, vývojAutomaticky generovaný popis Figure 2: Division of hydrogen production SWOT analysis of hydrogen economy 3.1 Storage of hydrogen in gas form For industry and large-capacity hydrogen storage, it is convenient to store hydrogen in a gas form. In gas form hydrogen can be stored in pressure vessels above the ground or undersea. For large-capacity hydrogen storage emptied underground reservoirs of natural gas or salt layers are the most advantageous. Every method for hydrogen storage requires different temperatures and pressures, see Figure 2. In this method of storage, energy losses are caused by compression devices for compressing hydrogen, or, in the case of underground reservoirs, some of the hydrogen settles in the micropores of the soil. 3.2 Storage of hydrogen in liquid form In the development of storage hydrogen in liquid form the NASA organization has a major share, where liquid hydrogen is used as rocket fuel. Liquefaction is an energy demanding process where the hydrogen must be cooled at a temperature around -253 °C. This process consumes 15,1 MJ/kg energy [1]. The energy needs for hydrogen storage in a liquid form are affected by gas purity, because it is necessary to separate other gases (expected helium) from the hydrogen. Mainly oxygen separation is very important, because the concentration of more than 1 mg of oxygen on 1 kg of hydrogen causes an explosion [1]. Other energy losses are caused by the transition of hydrogen from orthoform to paraform. Orthoform has symmetric spins of atoms, and in the paraform, these spins are not symmetric. Para-hydrogen is more stable at lower temperatures, and has a lower enthalpy capacity. Therefore, when hydrogen is passing from orthoform to paraform, the heat is released, which increases the energy requirement. 3.3 Storage of hydrogen in a hydrid form Storage reservoirs in the case of the hydrid form are smaller than other forms. This type of storage is suitable for end consumers. Hydrogen is bound to other energy carriers, like metal and metal alloys, which creates metal hydrids. For every metal alloy it is required to find the right temperature and pressure when the hydrogen is bound to the metal. It is an exothermic reaction, where, during the fulfilment of the reservoir heat is released and it is necessary for the reservoir to cool down, because this can cause the release of hydrogen. To release hydrogen from the reservoir, the reservoir must be heated or depressurized. 4 HYDROGEN TRANSPORT Hydrogen can be transported in gaseous, as well as liquid form. For longer distances hydrogen can be distributed through long-distance gas pipelines, which are developed in every economically advanced country. For transport over shorter and medium distances, up to approximately 500 km, it is economically advantageous to transport the hydrogen in liquid or hydrid form. Figure 3: Effect of bigger hydrogen concentration on the service life of the currently used pipelines 4.1 Transport of hydrogen in gas form To transfer the same amount of energy it is necessary to transport a three times bigger amount of hydrogen compared to natural gas, because hydrogen has a smaller heat value [1]. Hydrogen has a nine times smaller density than natural gas, so we can transport more hydrogen. The problem occurs at pressures higher than 5.6 MPa, when the heat value of natural gas increases and hydrogen cannot compete with natural gas. [1] Choosing the right gas flow, a turbulent flow, we can ensure the transport of up to 280% of the volume of hydrogen compared to natural gas, which represents approximately 95% of the energy equivalent. [1] The next problem of hydrogen transport in gas form is hydrogen embrittlement, where particles of the hydrogen penetrate to the material structure and cause hydrogen embrittlement. The larger amounts of pressures and concentration of hydrogen cause faster hydrogen embrittlement. It is an undesirable phenomenon which causes bigger financial investments. In Figure 3, we can see how the hydrogen concentration affects the service life of steel material. [7] 4.2 Transport of hydrogen in liquid form Despite energy losses, hydrogen transport in liquid form is preferable, mainly over short distances, see Figure 4. Obrázok, na ktorom je diagram, rad, text, potvrdenieAutomaticky generovaný popis Figure 4: Financial costs of transport for shorter distances Economically, costs for gaseous transport are affected by the demand for 3 times more hydrogen than natural gas. For comparison, the financial costs of different ways of hydrogen transport are shown in Table 3. Table 3: The comparison size of hydrogen containers. The calculated volume is needed for the storage amount of energy of 1 kWh. Method of storage Density [kg/m2] Energetic density [MJ/m3] Energetic density [kWh/m3] Volume [m3] Volume [l] Gaseous hydrogen 0.09 10 2.78 0.36 359.712 Gaseous hydrogen under a pressure of 30 MPa 22.5 2 700 750 0.0013 1.33 Liquid hydrogen 71.9 8 700 2 416.67 0.000414 0.41 Natural gas 0.668 37.4 10.39 0.096 96.25 Methanol 0.79 17 000 4 722.22 0.000212 0.21 5 USES OF HYDROGEN The use of hydrogen in power engineering and as fuel should help the transition to a less environmentally harmful way of producing electricity, heat, or fuel. Hydrogen is deemed to be a prospective secondary energy source. Its application is universal – e.g. power engineering (electricity and heat production), transport, metallurgy, synthetic fertilizer production, usage in the oil industry. 5.1 Uses in power engineering Hydrogen can help in the decarbonization of electricity production. Green hydrogen can potentially store 4 – 20% of energy from renewable sources. These percentages can increase with an increasing number of renewable sources. [4] We can use hydrogen in thermomechanical cycles via the Carnot turbine, because, when hydrogen is burned with oxygen, it does not produce CO2. If we burn hydrogen with air, it will have 1.88 mol of nitrogen that decreases part of the thermal energy [1]. During the burning of hydrogen with air, we do not achieve the same combustion temperature as in combustion with oxygen, so the whole process of accumulation of energy has lower efficiency. Hydrogen has a higher flame temperature (2400 K) than natural gas, so it can be good for heat production [1]. Also, lower energy is required for lighting the flame. Higher temperatures need appropriate technologies that can resist heat. Because 3 times more hydrogen than natural gas is needed to transfer the same amount of energy, hydrogen is currently only blended into gas pipelines. However, it is an opportunity to decarbonize the heating industry in the future. One of the remarkable methods for large-scale hydrogen production is a thermochemical water decomposition using heat energy from nuclear, solar, and other sources. Water splitting thermochemical cycles replace the thermal decomposition of water with several partial reactions, and they represent an environmentally attractive way for hydrogen production without using fossil fuels. Hydrogen produced via the mentioned cycles could be used for electricity and heat production, as well as a fuel. 5.2 Uses in fuel cells Fuel cells are electrochemical systems in which the chemical energy of the fuel is converted to electrical energy through the oxidation process. Losses in this system are caused by low-potential heat. The efficiency of this system depends on the activation overvoltage of the electrodes, ohmic and concentration overvoltage. Fuel cells have better efficiency up to a temperature of 800 °C [8]. With increasing temperature the equilibrium oxygen-hydrogen tension decreases, and, from a thermodynamic point of view, the efficiency also decreases. There are several types of fuel cells, which differ in functional principle and suitability for use. Nowadays, fuel cells do not represent an adequate large-capacity source. Fuel cells are applied in a direct current source for electric motors in cars. Fuel cells are used mainly in the automotive and aerospace industries. Fuel cells are, for example, a source of energy for space shuttles, and they were also used in the Apollo program. They are also used in submarines. Currently, some automobile manufacturers produce cars that run on hydrogen, and there are also buses which use hydrogen as a fuel. With the expansion of this type of cars, the network of hydrogen filling stations is expanding, for example, in Slovakia, the first hydrogen filling station was put into operation in 2022. Most hydrogen stations are in Japan (almost 150) and Germany (almost 100). 6 SWOT ANALYISIS SWOT analysis is a comprehensive assessment of internal and external factors. Th strengths of SWOT analysis are simplicity, clarity, and complexity. In the internal analysis we compare S (strengths) and W (weaknesses). Parts of the external analysis are O (opportunities) and T (threats). Table 4: Criteria of SWOT analysis   S – Strengths   W – Weaknesses   O – Opportunities   T – Threats S1 Accumulation method that doesn’t have a negative impact on the environment – depends on the production method W1 Hydrogen, due to its properties and high diffusion, causes hydrogen embrittlement of the material O1 Creation of new job opportunities – it is a new technology that requires new, professionally educated people T1 New technology – the possibility of higher danger S2 Use of renewable sources in production – electrolysis of water, thermochemical cycles W2 Requiring a 3 times more amount of hydrogen to transfer the same amount of energy as natural gas, due to lower calorific value O2 Energy independence – reduced dependence on imports T2 High investment, need for staff training, developing new technologies etc. S3 Slowdown in the decline of the Earth’s fossil fuel reserves (oil, natural gas) W3 High financial costs of hydrogen production O3 Reduction of environmental pollution – depending on the production method (green hydrogen) T3 Currently underdeveloped infrastructure S4 A new energy carrier – less dependence on fossil fuels W4 Energetic intensity of storage – liquefaction, gas compression O4 Opportunity to use old depleted underground natural gas reservoirs T4 Competition from cheaper energy sources (fossil fuels) S5 Building new refuelling stations for a hydrogen economy W5 Low efficiency of fuel cells, need to provide new technology to increase efficiency O5 Reducing commodity price fluctuations T5 Lack of information delivered to the public The result of the contribution is a SWOT analysis of the hydrogen economy. The criteria used in the SWOT analysis are shown in Table 4. In Table 5 there is a comparison matrix, from which we get specific results about strengths, weaknesses, opportunities, and threats. In Table 5, scoring is used on a scale of minus 5 to plus 5, where minus 5 represents the worst negative mutual influence and 5 represents the best positive mutual influence. Table 5: Comparison matrix Internal factors S – Strengths W - Weaknesses Key external factors O - Opportunities T – Threats S1 S2 S3 S4 S5 The sum of the ratings O,T/S W1 W2 W3 W4 W5 The sum of the ratings O,T/W Final evaluation O1 0 5 3 5 5 18 4 2 -2 3 3 10 28 O2 2 5 3 5 3 18 2 3 3 5 4 17 35 O3 5 5 3 3 3 19 3 2 4 3 3 15 34 O4 3 0 -4 2 1 2 1 4 3 1 0 9 11 O5 1 3 2 5 1 12 3 1 5 4 4 17 29 T1 0 -2 -4 -4 -2 -12 -5 -3 0 -4 0 -12 -24 T2 -1 -2 -4 -5 -3 -15 -3 -2 -5 -3 -5 -18 -33 T3 0 -1 -2 -3 -5 -11 -1 -3 -5 0 -3 -12 -23 T4 -5 -5 -5 -5 -5 -25 -4 -5 -4 -4 -3 -20 -45 T5 -5 0 -2 -2 -1 -10 -3 2 -3 0 -3 -7 -17 The sum of the ratings S,W 0 8 -10 1 -3 -4 -3 1 -4 5 0 -1 -5 Scale S / W 35 25 15 15 10 / 15 25 20 30 10     Dominik Oravec, Florinda F. Martins, Frantisek Janicek, Miroslava F. Smitkova JET Volume 16 (2023) p.p. Issue 4, 2023 SWOT analysis of hydrogen economy Dominik Oravec, Florinda F. Martins, Frantisek Janicek, Miroslava F. Smitkova JET Volume 16 (2023) p.p. Issue 4, 2023 SWOT analysis of hydrogen economy Dominik Oravec, Florinda F. Martins, Frantisek Janicek, Miroslava F. Smitkova JET Volume 16 (2023) p.p. Issue 4, 2023 7 CONCLUSIONS From the SWOT analysis we found out that the most prominent strength is S2 – Using renewable sources, immediately followed by S1 – the Accumulation method without a negative impact on the environment. In the strategy we should focus on these strengths, and ensure that T4 and T5 will be reduced. T4 – Competition from cheaper energy sources, can be countered by increasing renewable sources that will be used for hydrogen production, or possibly thermochemical cycles. T5 – Lack of information delivered to the public, can be countered by lectures, various discussions, articles, and general propagation. The biggest weaknesses are W2 – Requiring a bigger amount of hydrogen than natural gas, and W4 – The energetic intensity of storage. W2 is related to the opportunity of O4 – the Opportunity to use old depleted natural gas reservoirs. These depleted natural gas reservoirs are good for high-capacity storage. Storage of hydrogen is an energetic challenge, because there are big energy losses. When hydrogen is compressed to 350 bars, approximately 15 – 20% of the energy contained in the fuel is required for the function of compressors, measuring devices, etc. Hydrogen in liquid form has bigger losses, approximately 30 – 40% of energy contained in the fuel is needed for liquefaction. Despite the higher energy intensity of storage, some opportunities have positive impacts, like O2 – Energy independence, and O5 - Reducing commodity price fluctuations. Acknowledgements This work was supported by the Slovak Research and Development Agency under the Contract  No.  APVV-20-0157“. References [1] J. Balajka: Vodík a iné nosice energie, ALFA, 1982 [2] G. Franchi. et al.: Hydrogen production via steam reforming: a critical analysis of MR and RMM technologies, PubMed, 2022 [3] Hassanpouryouzband, A. et al., Thermodynamic and transport properties of hydrogen containing streams, Scientific Data, 2020 [4] Národná vodíková asociácia, [online], 2022, Available: nvas.sk (4.5.2023) [5] NATIONALGRID - The hydrogen colour spectrum, [online], 2022, Available: www.nationalgrid.com/stories/energy-explained/hydrogen-colour-spectrum (7.4.2023) [6] M.J. Ogden, Hydrogen Infrastructure Capital Costs Compared with Those for Methanol, Gasoline, and Synthetic Middle Distillates, Researchgate, p.p. 262, 2020 [7] V. Olej, Úskalia prepravy vodíka plynárenskou infraštruktúrou, Slovgas: 2020 [8] B. Petráš, T. Brestovic, Palivový clánok – zdroj energie, AT&P journal: Technická univerzita Košice, Strojnícka fakulta, 2007 [9] C. Vargas-Salgado, et al., Hydrogen Production from Surplus Electricity Generated by an Autonomous Renewable System. Scenario 2040 on Grand Canary Island, Spain, p.p.12, 2022 Authors names and surnames JET Volume 16 (2023) p.p. Issue 3, 2023