im Journal of JET v°lume 13 (2020) p.p. 11-26 Issue 2, September 2020 Type of article 1.01 Technology www.fe.um.si/en/jet.html MULTI-PURPOSE USE AND LIFECYCLE ANALYSIS OF SOLAR PANELS VEČNAMENSKA UPORABA IN ANALIZA ŽIVLJENJSKEGA CIKLA SOLARNEGA PANELA Dušan Strušnik1, Urška Novosel2, Jurij AvsecR Keywords: heat pump, life cycle analysis, Rankine cycle, solar panel, thermochemical cycle Abstract The combined use of renewable energy technologies and alternative energy technologies is a promising approach to reduce global warming effects throughout the world. In this paper, the solar panel is used in combination with a heat pump or with biomass sources to obtain heat, electricity, and hydrogen. Based on the Rankine thermodynamic cycle, hydrogen could be obtained from water with electrolysis and the CuCl thermochemical cycle. Furthermore, this study contains a life cycle analysis of solar panels. Povzetek Kombinirana uporaba tehnologij obnovljivih virov energije in tehnologij alternativnih energij je obetaven pristop za zmanjšanje učinkov globalnega segrevanja v svetu. V tem prispevku se sončna plošča uporablja v kombinaciji s toplotno črpalko ali z viri biomase za pridobivanje toplote, električne energije in vodika. Na podlagi Rankinovega termodinamičnega cikla bi lahko s pomočjo CuCl termokemičnim ciklom iz vode pridobivali tudi vodik. Poleg tega študija prikazuje analizo življenjskega cikla solarnega panela. R Corresponding author: Dušan Strušnik, Energetika Ljubljana d.o.o., TE-TOL Unit, Toplarniška 19, 1000 Ljubljana, E-mail address: dusan.strusnik@gmail.com 1 Energetika Ljubljana d.o.o., TE-TOL Unit, Toplarniška 19, SI-1000 Ljubljana, Slovenija 2 University of Maribor, Faculty of Energy Technology, Hočevarjev trg 1, SI-8270 Krško, Slovenia JET 11 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 1 INTRODUCTION The production of electricity and heat from renewable sources is becoming more efficient and economically viable. Given current environmental problems, the utilization of renewable energy sources is becoming desirable. The demand for thermal energy accounts for more than half of the world's total energy needs. Currently, most of that heat is generated from hydrocarbons and their derivatives. Some small amounts are produced through renewable energy sources throughout the world. In the future, it is expected that the production of heat from renewable sources will significantly exceed the current level. For this purpose, all types of renewable energy sources should be taken into account. Particularly interesting is the use of solar energy with solar collectors, which have a yield of over 60%, [1]. Currently, there are several solar thermal generation systems, including plate collectors, vacuum collectors, and hot-air collectors, with which solar and thermal energy can be simultaneously obtained. In the foreground, there are also solar panels, which can be used in different ways: mounted on the roof, to cover the facades of houses, and similar. In this way, they could acquire a good portion of the energy required for home and industrial heating. Fig. 1 shows a wall mounting and a roof mounting of a solar panel with aluminium tubes and rock wool insulation material. Figure 1: a) a wall mounting solar panel and b) a roof mounting solar panel In this case, the solar panel is comprised of aluminium tubes, rock wool insulation material, transparent cover, circulation pump, etc. The panels are usually roof-mounted; however, they can also be mounted on the building walls or on frames on the ground. The insulator located between represents the thermal building envelope and should keep heat losses as low as possible. If the solar panel is mounted in the wall, rock wool represents the thermal building envelope. Due to this sophisticated revision of sandwich panels, the field of application can be extended to office buildings, residential buildings, public buildings (e.g., education, culture, health, etc.). 12 JET Multi-purpose use and lifecycle analysis of solar panels 2 SOLAR PANEL MULTI-PURPOSE USE ANALYSIS 2.1 The solar panel as a hydrogen producer The main idea of the present article is the use of solar energy and biomass (wood chips) to produce cheap hydrogen. We combined two processes for hydrogen production: electrolysis and the thermochemical CuCl cycle. The working Rankine cycle system combined with the CuCl process, [2], and the electrolysis system is presented in Fig. 2 and Fig. 3. Additional energy source System with concentrated v _r solar power ¿¿3, ix 1 — Electric energy — Heat Distric heating Pump Figure 2: Solar panels in combination with Rankine cycle Figure 3: T-s diagram of the Rankine cycle Apart from hydrogen production in the process, we can also use waste heat from the Rankine cycle for district low-temperature heating of buildings and houses. All necessary data to calculate thermodynamic efficiency are presented in Table 1. JET 13 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Table 1: Results of the Rankine system calculation Rankine system and CuCl system State Pressure [bar] Enthalpy [kJ/kg] 1 300 3883.43 2 300 3599.4 3s 0.06 1972.8 3 0.06 2135.46 4 0.06 151.5 5 300 186.765 Parameter Value * 10 MW Ii 0.9 Til 6.831 kg/s S- -13.552 MW »V 403.346 kg/s, AT = 8 K Wi 240.9 kW Vu 0.85 Qald 25.252 MW WL.il 1.94 MW This relatively small cogeneration unit was built for the Posavje region of Slovenia. The idea of the present work is primarily to exploit solar energy for hydrogen production. Large amounts of solar energy are available, especially in the summer, spring, and autumn. To this end, we have used a model of covered solar panels, with which we could obtain approximately 20 °C of temperature increase. Additional heat for the processes is obtained from wood chips. With the help of solar calculation software found on the web page "The European Commission's science and knowledge service", [3], we have calculated the average amount of solar hours. For solar panels integrated into building for Posavje region, we calculated 1060 effective solar hours for solar angle 450 and 716 effective solar hours for solar angle 900. Fig. 4 shows the production of hydrogen per day with the Rankine cycle system, electrolysis and CuCl system. On the basis of thermodynamic calculation, we could determine the amount of hydrogen produced by the CuCl process and by electrolysis per day. As seen in Fig. 4, the total production of hydrogen is 3931.5 kg/day; the ratio between the hydrogen obtained by electrolysis and the CuCl process is more than 5. 14 JET Multi-purpose use and lifecycle analysis of solar panels Figure 4: The amount of produced hydrogen 2.2 The solar panel as a cooling system The use of thermal energy produced by a solar panel for cooling processes is also extremely interesting from a technical point of view. For this purpose, two cooling systems are presented. The first system represents cooling by means of an absorption refrigeration device and solar panels (Fig. 5). The second system represents cooling by means of solar panels, the ORC system and compressor heat pump (Fig. 6). Pump Figure 5: Cooling by means of an absorption cooling device and solar panel JET 15 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Figure 6: Cooling by means of solar panel, ORC system and compressor heat pump 3 LIFE CYCLE ANALYSIS OF SOLAR PANEL Life cycle analysis is a tool for assessing the energy and environmental profile of a product or technology from design to recycling. It provides global guidance and criteria, based on which decisions are made on further product development and which accompany the product or technology throughout the life cycle. Life cycle analysis covers the entire energy and environmental aspect from production, transport, installation, lifetime and decommissioning of a product. It is a methodology that includes four life cycle phases in a comprehensive and transparent way, on the basis of facts and expertise and in conformity with the ISO 14040 standard [4]. These phases are study goal and scope definition, data acquisition, modelling and interpretation of results. As regards new process and product development, the relationship between processes, product characteristics and environmental impacts have to be taken into consideration for each product. The international ISO 14025 standard, [5], was introduced to ensure comparable environmental efficiency among products. The main stages of life cycle analysis are presented in Fig. 7. 16 JET Multi-purpose use and lifecycle analysis of solar panels RESOURCES Figure 7: Main stages of life cycle analysis The life cycle analysis of solar panels comprises several phases, and each phase covers input-output data on materials, energies and environmental impact factors. Other authors developed life cycle analysis in a similar way, [6], [7]. In the solar panel production phase, the life cycle analysis includes extraction, production and transformation of raw materials required for the manufacture of a solar panel first as a semi-finished product, then as a product and finally an end product. The phase of a life cycle analysis involving solar panel production comprises three steps: material production, product manufacturing, packaging, and distribution. The phase of a life cycle analysis involving the solar panel application includes installation, use, and maintenance of a solar panel. The phase of a life cycle analysis involving recycling and waste management includes energy consumption for solar panel recycling and waste management. The environmental factor assessing the environmental burden accompanies all life cycle stages. The life cycle analysis model of a solar panel comprises input-output data and system boundaries. The input data relates to the data on raw materials, energy and hazardous waste used for solar panel manufacture. The output data relates to air emissions, aqueous waste, solid waste, energy, recycled material, and other products. The air emission data includes the data on produced or reduced greenhouse gases of the solar panel life cycle. Aqueous waste affects water management due to its discharge into the environment and the related environmental impacts in the solar panel life cycle. Solid waste is waste generated in the solar panel life cycle without the possibility of recycling. The energy on the output data side constitutes the solar panel energy life cycle and is the ratio between the energy invested, required for the solar panel production, and energy generated by the solar panel in its life cycle. Recycled material is material that can be reprocessed or reused in any other way and has been used in the solar panel life cycle. Other products are undefined products, occurring in the solar panel life cycle. A schematic arrangement of the analysis model of the solar panel life cycle is presented in Fig. 8. JET 17 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 1B (2020) Issue 2 Input Dataset Resource ■ Energy Hazardous Waste ~ Row Materials Exfraction ■ Bauxite ■ Basalt Rock ■ Dolomote Rock ■ Recycled Ahmiinntn AD Factors For Obtaining Row For STAF Pane! Natural Gas ' Transport Water 1 Cryolite Energy ■ Anode Block Manufacture ■ Aluminum AHoy ■ Rockwool ■ Water ■ Transport J STAF Pane! Energy And. Materials Needed ■ Natural gas ■ Energy Use And. Maintenance J STAF pane! technical action ■ Operation ■ Testing of performed factor ■ Spare parts ■ r.fiprnirak ■ Transport ■ Energy and file! ■ Ecology Recycling Management STAF Pane! Decommissioning Equipent And Material ■ Transport ■ Spare Part Demolition Fina! Disposa] Solid State Management Output Dataset fr Emissions To Air „ Water Waste t Solid Waste - Energy Recycling Materials Other Products Figure 8: Schematic arrangement of solar panel life cycle analysis model The quality of a life cycle analysis largely depends on the accuracy and precision of data and databases used. As a result of technological progress and increasingly stringent environmental regulations, the data and databases are constantly subject to changes and updates. The data from various databases differ because they are subject to various regional environmental regulations. The source of primary data in the life cycle analysis of a solar panel was the data provided by the solar panel manufacturer, i.e., Talum, d. d., [8]. As a secondary source of data, ee used the databases created by private or academic database developers: Ecoinvent Database, [9], Eurostat, [10], data from scientific literature, [11], [12], data from technical literature, [13], [14], etc. We split the data used in the life cycle analysis model of a solar panel into the following groups: materials, energy, waste, waste heat and air emissions. 3.1 Materials The materials group contains all materials used in the life cycle analysis model of a solar panel. They were split into two groups, namely aluminium materials for production, installation and packaging of aluminium and materials for production, installation, and packaging of rock wool. 18 JET Multi-purpose use and lifecycle analysis of solar panels Table 2 shows the database of average quantities of materials used for the solar panel manufacture. Table 2: Average quantities of materials for solar panel manufacture Aluminium Rock wool Material kg/panel kg/kg(AL) Material kg/panel kg/kg(Kv) Water 1558.336 193.8 Water - 4.468 Bauxite 39.774 5.100 Bauxite - 0.086 PE-foil 0.183 0.082 PE-foil - 0.009 Alumina 14.786 1.910 Briquettes 12.321 1.097 Anode blocks 3.502 0.450 Basalt rock 5.655 0.504 Coke 2.462 0.316 Portland cement 1.158 0.103 Aluminium 1.362 0.175 Dolomite rock 0.653 0.058 fluoride Tar pitch 0.494 0.063 Phenol 0.236 0.021 Green residue 0.045 0.006 Formaldehyde 0.236 0.021 Carbon residue 0.543 0.07 Impregnation 0.022 0.002 Calcium fluoride 0.008 0.001 Iron oxide 0.287 0.025 Cryolite 0.008 0.001 Acrylic dispersion 0.056 0.005 Calcined soda 0.004 0.0005 Total 6.399 Total - 201.974 Total 2 20.624 Total 1 1621.507 Total 1+2 1642.131 As much as 94.9% of water is consumed for the solar panel production, and such water is to a large extent disposed of into the environment as wastewater. The quantity of water required for alumina production is as high as 90%. On average, 39.77 kg of bauxite or 2.4% of the total material consumption is required for the manufacture of one panel. Total consumption of alumina and briquettes amounts to 1.6% of the overall material consumed for the manufacture of a single solar panel. The total quantity of material consumed is 1642.131 kg/panel. The overall amount of the material used for the production of one kilogram of aluminium is 201.974 kg/kg(AL), whereas the overall amount of the material used for the production of one kilogram of rock wool is 6.399 kg/kg(KV). 3.2 Energy The energy group comprises all energies dealt with in the life cycle analysis model of a solar panel and used in the production or processing stages for the solar panel manufacture. Energy consumed by a solar panel during the one-year or the forty-year operation period and energy generated by the solar panel during the one-year or forty-year operation period is also taken into consideration. In solar panel energy production, the average annual solar radiation for Central Europe [15] is taken into consideration for south-facing orientation and tilt angle of 15°. The energy consumption was split into three groups. We used the consumption of energy per JET 19 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 unit of one kilogram of aluminium for the aluminium production and transport, the energy consumption per unit of one kilogram of rock wool for the production and transport of rock wool and energy consumption per unit of solar panel for the manufacture and transport of solar panels. The one-year and forty-year energy consumption and production for solar panel operation are also included. The database of average energy amounts for the manufacture and operation of solar panels with south orientation and a tilt angle of 15° is shown in Table 3. Table 3: Average energy amounts for the manufacture and operation of solar panels with south orientation and a tilt angle of 15° Production, process, operation kWh/kg(AL) kWh/kg(Kv) kWh/pan Primary aluminium 23.99 - - Secondary aluminium 2.61 - - Briquettes - 0.579 - Rock wool - 1.879 - Ship transport 0.18 - - Rail transport 0.03 - - Other transport 0.01 0.024 - Aluminium panel manufacture - - 208.6408 Rock wool production - - 26.9895 Assembly and packaging - - 1.1772 Recycling - - 1.426 Consumption for one-year operation (1) - - 251.286 Production - one-year operation (2) - - 614.324 Consumption - 40-year operation (3) - - 698.616 Production - 40-year operation (4) - - 24572.96 Net production - one year (2-1) - - 363.038 Net production - 40 years (4-3) - - 23874.34 The amount of energy required for primary aluminium production and transport is 23.99 kWh/kg(AL) on average and 2.61 kWh/kg(AL) on average for secondary aluminium production and transport. The ratio between primary and secondary aluminium in the aluminium panel production is 80% to 20%. Rock wool is made from prefabricated briquettes. The briquette production requires 0.579 kWh/kg(KV) of energy on average, and the rock wool production and transport, however, requires 1.879 kWh/kg(KV) of energy on average. Therefore, the overall energy required for the production and transport of one kilogram of rock wool amounts to 2.388 kWh/kg(KV). We made a comparison between energy flows of average one-year and 40-year solar panel operation at the average annual solar radiation for Central Europe, south-facing orientation and a tilt angle of 15°. We also took into consideration the average consumption of energy for the operation of a circulating pump that sends a fluid to circulate through the solar panel. The average energy consumption for one-year operation, including the average energy consumption for solar panel manufacture and transport, amounts to 251.286 kWh/panel. In one year, a solar 20 JET Multi-purpose use and lifecycle analysis of solar panels panel fa cing south and having a tilt angle of 15°, feroduces 614.3241- kWh/panel on average. Net production in one year is the deference between tlie average annual energu produced and the average energy consgmpWon foo one-year operation, amounting to 363.038 kWh/panel. Furthermore, a similar calculation was made for the 40-year operation. Fig. 9 shows graphical presentations of average energies of the life cycle analysis of a solar panel. Thermal Electrolysis 13,75 SWf/Sg(AL) Alumina Manufacture 7,27 SWh/Sg(AL) Boxite Minin2 0,32 2Wh/Sf(AL) Anode Mia nufrcture 1,21 SWh/Sg(AL) Primary Casting 1,21 SWh/Sg(AL) Transport 0,23 SWh/Sg(AL) | Casting t,9 SWhWSg(AL) i Griding And Preparation 1 0,7 SWh/Sg(AL) | Transport 0,01 SWh/Sg(AL) Energy For Primary A luminum Production Energy For Secondary Aluminum Production Coal 1,514 kWh/kg(RW) Electricity 0, 296 kWÍVkg(RW) Gas 0,045 kWh/kg(RW) Eiesel 0,012 kWh/kg(RW) Transport 0,012 kWh/kg(RW) Electricity 0,452 kWh/kg(RW) Eiesel 0,045 kWh/kg(RW) Transport 0,012 kWh/kg(RW) Enersgyp For Roc kwool Production Production 614 kWh/panel Net Production 363 kWh/panel Operate Consumption 251 kWh/panel One Year Operation Energy Energy For Br iquettes Production Production 24573 kWh/panel Net Production 23874 kWh/panel Operate Consumption 698 kWh/panel 40 Years Operation Energy Figure 9: Graphical presentation of average energies of life cycle analysis of a solar panel JET 21 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 Over the one-year period of operation, a solar panel facing south and having at a tilt angle of 15° would produce 2.4 times more energy than the amount required for the manufacture, installation and one-year operation. Over the 40-year period of operation, a solar panel facing south and having a tilt angle of 15° would produce 35 times more thermal energy than the amount required for the manufacture, installation and 40-year operation of a solar panel. 3.3 Air Emissions In the air emissions group, we used all emissions of CO2, the greenhouse gas, covered by the model. The CO2 emissions were split into three groups: emissions in the production and transport of primary raw materials, emissions in the production and transport of rock wool, and emissions in the manufacture and transport of solar panels. The database of average amounts of CO2 for the manufacture and operation of a solar panel facing south and having a tilt angle of 15° is shown in Table 4. Table 4: Average amounts of CO2 for solar panel manufacture and operation Production, process, operation kg(CO2)/kg(AL) kg(CO2)/kg(KV) kg(co2)/panel Primary aluminium 10.471 - - Secondary aluminium 0.8447 - - Briquettes - 0.3734 - Rock wool - 0.6181 - Ship transport 0.0513 - - Rail transport 0.0081 - - Other transport 0.0027 0.007 - Aluminium panel manufacture - - 83.127 Rock wool production - - 10.399 Assembly and packaging - - 0.457 Recycling - - 0.546 CO2 production - one-year operation 1 - - 98.898 CO2 reduction - one-year operation 2 - - 226.865 CO2 production - 40-year operation 3 - - 277.818 CO2 reduction - 40-year operation 4 - - 9074.604 Net reduction of CO2 - one year (2-1) - - 127.97 Net reduction of CO2 - 40 years (4-3) - - 8796.786 The amount of greenhouse gas emissions in the primary aluminium production and transport is 10.471 kg(C02)/kg(AL) on average and 0,8447 kg(C02)/kg(AL) on average in the secondary aluminium production and transport. The ratio between primary and secondary aluminium taken into consideration in the aluminium panel manufacture is 80% to 20%. Rock wool is made of prefabricated briquettes. The amount of greenhouse gas emissions in the briquette production and transport is 0.3734 kg(C02)/kg(KV) on average and 0,6181 kg(C02)/kg(KV) on average in the rock wool production and transport. Therefore, the total amount of greenhouse 22 JET Multi-purpose use and lifecycle analysis of solar panels gas emissions in the production and transport of one kilogram of rock wool is 0.9915 kg(CO2)/kg(KV) on average. Graphical presentation of the average amount of released CO2 of the life cycle analysis of a solar panel is shown in Fig. 10. Thermal Electrolysis 6,89 kg(CO2)/kg(AL) Alumina Manufacture 2,57 kg(CO2)/kg(AL) Anode Manufacture 0,49 kg(CO2)/kg(AL) Boxite Mining 0,08 kh(CO2)/kg(AL) Transport 0,06 kg(CO2)/kg(AL) CO2 Emission For Rimary Aluminum Coal 0,454 kg(CO2)/kg(AL) Electricity 0,115 kg(CO2)/kg(AL) Transport 0,036 kg(CO2)/kg(AL) Gas 0,009 kg(CO2)/kg(AL) Diesel 0,0034 kg(CO2)/kg(AL) | Casting 0,57 kg(CO2)/kg(AL) I Griding And Preparation 1 0,23 kg(CO2)/kg(AL) | Transport 0,0017 kg(CO2)/kg(AL) CO2 Emission For Secondary Aluminum | Electricity 0,176 kg(CO2)/kg(AL) ] Process 0,149 kg(CO2)/kg(AL) ] Transport 0,036 kg(CO2)/kg(AL) | Diesel 0,0122 kg(CO2)/kg(AL) CO2 Emission For Rockwool CO2 Emission For Briquettes Figure 10: Graphical presentation of the average amount of released CO2 of the life cycle analysis of a solar panel 3.4 Carbon Footprint We made a comparison between the carbon footprint of one-year and 40-year operation of a solar panel facing south and having a tilt angle of 15°. All CO2 gas emissions generated in all stages of solar panel manufacture and transport were taken into consideration in the operation, as well as the greenhouse gas emissions generated in the solar panel operation and circulating pump drive. Those greenhouse gas emissions were reduced by the amount of reduced greenhouse gases to obtain the carbon footprint result in the one-year and 40-year period. Reduced greenhouse gases are gases emitted into the air if the energy generated by a solar panel is produced by burning fossil fuels. The carbon footprint of one-year and 40-year operation of a solar panel facing south and having a tilt angle of 15° is shown in Fig. 11. JET 23 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 .100 S 0 O -100 -200 Produced 98,9 CO2 Reduced -226,9 CO2 Net -127,9 CO2 5000 CM O o One Year Footprint -5000 -10000 Produced 227 CO2 Reduced -9074 CO2 - Net -8796 CO2 40 Years Footprint Figure 11: Carbon footprint of one-year and 40-year solar panel operation Over the one-year period of operation of a solar panel facing south and having a tilt angle of 15°, 98.898 kg(co2)/panel of greenhouse gas are emitted into the air and 226.9 kg(C02)/panel of greenhouse gas are reduced. The one-year carbon footprint is negative, since over the one-year period of a solar panel operation, 127,9 kg(C02)/panel less C02 is emitted into the air than if the energy generated by a solar panel in one year is obtained by burning fossil fuels. Over the 40-year period of operation of a solar panel facing south and having a tilt angle of 15°, the amount of C02 emitted into the air is 227.818 kg(C02)/panel and the amount of C02 reduced is 9074.604 kg(C02)/panel. The 40-year carbon footprint is negative also in this case, since over the 40-year period of a solar panel operation, the amount of C02 emitted into the air is by 8796.786 kg(C02)/panel lower than if the energy generated by a solar panel in the period of 40 years is obtained by burning fossil fuels. 0 4 DISCUSSION AND CONCLUSION The positive environmental impact of solar panels is reflected mainly in the green production of thermal energy and in its negative carbon footprint. The green production of thermal energy means that solar panels generate 35 times more thermal energy in their life cycle than the energy needed for raw materials production, manufacture, installation and transport of solar panels. The negative carbon footprint, in contrast, means that solar panels contribute in their life cycle to the C02 air emissions reduction in comparison with the thermal energy generated by solar panels by burning fossil fuels. Another advantage of solar panels is that at the end of their lifetime, the materials used in solar panels may be almost fully recycled and reused. A negative impact on the environment, however, is associated primarily with the production of aluminium used in solar panels. The aluminium production process requires huge amounts of water which, to a large extent, is disposed of as wastewater or red mud in alumina production. Moreover, the aluminium production process requires high consumption of electricity that is still largely generated in Slovenia by burning fossil fuels. The heat that is released in the aluminium production processes is almost entirely discharged into the environment. 0ther heating systems operating in accordance with the solar radiation exploitation principle have characteristics and properties similar to solar panels. Energy payback time ranges from 24 JET Multi-purpose use and lifecycle analysis of solar panels less than a year to three years. Carbon footprints of solar heating systems are negative, which means that they generate far fewer greenhouse gases than by using fossil fuel heating appliances. For example, a photovoltaic panel reduces greenhouse gas emissions, namely by 0.6 kg CO2 for each kWh of energy produced. Furthermore, energy for the manufacture of photovoltaic panels is 30 times lower than the energy generated by a photovoltaic panel in its lifetime. The advantage of solar panels in comparison with other solar panels lies mainly in the fact that the materials used for the manufacture of solar panels can be easily almost fully recycled and reused. References [1] Z. Chen, S. Furbo, B. Perers, J. Fan, E. Andersen: Efficiencies of flat plate solar collectors at different flow rates, Energy Procedia, Vol. 30, p.p. 65 - 72, 2012 [2] J. Avsec, U. Novosel: Application of alternative technologies in combination with nuclear energy, Transactions of FAMENA, ISSN 1333-1124, vol. 40, spec. issue 1, p.p. 23-32, 2016 [3] The European Commission's science and knowledge service, Available: http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php (10.07.2020) [4] ISO 14040. Environmental management - Life cycle assessment - Principles and Framework. [5] ISO 14025. 2006. Environmental labels and declarations - Type III environmental declarations - Principles and procedures. [6] I. Millera, E. Gen;era, S. H. Vogelbauma, R. P. Browna, S. Torkamanid, M. F. 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Mahmud: Impacts of aluminum production: A cradle to gate investigation using life-cycle assessment, Science of the Total Environment, Vol. 663, p.p. 958-970, 2019 JET 25 Dušan Strušnik, Urška Novosel, Jurij Avsec JET Vol. 13 (2020) Issue 2 [13] U.S. Energy Requirements for Aluminum Production, Industrial Technologies. Program Energy Efficiency and Renewable Energy U.S. Department of Energy, 2007 [14] Calculation of fuel consumption per mile for various ship types and ice conditions in past, present and in future, Arctic Climate Change, Economy and Society, 2014) [15] ARSO, http://www.arso.gov.si/vreme/napovedi%20in%20podatki/vreme avt.html, Available: (10.07.2020) 26 JET