Search

In this research, we present a new long-term energy planning model that considers endogenous capacity investment, energy dispatch, Power-to-X, and demand response technologies. A thorough literature review of existing energy planning models is also presented, allowing to present the distinctive characteristics of the proposed model. The proposed model considers an energy system with the objective of minimizing the total capacity investment cost, throughout all technologies, and the operational cost faced by the system in satisfying energy demand. The model also considers the links among different demand sectors, including the links between the electricity, industry, heat, transport, and electro-fuels (e.g., Hydrogen) sectors. The proposed model is used to study the decarbonization of the Croatian energy system under distinct policies associated to RES levels and CO2 emissions goals. We demonstrate that Power-to-X technologies can certainly provide the flexibility that is required by new capacity investments in variable renewable energy sources, obtaining systems with lesser levels of critical excess of energy production. Higher usage of battery storage and Power-to-heat technologies are adopted primarily for variable renewable shares and CO2 reductions of close to 80%, while below such levels, the adoption of such technologies is limited. Additionally, Power-to- heat flexibility options become the major technologies when limits on CO2 emissions from the heating sector are imposed and, particularly, when the variable renewable energy shares in the electricity sector gets close to levels of 60%.

In the EU around 40% of bio-waste (organic fractions of municipal solid waste including food waste) still goes to landfills. In some Member States this waste is almost completely landfilled. An estimation is that about one-third of Europe`s 2020 targets for renewable energy in transport could be met by using biogas produced from bio-waste (including food waste), and around 2% of the EU`s overall renewable energy target could be met if all bio-waste were turned into energy.Modern and environmentally friendly waste management is still not introduced in many European cities and regions. This problem is tackled by the Bin2Grid project which promotes the “food waste to biomethane” concept in four large European cities in order to serve as flagship examples for other cities.The objective of the Bin2Grid project is to support biomethane production and its use in transport by using segregated food waste from the food and beverage industry, catering sector, and from households(MSW) as feedstock. Focus of the Bin2Grid project is on the development of value chain concepts for four European cities: Zagreb (Croatia), Skopje (Macedonia), Malaga (Spain), and Paris (France). The Bin2Grid project highlights the multiple environmental benefits of source-separate waste collection and conversion of that feedstock into biomethane, in comparison to other treatment methods (landfilling, incineration, MBT, composting). A Benchmark Tool was developed by the project and is presented in this paper., Proceedings of the 25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden, pp. 204-209

Kontekst, vizija, ciljevi, scenariji, mjere, procjena utjecaja scenarija na okoliš, gospodarstvo i društvo, financiranje.

South East Europe consists of several smaller countries in terms of energy systems and thus, integrating energy systems of the whole region has significant benefits for all the countries included. However, as there are large differences between energy mixes of the countries included, careful energy planning needs to be carried out in order to satisfy energy needs of all the countries of the region. Due to the significant differences in geography and the climate of different parts of the region, many different technologies need to be introduced in order to have optimal, low-carbon energy mix. In this paper, steps toward the 100% renewable energy system (RES) for the year 2050 have been presented. Novelty in this paper, compared to the similar research already being carried out, is the sustainable use of biomass in 100% RES, as this is the only way in which biomass 1192-1 can be considered as carbon-neutral. Smart energy systems’ approach has been used in planning of 100% RES, which considers significant integration of the electrical, heating and gas sectors. Many technologies have been employed in the year 2050, but the major share is put on photovoltaics and wind energy, followed by geothermal, solar thermal, CHPs driven on biomass, hydro power and synthetic fuel technologies. Finally, it was shown that the 100% RES in the year 2050 is cheaper than the reference system, developed for the year 2012.

Horizontal liquid film flow sheared by an external air flow field is encountered in many engineering applications. Taking into account its physical complexity and high cost of experimental investigation, numerical simulations are nowadays considered as a valuable alternative. They are becoming a useful tool for detailed understanding of complex flow characteristics and transport phenomena, especially in situations where experimental measurements are infeasible or too expensive. The focus of this paper is the implementation and validation of a mathematical model of surface tension effects within the existing numerical framework in order to achieve a more accurate description of the liquid wall film phenomena. After literature review, optimum mathematical model has been chosen and implemented in commercial computational fluid dynamics (CFD) code. Validation was carried out using a well established case of isothermal droplet spreading for which there are analytical expressions. Comparison of simulation results with non- dimensional droplet profile shows excellent agreement with analytical results and gives confidence for commercial application of implemented model.

Primary energy import dependence of the European Union is currently around 53%, and it is expected that in the next 20-30 years it will reach or surpass 70%. The situation in Croatia is similar. In 2007 import dependence was 53.1%, while for 2030 it is predicted to reach 72%. Such import dependence leads to decreased security of energy supply, due to current geopolitical situation in which main sources of fossil fuels are in unstable regions and in which the competition for those resources from developing countries is growing. EU energy strategy, and a compatible Croatian strategy, is focused on policies and measures that will bring increase of share of renewable and distributed energy sources, increase in energy efficiency and energy savings and decrease in green house gas emissions. The results of previous research has shown that in order to increase efficiency and viability, there is need for energy storage, in the primary or secondary form, in order to transfer energy surplus form period of excess to the period when there is a lack. The problem of storage systems is that they increase the cost of already expensive distributed and renewable energy sources, making them, in market circumstances, even less economically viable. Although there are a number of storage technologies, as chemical, potential or heat energy, not all those technologies are optimal for each energy system. The paper shows results of energy planning and several cases where use of smart energy storage system could help with integration of the energy flows, the transformations and energy demand at the location of the energy end- use or close to it. Primary energy import dependence of the European Union is currently around 53%, and it is expected that in the next 20-30 years it will reach or surpass 70%. The situation in Croatia is similar. In 2007 import dependence was 53.1%, while for 2030 it is predicted to reach 72%. Such import dependence leads to decreased security of energy supply, due to current geopolitical situation in which main sources of fossil fuels are in unstable regions and in which the competition for those resources from developing countries is growing. EU energy strategy, and a compatible Croatian strategy, is focused on policies and measures that will bring increase of share of renewable and distributed energy sources, increase in energy efficiency and energy savings and decrease in green house gas emissions. The results of previous research has shown that in order to increase efficiency and viability, there is need for energy storage, in the primary or secondary form, in order to transfer energy surplus form period of excess to the period when there is a lack. The problem of storage systems is that they increase the cost of already expensive distributed and renewable energy sources, making them, in market circumstances, even less economically viable. Although there are a number of storage technologies, as chemical, potential or heat energy, not all those technologies are optimal for each energy system. The paper shows results of energy planning and several cases where use of smart energy storage system could help with integration of the energy flows, the transformations and energy demand at the location of the energy end- use or close to it.

Developing of new energy systems on the islands, where conventional technologies are costly and new solutions are more efficient, could represent a source of great knowledge which may be learnt by studying experiences from particular situations of decentralised energy generation and integration of renewable energy sources. These sources could offer clean and secure energy for local communities but also can contribute to employment of local population and rural development. The paper presents results of energy planning with renewable energy sources and hydrogen as energy carrier of Mljet Island in Adriatic Sea.

The transport sector is the only sector in which there have been no significant renewable energy penetrations and it is heavily dependent on oil with rapid growth in the last decades. Moreover, it is challenging to obviate the oil dependence due to the wide variety of modes and needs in the sector. Nowadays, biofuels are proposed as one of the main options for replacing fossil fuels in the transport sector, along with electricity. The main reasons for avoiding the direct usage of biomass in the transport sector, i.e. producing biomass derived fuels, are land use shortage, limited biomass availability, interference with food supplies, and other impacts on environment and biosphere. Hence, it is essential to do a detailed analysis of the transport sector in order to match the demand and to meet the criteria of a 100% renewable energy system in 2050. The transport sector is the only sector in which there have been no significant renewable energy penetrations and it is heavily dependent on oil with rapid growthin the last decades. Moreover, it is challenging to obviate the oil dependence due to the wide variety of modes and needs in the sector. Nowadays, biofuelsare proposed as one of the main options for replacing fossil fuels in the transport sector, along with electricity. The main reasons for avoiding the directusage of biomass in the transport sector, i.e. producing biomass derived fuels, are land use shortage, limited biomass availability, interference with food supplies,and other impacts on environment and biosphere. Hence, it is essential to do a detailed analysis of the transport sector in order to match the demandand to meet the criteria of a 100% renewable energy system in 2050.

The cement industry is one of the leading producers of the greenhouse gases, where carbon dioxide is the most significant anthropogenic greenhouse gas. There are two thermo-chemical processes involved in cement production which contribute to these emissions. One is the thermal decomposition of limestone, widely known as the calcination process, and the other is the combustion of fossil fuels. Recently, researchers have invested significant effort to improve the energy consumption and pollutant formation of the overall cement manufacturing process. One of these improvements was made by dividing the calcination and clinkering process into two separate furnaces, where the calcination process is performed in a furnace called a calciner, and the clinkering process is performed in a rotary kiln. Because this is a new technology in the cement manufacturing process, cement calciners are still in the research and development phase. The purpose of this paper is to present the first phase of the cement calciner's development, which is the CFD simulation of the cement calciner, with an implemented mathematical model of the calcination process. From the results gained by these simulations, researchers will have an in-depth understanding of all thermo-chemical reactions in a cement calciner. This understanding can be used for the optimization of the calciner's geometry, to have a more efficient production, to lower the pollutant formation and subsequently reduce greenhouse gases emission.

In this paper, an optimization model for incorporating seasonal heat energy storage and biomass trigeneration power plant is presented. Currently in Croatia, overall efficiency of biomass CHP or CCHP has to be above 50% on an annual basis in order to be eligible for a feed-in tariff. Consequently, biomass power plants use the excess heat production for drying biomass which is currently allowed. However, it is expected that it will not be allowed in the future due to inefficient use of heat. Thus, this paper provides a solution for managing excess heat in biomass CHP and CCHP power plants, as well as a way to shave peak energy demand. The objective of the optimization model is to maximize net present value (NPV) using hybrid optimization method. It is a demand driven model, covering real heating and cooling energy need by end-use customers. Optimization model is easy to adopt in different regions and can be used for evaluating economic feasibility of the investment in trigeneration system that covers all heating and cooling energy demand. Two case-studies were done in order to show the impact of minimum allowed overall power plant efficiency on overall economic indicators. Moreover, the financial data for the possible shift from feed-in-tariffs to fixed and variable feed-in-premiums was presented.

The share of energy from renewable energy sources (RES) in the final gross energy consumption in Macedonia is about 14%, mostly due to the electricity produced by large hydro power plants and the use of biomass for heating. Macedonian energy sector is the main emitter of greenhouses gases (GHG) with share of about 70 % in the total annual emissions. Also, 70-75 % of emissions are associated with the electricity generation due to the predominant role of the lignite fuelled power plants. Recently, the government has adopted a strategy for the use of RES which identifies a target of 21% of final energy consumption from RES by 2020. In this paper analyses are conducted in order to investigate to which extent and in which way the absorption capacity of the power system for RES electricity can be improved. For this purpose, combining various conventional and RES technologies, including pump storage hydro power plant and revitalisation of the existing lignite power plants six scenarios for the power system expansion are developed by making use of EnergyPLAN model. Critical excess of electricity (CEEP) analyses are conducted in order to identify the maximal penetration of wind electricity. The results have shown that in the exiting capacities maximal penetration of wind electricity in 2020 is 13 % of total electricity consumption. The revitalization of the existing lignite power plants and building of pump storage power plant would increase the wind penetration. Furthermore, the developed scenarios are comparatively assessed in terms of the associated greenhouse gases emissions and import of electricity.

Today, coal is responsible for 40% of annual CO2 emissions. At the same time, global warming causes climate changes accompanied with catastrophic meteorological phenomena all over the world. After the 2015 Paris Agriment many countries set ambitious energy policy to reduce the annual greenhouse gas emission. The 2021 UN Climate Change Conference, COP26 - Glasgow, ended with the adoption of a less stringent resolution than some anticipated: countries only agreed to “phase down” rather than “phase out” coal. Is possible the realization of the Paris Agreement after COP-26? For achieving this ambitious targets in such conditions, the support of the multi-disciplinary scientific knowledge is needed. Since 2002 a series of SDEWES Conferences were founded. This paper presents an overview of published researches in special issues of leading journals dedicated to the series SDEWES Conferences, including also the papers in current special issue presented on Conferences held in 2020: 2nd LA SDEWES Conference - Buenos Aires, 1st AP SDEWES Conference - Gold Coast, 4th SEE SDEWES Conference - Sarajevo and 15th SDEWES Conference - Cologne. The focus is on five main fields: (1) energy system analysis ; (2) energy savings in the building sector ; (3) district heating ; (4) electrification of transport and (5) water-energy nexus. Undoubtedly, the researches presented in this special issue as well as in previous ones, will contribute to the achievement of the goals of the Paris Agreement in difficult conditions after COP26.

Nowadays maritime industry is focused on reduction of greenhouse gas (GHG) emissions from shipping. Alt-hough about 2.89 % of the total global anthropogenic CO2 emissions comes from shipping industry, in 2018 the International Maritime Organization (IMO) adopted the strategy to lower the total annual GHG emissions by at least 50 % by 2050, in comparison to 2008. Different measures to mitigate the emissions are proposed and used in the shipping industry, which can be classified into technological and operational measures. The use of alternative fuels and renewable energy sources could be considered as a third category of mitigation measures. One of the short-term operational measures that is being implemented in maritime transport is slow steaming. It is a low- cost measure that can greatly reduce the emissions since fuel consumption depends on the sailing speed. However, it is important to investigate whether the savings in fuel consumption due to lower sailing speed can exceed the costs of a higher number of vessels that have to be engaged to keep the yearly transport work constant. The ship operators would gladly implement this measure if the savings achieved by speed reduction would be greater than the capital and operating costs.

Characteristic nodular form of graphite in ductile irons is achieved by inoculation and nodulation with magnesium and rare earth elements addition to the melt before or during pouring process. This contributes to the improvement of properties such as castability, strength and toughness of ductile iron. The properties of ductile iron are mainly influenced by alloying elements, casting technology, wall thickness and solidification rate which can affect the shape of graphite and metal matrix transformation. Graphite form in ductile irons is controlled by the growth through eutectic solidification till the eutectoid transformation temperature. Graphite nodule degeneration occurs in thick-walled castings due to the carbon diffusion on graphite nodules during slow cooling. In order to ensure required properties of ductile iron the focus of investigation will be on the mechanism of graphite growth, solidification and degeneration under different solidification conditions.

Spatial resolution is often cited as a crucial determinant of results from energy systems models. However, there is no study that comprehensively analyses the effect of spatial resolution. This paper addresses this gap by applying the Heat Infrastructure and Technology heat decarbonisation optimisation model in six UK Local Authorities representing a range of rural/urban areas, at three levels of spatial resolution, in order to systematically compare results. Results show the importance of spatial resolution for optimal allocation of heat supply technologies and infrastructure across different urban/rural areas. Firstly, for the studied cases, differences of up to 30% in heat network uptake were observed when comparing results between different resolutions for a given area. Secondly, for areas that generally exhibit the high and low extremes of linear heat density, results are less dependent on spatial resolution. Also, spatial resolution effects are more significant when there is higher variability of linear heat density throughout zones. Finally, results show that it is important to use finer resolutions when using optimisation models to inform detailed network planning and expansion. Higher spatial resolutions provide more detailed information on zones that act as anchors that can seed network growth and on location of network supply technologies.

The paper aims to understand sustainability in the profession of architecture. The purpose is to investigate the ability to make architectural and spatial design choices on different scale environmentally sustainable. The paper intends to explore examples of good practice in Croatia from implementing environmentally responsible and energy efficient techniques in the planning, budgeting, design and construction of the municipal projects, technology development and investments in energy efficiency as well as new construction considering energy-efficient design. The paper presents the work of different teams of architects in small and large-scale building and landscape architecture. The paper ends with important lesson how the future projects of different scales can be developed to be more sustainable. More research and innovation is needed. Different approaches may serve as inspiration for architects and others interested in architecture in relation to design, functionality, construction, sustainability and environmentally responsible actions.

Today, strategies for emergency preparedness, in presence of accidental scenarios in high-risk plants with releases into the atmosphere, have become a priority. To achieve this goal, it is important to have forecast meteorological data in local areas to use in dispersion and transport models and so to respond in advance emergency situations. The paper reports results of research performed to develop a new tool, called FORCALM that is capable to elaborate European Centre for Medium-Range Forecasts (ECMWF) forecast data to use for simulations by CALMET/CALPUFF modeling system. A case study, relevant to an accident occurred in Mediterranean Refinery at Milazzo (Italy), has been examined to validate the procedure and the capacity to evaluate the transport and depositions pollutant in terms of forecast information. The results were compared with those obtained using CALMET/CALPUFF simulations based on measured meteorological, covering the area under study.

Sustainability is one of the most relevant themes within the architectural profession. Climate changes and limited energy resources require a need to focus on low energy consumption and environmentally responsible architecture. Architects combine creative design with technical knowledge to provide integrated solutions for built and natural environments. Energy efficient and resource conscious approaches are incorporated into architecture as technical innovations including a particular use of materials based on the location or as utilisation of the climatic conditions. Energy efficiency is at the heart of the integrated European Union energy policy, aiming to reduce total consumption of energy. The Republic of Croatia is a member country of the EU (since July 1, 2013) and in compliance with EU directives Croatia has adjusted its development strategy to the principles of sustainability. Therefore, it is interesting to see what is actually built and how a number of Croatian architects studios approach architectural themes in relation to environmental sustainability. The paper aims to understand sustainability in the profession of architecture. The purpose is to investigate the ability to make architectural and spatial design choices on different scale environmentally sustainable. The paper intends to explore examples of good practice in Croatia from implementing environmentally responsible and energy efficient techniques in the planning, budgeting, design and construction of the municipal projects, technology development and investments in energy efficiency as well as new construction considering energy-efficient design. The paper presents the work of different teams of architects in small and large-scale building and landscape architecture. The paper ends with important lesson how the future projects of different scales can be developed to be more sustainable. More research and innovation is needed. Different approaches may serve as inspiration for architects and others interested in architecture in relation to design, functionality, construction, sustainability and environmentally responsible actions.

The large amount of waste toner cartridges has been generated as a consequence of it’s use in printers and duplicators on the everyday basis. Waste toner cartridge contains heavy metals, plastics as well as toxic residual toner and has been characterized as hazardous waste. Therefore the management of the waste toner presents significant issue in the environmental protection. The use of the hazardous substances in electrical and electronic equipment as well as promoting the collection, recycling and recovery targets for all types of electrical goods was prescribed by EU legislation, particularly Directive 2009/95/EC (WEEE Directive) and together with the Restriction of Hazardous Substances Directive 2002/95/EC (RoHS) has been in force since February 2003. At the moment, Republic of Croatia is in the process of becoming a full EU member so it has been obliged to implement EU legislation as well. Concerning the management of electrical and electronic equipment in Croatia according to WEEE Directive, the system has been established for the last five years but there was no practical possibility for the treatment of the collected waste toner in the country. In this work, the study of the possibility of waste toner and further recycling and reuse has been performed with the special emphasis on the reuse of the residual toner. In order to decrease explosive properties of the residual toner, the material was mixed with the calcite. After performed analyses of the mixture it was found that the mixture can not be disposed to the landfill as inert waste material since the value of the total organic carbon content (TOC) has found to be above the limit prescribed by the law. All other analyzed parameters have found to be below the limits prescribed by the law. Moreover, it was found that the mixture of residual toner which contains 10% of calcite is an excellent bitumen additive since it improved bitumen’s application properties. So, the mixture of the residual toner and calcite can be used as valuable raw material in bitumen production and used in different construction works.

The large amount of waste toner cartridges has been generated as a consequence of it’s use in printers and duplicators on the everyday basis. Waste toner cartridge contains heavy metals, plastics as well as toxic residual toner and has been characterized as hazardous waste. Therefore the management of the waste toner presents significant issue in the environmental protection. The use of the hazardous substances in electrical and electronic equipment as well as promoting the collection, recycling and recovery targets for all types of electrical goods was prescribed by EU legislation, particularly Directive 2009/95/EC (WEEE Directive) and together with the Restriction of Hazardous Substances Directive 2002/95/EC (RoHS) has been in force since February 2003. At the moment, Republic of Croatia is in the process of becoming a full EU member so it has been obliged to implement EU legislation as well. Concerning the management of electrical and electronic equipment in Croatia according to WEEE Directive, the system has been established for the last five years but there was no practical possibility for the treatment of the collected waste toner in the country. In this work, the study of the possibility of waste toner and further recycling and reuse has been performed with the special emphasis on the reuse of the residual toner. In order to decrease explosive properties of the residual toner, the material was mixed with the calcite. After performed analyses of the mixture it was found that the mixture can not be disposed to the landfill as inert waste material since the value of the total organic carbon content (TOC) has found to be above the limit prescribed by the law. All other analyzed parameters have found to be below the limits prescribed by the law. Moreover, it was found that the mixture of residual toner which contains 10% of calcite is an excellent bitumen additive since it improved bitumen’s application properties. So, the mixture of the residual toner and calcite can be used as valuable raw material in bitumen production and used in different construction works.

In a global perspective, it is essential that the world transfers from fossil fuels to renewable energy sources in order to minimise climate change effects. As a part of such transition energy savings are also important, as they can decrease production costs effectively. The nature of such a change is that it has to be implemented on a local level. Energy saving technologies are placed with the demand decrease and renewable energy is typically distributed where the resources are. In some parts of the world, energy savings have resulted in a stabilisation of the energy demands, however in the world as such, demands are still increasing in buildings, transport and industry. Although the demand has increased approx. 32% overall, the share of renewable energy has increased from 12.7% in 1990 to 13% in 2010, in this way demonstrating that renewables can effectively cope with the world energy requirements – even in a context characterized by a continuously increasing demand. Even in the current financial crisis, renewable energy is expanding heavily . The most used renewable energy is biomass; however there has been a significant increase in wind power and in photovoltaic in the last ten years. Such development in the intermittent renewable energy sources requires knowledge about the interaction between supply and demand sides of energy. At the 6th Dubrovnik Conference on Sustainable Development of Energy, Water and Environmental Systems, September 25–29 2011, in Dubrovnik, Croatia, these issues were addressed among others. The conference was dedicated to research concerning methods, policies and technologies for increasing the sustainable development as well as methods for assessing and measuring sustainability of development, regarding energy, transport, water and environment systems and their many combinations. At the conference 418 scientists from 55 countries representing six continents participated. In this Special Issue the interaction between sectors and renewable energy systems through selected papers from this conference is addressed from a range of technical system analyses to environmental and economic feasibility.

Located between the regions rich in fossil fuels (Russia, Caspian states and the Middle East) and main Central and West European markets, South-East European (SEE) countries might become increasingly important as an alternative transit route for energy supplies. Transit is a key factor in project planning and investment decisions. In addition to the geographical position, transit countries and regions have to be politically stable with supportive investment climate, including legally ensured rights of way in order to be attractive for investors. On the other hand, the investments have to be environmentally sustainable and economically viable to be attractive for transit countries. As following the construction phase the roles and negotiating powers change, legally binding and enforceable rules have significant impact on investment decisions. The South East Europe is in this respect an interesting case. By adhering to Energy Community, countries of the region have signed to the EU competition, environment and transit rules. The aim of the paper is to outline a complex relationship between energy and climate change considerations in decision making relevant for SEE. Relevant decision making is analyzed from perspective of domestic decision-making ; project decision making at international level (e.g. investment decisions) and on the level of international legal instruments that can have significant impact on energy security and environmental sustainability in SEE. The paper starts with brief overview of major planned infrastructure projects. Based on formal support for selected projects it is examined how interests of energy security and environmental sustainability are balanced in decision-making process in South East Europe. Second, the role of international instruments (primarily Kyoto and post-Kyoto regime, Aarhus convention, the Energy Community and the Energy Charter Treaty) for decision – making at national and project level is examined. Next, the importance of commercial, political and environmental considerations for decision making is outlined. As a result, geopolitics of energy and climate change of SEE is outlined.

Our civilization is facing an unavoidable transition from convenient but environmentally not so friendly, and ultimately scarce energy sources to less convenient, but preferably clean and sustainable ones. Regardless on the energy sources, there will always be a need for convenient, clean, safe, efficient and versatile energy carriers or forms of energy that can be delivered to the end users. Both, hydrogen and electricity are energy carries that together may satisfy all the energy needs of modern civilization. Hydrogen and electricity should not compete with each other, but rather complement each other. With their complementary versatility, they can help in increasing the acceptance and market penetration of renewable energy technologies. However, market penetration of renewable energy sources cannot be left depending solely on market forces. The benefits of a clean and permanent energy system based on renewable energy sources, and hydrogen and electricity as the energy carriers, are reaching far beyond a horizon of an ordinary customer. They are also beyond the horizon of a utility or energy company, and even the nation. The decision on employing the renewable energy sources must be a conscious one, made on a national and international level, and based on clear but far reaching benefits to the nation and to the global environment. This paper attempts to identify and quantify those benefits, with the help of a global energy/environment/economy model based on energy language diagram. Although all economic models are based on growth, from a thermodynamic point of view it is clear that no system based on finite sources can continue to grow forever. A system based on utilization of constant flow of incoming energy (such as solar energy) will eventually reach a steady state. A steady-state level which the human civilization can obtain, depends on the rate of utilization of available solar energy and the effort required to convert solar energy into more useful forms of energy (hydrogen and electricity being only the intermediary steps). The model has been used to predict the level at which the renewable energy sources would be sustainable as a function of timing and net energy (emergy) ratios.