Thermo-ecological Cost Research Articles

Sustainability assessment of hydrogen production based on nuclear energy

Hydrogen is expected to be a key energy carrier in the global energy transition. A promising method of hydrogen production is water electrolysis powered by nuclear energy. This energy source can also be used in other hydrogen production technologies, such as copper-chlorine cycle. Proper comparison of various hydrogen production methods from the sustainability perspective requires the use of analysis in a global balance boundary. The paper presents a comparison of sustainability of various hydrogen generation methods, with emphasis on the methods exploiting nuclear energy. Instead of local energy efficiency, the index of Thermo-Ecological Cost (TEC) is proposed. TEC is a measure of the depletion of non-renewable resources burdening the production of a given product. Other criteria used in the assessment are: availability of energy supply (capacity factor), cumulative greenhouse gas emissions and resources to production ratio. In addition, water electrolysis and copper-chlorine cycle have been considered cogeneration processes, providing oxygen as a useful by-product. Taking into account all the criteria suggests that obtaining hydrogen with the use of nuclear technologies will provide a fair, long-term compromise compared to other hydrogen generation technologies.

Thermo-ecological analysis of the power system based on renewable energy sources integrated with energy storage system

Energy systems based on Variable Renewable Energy (VRE) such as solar energy (PV, PV/T) and wind energy (wind turbine) are intermittent by weather and climate conditions. This poses challenges for managing to obtain a stable energy supply. Microgrids based on VRE must accommodate the variability using, for example, energy storage. The second options for adjustment are backup generators or sources with firm capacity cooperating with VRE. The article presents an analysis of individual RES sources PV, PV/T system, wind turbine and biogas plant indicating the advantages of individual components and the possibility of their cooperation in a microgrid. The analysis for the assumed climatic conditions (location: Katowice, Poland) showed the benefits of the combination in the energy mix sources based on solar radiation and wind energy. The analysis also covers the use of the energy stored (based on electrolyser, hydrogen store and fuel cell) and presents the possibilities of using energy storage technology in various options of the energy mix. The most advantageous was a mixed system based on renewable energy sources using solar irradiation and wind energy with the stabilizing participation of a biogas plant - in this case, the capacity of the energy storage was fully used. In the further part of the article an exergo-ecological analysis using the TEC concept (thermo-ecological cost) is presented. TEC indicators for different versions of the energy mix were presented, analysing the systems in terms of natural resource management. The thermo-ecological analysis showed that the best energy mixes in terms of assessing the efficiency of natural resource management are systems that use the advantages of each component, supporting by energy storage.

Thermo-ecological cost – System evaluation of energy-ecological efficiency of hydrogen production from renewable and non-renewable energy resources

Hydrogen is expected to be a key fuel in the global energy transition. It is characterised by diverse potential applications in the industrial, transport, energy and building sectors. An increase of hydrogen production from renewable energy (RES) is especially important from the point of view of further sustainable development. However, a dominant share of hydrogen production is still covered by steam methane reforming (SMR). In order to facilitate the increase of the share of H2 from RES, efficiency of various hydrogen production technologies should be properly assessed. Majority of scientific publications consider only the local energy efficiency of the hydrogen production methods. From this perspective the production of hydrogen by SMR is characterised by higher efficiency than production of hydrogen from RES. In order to properly evaluate the global efficiency of hydrogen production technologies, we propose an advanced system exergy analysis – Thermo-Ecological Cost (TEC). Additionally, we propose to consider the production of hydrogen via electrolysis as cogeneration of two useful products - hydrogen and oxygen. Such approach allows to decompose the energy expenditure for the process and assign a lower burden for the main product (hydrogen). The results of TEC analysis for hydrogen production from non-renewable and renewable resources are presented and compared with the local energy efficiency of these technologies. The presented results confirm the thesis that local energy efficiency is not a proper tool for evaluation of effectiveness of hydrogen technologies, especially when production of hydrogen from non-renewable and renewable energy is to be compared.

Dynamic performance and sustainability assessment of a PV driven Carnot battery

This study investigates the performance of a Carnot Battery and performs a thermodynamic-based sustainability analysis using different methods. Carnot batteries have two different operational processes, charge and discharge. Electricity generated from a renewable source is used to operate a heat pump and the heat rejected by the heat pump is stored in the battery, which is then used to generate electricity in the Organic Rankine Cycle (ORC) at night and called as the discharge process. Climatic data from the city of Izmir, the third largest city by population in Turkey, has been chosen for the dynamic analysis. Exergy-based sustainability and thermo-ecological cost analyses are performed. The results show that the maximum Coefficient of Performance (COP) of the heat pump system is 4.5, the exergy efficiency can reach 0.78 and its the maximum sustainability index is 4.5. For the discharge process, energy efficiency of the ORC is 0.118 while the exergy efficiency is around 0.49 with a sustainability value of about 2.0.

Energy prosumerism using photovoltaic power plant and hydrogen combustion engine: Energy and thermo-ecological assessment

Renewable Energy Sources (RES) represent an attractive way to save natural resources and improve the overall impact of power systems on the environment. A continuous increase of share of RES in national energy mixes is observed, and due to the energy policy of the European Union and many other countries, further increase is expected. A disadvantage of RES is their random, weather-dependent availability, which requires energy storage. A promising method of integrating RES with the energy system is the use of hydrogen as an energy carrier (e.g. coupling RES with electrolyzers in order to directly use the renewable electricity for production of hydrogen). In the present work, a simulation of cooperation of a photovoltaic power plant with a gas piston engine fueled by hydrogen was performed, with and without the presence of energy storage. The aim of the analysis is twofold. First, the “compensation losses” due to forced part-load operation of the engine coupled with RES are evaluated and compared with “storage losses” resulting from the thermodynamic imperfectness of the storage; this allows to calculate the minimum round-trip efficiency of storage required for positive energy effect. The “compensation losses” have been determined to be of the order of magnitude of 2%, and the minimum round-trip efficiency of storage to be at the level of 85%. Second, a thermo-ecological analysis was carried out to determine the impact of the source of hydrogen on the overall ecological effectiveness of the system. Contrary to the commonly used measure of “energy efficiency” describing a local balance boundary, thermo-ecological cost (TEC) evaluates the consumption of non-renewable exergy within a global balance boundary. The analysis confirmed that comparing various hydrogen production methods (especially renewable and non-renewable) in terms of local energy efficiency is inadequate, because it does not tell much about their sustainability. For a hydrogen energy system basing on the water electrolysis – hydrogen transport/storage – combustion in a gas piston engine pathway to be considered sustainable, the input electricity to the electrolysis process should be characterized by TEC lower than ∼0.15 J∗/J, a value which even some renewable energy sources fail to achieve.

Thermo-ecological analysis - The comparison of collector and PV to PV/T system

The use of solar radiation energy is one of the important elements to achieve energy transformation. This potential can be utilized by generating electricity with PV modules or heat from collectors. It is also possible to combine these elements into one system and more efficient use of solar radiation, as is the case with the Photovoltaic thermal collectors (PV/T system), which is considered in the article below. The amounts of produced electricity and heat are compared and the energy efficiency of electricity production by PV or PV/T. Local energy analysis from the point of view of resource efficiency, however, becomes insufficient, because it ignores the issue of the quality of individual energy carriers, therefore also in the rest of the article presents an exergo-ecological analysis using the TEC concept (thermo-ecological cost). It has been demonstrated that the TEC for generated carrier (electricity/heat) produced from solar radiation is lower for combined systems and depends on a few factors: the type of generated carrier and implementation of division of allocation of fuel between heat and electricity (for combined systems). Local analysis leads to conclusions other than the global one, as demonstrated by the results presented in the article.

Thermo-ecological cost optimization of a solar thermal and photovoltaic integrated energy system considering energy level

Integrating renewable resources into traditional tri-generation systems helps to reduce fossil fuel use and emissions. A solar thermal and photovoltaic assisted integrated energy system is proposed here using high- performance cooling approaches to provide cooling, heating, and electricity. To find the best system configurations with a focus on the ecological performance, the specific thermo-ecological cost of the energy products considering energy level is optimized employing the cumulative exergy consumption over the whole life-cycle. The results show that the ideal specific costs for cooling, heating and electricity demands are 8.699, 7.129, and 1.970 J/J, respectively. Compared to the method without the energy level consideration, the specific cost of the hybrid system is 0.47 J/J higher due to the lower energy level of water products. Moreover, the specific thermo-ecological cost of natural gas has higher impacts on the performance of hybrid system than the other parameters.

Thermo-Ecological Cost (TEC) –comparison of energy-ecological efficiency of renewable and non-renewable energy technologies

The article presents problems related to the assessment of local energy efficiency of energy systems. In practice, local energy efficiency is commonly used to evaluate these systems, which is not a correct criterion to compare different energy technologies, especially non-renewable and renewable energy systems. For the correct assessment of efficiency, a system analysis in the global balance boundary should be used. In the paper system analysis algorithm is discussed - Thermo-Ecological Cost (TEC), which is a correct tool to compare energy and ecological efficiency of different energy systems. Problems with the correct application of the energy and environmental efficiency assessment are illustrated with examples of results of local and system (TEC) evaluation of non-renewable and renewable energy systems efficiency.

Dynamic thermo-ecological cost assessment and performance analyses of a multi generation system

The main objectives of this study are to perform a dynamic thermo-ecological cost (TEC) assessment and performance analyses of a multi generation system using the TRNSYS 18 software package for comparison purposes. The system has five outputs consisting of electricity, clean water, heating, hydrogen, and cooling. Multigeneration is made of an internal combustion engine fueled by natural gas, a heat pump, a reverse osmosis desalination plant and a magnesium-chlorine (Mg–Cl) thermochemical (TC) water splitting cycle. This cycle, which appears to be a promising TC hydrogen production method, is integrated to the multi generation system for producing hydrogen for waste heat recovery. Environmental effect of the system is also considered using the TEC method. In this contribution, a new index, namely the TEC of the irreversibility, is presented and applied. Variation of emissions, electricity, exergy destruction and energy loss values for the considered system and Mg–Cl TC water splitting cycle as well as TECs of the electricity, heat and the hydrogen are calculated through some parametric studies undertaken and presented in figures. It is determined that the multigeneration system has an energy efficiency value of 0.43 and a corresponding exergy efficiency of 0.38. As a result, TECEL, TECHEAT and TECH2values of the considered system are obtained to be 2.98, 0.72 and 2.90, respectively. It may be concluded that the TEC is an effective method to assess the environmental performance of various energy systems and compare them with each other.

Sustainability analysis of a solar driven hydrogen production system using exergy, extended exergy, and thermo-ecological methods: Proposing and comparing of new indices

This paper aims at investigating and comparing some sustainability indices in the literature while proposing some new indices. A solar driven hybrid system made of a PV cell, an alkaline electrolyzer and a PEM fuel cell is chosen to apply these indices because renewable-based stand-alone hybrid systems for generating electricity seem to be very promising for the future. Some sustainability indices and methods, such as sustainability index, exergetic sustainability index, extended exergy accounting and thermo ecological cost analysis, exist in the literature. In addition to these indices, new indices proposed in this paper contain thermo-ecological cost (TEC) of irreversibilities, extended TEC, extended exergy-based sustainability index and the extended exergetic ecological index. A daily dynamic performance analysis is made for one year. According to the results, exergy efficiency values range from 0.027 to 0.121 while extended exergy efficiencies vary between 0.08 and 0.14. Finally, the proposed indices are classified for designing environmental cycles, assessing environmental effects under operation conditions, and evaluating sustainability in every aspect.

Thermodynamic performance analysis and modified thermo-ecological cost optimization of a hybrid district heating system considering energy levels

Utilization of the renewable resources in district heating systems can reduce the use of fossil fuels, operating costs and protect the environment. In this study, an integrated hybrid system consisting of concentrating photovoltaic/thermal collectors (PV/T), geothermal (GSHP) and absorption (AHP) heat pumps is considered for district heating. The thermodynamic performance of the system at various conditions is explored through detailed simulations. A modified thermo-ecological cost (TEC) method is used to optimize the structure of the PV/T by considering contributions of different flows. The results show that a higher solar irradiance level and a higher PV coverage ratio have a positive impact on the thermal performance of the hybrid system. The TEC-based optimization shows that a 66% PV coverage ratio of PV/T yields a minimum thermo-ecological heating cost of 6.86 J/J, which is slightly lower than cost with a conventional method. Based on the sensitivity analysis, other key parameters except the operating time and the PV coverage ratio have a negative influence on the economic performance of the district heating system, because of the increasing cumulative exergy consumption of the GSHP or PV/T.

Influence of the wind energy sector on thermal power plants in the Polish energy system

Abstract Wind as a renewable energy source is characterized by rapid growth of installed power in many countries, including Poland, where its share in the electricity production has grown over 25 times in the last decade, now reaching about 10%. Since renewable energy has priority in access to the grid, it forces the dispatchable coal-fired power plants to adjust their load. This causes additional consumption of primary energy due to more frequent shut-downs/start-ups and due to efficiency penalty when operating below nominal parameters. In this paper, actual data on the operation of Polish power plants in several years are analysed. The analysis, together with simulations of performance of the power system without the presence of wind energy, focuses on the influence of wind power plants on the utility ones. The results of simulations are additionally processed using the concept of thermo-ecological cost to compare the “operational” impact of wind farms on the power system with their “investment” environmental burden. A conclusion is that current share of wind energy at the level of 10% is enough to have an adverse effect on the coal power plants, but depending on the structure of the power system it may actually increase its overall efficiency.

Natural gas liquefaction using the high-pressure potential in the gas transmission system

This article concerns natural gas liquefaction using high-pressure potential, which is available in pressure letdown stations. The article proposes an integration of a pressure letdown station with a natural gas liquefaction line which enables partial exergy recovery and decreasing natural resources consumption to produce LNG. Exergy recovery is carried out by a replacement of the pressure reduction valve by a turboexpander, which can recover exergy from high-pressure natural gas flowing through a pressure reduction stage. The recovered energy may be used to drive a natural gas liquefaction unit, coupled with the reduction station. A case study concerning an existing pressure letdown station includes two chosen model of a turboexpanders with low and high internal efficiency and several natural gas liquefaction units possible to integrate. The varying size of the liquefaction unit corresponds to a different degree of utilization of energy generated in the expander. Turboexpander produces electric power supplying the liquefaction unit, however, it requires the use of additional energy to heat the gas before the reduction stage, which increases the thermoecologic cost of natural gas transferred to distribution network. Energy, exergy and thermoecological cost analysis was carried out for three system design configurations and for six sizes of the liquefaction line with different turboexpander efficiency. The first configuration included a basic configuration with the pressure letdown station and the liquefaction unit, the second configuration also included an integration with a waste heat source (ICE exhaust gases), and the third configuration used multi-stage expansion. Energy efficiency of the integrated expansion-liquefaction system varies from 35.40% to 66.64%, while its exergy efficiency ranges from 15.75% to 46.33% depending on the size of the liquefaction unit and the gas liquefaction method. It was proved that it is possible to reduce thermo-ecological cost of LNG by 8.2%. Reducing raw material consumption needed for LNG production increases natural gas thermo-ecological cost by only 1%. A preliminary economic analysis based on prices of energy carriers was done. It was found that the boundary price was estimated at 0.0246 €/kWh for one of chosen systems.

Thermo-ecological assessment of Stirling engine with regenerator fed with cryogenic exergy of liquid natural gas (LNG)

The paper presents a thermo-ecological analysis of a liquefied natural gas regasification system equipped with a Stirling engine. The proposed system includes an alpha configuration machine, working as a cold engine with the heat sink acting as the evaporator for the LNG and the upper heat source being at ambient temperature (sea water) or moderately higher. The engines are modelled using two approaches developed by the authors, that is a CFD model and a second-order one-dimensional model. First a small engine is modelled by both CFD and the second order approach to compare results and after confirming their similarity, due to a lower computational cost a larger machine is modelled with the second order model. Due to the heat transfer conditions being crucial for a Stirling cycle machine's performance, those are investigated. It is shown that the internal, convective heat transfer coefficients are much higher in cryogenic conditions than in typical ones. The results of engine assessment are used for the Thermo-ecological cost (TEC) analysis. Within the thermo-ecological analysis, the influence of selected parameters is demonstrated. Additionally the TEC of electricity generated in cold power plant is presented for different configurations. In the case of analysed Stirling systems savings of natural gas reach the level of only 0.5%. However, when TEC of electricity is calculated, the savings are at the level of 72%. The proposed theoretical investigations are the base for the acquisition of new knowledge in the field of possible ways of converting cryogenic exergy of LNG into electricity and optimization of this cycle with strong focus on ecological effects, including the TEC.

Thermo-ecological cost analysis of cogeneration and polygeneration energy systems - Case study for thermal conversion of biomass

The aim of the paper is the thermo-ecological cost analysis of cogeneration and polygeneration energy systems. Within the paper biomass-fired CHP plants and their integration with thermal conversion of biomass units are investigated. In order to estimate the environmental effects of integration, the allocation of the thermo-ecological cost between different products is required. Some of the allocation methods have their origins in economic cost allocation, others in energy, emission or exergy analysis. Within this paper four different methods are investigated: avoided production in national energy system, avoided production in single-product processes, and physical and exergetic allocation. When applied to cogeneration technology, the avoided production in national energy system can give misleading results, mainly due to the nature of the thermo-ecological cost. In polygeneration energy systems, the avoided production in separate processes method can also lead to wrong conclusions due to the assumptions concerning reference efficiencies. At the end, the exergetic allocation method is proposed as a suitable way to allocate the thermo-ecological cost in cogeneration and polygeneration energy systems. Additionally, positive environmental effects of integration can be observed.

Reducing the impact of wind farms on the electric power system by the use of energy storage

The deployment of wind power is rapidly growing worldwide. Intermittent, unpredictable availability of wind energy destabilizes the work of the whole power system, which causes additional consumption of resources. When fossil fuel power plants are affected by this phenomenon, they are forced to cycle (change their load) more often, which results in higher consumption of fuel. This negative effect, expressed by means of thermo-ecological cost (TEC) can be significant in comparison to the TEC of construction phase of wind turbines. TEC is defined as the cumulative consumption of non-renewable exergy connected with the fabrication of a particular product. Power plant cycling could be minimized by applying an energy storage system responding to variations in wind power availability. In the present work, several scheduling strategies for cooperation of an energy storage system with wind turbines are investigated. The effect is assessed in local and global balance boundaries. Employing energy storage reduces the energy losses in thermal power plants, but at the same time, energy losses appear in the storage itself. However, depending on the strategy of energy storage scheduling, in some cases the overall consumption of primary exergy in the whole system may be lower.

Thermo-ecological cost assessment and optimization for a hybrid combined cooling, heating and power system coupled with compound parabolic concentrated-photovoltaic thermal solar collectors

The aim of this work is to optimize and minimize the thermo-ecological cost (TEC) of a novel hybrid combined cooling heating and power (CCHP) system integrated with solar energy. A basic natural gas CCHP system based on internal combustion engine (ICE) is coupled with compound parabolic concentrated-photovoltaic thermal (CPC-PVT) collectors to construct a novel hybrid CCHP system. To minimize the TEC, an optimization methodology was proposed to optimize the configurations and installations of ICE and CPC-PVT, as well as the operation strategies. The TECs of multi-products of the CCHP system were assessed and compared in the following electrical load (FEL) and following thermal load (FTL) modes. The impacts of key parameters on TEC were analyzed and discussed. The results of a case study indicated that the system integrated with 100% photovoltaic covered ratio and 400 kW ICE gets the lowest TEC of 2.36 J/J in the FTL mode. The TECs of electricity decline 28.8% and 17.0% in the FEL and FTL modes, respectively when the photovoltaic covered ratio increases from 0 to 1.0. The increasing heat storage ratio leads to the increase of TEC of heat exergy carried by water due to the heat loss.

Exergy-based ecological indicators: From Thermo-Economics to cumulative exergy consumption to Thermo-Ecological Cost and Extended Exergy Accounting

This paper presents a summary of the conceptual development and the practical applications of exergy-based Environmental Indicators. After a brief historical introduction, the two most popular methods are presented and discussed: the Exergo-Environmental Analysis (here TEA, as a memento of Jan Szargut's original denomination “Thermo-Ecological Analysis”, currently adopted also by Valero's school) and the Extended Exergy Accounting (EEA). Both emerged from Szargut's idea of the existence of a consumption index, the Cumulative Exergy Consumption (CExC), which can be used to quantify the consumption of primary resources “embodied” in a final product or service. The extension introduced by both methods with respect to CExC consists in the explicit inclusion in the exergy budget of one or more of the Externalities, lumped in the original CExC formulation into the exergetic material contents of the single commodities. The differences between the three formulations are obviously reflected in the numerical values of the resulting indicators. The Thermo-Ecological Cost (TEC) and the CExC differ because of the inclusion in the former of the exergetic resources that reflect the “penalty” in the use of primary non-renewable consumption caused by the anthropic intervention. The CExC index and the Extended Exergy Cost EEC differ because the latter explicitly includes in the calculation a “Labour and Capital equivalent exergy consumption” that allows for the survival of the individuals in a given region according to the respective life standards (variable in space and time). Another difference is the way the Environmental Externality is computed: while TEA takes an ex-post assessment, EEA introduces a calculation of the -ideal or real-remediation costs.

Thermo-Ecological Cost of Electricity Generated in Wind Turbine Systems

Wind power is one of the most popular renewable energy sources (RES), characterized by rapid growth of installed power in the energy mix of many countries. Usually, the influence of wind technologies on the depletion of nonrenewable resources is evaluated taking into account the consumption of energy and materials in the construction phase. However, it should be noted that the major drawback of wind energy is its random availability which also influences the consumption of resources. This consumption results from the necessity of compensation for random operation of wind power plants by conventional ones operating in off-design point. In the present work, thermo-ecological cost (TEC) is proposed for the evaluation of the performance of wind generation systems operating with random accessibility of wind energy. The presented analysis focuses on the estimation of additional non-renewable energy consumption due to the part-load operation of the conventional power units. Different strategies are assumed for the compensation for the hourly wind power variations. The presented results of TEC analysis show that the part of TEC resulting from induced losses can be significant. The authors prove that, within the assessment of wind turbines, the induced losses cannot be omitted.

Thermo-ecological cost – Szargut's proposal on exergy and ecology connection

Professor Jan Szargut was one of the world pioneer of exergy analysis and his adventure with exergy going back to its beginnings in world science. His subsequent and significant contribution to the field of exergy analysis is certainly not to be overestimated. Within the paper a short overview of Professor Szargut activity is presented. One of the important application of exergy analysis proposed by Szargut is the Thermo-Ecological Cost (TEC) let to connect exergy and ecology. The general theory and algorithm of TEC is presented in the paper. The potential results obtained using TEC are presented based on trigeneration system, nuclear power plant and metallurgical process. Finally, the pro-ecological tax is described.