Multi-generation Energy System Research Articles

Development of a novel flexible multigeneration energy system for meeting the energy needs of remote areas

This paper introduces a flexibility concept in development of a novel multigeneration energy system driven by a renewable energy heat source. Nevertheless, the energy system can be upgraded to a highly productive system by incorporating other subsystems for achieving more production such as domestic hot water and freshwater. A novel design is proposed for a system comprising organic Rankine cycle, absorption compression heat pump, liquid natural gas to natural gas converting system, domestic water heater, and humidifier-dehumidifier desalination to exploit the Sabalan geothermal source for multigeneration purposes. Due to its high-efficient and environmentally friendly characteristics, n-pentane is utilized in the organic Rankine cycle. Also, the Ammonia-water is employed in the absorption compression heat pump subsystem. Energy, exergy, and thermoeconomic analysis is conducted on the plant along with multi-objective optimization based on the parametric study of key variants. According to the results, the novel step-by-step flexibility analysis can give a wide viewpoint to the designers to make the best multiple plant. The results of multi-objective optimization indicate that the freshwater production increases from 0.803 kg/s to 0.834 kg/s, the capacity of the domestic water heater rises from 1254 kW to 1265 kW, and the net output power surges up by 137.96 kW. However, the heating production falls from 1276 to 1088 kW. Furthermore, the total energy and exergy efficiencies increase by 6.43% and 4.47% with a 2.08 $/GJ reduction in the unit cost of the product.

Multi-optimal design and dispatch for a grid-connected solar photovoltaic-based multigeneration energy system through economic, energy and environmental assessment

Solar photovoltaic-based multigeneration energy systems (SPVMES) which can use the excess energy of photovoltaic (PV) systems for heating and hydrogen production to improve the self-consumption of solar PV, have gained wide attention as a promising solution for clean and efficient production. To reliably meet diverse energy demands, gird system is integrated into a SPVMES as a backup energy source. In this paper, a grid-connected SPVMES is established to meet the electricity, heating and hydrogen loads, including PV, electrolysis, solid oxide fuel cell, electric heater for small-scale centralized heating and energy storage devices for electricity, heating and hydrogen storage, respectively. The emphasis to focus on when designing and dispatching the SPVMES lies in system performance evaluation. The innovation of this paper is to design and dispatch such a grid-connected SPVMES in a preliminary design stage through economic, energy and environmental assessment by considering cost of energy (COE), energy rate (ER) and renewable fraction (RF). Simultaneously, to explore which single objective/multi-objective optimization has better performance in comprehensive system evaluation, four different scenarios named COE optimization, RF optimization, ER optimization and multi-objective optimization are analyzed and compared. The specific application processes of component sizing and system dispatching with different optimization objectives are presented in detail. The results show that the proposed system has the COE of 0.0343$ in COE optimization scenario, the ER of 0.9128 in ER optimization scenario and the RF of 0.8811 in RF optimization scenario, which shows its significant potential in economic, energy efficiency and environmental performance. By comprehensively scoring the four optimization scenarios, it can be found that the multi-objective optimization scenario has better performance in system performance evaluation compared to the other three single objective optimization scenarios. Additionally, the multi-objective optimization could balance the tradeoff of COE, RF and ER and compromise the results of the single objective optimization scenarios. Potentially, sensitivity analysis is conducted to point out the effect of discharging depth of battery, PV subsidy, linear increasement of loads and seasonality effect on system performances.

Towards Global Cleaner Energy and Hydrogen Production: A Review and Application ORC Integrality with Multigeneration Systems

The current evidential effect of carbon emissions has become a societal challenge and the need to transition to cleaner energy sources/technologies has attracted wide research attention. Technologies that utilize low-grade heat like the organic Rankine cycle (ORC) and Kalina cycle have been proposed as viable approaches for fossil reduction/carbon mitigation. The development of renewable energy-based multigeneration systems is another alternative solution to this global challenge. Hence, it is important to monitor the development of multigeneration energy systems based on low-grade heat. In this study, a review of the ORC’s application in multigeneration systems is presented to highlight the recent development in ORC integrality/application. Beyond this, a new ORC-CPVT (concentrated photovoltaic/thermal) integrated multigeneration system is also modeled and analyzed using the thermodynamics approach. Since most CPVT systems integrate hot water production in the thermal stem, the proposed multigeneration system is designed to utilize part of the thermal energy to generate electricity and hydrogen. Although the CPVT system can achieve high energetic and exergetic efficiencies while producing thermal energy and electricity, these efficiencies are 47.9% and 37.88%, respectively, for the CPVT-ORC multigeneration configuration. However, it is noteworthy that the electricity generation from the CPVT-ORC configuration in this study is increased by 16%. In addition, the hot water, cooling effect, and hydrogen generated from the multigeneration system are 0.4363 L/s, 161 kW, and 1.515 L/s, respectively. The environmental analysis of the system also shows that the carbon emissions reduction potential is enormous.

Comparative transient simulation of a renewable energy system with hydrogen and battery energy storage for residential applications

Energy systems for the building sector nowadays are moving towards using renewable energy sources such as solar and wind power. However, it is nearly impossible to fully develop a multi-generation energy system for a building only relying on these sources without convenient energy storage, backup systems, or connection to the grid. In this work, using TRNSYS software, a model was developed to study the transient behavior of an energy system applicable for residential buildings to supply the heating, cooling, domestic hot water, and electricity in demand. This study contains the comparison of two methods of energy storage, a hydrogen fuel cell/electrolyzer package and a conventional battery system. This study also provides information on environmental impacts and economical aspects of the proposed system. The results show that for an HVAC system when using hydrogen storage system the capital cost is twice the cost of using a battery system. However, the hydrogen system shows better performance when used at higher loads. Hydrogen storage systems show higher performance when used at higher size units.

Multi-objective optimization and multi-aspect analysis of an innovative geothermal-based multi-generation energy system for power, cooling, hydrogen, and freshwater production

Considering the feasibility of geothermal wells employed worldwide in the energy sector, this study was motivated to examine a novel multi-generation system devised to enhance the feasibility of flash-binary geothermal systems through innovative heat recovery in five stages. Accordingly, the main system consists of a flash-binary geothermal cycle, an ejector refrigeration cycle, a Kalina cycle integrated with another ejector refrigeration cycle, a humidification dehumidification desalination unit, and a low-temperature electrolyzer. Due to the five stages of innovative heat recovery, this system achieved a cost-effective and efficient design framework, introducing it as a high-quality alternative for stand-alone flash-binary geothermal cycles. To study the feasibility of the proposed system, a sensitivity analysis based on energy, exergy, and exergoeconomic concepts was employed. Moreover, the genetic algorithm in different multi-objective optimization scenarios was implemented to reach stable and high-efficiency products. According to the obtained results, the capability of the system to produce electricity, cooling, freshwater, and hydrogen are calculated to be 782 kW, 881.6 kW, 0.286 kg/s, and 0.181 kg/h, respectively. Also, in the exergy-cost optimization scenario, the system's optimum exergy efficiency and sum unit cost of products were obtained to be 46.44% and 3.98 $/GJ, respectively based on LINMAP decision-making method.

Optimal operation of a multi-generation district energy hub based on electrical, heating, and cooling demands and hydrogen production

In this study, a new configuration of a multi-generation energy system is proposed based on waste heat recovery from a regenerative gas turbine cycle (as the driver cycle) for running a district heating heat exchanger, a Rankine cycle, an ejector refrigeration cycle, and a proton exchange membrane electrolyzer cycle. In the first phase of the study, a thorough parametric model of the system is developed in EES software based on the eco-exergy and enviro-exergy analyses. The second phase is focused on the optimal operation of the system utilizing a robust multi-criteria optimization in Matlab software. Results of the parametric study showed that: (i) the share of fuel, capital, and environmental penalty costs rates in the system's total cost rate are respectively 46.95%, 29.38%, and 23.67%, at the optimal conditions. (ii) although the design variables of the bottoming cycles are not effective on the amount of pollutants, they have a significant effect on the enviro-exergy assessment criterion. The optimal system productions are included 21.42 MW of power, 26.81 MW of heat, 8.89 MW of cold, and 11.96 kg/h of hydrogen. The energy and exergy efficiencies are found to be 89.75% 35.21%, respectively. In such conditions, the payback period is approximately 5 years, demonstrating the economic feasibility of the proposal. Recovering the waste heat of conventional cycles to develop an energy production hub with minimal energy loss is one of the most important challenges in the energy matrix and relying on the results of the present study, it can be concluded that the proposed system has done this task well.

Exergy and exergo-economic investigation of a novel hydrogen production and storage system via an integrated energy system

The main purpose of the current research work is to suggest a novel integrated multi-generation energy system and scrutinize 4E evaluation. This system consists of a solid oxide fuel cell, a PEM electrolyzer for hydrogen production, and an ejector-based absorption chiller for the coefficient of performance improvement. All parts of this system are verified with existing reports and papers. Effect of fuel cell current density, SOFC fuel cell temperature, absorption chiller evaporator temperature, and condenser temperature, and outlet turbine pressure has been investigated and reported. The effect of mentioned parameters on the exergy and cost rate has been considered. Data illustrate that the maximum exergy destruction rate belongs to the SOFC contributing 60% of the total exergy destruction rate of the system. Under the given condition of the system, the net produced power is about 200 kW with an exergy efficiency of 30.2% and thermal efficiency of 60.4%. At the considered condition the total cost rate of the system is estimated about 22.29 $/hr. The results of the present work provide a scientific base for designing poly-generation systems with high efficiency and reasonable cost rate.

Simultaneous optimization of the design and operation of multi-generation energy systems based on life cycle energy and economic assessment

Multi-generation energy systems could mitigate global energy consumption, carbon emissions and economic costs. The promising energy, environmental and economic advantages of these systems are greatly dependent on their design and operational strategy. Consequently, methods and guidelines for the optimal design and operation of such systems, also taking into consideration their life cycle, are needed to fully exploit their potential. This paper proposes a general methodology for the simultaneous optimization of the design and operation of multi-generation energy systems by considering life cycle energy and economic assessment. The design optimization problem is solved by means of surrogate modeling and the operation optimization problem by means of dynamic programming. The multi-generation energy system considered in this paper comprises renewable energy systems, fossil fuel energy systems and energy storage technologies. Different multi-objective optimizations were performed by considering the minimization of fossil cumulative energy demand, and total investment and operational costs. The validity of the proposed methodology is demonstrated by using the campus of the University of Parma (Italy) as a case study. Compared to a conventional plant, the optimal solution allows a life cycle energy saving of about 17% and total cost reduction of about 18%. Moreover, compared to an optimization method based on particle swarm optimization and dynamic programming, the proposed methodology provides comparable results, but the computation time is 78% lower. The proposed methodology outperforms commonly used optimization algorithms and provides an effective and flexible framework for the optimal design and operation of multi-generation energy systems.

Can a Wastewater Treatment Plant Power Itself? Results from a Novel Biokinetic-Thermodynamic Analysis

The water–energy nexus (WEN) has become increasingly important due to differences in supply and demand of both commodities. At the center of the WEN is wastewater treatment plants (WWTP), which can consume a significant portion of total electricity usage in many developed countries. In this study, a novel multigeneration energy system has been developed to provide an energetically self-sufficient WWTP. This system consists of four major subsystems: an activated sludge process, an anerobic digester, a gas power (Brayton) cycle, and a steam power (Rankine) cycle. Furthermore, a novel secondary compressor has been attached to the Brayton cycle to power aeration in the activated sludge system in order to increase the efficiency of the overall system. The energy and exergy efficiencies have been investigated by varying several parameters in both WWTP and power cycles. The effect of these parameters (biological oxygen demand, dissolved oxygen level, turbine inlet temperature, compression ratio and preheater temperature) on the self-efficiency has also been investigated. It was found here that up to 109% of the wastewater treatment energy demand can be produced using the proposed system. The turbine inlet temperature of the Brayton cycle has the largest effect on self-sufficiency of the system. Energy and exergy efficiencies of the overall system varied from 35.7% to 46.0% and from 30.6% to 33.55%, respectively.

Exergy, economic, and optimization of a clean hydrogen production system using waste heat of a steel production factory

In this present research study a multi-generation energy system which is coupled with CO2 capture unit which is based on Rankine cycle, organic Rankine cycle, ejector cooling system and absorption chiller has been analyzed via energy, exergy, exergy-economic aspects by developing MATLAB, also to achieve the optimum operating condition genetic algorithm has been applied for system optimization. The objective of this study is to propose an optimized efficient integrated energy system to recycle the energy waste of a typical industrial factory. The optimization has been illustrated on a Pareto frontier to achieve the optimum scheme of the multi-generation system regarding technical and economic viewpoints. Results indicate the optimal condition of this system has occurred at 0.37 exergy efficiency with 0.03 $/s. Furthermore, by surging the mass flow rate of waste gases up to 70 kg/s, net power output augmented up to 7500 kW. Besides, hydrogen production and produced desalinated water rise up to 8.5 g/s and 16 kg/s, respectively.

Modeling, Control, and Optimization of Multi-Generation and Hybrid Energy Systems

As renewable energy technologies decrease in cost and become more prevalent, there is an increasing trend towards electrification of many energy systems [...]

Multi-generation energy system based on geothermal source to produce power, cooling, heating, and fresh water: Exergoeconomic analysis and optimum selection by LINMAP method

The current study deals with thermodynamic modeling and multi-objective optimization of a new multi-generation energy system using geothermal as the primary energy source. The proposed system includes a Kalina cycle, a refrigeration unit, thermoelectric module, steam turbine, and heating unit. The new aspects of the proposed system are using the thermoelectric system to low temperature heat recovery and using the benefit of the multi-product. The system exergy analysis shows that the reverse osmosis desalination unit with 449.1 kW has the highest exergy destruction rate in the system. Additionally, three components i.e., reverse osmosis unit, heating system, and steam turbine are responsible for 82.8% of exergy destruction of the system. Exergo-economic analysis revealed that the turbine and the thermoelectric module have the highest cost rates of 12.51 US$/h and 3.62 US$/h respectively. It also concludes that the sum of the cost rate of component and associated exergy destruction cost rate, a significant exergo-economic parameter, for the turbine and reverse osmosis unit are the highest values. Parametric analysis of the proposed system for geothermal source pressure, steam turbine backpressure, Kalina turbine backpressure, and ammonia mass fraction of basic solutions are carried out. The unit cost of product and exergy efficiency are objective functions for optimization. Multi-criteria optimization indicates that using the Linear Programming Technique for Multidimensional Analysis of Preference (LINMAP) method based on suggested design variables, can reduce the unit cost of the product to 0.107 US$/kWh, and the exergy efficiency can be increased up to 15.86%.

Thermodynamic analysis of a hybrid wind turbine and biomass gasifier for energy supply in a rural off-grid region of Nigeria

ABSTRACT In this research, a thermodynamic study is executed for a multi-generation hybrid renewable energy system (MG-HRES) for off-grid energy supply to a rural settlement in Katsina state, Nigeria. In the system, a downdraft biomass gasifier (BMG), syngas electrical engine (SGE) attached with an absorption refrigeration system and wind turbine generator are integrated to relieve wind variability and deliver three useful outputs. The integrated system, which is sized to supply the average electricity load of 2000 dwellings, is modeled and analyzed thermodynamically through Matlab computer code. The overall energetic and exergetic efficiencies are 0.48 and 0.25, respectively, with hot water and cooling outputs of 130 and 393 kW. To ascertain the quantities and locations of irreversibility within the MG-HRES, exergy destruction analysis is deployed to scrutinize the thermodynamics process in every part of the system. The major exergy destruction of about 95% of the total cycle irreversibility occurs in the BMG, followed by SGE, 3%. The variation of exergy destruction, exergy and energy efficiency for the MGHRES and its constituents are determined against fluctuations in the exhaust temperature, capacity factor, load factor, and reference temperature of the environment.

Thermodynamic modeling and analysis of a solar and geothermal assisted multi-generation energy system

A geothermal and solar energy-assisted multi-generation energy system supplying electricity for the residences is modeled and analyzed. The system considered is a novel configuration consisting of a binary geothermal power plant and a parabolic trough concentrating solar power plant for electricity production and water electrolysis and fuel cell unit for hydrogen storage and utilization. Thermodynamic performance evaluation of the system is performed using Afyonkarahisar's geothermal and solar energy values. In Afyonkarahisar province, geothermal water temperature ranges between 70 and 130 °C and mass flow rate between 70 and 150 kg/s. Also, solar radiation incident varies between 300 and 1000 W/m2. The geothermal and solar power plants could produce 2900 kW power. If this is used entirely for hydrogen production, 0.0185 kg/s hydrogen could be produced. One can produce 1615 kW power by using this hydrogen in the fuel cell. The overall system's energy and exergy efficiencies are calculated to be 5.90% and 18.99%, respectively. The system's parametric study is performed considering geothermal resource temperatures and solar radiation values on the power output and hydrogen production.

Exergo-economic assessment and sensitivity analysis of a solar-driven combined cooling, heating and power system with organic Rankine cycle and absorption heat pump

District energy systems based on renewable resources help to reduce greenhouse-gas emissions and fossil-fuel use. Here, a multi-generation energy system combining cooling, heating, and power is realized by employing organic Rankine cycle (ORC) and absorption heat pump (AHP) technologies, which enable cascading the utilization of solar heat. The AHP can operate steadily providing cooling, heating and hot water from solar thermal and geothermal sources. A modelling approach presented to evaluate the energy, exergy, economic, and exergo-economic performance of the above system. The results show that the AHP could reach a coefficient of performance (COP) between 1.38 and 2.37 depending on the mode of operation. The yearly energy and exergy efficiency of the tri-generation system is 56.5% and 9.6%, respectively. Compared to a separate system, the simple economic payback time of the tri-generation system is 3.5 years. The specific exergo-economic cost of electricity produced is 0.12 $/kWh, whereas the cost of hot water is much higher, or 0.31 $/kWh. The sensitivity analysis performed shows that the inlet and outlet temperatures of the AHP together with the yearly solar irradiance have the highest impact on the performance. This study provides a new direction on cost-effective utilization of renewable sources in district energy systems.

A highly innovative yet cost-effective multi-generation energy system for net-zero energy buildings

This study introduced an innovative yet feasible and cost-effective solution to make a big step forward in the state-of-art of smart energy buildings and obtain a real meaning of net-zero energy building. In this study, the main cornerstones of the developed solution combined the following technologies: the use of novel trigeneration solar collectors without a battery, a very clever method of heat pump integration with minimal size and cost required, and two-way interaction of the building with local energy networks. Different system configurations based on the included components were suggested and analyzed for an apartment building in Denmark. A thorough techno-economic and environmental evaluation of the proposed solution and the most competent ones already proposed for the same application was carried out to rank the best configuration from various facets. A comparative parametric study was accomplished to examine and compare the variation of performance indicators with significant decision variables. In addition, the tri-objective optimization was implemented for each configuration to specify the best optimum condition from energy, economic, and environmental standpoints. According to the economic results, the configurations integrated with battery and regular heat pumps were not favorable due to the highest total cost and the payback period. Here, the proposed system, owing to its resilient energy trade possibility with the energy networks and the scaled-down heat pump, gave larger energy-saving and CO2 emission reduction rates of 16.6% and 21.6%, respectively. The multi-objective optimization showed that the capacities of the battery and the cold storage were the most effective parameters on the performance of the system.

Energy and exergy analyses of a solar-based multi-generation energy plant integrated with heat recovery and thermal energy storage systems

By the depletion of natural resources, the utilization of solar energy to provide the required needs of societies attracted many researchers across the globe. An innovative multigeneration energy system driven by solar energy is proposed in this paper. The proposed system utilizes a pressurized cavity-based solar power tower and latent thermal energy storage (TES) to continuously harness the solar energy. Considering the high-temperature nature of solar tower technology, a four-step Copper-Chlorine (Cu-Cl) thermochemical cycle is used to produce hydrogen, oxygen, and steam. Using an unfired gas turbine unit, air is used as the heat transfer fluid of the solar tower unit, instead of molten salt, to supply the required heat for the thermolysis and hydrolysis reactions of the Cu-Cl cycle. Therefore, the deficiencies of molten salts are eliminated. Moreover, recovering heat within the integrated system improves the performance of the system significantly. Also, By utilization of a high-temperature ternary eutectic phase change material (PCM), a dynamic model is developed to deal with the intermittency of solar energy. Using energy and exergy approaches, the proposed system is investigated to assess exergy destruction rates and the overall system performance. A parametric study is performed to investigate the influence of design parameters such as the number of heliostats, pressure ratio of GT, and temperatures of reactions on the system performance. The results show that the system produces electricity, steam, hydrogen, and oxygen at a rate of 41.9 MW, 12.6 kg/s, 0.19 kg/s, and 0.76 kg/s, respectively. Energy and exergy efficiencies of the integrated system are found to be 49.9%, and 44.9%, respectively. The proposed system is compared with other alternative systems available in the literature and shows the best performance among others.

A novel multi-generation energy system based on geothermal energy source: Thermo-economic evaluation and optimization

A multi-generation system including an absorption chiller, an organic flash cycle, a concentrated photovoltaic module, a reverse osmosis unit, and thermoelectric modules are integrated to produce cooling, heating, electrical power, and freshwater. The important parameters including energy efficiency, exergy efficiency, exergy destruction rate, net output power, and electrical cost rate are identified. The behavior of main outputs are examined with varying decision variables namely geothermal temperature, flash vessel inlet pressure, and pump Ι outlet pressure. Thermal modeling of the proposed system indicates that the energy efficiency, exergy efficiency, and net output power are 5.46%, 20.16%, and 70.85 kW higher than the conventional system. Moreover, exergo-economic outputs demonstrate that the thermoelectric generator module with 11.34 $/h and heat exchanger 2 with 8.98 $/h have the maximum exergy destruction cost rate. Finally, according to different multi-objective optimization scenarios it is found that through the first scenario, the electricity cost rate shows the minimum value of 108.4 $/h.

Energetic, economic, exergetic, and exergorisk (4E) analyses of a novel multi-generation energy system assisted with bagasse-biomass gasifier and multi-effect desalination unit

This study presents a novel multi-generation system (MGS) assisted by sugarcane bagasse to produce power, freshwater, and cooling. The proposed integrated MGS consisted of a bagasse-biomass based gasifier-Brayton cycle, a Rankine cycle, a Kalina cycle, an ejector refrigeration cycle, and a multi-effect desalination unit. Comprehensive energy, economic, exergy, exergorisk (4E) analyses of the proposed system were performed. The effects of operating parameters on thermodynamic performance and economic feasibility were investigated. An optimal configuration of the proposed system was determined via weighted multi-objective optimization approach considering exergorisk, exergy, and economic analyses. The results showed that bagasse-biomass flowrate was the dominant factor affecting variation in energy and exergy efficiencies, and total cost rate. An increase in bagasse-biomass flowrate from 1.5 kg/s to 10 kg/s led to decreases of 34.42% and 50.75% in overall energy and exergy efficiencies. The most substantial increase (43.07%) in exergy efficiency occurred at a high compression ratio. The optimization results showed that the total accidental risk impact was improved by 92.59% and energetic and exergetic efficiency was increased to 92.10% and 77.49%, respectively. The proposed optimum system can provide power, cooling, and freshwater at loads of 28.72 MW, 13.64 kg/s, and 3.43 MW, respectively.

Thermodynamic assessment of a new solar power-based multigeneration energy plant with thermochemical cycle

In this study, a novel solar energy assisted multigeneration energy plant by using the solar radiation as a renewable energy resource is designed to produce some useful products, such as electricity, heating-cooling, and hydrogen, and modelled to increase the system performance. This designed multigeneration energy system consists of the solar power tower, steam Rankine cycles, absorption heating-cooling system, Cu-Cl thermochemical cycle, and hydrogen liquefaction unit. A thermodynamic assessment is developed by using the energetic and exergetic analyses to determine the irreversibilities of Cu-Cl thermochemical reaction-based integrated system at different working conditions. The energy and exergy performances of solar power assisted multigeneration system are computed as 22.21% and 14.02%. In the present study, the highest exergy destruction of this plant is determined for the solar power tower, and also, 5,738 and 4,812 kW of exergy destruction happens in the heliostat and central receiver, respectively. Moreover, the parametric works are carried out by changing the reference conditions and design indicators.