• Energy Research

In the present work, a novel hybrid solar-based smart building energy system is introduced and studied. The system comprises innovative photovoltaic-thermal-cooling (PVTC) panels integrated with hot and cold storages with two-way interaction with electricity, heat, and cooling networks (if any). The proposed system is compared with PV-based systems integrated with battery and heat pump for a case study complex building in Aarhus, Denmark. The comparison is conducted by evaluating the performance and economic indicators and investigating the effect of significant parameters on each scenario via a parametric study. Furthermore, the optimal operating conditions and sizing of the proposed system are determined using the genetic algorithm method considering initial cost and traded energy with local energy networks as the objective functions. The comparison results show that the proposed solution is the most cost-effective scenario with the lowest initial cost of about 457,000 $ and a payback period of 6.6 years. This is mainly due to the simultaneous interaction with electricity/heat/cooling networks as well as the elimination of the battery and the heat pump, which are offered by the proposed scenario. It is shown that, in comparison to PV panels, the PVTC can produce 328.7 MWh and 125.6 MWh extra heat and cooling annually. The scatter distribution of significant parameters shows that the panel area and heat storage capacity are not sensitive parameters, and keeping the cold storage capacity at the lower bound is a techno-economically better option.

In the present study, a novel design of large-scale biomass-based heat-driven building cooling system is proposed and investigated for different regions of India. The study is enriched by a thorough benchmarking analysis of various scenarios (24 scenarios in total) for assessing the influence of different types of biomass, various configurations of the cooling system, and different biomass heater layouts on thermodynamic, economic, and environmental aspects of the proposed solution. For this, developing a MATLAB code, hourly, monthly, and annual comparisons are made to ascertain the best scenario from different aspects. The economic investigations reveal the superiority of the scenario comprising a specific design of biomass-heater using Prosopis and double-effect chiller with the lowest levelized cost of cooling (LCOC) of 0.031 $/kWh. The integration of a double-effect chiller with this heater using wood chips leads to the lowest emission index of 0.19 kg/kWh. The results further demonstrate that the LCOC is highly sensitive to the fluctuation of the cost of the biomass type, which is a function of availability in different regions of India. Therefore, the study is a secure reference indicating which scenario would result in the best techno-economic-environmental performance among all possibilities in different areas of the country.

Abstract In the present paper, a novel method is proposed to enhance the power production and resolve the inconsistent electricity generation of solar chimney power plants (SCPPs) during nighttime. For this purpose, an integrated renewable cycle is proposed by incorporating two technologies: solar chimney and waste-to-energy. The combination is performed by exploiting the warm air of the condensers outlet into the SCPP. The waste-to-energy (WTE) plant in Tehran is thermodynamically analyzed and the mass flow rate of the condensers cooling air is found. Results indicate that by decreasing the humidity of the municipal solid waste (MSW) from 40% to 30% or by increasing MSW feeding rate (0.934–1.146 kg/s), the mass flow rate of the condenser cooling air increases from 190.3 kg/s to 233.7 kg/s. In addition, by increasing the feeding rate or by decreasing the humidity of MSW in the mentioned range, net power output of the WTE plant increases from 1350 kW to 1650 kW. The best injection method is proposed for the warm air of the condensers outlet into the SCPP. Subsequently, the average power increase is examined in different months and parametric study is performed to assess the influence of the effective WTE parameters and meteorological variables on the power output of the SCPP. The final power of the SCPP reaches 20–70 kW (even at the hottest night of the year with 5% relative humidity) and increases 20–1200% and 65–94% (monthly average) compared to the case of without injection. Results demonstrate that in the integrated system, by a 22% increase in the MSW feeding rate (from 0.934 kg/s to 1.146 kg/s) or by decreasing the MSW moisture content (from 40% to 30%), power output of the WTE plant and SCPP increases by 22% and 7%, respectively. Additionally, relative humidity of the surrounding air can increase the SCPP power production by 25%. In addition, the results indicate that wind speeds higher than 12.5 m/s will not affect power production of the SCPP, while relative humidity of the surrounding air, ambient temperature, the MSW feeding rate, and humidity of the MSW have considerable effects on the SCPP power production. In average, total energy and useful exergy efficiency of the proposed system is increased by 0.15% and 0.12% compared to the standalone WTE plant during nighttime. The integration of SCPP with the WTE plant is an applicable method to enhance the power generation and overcome the inconsistent power production of SCPP during nighttime.

Abstract In this study, a biomass-based solid oxide fuel cell integrated with a gas turbine, a reverse osmosis desalination unit, and double-effect absorption chiller is proposed for power generation, cooling and fresh water production. Accordingly, environmental contamination of the proposed system is mitigated by capturing and recycling emitted CO2 into the gasifier. Subsequently, a parametric study is performed to analyze the proposed multi-generation system from energy, exergy, exergoeconomic, and environmental impact viewpoints. In addition, considering the exergy efficiency as a performance indicant (to be maximized) and total product cost as an economic indicator (to be minimized) multi-objective optimization is implemented to ascertain the best operating conditions. The results of exergy and exergoeconomic analysis reveal that gasifier is the primary source of irreversibility with exergy destruction rate of 179.8 kW and the exergoeconomic factor of the cooling system components is lower than 20%. Multi-objective optimization results show that exergy efficiency and total product unit cost of the proposed system is 38.16% and 69.47 $/GJ, respectively at the optimum operating condition. Furthermore, scatter distribution of the effective parameters demonstrates that, the stack temperature difference, gas turbine pressure ratio and CO2 recycling ratio are the most sensitive parameters, which should be kept at their lowest value.

There is a variety of solar-based energy system designs for buildings. Although these systems are economically profitable, reducing the energy cost of the buildings over time, their penetration has not been that impressive yet due to their high initial cost. In this study, an energy system comprising a few PVT panels (without any batteries) and a heat storage tank is proposed and investigated for smart buildings with two-way interactions with both heat and electricity grids. Removing the battery from the system would result in a sharp reduction of the cost of the system and, thereby, will make incentives for the end-users to adopt the solution. This novel system will not only supply the buildings’ real-time electricity and domestic hot water needs but also will compensate for a significant portion of the buildings’ energy expenses by selling the surplus generations to the electricity and heat networks. The dynamic model of the proposed system is comprehensively analyzed from thermodynamic and economic points of view using TRNSYS software. Additionally, defining the overall annual exergy efficiency, and the total product cost as the objective functions, optimization of the design and size of the system employing the TRNOPT tool has been done. It is shown that the optimized system results in 16.7 €/MWh and 7.7 €/MWh lower energy costs for electricity and heat of the buildings compared to when the buildings’ demand is only supplied by heat and electricity grids.

This work proposes a novel hybrid renewable-based cold production system consisting of an innovative yet simple design of evacuated solar collectors integrated with a biomass heater, thermal storage tanks, and an absorption machine. The optimal design, sizing of the components, and operating conditions of the hybrid system are investigated via thorough techno-economic modeling and dual-objective optimizations for a case study in India. In addition, the assessments cover different designs of biomass heaters and various biomass types. Finally, using the coefficient of performance (COP), the levelized cost of cooling (LCOC), and the emission index as the prioritization parameters, the most efficient, the most cost-effective, and the most environmentally-friendly configurations are indicated. The results show that integrating evacuated plate collectors with a specific design of biomass-heater burning sugarcane baggas is the most appropriate option from all aspects. According to the optimization results, at the best solution point, emission index and LCOC are, respectively, 440.62 kg/MWh and 47.1 USD/MWh. Moreover, the scatter distribution of major decision parameters indicates that while the volume of the hot storage tank is not a sensitive parameter, the chiller temperature and volume of the cold storage tank should be kept at their lowest bounds.

In the present study, a comparative optimization analysis of a hydrogen-based proton exchange membrane (PEM) fuel cell integrated with an organic Rankine cycle (ORC) using twenty different zeotropic mixtures is accomplished. Accordingly, considering the mixture type as a qualitative decision variable, a novel method of integer single/multi-objective optimization is implemented from thermodynamic and economic aspects. Using a developed genetic algorithm code in MATLAB software, histogram and scatter distributions are presented to determine the density of optimum points and optimum fraction for each mixture. The optimal solution points of exergy efficiency and total cost rate for each mixture are extracted via a Pareto frontier diagram. Eventually, to assess the influence of major decision variables on system performance, a comparative parametric study on five optimal mixtures is carried out. Referring to single-objective optimization results of the ORC unit and the overall system, the use of R601/Cis-2-Butene (2/98) and R601a/Cis-2-Butene (1.32/98.68), respectively, lead to the highest exergy efficiency. Also, considering exergy efficiency as objective, the results of optimization indicates that at optimal condition, the temperature difference between the PEM fuel and evaporator temperature is 13 K. Results further indicate that while a high-temperature PEM fuel cell is a suitable option from an exergy maximization aspect, a low-temperature PEM fuel cell is superior from multi-objective optimization viewpoint. Results of multi-objective optimization reveal that R601a/Hexane (13.32/86.68) and R601a/C-2-Butene (20.14/79.86) are the best mixtures. Furthermore, what stands out from scatter distribution is that most of the optimal points of evaporator temperature are between 305 K and 380 K. Comparative parametric study results demonstrate that in the selected range of major decision variables, R601a/Cis-2-Butene (20.14/79.86) and R601a/Hexane (13.32/86.68) are the best optimum mixtures from an economic facet.

Abstract The Waste-to-Energy technology through gasification, pyrolysis, combustion, and digestion has recently turned into an unavoidable alternative for the municipalities in various parts of the World. Besides a considerable reduction in the waste volume, it can generate steam and electricity. In the present work, two techniques (gasification and digestion) are implemented in the Tehran’s 3 MW Waste-to-Energy power plant; where these technologies are investigated and compared from the viewpoint of thermodynamics, thermoeconomic, and environmental impacts. Also, multi-objective optimization based on genetic algorithm is applied to find the optimum exergy efficiency and total product unit cost of each model. The input municipal solid waste is converted to a high enthalpy syngas via gasification or biogas via digestion to provide the required heat for steam generation in a Rankine power cycle. The best ranges of the effective parameters in optimal point for both models are obtained from the scattered distribution method. Also, the exergy destruction and the exergetic efficiency of every component is calculated to assess the irreversibilities in the system. Results show that the gasifier and the combustion chamber have the highest exergy destruction in the models (a) and (b). Parametric study and environmental impact analysis indicate that model (b) is the more suitable option from energy, exergy, exergoeconomic, and environmental viewpoints. From the multi-objective optimization results, it is inferred that the exergy efficiency for the model (a) and (b) at the optimum point is 17.98% and 19.02%, respectively while the corresponding total product unit cost is 28.31 $/GJ and 27.68 $/GJ.