Simulation of a solar‐biogas hybrid energy system for heating,fuel supply,and power generation

Biogas production from organic wastes has been widely utilized for several decades, but maintaining right temperature for anaerobic bacteria is a challenge. In order to overcome the inhibition of the bacteria growth and biogas production due to the low temperature, a solar‐biogas hybrid energy system for heating, fuel supply, and power generation has been proposed for converting domestic garbage into biogas in a rural area of China. In this system, the solar energy has been included as one of the heating sources during an anaerobic digestion process. A mathematical model has been developed to evaluate the influence of system operating characteristics. Based on the simulation results, the biogas production rate, thermal efficiency, temperature of the digester, energy distributions in the system, optimal operating parameters, economic efficiency, and thermodynamic characteristics of the system were analyzed. The impact of solar irradiation on the efficiency of the system was also studied. According to the results, in cloudy days, the reactor volume and solar collector area greatly influenced the steady energy supply. In winter, the produced biogas is mostly utilized by the aided boiler to maintain the proper organic mixture temperature in the bioreactor. Heat loss from bioreactor dramatically increases the organic mixture volume. Per simulation, the longest return on the investment of this type of the biogas system is about 5.54 years, and the shortest return on the investment is less than 4 years if the battery is removed and the electric grid can be used. Therefore, in this study, the feasibility of a hybrid energy system for converting domestic garbage into energy has been validated. Copyright © 2017 John Wiley & Sons, Ltd.     

太阳能加热沼气发酵系统数值方法的研究

以太阳能加热沼气发酵系统为对象,应用Fluent软件进行模拟计算,分析沼气池内的温度场,同时对非稳态计算的数值方法进行研究。对同一计算模型分别采用定迭代方式和变迭代方式进行计算,结果发现,应用Fluent软件进行非稳态计算时,可以根据实际情况适当调整时间步内的迭代次数,从而减少计算时间,这对非定常计算有很大的实用意义。同时,对换热管内的经济流速进行了计算,结果显示,水流速度宜采用0.8～1.0m/s。     

Assessing the sustainable abilities of a pilot hybrid solar-pyrolysis energy system using emergy synthesis

With the increasingly serious global climate and energy problems, hybrid renewable energy systems have been widely developed. Sustainability of a pilot hybrid solar-pyrolysis energy system (HSPES) was evaluated using emergy analysis. The total emergy input of the system was 6.90E+15 sej/yr, and it was greatly dependent on the renewable resources from external environment. Suitable emergy indices such as unit emergy value, renewability, emergy yield ratio, environmental load rate, and emergy sustainability index, were introduced and analyzed in detail, with values of 7.45E+04 sej/J, 63.51%, 1.00, 0.57, and 1.74, respectively. The results showed that the system was more dependent on renewable resources, had less impact on the environment, and had relatively good sustainability, but the utilization of local resources was quite low. However, this system was relatively weak in the exploitation and utilization of local resources. On the basis of life cycle assessment and emergy analysis, the Pollutant Degradation Emergy (PDE) result of the system was 2.77E+14 sej/yr. There was no significant difference between the emergy indices results based on PDE and its original value, the pollutants emissions of the system did not show a significant impact on the results of selected emergy indices, and the impact of system pollutants on the environment was relatively weak.     

Study on a direct‐expansion solar‐assisted heat pump water heating system

Analytical and experimental studies were performed on a direct‐expansion solar‐assisted heat pump (DX‐SAHP) water heating system, in which a 2 m² bare flat collector acts as a source as well as an evaporator for the refrigerant. A simulation model was developed to predict the long‐term thermal performance of the system approximately. The monthly averaged COP was found to vary between 4 and 6, while the collector efficiency ranged from 40 to 60%. The simulated results were used to obtain an optimum design of the system and to determinate a proper strategy for system operating control. The effect of various parameters, including solar insolation, ambient temperature, collector area, storage volume and speed of compressor, had been investigated on the thermal performance of the DX‐SAHP system, and the results had indicated that the system performance is governed strongly by the change of solar insolation, collector area and speed of compressor. The experimental results obtained under winter climate conditions were shown to agree reasonably with the computer simulation. Copyright © 2003 John Wiley & Sons, Ltd.     

Parametric analysis and yearly performance of a trigeneration system driven by solar‐dish collectors

Solar‐driven polygeneration systems are promising technologies for covering many energy demands with a renewable and sustainable way. The objective of the present work is the investigation of a trigeneration system, which is driven by solar‐dish collectors. The examined trigeneration system includes an organic Rankine cycle (ORC), which operates with toluene, and an absorption heat pump, which operates with LiBr/H₂O. The absorption heat pump is fed with heat by the condenser of the ORC, which operates at medium temperature levels (120°C to 150°C). The absorption heat pump produces both useful heat at 55°C and cooling at 12°C. The ORC produces electricity, and it is fed by the solar dishes. The examined ORC is a regenerative cycle with superheating. The total analysis is performed with a developed model in Engineering Equation Solver (EES). The system is investigated parametrically for different ORC heat‐rejection temperatures, different superheating levels in the turbine inlet, and various solar‐beam irradiation levels. Furthermore, the system is investigated on a yearly basis for the climate conditions of Athens (Greece) and for Belgrade (Serbia). It is found that the yearly system energy and exergy efficiencies are 108.39% and 20.92%, respectively, for Athens, while 111.38% and 21.50%, respectively, for Belgrade. The values over 100% for the energy efficiency are explained by the existence of a heat pump in the examined configuration. For both locations, the payback period is found close to 10 years and the internal rate of return close to 10%. The final results indicate that the examined configuration is a highly efficient and viable system, which operates only with a renewable energy source.     

Efficiency analysis of a combined PEFC and bioethanol‐solar‐reforming system for individual houses

In this research, the development of a bioethanol reforming system for fuel cells (FBSR: fuel cell with bioethanol steam reforming) using sunlight as a heat source was investigated. The system was investigated using the experimental result of catalyst performance, and numerical analysis. If ethanol purity is high, the production method of the bioethanol used for the proposal system will not be limited. The overall efficiency of the production of electricity and heat power of this system was determined by examining its thermal output characteristic. The FBSR was introduced into standard individual houses in Sapporo, Japan, for analysis. The amount of hydrogen production, the production‐of‐electricity characteristic, and the thermal output characteristic were examined using meteorological data on representative days in March and August. Compared with the representative day in March (28.0 MJ day⁻¹), the solar radiation of the representative day in August (37.0 MJ day⁻¹) is large. However, the amount of solar radiation fluctuation of the representative day in August in this analysis is large compared with the representative day in March. It depends for the overall efficiency of the system on the amount of solar radiation fluctuation rather than the amount of solar radiation. As a result, the overall efficiency of the system, defined as the rate of power and heat output compared with the amount of solar heat collected, was calculated to be 47.4 and 41.9% on the representative days in March and August, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of the electrical energy consumption of a building for the dimensioning of a solar‐hydrogen energy system

The photovoltaic (PV) applications where the dimensioning is effected through the daily energy balance criteria obtained by the estimation of the energy consumption depending on the power and time of use of the electrical apparatus are limited to autonomous PV systems with well‐defined end use. Applications where one would like to electrify complex end use, such as office buildings, schools, hospitals, laboratories, residential units, etc., quantifying the daily energy consumption is difficult mainly due to two aspects. First, there will be great number of a variety of electrical appliances and second the proportionate electrical consumption of each one of them is unpredictable. For this reason it is necessary to establish a methodology that permits one to quantify precisely the daily energy consumption pattern to predict the energetic functioning of the PV system whose size may be determined by this procedure. In this work we describe a methodology for the energetic quantification of the installed equipments by using a Power Quality Analyzer to obtain the historical global energy consumption, daily energy consumption (kWh day⁻¹, kVAh day⁻¹) and the energy quality for the dimensioning of the PV system. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparative analysis of a solar‐driven novel salt‐based absorption chiller with the implementation of nanoparticles

The present study exemplifies the comprehensive thermal analysis to compare and contrast ammonia‐lithium nitrate (NH₃‐LiNO₃) and ammonia‐sodiumthiocynate (NH₃‐NaSCN) absorption systems with and without incorporation of nanoparticles. A well‐mixed solution of copper oxide/water (CuO/H₂O) nanofluid is considered inside a flat‐plate collector linked to an absorption chiller to produce 15‐kW refrigeration at ?5°C evaporator temperature. Enhancements in heat transfer coefficient, thermal efficiency, and useful heat gain of the collector are evaluated, and the effect of these achievements on the performance of both absorption chillers have been determined for different source temperatures. A maximum 121.7% enhancement is found in the heat transfer coefficient with the application of the nanofluid at 2% nanoparticle concentration. The maximum coefficient of performance observed for the NH₃‐NaSCN chiller is 0.12% higher than that for the NH₃‐LiNO₃ chiller at 0°C evaporator temperature. Contradictory to this, the average system coefficient of performance of the NH₃‐LiNO₃ absorption system has been found 5.51% higher than that of the NH₃‐NaSCN system at the same evaporator temperature. Moreover, the application of the nanofluid enhanced the performance of the NH₃‐NaSCN and NH₃‐LiNO₃ systems by 2.70% and 1.50%, respectively, for lower generator temperature and becomes almost the same at higher temperatures, which altogether recommends the flat‐plate collector–coupled NH₃‐LiNO₃ absorption system be integrated with a nanofluid.     

Modelling and testing of a hybrid solar‐biomass ORC‐based micro‐CHP system

Expanders employed recently in organic Rankine cycle (ORC)‐based systems suffer from key problems including excessive working fluid leakage, thermal losses, low isentropic efficiency and high cost. The majority of the units available in the market are for medium and large‐scale applications (>100 kW) with no commercial micro‐scale expanders available and applicable for ORC units for residential and building applications. Moreover, the majority of the studies conducted on ORC expanders employed HFC and HCFC working fluids which have high global warming potential leading to negative environmental impacts. In this study, a micro‐scale CHP system based on the ORC technology is theoretically and experimentally investigated to provide the thermal needs and part of the electrical demands for residential applications. An innovative design for a hybrid ORC‐based micro‐CHP system is proposed using a biomass boiler and a solar concentrator to run the CHP system providing more reliable and clean operation compared to conventional natural gas‐driven units. The micro‐CHP system employs a new type small‐scale scroll expander with a compact design, integrating the generator and the turbine in a single unit. A numerical model was developed using the Engineering Equation Solver (EES) software to simulate the thermodynamic behaviour of the ORC unit predicting the thermal and electrical performance of the overall CHP system. In addition, an experimental setup was built to test the whole ORC–CHP system performance under different conditions, and the effect of various operational parameters on the system performance has been presented using an environmentally friendly HFE7100 working fluid. The maximum electric power generated by the expander was in the range of 500 W at a pressure differential of about 4.5 bars. The attained expander isentropic efficiency was over 80% at its peak operating conditions with no fluid leakage observed. Being mass‐produced with low cost in the automotive industry along with the high isentropic efficiency and the leakage‐free performance, the proposed compact scroll expander represents a potential candidate to be used in the development of micro‐scale ORC–CHP units for building applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental investigation of the performance of a solar‐assisted ground‐source heat pump system for greenhouse heating

The main objective of the present study is to investigate the performance characteristics of a solar‐assisted ground‐source heat pump system (SAGSHPS) for greenhouse heating with a 50 m vertical 1¼ in nominal diameter U‐bend ground heat exchanger. This system was designed and installed in the Solar Energy Institute, Ege University, Izmir (568 degree days cooling, base: 22°C, 1226 degree days heating, base: 18°C), Turkey. Based upon the measurements made in the heating mode, the heat extraction rate from the soil is found to be, on average, 54.08 Wm^?1 of bore depth, while the required borehole length in meter per kW of heating capacity is obtained as 12.57. The entering water temperature to the unit ranges from 8.2 to 16.2°C, with an average value of 9.1°C. The greenhouse air is at a maximum day temperature of 25°C and night temperature of 14°C with a relative humidity of 40%. The heating coefficient of performance of the heat pump (COP_HP) is about 2.13 at the end of a cloudy day, while it is about 2.84 at the end of sunny day and fluctuates between these values in other times. The COP values for the whole system are also obtained to be 5–15% lower than COP_HP. Copyright © 2004 John Wiley & Sons, Ltd.     

蒸汽爆破预处理技术应用于秸秆厌氧发酵的技术经济分析

为获得蒸汽爆破技术应用于实际秸秆厌氧发酵工程的经济参数和论述项目可行性,文章对经蒸汽爆破预处理和未经预处理的秸秆厌氧发酵工程分别进行了技术经济分析,并对二者的经济参数进行了对比。结果表明,采用蒸汽爆破预处理技术的工程项目具有较好的经济性,其净现值(NPV)为250.47万元,投资回收期7.53年,益本比(B/C)为1.22,内部收益率达17.70%,具有一定的投资价值;而不做预处理的秸秆厌氧发酵(同样产量为54万m3)的工程项目,在整个项目存在期内的NPV值为是-166.76万元,不具有投资价值。     

The performance analysis and evaluation of C‐PV/T aided power generation system

In this paper, a novel solar aided power generation (SAPG) hybrid system based on the structural characteristics of coal‐fired power generation is established. In this system, the extraction steam of No.8 low pressure heater is replaced by the hot water coming from a concentration‐photovoltaic/thermal (C‐PV/T) module. The extraction steam returns into the steam turbine to do work, which increases the output power. And the electricity from the parallel C‐PV/T module goes directly into the power grid, which increases the generated power. The C‐PV/T module coupled with coal‐fired power generation improves the solar energy efficiency and provides hot water. As a case study, the economic calculation is performed with actual operation data extracted from a 600‐MW coal‐fired unit. The results show that the total efficiency increased by 1.3%, the coal fuel consumption is lowered by 11 g/kW·h, and the investment recovery period is approximately 7 years. This study offers a theoretical support to the engineering demonstration.     

Economic analysis of renewable heat and electricity production by sewage sludge digestion—a case study

In this paper, we assess the total cost of energy recovery from sewage sludge through anaerobic digestion with biogas utilization in combined heat and power (CHP) system. The important advantage of anaerobic digestion process is the production of biogas, which can be used to generate electricity and heat as a source of renewable energy. From this study, it can be retained that the generated thermal energy from the anaerobic digestion process meets the needs of the wastewater treatment plant (WWTP) and guarantees its self‐sufficiency in heat. The surplus of renewable heat produced by CHP is not a primary factor to improve the economic viability of the process. Moreover, the sales of electricity output represent about 76% of the operating costs of anaerobic digestion process. Renewable energy production is not economically viable by its own, without considering the wastewater treatment function and the associated incomes. Nevertheless, sludge digestion helps to reduce the wastewater treatment costs mainly by giving a good source of revenue via electricity production. Copyright © 2014 John Wiley & Sons, Ltd.     

First and second law investigations of a new solar‐assisted thermodynamic cycle for triple effect refrigeration

This investigation is persuaded for the first and second law analyses of a new solar‐driven triple‐effect refrigeration cycle using Duratherm 600 oil (Duratherm Extended Life Fluid, NY, USA) as the heat transfer fluid is performed. The proposed cycle is an integration of ejector, absorption, and cascaded refrigeration cycles that could produce refrigeration output of different magnitude at different temperature simultaneously. Both exergy destruction and losses in each component and hence in the overall system are determined to identify the causes and locations of the thermodynamic imperfection. The effects of some influenced parameters such as hot oil outlet temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector and cascaded refrigeration cycle have been observed on the first and second law performances. It is found that maximum irreversibility occurs in central receiver as 52.5% and the second largest irreversibility of 25% occurs in heliostat field. The second law efficiency of the solar driven triple effect refrigeration cycle is 2%, which is much lower than its first law efficiency of 11.5%. Analysis clearly shows that performance evaluation based on the first law analysis is inadequate and hence, more meaningful evaluation must be included in the second law analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Reliability evaluation of the solar power system based on the Markov chain method

Energy shortages and environmental problems associated with nonrenewable energy generation techniques have become increasingly prominent worldwide. Solar photovoltaic power generation is able to supply clean, environmentally friendly, and inexhaustible energy. Together with issues related to the expansion of scale, strong stochastic volatility and unpredictability have posed huge challenges to the stability and reliability of this power generation system. The present study proposed a reliable method to evaluate the stationary distribution probability based on the Markov chain method. First, the solar generation system was modeled based on the solar battery. Second, the stochastic property of the solar energy output power was derived and the simulation experiment adopted to verify the feasibility of results. Third, the energy storage device discharge process was modeled based on the Markov chain method and the evaluation method for the reliability of the solar power generation system obtained. Finally, validity of the method was simulated and verified.     

Balancing power supply and demand in remote off‐grid regions by means of a novel micro‐scale combined feedstock biomass generation plant

Providing electricity to a group of remote domestic or industrial customers can be achieved by a grid connection, or by an off‐grid (island) generator. While the former can become costly and will likely be prone to disruption, the latter is normally based on fossil fuels, which makes fuel sourcing and transport critical. To overcome these obstacles, a novel micro‐scale biomass generation plant was developed. This plant uses locally available renewable biomass feedstock to generate decentralized power at the point of demand and without the necessity of a grid connection. In this paper, load simulations on the basis of a process simulation model of the plant are performed to achieve a continuous match of supply and demand. It is analysed which load characteristics and fluctuations have to be expected when generating for a remote group of domestic customers, and it is evaluated how the plant needs to be operated to always provide sufficient power. Additionally, the fuel storage system of the plant system is investigated: The plant does not employ electrical storage, but instead matches demand and supply by means of internal usage of heat and power and through fuel storage. Relative and absolute storage levels as well as the storage charge/discharge cycles are analysed, and it will be shown that the plant can easily accommodate severe load fluctuations. Finally, the plant load factors are evaluated, and the findings show that this design is an interesting alternative to common island generators or to a conventional grid connection for remote customers. Copyright © 2009 John Wiley & Sons, Ltd.     

Parametric analysis and optimization of a building cooling heating power system driven by solar energy based on organic working fluid

Building cooling heating power (BCHP) systems as a kind of distributed energy resource have shown a great potential in improving energy efficiency and meeting multiple energy demands in buildings. In this paper, we present a BCHP system driven by solar energy with flat‐plate solar collectors. A modified system efficiency is introduced to evaluate the whole day performance of the system more accurately. Based on the mathematical models and simulation platform established, we have investigated the influences of some key thermodynamic parameters, namely condensation temperature, turbine inlet temperature and turbine inlet pressure on the system performance. In order to find the optimum combination of these parameters that leads to the best performance, we have performed parametric optimization by means of the genetic algorithm. Results indicate that the best performance and the highest efficiency of the system are achieved when the working fluid reaches its saturated state and the corresponding efficiencies of the system operating in the combined heating power mode, the combined cooling power mode and the power production mode turn out to be 19.10%, 27.24% and 10.47%, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Design,optimization and economic analysis of a monoethylene glycol recovery process: salt precipitation and vacuum operation

In the present study, the energy requirements, performance and economic feasibility of monoethylene glycol (MEG) recovery process (MEG-R-P) were establish based on Aspen Plus simulation. The simulation was carried out in two designs and four scenarios related to the composition (mono and divalent salts) of rich-MEG. The results revealed that, under optimized conditions, a process consists of a vacuum flash separator and distillation column operated at 0.05 bar recovered 99.7% of MEG with a purity of 99.9 wt% MEG for all scenarios. The concentration and type of dissolved solids showed a minimal effect on the process of energy and performance due to high dilution. The net present worth (20 years, 8%) of the capital and operating costs associated with MEG-R-P were 11.5 and 11.7 MMUSD, respectively, representing two to four folds saving compared with published results. The recovered MEG can be recycled 10 times with an estimated saving of 50% of the total MEG purchasing cost for one-time recycling, and up to 80% saving for five times recycling. Obtained results confirm the high economic and environmental benefits achieved by applying the proposed MEG-R-P.     

Energy and exergy analyses of an integrated solar‐based desalination quadruple effect absorption system for freshwater and cooling production

In this paper, a novel integrated solar photovoltaic thermal absorption desalination system for freshwater and cooling production is proposed and analyzed thermodynamically. Ammonia–water pair is considered as a working fluid for the absorption system. Effect of average solar radiation for different months, time period of solar radiation availability in Abu Dhabi, salinity of seawater, and temperature of the seawater on energetic and exergetic COPs, production rate of freshwater, and overall performance of the system are investigated under different operating conditions. It is found that energetic and exergetic COPs, production rate of freshwater, energetic and exergetic utilization factors, and performance ratios vary greatly from one month to another because of the dynamic variation in solar radiation and its time of availability. The highest amount of freshwater is produced in the month of July as calculated to be 152 kg/h for a collector area of 100 m² and solar power of 4.8 kW. The highest energetic and exergetic COPs and utilization factors are also obtained for the month of July. Moreover, the highest performance ratio is found to be 0.056 as obtained in the month of July when solar radiation intensity is highest as available for more than half of a day. Copyright © 2012 John Wiley & Sons, Ltd.     

Techno‐economic analysis of renewable energy source options for a district heating project

With the increased interest in exploiting renewable energy sources for district heating applications, the economic comparison of viable options has been considered as an important step in making a sound decision. In this paper, the economic performance of several energy options for a district heating system in Vancouver, British Columbia, is studied. The considered district heating system includes a 10 MW peaking/backup natural gas boiler to provide about 40% of the annual energy requirement and a 2.5 MW base‐load system. The energy options for the base‐load system include: wood pellet, sewer heat, and geothermal heat. Present values of initial and operating costs of each system were calculated over 25‐year service life of the systems, considering tax savings due to depreciation and operating costs, and salvage value of equipment and building and resale price of land in the cash flow analysis. It was shown that the natural gas boiler option provided less expensive energy followed by the wood pellet heat producing technologies, sewer heat recovery, and geothermal heat pump. Among wood pellet technologies, the grate burner was a less expensive option than powder and gasifier technologies. It was found that using natural gas as a fuel source for the peaking/backup system accounted for 37% of the heat production cost for the considered district‐heating center. The results show that the cost of produced heat from wood pellet grate burner is well comparable to that of the natural gas boiler. Emissions of the systems are also calculated in this study. It is shown that the natural gas boiler for the base‐load heat production would produce more than 4300 tonnes of GHG emission per year, while wood pellet burning systems are GHG neutral. Sensitivity analysis on various inputs to the economic model has been carried out. It was shown that 20% increase in capital cost of the natural gas base‐load system or 1% decrease in wood pellet price inflation would make the wood pellet grate burner economically preferable to the natural gas boiler. Copyright © 2009 John Wiley & Sons, Ltd.