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1.
Renewable energy resources play a very important rule these days to assist the conventional energy systems for doing its function in the UAE due to high greenhouse gas (GHG) emissions and energy demand. In this paper, the analysis and performance of integrated standalone hybrid solar PV, fuel cell and diesel generator power system with battery energy storage system (BESS) or supercapacitor energy storage system (SCESS) in Khorfakkan city, Sharjah were presented. HOMER Pro software was used to model and simulate the hybrid energy system (HES) based on the daily energy consumption for Khorfakkan city. The simulation results show that using SCESS as an energy storage system will help the performance of HES based on the Levelized cost of energy (LCOE) and greenhouse gas (GHG) emissions. The HES with SCESS has renewable fraction (68.1%) and 0.346 $/kWh LCOE. The HES meets the annual AC primary load of the city (13.6 GWh) with negligible electricity excess and with an unmet electrical load of 1.38%. The reduction in GHG emissions for HES with SCESS was 83.2%, equivalent to saving 814,428 gallons of diesel.  相似文献   

2.
Proton-exchange membrane fuel cell (PEMFC) and liquid hydrogen are gaining attention as a power generation system and alternative fuel of ship. This study proposes a novel PEMFC system, integrated with the organic Rankine cycle–direct expansion cycle (ORC-DEC), which exploits cold exergy from liquid hydrogen and low temperature waste heat generated by the PEMFC for application in a liquid hydrogen fueled ship. A thermodynamic model of each subsystem was established and analyzed from the economic, energy, and exergy viewpoints. Moreover, parametric analysis was performed to identify the effects of certain key parameters, such as the working fluid in the ORC, pressure exerted by the fuel pump, cooling water temperature of the PEMFC, and the stack current density on the system performance. The results showed that the proposed system could generate 221 kW of additional power. The overall system achieved an exergy and energy efficiency of 43.52 and 40.45%, respectively. The PEMFC system had the largest exergy destruction, followed by the cryogenic heat exchanger. Propane showed the best performance among the several investigated ORC working fluids and the system performance improved with the increase in the cooling water temperature of the PEMFC. The economic analysis showed that the average payback time of ORC-DEC was 11.2 years and the average net present value (NPV) was $295,268 at liquid hydrogen costing $3 to $7, showing the potential viability of the system.  相似文献   

3.
Many universities have plans to reduce campus energy consumption with developed energy efficiency strategies, supply the energy needs of the university campus with renewable energy and create a green campus. In order to serve this purpose, this study focuses on the simulation of the installation of an on-grid photovoltaic (PV) power system at the Vocational Colleges Campus, Hitit University. On the other hand, the integration of the simulated PV system with a gas fired-trigeneration system is discussed. Moreover, the study explores opportunities for solar hydrogen generation without energy storage on campus. For the PV system simulation, three different scenarios were created by using web-based PV system design software (HelioScope). Installed powers in the simulation were found as 94.2 kWe, 123.9 kWe, and 157.5 kWe for the low scenario (on the rooftop), high scenario (on the rooftop), and the high + PV canopy arrays scenario (on the rooftop and an outdoor parking area), respectively. The levelized cost of electricity (LCOE) values were 0.061 $/kWh, 0.065 $/kWh, and 0.063 $/kWh for the low scenario, high scenario, and the scenario including PV canopy, respectively. The energy payback time is found to be 6.47–6.94 years for the 20–25 years lifetime of the PV plant. The simulation results showed that the PV system could support it by generating additional electrical energy up to 25% of the existing system. The campus can reduce GHG emissions of 1546–2272 tonnes-CO2eq, which is equivalent to 142–209 ha of forest-absorbing carbon unused during the life of the PV system. Depending on the production and consumption methods utilized on campus, which is a location with relatively large solar potential, the levelized cost of hydrogen (LCOH) of hydrogen generation ranged from 0.054 $/kWhH2 (1.78 $/kgH2) to 0.103 $/kWhH2 (3.4 $/kgH2). Consequently, with proper planning and design, a grid-connected PV-trigeneration-hydrogen generation hybrid system on a university campus may operate successfully.  相似文献   

4.
Solar energy is an attractive renewable energy source because the sun's energy is plentiful and carbon-free. However, solar energy is intermittent and not suitable for base load electricity generation without an energy backup system. Concentrated solar power (CSP) is unique among other renewable energy options because it can approach base load generation with molten salt thermal energy storage (TES). This paper describes the development of an engineering economic model that directly compares the performance, cost, and profit of a 110-MW parabolic trough CSP plant operating with a TES system, natural gas-fired backup system, and no backup system. Model results are presented for 0–12 h backup capacities with and without current U.S. subsidies. TES increased the annual capacity factor from around 30% with no backup to up to 55% with 12 h of storage when the solar field area was selected to provide the lowest levelized cost of energy (LCOE). Using TES instead of a natural gas-fired heat transfer fluid heater (NG) increased total plant capital costs but decreased annual operation and maintenance costs. These three effects led to an increase in the LCOE for PT plants with TES and NG backup compared with no backup. LCOE increased with increasing backup capacity for plants with TES and NG backup. For small backup capacities (1–4 h), plants with TES had slightly lower LCOE values than plants with NG backup. For larger backup capacities (5–12 h), plants with TES had slightly higher LCOE values than plants with NG backup. At these costs, current U.S. federal tax incentives were not sufficient to make PT profitable in a market with variable electricity pricing. Current U.S. incentives combined with a fixed electricity price of $200/MWh made PT plants with larger backup capacities more profitable than PT plants with no backup or with smaller backup capacities. In the absence of incentives, a carbon price of $100–$160/tonne CO2eq would be required for these PT plants to compete with new coal-fired power plants in the U.S. If the long-term goal is to increase renewable base load electricity generation, additional incentives are needed to encourage new CSP plants to use thermal energy storage in the U.S.  相似文献   

5.
Hydrogen is one of the energy carriers that can be produced using different techniques. Combining multiple energy sources can enhance hydrogen production and meet other electrical demands. The hybrid arrangement allows the produced hydrogen to be stored and used when the electrical energy sources are not adequate. In this study, utilizing the meteorological data was investigated using HOMER (Hybrid Optimization of Multiple Energy Resources) software for the optimal solution. The results demonstrated that the “best-optimized system has 270 kW of photovoltaic (PV), 1 unit of 300 kW of wind turbine (WT), 500 kW of electrolyzer, 100 kg/L of the hydrogen tank, 70 units of 1 kWh lithium-ion battery, and 472 kW of the converter. The selected hybrid energy system has the lowest Levelized cost of energy (LCOE), Levelized cost of hydrogen (LCOH), and net present cost (NPC) of $/kg 0.6208, $/kg 9.34, and $ 484,360.00 respectively which judged the system to be the best choice for the proposed hydrogen project in AI-Kharj. This investigation will help stakeholders and policymakers optimize hybrid energy systems that economically meet the hydrogen production and refueling station demands of the AI-Kharj community.  相似文献   

6.
Large scale, low cost, and low carbon intensity hydrogen production is needed to reduce emissions in the energy and transportation sectors. We present a techno-economic analysis and life cycle assessment of natural gas pyrolysis technologies for hydrogen production, with carbon black (CB) as a co-product. Four designs were considered based on the source of heat to the pyrolysis system, the combustion medium, and use of carbon capture (CC) technology. The oxygen-fired-CB design with CC is the most attractive from financial and environmental perspectives, superior to a conventional steam methane reformer (SMR) process with CC. The estimated pre-tax minimum hydrogen selling prices for the pyrolysis technologies range between $1.08/kg and $2.43/kg when natural gas (NG) costs $3.76/GJ. Key advantages include near-zero onsite GHG emissions of the oxygen-fired-CB design with CC and up to 41% lower GHG emissions compared to the SMR + CC process. The results indicate that natural gas pyrolysis may be a feasible pathway for hydrogen production.  相似文献   

7.
In this study, exergoeconomic and environmental impact analyses, through energy, exergy, and sustainability assessment methods, are performed to investigate a hybrid version renewable energy (including wind and solar) based hydrogen and electricity production system. The dead state temperatures considered here are 10 °C, 20 °C and 30 °C to undertake a parametric study. An electrolyzer and a metal hydride tank are used for hydrogen production and hydrogen storage, respectively. Also, the Proton Exchange Membrane Fuel Cell (PEMFC) and battery options are utilized for electricity generation and storage, respectively. As a result, the energy and exergy efficiencies and the sustainability index for the wind turbine are found to be higher than the ones for solar photovoltaic (PV) system. Also, the overall exergy efficiency of the system is found to be higher than the corresponding overall energy efficiency. Furthermore, for this system, it can be concluded that wind turbine with 60 gCO2/month is more environmentally-benign than the solar PV system with 75 gCO2/month. Finally, the total exergoeconomic parameter is found to be 0.26 W/$, when the energy loss is considered, while it is 0.41 W/$, when the total of exergy loss and destruction rates are taken into account.  相似文献   

8.
In addition to the high financial cost of energy resources required to meet the rising demand for electricity consumption in Kuwait, the negative environmental impact of fossil fuel is increasing. Hence, the objective of this paper is to determine the economic feasibility and viability of implementing PV solar energy in the State of Kuwait. It was found that the positive characteristics of solar radiation in Kuwait play a critical role in enhancing the feasibility of implementing solar systems. Under the present price of 5$/W and 15% efficiency, the LCOE of a 1 MW station is estimated to be around $0.20/kWh. This LCOE can be feasible only when the cost of oil is around 100$/barrel. The Cost Benefit Analysis showed that when the value of saved energy resources used in producing traditional electricity, and the cost of lowering CO2 emissions are accounted for, the true economic cost of LCOE of a PV system will decline significantly. The preliminary economic analysis recommends the implementation of PV technology in Kuwait.  相似文献   

9.
Diesel engine power plants are still widely used on many remote islands in South Korea, despite their disadvantages. Aiming to solve economic and environmental pollution problems, a remote island case study was conducted on Ui Island, aiming to offer a zero-emissions solution by using renewable energy sources in an off-grid application. Power was generated from solar, wind, and hydrogen sources. Li-ion batteries and hydrogen were used as energy storage systems. In addition, PV/battery, wind/battery, PV/wind/battery, PV/battery/PEMFC, wind/battery/PEMFC, and PV/wind/battery/PEMFC systems were simulated using the HOMER software to determine the optimal sizes and techno-economic feasibility. The results show that the PV/wind/battery/PEMFC system is the best system. The configuration of the system consists of 990-kW PV panels, 700-kW wind turbines, a 1088-kWh Li-ion battery bank, 534-kW converter, 300-kW PEMWE system, 300-kg hydrogen tank, and 100-kW PEMFC system. The total NPC of the system is $5,276,069, and the LCOE is 0.366 $/kWh.  相似文献   

10.
The increasing threat to environmental sustainability as a result of greenhouse gas (GHG) emissions from fossil fuel base power plants has necessitated the need to find sustainable energy sources to meet the world's energy demands. This study focuses on assessing the potential of a hybrid power plant for the production of electricity, hydrogen for the production of fertilizer for agricultural activities, farmland irrigation, environmental impact as well as its employment potential in northern Ghana. The Shannon entropy weight and TOPSIS multi-criteria decision-making approach were adopted to rank and identify the optimal configuration out of five possible options for the study area. Results from the simulation show that the winning system, i.e., Hydro + Battery system would generate a total electricity of 1,095,679 kWh/year. A cost of electricity of 0.06 $/kWh with an operating cost (OC) of $18,318 was recorded for the winning system. The total produced hydrogen by the optimum configuration is 8816 kg/year at a levelized cost of hydrogen (LCOH) of 4.47 $/kg. The quantity of low-carbon fertilizer that can be produced from the produced hydrogen is also assessed. The optimum configuration also recorded an employment potential of 4 persons in 25 years. A total GHG equivalence of 383.49 metric tons of CO2 equivalent indicating the level of emissions that will be avoided should the optimum system be used to meet the demands specified in this study was obtained.  相似文献   

11.
Multi-energy complementary distributed energy system integrated with renewable energy is at the forefront of energy sustainable development and is an important way to achieve energy conservation and emission reduction. A comparative analysis of solid oxide fuel cell (SOFC)-micro gas turbine (MGT)-combined cooling, heating and power (CCHP) systems coupled with two solar methane steam reforming processes is presented in terms of energy, exergy, environmental and economic performances in this paper. The first is to couple with the traditional solar methane steam reforming process. Then the produced hydrogen-rich syngas is directly sent into the SOFC anode to produce electricity. The second is to couple with the medium-temperature solar methane membrane separation and reforming process. The produced pure hydrogen enters the SOFC anode to generate electricity, and the remaining small amount of fuel gas enters the afterburner to increase the exhaust gas enthalpy. Both systems transfer the low-grade solar energy to high-grade hydrogen, and then orderly release energy in the systems. The research results show that the solar thermochemical efficiency, energy efficiency and exergy efficiency of the second system reach 52.20%, 77.97% and 57.29%, respectively, 19.05%, 7.51% and 3.63% higher than those of the first system, respectively. Exergy analysis results indicate that both the solar heat collection process and the SOFC electrochemical process have larger exergy destruction. The levelized cost of products of the first system is about 0.0735$/h that is lower than that of the second system. And these two new systems have less environmental impact, with specific CO2 emissions of 236.98 g/kWh and 249.89 g/kWh, respectively.  相似文献   

12.
Hydrogen fuel production from methane cracking is a sustainable process compared to the ones currently in practice due to zero greenhouse gas emissions. Also, carbon black that is co-produced is valuable and can be marketed to other industries. As this is a high-temperature process, using solar energy can further improve its sustainability. An integrated solar methane cracking system is proposed where hydrogen and carbon products are sent to fuel cells to generate electricity. The CO2 exhaust stream from the carbon fuel cell is captured and reacted with hydrogen in the CO2 hydrogenation unit to produce liquid fuels – Methanol and dimethyl ether. The process is simulated in Aspen Plus®, and its energy and exergy efficiencies are evaluated by carrying out a detailed thermodynamic analysis. In addition, a sensitivity analysis is performed on various input parameters of the system. The overall energy efficiency of 41.9% and exergy efficiency of 52.3% were found.  相似文献   

13.
In this study, design and optimization of the hybrid renewable energy system consisting of Photovoltaic (PV)/Electrolyzer/Proton Exchange Membrane Fuel Cell (PEMFC) was investigated to provide electricity and heat for Greenhouse in ?anl?urfa (Turkey). The coupling of a photovoltaic system with PEMFC was preferred to supply continuous production of electric energy throughout the year. Additionally, produced heat from PEMFC was used to heating of the greenhouse by micro cogeneration application. The MATLAB/Simulink was applied to the design and optimization of the proposed hybrid system. In the designed system, solar energy was selected to produce the Hydrogen (H2) required to run the electrolyzer. In cases where the solar energy is not sufficient and cannot meet the electricity requirement for the electrolyzer; the H2 requirement for the operation of the PEMFC was met from the H2 storage tanks and energy continuity was ensured. The electrolyzer was designed for H2 demand of the 3 kW PEMFC which were met the greenhouse energy requirement. PEMFC based hybrid system has 48% electrical and 45% thermal efficiencies. According to optimization results obtained for the proposed hybrid system, the levelized cost of energy was found 0.117 $/kWh. The obtained results show the proposed PV/Electrolyzer/PEMFC hybrid power system provides an applicable option for powering stand-alone application in a self-sustainable expedient.  相似文献   

14.
For data centers with high humidity requirements, a novel combined cooling, heating and power (CCHP) system with dehumidification is proposed, which can provide cooling, heating, electricity and dehumidification simultaneously. The dynamic responses and economic characteristics of three different dehumidification methods with integrated dehumidification wheel, desiccant or parabolic trough solar collector (PTSC) as an auxiliary heat source are analyzed. The results show that the use of desiccant instead of the dehumidification wheel is beneficial to the stability of system power and temperature, and reduces the installed capacity of proton exchange membrane fuel cell (PEMFC) stacks by about 78%, thereby reducing the cost of the stacks and hydrogen. With the assistance of PTSC as an auxiliary heat source, the PEMFC stacks can reduce about 110 kW of electricity and save about 62 kg of hydrogen per day. Taking the average annual cost as an economic evaluation index, when hydrogen price is higher than $0.16 kg?1, using PTSC to assist the PEMFC stacks to provide the heat source is a better choice than using the PEMFC stacks alone.  相似文献   

15.
In this paper, a salinity gradient solar pond (SGSP) is used to harness the solar energy for hydrogen production through two cycles. The first cycle includes an absorption power cycle (APC), a proton exchange membrane (PEM) electrolyzer, and a thermoelectric generator (TEG) unit; in the second one, an organic Rankine cycle (ORC) with the zeotropic mixture is used instead of APC. The cycles are analyzed through the thermoeconomic vantage point to discover the effect of key decision variables on the cycles’ performance. Finally, NSGA-II is used to optimize both cycles. The results indicate that employing ORC with zeotropic mixture leads to a better performance in comparison to utilizing APC. For the base mode, unit cost product (UCP), exergy, and energy efficiency when APC is employed are 59.9 $/GJ, 23.73%, and 3.84%, respectively. These amounts are 47.27 $/GJ, 29.48%, and 5.86% if ORC with the zeotropic mixture is utilized. The APC and ORC generators have the highest exergy destruction rate which is equal to 6.18 and 10.91 kW. In both cycles, the highest investment cost is related to the turbine and is 0.8275 $/h and 0.976 $/h for the first and second cycles, respectively. In the optimum state the energy efficiency, exergy efficiency, UCP, and H2 production rate of the system enhances 42.44%, 27.54%,15.95%, and 38.24% when ORC with the zeotropic mixture is used. The maximum H2 production is 0.47 kg/h, and is obtained when the mass fraction of R142b, LCZ temperature, pumps pressure ratio, generator bubble point temperature are 0.603, 364.35 K, 2.12, 337.67 K, respectively.  相似文献   

16.
Alternative hydrogen production technologies are sought in part to reduce the greenhouse gas (GHG) emissions intensity compared with Steam Methane Reforming (SMR), currently the most commonly employed hydrogen production technology globally. This study investigates hydrogen production via High Temperature Steam Electrolysis (HTSE) in terms of GHG emissions and cost of hydrogen production using a combination of Aspen HYSYS® modelling and life cycle assessment. Results show that HTSE yields life cycle GHG emissions from 3 to 20 kg CO2e/kg H2 and costs from $2.5 to 5/kg H2, depending on the system parameters (e.g., energy source). A carbon price of $360/tonne CO2e is estimated to be required to make HTSE economically competitive with SMR. This is estimated to potentially decrease to $50/tonne CO2e with future technology advancements (e.g., fuel cell lifetime). The study offers insights for technology developers seeking to improve HTSE, and policy makers for decisions such as considering support for development of hydrogen production technologies.  相似文献   

17.
Hydrogen-based microgrids are receiving attention as critical pathways are being charted for the decarbonization of our thermal, transport, and power grids. In this article, clean, cost-effective, and reliable hybrid microgrid designs are developed to satisfy hydrogen and electricity loads in three energy-stressed islands of Eastern Canada, namely Pelee, Wolfe, and Saint Pierre. The design iterations incorporate elements of solar, wind, fuel cells, Hydrogen, and electricity storage. Real-time field irradiation, wind speed, ambient temperature, and load data over 8760 h have been used to drive the designs. Although the anticipated inflation rate in Newfoundland is higher than in Ontario, the lowest net present cost (NPC) of the hybrid solution is found in Saint Pierre Island. The hydrogen cost, in this case, is $7.5/kgH2 and $15.8/kgH2 lower than that of Pelee and Wolfe islands, respectively. The maximum H2 tank capacity (≥680 kgH2) on Pelee Island is 3000 h/yr and 1000 h/yr lower than optimal cases in Saint Pierre and Wolf Islands, respectively. LCOE is more sensitive to market changes in fuel cell costs than other components. The highest LCOE reduction (~63%) is observed when the optimal case in Pelee Island increases its lifetime. Analyzing the volatility in resource assessment indicates that predicting the energy cost over a short-term project is challenging. The salvage share in the long-term project is more than that of the short-term, indicating that the long-term project can be more cost-effective taken overall.  相似文献   

18.
In this research study, a novel integrated solar based combined, cooling, heating and, power (CCHP) is proposed consisting of Parabolic trough solar collectors (PTSC) field, a dual-tank molten salt heat storage, an Organic Rankine Cycle (ORC), a Proton exchange membrane fuel cell (PEMFC), a Proton exchange membrane electrolyzer (PEME), and a single effect Li/Br water absorption chiller. Thermodynamics and economic relations are used to analyze the proposed CCHP system. The mean of Tehran solar radiation as well as each portion of solar radiation during 24 h in winter is obtained from TRNSYS software to be used in PTSC calculations. A dynamic model of the thermal storage unit is assessed for proposed CCHP system under three different conditions (i.e., without thermal energy storage (TES), with TES and with TES + PEMFC). The results demonstrate that PEMFC has the ability to improve the power output by 10% during the night and 3% at sunny hours while by using TES alone, the overnight power generation is 86% of the power generation during the sunny hours. The optimum operating condition is determined via the NSGA-II algorithm with regards to exergy efficiency and total cost rate as objective functions where the optimum values are 0.058 ($/s) and 80%, respectively. The result of single objective optimization is 0.044 ($/s) for the economic objective in which the exergy efficiency is at its lowest value (57.7%). In addition, results indicate that the amount of single objective optimization based on exergetic objective is 88% in which the total cost rate is at its highest value (0.086 $/s). The scattered distribution of design parameters and the decision variables trend are investigated. In the next step, five different evolutionary algorithms namely NSGA-II, GDE3, IBEA, SMPSO, and SPEA2 are applied, and their Pareto frontiers are compared with each other.  相似文献   

19.
In this study, the cracking phenomenon of methane taking place in a cylindrical cavity of 16 cm in diameter and 40 cm in length under the heat of concentrated solar radiation without any catalyst is analysed. Three cases have been chosen; in all cases the primary phase contains methane and hydrogen gases. In the first case, we consider two phases; the secondary phase is a homogeneous carbon black powder with 50 nm of diameter; in the second case we have three phases where the two secondary phases are a particles powder with two diameters 20 and 80 nm and finally, a third case of five phases with a powder of four different diameters 20, 40, 60 and 80 nm. The low Reynolds K-ε turbulence model was applied. A calculation code "ANSYS FLUENT" is used to simulate the cracking phenomena where an Eulerian – Eulerian model is applied. The choice of several diameters greatly increases the calculation time but it approaches more of the physical reality of the radiation by these particles during the cracking. Results have shown that increasing the number of diameters gives higher cracking rates; the case of the powder of 4 different diameters gives the highest cracking rate. A parametric study as a function of the inlet velocity, carbon particle diameters and the intensity of solar radiation is realized. For the cracking heat, provided by the choice of the two concentrators of 5 and 16 MW/m2 used in this simulation, the CH4 inlet velocity is a decisive parameter for the cracking rate. Any increase in the inlet velocity requires more heat and this leads to a decrease in the cracking rate. For a velocity not exceeding 0.177 m/s (i.e. 0.3 L/min), both solar concentrations give the same amount of hydrogen produced. These quantities of hydrogen obtained reach maximum values for an inlet flow rate of CH4 between 0.58 L/min (i.e. 0.34 m/s) and 0.62 L/min (i.e. 0.3655 m/s) for both reactors. The results are interpreted and compared with experimental work.  相似文献   

20.
The rapidly growing of population in the developing countries and their lack of access to electricity, especially in the remote or rural areas, is causing huge challenges for on energy production. Energy is an enabler and a reliable energy supply is critical to sustainable socio-economic development for any nation. Most of Chad's people live in villages with no particular power supply system. Exploiting renewable energies is the only means of fostering development and improving people's welfare. This paper attempts at proposing an energy profile and storage model for Chad in vast remote towns. The paper addresses the key energy gap that is hindering on the development of such systems, it models and assess the potential on electricity generation and using hydrogen as surplus power storage system. A techno-econo-environmental survey on a solar-wind hybrid system in 25 towns in Chad is undertaken using NASA data and HOMER Software. Several hybrid scenarios of energy production and storage is analyzed. The results showed that in the electricity generation scenario, the average total NPC for the studied stations was $ 48164 and the average LCOE was $0.573. The lowest LCOE was related to Aouzou station with 0.507 $/kWh and the highest LCOE was obtained for Bol station with 0.604 $/kWh. In the simultaneous electricity and hydrogen generation scenario, the cheapest hydrogen ($4.695/kg) was produced in the “Grid” scenario, which was the same for all of the stations, with a total NPC of $2413770. The most expensive hydrogen ($4.707/kg) was generated in the “Grid-Wind” scenario and Bol stations with a total NPC of $2420186. The paper develops cost effective models for all hybrid systems combination for both electricity and hydrogen generation across Chad. These findings could help policy makers, investors and other developmental agencies make informed choices on energy access for sustainable development for rural communities in Sub Saharan Africa.  相似文献   

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