Research On The Establishment And Comprehensive Assessment Of A Distributed Hybrid Solar-Biomass Heating System

In recent years,with the depletion of fossil fuels and the frequent occurrence of environmental pollution problems,people are in urgent need of environmentally friendly and abundant energy resources.Distributed renewable energy systems based on biomass and solar energy are gradually receiving attention.Based on the characteristics of local climate and energy resources in Guanzhong area of Shaanxi Province,this study designed a hybrid heating system consisting of a solar subsystem and a biomass subsystem to provide thermal energy for and a nearby building as well as the system itself,and the excess energy produced every day is used to produce domestic hot water and cooking fuel for the community or sold to the market.In addition to technical performance assessment based on thermodynamic analysis,this study uses life cycle assessment?LCA?to investigate the environmental performance of the system from different life cycle stages.Since the techno-economic status of renewable energy systems has always been a key factor that directly determines the feasibility,this study carried out detailed energy and mass balance analysis,economic assumptions and calculations as well as sensitivity analysis of the proposed heating system.The economic feasibility of the system was analyzed by the established model.In order to reflect the comprehensive performance of the system,this study also conducted an emergy assessment to further verify the sustainability of the system.Main findings are as follows:?1?This study carried out dynamic simulation of the system throughout the year by using TRNSYS software and built a complete transient thermodynamic model of the system.On the selected typical day,the average temperature of the ambient environment was-5.1oC,the average solar radiation intensity in local area was 313.7 W/m²,and the daily exposure time was 9.8 h.During the entire heating process,the average heat collection efficiency of the parabolic trough colletor was 34.6%.From the perspective of energy supplying characteristics,the biomass subsystem was running all day,while the solar subsystem was mainly used to assist.When the solar radiation intensity increases from zero,the heat collection efficiency of the collector is relatively low,and the efficiency of the biogas boiler will also be reduced.At the same time,the cooking fuel produced by the system will gradually increase with the increase of solar hot water,so the COP?coefficient of performance?of the system rises after 8:00.After 14:00,as the proportion of solar energy decreased,COP began to decline.The main reason for lower COP value is that part of the heat output will be used to maintain the stable operation of the anaerobic reactor.When the solar subsystem cannot meet the heat requirements of the anaerobic reactor,the biogas produced will be consumed,which will lead to a reduction in the amount of biogas available for external use and thus a reduction in COP.The heat demand and energy consumption in winter were greater than in other seasons.The heat consumption of the system decreases first and then rises.Therefore,the PES value rises first and then decreases,it reached a minimum value the 12^thday and a maximum value on the 202^ndday.The system as a whole shows good technical performance,the comparison also shows that the system has a good primary energy saving rate and greenhouse gas emissions reduction ability.It's especially suitable for remote areas where is rich in solar energy and biomass resources and is suitable for implementing distributed energy systems.?2?LCA was adopted for the environmental assessment of the system,it was found that the construction stage and the disassembling&recycling stage of the system have little impact on the environment of the whole life cycle.The glass reflector and support of the solar collector accounted for less than 20%of the impact of every selected LCA indicator,for example,they only accounted for 8.14%of the GWP?global warming potential?.Therefore,it was found that the major emissions of solar subsystem was not from the reflector on the solar collector,but the fixed stakes between the ground and reflector.External energy consumption contributed 13.26 MJ to the primary energy consumption?PED?of the system,of which 60.55%was due to the utilization of the external electricity and 32.95%was due to the diesel consumed by transportation.The utilization of final products can help decrease greenhouse gas emissions and reduce the potential impacts of both primary energy consumption,acidification and eutrophication.LCA also showed that in northwest China,the solar subsystem contributed the most environmental emissions in the construction phase,its proportion in the hybrid system is not the higher the better,hence the excessive pursuit of high solar energy may lead to more serious environmental problems.?3?The calculation of techno-economic analysis indicated that the NPV of the system was$56,473,the payback period was 6.16 years,and the ROI was 63.44%,IRR was21.18%.It can be seen that the overall economic benefits of the system are considerable.However,the payback period of this system is slightly longer than that of other similar biomass systems,which might be the result of the relatively high cost of solar subsystem,of which the profitability compared with the biomass systems is not obvious.Labor costs were the main source of annual operating costs,accounting for approximately 48%of total costs,followed by facilities-related costs?accounted for 42%of the total costs?.In addition,based on the operating cost and total net energy yield,the unit cost of energy production of the system was calculated to be$0.049/kwh,the heating cost was relatively low,which had a good market competitiveness.According to the results of sensitivity analysis,it was found that the prices of labor,anaerobic reactor etc.were the most sensitive factors to the economic performance of the system.Reasonable control of human resources cost,the increase of internal resource recycling and recovery,as well as further improvement of the quality of products can effectively decrease the cost the whole system.?4?Using emergy analysis to evaluate the comprehensive sustainability of the system can explore the key factors to further improve the system's energy production efficiency,balance the ecology and economic development.The ELR of the system was less than 3,indicating that it caused less pressure on the environment.At the same time,ESI>5,which directly indicated that the system had relatively good sustainability.In terms of EYR,the current system was lower than independent biogas-based energy system,showed that the addition of solar energy was not a significant energy output.Compared with other systems,the productivity of the proposed system was fair,but it might need to be further optimized and improved,such as using more suitable solar collector materials to reduce the impact of solar radiation changes on the stability of the system.Compared with the common centralized solar power system,it can be found that the energy conversion rate of this system is higher,which means that the system needs to input more resources to produce the same amount of energy.This may be due to daily operation need to input a large number of raw materials.Moreover,this study compared with several other typical energy systems,proved that the current system had good comprehensive sustainability,which was worthy of further research and application.This study designed a novel distributed hybrid solar-biomass heating system and evaluated its performance.It is found that the system has the technical performance of stable and efficient operation and favorable sustainability.However,in terms of external energy consumption,related raw materials,cost control of labor and equipment,there is some room for further optimization.This study may be helpful to understand the internal relationship between the current energy system and the economic,environmental and social systems,and may have reference value for improving the comprehensive assessment methodologies of renewable energy systems and promoting the sustainable development of the energy industry.