Solar-assisted System Research Articles

A comprehensive approach of design and analysis of hybrid solar and pedal assisted electric three-wheeler

Electric three-wheelers consume a great deal of power causing load shedding in industrial and residential areas. This research investigates the feasibility of a solar-assisted electric three-wheeler for deployment in Bangladesh, integrating solar photovoltaic system and pedaling generator. This research focused on enhancing the energy efficiency and sustainability of electric three-wheelers using renewable energy reducing dependency on the national grid. The rooftop space of the vehicle is insufficient for the solar PV system, necessitating the whole surface area of the vehicle with a 600 W solar panel. Simulations for Dhaka, Cox’s Bazar, and Rangpur assessed the solar energy potential across Bangladesh. A 48 V solar PV array and a Maximum Power Point Tracking (MPPT) charge controller were designed to optimize battery charging, achieving converter efficiencies between 97%–99.2%. Partial shading significantly impacted performance, while tilt angle optimization suggested a 0∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ ^{\\circ }$$\\end{document} tilt for moving vehicles and a 23∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ ^{\\circ }$$\\end{document} tilt during idle periods from October to March for optimal energy capture. A pedaling DC generator was introduced to charge the battery during idle times without grid reliance. The simulations for energy harvesting estimated an annual energy production of approximately 820 kWh. The integration of these systems increased drag, reducing maximum speed and requiring additional power. 172.28 kWh annual additional energy consumption was calculated for the solar PV system and 200.75 kWh for the pedaling charger. The study found the solar-assisted system with enhanced efficiency and sustainability but the limited economic viability of the pedaling generator. In future, the system can be developed for other countries with different vehicles.

Study and optimization of the influence of the water tank temperature on the performance of a solar assisted multi-source heat pump drying system

Solar assisted air source heat pump drying (SASHPD) system has been widely studied due to its excellent energy saving and high dried quality of product. To improve system performance, the control logic of a solar assisted multi-source heat pump drying (SMSHPD) system was investigated, and the simulation model and the experimental platform were established in this paper. The seasonal operating characteristics of the air source heat pump drying (ASHPD), the SASHPD and the SMSHPD modes were studied. The energy consumption, coefficient of performance (COP) and specific moisture extraction rate (SMER) of the three drying systems were calculated and analyzed. Additionally, the water tank temperature were also measured to determine the seasonal control logic of the drying system. It was found that compared to the ASHPD system, in summer, the energy consumption of the SASHPD system was reduced by 33.06 %, and COP and SMER was increased by 49.4 % and 49.38 %, respectively. Moreover, because of the high ambient temperature and water tank temperature, the experimental results indicated that only the SASHPD control logic should be implemented in summer. The maximum error of the simulation results was 9.1 % and the accuracy of the simulation model was confirmed. In autumn, the lower water tank temperature after drying illustrated that the solar energy can be more fully utilized, which explained why the performance of the SMSHPD mode was increased by 6.5 % compared to the SASHPD mode. Consequently, it is necessary to implement the SMSHPD control logic in autumn. Moreover, the operating temperature of the water source heat pump drying mode in autumn was optimized and the optimal temperature range was 28–54 °C. The average COP in one week after optimization was 6.21 % higher than that of the original operating temperature. Based on the validated simulation model, the optimal operating temperatures in spring and winter were also calculated and the control logic of the SMSHPD system operating in the four seasons were all obtained. This paper has important guiding significance for the reasonable choice of the control logic of a solar combined air source heat pump drying system.

Integration of energy storage and determination of optimal solar system size for biomass fast-pyrolysis

This study presents a model and analysis of a heliostat field collector (HFC) system integration with fast-pyrolysis of biomass and determination of the optimal solar system size for this integrated system. Given the intermittent nature of solar energy, an auxiliary heater and a thermochemical energy storage system (TCES) are included. Four cases of HFC integration with the fast-pyrolysis process have been studied: 1) low solar radiation, 2) sufficient solar radiation, 3) high solar radiation, and 4) no solar radiation with available stored energy in TCES. The solar energy system was modeled and calculated using the Engineering Equation Solver (EES) software, while the fast-pyrolysis process and the TCES were simulated using the Aspen Plus software. A thermodynamic and economic analysis has been conducted to estimate the share of solar energy for different process configurations. Economic calculations have been conducted for three different heliostat filed areas: 4000, 8000, and 12000 m2. Solar fraction, investment and operational costs, as well as total cost were calculated for these three heliostat field areas. The results indicate that the optimum heliostat field area for the studied biomass pyrolysis plant is 8000 m2 and the average solar fraction of the required energy in summer is 0.39 and while it is 0.34 for the whole year. Simulation results considering this optimized heliostat filed area indicate that 6.27 t/h of bio-oil is produced from 10 t/h of hybrid poplar biomass. Implementing this solar-assisted system reduces CO2 emissions, increases efficiency of the system and lowers thermal energy requirement for the fast-pyrolysis process from 6 MW to 3.99 MW.

Experimental and simulation study on the performance of a solar assisted multi-source heat pump drying system in Zhengzhou area

Zhengzhou of Henan province is an important agricultural production base. To improve the performance of the combined drying system and promote the development of agricultural products in Zhengzhou area, a solar assisted multi-source heat pump (SMSHP) drying system was proposed based on a traditional solar assisted air source heat pump (SASHP) drying system. The simulation models were developed for the air source heat pump (ASHP), SASHP, and SMSHP drying system respectively. The coefficient of performance, energy consumption and specific moisture extraction rate of the drying systems under different seasons were analyzed. Moreover, to validate the simulation models, an experimental platform of the combined drying system was designed and set up, and the experimental tests were carried out on the ASHP, SASHP, and SMSHP drying system. The simulation results revealed that the SMSHP drying system had lower energy consumption, higher coefficient of performance and specific moisture extraction rate than that of the SASHP drying system. The most significant performance enhancement was observed in spring, where the SMSHP system demonstrated a 22.69 % increase in coefficient of performance, a 19.2 % increase in specific moisture extraction rate, and a 16.11 % decrease in energy consumption compared to the SASHP drying system. Comparing with the experimental data, the simulation model errors of the energy consumption, coefficient of performance, and specific moisture extraction rate of the SMSHP drying system were 3.19 %, 0.28 %, and 2.27 %, respectively. Therefore, the accuracy of the simulation results was confirmed. To better calculate the heat provided by the solar collection system, the concept of the tank heating guarantee rate was first introduced, and it was found to be more scientific than the solar energy guarantee rate. At last, The economic and environmental benefit of the drying systems were analyzed during the life cycle, and the SMSHP drying system exhibited better comprehensive performance than the SASHP drying system. This paper provides valuable insights into the comprehensive utilization of solar energy and the control logic of solar assisted air source heat pump combined drying system under different seasons.

Development and performance evaluation of a high solar contribution resorption-compression cascade heat pump for cold climates

Absorption-resorption heat pumps (ARHPs) have great potential in utilizing low-temperature solar heat for efficient winter heating, but are limited by their weak adaptability to cold climates relative to absorption heat pumps (AHPs) and vapor compression heat pumps (VCHPs). In this work, a resorption-compression cascade system consisting of ARHP and VCHP subsystems is proposed and investigated, with the goal of achieving efficient winter heating with improved solar contribution in cold climates. Thermodynamic models of the two subsystems and of the whole cascade system are developed for system feasibility verification and performance evaluations. Feasible operation temperature and pressure conditions are identified in terms of internal subsystem matching. Based on these operation conditions, the primary energy ratio (PER) – which is a key performance evaluation index – is investigated over a range of solar fractions (f). The results show that for cases without solar contribution, the PER can be generally >0.95 under feasible operating conditions. In addition, the primary energy saving ratio (PESR) and heating capacity lift ratio (εlift), as well as the heat source temperature (Th) and ambient temperature (Tamb) restriction, are all investigated and compared to those of other, competing heating systems. The results show that the proposed system can reduce the Th demand to 69 °C (with a minimum Tamb of −21 °C) and extend the operational Tamb to −31 °C (with a minimum Th of 90 °C), while importantly achieving PESR > 0.20 and εlift > 20 % under the above extreme conditions. Moreover, when integrating the system with solar heat with f > 43 %, the proposed solar-assisted system has a clear PER advantage over an equivalent VCHP system in the Tamb range from −31 °C to 10 °C, highlighting the possibility of achieving higher solar contribution in cold climates.

Dynamic price optimization of a solar integrated cogeneration system considering uncertainties of building demands

Introducing renewable and high-efficiency devices into conventional cogeneration systems has the potentials to reduce fossil fuel consumption and mitigate environmental issues. This study aims to incorporate solar power and thermal energy into the power and waste heat generated by the gas turbine, respectively, while utilizing a double-effect absorption heat pump to meet the total heat demands. Following the creation of thermodynamic models, a trading mechanism is introduced involving an operating participant known as the product seller, which is analogous to electricity companies in power trading models. To maximize the interests of the participants with different confidence levels, the master-slave game is employed, using Genetic and Quadratic programming algorithms. The hourly outputs of devices and responded demands are evaluated based on the dynamic purchasing and selling price of products. The results indicate that the optimal interest of the cogeneration system is the lowest among all the participants. The power proportions from gas turbine and power grid exceed 60 %, while the contribution of gas turbine decreases by 11.0 % due to the lower heat demands caused by reduced confidence level. Overall, this study offers valuable insights into the market-oriented development of solar assisted cogeneration systems.

Performance analysis and optimization of a solar assisted heat pump-driven vacuum membrane distillation system for liquid desiccant regeneration

Liquid desiccant air-conditioning (LDAC) system is one of the excellent alternatives to conventional vapor compression refrigeration system due to its great energy-saving potential. However, regeneration of diluted liquid desiccant is the main energy-consuming process, and its performance plays a significant role in LDAC system. Recently vacuum membrane distillation (VMD) is becoming an emerging and promising separation process rely on the advantage of high permeate flux and low energy losses. The interest of usage solar energy techniques for feed solution heating in VMD systems is regarded as a sustainable path for membrane distillation process. In this work, a solar-driven VMD system incorporating a vapor-compression heat pump for liquid desiccant regeneration is introduced. An adapted solar/heat pump hybrid heating strategy has been devised to establish a connection between the heat-demanding process and the solar thermal supply. A comprehensive multicriteria assessment of energy, exergy, and environmental evaluation is conducted, and the influences of crucial parameters on both key components and system performance are evaluated to ensure a systematic examination. Results show that both the COP and STEC decrease obviously with the growth of the inlet solution temperature, whereas SEEC is improved abviously from 410.6 kW·h/m3 to 566.1 kW·h/m3 due to the effect of heat pump. The exergy analysis indicates that exergy losses in solar collector and stratified heat storage tank accounted for over 80 % of the total exergy losses. Additionally, single-objective optimization and multi-objective optimization are employed to explore the optimum operating conditions of key componets and whole system. Results show the ideal optimal solution can be obtained with a COP of 19.92 and a SEEC of 142.89 kW·h/m3 when the weights of COP and SEEC are taken as [0.5, 0.5].

Thermodynamic characteristics analysis of solar hot water heating composite system for low carbon heating

The low carbon renewable energy complementary cogeneration system has broad application prospects in the field of regional comprehensive energy utilization. The author proposes a trough solar assisted biomass cogeneration system that utilizes medium to low temperature trough solar energy to heat conduction oil and drive an absorption heat pump to preheat the water in the heating network, saving heating and steam extraction and increasing power output while maintaining a constant biomass fuel and heating volume. The EBSILON Professional software was used to model and simulate the case unit and integrated system, and based on this, thermodynamic characteristics such as system energy flow and energy loss were analyzed. The results show that under design conditions, a solar power generation capacity of 1.79 MWh can be generated, with a photoelectric efficiency of 20.07% and a photoelectric conversion efficiency of 21.61%. This can provide theoretical guidance for the research and practical application of solar energy and biomass energy in integrated cogeneration systems.

Investigation of the thermodynamic performance of a direct-expansion solar-assisted heat pump under very cold climatic conditions with and without glazing

This study investigates the long-term thermodynamic performance of a direct-expansion solar-assisted (DX-SAHP) system for hot water production in an average Canadian household. Performance is evaluated using realistic time-varying demand profiles and DX-SAHP with and without glazing under cold climatic conditions. A mathematical model for determining the system's long-term thermodynamic performance based on the first law of thermodynamics and heat transfer fundamentals is developed and thoroughly validated. The solution is implemented in MATLAB®. The CoolProp® database is coupled with MATLAB® and used to determine the working fluid's thermal physical properties. Besides, the thermodynamic performance of the DX-SAHP throughout the year, operating with low global warming potential (GWP) and class A safety refrigerants, was evaluated. Moreover, the influence of solar irradiation and ambient air temperature on the DX-SAHP's thermodynamic performance is studied. Results indicate that the monthly average coefficient of performance (COP) varies between 2.5 and 3.8, while the monthly average energy consumption of the system varies between 170 and 275 kWh. The obtained figures for COP and power consumption demonstrate the high-efficiency potential of the DX-SAHP system, making it an attractive alternative to reduce energy costs and CO2 emissions in residential water heating. In addition, results show that R1233zd gives the highest COPs, followed by R152a, R1234ze, R134a, R1234yf and R32. Besides, the long-term simulation results indicate that the DX-SAHP water heater without glazing has superior thermal performance compared to one with glazing. Also, results show that the COP rises as the ambient temperature or solar radiation level increases.

An effective solar assisted semi-cylindrical saline water desalination system with direct atomizer and energy storage materials for domestic use: an experimental investigation.

Solar still is the easiest method to purifying the saline water for domestic usage, but this method needs much improvement for better performance since it has lower productivity. In this paper, an experimental investigation is completed to analyse the semi cylindrical solar productivity still. The semi-cylindrical still is incorporated with direct atomizer and scrap used as an energy storage medium. Experiments are carried out during March 2020 in Kovilpatti, the southern part of India, with a depth of 2 and 4 cm saline water. Comparative performance analysis is made for conventional semi-cylindrical still, semi-cylindrical still with an atomizer, and semi-cylindrical still with atomizer and storage materials. The experimental study shows that the productivity of still increases while decreasing the water depth. Compared with 2-cm and 4-cm depth, solar still with 2-cm depth gives promising distillate productivity. The solar productivity still having 4-cm depth of water without atomizer gives only 2670 ml; on the other side, 2-cm water depth without atomizer gives 3100-ml productivity. The maximum productivity of solar still is found on a semi-cylindrical solar still combined with atomizer and energy storage medium having 2-cm water depth. Results revealed a higher freshwater production rate of 3610 ml found while incorporating atomizer and energy storage with the solar still. The system efficiency improved up to 35.20% compared to conventional semi-cylindrical still with 4 cm of saline water depth.

Geothermal heat pumps to reduce diesel consumption in an off-grid subarctic community: Comparison of solar assisted systems with optional underground energy storage

Overdependence on fossil fuels for heating and electricity poses significant challenges for remote communities in northern Quebec. This study evaluates the efficiency, heating costs and relevance of solar-assisted geothermal systems in a subarctic climate. Detailed subsurface data collected from Whapmagoostui–Kuujjuarapik were used to simulate heat pumps coupled to borehole heat exchangers, taking into account the possibility of thermal energy storage. Results show that a conventional configuration of borehole heat exchanger effectively meet low heating demands, while borehole thermal energy storage enables the annual balancing of ground loads and meets the high unbalanced heating demands. This work offers valuable insights for optimizing ground heat exchanger configurations in a harsh climate.

Energy and Exergy Analysis of a Combined Cooling Heating and Power System with Regeneration

Solar assisted trigeneration system has proved to be a potential method in generating power with net zero carbon emissions. The present work aims to address the potential ways to improve the efficiency of the solar energy-integrated carbon dioxide trigeneration system. A regeneration integrated combined cooling, heating, and power system is proposed. With a comprehensive thermodynamic model, the proposed system is simulated for various operating conditions. A component-level exergy analysis is also conducted to estimate the total irreversibility of the system. As the gas cooler exit temperature increases, the overall system irreversibility also increases. When the bleed mass is 20% of the total mass, the system has the lowest energy destruction rate. The potential component that contributes most to system irreversibility is the gas cooler, followed by the regenerator and expansion valve. The proposed system with regeneration yields 29% more COP than the conventional system when operating at lower compressor discharge pressure and a gas cooler exit temperature of 34 °C. It is inferred from the obtained results that to reduce the total irreversibility of the system, it is advised to operate the system at a lower compressor discharge pressure and gas cooler exit temperature.

Converter Control During Low Voltage Ride Through Operation for Grid-Interfaced Solar PV Battery Assisted System

The grid interfaced solar PV based distributed generation system (DGS) installations have increased tremendously. The penetration of DGS into the grid requires the DGS converter to pose the fault ride through capability. It demands the converter to remain connected during sags and to provide reactive power support to the grid. In this work, the grid interfaced solar PV-battery assisted system for balanced as well as unbalanced power generation along with low voltage ride through (LVRT) functioning is presented. An efficient and simple control technique is developed for the system, such that the DGS converter stays connected to the grid under fault conditions till the LVRT required standards are fulfilled. The DC link voltage variations and LVRT control are achieved by the battery energy storage (BES) bidirectional DC-DC converter (BDDC). The positive sequence grid current components are considered to meet the LVRT standards. The controller ensures the DGS converter currents are within the rated limits. The presented control strategy of DGS converter operation during voltage sags and unbalanced power generation is simulated and validated in MATLAB/Simulink. The developed topology and its control are validated through test results.

An insight into environmental footprints of emerging air-conditioning systems towards sustainable cities

In this study, the environmental impacts of six conventional and modern air conditioning systems, including vapor-compression air conditioning (VAC), hybrid membrane-based air conditioning (HMBAC), desiccant enhanced evaporative air conditioning (DEVap), solar HMBAC, solar DEVap, and inverter VAC, are analyzed using a cradle-to-gate life cycle assessment (LCA) approach. The assessment is based on climate change, ozone depletion, terrestrial acidification, freshwater eutrophication, human toxicity, photochemical oxidant formation, ecotoxicity, water depletion, and fossil fuel depletion impacts. The LCA findings reveal that membrane-based systems (HMBAC and DEVap) are highly environmentally-friendly in comparison to the regular VAC systems (household split coolers), showing the capability of membranes in developing efficient air conditioning systems. In addition, solar-assisted systems reduce seven out of eleven environmental impacts, while they cause severe eutrophication, marine and freshwater ecotoxicity, and human toxicity consequences. Furthermore, it is unveiled that the inverter can reduce up to 38% of the environmental impacts of VAC systems which are the most common air conditioning system in buildings. Therefore, the manipulation of the inverter system in VACs can be considered as one of the short-term solutions in reducing the environmental footprints of air conditioning. Finally, the sensitivity analysis is applied to show the reliability of the outcomes.

Experiment study on startup characteristics and operation performance of PV/T solar assisted heat pump water heater system driven by direct current variable frequency compressor

The use of renewable energy can alleviate climate warming and environmental pollution. PV/T (photovoltaic/thermal) system has been widely concerned and rapidly developed owing to its capability of generating electric and thermal energy simultaneously. In the article, a PV/T solar assisted heat pump water heater system driven by direct current variable frequency compressor was proposed to meet the growing needs of residents for domestic hot water. This system was tested in different working conditions in Lanzhou, and the startup characteristics and operation performance were evaluated. The results indicate that at the same ambient temperature, low speed is conducive to the continuity of the refrigerant cycle and improves the system performance. In this system, the initial water temperature of the water tank was 23.1 °C and after 2.5 h it reached 53 °C. The average power generation efficiency is 13.64%, the average thermal efficiency is 26.42%, the overall efficiency is 62.69% and the average COP (coefficient of performance) is 4.87. Compared with traditional PV (photovoltaic) modules, the average temperature reduction is 11.2 ℃. With the increase of solar radiation intensity, the electrical power of the system will increase and the electrical efficiency will decrease. The average daily electrical efficiency of PV/T system is 13.64%, which is 6.25% higher than that of uncooled PV panel. In addition, controlling a proper compressor speed is crucial for enhancing system performance. The PV/T collector can remarkably reduce the temperature of PV panel, improve power generation efficiency and comprehensive utilization efficiency of solar energy.

Investigation on the thermal performance and economy of a solar assisted air source heat pump domestic hot water system

In order to increase the utilization of renewable energy and reduce carbon dioxide emissions, a solar assisted - air source heat pump (SA-ASHP) domestic hot water supply system is proposed, designed and built, the thermal performance and economy are numerically simulated and experimentally verified, the optimal design parameters are determined based on the economic optimization analysis. The results show that the coefficient of performance (COP) of air source heat pump (ASHP) varies from 2.62 to 3.93 and the COP of SA-ASHP system varies from 2.76 to 6.26. The solar fraction varies from 8.83% to 45.51%, and varies greatly in different seasons. The simulated heat collection of solar collector, the power consumption and heating capacity of ASHP, and the total power consumption of water pump are in good agreement with the measured results. Compared with the existing SA-ASHP system, the annual cost has decreased by 1998.32USD, annual cost converted from initial investment has decreased by 629.08USD, operating cost has decreased by 1369.25USD and total power consumption has decreased by 16897.79 kWh of the optimized SA-ASHP system. The optimum ratio between the input power of ASHP and the collector area is 0.078 kW/m2. The research results play an important role in guiding the design, operation and heat source selection of domestic hot water (DHW) system in student dormitory.

Güneş enerjisi destekli ısıtma sistemlerinde güneş kolektörü ve sıcak su deposu kapasitesi seçimi için parametrik analiz

In this study, a study was carried out on integrating solar assisted systems into heating systems in a building. For the study, an existing building was modeled with the DesignBuilder building energy simulation program. The scenarios were created on the model to determine the number of solar collectors and the capacity of the water tank used in solar assisted heating systems. The primary energy consumption, global costs and payback periods of the scenarios created were obtained by parametric analysis. According to the results obtained, the solution that reduces primary energy consumption the most is SYS20, the solution that reduces the global cost the most is SYS1 and the optimum solution is SYS7. Considering the payback periods, SYS1 was determined as the most appropriate solution to be applied in the study since it was the solution with the minimum payback period. At the end of the study, it was seen that primary energy savings could be reduced by up to 47% with solar energy assisted heating system. Thanks to the study, a reference source for the number of solar collectors and water tank capacity selection in Isparta and provinces with similar climates has been created.

Impact of optimal sizing and integration of thermal energy storage in solar assisted energy systems

It is becoming increasingly important for human societies to use renewable energy. More effective energy storage solutions are crucial to increase the share of renewable energy in the domestic and industrial sectors, which consumes a large amount of thermal energy for heating and cooling purposes. There has been little quantitative analysis of thermal energy storage in solar-based cold production units. An efficient method of designing heat and/or cold storage systems and smart operation planning can help a cooling/heating system to be smaller for the same capacity of supply and thereby reducing the costs of initial investment and costs of operation. This paper attempts to show how the size of a heat and cold storage system affects its thermal performance and how it can lower costs and emissions. For this, a solar-assisted thermally driven cooling supply system with various designs and integrations of their cold storage unit is simulated dynamically through a whole year in Qassim region as the case study. The results show that a system design with double solar heat storage and double cold storage in parallel arrangement results in the best techno-economic-environmental performance. For this case, the levelized cost of cooling will be 383 USD/MWhr, which will be at least 3% lower than the typical hot/cold buffer tank design scenario.

Feasibility of annual wet anaerobic digestion temperature-controlled by solar energy in cold areas

• Propose a novel anaerobic digestion system heated by solar energy. • The pilot experiments are carried out to prove the feasibility of the system. • Proved the operate feasibility of solar heated AD system in the cold area. • Show the annual performance and control strategy of solar heated AD system. In cold rural areas of China, variation in ambient temperature leads to higher heat loss of anaerobic digester, low digestion efficiency, and reduction of biogas production. Solar energy is publicly regarded as economical and suitable energy for steady biogas production. However, the high initial investment; and unstable energy supply of the solar-assisted system was the higher challenge of the steady biogas production system. This work aimed to develop a solar water heated anaerobic digestion system with efficient temperature control and present the feasibility of the annual biogas production system temperature-controlled by solar energy in the pilot study. Energy balance was analyzed theoretically between the evacuated tube solar water collector and the anaerobic digester at first. Then a biogas production system was developed in Lanzhou City, China and it mainly consists of a 3m3 insulated anaerobic digester and solar collector of 30 Φ58×1800mm evacuated tubes. Annual batch pilot experiments have been carried out to test the feasibility of the steady biogas production system temperature-controlled by solar energy in cold and arid areas. The result shows that the temperature-controlled solar energy anaerobic system can start successfully on the 10th, 8th, and 13th during the reaction period and operate smoothly during the whole year in different seasons. The slurry temperature of the three batches was all maintained at 26±1.1℃,37±1.3℃, and 52±1.1℃, while the temperature difference of solar water was 19.9℃, 15.5℃, and 30.5℃ under 3-4 days snowy or cloudy weather. The cumulative methane production at three temperatures was 0.562,0.632 and 0.846 m 3 /kg VS. The system runs steadily during the whole year by psychrophilic and mesophilic anaerobic (26℃ and 37℃) digestion in winter and spring and by thermophilic (52℃) anaerobic digestion in summer and autumn, which implies a high efficient operation strategy for agricultural and animal husbandry wastes treatment in cold and arid areas. These theoretical and experimental results provide a scientific basis and engineering reference for the application of biogas production temperature-controlled by solar energy and have important value and significance for the efficient and low-cost anaerobic digestion treatment of agricultural and animal husbandry wastes in cold and arid areas.

Thermo-ecological cost optimization of a solar thermal and photovoltaic integrated energy system considering energy level

Integrating renewable resources into traditional tri-generation systems helps to reduce fossil fuel use and emissions. A solar thermal and photovoltaic assisted integrated energy system is proposed here using high- performance cooling approaches to provide cooling, heating, and electricity. To find the best system configurations with a focus on the ecological performance, the specific thermo-ecological cost of the energy products considering energy level is optimized employing the cumulative exergy consumption over the whole life-cycle. The results show that the ideal specific costs for cooling, heating and electricity demands are 8.699, 7.129, and 1.970 J/J, respectively. Compared to the method without the energy level consideration, the specific cost of the hybrid system is 0.47 J/J higher due to the lower energy level of water products. Moreover, the specific thermo-ecological cost of natural gas has higher impacts on the performance of hybrid system than the other parameters.