• Energy Research
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Abstract Compared with other traditional energy sources, renewable energy, which results the less pollution and has numerous resources, is a significant factor in addressing the current issues of the serious environmental pollution and the resource depletion. Large-scale renewable energy integrated to the grid could bring change in both morphological structure and operation modes of energy transmission. Therefore, it is necessary to research the evolution mechanism of the future transmission network with a high proportion of the renewable energy. In this paper, an evolution framework of power system with high proportion of renewable energy is proposed. Firstly, a network equivalence and simplification based on power transfer distribution factors (PTDFs) is proposed, which can effectively simplify the decision-making process of evolution of large-scale power system. Then, an annual production simulation (8760 h) which takes into account renewable energy and load fluctuations is used to find out the bottleneck of the power grid. Based on the above methods, evolution strategy of power system with high proportion of renewable energy is studied for finding out optimal expansion strategy. A real power system of Zhejiang province is used as a test system. Test results demonstrate the feasibility of the proposed evolution framework.

Abstract Standardization of biogas technology is immensely important for the promotion of the biogas industry worldwide. China has built a complete biogas standard system, which is divided into common, household biogas, biogas engineering, biogas digester for domestic sewage treatment, output utilization, and service system standards. The problems and potential barriers for biogas standardization in China are analyzed and come down to sluggish standard, overlapped standard, government-dominated standard, and lagging international standard. Accordingly, all potential biogas standards should be evaluated and placed under the same department. China Biogas Society and China Association of Rural Energy Industry play leading roles in developing enterprise or group/association biogas standards and ISO biogas standards. The bio-natural gas standard system and experimental standardization should be developed as well to replenish biogas standard system. A paradigm shift in biogas standardization should be from government-dominated to market-oriented model. The lessons learned for other developing countries includes expanding standardization to multi-aspects to realize full lifecycle control and management, building rapid responding mechanism of standardization to adopt industry transformation, integrating outdated standards into new versions, and establishing market-based standard system.

Abstract A novel solar concentrating PV and thermal (CPVT) combined system with beam splitter and compact concentrator structure is proposed in this study. The system structure and its design method are provided. The optical filter is designed and the incident light angle effect on the beam splitting performance is investigated. Solar concentrating simulations are conducted and the relevant results reveal that the CPVT combined system can provide a high solar concentration uniformity. The evaluation results of configuration and optical analyses indicate that when all the other parameters are settled, the optimal installation height of the solar receiver tube is 923.0 mm. The influence study of sun tracking accuracy on the system optical performance is launched. It is concluded that when the tracking error increases to 1.0°, the overall optical efficiency is 66.2%. The thermodynamic analysis results indicate that the PV conversion and overall energy efficiencies of the CPVT system are 30.5% and 26.6%, which are both higher than those of the normal CPV system. Moreover, the operating temperature effect investigation of solar thermal receiver tube is conducted. The results show that an optimal solar thermal receiver tube temperature (356.0 °C) exists, which can result in the maximum total output power.

Oxy-MILD (Oxygen Moderate and Intense Low- Oxygen Dilution) combustion is one of the most promising technologies for the mitigation of CO2 emissions from coal-fired furnaces, benefiting from its good performance in flame- temperature controlling and NOx reduction. Under oxy-MILD mode, the combustion or co- firing of biomass (CO2-neutral) can achieve “negative CO2 emissions”. In this paper, oxy- MILD biomass co-firing is numerically studied by CFD modeling for the IFRF furnace NO.1, where Guasare coal and Olive waste are co-fired under air-MILD and oxy-MILD conditions, respectively. The effects of biomass co-firing ratio (0–30%, energy basis) and atmosphere on the temperature and heat flux distribution, and NOx emissions are discussed. The modeling results show that under MILD combustion mode, both oxy-combustion and biomass co-firing can generate a more moderate temperature distribution and lower NOx emissions than air- combustion and coal combustion, respectively. When biomass co-firing ratio increases from 0% to 30%, under oxy-MILD combustion mode, the peak temperature linearly decreases by 28 K and the NOx emissions decrease by 141 ppm ; while under air-MILD combustion mode, the peak temperature increases by 15 K and the NOx emissions decrease by only 73 ppm. This modeling work suggests that oxy-MILD biomass co-firing is a more promising technology to achieve “negative CO2 emissions” in coal combustion, with lower furnace temperatures as well as NOx emissions.

Abstract Sunlight Concentrated and transmission for daylighting via optical fibers is a booming technology of direct utilization of solar energy. It uses optical fibers to introduce sunlight deep into building interior. In this work, a sunlight concentrating and transmitting system via plastic optical fibers was developed and tested. This study addressed the cooling problem of the plastic optical fibers under highly irradiation. Polymethylmethacrylate (PMMA) plastic fibers have a strong absorption effect on infrared light, which means that plastic fibers heat up so much when they transmit focused sunlight that they burn. In this study, a comprehensive cooling approach was developed to solve the overheating problem of plastic optical fibers, which consists of an infrared filter, cooling water and a homogenizer. The transmission efficiency of the system was measured to be about 15%. Experiments show that the comprehensive cooling measures developed can ensure that PMMA plastic optical fibers are in a safe temperature range. This shows that it is feasible to use low-cost plastic optical fibers instead of expensive silica fiber to transmit high flux for daylighting.

By establishing a two-stage model in which a monopolization firm first chooses R&D input and then the quantity of energy, this paper compares the different effects of two regulatory policies: feed-in tariff (FIT) and renewable portfolio standard (PRS). The results show that FIT is more efficient than RPS to increase the quantity of renewable energy (installed capacity) and to stimulate the R&D input to reduce costs. And RPS policy is more efficient to reduce the carbon emissions and to improve the consumer surplus. Apart from existing findings, we cannot obtain the accurate conclusion about the effects of social welfare under the two policies. The effects of two policies on the social welfare heavily depend on the level of negative externality.

Understanding and simulating the dynamic characteristics of the hydro-turbine governor system is essential to guarantee the safety of the hydro-power systems. This study proposes a modification method of the water head at the draft tube inlet, which is to discretize the draft tube and introduce the excitation term of the vortex rope. The proposed approach is applied for the modeling of the hydro-turbine governor system. The proposed model (Model I) is verified by means of a comparison with a second model (Model II) of the hydro-turbine governor system model without considering the vortex rope and verified against the experimental data during the load reduction. The model developed is accurate providing errors of the water head, inlet water head and flow of the hydro-turbine for Model ¿ are within ±3.3%, ±2% and ±5%, respectively. The proposed model overcomes the limitations of Model ¿ in the time-domain and frequency-domain since that only provides the average pressure at the draft tube, which do not reflect the pressure fluctuation and energy fluctuation. Instead the proposed model allows to capture and model the energy fluctuation during the load reduction as shown in the experimental results. The proposed model promotes the development of the hydro-turbine governor system model. Peer Reviewed

Abstract Large volumes of polymeric waste, including natural biomass residues and synthetic waste, motivate the development of a general, robust and flexible process for mining the energy and resources contained in these wastes. By analyzing the positive and negative aspects of current, conventional technologies for the recovery of energy from polymeric waste, an integrated concept of a hybrid technology combining biochemical (anaerobic digestion, gas fermentation, carbon chain elongation) and thermochemical conversion processes (pyrolysis, gasification, hydrothermal carbonization) was proposed. The hybrid technology aims at simultaneously enhancing the efficiency and stability of biochemical conversion, controlling the gaseous and aqueous pollution from thermochemical conversion, and sequestering carbon. This paper presents a detailed review of state-of-the-art research relating to the principles, technical feasibility and practices involved in each technical link between the two conversion processes.