| 1. |
- Zhang, Tingshen, et al.
(författare)
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Vibration energy harvesting system based on track energy-recycling technology for heavy-duty freight railroads
- 2022
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Ingår i: Applied Energy. - : Elsevier Ltd. - 0306-2619 .- 1872-9118. ; 323
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Tidskriftsartikel (refereegranskat)abstract
- To ensure the efficient and safe operation of train transportation systems, the track vibration resulting from train movement can be utilized to power the sensors for intelligent applications. This paper presents a vibration energy harvesting system based on track energy-recycling technology for heavy-duty freight railroads. The energy-recycling system includes a vibration conversion module, a generator module and a power storage module. The irregular vertical vibrations produced by contact between the wheel and railroad are considered. The vibration conversion module converts the reciprocating vertical displacement into a one-way rotation through a scissor linkage and slider mechanism. A three-phase generator is coupled with an energy conversion module shaft and generates a three-phase direct current. Then, after rectification and filtering, the electricity is stored in the supercapacitors. Theoretical analysis, dynamic model analysis and mechanical simulation verify the dynamic response of the system under input excitation. Furthermore, mechanical testing and sensing (MTS) machine tests yield a 73.38% maximum mechanical efficiency with a 7.44 W peak power. Moreover, the charging tests of the proposed system with a supercapacitor indicate that the proposed system is suitable for self-powered sensors in railroads.
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| 2. |
- Zhang, Z., et al.
(författare)
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Carbon mitigation potential afforded by rooftop photovoltaic in China
- 2023
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Ingår i: Nature Communications. - : Nature Research. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Rooftop photovoltaics (RPVs) are crucial in achieving energy transition and climate goals, especially in cities with high building density and substantial energy consumption. Estimating RPV carbon mitigation potential at the city level of an entire large country is challenging given difficulties in assessing rooftop area. Here, using multi-source heterogeneous geospatial data and machine learning regression, we identify a total of 65,962 km2 rooftop area in 2020 for 354 Chinese cities, which represents 4 billion tons of carbon mitigation under ideal assumptions. Considering urban land expansion and power mix transformation, the potential remains at 3-4 billion tons in 2030, when China plans to reach its carbon peak. However, most cities have exploited less than 1% of their potential. We provide analysis of geographical endowment to better support future practice. Our study provides critical insights for targeted RPV development in China and can serve as a foundation for similar work in other countries.
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| 3. |
- Qiu, R., et al.
(författare)
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A model-experience-driven method for the planning of refined product primary logistics
- 2022
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Ingår i: Chemical Engineering Science. - : Elsevier Ltd. - 0009-2509 .- 1873-4405. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Logistics planning is regarded as the most complex part of supply chain management for refined products. A vital knowledge gap still exists in understanding the trade-offs between the economy and the practicability of logistics schemes. Focus on this issue, this paper proposes a model-experience-driven method for the planning of refined product primary logistics. The method couples three sub-modules: (1) use coordinator's preference information and convex function interpolation to construct satisfaction indicator; (2) set up a multi-objective model for logistics coordination and optimization considering supply adjustment and secondary delivery; (3) adopt the augmented ɛ-constraint method to obtain the Pareto solutions and balance the economy and satisfaction indicators. The method is verified by a small-scale system, where the satisfaction degree increases by 77% while the logistics cost remains unchanged. The method is also successfully applied to a large-scale system with 29 refineries and 196 market depots, where Pareto logistics schemes are obtained and the supply–demand imbalance is greatly eased. The proposed method can help provide theoretical guidance for real-world logistics planning.
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| 4. |
- Wei, X., et al.
(författare)
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Assessing benefits in the flexibility of refined oil logistics from pipeline network integration reform : A case from South China
- 2022
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Ingår i: Chemical Engineering Science. - : Elsevier Ltd. - 0009-2509 .- 1873-4405. ; 253
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Tidskriftsartikel (refereegranskat)abstract
- The pipeline network integration reform enables unified management of pipelines from different entities. For refined oil logistics, this paper proposes a framework based on the MILP optimization model to quantify its flexibility. Considering the uncertainty, three disturbances occur in the logistics concurrently, and 10,000 simulations are performed to obtain the turnover cost. The ratio of pipeline transportation cost to the calculated average turnover cost is defined as the flexibility indicator. Taking China's largest refined oil pipeline network as an example, the results show that the flexibility rises 8.9% after the reform. The paper also quantifies the impact of the reform on logistics flexibility in South China, which is embodied in achieving lower freights and GHG emissions, lower impact by fluctuations, higher pipeline utilization, more efficient oil product turnover, and the avoiding of depot shortages when facing logistical disturbances. The underlying reasons for the results and 3E analysis are analyzed.
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| 5. |
- Zhang, Y., et al.
(författare)
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A techno-economic sizing method for grid-connected household photovoltaic battery systems
- 2020
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Ingår i: Applied Energy. - : Elsevier Ltd. - 0306-2619 .- 1872-9118. ; 269
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Tidskriftsartikel (refereegranskat)abstract
- Battery storage provides an effective solution to alleviate the burden of the intermittent photovoltaic production on the grid and increase photovoltaic penetration in residential houses. Despite several existing work dedicated to the evaluation of photovoltaic battery system, the research on system sizing and operation strategy of the household system still has substantial areas to be explored such as techno-economic analysis under different electricity tariffs and comprehensive parametric analyses. In this paper, the mathematical model of a photovoltaic battery system is developed to investigate system performance, based on the various economic and technical indicators. This study demonstrates that the integration of battery energy storage could increase the value of self-consumption and self-sufficiency rates while making payback period longer. Substantial photovoltaic battery systems have been simulated under practical dynamic electricity tariffs in a typical electricity market. Eight cases with different technical performances from the recommended reference combinations are compared and studied in detail. The energy flows among photovoltaic, battery bank, grid and household user are discussed, revealing that systems with high self-sufficiency rate lead to more schedulable photovoltaic production, sold electricity and lower battery usage rate than those with high self-consumption rate. Besides, the entire lifecycle economic analysis indicates that a higher self-sufficiency rate refers to higher initial investment but shorter payback period and larger profit. The revenues breakdown of the cases shows that subsidies have a significant impact, especially for cases with high self-sufficiency rate. The levelized cost of electricity of photovoltaic and photovoltaic battery systems ranges from 0.373 to 0.628 CNY/kWh, demonstrating the possibility of partial grid parity under the current situation in Shanghai. © 2020 Elsevier Ltd
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| 6. |
- Zhu, L., et al.
(författare)
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Unpacking the effects of natural gas price transmission on electricity prices in Nordic countries
- 2024
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Ingår i: iScience. - : Elsevier Inc.. - 2589-0042. ; 27:6
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Tidskriftsartikel (refereegranskat)abstract
- Since the Russia-Ukraine war in February 2022, European electricity prices have experienced considerable turbulence, primarily attributed to a shortage in the natural gas supply. We investigate the relationship between natural gas prices in the European continent and electricity prices in Nordic countries before and after the outbreak of war. Despite the low proportion of natural gas electricity generation, the empirical analysis reveals both direct and indirect transmission paths for natural gas prices in Nordic countries. Meanwhile, the theoretical analysis demonstrates how Nordic renewable (wind and solar) and other non-gas generators exercise market power through price bidding in the anticipation of an increase in gas prices or a shortage of gas supply, which results in higher electricity prices. Understanding the underlying factors and dynamics driving substantial price fluctuations in the Nordic electricity market is essential for comprehending the intricate interconnections within the European energy landscape.
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| 7. |
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| 8. |
- Chen, Y., et al.
(författare)
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Theory-guided hard constraint projection (HCP) : A knowledge-based data-driven scientific machine learning method
- 2021
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Ingår i: Journal of Computational Physics. - : Academic Press Inc.. - 0021-9991 .- 1090-2716. ; 445
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Tidskriftsartikel (refereegranskat)abstract
- Machine learning models have been successfully used in many scientific and engineering fields. However, it remains difficult for a model to simultaneously utilize domain knowledge and experimental observation data. The application of knowledge-based symbolic artificial intelligence (AI) represented by expert systems is limited by the expressive ability of the model, and data-driven connectionism AI represented by neural networks is prone to produce predictions that might violate physical principles. In order to fully integrate domain knowledge with observations and make full use of the strong fitting ability of neural networks, this study proposes theory-guided hard constraint projection (HCP). This deep learning model converts physical constraints, such as governing equations, into a form that is easy to handle through discretization, and then implements hard constraint optimization through projection in a patch. Based on rigorous mathematical proofs, theory-guided HCP can ensure that model predictions strictly conform to physical mechanisms in the constraint patch. The training process of theory-guided HCP only needs a small amount of labeled data (sparse observation), and it can supervise the model by combining the coordinates (label-free data) with domain knowledge. The performance of the theory-guided HCP is verified by experiments based on a published heterogeneous subsurface flow problem. The experiments show that theory-guided HCP requires fewer data, and achieves higher prediction accuracy and stronger robustness to noisy observations, than the fully connected neural networks and soft constraint models. Furthermore, due to the application of domain knowledge, theory-guided HCP possesses the ability to extrapolate and can accurately predict points outside of the range of the training dataset.
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| 9. |
- Ding, Y., et al.
(författare)
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Economical flexibility options for integrating fluctuating wind energy in power systems : The case of China
- 2018
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Ingår i: Applied Energy. - : Elsevier Ltd. - 0306-2619 .- 1872-9118. ; 228, s. 426-436
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Tidskriftsartikel (refereegranskat)abstract
- The inherent stochastic nature of wind power requires additional flexibility during power system operation. Traditionally, conventional generation is the only option to provide the required flexibility. However, the provision of the flexibility from the conventional generation such as coal-fired generating units comes at the cost of significantly additional fuel consumption and carbon emissions. Fortunately, with the development of the technologies, energy storage and customer demand response would be able to compete with the conventional generation in providing the flexibility. Give that power systems should deploy the most economic resources for provision of the required operational flexibility, this paper presents a detailed analysis of the economic characteristics of these key flexibility options. The concept of “balancing cost” is proposed to represent the cost of utilizing the flexible resources to integrate the variable wind power. The key indicators are proposed respectively for the different flexible resources to measure the balancing cost. Moreover, the optimization models are developed to evaluate the indicators to find out the balancing costs when utilizing different flexible resources. The results illustrate that exploiting the potential of flexibility from demand side management is the preferred option for integrating variable wind power when the penetration level is below 10%, preventing additional fuel consumption and carbon emissions. However, it may require 8% of the customer demand to be flexible and available. Moreover, although energy storage is currently relatively expensive, it is likely to prevail over conventional generation by 2025 to 2030, when the capital cost of energy storage is projected to drop to approximately $ 400/kWh or lower.
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| 10. |
- Gao, X., et al.
(författare)
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Experimental investigation of the cubic thermal energy storage unit with coil tubes
- 2017
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Ingår i: Energy Procedia. - : Elsevier Ltd. ; 142, s. 3709-3714
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Konferensbidrag (refereegranskat)abstract
- This study presented experimental investigations on the thermal performance of a thermal energy storage (TES) unit with coil tubes. A designed test rig was built and the melting heat transfer characteristics (melting front and temperature distribution) inside the TES unit were examined. The effects of charging flow rate on the overall phase change process were examined. The results showed that natural convection accelerated the thermal energy transport in the melt phase in the top region, but weakened the heat transfer in the bottom region; this resulted in the unmelt PCM at the bottom. The melting heat transfer was overall enhanced by the increase in inlet flow rate, indicating that the full charging time can be shortened by a larger flow rate.
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