| Author: | Zhang, Yijie |
| Title: | Investigation of flexible energy supply with pavement-integrated solar photovoltaics toward carbon neutrality in urban areas |
| Advisors: | Yang, Hongxing (BEEE) Xu, Zhao (EEE) Cao, Sunliang (BEEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Pavements Pavements -- Environmental aspects Solar energy Photovoltaic power generation Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Environment and Energy Engineering |
| Pages: | viii, 11, 194 pages : color illustrations |
| Language: | English |
| Abstract: | The energy crisis and environmental challenges have spurred the advancement of renewable energies, particularly solar photovoltaic (PV) systems, to meet global carbon neutrality targets. However, the installation of PV systems in limited urban spaces, coupled with the need for onsite electricity provision, underscores the necessity for innovative solutions, such as the novel solar pavement technology, pavement-integrated photovoltaic/thermal (PIPV/PIPVT) technology. Additionally, the rapid proliferation of PV installations, characterized by intermittent and fluctuating power generation, imposes a strain on grid transmission and exacerbates renewable energy curtailment. To address these challenges, the integration of energy storage into the distributed energy community is imperative for facilitating high penetration of renewable generation. Key research priorities include system sizing and flexible operation design. Despite the current prominence of distributed renewable energy systems in research, their models often lack accuracy due to the absence of reliable experimental validation and oversight of critical economic considerations. Furthermore, the potential of novel renewable forms and energy storage applications, such as PIPV, façade PV, and bi-directional electric vehicles, remain largely untapped, hindering efforts to enhance the flexibility and resilience of urban energy communities. This study first initiates an exploration of a fundamental model for innovative solar pavement technology within urban environments, namely pavement-integrated photovoltaic (PIPV). Through a combination of numerical analysis and field experimental trials, a thermal-electrical mathematical model is developed for PIPV modules. This model is constructed using the 2D alternative direction finite difference method and a 5-parameter PV model, resulting in mean absolute percentage errors of 1.68% and 3.60% for PV cell temperature and output, respectively. Experimental findings reveal that, on a sunny day, PIPV systems can achieve an accumulative output of 0.68 kWh/m2, with a corresponding PV generation efficiency of 14.7%. Parametric analyses suggest the use of epoxy resin filling over air filling, with the former resulting in an annual maximum reduction of PIPV module surface temperature by 8.4% in Hong Kong. In addition to the evident mitigation of heat island effects during summer, our observations indicate the potential for snow melting potential in winter, as evidenced by a surface temperature increase of 1.02°C in Shanghai. Furthermore, the incorporation of a thermal collector extends the functionality of the proposed solar pavement to encompass the PIPVT module, capable of supplying both electricity and hot water. The mathematical models for the PIPVT system are meticulously established and validated through a series of outdoor and laboratory experiments. Comparative analysis of 2D finite difference models for PIPV/PIPVT modules, considering both adiabatic and diabatic ground boundary conditions, demonstrates the improvement of introduction ground heat transfer. Experimental results demonstrate high accuracy in predicting both module surface temperature and electricity generation, with mean absolute percentage errors within 2.5% and 3.10%. Parametric analyses on crucial system design, ground boundary influence, and weather conditions provide valuable insights. The thermal efficiency variations, influenced by ground conditions, can reach up to 12.28% for high mass flow rates, with water tank temperature peaking at 34.7°C. Moreover, the impact of the tank volume is significant, with a 32.76% increase in thermal efficiency observed when transitioning from 25L to 150L. Increasing solar irradiance amplifies total heat flux, resulting in a 41.47% thermal efficiency enhancement, with 11.38% ground heat flux influence, for medium water tank volumes and velocities under 1000W/m2 solar radiation. Introducing a novel operation strategy aimed at renewing inlet water after achieving the desired tank temperature leads to a marked reduction in average summer tank temperatures. Correspondingly, electrical efficiency increases by 1.26% (Hong Kong), 0.93% (Shanghai), and 0.52% (Beijing), compared to the basic fixed operation time strategy. This strategy also correlates with a corresponding reduction in the average summer road surface temperature gap of -1.88 °C (Hong Kong), -1.51°C (Shanghai), and -0.93°C (Beijing), with the conventional asphalt concrete road, showcasing its efficacy in mitigating the urban heat island effect in metropolitan areas. To better develop the novel renewable energy technology, the utilization potential of the innovative solar pavement technology is assessed across different cities in various climate zones. Initially, the potential of PIPV application is analyzed seasonally in 255 Chinese cities, revealing significant reductions in average road surface temperature during summer, with a maximum decrease of -4.18°C, and increases during winter, such as in Beijing reaching up to 3.36°C. These results indicate alleviation of the heat island effect and enhanced snow melting capacity, with average road surface temperature reductions ranging from -1.37°C to -4.18°C during summer and a maximum increase of 0.47℃ during winter. The annual electricity potential of PIPV systems ranges from 0.70 to 1.83 kWh/Wp, with cities in western and northeastern China exhibiting higher PV generation potential. Subsequently, techno-enviro-economic analyses of the novel PIPVT module are conducted for six provincial metropolises across different climate zones in China. Results demonstrate that Hong Kong excels in summer energy, economic, and environmental aspects, with a summer tank temperature of 34.23°C, thermal efficiency 𝜂𝑡 at 59.18%, temperature gap with the conventional road surface Tgap at -4.33°C, and annual reduced carbon emission Ecar at 290.22 kg CO2. Regarding annual electrical output and winter Tgap, Lhasa performs optimally with 58.92 kWh/m2 and 18.57°C, respectively. Additionally, northern provincial cities are advised to implement PIPVT with seasonal mode changes to facilitate summer hot water supply and winter road surface temperature increase. The proposed urban renewable technology serves as the foundation for establishing a novel distributed energy system prototype with enhanced energy flexibility and resilience. Expanding beyond conventional distributed rooftop solar PV battery systems, this distributed energy system incorporates bi-directional electric vehicles, onsite PV façades, and nearby PIPV systems. In Hong Kong, diverse PV installation types yield varying annual renewable outputs of 1.34 (rooftop), 0.81 (façade), and 0.97 (pavement) kWh/Wp. Integration of bi-directional vehicle storage and remote PIPV installations notably boosts the community’s renewable self-sufficiency while reducing the annual equivalent battery cycle number. Furthermore, to increase the system flexibility, this study proposes an improved time-of-use (TOU) strategy based on the battery pre-charging schedules during valley grid tariff hours and predictions for renewable generation and load demand. This study employs the two-layer long short-term memory machine learning model and establishes a multi-physics 2D room model to estimate the uncertain load demand and renewable supply, achieving PV generation RMSE of 0.052 (pavement), 0.059 (rooftop), and 0.042 (facade) kWh, space cooling load RMSE of 6.96W/m2 and MAPE for indoor air temperature at 2.21%. Implementing the proposed TOU strategy significantly enhances the community's net present value, albeit with a decrease in renewable self-sufficiency rate. To conclude, this study develops the pavement-integrated solar photovoltaics(/thermal) module models and, on the basis of which, investigates the flexible energy supply system for a distributed energy community with different load characteristics and electric mobility, targeting higher system flexibility and resilience. With solid experimental and numerical simulations, this study investigates the design guidance for pavement-integrated solar photovoltaics(/thermal) systems under different climate zones and assesses the ground transfer condition impact for the solar pavement technology, especially in the urban area. The result of this study also unveils the application potential for different metropolises in China from the techno-enviro-economic aspects. Based on the flexible energy community design, this study proposes a novel energy community prototype with additions of the solar pavement, onsite battery for the building cluster, and bi-directional electric mobility. The system performance comparison with the basic building-to-vehicle-to-building prototype is investigated and the operation strategy design recommendations are provided for the proposed energy community prototype with higher system flexibility. The results of this study could provide a valuable research foundation for future distributed renewable energy community design and solid guidance for researchers in the field of renewable energy system design. |
| Rights: | All rights reserved |
| Access: | open access |
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