Abstract

In this study, a coordinated charging scheduling model for EVs connecting to microgrid is proposed to achieve peak shaving and valley filling. In the model, we develop an EV Charging Emergency Indicator (CEI) that used to measure whether the EVs have emergent charging demand. For the EVs that have emergent charging demand, the emergent charging strategy is employed. Considering the emergent EV charging, the optimal dispatch model including all the EVs (both emergent charging EVs and usual charging EVs) is developed. The objective of the model is to minimize the overall peak-valley load difference. The proposed model considered both the randomness of the EVs connected to the microgrid and the emergent charging demand of some EVs. Finally, the simulation results show the effectiveness of the proposed model.

Abstract

Large-scale of intermittent renewables such as wind and solar are used to reduce carbon emission. Energy storage is needed to provide controllability of power flows for the energy system. Specifically, Generation-in- tegrated energy storage (GIES) systems store energy at an instance during the transformation between the primary energy (e.g., kinetic or thermal) form and electricity. The successful deployment of GIES systems requires a financing method to minimize investment risk. This includes identifying the role and interactions between stakeholders. A contract is a legally-binding agreement, which recognizes and governs the duties and rights of the contracting parties (e.g. stakeholders) to the agreement. Despite the importance of contracts, there is a limited amount of literature on project financing and the contractual models for renewable energy projects, in particular for energy storage and GIES systems. Project financing is the long-term financing of infrastructure using the projected cash as collateral. In this paper, the public private partnership (PPP) schemes for financing renewable energy projects are reviewed. This work presents a generic contractual model for the GIES system in the U.K. context. The challenges in contractual agreements be- tween contracting parties are described.

Abstract

Application of heat recovery units in building HVAC systems can significantly save the energy consumed by conditioning fresh air. The indirect evaporative cooler (IEC), used as a pre-cooling device for fresh air in the hot-humid area, recovers both latent and sensible energy from the exhaust air. In this paper, a year-around on-site performance test was carried out in a wet market located in Hong Kong. The energy performance of the two A/C systems with exhaust air heat recovery units was analyzed and compared: an IEC coupled to an AHU; a traditional heat recovery wheel (HRW) coupled to an AHU. The heat recovery of IEC and HRW were collected under typical summer operation conditions. The results show that the HRW has better dehumidification performance than IEC, but the IEC can largely reduce the fresh air temperature by handling the sensible cooling load. During the whole year, the difference in the total heat recovery between IEC and HRW is within 2%. In cooling seasons, the energy efficiency of the two systems with IEC and HRW for exhaust air heat recovery can be improved by 27.6% and 25.7% respectively.

Abstract

To meet and adapt to the increasing multiple energy demands, smart city has become the trend of the urban development. Based on this background, an operation optimization framework of urban multi-energy systems is proposed, where the power distribution network, natural gas network and transportation network are coupled by integrated energy stations. With the aim of minimizing operation costs, the model optimizes the operation strategies of renewable energy generation, combined heat and power, gas boiler, power to gas, electric chiller, absorption chiller and fast charging facilities coordinately. This model considers the traffic assignment problem for both non-electric and electric vehicles in the transportation network. Due to the advanced communication technologies, the optimal routes (with minimum travel expense) for both traveling and charging can be identified and provided for all drivers, and this routing behavior would lead to the traffic equilibrium state. To describe the steady state distribution of traffic flow, a mixed user equilibrium model is established, where the route selections for nonelectric vehicle and charging navigations for electric vehicle are incorporated. To solve the proposed nonlinear model, convex relaxation is performed. Finally, the simulation results illustrate the effectiveness of the proposed model.

Abstract

In CO2 reforming of methane solar thermochemical energy storage, the endothermic methane reforming with CO2 reaction is utilized to absorb solar energy. Although a lot of research has been done to enhance the thermochemical performance of the solar driven CO2 reforming of methane reactor, there is little research conducted investigating the geometrical effect of reactor on the reactor thermochemical performance. Moreover, the catalyst cost is anticipated to be large. Minimizing the required catalyst volume is the key to reduce the capital cost of the CO2 reforming of methane solar thermochemical energy storage system. But there is not much research investigating the geometrical effect on the catalyst volume. In this paper, a pseudohomogeneous computational model is used to simulate methane reforming with CO2 reaction in a tubular packed bed reactor. A parametric study is performed to investigate the geometrical effects of reactor on the reactor performance. The results show that methane conversion as well as outlet gas temperature increase with reactor diameter and/or reactor length increasing while the energy efficiency decreases with reactor diameter and/or reactor length increasing. There is a trade-off between increasing methane conversion and decreasing energy efficiency. As the required catalyst volume increases with reactor size increasing, there is a trade-off between increasing methane conversion and increasing catalyst volume. Another parametric study has been conducted to study the effects of reactor geometries on the required catalyst volume. The results show that the required catalyst volume can be saved by decreasing the reactor diameter due to enhanced heat transfer.

Abstract

As a high-efficiency and low-carbon energy supply mode, district energy systems (DESs) have gained rapid development recently. This paper proposes a framework for energy trading among DESs, with the aim of exploiting the synergies and complementary advantages of various energy demand profiles in DESs. Blockchain technology is utilized to facilitate energy trading. The distributed algorithm based stochastic decision-making process is developed to determine the energy trading, including the transaction quantities and prices. A chance-constrained programming model is developed for dealing with the uncertainties. The illustration of the technique is provided based on a test system.

Abstract

The distributed energy system becomes increasing popular in recent years because it can realize the cascade utilization of primary energy and integrate with renewable energy, which is energy efficient and environment-friendly. Thermal energy storage system can supplement the absorption chillers or boilers to utilize the surplus cooling and heating energy so that the primary energy efficiency of the system can be improved. This study investigates the feasibility of distributed energy system integrated with thermal storage systems in hot summer and cold winter areas. The energy and economic performance of the integrated system is evaluated and compared with that without thermal storage system. The impacts of climates and building mix are analyzed. Results show that the improvement of the energy and economic performance by using the thermal storage system is limited. The primary energy efficiency of the distributed energy system is improved by around 2%. The payback period is more than 20 years.

Abstract

Heat pumps will be a major player in the future energy system for their ability to efficiently extract heat from a source at lower temperature and provide it at higher temperature using electrical work. If coupled with a heat storage tank, the system can store heat and provide it at the point in time when the electricity price is more favorable.
In this study, we present a model of the heat pump energy performance using the coefficient of performance (COP) and the Lorentz efficiency. The latter gives an indication of the offset of the actual COP from the theoretical COP. We then compare different refrigerants performance to find out which one provide the best performance for district heating application. Finally, we study the cost-optimal operation of a heat pump with and without a thermal storage tank.
Results show that ammonia is a better candidate in terms of performance compared to other selected refrigerants. The performance analysis shows that the heat pump has a better Lorentz efficiency for lower COPs. Finally, we show that coupling the heat pump to a thermal storage tank can reduce the electricity cost of operation.

Abstract

Distributed energy systems (DESs) exhibit potential to promote the energy market reform worldwide. In this study, a bi-level optimization model is proposed to analyze the operation of a DES that purchases high-voltage electricity and natural gas from utility companies, and supplies low-voltage electricity and heat to multiple users. To simplify the resolution process, the bi-level optimization is transformed into a single-level mixed integer linear programming model using the Karush-Kuhn-Tucker approach and Big M method. The results indicate that (i) the time-sensitive energy prices offered by the DES could smoothen the load profiles of users; and (ii) the tiered pricing scheme set up by the utility companies could maximize the utility of the ESS integrated into the DES, but the capacity of the ESS should be accurately designed to fit the corresponding pricing scheme.

Abstract

The allocation of public service resources in counties is more dependent on government investment than that in urban areas, which would reduce the availability of these services. Besides, the layout of public service facilities has a great impact on the spatial distribution of residents’ travel demands, which may affect the CO2 emissions generated by travel behaviors. Therefore, the environmental costs should be emphasized when considering the layout of public service facilities in county areas. In this study, we established a residents-autonomous-choice-based travel CO2 emissions evaluation method by introducing scale characterization factor. With this method, we figured out the total amount, the spatial distribution and reduction potential of CO2 emissions generated by residents’ medical trips in Changxing County. The results show that the total monthly CO2 emissions of residents’ medical travel behaviors in Changxing are 243.56 tons. Besides, the central area of Changxing county and Sian town have formed obvious cold spots of per capita CO2 emissions from medical travel, while Baixian and border of Xiaopu Town and Sian Town have formed obvious hot spots. By calculation, the potential capacity of CO2 reduction by optimizing the layout of medical facilities is 154.81 tons, accounting for 63.56% of the current emissions.