Abstract

Energy system models need to adapt to better represent the new challenges brought by a changing scenario regarding technologies development and policy making. The mixed integer linear programming based approach proposed in this study wishes to handle the impacts of these changes on potential investments in distributed energy systems, whose design is to be determined for a time horizon lasting several years with parameters that might change even substantially in such timespan. In order to test the approach, a scenario representing a residential district with high penetration of electricity production from non controllable sources (photovoltaic panels) is used as a test case. The investment decision under examination is when to possibly deploy a battery system to deal with the production surplus generated during the day by the mismatch in production and demand. While electricity can be fed into the grid by taking advantage of a feed-in tariff scheme, this could not be the most economically favorable approach due to the dropping costs of the Lithium-ion battery systems in the near future. Results show that for the case study under analysis investing into batteries appears not convenient in terms of overall costs, although the best alternative solution provided with storage systems is only slightly more expensive.

Abstract

A district energy system based on “thermal bus” was proposed, in which the heating and cooling water transmission processes shared one set of the distribution pipe network. Combined with the gas energy stations, ground source heat pumps, small-scale photovoltaic power stations and rooftop solar collectors and other facilities, it provided the users in the region with heating in winter, cooling in summer and power supply all year round. From the perspective of the bidirectional (supply/return) flow of heat energy along the thermal bus, the mathematical model of the main equipment applied for the source, pipe network, load and storage was established. The optimization model with the lowest system operation cost was proposed considering the fuel cost, the external electricity purchase fee and the satisfaction degree of all users’ energy demand. The operation cost and energy consumption of the regional energy system scheme and the traditional distributed energy system scheme are studied by a practical case study. The results showed that the new scheme reduces the operating cost by 21.5% and 16.8% respectively under the typical weekly scenarios of cooling in summer and heating in winter. When no storage equipment was used, the new scheme reduced the amount of purchased electricity in summer and winter by 4.1% and 5.2% respectively.

Abstract

The article presents an experimental validation of an algorithm for determining transient stresses within pressure components which are extensively employed in industry. The algorithm is based on the solution of the Inverse Heat Conduction Problem (IHCP) and incorporates temperature measurements on the outer surface of the analysed components. For validation purposes, a laboratory stand was modernised and 19 new dedicated strain gauges (SG) were installed. The novelty of this work is the validation of calculated transient stresses on the component’s outer surface by means of tensometric methods. A crucial aspect is the appropriate correction of the measured values of strains because the measure properties of SGs vary with temperature. The scope of the article covers an analysis of the stresses on the cylinder’s inner surface as well. The calculated and measured values were compared to values obtained from a generalized theory of quasi-state heating, which incorporates a thermocouple located in the component wall. The agreement between all methods was satisfactory. This broadly validated inhouse algorithm is suitable for comprehensive monitoring of working conditions of critical components in various industrial installations.

Abstract

The high penetration of renewable energy incurs serious power fluctuations in the power system. The electric vehicles (EVs) under the centralized control tend to provide considerable regulation capacity for the power system. In the existing modeling methods for centralized EVs, the accurate control results for the regulation services were achieved by modeling each EV individually. However, the computational complexity was a serious problem for modeling large scale EVs. In this paper, a reduced modeling method for centralized EVs is developed by describing a population of EVs with a partial differential equation (PDE). This PDE modeling method uses a finite number of state-of-charge (SOC) intervals to describe the flows of charging, idle and discharging EVs. Considering the three connecting states (CNS) of EVs, this PDE modeling method realizes the power regulation for centralized EVs by changing the CNS of EVs located in different SOC intervals. Comparative simulations validate that the PDE modeling method for large scale centralized EVs achieves high control accuracy and high computational efficiency.

Abstract

In the last decade, the behavior of granular materials has great significance for chemical engineering and petroleum engineering. This multiple process can affect how a granular material responds when exposed to external perturbations. Traditional studies mainly focus on the macroscopic performance of granular materials by using experimental methods, which tend to be implicitly agnostic to granular structures, however, there are few reports on the mechanism of the mechanism such as the mechanism of rupture and evolution. To address this challenge, we treat granular materials as spatially-embedded networks in which the particles (nodes) are connected by weighted edges. We employ community detection network analysis method to find sets of closely connected particle clusters and characteristic chain-like structure that is reminiscent of force chains based on the discrete element method. A group of tightly connected communities and branching chain structures are founded and the three-dimensional properties of granular materials under different fluid conditions are studied. The results show that the granular contact network exhibit a very clear community structure and network analysis method provides new viewpoints to underlying and generate a new perspective of describing granular material problem compared with traditional methods. The distribution of force chain is consistent with an exponential distribution and the high-pressure force chain network exhibit compact instead of branching structure communities. And granular matter displays traits of self-organization forming complex force network which arrange in response to applied load or compression and more specifically force network rearranges prominently when the applied pressure is disturbed. These results provide new tools for considering and reducing descriptions for the structure of force chain network.

Abstract

The North China Plain (NCP) is the largest groundwater irrigation area in China, with about 6.5 million hectares of cultivated land and more than 1 million irrigation wells. Totally there are about 20 billion m3 of groundwater that pumped for irrigation each year. The exploitation of groundwater in NCP leads to the continuous decrease of groundwater level. The average depth of groundwater is more than 20 m, and the deepest groundwater level is 100m beneath the ground surface. As the groundwater level is low, the energy use for pumping in NCP is huge, which leads to high carbon emission. This paper reveals the nexus of water-energy in NCP based on the experiments of agricultural irrigation wells. The volume of the pumped water and the energy is measured, and the correlations between the water and energy are established for irrigation wells of different depth. Based on the groundwater level of NCP and the location of irrigation wells, the total energy use for agricultural pumping is calculated. As a comparative study, this paper calculates the potential benefit of CO2 emission reduction, assuming the groundwater is pumped by a photovoltaic system instead of the state power grid. The results show that the photovoltaic pumping system can reduce CO2 emission by 1.87 million ton/year, comparing to the state power grid. The surplus electricity could replace thermal power and bring additional 2.67 million ton of emission reduction benefit per year.

Abstract

Energy production and consumption in cities are both inextricably linked to urban form that in itself is driven by land use planning. Yet, little is known as to how changes in land use can impact energy self-sufficiency in cities, whereby in-boundary energy production is able to satisfy in-boundary consumption needs. In this paper, we develop a workflow to model how urban energy selfsufficiency changes under various scenarios of land use change. We then apply this method to an empirical dataset for Palo Alto, a mid-size city in California, USA. Results indicate that as urban density is increased through land use change, urban energy self-sufficiency decreases, prompting the need for the joint consideration of energy efficiency and other measures with land use planning. In addition to demonstrating the importance of land use as an underexplored lever for urban energy use, our results have practical implications for the deployment of distributed energy resources (DERs) in cities, particularly solar energy.

Abstract

High solar irradiance concentration on multi-junction (MJ) solar cells leads to extremely high cell temperature, which significantly reduces cell efficiency and can lead to cell damage. Therefore, heat dissipation via cooling techniques is essential for photovoltaic solar cells under high concentration. This work develops a 3D thermal model for an assembly of four MJ solar cells with a Fresnel-based HCPV/T system and investigates the capability of active cooling to maintain a maximum solar cell surface temperature under the operating limit (i.e. 80°C). Solar cells temperatures are predicted for different concentration ratios (CRs) and inlet water velocities, varying between 200X–1000X and 0.01–0.4 m/s, respectively. At a CR of 1000X and a water velocity of 0.3 m/s, a maximum cell temperature of 79.2°C can be achieved, which is below the maximum operating temperature. Furthermore, the outlet water average temperature for multiple concentrator photovoltaic (CPV) assemblies were performed. The results showed that the solar cells’ temperatures decreased with increased inlet water velocity, and sufficient temperature uniformity was achieved by active water cooling. In addition, the outlet water’s average temperature increased considerably with the number of CPV assemblies. It was found that with four CPV assemblies using a moderate inlet water velocity of 0.01 m/s, the average outlet water temperature rose from input temperature i.e. 25°C to 44°C and 62°C for a CR of 300X and 600X, respectively.

Abstract

Although not yet a mature technology, biomass energy with carbon capture and storage (BECCS) is expected to be the leading negative emissions technology deployed over the 21st century to reduce greenhouse gas (GHG) emissions. In this paper, a novel BECCS cycle using exhaust gas recycling (EGR)-enhanced biomass gasification is described and analysed. This cycle combines an atmospheric gasifier and an Otto cycle engine operating under an oxy-gasification/combustion CCS scheme. Exhaust gasses from the Otto cycle, rich in CO2 and at high temperature, are recycled to the gasifier to enhance syngas production. Analysis of a representative numerical model illustrates how EGR creates higher system efficiency and lower specific CO2 emissions while allowing for lower gasifier O2 equivalence ratios (E/R). Compared to a similar power cycle without EGR, the proposed cycle improved system efficiency from 21.7% to 28.8% while reducing specific CO2 emissions from the cycle by 25%.

Abstract

Influenced by the increasing human activities, the urban water balance system and energy balance system have undergone significant changes. The interaction between urban water system and energy system is more significant. Based on the traditional urban water-heat coupling scheme, urban water consumption and urban anthropogenic heat emission are considered in the process of the water balance and energy balance in this study. A new coupling scheme of urban water balance and energy balance is constructed. It provides technical support for urban water-heat coupling simulation.