Abstract

Among various solar energy converting technologies, photovoltaic cells (PV) is the most widely used. However, the mismatch between the broad solar spectrum and the mono-energetic absorption of PV results in the non-absorption of photons with energy below the bandgap (Eg). Previous CPV-T systems were proposed to recycle the below Eg loss of PV. Another dominant loss, thermalization loss, could not be reduced in CPV-T systems. Moreover, CPV-T systems recycle all the energy loss as heat. In these systems, solar energy is converted to thermal energy firstly, which is further utilized to generate other products. Two converting processes increase the irreversible loss. In our opinion, the two different kinds of loss should not be treated equally without discrimination. So we proposed a solar cascade utilization system with concentrated photochemical-photovoltaic-thermochemical (CP-PV-T) processes to make the most use of the full spectrum of solar energy. The photons with energy far above Eg of PV are utilized in the photochemical process, and thus the thermalisation loss of PV cell is reduced. The below Eg loss of PV is recycled to provide heat for thermochemical process. Results show that the utilization rate of photon energy at the first 600 nm is increased to 80.68% from 44.01% with the addition of photochemical process in front of PV, and the total solar energy utilization efficiency of the proposed system is 64.24% on the design condition.

Abstract

Carbon dioxide is one major component of greenhouse gases and is mainly caused by fossil fuels combustion.Renewable energy provides a great substitution for traditional fossil fuels because of its environmental friendness and high abundance. The deployment and application of renewable energy resources is, therefore, of great significance for improving the decarbonization and availability of island’s power system. In order to address the problems caused by fluctuation features of renewable energy power generation, the utilization of energy storage measures has been increasingly proposed in recent years. This article takes the Liugong island, which is located in the Yellow Sea, as a study case and constructs an off-grid hybrid renewable energy system for this 3.15 km2 islands. Hybrid Optimization of Multiple Energy Resources (HOMER) model based on multi-objective optimization is applied to conduct the technologyeconomic- environmental analysis of proposed renewable energy systems equipped with different energy storage modes. Major simulation results demonstrate that the cost of energy, the net present cost, and the reduction rate of carbon dioxide emissions for two alternative systems are 0.191 $/kWh, 7.0 million, 89.9% and 0.293 $/kWh 10.8 million, 47.6%, respectively. According to the simulation results, hybrid renewable systems with battery storage methods perform higher feasibility at current stage.

Abstract

With the development of research on renewable energy, lignin, as the second abundant component in biomass, has attracted more and more attention. In this study, the effects of the catalyst compositions on lignin depolymerization were investigated. Ru-W/Sn-AlOx, converted about 95% lignin into liquid product and 2/3 of the liquid product can be soluble in petroleum ether at 300 °C after 12 h reaction. It meant that 2/3 of the liquid product were depolymerized to a mixture whose number-average molecular weight (Mn) was about 364. Meanwhile, the catalyst effectively reduced the char to 2%. In detail, the monomers was characterized by GC and 6% phenolic compound was get at optimized condition.

Abstract

Climate change caused by increased greenhouse gases (GHGs) is having an increasingly profound impact on human society. Urban sewage treatment processes and tailwater pollutant emissions generate large amounts of carbon dioxide, methane, and nitrous oxide, which are considered important anthropogenic GHGs. Based on the emission factor method recommended by the IPCC (Intergovernmental Panel on Climate Change) this study analyzed the carbon dioxide equivalent (CO2e) of wastewater treatment in Xiamen in 2016 and the emission reduction effect of the development of wastewater treatment for tailwater pollutants after the completion of the sponge city in 2030. The results showed that the CO2e of sewage treatment in Xiamen in 2016 was 71,366,300 t, of which direct carbon emissions comprised 29,200 t and energy consumption and indirect carbon emissions from flocculants comprised 71,337,100 t. In 2016, the amount of GHGs directly generated from the discharge of sewage tailwater pollutants was effectively reduced by 34.11%. Under the same sewage discharge in 2030, compared with the traditional model before the upgrade, the construction of sponge city can effectively reduce carbon emissions by 27.12%, and the emission reduction effect would be significant.

Abstract

This paper developed a new control strategy of distributed battery storage in response to price signal as an effective way of demand side management, using dynamic programming algorism to calculate the hourly power use from grid. An office building in Shenzhen, China was studied, verifying the feasibility of the control strategy. The result turned out that the total electricity cost can be saved by 28.1% comparing with a system without distributed battery storage, and by 8.1% comparing with a system where the distributed battery storage operates in the strategy of constant grid power taking.
Furthermore, the relationship of electricity cost with battery size and maximum charging/discharging power was studied. Based on the model, capacity and maximum charging/discharging power of battery fit well with a segmented linear model, in the range of practical application. The maximum charging/discharging power of battery storage system and minimum electricity fee could be fitted into a quadratic polynomial model. These findings could provide information and give reference for battery storage system design and operation.

Abstract

In this paper, a transient preventive control method for wind power system, based on the information of generator power angle, angular velocity and voltage, is proposed. The objective function is the minimum of the total control amount. The required preventive control action can be efficiently solved via a linear programming model with the phase trajectory sensitivities-based constraints. The method aims to keep the online preventive transient stability with the wind power integration. The validity of the method is verified through 2DC system.

Abstract

Most of phase change materials have an obvious density change during solid-liquid phase change, which is along with the volume change of phase change materials, and results in the formation or disappearance of the void cavities based on the encapsulation methods. Void cavities play ignorable roles in the phase-change process, while their influence in the composite porous phase change materials were hardly taken into account in the literatures. In this work, the effect of void cavities on the heat transfer of the porous phase change material has been studied for the first time by a two-dimensional lattice Boltzmann method. The high thermal diffusion coefficient and low conductivity of void cavities show significant influence on not only the temperature distribution but also the energy storage performance. This simulation model gets closer to the real application, which holds great promising for being applied in the guidance on the thermal management system design.

Abstract

In the case of small current grounding system, the fault current is too small to select the fault feeder. In order to solve this problem, this paper proposes a method based on Ensemble Empirical Mode Decom-position (EEMD) for fault feeder selection of distribution lines. Firstly, the zero-sequence current of all feeders is decomposed by the ensemble empirical mode decom-position, then the kurtosis calculation is performed on the decomposed Intrinsic Mode Function (IMF), and the transient high-frequency components are adaptively selected and the transient high-frequency energy is calculated. Defining fault credibility based on transient high frequency energy. Finally, the fault credibility of all feeders is compared, and the fault feeder selection result is given. The simulation results of PSCAD show that the method has high precision and is not affected by factors such as transition resistance, fault distance and initial fault angle.