Abstract

The efficient operation of Integrated Energy Systems (IES), which combine electricity, heat, and cooling, is challenged by the low predictability inherent in renewable energy sources like wind and solar power. Traditional scheduling methods, relying on day-ahead and intra-day forecasts, often fail to accommodate the deviations between forecasted and actual energy generation, leading to suboptimal performance and increased operational costs. This paper proposes an enhanced scheduling method that incorporates multiple scenarios outside the probabilistic prediction intervals to address forecast deviations. By calculating optimal scheduling schemes for these extra scenarios, the proposed method ensures that IES can adapt dynamically to real-time conditions, maintaining closer proximity to the optimal operating point. Simulation results using real power grid data from Belgium demonstrate that this method significantly reduces system costs compared to traditional scheduling approaches, effectively mitigating the economic impact of forecast inaccuracies. The study highlights the potential of scenario-based scheduling in improving the reliability and efficiency of IES under uncertainty.

Abstract

Coal-fired power units may have safety risks during deep peak shaving and rapid load changing. Therefore, a comprehensive estimating method based on Finite Element Analysis (FEA) and boiler design rules is proposed in this study. Measured data is taken as the boundary conditions for FEA, and the time related restrictions from boiler design rules are used to calculate the primary stress, inelastic strain and creep-fatigue lifetime indicators. The header at the outlet of the final-stage superheater of a 350MW supercritical boiler is analyzed, and the results show that under operating conditions of cold start-up, up to 55% depth of peak shaving and up to 1.4%/min of load change, there is no risk of plastic collapse. Inelastic strain mainly accumulates during start-up process, rather than during peak shaving. Creep-fatigue damage mainly occurs around the fillets of the branch tubes. The fatigue damage is only 0.2% after 30 years operation, with no significant thermal fatigue. But the creep damage is excessive, exceeding the limit after operation of 300 days.

Abstract

For energy efficient design, the widely used V-shaped air-cooled condensing units are not proper for the Installation space with height restrictions. This paper proposes a comprehensive design framework for air-cooled condensing unit, comprising structural design, CFD simulation, system modeling, and prototype test. A case study on an air cooler confirms the effectiveness of the design framework. The implementation of a blow-through configuration for air-cooled condensing unit enhances air flow rate, achieves dynamic pressure recovery, and optimizes component installation.

Abstract

All-day passive radiative cooling materials, which are dedicated to cool objects by reflecting solar light and dissipating heat to the cold outer space, have received extensive attention in recent years. As a common radiative cooling material, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) has high atmospheric window infrared emittance. However, the PVDF-HFP-based radiative cooler has low reflectance of sunlight and is prone to be contaminated, which would reduce the radiative cooling performance in outdoor applications. Therefore, in order to enhance the optical property and self-cleaning capability of the PVDF-HFP membrane, we herein prepared a hierarchical superhydrophobic SiO2/PVDF-HFP nanofibrous membrane by electrospinning and electrostatic spraying technique; the radiative cooling performance of the as-prepared membrane is compared with that of the commercial PVDF-HFP membrane. The results demonstrate that the hierarchical superhydrophobic SiO2/PVDF-HFP nanofibrous membrane consists of numerous stacked nanofibers and is uniformly distributed by SiO2 particles, which enable the membrane to exhibit an average solar spectral reflectance of 97.8% and an average atmospheric window infrared emittance of 96.6% (both values are higher than those of the commercial PVDF-HFP membrane). The hierarchical SiO2/PVDF-HFP membrane achieves sub-ambient temperature up to 11.5℃ under direct sunlight and 4.1℃ at night, demonstrating superior radiative cooling performance. Moreover, the hierarchical SiO2/PVDF-HFP membrane possesses excellent self-cleaning property, remarkable flexibility, and mechanical stability, which endows the membrane with promising applications in cooling vehicles, buildings, large-scale equipment, etc.

Abstract

Supercritical heat exchangers encounter a variety of non-uniform heat flux during operation, which significantly influence the flow and heat transfer processes. Numerical simulation is employed to investigate the process of supercritical water entering and leaving the heated section, which are divided into three stages: Thermal Establishment Stage, Axially Asymptotic Developed Stage, and Thermal Removal Stage. During Thermal Establishment Stage, influenced by entrance effect, the affected range in this study extends up to 150 z/d. This stage is characterized by a heat transfer coefficient higher than that of the stable state with the same bulk enthalpy. Following sufficient heating, supercritical water reaches the Axially Asymptotic Developed Stage, where the flow and heat transfer processes become independent of inlet parameters. After heating, the top wall temperature drops rapidly, primarily due to the convective heat transfer of the supercritical fluid inside the tube. The Multi-Stage Heating Approach proposed on the basis of this study can effectively relieve the heat transfer deterioration and significantly enhances the overall heat transfer performance of the heat exchanger near the pseudo-critical temperature. Results indicate that, compared to conditions without entrance effect, the overall heat transfer coefficient can increase by up to 28.15%, 58.01%, and 92.24% for one-stage, two-stage, and three-stage heating, respectively.

Abstract

Extreme high-temperature weather circumstances have also created notable opportunities for harnessing medium and low-temperature energy, particularly solar thermal energy. This study introduces an innovative binary Rankine cycle (BRC) system intending to optimise the available temperature range and enhance the energy conversion capacity. The proposed system comprises two subsystems: a reheating steam Rankine cycle (RSRC) system and a supercritical organic Rankine cycle (SORC) system. The numerical simulation demonstrates that the proposed BRC system exhibits great superiority in energy conversion compared to a single RSRC or SORC system. The proposed BRC system has a significant system efficiency of up to 25.4%, surpassing the individual RSRC (23.23%) or SORC (7.59%) system. This feature makes it highly promising for harnessing medium and low-temperature heat sources and its scale development can potentially mitigate harsh high-temperature weather conditions.

Abstract

District heating networks (DHNs) play a vital role in the transition of the heating supply of buildings to renewable sources. The sizing of the pipes of the DHN and the temperatures within the DHN each affect the heat losses and the required pumping power. In addition, the efficiency of a heat pump supplying the DHN is affected as well. Therefore, a co-planning approach that includes the operation of the DHN in the planning is required. This paper presents a co-planning approach based on real GIS data. The approach uses only five design variables (two for dimensioning the pipes, two for the supply temperature, and one for the producer). The optimal design variable configuration is determined by an optimization algorithm. The optimization includes a full year simulation of the DHN. The result of the planning process is a fully parameterized DHN with a matching supply temperature.

Abstract

Proton exchange membrane water electrolysis
(PEMWE) have received great attention for renewable
hydrogen production. In present work, a 3D multi-phase,
non-isothermal cell-level model that consider all the
physical characteristics in water electrolysis, such as
liquid water transport, proton transport in membrane
electrode assembly (MEA), electron transport in solid
electrode, gas diffusion in porous electrodes, water
evaporation, dissolved water transport in MEA and
hydrogen permeation from cathode to anode. The
numerical results show good agreement with
experimental data. The validated model is used to
analyze the effect of key operating conditions on the
voltage losses and efficiency. T0 = 80 °C is optimal for the
full range of operating current densities. However, as
current density increases, lower temperatures become
more beneficial for performance. Performance can be
improved through the development of CLs with good
activity, especially on the anode side. The above findings
provide the characteristics of gas distribution and the
influencing mechanisms of key parameters within the
cell, providing a theoretical foundation for optimal
design of PEMWE.

Abstract

For power generation compony, decisions are made rely on regulation, policy, capacity factor and company’s financial situation. The coupled use of multiple energy sources can take advantage of the complementarity of multiple energy sources to improve energy efficiency. However, the increasing number of renewables and multi-energy loads entering the energy system increases the multiple uncertainties of energy system. These decision models must capture the challenge induced by the penetration of renewable energy (RE) and the role of energy storage. In this paper, we establish a two-stage stochastic optimization model and apply Latin hypercube sampling (LHS) to dealing with correlated random variables and study the investment portfolio among conventional power generators and renewable energy with different levels of volatility. Then, multi-dimensional correlation scenario set are generated to confirm the applicability of the model. The results shown that the volatility of renewable energy increases the proportion of flexible scheduling units in the system as well as the system cost in investment and operation. Energy storage capacity is being used to address intermittence of RE to make power system stable.

Abstract

Proton exchange membrane water electrolysis
(PEMWE) has a certain fluctuating load following ability
and is an effective way to realize renewable energy
consumption. The performance and stability of PEMWE
are seriously affected by the gas-liquid countercurrent
that occurs at the interface of the anode catalytic layer
(ACL) and the porous transport layer (PTL). In this work,
polyethylene glycol (PEG) was used as an ACL ink additive
to improve slurry stability and to control the wettability
of the catalyst layer by varying the mass ratio of PEG to
Nafion. Single flow channel modelling was used to obtain
the water saturation of the ACL. The results show that
the addition of PEG to the slurry can make the slurry
more stable and improve the hydrophilicity of the ACL.
When the mass ratio of PEG to Nafion is 5:5, the water
contact angle of the catalytic layer is 72.3°, and the
performance of the electrolyzer can reach 3.07 A·cm-
2@1.9 V, which is 0.07 A·cm-2 higher than that of DOE
2025 target. This paper is innovative and instructive for
the design of CL/PTL interface in electrolyzer