The carbon‒oxygen balance has always been problematic in constructed wetlands (CWs), putting pressure on stable and efficient nitrogen removal. In this study, a novel partial siphon operational ...strategy was developed to further optimize the carbon and oxygen distributions of a partially saturated vertical flow CW (SVFCW) to enhance nitrogen removal. The removal performances of the partial siphon SVFCW (S-SVFCW) were monitored and compared with those of the SVFCWs at different partial siphon depths (15 cm, 25 cm and 35 cm) in both the warm and cold seasons. The results showed that the partial siphon operating strategy significantly facilitated the removal of ammonia and total nitrogen (TN) in both the warm and cold seasons. When the partial siphon depth was 25 cm, the S-SVFCWs had the highest TN removal efficiency in both the warm (71%) and cold (56%) seasons, with an average improvement of 46% and 52%, respectively, compared with those of the SVFCWs. The oxidation‒reduction potential (ORP) results indicated that richer OPR environments and longer hydraulic detention times were obtained in the S-SVFCWs, which enriched the denitrification bacteria. Microbial analysis revealed greater nitrification and denitrification potentials in the unsaturated zone with enriched functional genes (e.g., amo_AOA, amo_AOB, nxrA and nirK), which are related to nitrification and denitrification processes. Moreover, the strengthening mechanism was the intensified oxygen supply and carbon utilization efficiency based on the cyclic nitrogen profile analysis. This study provides a novel partial siphon operational strategy for enhancing the nitrogen removal capacity of SVFCWs without additional energy or land requirements.
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•A partial siphon strategy created periodic redox conditions in partial-unsaturated zone.•A partial siphon strategy promoted oxygen supply and carbon utilization abilities in VFCWs.•A partial siphon strategy in VFCWs increased TN removal by 40 % compared to the control.•At low temperature, 25 cm siphon depth improved TN removal by 52 % compared to the control.•A partial siphon strategy enriched DNB population of the unsaturated zone from 17.6 % to 34.5 %.
This study introduces a novel concept to provide both electric charging and hydrogen refueling at the same location. A hybrid hydrogen/electricity refueling station (HERS) powered only by solar ...photovoltaics in a remote area without access to the electrical grid is proposed. This station provides electricity for battery electric vehicles (BEVs) and simultaneously produces hydrogen for hydrogen fuel cell vehicles (HFCVs). Owing to the variability of PV power output and electricity price, electricity and hydrogen demands, this study investigates a possible operational strategy for the offgrid HERS. The objective is to propose optimal operational strategies for such a station to maximize profits by selling electricity and hydrogen to owners of both BEVs and HFCVs. Failure to supply electricity and hydrogen is treated as a penalty in the target function. The scenario-based stochastic method is adopted for this uncertainty modeling, and the conditional value-at-risk is also considered for evaluating the financial risks. The results reveal that 1) the proposed HERS can simultaneously supply the demands of the BEVs and HFCVs and 2) the behavior of HERS (providing energy to BEVs or HFCVs) is determined by several major factors, namely, electricity and hydrogen prices, and the penalty coefficients.
•A novel concept of a hybrid hydrogen/electricity refueling station is proposed.•The uncertainties are considered and their potential risk is quantified.•The optimal strategy is obtained by reformulating the problem into a MILP model.
This study introduces a novel framework of an electricity and hydrogen supply system integrating with a photovoltaic power station for a residential area. The non-residential parts including the ...power grid and non-residential vehicles are added to ensure power balance and bring benefits, respectively. The optimal operational strategy of the proposed framework with considering uncertainties is proposed. The objective function minimizes the expected operational cost (EOC) by reducing the imported electricity from the power grid and increasing exported electricity/hydrogen to non-residential vehicles. Additionally, the demand response program (DRP) is applied in the residential load to achieve operational cost reduction. The uncertainties are modeled via various scenarios by using scenario-based stochastic optimization method. Notably, existing research for similar frameworks both lacks the consideration of uncertainties and DRP, and fails to distinguish the residential and non-residential vehicles with different charging behaviors. The results indicate that 1) The feasibility of the proposed framework is validated which can ensure the power balance of the residential area and reduce the operational cost. 2) The EOC is reduced when considering DRP.
• A novel framework of an electricity and hydrogen supply system for a residential area is proposed.• The operational strategy of the framework is proposed with considering the uncertainties.• Residential vehicles and non-residential vehicles are modeled separately.• The DRP is introduced to reduce the expected operational cost of the framework.
•An optimal sizing scheme and an operating strategy are developed for an island microgrid.•System unit sizing and operating strategy are jointly optimized for the microgrid.•A genetic algorithm-based ...method was used to optimize the microgrid multi-objective solution.•The proposed methods are verified using the operational data obtained from the microgrid developed.•Practical considerations and realistic lessons learned are presented.
An optimal unit sizing method is presented for stand-alone microgrids with practical system and component life-cycle considerations. The proposed method has been applied to the design and development of a real microgrid system on Dongfushan Island, Zhejiang Province, China, consisting of wind turbine generators, solar panels, diesel generators and battery storage units. A genetic algorithm (GA)-based method is used to solve the sizing optimization problem with multiple objectives including the minimization of life-cycle cost, the maximization of renewable energy source penetration and the minimization of pollutant emissions. The actual system configuration and the operating strategy are discussed in detail in this paper, as well as the operational experience regarding the unique microgrid issues observed and lessons learned that may be useful for future microgrid design and development.
Liquid water is sometimes found exhausted from the anode exit of an air-cooled proton exchange membrane fuel cell (ACFC) even if dry hydrogen is input as fuel while its utilization rate is kept ...constant, i.e., having the forced convection of H2 in the anode. The anode liquid water accumulation may block the hydrogen into the anode catalyst layer (CL). However, no research has been dedicated to how the ACFC anode flooding appears, extends and intensifies under different operating conditions. In this research, a computational fluid dynamics model of ACFC proves the existence of anode two-phase flow based on some air stoichiometry, operating current density and relative air humidity (ARH). The results show that when the current density is increased to a high level of 840 mA cm−2, even though the air stoichiometric ratio (ASR) is set as the medium level of 150, the water flooding can cover two-thirds of the anode interface; as both the ARH and the current density increase to high levels of 90% and 700 mA cm−2, heavy flooding appears across the entire anode interface and the average liquid saturation is beyond 7 × 10−2. Finally, incorporating ARH and current density as the independent parameters and ASR as the dependent parameter, a rough operational strategy for ACFCs is put forward for the first time to try to avoid internal low or high humidity to stabilize the performance.
•The transport characteristics of the anode two-phase flow of an ACFC are analyzed.•Elevated air stoichiometry and air relative humidity exacerbate anode flooding.•Higher current density leads to the anode flooding due to more generated water.•A rough operational strategy for ACFCs is put forward.
The techno-economic advantages of grid-connected hybrid energy system (HES) exploit synergies to improve reliability and economic efficiency while maintaining grid stability. Therefore, this paper ...proposes a risk-averse optimal operational strategy of grid-connected photovoltaic/wind/battery/diesel HES to participate into two energy markets including electricity and hydrogen markets. The grid company can flexibly trade power into two markets to maximally achieve profits based on price arbitrage. The risk influences of the uncertainties, i.e., photovoltaic/wind generation, and electricity prices on the expected revenue are evaluated with CVaR model. For a better exhibition of seasonal variability effects on HES optimal operation strategy, two typical Spring/Summer days are chosen. The proposed risk-averse optimal operational strategy is formulated as a two-stage mixed-integer linear programming (MILP) model. The results in a Spring day simulation under non-risk situation indicate that the overall expected revenue can be improved 2.74 times larger if considering hydrogen market. Moreover, the optimal operational strategy of hydrogen production is considerably affected by unpredictable wind farm. Sensitivity analysis also validates that the changes of PV/WT curtailment penalty have a profound influence than battery degradation coefficient on the HES expected revenue.
•A grid-connected hybrid energy system participation in EM/HM is investigated under different seasonal conditions.•The risk-averse based optimal operational strategy is evaluated with CVaR and converted into a two-stage MILP model.•The expected profitability can be enhanced 2.74 times larger if HM is considered.
In facing urgent climate issues, large electricity customers committed to the RE100 initiative, aiming to transition entirely to renewable energy sources (RES). However, they encounter significant ...challenges in managing the unpredictability of RES generation and the volatility of market prices. This study unveils a groundbreaking hybrid procurement model that integrates Power Purchase Agreements (PPAs) with Battery Energy Storage Systems (BESS) to mitigate these financial risks through a novel method. Employing a sophisticated Mixed Integer Linear Programming (MILP) model alongside an innovative deep learning forecast for long-term PPAs planning, we present a unique solution that significantly boosts financial returns and enhances risk mitigation for large electricity customers. Validated with real-world data across three distinct customer profiles, our model demonstrates a notable increase in expected Net Present Value (NPV) by up to 13.58% compared to traditional strategies and improved earnings stability under adverse market conditions. Our proposed study not only charts a path toward more effective long-term RES procurement strategies but also provides large electricity customers with a strategic framework to skillfully navigate the complexities of the electricity market in alignment with their sustainability commitments.
•A novel hybrid power purchase agreements strategy with storage enhances risk management.•Customized plans for large customers with varied load types are developed.•Long-term electricity price forecast is enabled by a modified deep learning model.•Policy insights for Japan's power purchase agreements regulatory framework offered.
•This study proposed a Temperature and humidity independent control system in temperate semi-humid continental monsoon climate regions.•A dual-source heat pump system and air-handling units are used ...to form a central air-conditioning system that can simultaneously control indoor temperature and humidity.•The COP and cooling capacity of the DSHP system increase from 1.76 to 3.63 and from 1.19 kW to 3.38 kW, respectively.
A temperature and humidity independent control (THIC) system is a promising solution for hot and humid indoor working environments. This study proposes a dual-source heat pump air-conditioning (DSHPAC) system composed of a dual-source heat pump (DSHP) and air handling unit (AHU) as a THIC system. The proposed THIC system indirectly adjusts the cooling capacity of the high-temperature evaporator (Eva1) and low-temperature evaporator (Eva2) by controlling the refrigerant mass flow rate of the system to meet the cooling and dehumidifying requirements under different operational conditions. The proposed THIC system can switch among three operational modes by using the designed operational strategy, ensuring that the requirements for indoor temperature and humidity are met. In addition, the mathematical model and equilibrium equations of the THIC system are established. This study uses an office building in Xi'an on a typical summer day as a simulation case in dynamic simulations. The coefficient of performance (COP), cooling capacity, and compressor power consumption of the proposed DSHP system are analyzed. The results demonstrate that the COP of the proposed system increases with the temperature of Eva1 (TEva1), the COP of the proposed system varies from 1.76 to 3.62, and the cooling capacity increases from 1.19 kW to 3.38 kW when TEva1 increases from 6.24 °C to 36.4 °C. The analysis of different values of φR (refrigerant mass ratio) shows that the highest COP is achieved at φR = 0.1. The results prove the application potential of the dual-source heat pumps to the THIC air-conditioning systems.
Cold climates around the world are seeing increasing investment in wind power generation. The benefits of cold regions, however, come with unique challenges such as the accumulation of ice on wind ...turbine blades, which impacts the aerodynamic properties of the blades and, in turn, power production. One decision that must be made when facing an icing event is whether to maintain operation of the turbine or to pause the rotor until the event has passed. Powering through an icing event allows the operator to maintain power production, but with an increase in ice accumulation and associated adverse effects. Pausing the wind turbine results in less ice accumulation and may therefore provide higher power production once operation is resumed. The aim of this research was to complete a comparative assessment of these two strategies with regards to overall impact on power production. A numerical Ice and Power Model was developed, validated, and employed to assess power production impacts on a 1.5 MW wind turbine for five 2-h icing events with varying atmospheric parameters. The simulation results on short icing events provide evidence that while pausing the turbines does indeed result in significantly less ice accumulation, the positive impact on power production compared to the power-through strategy is insufficient to justify the shut-down strategy. This is found to be due to the overpowering impact of surface roughness from ice crystal beading on blade aerodynamics, which occurs whether or not the blades are rotating.
•This paper reports a comparative assessment of two operational strategies based on overall impact on power production during short icing events.•A numerical Ice and Power Model was developed, validated, and employed to assess power production impacts on a 1.5 MW wind turbine for five 2-h icing events with varying atmospheric parameters.•The simulation results provide evidence that while pausing the turbines does indeed result in significantly less ice accumulation, the positive impact on power production compared to the power-through strategy is insufficient to justify the shut-down strategy.•This is found to be due to the overpowering impact of surface roughness from ice crystal beading on blade aerodynamics, which occurs whether or not the blades are rotating.
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