Intermittent Availability Research Articles

Parametric effects of phase change material on solar still productivity: Thermal modeling and selection guides

A solar still utilizes solar energy to produce freshwater by evaporating and condensing saline water, known for its simplicity but limited by low productivity and intermittent solar availability. Phase change materials (PCMs) provide an attractive technique to overcome these drawbacks. In order to investigate the effect of PCM parameters besides providing a clear guide for PCM selection, the current paper presents a thermal modeling on solar sill-PCM behavior for different parameters. The results indicated improved productivity with higher PCM mass, melting point, latent heat of fusion, specific heat, or thermal conductivity. Under extreme conditions, moderate PCM mass or high melting point is optimal, while moderate conditions benefit from high PCM mass or moderate melting point. Long-term use favors high PCM mass or large latent heat of fusion. Combining high mass and melting point mitigates extreme condition challenges. Enhanced thermal conductivity alongside other parameters significantly boosts productivity, though excessive specific heat can reduce output. Improving the heat storage capacity holds significant promise for mitigating the challenges associated with selecting an appropriate melting point. Optimizing PCM selection by prioritizing mass, latent heat of fusion, thermal conductivity, melting point, and specific heat enhances solar still efficiency across diverse environments.

Transient transition from Stable to Dissipative Assemblies in Response to the Spatiotemporal Availability of a Chemical Fuel

AbstractThe transition from inactive to active matter implies a transition from thermodynamically stable to energy‐dissipating structures. Here, we show how the spatiotemporal availability of a chemical fuel causes a thermodynamically stable self‐assembled structure to transiently pass to an energy‐dissipating state. The system relies on the local injection of a weak affinity phosphodiester substrate into an agarose hydrogel containing surfactant‐based structures templated by ATP. Injection of substrate leads to the inclusion of additional surfactant molecules in the assemblies leading to the formation of catalytic hotspots for substrate conversion. After the local disappearance of the substrate as a result of chemical conversion and diffusion the assemblies spontaneously return to the stable state, which can be reactivated upon the injection of a new batch of fuel. The study illustrates how a dissipating self‐assembled system can cope with the intermittent availability of chemical energy without compromising long‐term structural stability.

Transient transition from stable to dissipative assemblies in response to the spatiotemporal availability of a chemical fuel.

The transition from inactive to active matter implies a transition from thermodynamically stable to energy-dissipating structures. Here, we show how the spatiotemporal availability of a chemical fuel causes a thermodynamically stable self-assembled structure to transiently pass to an energy-dissipating state. The system relies on the local injection of a weak affinity phosphodiester substrate into an agarose hydrogel containing surfactant-based structures templated by ATP. Injection of substrate leads to the inclusion of additional surfactant molecules in the assemblies leading to the formation of catalytic hotspots for substrate conversion. After the local disappearance of the substrate as a result of chemical conversion and diffusion the assemblies spontaneously return to the stable state, which can be reactivated upon the injection of a new batch of fuel. The study illustrates how a dissipating self-assembled system can cope with the intermittent availability of chemical energy without compromising long-term structural stability.

Business process simulation: Probabilistic modeling of intermittent resource availability and multitasking behavior

In business process simulation, resource availability is typically modeled by assigning a calendar to each resource, e.g., Monday–Friday, 9:00–18:00. Resources are assumed to be always available during each time slot in their availability calendar. This assumption often becomes invalid due to interruptions, breaks, or time-sharing across processes. In other words, existing approaches fail to capture intermittent availability. Another limitation of existing approaches is that they either do not consider multitasking behavior, or if they do, they assume that resources always multitask (up to a maximum capacity) whenever available. However, studies have shown that the multitasking patterns vary across days. This paper introduces a probabilistic approach to model resource availability and multitasking behavior for business process simulation. In this approach, each time slot in a resource calendar has an associated availability probability and a multitasking probability per multitasking level. For example, a resource may be available on Fridays between 14:00–15:00 with 90% probability, and given that they are performing one task during this slot, they may take on a second concurrent task with 60% probability. We propose algorithms to discover probabilistic calendars and probabilistic multitasking capacities from event logs. An evaluation shows that, with these enhancements, simulation models discovered from event logs better replicate the distribution of activities and cycle times, relative to approaches with crisp calendars and monotasking assumptions.

Reversible Long-Term Operation of a MK35x Electrolyte-Supported Solid Oxide Cell-Based Stack

High-temperature reversible solid oxide cells (rSOC) combine electrolyzer and fuel cell in one process unit which promises economic advantages with unrivaled high electrical efficiencies. However, large temperature gradients during dynamic rSOC operation can increase the risk of mechanical failure. Here, the degradation behavior of a 10-cell stack of the type “MK35x” with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated in rSOC operation at DLR. Its degradation was evaluated during nominal rSOC operation for more than 3400 h with 137 switching cycles between solid oxide fuel cell and solid oxide electrolysis cell operation of 24 h reflecting intermittent availability of solar energy. The voltage degradation rates of +0.58%/kh and −1.23%/kh in electrolysis and fuel cell operation, respectively, are among the lowest reported in literature. Comparison to a previously published long-term test in steam electrolysis did not show any indication for an increased degradation. Electrochemical impedance spectroscopy measurements were performed for all repeat units to evaluate the degradation behavior in detail. An overall polarization resistance decrease due to an improvement of the oxygen electrode was observed during electrolysis operation but was absent during fuel cell operation.

Expediting Photo‐Charging of Semiconductors through a Bipolar Charge Storage Junction for Responsive Dark Photocatalysis

AbstractPhoto‐charging of semiconductors stores electrons for decoupled solar utilization, overcoming intermittent sunlight availability. However, the sluggish photo‐charging process impedes responsive charge storage. Herein, a bipolar charge storage junction is demonstrated to expedite the photo‐charging process within a renowned ionic‐CN/Co3O4 configuration, benefiting from their mismatched photo‐charging kinetics. Rapid photo‐hole storage associated with structural evolution at geometrically dependent Co sites in Co3O4 improves sluggish electron storage for ionic‐CN, while slow recovery of altered [CoO4] and [CoO6] structures delayed electron‐hole recombination. By passivating individual atomic sites, rapid hole storage is attributed to synergistic contributions of tetrahedral Co2⁺ and octahedral Co3⁺ species. The bipolar charge storage junction is photo‐charged at 0.86 A g−1, rivaling the electrical charging rate in ion batteries. With 60 s photo‐charging, the junction yields 0.27 mmol g−1 of “dark” hydrogen, the benchmark for such a short photo‐charging timeframe. This proof‐of‐concept design empowers the fast photo‐charging ability of bipolar charge storage junctions, advancing responsive photo‐charge storage for decoupled solar utilization.

Unveiling morphophysiological and metabolic adaptive strategies of the CAM epiphytic bromeliad Acanthostachys pitcairnioides to drought

Ongoing climate changes are expected to intensify drought periods in tropical regions, directly impacting epiphytic bromeliads that depend on intermittent water availability. This study aimed to elucidate if Acanthostachys pitcairnioides, an epiphytic bromeliad of Atlantic Forest, tolerates extended drought periods and the potential strategies involved in its tolerance and recovery capacity. We suppressed irrigation for 42 days, rehydrated plants for four days, and evaluated leaf water status, and photochemical, metabolic, and anatomical changes. During the initial 28 days of drought, translocation of water from hydrenchyma to chlorenchyma, higher chlorophyll content, and accumulation of abscisic and salicylic acid and antioxidants contributed to maintaining the cell turgor and functionality of photosynthetic apparatus. At 42 days, a significant reduction in leaf water content to 45.5% was accompanied by a 2.5-fold increase in non-photochemical quenching and enhanced levels of carotenoids, anthocyanins, osmoregulators (proline, myo-inositol, and trehalose), and phytohormones (abscisic acid and jasmonates). After rewatering, water storage in the hydrenchyma and almost all pigments, hormones, and metabolites were restored to pre-stress conditions. Leaf succulence, carbohydrate and organic acid accumulation, and carbon isotope data (δ13C−14.5‰) provide evidence of induction of CAM metabolism by water limitation in A. pitcairnioides. Our findings indicate the prevalence of water accumulation strategy during the first half of the drought stress. At the end of the drought period, the complete depletion of water from the hydrenchyma favored the osmotic adjustment. Considering this set of tolerance strategies and the rapid recovery after rehydration, A. pitcairnioides can successfully withstand environments with restricted water availability.

Process stability in anaerobic Digestion: Unveiling microbial signatures of full-scale reactor performance

Anaerobic digestion is responding to the growing demand for sustainability by exploring alternatives for methane production through renewable processes. The target is to implement stable production systems at industrial scale that can accommodate heterogeneous feedstocks with seasonal or intermittent availability. In this study, we investigated the microbiomes of six full-scale biogas plant digesters, operated under continuous production with distinct feedstock and varying operating parameters, by monitoring multiple time points over an 18-month period. This time-course experiment analyzed 114 Metagenome-Assembled Genomes alongside physico-chemical assessments to identify common and plant-specific indicators for operational management. Results identify a Limnochordia and a Dysgonomonadaceae bacteria, as well as Candidatus Methanoculleus thermohydrogenotrophicum, as widespread and potentially desirable components of the microbiota for resilient digestion of varying waste, including the peculiar olive pomace. The abundance of individual taxonomic groups and their reconstructed metabolic pathways aligned with the availability of their fermentation substrates, finding a prevalence of beta-oxidizing bacteria with lipid-rich olive pomace. Monitoring through perturbation events revealed possible causative and remediative microbiological factors, in particular Methanosarcina flavescens and Candidatus Syntrophosphaera thermopropionivorans could contribute to restoration of reactor performance. This work showcases relationships between digester operation and its microbiome, supporting microbial monitoring as a tool to increase biogas production efficiency.

A Critical Analysis of Challenges and Prospects of the National Health Insurance Scheme in Zambia-A Case Study of Lusaka District

Zambia’s National Health Insurance (NHI) was established by the enactment of the NHI Act No. 2 of 2018 and supported by statutory instrument No. 63 of 2019 which led to the establishment of the National Health Insurance Scheme (NHIS) under the management of the National Health Insurance Management Authority (NHIMA). The goal of the NHIS was to guarantee the provision of universal health insurance coverage for all residents, regardless of their socioeconomic status. As one of the prospective financing solutions for protecting populations from high health care service prices, NHIS is receiving increased attention from the international community. This study set out to investigate the difficulties and opportunities that the plan faces from the standpoint of the service providers and subscribers in Lusaka, Zambia. The study used the descriptive research design since it seeks to analyze the prospects and challenges of the national health insurance scheme in Lusaka, Zambia. The study came to a conclusion that in Lusaka, Zambia, consumers who wish to utilize the NHIS plan face challenges related to health literacy and awareness, fraud, and corruption, as well as, subpar service quality. The survey also discovered that consumers in Lusaka have difficulties with enrolment and registration while attempting to use the NHIS program due to intermittent availability and constant breakdown of the NHIMA system. The study further came to conclude that some of the prospects for the NHIS plan in Lusaka is public knowledge and involvement, enhancing monitoring and evaluation of the private and public health facilities accredited with NHIMA and improving the internet connectivity of the NHIMA system to enhance service delivery.

New insights into the role of the root system of epiphytic bromeliads: comparison of root and leaf trichome functions in acquisition of water and nutrients.

In epiphytic bromeliads, the roots were previously considered to be poorly functional organs in the processes of absorption and metabolization of water and nutrients, while the leaves were considered to always act as protagonists in both functions. More recent discoveries have been changing this old view of the root system. In this review, we address previous ideas regarding the function performed by the roots of epiphytic bromeliads (mere holdfast structures with low physiological activity) and the importance of a reduced or lack of a root system for the emergence of epiphytism. We present indirect and direct evidence that contradicts this older hypothesis. Furthermore, the importance of the root absorptive function mainly for juvenile tankless epiphytic bromeliads and the characteristics of the root absorption process of adult epiphytic tank bromeliads are discussed thoroughly from a physiological perspective. Finally, some factors (species, substrate, environmental conditions) that influence the absorptive capability of the roots of epiphytic tank bromeliads are also be considered, highlighting the importance that the absorptive role of the roots has for the plasticity of bromeliads that live on trees, which is an environment characterized by intermittent availability of water and nutrients. The roots of tank-forming epiphytic bromeliads play important roles in the absorption and metabolization of nutrients and water. The importance of roots is greatest for juvenile tankless bromeliads since the root is the main absorptive organ. In larger plants with a tank, although the leaves become the protagonists in the resource acquisition process, the roots complement the absorptive function of the leaf trichomes, resulting in improved growth of these bromeliad. The physiological and biochemical properties of the processes of absorption and distribution of resources in the tissues appear to differ between absorption by trichomes and roots.

Harmonic modelling and control of dual active bridge converter for DC microgrid applications

Due to the intermittent power availability from renewable sources, the bidirectional DC-DC converter (BDC) must integrate with the energy storage system for bidirectional power flow. Among many BDCs, the Dual Active Bridge (DAB) converter is the most promising because of the system's power handling capacity and efficiency. DAB bidirectional DC-DC converter is a topology with the advantages of a decreased number of devices, soft-switching commutations, low cost, and high efficiency. This work describes the guidelines for designing a DAB converter for small DC microgrid applications. It is shown that the judicial selection of reactive elements leads to soft switching for all the switches in the converter in varying load conditions. A guideline for the controller design is given and the operations are validated through the simulation. A harmonic modelling technique has been implemented to model the DAB converter based on an efficient closed-loop regulator. A solar PV system has also been implemented here with a SEPIC converter that is used as an interfacing element between the PV system and the load bus. At last, a DC Microgrid is simulated in a PSIM environment to showcase its various modes of operation. It is shown that the battery bank can support variable loads independently through the DAB converter. In inadequate solar power generation, load power demand is shared between the battery and PV system. In case of deep discharge of the battery, the PV system can charge the battery through a DAB converter.

Development of a novel LED-IoT photoreactor for enhanced removal of carbamazepine waste driven by solar energy

This study introduces an innovative LED-IoT photoreactor, representing a significant advancement in response to the demand for sustainable water purification. The integration of LED-IoT installations addresses the challenge of intermittent sunlight availability, employing LEDs with a spectrum mimicking natural sunlight. Passive Infra-Red (PIR) sensors and Internet of things (IoT) technology ensure consistent radiation intensity, with the LED deactivating in ample sunlight and activating in its absence. Utilizing a visible light-absorbing photocatalyst developed through sol-gel synthesis and mild-temperature calcination, this research demonstrates a remarkable carbamazepine removal efficiency exceeding 95% under LED-IoT system illumination, compared to less than 90% efficiency with sunlight alone, within a 6-h exposure period. Moreover, the designed photocatalytic system achieves over 60% mineralization of carbamazepine after 12 h. Notably, the photocatalyst demonstrated excellent stability with no performance loss during five further cycles. Furthermore, integration with renewable energy sources facilitated continuous operation beyond daylight hours, enhancing the system's applicability in real-world water treatment scenarios. A notable application of the LED-IoT system at an operating sewage treatment plant showed nearly 80% efficiency in carbamazepine removal from sewage in the secondary settling tank after 6 h of irradiation, coupled with nearly 40% mineralization efficiency. Additionally, physicochemical analyses such as XPS and STA-FTIR confirm that the carbamazepine photooxidation process does not affect the surface of the photocatalyst, showing no adsorption for degradation products.

Photo-Stimulated Zn-based Batteries: Progress, Challenges, and Perspectives.

Solar energy, as a renewable energy source, dominates the vast majority of human energy, which can be harvested and converted by photovoltaic solar cells. However, the intermittent availability of solar energy restricts the actual utilization circumstances of solar cells. Integrating photo-responsive electrodes into an energy storage device emerges as a dependable and executable strategy, fostering the creation of photo-stimulated batteries that seamlessly amalgamate the process of solar energy collection, conversion, and storage in one system. Endowed by virtues such as cost-effectiveness, facile manufacturing, safety, and environmental friendliness, photo-stimulated Zn-based batteries have attracted considerable attention. The progress report furnishes a brief overview, summarizing various photo-stimulated Zn-based batteries. Their configurations, operational principles, advancements, and the intricate engineering of photoelectrode designs are introduced, respectively. Through rigorous architectural design, photo-stimulated Zn-based batteries exhibit the ability to initiate charging by saving electricity usage, and in certain instances, even without the need for external electrical grids under illumination. Furthermore, the compensation of solar energy can be explored to improve the output electric energy. At last, opportunities and challenges toward photo-stimulated Zn-based batteries in the process of development are proposed and discussed in the hope of expanding their application scenarios and accelerating the commercialization progress.

A Comparative Life Cycle Assessment of Hydrogen Production & Storage with Renewable Energy Source and Grid Electricity Source

The role of electricity is becoming significant in our advancing world. Currently, Ireland’s energy mix heavily relies on carbon-polluting fossil fuels, posing an environmental challenge. As per the Paris Agreement 2015, Ireland is ambitiously targeting to meet net zero carbon dioxide (CO2) emissions by 2050 and a 51% reduction by 2030. The country is shifting towards renewable energy sources to generate power to achieve this target. With abundant wind energy available, Ireland can meet its goal. However, due to the intermittent availability of wind energy, an energy backup for power generation is necessary. The use of curtailed or dedicated wind for producing hydrogen gas through electrolysis, and storing it in underground salt caverns is one approach to the problem. Northern Ireland has a rich source of Permian salt deposits offering a better place to store hydrogen which can be withdrawn for electricity generation, or used as fuel in transportation sectors. The Life Cycle Assessment (LCA) of the hydrogen systems can scrutinise the environmental impact of carbon emissions. This study analyses routes to reduce the environmental impact by evaluating polluting hotspots during the construction and operation phase of the system. This paper compares the impacts of the LCA on a hydrogen system which consists of a wind energy source for hydrogen production through electrolysis, transportation in pipelines and compression before storing it in salt caverns. A comparative analysis is carried out with the LCA of the hydrogen system with an electrical grid supply source. The results show that the impacts contributed by a renewable source are less than the electricity from the grid for the island of Ireland.

A System for the Combined Carbon Capture and Utilization to Produce Renewable Methanol from Biogas

AbstractCoupling of biogas upgrading and power‐to‐X is challenging due to the intermittent cheap energy availability. A system was designed that overcomes the technical challenges in this coupling. This is possible by alternating biogas upgrading and methanol synthesis in a reactor operating both as sorption‐enhanced synthesis reactor and as upgrading unit by pressure swing adsorption. It was observed that this concept is feasible in both fixed‐ and fluidized‐bed reactors, and the potential for economic performance improvement was quantified in approximately 20 % increase of the internal rate of return.

Performance analysis and ANFIS computing of a Markovian queuing model with intermittently accessible server under a hybrid vacation policy

In this study, we investigate a heterogeneous queueing model with intermittent server availability, server catastrophes, and a hybrid vacation policy. Our focus is on a specific scenario: server 1 is always available, while server 2 may experience breakdowns or vacations, making it intermittently accessible. Using the matrix-geometric approach (MGA), we derive matrix-based expressions for the stationary probability distribution of the number of customers in the system and various system performance measures. Additionally, we evaluate the cost function per unit of time to determine optimal values for the system’s decision variables. Furthermore, we employ an adaptive neural fuzzy inference system (ANFIS) based on soft computing technology to compare and analyze the numerical results obtained. Through this comprehensive analysis, our study contributes to the understanding and optimization of this complex queueing system, attracting the attention of researchers in the field and offering practical insights for real-world applications.

Physics-Based Modeling and Parameter Tracing for Industrial Demand-Side Management Applications: A Novel Approach

The transition to sustainable energy sources presents significant challenges for energy distribution and consumption systems. Specifically, the intermittent availability of renewable energy sources and the decreasing usage of fossil fuels pose challenges to energy flexibility and efficiency. An approach to tackle these challenges is demand-side management, aiming to adapt energy consumption and demand. A key requirement for demand-side management is the traceability of the energy flow among individual energy consumers. In recent years, advancements in industrial information and communication technology have provided additional potential for data acquisition. Complementary to acquired data, a physics-based modeling and analysis approach is proposed, which describes the energy consumption with physical parameters. This results in comprehensive options for monitoring actual energy consumption and planning future energy demand supporting energy efficiency and demand-response goals. To validate the proposed approach, a case study with a 3D printer covering approximately 110 h of active printing time is conducted. The medium-term study results indicate a consistent parameter trend over time, suggesting its conceptual suitability for industrial application. The approach helps to monitor energy efficiency among manufacturing assets by identifying peak loads and consumption hotspots, and provides parameters to estimate energy consumption of manufacturing processes. Results indicate up to 50% energy savings when switching the printing material and indicate further potentials.

Economic feasibility of integrating solar energy into water utility operations in Ciudad Juárez, Mexico

We perform an economic feasibility analysis for installing grid-connected solar arrays with batteries to power ten water supply, distribution, and treatment stations in Ciudad Juárez in tandem with the existing local grid. This article covers detailed results from the four stations that represent the topographical and geographical variability of the city and the variable electricity demand across sites. Using data from the city’s water utility and calculations from the HOMER and RETScreen models, we find contrasting results. The HOMER model finds that solar arrays with or without batteries are economically viable while RETScreen reaches the opposite conclusion. One key reason for this is the two models’ differing predictions on the amount of electricity the proposed solar arrays would supply. Further, having reliable battery storage is paramount to overcoming grid outages and the intermittent availability of solar power to ensure the success of solar projects. Global scientific consensus recognizes the need for more renewable energy. With a sunny-climate and its status as a manufacturing hub on the US-Mexico border, Ciudad Juárez has the potential to lead the way forward in promoting solar energy. The comparative results of the HOMER and RETScreen models provide a more complete understanding of the feasibility of solar power for Ciudad Juárez’s water infrastructure as well as vital insight into the factors that shape the success of solar projects.

Sizing and cost analysis for integrated renewable energy system in a study area

The renewable energy sources such as micro hydro, biomass, wind, solar photovoltaics can provide clean and sustainable electricity, as a result, many of sources are already proving cost-competitive contributing about 2% of the total electricity supply of the country. However, one of the issues limiting their greater penetration is done to its intermittent and seasonal availability for energy production. The availability of renewable power depends upon the resources potential and size of the system. The sizing for integrated renewable energy systems (IRES) depends on the uses of the system (load on the system) and the tariffs available from the local utility. In this paper, the sizing and cost analysis of MHP, biomass, wind and SPV system has been under taken.

Responses of digestive enzyme profiles in newly-hatched (Zoea I) larvae of the mud crab Scylla serrata to intermittent food availability and food deprivation.

Activities (mU larva-1) of enzymes critical to digestion were examined to better understand how newly-hatched (Zoea I) larvae of the mud crab Scylla serrata respond to intermittent food availability and food deprivation. Specifically, this study examined the activities of trypsin-like proteases, nonspecific esterases, and α-amylase across three experiments that simulated scenarios in which larvae hatch and experience rearing conditions where food was either: (1) continuously available or unavailable; (2) initially unavailable, but subsequently available; or (3) initially available, but subsequently unavailable. Results showed that food availability exerts a significant influence on enzyme profiles in newly-hatched larvae, with nutritional history influencing their response to food deprivation. When food was unavailable from hatch, there was no significant change in larval enzyme activities between 6 and 78h post-hatch. If food became available at any point during this period, however, newly-hatched larvae were capable of rapidly (within 12-24h) adjusting enzyme activities in response. Furthermore, a short (36h) period of food availability appears sufficient to permit continuous substrate utilization during subsequent food deprivation of equivalent duration. Such flexibility is an important physiological strategy allowing newly-hatched larvae of S. serrata to adapt and thrive in challenging tropical oceanic environments and provides a basis for optimizing protocols for hatchery production of this species.