Sufficient Reserve Capacity Research Articles

Spatial national multi-period long-term energy and carbon planning scenarios in Ecuador’s electric system

The Republic of Ecuador is developing a comprehensive plan to meet the increasing residential, industrial, and commercial energy demands. With a population of 17.08 million in 2018, the country is experiencing an annual average energy growth of approximately 7.13% until 2027. This research aims to model the incorporation of new and proposed power plants strategically planned to cater to the expanding demand needs. Ensuring that our existing energy infrastructure can adequately meet the current and growing needs of the residential, commercial, and industrial sectors should be made possible. In this paper, we present several hypotheses that need to be made to identify the potential demands for residential, industrial, and commercial requirements, making it more accessible to build new facilities that use renewable energy. Traditional and unconventional renewable energy sources, such as hydro-power, wind, and solar power, are being explored to generate electricity. The research employs quantitative methodology, beginning with gathering information and a detailed data analysis. Subsequently, a scenario-based model will examine the impact on energy demand and supply from 2020 to 2035. The results show that the Santiago hydroelectric project is becoming essential for the country’s energy development and that the current national power system will only be able to supply the electricity demand when the industrial city of Posorja is being developed. We suggest that to maintain Ecuador’s electricity trade balance as an electricity exporter, we continue with the energy investment plans currently issued by the Ministry of Energy and Mines. This study is relevant for establishing global financing arrangements involving the public and private sectors. In doing so, we can meet our hypothetical scenarios, ensuring that all energy needs are met by 2035. This will involve developing a robust national grid system with sufficient reserve capacity, meeting residential and projected commercial and industrial demand.

Short-Term Hydro-Wind-PV peak shaving scheduling using approximate hydropower output characters

With the massive construction of wind and photovoltaic (PV) power plants, the uncertainty of their output poses challenges for grid peak regulation. Hydropower, characterized by convenient regulation, fast response speed, and low cost, is an ideal choice for compensating for wind and PV energy generation. Mixed-Integer Linear Programming (MILP) is employed to work out short-term scheduling of hydro-wind-PV power. However, considering hydropower scheduling alone is already highly complex, and incorporating the deviations in wind and PV energy further reduces the solution efficiency. In practical scheduling, operators often rely on empirical scheduling methods that can yield satisfactory results. To enhance solution quality and improve the scalability and efficiency of the MILP method, a short-term optimization scheduling model for hydropower plants has been proposed and applied to the Hongshui River cascade system. The case study shows that the model can perform calculations in just 2 s, demonstrating extremely high computational efficiency. This can significantly enhance decision-making in cascaded hydropower scheduling. At the same time, the model leaves sufficient reserve capacity to address the uncertainty of wind and solar power output while reducing the residual load by 0.8 %, which is beneficial for the stable operation of the grid.

Hemodynamic imaging parameters in brain metastases patients – Agreement between multi-delay ASL and hypercapnic BOLD

Arterial spin labeling (ASL) MRI is a routine clinical imaging technique that provides quantitative cerebral blood flow (CBF) information. A related technique is blood oxygenation level-dependent (BOLD) MRI during hypercapnia, which can assess cerebrovascular reactivity (CVR). ASL is weighted towards arteries, whereas BOLD is weighted towards veins. Their associated parameters in heterogeneous tissue types or under different hemodynamic conditions remains unclear. Baseline multi-delay ASL MRI and BOLD MRI during hypercapnia were performed in fourteen patients with brain metastases. In the ROI analysis, the CBF and CVR values were positively correlated in regions showing sufficient reserve capacity (i.e. non-steal regions, rrm = 0.792). Additionally, longer hemodynamic lag times were related to lower baseline CBF (rrm = −0.822) and longer arterial arrival time (AAT; rrm = 0.712). In contrast, in regions exhibiting vascular steal an inverse relationship was found with higher baseline CBF related to more negative CVR (rrm = −0.273). These associations were confirmed in voxelwise analyses. The relationship between CBF, AAT and CVR measures seems to be dependent on the vascular status of the underlying tissue. Healthy tissue relationships do not hold in tissues experiencing impaired or exhausted autoregulation. CVR metrics can possibly identify at-risk areas before perfusion deficiencies become visible on ASL MRI, specifically within vascular steal regions.

Reserve provision of combined-cycle unit in joint day-ahead energy and reserve markets

With the continuous development of natural gas-fired combined cycle power generation technology, the combined cycle (CC) unit's installed capacity is gradually increasing in the power system because of its flexible operation characteristics. Participating in the energy and reserve markets and taking advantage of flexible mode transfer characteristics, the CC unit can provide the system with energy and sufficient reserve capacity. This paper proposes a bi-level strategic bidding model to study the CC unit’s bidding behavior in the day-ahead energy and reserve markets. The upper-level model is an optimal bidding model for the configuration-based CC unit aiming to maximize its profit. The lower-level model is the joint market clearing model of the energy and reserve markets managed by the independent system operator (ISO). CC unit and ISO in this model influence each other by the locational marginal electricity prices (LMEP) and the locational marginal reserve prices (LMRP) obtained from the lower-level market-clearing model. The CC unit submits the bids to the ISO and arranges the generation plan according to the market clearing results of the lower-level market-clearing model carried out by the ISO. The proposed bi-level optimization model is transformed into a mathematical equilibrium constraint (MPEC) problem by Karush-Kuhn-Tucker (KKT) conditions and duality theory. In this paper, the improved IEEE-6 bus and IEEE-57 bus systems are used as case studies to verify the effectiveness of the proposed bidding strategy for the CC unit. The results show that the proposed bidding strategy can effectively improve the profits of the CC unit in the electricity market. Compared with the case of the CC unit only participating in the energy market, the profits of the CC unit in the market increased by 8.84% and 12.3%.

Vitamin D in the older population: a consensus statement.

BackgroundThis paper reports results from the 5th International Conference “Controversies in Vitamin D” that was held in Stresa, Italy, 15–18 September 2021. The conference is part of this series that started in 2017 and has been conducted annually since. The objective of these conferences is to identify timely and controversial topics related to Vitamin D. Dissemination of the results of the conference through publications in peer-reviewed journals is an important means by which the most up to date information can be shared with physicians, investigators, and other health care professionals. Vitamin D and aging, the subject of this paper was featured at the conference.MethodsParticipants were selected to review available literature on assigned topics related to vitamin D and aging and to present their findings with illustrative material, the intent of which was to stimulate discussion and to arrive at a consensus. The presentations were directed towards the following areas: impact of aging on vitamin D production and levels; skeletal effects of vitamin D deficiency in the older population; falls and vitamin D in the aging; potential extra skeletal effects of vitamin D; and strategies to prevent vitamin D deficiency. A final topic was related to how vitamin D might influence the efficacy of vaccines for Covid-19.ResultsHypovitaminosis D can lead to several skeletal and extra-skeletal outcomes. Older adults are at risk for vitamin D deficiency as both production and metabolism of vitamin D change with aging due to factors, such as reduced sun exposure and reduced production capacity of the skin. Skeletal consequences of these age-related changes can include reduced bone mineral density, osteomalacia and fractures. Potential extra-skeletal effects can include added risks for falls, reduced muscle strength, diabetes, cancer, and cardiovascular disease. Strategies to avoid these vitamin D deficiency-related negative outcomes include sun exposure, food fortification, and supplementation. While aging does not diminish sufficient reserve capacity for cutaneous vitamin D production, concerns about skin cancers and practical matters for the institutionalized elderly limit this option. Supplementation with vitamin D is the best option either pharmacologically or through food fortification. Regardless of treatment strategies, interventions to restore sufficient vitamin D status will show positive results only in those who are truly deficient. Thus, treatment goals should focus on avoiding 25(OH)D serum levels <30 nmol/l, with a goal to reach levels >50 nmol/l.ConclusionsThe results of this conference has led to consensus on several issues. Vitamin D supplementation should be combined with calcium to reduce fractures in the older population. The goal for adequate Vitamin D status should be to reach a serum level of 25(OH)D >50 nmol/l. It appears that daily low-dose vitamin D regimens reduce the risk of falling, especially in the elderly, compared with infrequent, large bolus doses that may increase it. The role of Vitamin D supplementation on muscle strength remains to be clarified. On the other hand, supplementation decreases the risk of progression to T2D from prediabetes among those who are Vitamin Ddeficient. Of three possible strategies to establish vitamin D sufficiency – sunshine exposure, food fortification, and supplementation – the latter seems to be the most effective and practical in the aging population.

Динамика объема функционирующей паренхимы и раздельной почечной функции до и после резекции почки по поводу опухоли

Objective. To assess functions of each kidney in dynamics using mathematical analysis of contrast-enhanced computed tomography findings in patients with unilateral kidney tumors. Patients and methods. We present preliminary results of a prospective study within the protocol "Assessment of the functioning renal parenchyma volume and functions of each kidney in patients with tumors before and after resection" conducted in the Institute of Urology and Human Reproductive Health, I.M.Sechenov First Moscow State Medical University. This study included 20 patients of both sexes who had undergone resection of unilateral kidney tumors with compression of the main renal artery. We performed mathematical analysis of contrast-enhanced computed tomography findings before surgery and 3–6 months postoperatively to evaluate functions of each kidney. In addition to that, we measured the dynamics of total glomerular filtration rate (GFR) using a special formula. Results. We observed no significant dynamics in any total functional renal parameters (creatinine level, total GFR, total functioning renal parenchymal volume) and in 3D-GFR of each kidney. However, there were significant differences in the dynamics of functional parameters measured for each kidney individually, including 3D renal perfusion and functioning parenchyma volume of each kidney. The volume of functioning renal parenchyma in the affected kidney decreased significantly (p = 0.006). In the subgroup with no lesions, we observed no significant dynamics (p = 0.236). Changes in perfusion affected both sides. Conclusion. We found no significant changes in the total kidney function after surgery, which suggests a sufficient reserve capacity of this paired organ. Increased postoperative perfusion in the intact kidney is likely to reflect redistribution of functional loads between the kidneys and can be considered as an adaptive mechanism. This hypothesis is also confirmed by redistribution of the functioning parenchyma volume 3–6 months postoperatively. The intact kidney probably compensates the loss of function in the affected kidney.

ГЛОБАЛЬНОЕ УПРАВЛЕНИЕ ПАНДЕМИЕЙ COVID-19: УСПЕХ ИЛИ НЕУДАЧА?

The paper summarises the extent and incidence of the Covid-19 pandemic and evaluates government policies in different countries. The consequences of lock-down policy are discussed. The most negatively affected groups of the population are the low-skilled workers and self-employed. Psychological welfare has seriously declined and provision of health services have deteriorated. Population density, age structure and state management strongly influence the spread and containment of the disease. State coordinated economies and social-democratic countries have managed the effects of the disease better than market coordinated economies, though there are important exceptions. A failure of some governments to provide sufficient reserve capacity of healthcare facilities indicates government policy failure. The paper suggests that a more focused policy of social isolation of people susceptible to coronavirus with less stringent lockdown measures would have significantly reduced social costs and increased public health benefits.

Adaptive robust energy and reserve co-optimization of integrated electricity and heating system considering wind uncertainty

The uncertainty and variability of wind power pose significant challenges to secure and reliable operation of power systems. Coordinated operation of the electric power system and district heating system, which can provide sufficient reserve capacity and flexibility, is an effective way to cope with the uncertainty. This paper proposes an adaptive robust energy and reserve co-optimization for the integrated electricity and heat system to minimize the total system cost under the worst-case realization of wind uncertainty considering spatial correlations of wind uncertainties. The available reserve capacity and flexibility provided by the district heating system is fully used by exploiting the regulation capabilities of combined heat and power units and electrical boilers, as well as utilizing the building thermal inertia. To reduce the conservatism of the robust solution, the spatial correlation of wind uncertainties is considered in the uncertainty set. The column-and-constraint generation algorithm is adopted to solve the adaptive robust model iteratively by reformulating the second stage with its Karush-Kuhn-Tucker conditions. Simulation results demonstrate that the economic efficiency is improved by utilizing the reserve flexibility from the district heating system and considering wind farm spatial correlations. Compared with the conventional single-stage optimized model, the feasibility of the two-stage robust solution is always guaranteed by considering the real-time operation constraints of the electric power system and district heating system.

Control Performance Based Dynamic Regulation Reserve Allocation for Renewable Integrations

A sustainable power grid involves variable and uncertain generation, load and equipment availability. In order to ensure the frequency quality, power system needs to maintain sufficient reserve capacity to meet the demand and generation variations, and to withstand contingency events. To limit the operation risk to an acceptable level, an operation practice driven and control performance based reserve allocation method is proposed in this paper to determine adequate frequency regulation reserve in an island power system with increasing renewable integrations. Analyses of on-line available frequency regulation reserves and control performance data recorded in Energy Management System are conducted to appraise and manage the risk of non-compliance of frequency control standard. The proposed method is based on the conditional probabilities of reaching certain Control Performance Standard 1 (CPS1) score under the availability of Automatic Generation Control ramping and droop response capability. Comparisons of estimated reserve requirements and expected performance of four dynamic reserve allocation schemes to comply with CPS1 are presented.

Security-Constrained Design of Isolated Multi-Energy Microgrids

Energy supply in rural and off-grid communities has traditionally relied on diesel-based microgrids, due to limited access. But global environmental concerns are pushing for the transformation of these systems into renewable-based microgrids. This transition to more complex systems with a mix of dispatchable and nondispatchable resources requires new planning tools that ensure the security of supply. This paper presents a novel mixed-integer linear optimization model that determines optimal technology mix, size, placement, and associated dispatch for a multi-energy microgrid. The model satisfies microgrid's electrical and heat transfer network limitations by integrating linear power flow and heat transfer equations. It captures the efficiency gains from waste heat recovery through combined heat and power technologies, by modeling the interplay between electrical and heat sources. To ensure a secure design against generator outages, the optimization maintains sufficient reserve capacity in the system, which is dynamically allocated based on system operating conditions. Several case studies on an isolated microgrid model, developed based on a real microgrid in Alaska, illustrate how the proposed model works. The results show the effectiveness of the model and are used to discuss various aspects of the optimization solution.

Effect of ambient air temperature on the performance of regenerative air preheater of pulverised coal fired boilers

The air preheater (APH) is the last heat trap in flue gas path of boiler. Efficient performance of APH is possible with efficient pre-combustion coal drying and effective combustion in the furnace. The characteristic of ambient air temperature (AAT) has a significant role on the efficiency of heat transfer in APH. The change in AAT in turn changes heat capacity of air that depends on relative humidity (RH) and air density. An increase in AAT will reduce the waste heat recovery opportunity, if sufficient reserve capacity of heat exchange is not available in APH. Besides, change in AAT will have an impact on the power consumption of the fans and leakage through different seals. In this paper, the effect of these factors due to change in AAT is evaluated to assess the performance of regenerative APH with reference to a field study of 135 MWe subcritical steam power plant.

Análisis de Confiabilidad de la Generación Considerando el Ingreso de Energías Renovables No Convencionales en los Sistemas de Potencia

El presente trabajo pretende realizar un análisis de la reserva rodante de los generadores sincrónicos que tendrá que ser considerada para compensar las posibles fluctuaciones en los sistemas de potencia debido al ingreso de generación de energías renovables no convencionales (ERNC). El interés es desarrollar un estudio de confiabilidad de generación (Generation Adequacy), considerando el ingreso de ERNC. Utilizando el software de simulación PowerFactory de DIgSILENT, se realiza una modelación del sistema de prueba IEEE New England, donde se considera generación de energía convencional y no convencional. Se plantea una metodología que considere la variabilidad de los recursos eólicos y fotovoltaicos, contando con modelos de predicción de estas fluctuaciones, permitiendo estimar el efecto del incremento o disminución de este tipo de tecnologías sobre la generación de las centrales hidráulicas, térmicas y confiabilidad del sistema. Los resultados del presente trabajo sobre la inclusión de energías renovables no convencional, permitirá recomendar los niveles adecuados de capacidad instalada de este tipo de generación no convencional y permitirá sugerir las acciones operativas en el sistema con el objetivo de asegurar suficiente capacidad de reserva ante las fluctuaciones de la ERNC.

Schedule Recovery: Unplanned Absences in Service Operations*

ABSTRACTThe U.S. service sector loses 2.3% of all scheduled labor hours to unplanned absences, but in some industries, the total cost of unplanned absences approaches 20% of payroll expense. The principal reasons for unscheduled absences (personal illness and family issues) are unlikely to abate anytime soon. Despite this, most labor scheduling systems continue to assume perfect attendance. This oversight masks an important but rarely addressed issue in services management: how to recover from short‐notice, short‐term reductions in planned capacity.In this article, we model optimal responses to unplanned employee absences in multi‐server queueing systems that provide discrete, pay‐per‐use services for impatient customers. Our goal is to assess the performance of alternate absence recovery strategies under various staffing and scheduling regimes. We accomplish this by first developing optimal labor schedules for hypothetical service environments with unreliable workers. We then simulate unplanned employee absences, apply an absence recovery model, and compute system profits.Our absence recovery model utilizes recovery strategies such as holdover overtime, call‐ins, and temporary workers. We find that holdover overtime is an effective absence recovery strategy provided sufficient reserve capacity (maximum allowable work hours minus scheduled hours) exists. Otherwise, less precise and more costly absence recovery methods such as call‐ins and temporary help service workers may be needed. We also find that choices for initial staffing and scheduling policies, such as planned overtime and absence anticipation, significantly influence the likelihood of successful absence recovery. To predict the effectiveness of absence recovery policies under alternate staffing/scheduling strategies and operating environments, we propose an index based on initial capacity reserves.

Bridge design with reserve and residual reliability constraints

System reliability is evolving as an important design method for selecting components and topology. It should be used to investigate the original intact structure behavior as well as providing sufficient reserve capacity under likely accident and damage scenarios. Highway bridges are an area of special concern since effort to optimize the cost of construction may not provide adequate redundant capacity. The paper describes an example in which a typical girder bridge structure is optimized (both size and girder spacing) to achieve target system performance. System reliability constraints are imposed on the behavior of the intact structure under highway loads. Also, residual system reliability constraints are imposed to control safety under specified accident scenarios corresponding to damage and “lost” members due to corrosion, fatigue, fire or accidental collisions. An optimal design framework for controlling safety under all these life cycle situations is thus provided.

Primary active sodium transport, oxygen consumption, and ATP: Coupling and regulation

Several metabolic aspects of primary active transport have been explored in this communication. One emphasized theme entailed the need to investigate the properties of the mitochondria and the active transport systems within the intact cell. Several methodological and conceptual approaches were described that permitted such an analysis. The answers provided were sometimes qualitative or quantitative. Qualitative information was provided regarding the cytosolic signal linking active transport with respiration, suggesting that the cytosolic ADP concentration was an important element in that link. The intact renal cell was found to work normally at 50 to 60% of its maximal respiratory capacity, indicating that sufficient reserve capacity was present for increased metabolic demands. Several examples were described in which a combination of qO2 measurements and/or optical techniques were used to differentiate between effects of agents which act primarily on transport or metabolic events. Finally, the control of transport by metabolism was discussed, primarily emphasizing the role of ATP and Pi. One of the overall conclusions from these studies is that, in general, the mitochondria and the transport systems seem to display similar properties in the intact cell as they do in isolated form. However, uncertainties concerning the cellular microenvironment surrounding the mitochondria and the plasma membrane transporters have produced some interesting surprises concerning their function in the intact cell. More quantitative information on the energy compartmentation of the renal cell would be helpful to clarify numerous aspects of metabolic function.