It is expected that electric vehicles (EVs) will soon represent a large share of the demand for electricity. Several research works have extolled the advantages of these devices as flexible demands, ...not only to charge their batteries when it is cheaper to do so, but also to provide services in the form of vehicle-to-grid (V2G) power injections to the system. These services, however, could reduce the useful life of the battery and thus introduce a cost that needs to be taken into account when scheduling the charging of these vehicles. This study presents a scheduling algorithm for EVs under a real time pricing scheme with uncertainty. The objective function explicitly takes into account the cost of battery degradation not only when used to provide services to the system but also in terms of the EV utilisation for motion. The results show that the scheduling of the V2G services is sensitive to the electricity prices uncertainty and to the degradation costs derived from the energy arbitrage. Also, the optimal energy state of charge of the batteries is highly dependent on whether the cost of battery degradation is taken into account or not.
An aggregator acts as a mediator between the system operator and residential customers, enabling mutually beneficial coordination for electric vehicle (EV) owners and the power system. The aggregator ...aims to maximize its profits from trading energy and regulation reserve in wholesale markets. Since the aggregator does not own EV batteries, the EV owners must be reimbursed for the degradation of their batteries due to the additional cycling beyond transportation needs. This paper proposes a bidding strategy for the aggregator to maximize its profits from participating in competitive energy and different regulating reserves markets, while compensating EV owners for degradation. The results show that depending on the battery cost, the aggregator splits its resources between the energy and reserves markets. The results also show the system operator attains cost savings, if an aggregator uses EVs to provide services.
Polysilicon is a key commodity required for both electronics and solar photovoltaic modules. The traditional route to produce polysilicon involves the Siemens reactor, an energy intensive batch ...process. A more efficient, but more complex alternative process is the fluidized bed reactor (FBR). In an FBR silane is pyrolysed producing chemical vapor deposition (CVD) and aerosols. Efficient FBR operation requires yield optimization together with continuous and stable operation of the reactor. Such optimization is not straightforward because the aerosol formation mechanisms and incorporation into the FBR beads are not completely understood. In this work, two model aerosols with different morphology were tested and their filtration efficiency between 20 and 800 nm was determined. Bead saturation at different times was determined for each morphology and the scavenging factor over time for each case is reported. Such information can be of interest for establishing bed recirculation needs in a silicon FBR.
For a successful rollout of electric vehicles (EVs), it is required to establish an adequate charging infrastructure. The adequate access to such infrastructure would help to mitigate concerns ...associated with limited EV range and long charging times. Battery swapping stations are poised as effective means of eliminating the long waiting times associated with charging the EV batteries. These stations are mediators between the power system and their customers. In order to successfully deploy this type of stations, a business and operating model is required, that will allow it to generate profits while offering a fast and reliable alternative to charging batteries. This paper proposes an optimization framework for the operating model of battery swapping stations. The proposed model considers the day-ahead scheduling process. Battery demand uncertainty is modeled using inventory robust optimization, while multi-band robust optimization is employed to model electricity price uncertainty. The results show the viability of the proposed model as a business case, as well as the effectiveness of the model to provide the required service.
Assessing flexibility requirements in power systems Dvorkin, Yury; Kirschen, Daniel S; Ortega-Vazquez, Miguel A
IET generation, transmission & distribution,
11/2014, Letnik:
8, Številka:
11
Journal Article
Recenzirano
This study proposes a methodology to assess the effect of wind power production on the flexibility requirements of a power system. First, the study describes the probabilistic characteristics of the ...intra-hour net load variability and demonstrates that they are best captured by non-parametric statistics. Then, this non-parametric approach is used to determine simultaneously the hourly flexibility requirements at a given probability level for large and small, continuous and discrete disturbances. This approach allocates the required flexibility among primary, secondary and tertiary regulation intervals. The usefulness of this method is then illustrated using actual 1 min resolution net load data, which has been clustered to take advantage of seasonal and daily differences in flexibility requirements.
In response to the need for the decarbonization of the transport sector, it is expected that large fleets of electric vehicles (EVs) will constitute an important share of the electricity demand. This ...evolution is likely to be accompanied by a parallel evolution of the electricity supply business with the deployment of smart grid technologies. As a consequence, it is expected that demand will feature higher potential for communication and control, which will enable its active participation in the daily operational planning of power systems. In particular, EVs being equipped with a battery can both defer their demand or inject electricity back into the system. However, to achieve volumes that can have an impact on the system, these demands need to be aggregated and operated as an ensemble. This paper proposes the necessary adaptations to include the input of EV aggregation to electricity markets. This permits the scheduling of EV charging and services in coordination with the system operator thus enhancing the power system's efficiency and security while reducing its environmental impact. Results show that the EVs penetration levels that the system would be able to absorb without requiring expansion of the supply side, are significantly increased when coordination over their charging schedule is performed.
Background and Aims
In general, physical activity (PA) and nonalcoholic fatty liver disease (NAFLD) have an inverse association. However, studies assessing the impact of the widely accepted Physical ...Activity Guidelines for Americans (PA Guidelines) on NAFLD are lacking.
Approach and Results
We performed a serial, cross‐sectional analysis among adults by using the 2007‐2016 US National Health and Nutrition Examination Survey. NAFLD and advanced fibrosis were defined by using various noninvasive panels. A PA questionnaire assessed the leisure‐time PA, occupation‐related PA, transportation‐related PA, and total sitting time as sedentary behavior. PA was categorized according to the PA Guidelines. Of the 24,588 individuals (mean age, 47.4 years; 47.9% males), leisure‐time PA (≥150 minutes per week) demonstrated 40% lower odds of NAFLD, whereas transportation‐related PA was associated with a 33% risk reduction in NAFLD. Analysis of total PA and sitting times simultaneously showed a dose‐response association between sitting time and NAFLD (P for trend < 0.001). Compliance with the PA Guidelines was lower in individuals with NAFLD versus those without NAFLD. The trends in compliance with the PA Guidelines for any type of PA remained stable in individuals with NAFLD except for a downtrend in transportation‐related PA. In contrast, an improvement in compliance with the PA Guidelines for leisure time was noted in the cohort without NAFLD. Although PA demonstrated a 10% stronger association with risk reduction of NAFLD in women, women showed a lower tendency of meeting the PA Guidelines. Trends in total sitting time increased significantly regardless of NAFLD status.
Conclusions
Sedentary behavior emerged as an independent predictor of NAFLD. Overall compliance with the PA Guidelines was lower in the cohort with NAFLD, with sex‐ and ethnicity‐based differences. Implementation of these observations in clinical practice may improve our understanding as well as clinical outcomes.
Charging stations are the basic infrastructure for accommodating the energy needs of electric vehicles (EVs). Companies are expected to invest in these charging stations by installing them at ...locations with a dense concentration of vehicles, such as parking places, commercial centres, and workplaces. In order for investors in EV charging stations to maximise their profits and mitigate the impact on the power grid, these stations would benefit from coupling with an energy storage system (ESS). ESS would be used to arbitrage energy and to balance out the time-variant and uncertain EV energy demand. This study proposes a framework to optimise the offering/bidding strategy of an ensemble of charging stations coupled with ESS in the day-ahead electricity market. The proposed framework accounts for degradation of the ESS, robust scheduling against price uncertainty, as well as stochastic energy demand from EVs. The results show the viability of the proposed framework in providing cost savings to an ensemble of EV charging stations.
The most dangerous effects of anthropogenic climate change can be mitigated by using emissions taxes or other regulatory interventions to reduce greenhouse gas (GHG) emissions. This paper takes a ...regulatory viewpoint and describes the Weighted Sum Bisection method to determine the lowest emission tax rate that can reduce the anticipated emissions of the power sector below a prescribed, regulatorily-defined target. This bilevel method accounts for a variety of operating conditions via stochastic programming and remains computationally tractable for realistically large planning test systems, even when binary commitment decisions and multiperiod constraints on conventional generators are considered. Case studies on a modified ISO New England test system demonstrate that this method reliably finds the minimum tax rate that meets emissions targets. In addition, it investigates the relationship between system investments and the tax-setting process. Introducing GHG emissions taxes increases the value proposition for investment in new cleaner generation, transmission, and energy efficiency; conversely, investing in these technologies reduces the tax rate required to reach a given emissions target.
An important function of aggregators is to enable the participation of small energy storage units in electricity markets. This paper studies two generally overlooked aspects related to aggregators of ...energy storage: 1) the relationship between the aggregator and its constituent storage units and 2) the aggregator's effect on system welfare. Regarding 1), we show that short-term outcomes can be Pareto-inefficient: all players could be better-off. In practice, however, aggregators and storage units are likely to engage in long rather than short-term relationships. Using Nash bargaining theory, we show that aggregators and storage units are likely to cooperate in the long-term. A rigorous understanding of the aggregator-storage unit relationship is fundamental to model the aggregator's participation in the market. Regarding 2), we first show that a profit-seeking energy storage aggregator is always beneficial to the system when compared to a system without storage, regardless of size or market power the aggregator may have. However, due to market power, a monopolist aggregator may act in a socially suboptimal manner. We propose a pricing scheme designed to mitigate market power abuse by the aggregator. This pricing scheme has several important characteristics: its formulation requires no private information, it incentivizes a rational aggregator to behave in a socially optimal manner, and allows for regulation of the aggregator's profit.
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