Flexibility Characterization, Aggregation, and Market Design Trends with a High Share of Renewables: a Review

Purpose of Review Balancing a large share of solar and wind power generation in the power system will require a well synchronized coordination of all possible flexibility sources. This entails developing market designs that incentivize flexibility providers, and define new flexibility products. To this end, the paper reviews latest trends in the characterization of flexibility by understanding its dimensions in terms of time, spatiality, resource type, and associated risks. Also, as aggregators have emerged as important actors to deliver, and to reward end-user flexibility, the paper reviews latest trends in the topic. Recent Findings The review reports latest trends and discussions on power system flexibility and their relations to market design. The current academic literature indicates that there are open question and limited research on how to reward shortterm flexibility while considering its long-term economic viability. Demand-side flexibility through aggregation holds great potential to integrate renewables. Summary Research in power system flexibility has to put effort on analysing new time-structures of electricity markets and define new marketplaces that consider the integration of new flexibility products, actors (e.g. aggregators, end-users), and mechanisms (e.g. TSO-DSO coordination).Flexibility Characterization, Aggregation, and Market Design Trends with a High Share of Renewables: a ReviewpublishedVersio

Diagnosis of comorbid migraine without aura in patients with idiopathic/genetic epilepsy based on the gray zone approach to the International Classification of Headache Disorders 3 criteria

BackgroundMigraine without aura (MwoA) is a very frequent and remarkable comorbidity in patients with idiopathic/genetic epilepsy (I/GE). Frequently in clinical practice, diagnosis of MwoA may be challenging despite the guidance of current diagnostic criteria of the International Classification of Headache Disorders 3 (ICHD-3). In this study, we aimed to disclose the diagnostic gaps in the diagnosis of comorbid MwoA, using a zone concept, in patients with I/GEs with headaches who were diagnosed by an experienced headache expert.MethodsIn this multicenter study including 809 consecutive patients with a diagnosis of I/GE with or without headache, 163 patients who were diagnosed by an experienced headache expert as having a comorbid MwoA were reevaluated. Eligible patients were divided into three subgroups, namely, full diagnosis, zone I, and zone II according to their status of fulfilling the ICHD-3 criteria. A Classification and Regression Tree (CART) analysis was performed to bring out the meaningful predictors when evaluating patients with I/GEs for MwoA comorbidity, using the variables that were significant in the univariate analysis.ResultsLonger headache duration (<4 h) followed by throbbing pain, higher visual analog scale (VAS) scores, increase of pain by physical activity, nausea/vomiting, and photophobia and/or phonophobia are the main distinguishing clinical characteristics of comorbid MwoA in patients with I/GE, for being classified in the full diagnosis group. Despite being not a part of the main ICHD-3 criteria, the presence of associated symptoms mainly osmophobia and also vertigo/dizziness had the distinguishing capability of being classified into zone subgroups. The most common epilepsy syndromes fulfilling full diagnosis criteria (n = 62) in the CART analysis were 48.39% Juvenile myoclonic epilepsy followed by 25.81% epilepsy with generalized tonic-clonic seizures alone.ConclusionLonger headache duration, throbbing pain, increase of pain by physical activity, photophobia and/or phonophobia, presence of vertigo/dizziness, osmophobia, and higher VAS scores are the main supportive associated factors when applying the ICHD-3 criteria for the comorbid MwoA diagnosis in patients with I/GEs. Evaluating these characteristics could be helpful to close the diagnostic gaps in everyday clinical practice and fasten the diagnostic process of comorbid MwoA in patients with I/GEs

Stochastic programming in analyses of flexibility in power systems and markets

Summary of the thesis In the research for this thesis, operations research techniques are applied in power markets and systems to investigate the usage of flexibility under conditions of uncertainty. Economic dispatch models and optimal power flow models are used for designing and analyzing power markets and systems. In the economic dispatch models, economic factors and their relations with power markets are analyzed, while in optimal power flow models, answers to power grid operations for voltage and network congestion are searched. During the research, the first research question addressed was how to determine the flexibility concept, products, and services about various power and energy markets. This led to the development of a theoretical and empirical taxonomy for flexibility trading and related market structures. The second question addressed during the research considered how to use flexibility according to two separate systemic approaches, different tariff designs to exploit flexibility usage for reducing peak pricing, and a stochastic optimal scheduling methodology for end user’s flexibility assets to solve grid problems. The third and final question addressed during the research concerned how it is possible to have a cost-efficient and productive local flexibility market design for grid operations under uncertainty. Answers to the research questions are provided in the four papers that form the basis of this thesis. Paper I explains the taxonomy and provides an overview of flexibility and its products along four dimensions—time, spatiality, resource, and risk profile—according to the market design. Paper II shows how to activate and use flexibility with a dynamic tariff design for peak shaving. Paper III provides solutions to grid problems under uncertainty (i.e., voltage and congestion) by using flexibility from the demand side, storage side, and supply side. Lastly, Paper IV proposes a stochastic local flexibility market design, bidding, and dispatch methodology to contribute grid operations on a local scale. Sammendrag av avhandlingen I forskningen for denne avhandlingen brukes operasjonsforskningsteknikker i kraftmarkeder og systemer for å undersøke bruken av fleksibilitet under forhold med usikkerhet. Økonomiske forsendelsesmodeller og optimale strømflytmodeller brukes til å designe og analysere kraftmarkeder og systemer. I de økonomiske forsendelsesmodellene analyseres økonomiske faktorer og deres relasjoner til kraftmarkeder, mens det i optimale kraftstrømmodeller søkes etter svar på kraftnettdrift for spenning og overbelastning av nett. Under undersøkelsen var det første forskningsspørsmålet som ble tatt opp, hvordan man kan bestemme fleksibilitetskonseptet, produktene og tjenestene om ulike kraft- og energimarkeder. Dette førte til utviklingen av en teoretisk og empirisk taksonomi for fleksibilitetshandel og relaterte markedsstrukturer. Det andre spørsmålet som ble adressert under forskningen vurderte hvordan man kan bruke fleksibilitet i henhold til to separate systemiske tilnærminger, ulike tariffdesign for å utnytte fleksibilitetsbruken for å redusere topprising, og en stokastisk optimal planleggingsmetodikk for sluttbrukerens fleksibilitetsressurser for å løse nettproblemer. Det tredje og siste spørsmålet som ble tatt opp under forskningen handlet om hvordan det er mulig å ha et kostnadseffektivt og produktivt lokalt fleksibilitetsmarkedsdesign for nettdrift under usikkerhet. Svar på forskningsspørsmålene er gitt i de fire paperne som ligger til grunn for denne avhandlingen. Paper I forklarer taksonomien og gir en oversikt over fleksibilitet og dens produkter langs fire dimensjoner – tid, romlighet, ressurs og risikoprofil – i henhold til markedsdesignet. Paper II viser hvordan du aktiverer og bruker fleksibilitet med en dynamisk tariffdesign for toppbarbering. Paper III gir løsninger på nettproblemer under usikkerhet (dvs. spenning og overbelastning) ved å bruke fleksibilitet fra etterspørselssiden, lagringssiden og tilbudssiden. Til slutt foreslår Paper IV en stokastisk lokal fleksibilitetsmarkedsdesign, budgivnings- og utsendelsesmetodikk for å bidra med nettdrift i lokal skala

Paralel şerit belirsizliği altında sağlam koşullu riske maruz değer: portföy optimizasyonu uygulaması.

In markets with high uncertainties, the trade–off between maximizing expected return and minimizing the risk is one of the main challenges in modeling and decision making. Since investors mostly shape their invested amounts towards certain assets and their risk version level according to their returns; scientists and practitioners has done studies on this subject since the beginning of the stock markets’ establishment. Developments and inventions in the mathematical optimization provide a wide range of solutions to handle this problem. Mean–Variance Approach by Markowitz is one the oldest and best known approaches to the risk–return trade–off in the markets. However, it is a one time–step model and not very much prepared for highly volatile markets. After Markowitz, different optimization approaches have been invented for portfolio Optimization, especially, in the tradition of Conditional Value–at–Risk. In this study, we modeled a Robust Optimization problem based on the data and used Robust Optimization approach to find a robust optimal solution to our portfolio optimization problem. This approach includes the use of Robust Conditional Value–at–Risk (RCVaR) under Parallelpipe Uncertainty sets, an evaluation and a numerical finding of the robust optimal portfolio allocation. We obtained and then traced back our robust linear programming model to the Standard Form of a Linear Programming model; then we solved it by a well–chosen algorithm and software package. The main idea is modeling a robust portfolio optimization problem that includes our development of RCVaR based on uncertainty–set–valued data. Our aim is, by considering the return–risk trade–off analysis under uncertain data, to obtain more robust, in fact, lower, risk–level under worst–case scenario by using RCVaR. Uncertainty in parameters, based on uncertainty in the prices, and a risk–return analysis are crucial parts of this study. Hence, the trade–off (antagonism) between accuracy and risk (variance), and robustness are our main issue. A numerical experiment is presented containing real–world data from stock markets. The thesis ends with a conclusion and an outlook to future studies. M.S. - Master of Scienc

Comparing individual and coordinated demand response with dynamic and static power grid tariffs

This paper investigates cost-optimal operation of flexible electricity assets with a capacity-based power grid tariff involving power subscription. The purpose of this research is to identify the characteristics of a subscribed capacity-based tariff that promotes efficient network development through demand response. Using historical load data, we compare two consumers with flexible assets being billed by their individual load versus their combined and coordinated loads in a two-stage stochastic program. The frequency of adjusting the subscribed capacity level (weekly versus annually) influences the effectiveness of the tariff in terms of reducing loads that dimension the grid. The results show that weekly subscription on average provides cost savings, while annual subscription on average provides 3% cost savings. A combined annual peak load reduction of occurs when the combined subscription level is adjusted weekly. We also find that when the subscription level is adjusted weekly, the load reduction is cost efficient even when capacity is not scarce, which ought to be avoided. Depending on where a bottleneck in the grid is located, the price signal should be based on the combined load of several consumers rather than individual loads if combined peak load shaving is to be cost-optimal

Characterizing flexibility in power markets and systems

The increasing share of variable renewable energy sources creates a need for flexibility resources in the power system operations. This paper presents suggestions for characterizing flexibility, including dimensions of time, spatiality, resource type, and risk in power systems. We present interrelations between these flexibility dimensions, products, services, and suitable market designs. In light of this, we discuss TSO–DSO coordination and optimal flexibility resource allocation

Stability advances in robust portfolio optimization under parallelepiped uncertainty

In financial markets with high uncertainties, the trade-off between maximizing expected return and minimizing the risk is one of the main challenges in modeling and decision making. Since investors mostly shape their invested amounts towards certain assets and their risk aversion level according to their returns, scientists and practitioners have done studies on that subject since the beginning of the stock markets’ establishment. In this study, we model a Robust Optimization problem based on data. We found a robust optimal solution to our portfolio optimization problem. This approach includes the use of Robust Conditional Value-at-Risk under Parallelepiped Uncertainty, an evaluation and a numerical finding of the robust optimal portfolio allocation. Then, we trace back our robust linear programming model to the Standard Form of a Linear Programming model; consequently, we solve it by a well-chosen algorithm and software package. Uncertainty in parameters, based on uncertainty in the prices, and a risk-return analysis are crucial parts of this study. A numerical experiment and a comparison (back testing) application are presented, containing real-world data from stock markets as well as a simulation study. Our approach increases the stability of portfolio allocation and reduces the portfolio risk

Abant Dağları’ındaki Uludağ Göknarı (Abies nordmanniana subsp. bornmuelleriana) ağaçlarının epifitik bryofitleri

Bu çalışmada Abant Dağları’nda yayılış gösteren Abies nordmannia (Stev.) Spach subsp. bornmuelleriana (Matff.) Coode & Cullen. ağaçlarının epifitik bryofitleri araştırılmıştır. Çalışma 2010-2011 yılları arasında gerçekleştirilmiştir. A.nordmannia subsp. bornmuelleriana gövdesi üzerinden toplanan bryofit örnekleri değerlendirilerek 18 familyaya ait 23 cins ve bunlara bağlı 37 takson (7 ciğerotu, 30 karayosunu) tanımlanmıştır. Ayrıca, türlerin ekolojik karakteristikleri metin içerisinde (hayat formu, nem isteği, ışık isteği) tartışılmıştır. Taksonların hayat formu analizine göre 7 faklı hayat formu belirlenmiştir. Weft (saçak şeklinde) hayat formunun dominant olduğu saptanmıştır. Mezofitik ve skafit (gölge seven) türler hakim olurken kserofit (kurakçıl) ve fotofit (güneş seven) türlerin yoğunluğunun nispeten düşük olduğu belirlenmiştir.In this study, the epiphytic bryophytes of Abies nordmannia (Stev.) Spach subsp. bornmuelleriana (Matff.) Coode & Cullen. on Abant Mountains are investigated. The study carried out between the years 2010 and 2011. 37 taxa (7 liverwort, 30 moss) belonging to 18 families and 23 genera were identified by evaluated bryophyte specimens collected from A.nordmannia subsp. bornmuelleriana trunks. In addition, ecological characteristics (life-form, humidity, light regime) of the species were discussed in text. According to life-form analysis of taxa, seven different life-forms were determined. Weft (We) determined as the most dominant life-form. While mesophytic and sciophyt species are dominant, xerophytic and photophyt species are relatively less dominant