Flexibility products and markets: Literature review

The penetration of distributed renewable energy sources in the distribution grid is increasing considerably in the last years. This is one of the main causes that contributed to the growth of technical problems in both transmission and distribution systems. An effective solution to improve system security is to exploit the flexibility that can be provided by distributed energy resources (DER), which are mostly located at the distribution grids. Their location combined with the lack of power flow coordination at the system operators interface creates difficulties in taking advantage of these flexible resources. This paper presents a methodology based on the solution of a set of optimization problems that estimate the flexibility ranges at the distribution and transmission system operators (TSO-DSO) boundary nodes. The estimation is performed while considering the grid technical constraints and a maximum cost that the user is willing to pay. The novelty behind this approach comes from the development of flexibility cost maps, which allow the visualization of the impact of DER flexibility on the operating point at the TSO-DSO interface. The results are compared with a sampling method and suggest that a higher accuracy in the TSO-DSO information exchange process can be achieved through this approach.

Estimating the Active and Reactive Power Flexibility Area at the TSO-DSO Interface

The Concise Encyclopedia of Statistics presents the essential information about statistical tests, concepts, and analytical methods in language that is accessible to practitioners and students of the vast community using statistics in medicine, engineering, physical science, life science, social science, and business/economics. The reference is alphabetically arranged to provide quick access to the fundamental tools of statistical methodology and biographies of famous statisticians. The more than 500 entries include definitions, history, mathematical details, limitations, examples, references, and further readings. All entries include cross-references as well as the key citations. The back matter includes a timeline of statistical inventions. This reference will be an enduring resource for locating convenient overviews about this essential field of study.

The Concise Encyclopedia of Statistics

Meetings of the Advisory Technical Committees of the International Electrotechnical Commission were held in Brussels March 27th to April 1st. The meetings were attended by delegates from eight national committees — Belgium, France, Great Britain, Holland, Italy, Spain, Switzerland, and the United States. There were about 40 delegates in all.

https://ieeexplore.ieee.org/iel5/5308791/5321388/05321395.pdf

The International Electrotechnical Commission

As a result of the increased awareness of the dangers posed by global climate changes (mainly caused by growing global energy consumption needs), the quest for clean and sustainable energy future is becoming of paramount importance. This can be largely realized via a large-scale integration of variable renewable energy sources (RESs) such as wind and solar, which have relatively low carbon footprints. In many power systems, the level of integration of such resources is dramatically increasing. However, their intermittent nature poses significant challenges in the predominantly conventional power systems that currently exist. Among others, frequency and voltage regulation issues can, for example, arise because of improperly balanced and largely uncoordinated RES supply and demand. Generally, the higher the integration level of intermittent power sources is, the higher the flexibility needs are in the system under consideration. Flexibility, in a power systems context, refers to the ability of such a system to effectively cope with unforeseen changes in operational situations, which are mainly induced by the inherent uncertainty and variability arising from the supply side, demand side or any other external factors. In the absence of appropriate flexibility mechanisms, it is increasingly difficult to manage the imbalances between generation and demand as a result of their natural variations in real-time. This paper presents an extensive and critical review of the main existing and emerging flexibility options that can be deployed in power systems to support the integration of “carbon-free” and variable power production technologies. Starting from a broader definition of flexibility, we highlight the growing importance of such flexibility in renewable-rich energy systems, and provide insights into the challenges and opportunities associated with various flexibility options provided by different technologies.

A comprehensive survey of flexibility options for supporting the low-carbon energy future

Due to the increasing installation of decentralized generation units and the increasing demand of electrical power on distribution level the low voltage grids in Europe are facing different problems, e.g. deviations of the permitted voltage range or local inner overloads of the grid equipment. To overcome these problems a self-sustaining monitoring and control system for low voltage grids has been developed, which monitors the actual power flow situation and controls individual decentralized generation units and consumer loads if necessary. In this context new approaches for power flow calculation and control intelligence are inevitable. This paper describes a newly developed power flow algorithm to be used for online-monitoring of the grid state. In case of critical grid states identified by this power flow algorithm a control intelligence determines and executes possible strategies for elimination of the critical grid state. The developed algorithms have been tested and validated in comprehensive scenarios in consideration of plausibility, calculation speed and reliability of the results.

State identification and automatic control of smart low voltage grids

Due to the ascending capacity of Renewable Energy Sources, new challenges arise in the operation of distribution grids. Existing Smart Grid solutions have shown, that direct control interventions into distributed generation and demand facilities may contribute to ensure a reliable and economic grid operation. In extension of these direct control methods, this paper presents a new approach for an economic dispatch of flexibility options for grid services on distribution level. The developed modelling framework for a local flexibility market offers the possibility to simulate the market behavior. The modular set up of a grid operator model and several unit operator models allows research on the interaction between both domains in order to find the economically optimal operation mode for avoidance of critical grid states. The results of a one year simulation of a distribution grid are showing the advantageousness of the system.

Economic dispatch of flexibility options for Grid services on distribution level

The ongoing shift towards a more decentralized and renewable energy system in Germany requires extensive modifications to existing grids and their operating principles - especially at the distribution level. Furthermore, the integration of e-mobility will have a significant effect on distribution grids. Smart distribution systems are one way of handling these new supply scenarios. Hence, a self-sustaining monitoring and control system for LV-grids has been developed. It monitors the power flow situation and is able to control the grid if necessary. The system has been implemented in four LV-grids in Germany. The present paper describes the automation system and our initial experience with this smart grid approach. (4 pages)

/pdf/experience-with-first-smart-autonomous-lv-grids-in-germany-8yv6kabc1z.pdf

Experience with first smart, autonomous LV-grids in Germany

Due to the high penetration of distributed power generation, many German medium voltage distribution grids are reaching their capacity limits. Meshed grid topology such as “closed loop”operation and interconnections between grids on the same voltage level can contribute to a reliable operation of the critical infrastructure and reduce costs by avoiding additional conventional grid expansion.

Impact of meshed grid topologies on distribution grid planning and operation

Due to the increasing installation of decentralized generation units and the increasing demand of electrical power on distribution level the low voltage grids in Germany are facing different problems, e.g. deviations of the permitted voltage range or local inner overloads of the grid equipment. To overcome these problems a self-sustaining monitoring and control system for low voltage grids has been developed, which monitors the actual power flow situation and controls individual decentralized generation units and consumer loads if necessary. The control system has been implemented into several low voltage grids in Germany. This paper describes first practical experience with the developed smart grid approach.

Markus Zdrallek

Papers

State identification and automatic control of smart low voltage grids

Economic dispatch of flexibility options for Grid services on distribution level

Experience with first smart, autonomous LV-grids in Germany

Impact of meshed grid topologies on distribution grid planning and operation

First practical experience with smart low voltage grids