Eamonn Lannoye

Evaluation of Power System Flexibility

As the penetration of variable renewable generation increases in power systems worldwide, planning for the effects of variability will become more important. Traditional capacity adequacy planning techniques have been supplemented with integration studies, which have been carried out in power systems with high targets for renewable generation. These have highlighted the increased variability that a system may experience in the future. As system generation planning techniques evolve with the challenge of integrating variable generation, the flexibility of a system to manage periods of high variability needs to be assessed. The insufficient ramping resource expectation (IRRE) metric is proposed to measure power system flexibility for use in long-term planning, and is derived from traditional generation adequacy metrics. Compared to existing generation adequacy metrics, flexibility assessment is more data intensive. A flexibility metric can identify the time intervals over which a system is most likely to face a shortage of flexible resources, and can measure the relative impact of changing operational policies and the addition of flexible resources. The flexibility of a test system with increasing penetrations of variable generation is assessed. The results highlight the time horizons of increased and decreased risk associated with the integration of VG.

Evolution of operating reserve determination in wind power integration studies

The growth of wind power as an electrical power generation resource has produced great benefits with reductions in emissions and the supply of zero cost fuel. It also has created challenges for the operation of power systems arising from the increased variability and uncertainty it has introduced. A number of studies have been performed over the past decade to analyze the operational impacts that can occur at high penetrations of wind. One of the most crucial impacts is the amount of incremental operating reserves required due to the variability and uncertainty of wind generation. This paper describes different assumptions and methods utilized to calculate the amount of different types of reserves carried, and how these methods have evolved as more studies have been performed.

Transmission, Variable Generation, and Power System Flexibility

Long-term transmission and generation planning face numerous challenges to accommodate the integration of a high penetration of variable generation (VG). System flexibility, or the ability of a system to meet changes in demand and VG production, is one such issue receiving much attention. This paper presents a methodology to assess the flexibility of a power system while explicitly considering the limitations of the transmission network. By determining only the flexibility available from resources which could be realized in real-time operation due to transmission constraints, a more realistic assessment of a systems flexibility can be made. The flexibility of the IEEE Reliability Test System is assessed using two metrics. Transmission is shown to have a significant effect on the availability of flexibility and the risk posed to the system by net load ramps. The impact is seen to be strongly dependent on the variability of the net load and on the distribution of online resources. A nonlinear relationship between the installed VG and system flexibility is found, with regions of significant inflexibility occurring at certain VG penetrations.

Flexibility in 21st Century Power Systems

Flexibility of operation--the ability of a power system to respond to change in demand and supply--is a characteristic of all power systems. Flexibility is especially prized in twenty-first century power systems, with higher levels of grid-connected variable renewable energy (primarily, wind and solar). This paper summarizes the analytic frameworks that have emerged to measure this characteristic and distills key principles of flexibility for policy makers.

Experience and Challenges With Short-Term Balancing in European Systems With Large Share of Wind Power

The amount of wind power in the world is quickly increasing. The background for this development is improved technology, decreased costs for the units, and increased concern regarding environmental problems of competing technologies such as fossil fuels. Some areas are starting to experience very high penetration levels of wind and there have been many instances when wind power has exceeded 50% of the electrical energy production in some balancing areas. The aims of this paper are to show the increased need for balancing, caused by wind power in the minutes to hourly time scale, and to show how this balancing has been performed in some systems when the wind share was higher than 50%. Experience has shown that this is possible, but that there are some challenges that have to be solved as the amount of wind power increases.

The Flexibility Workout: Managing Variable Resources and Assessing the Need for Power System Modification

Wind and solar generation may consequently be difficult to predict over some time scales. Large penetrations of variable generation (VG) lead to increases in the variability and uncertainty in the systems generation output, driving a need for greater flexibility. This flexibility will need to come either from flexible generation technologies or from alternative sources of flexibility such as flexible demand and storage. This article will discuss the additional flexibility needs introduced by variable generation from wind and solar power and will describe general approaches to analyzing the need for and provision of additional flexibility in the power system in both the operational and planning time frames.

Integration of variable generation: Capacity value and evaluation of flexibility

As integration of variable generation continues to grow rapidly in power systems globally, system planners are seeking new tools to understand the role of variable output generators and the challenges experienced with their integration. The North American Electric Reliability Corporation (NERC) has established a task force to examine the integration of variable generation. This paper details the achievements to date and outlines ongoing efforts from Task 1.2 on the capacity value of variable generation and from Task 1.4 on the concept of flexibility in power systems and options for its definition. Arising from international collaboration with the International Energy Agency, a discussion on the definition of flexible resources is presented. A potential metric for flexibility offered by conventional plant is developed and applied to a test system.

The role of power system flexibility in generation planning

As the penetration of variable renewable generation increases in power systems worldwide, planning for the effects of variability will become more important. Traditional capacity adequacy planning techniques have been supplemented with integration studies, which have been carried out in power systems with high targets for renewable generation. These have highlighted the increased variability that a system may experience in the future. As system planning techniques evolve with the demands from variable generation, the flexibility of a system to manage periods of high variability will need to be assessed. A metric may be required to measure the flexibility of a power system for use in planning studies with multi-year horizons. Compared to generation adequacy metrics, system flexibility assessment is more data intensive and requires more detailed system modeling. An algorithm for scenario development in generation planning with high penetrations of variable generation is presented.

Power system flexibility assessment — State of the art

Recent research has led to the development of a number of metrics for the assessment of flexibility in a power system. This paper presents an overview of the tools currently available to those involved in planning and operations to directly incorporate the assessment of the requirements for flexibility, the flexibility resource available in each system and methodologies to assess the overall flexibility of a system including operational and transmission constraints. Current challenges and areas for future development are also highlighted.

Assessment of power system flexibility: A high-level approach

The targeted growth of variable generation capacity in many power systems has led to concern that future systems may have insufficient flexibility to meet ramps in variable generation (VG) production and system demand. This paper introduces a high-level flexibility assessment methodology for use by those involved in planning, and with little experience of the integration of large quantities of variable generation. This is proposed as a first step in assessing the future needs of a system. Comparison is drawn between the proposed high-level flexibility assessment and a more detailed flexibility assessment. The insufficient ramp resource expectation (IRRE) highlights those time horizons in which the system may have insufficient flexibility to meet changes in the net load. The methodology is demonstrated on a test system from which high-level conclusions may be drawn. A number of other insights are also offered by the proposed methodology, including the distributions of the size of the deficit, and surplus, of ramping capability.