Aidan Tuohy

Unit Commitment for Systems With Significant Wind Penetration

The stochastic nature of wind alters the unit commitment and dispatch problem. By accounting for this uncertainty when scheduling the system, more robust schedules are produced, which should, on average, reduce expected costs. In this paper, the effects of stochastic wind and load on the unit commitment and dispatch of power systems with high levels of wind power are examined. By comparing the costs, planned operation and performance of the schedules produced, it is shown that stochastic optimization results in less costly, of the order of 0.25%, and better performing schedules than deterministic optimization. The impact of planning the system more frequently to account for updated wind and load forecasts is then examined. More frequent planning means more up to date forecasts are used, which reduces the need for reserve and increases performance of the schedules. It is shown that mid-merit and peaking units and the interconnection are the most affected parts of the system where uncertainty of wind is concerned.

Experience From Wind Integration in Some High Penetration Areas

The amount of wind power in the world is increasing quickly. 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. The amount of wind power is not spread equally over the world, so in some areas, there is comparatively a high concentration. The aims of this paper are to overview some of these areas, and briefly describe consequences of the increase in wind power. The aim is also to try to draw some generic conclusions, in order to get some estimation about what will happen when the amount of wind power increases for other regions where wind power penetration is expected to reach high values in future

Impact of pumped storage on power systems with increasing wind penetration

In this paper, the unit commitment and dispatch of a power system with and without a pumped storage unit is examined for increasing levels of installed wind power, from 17% of total energy to 80% of total energy generated by wind 3 (3GW to 15GW of installed wind on the Irish system in 2020). At high levels of installed wind, it is shown that storage reduces curtailment and increases the use the base loaded plant on the system. This reduces system costs. However, when the additional capital costs of storage are taken into account, it is shown that storage is not viable from a system perspective until extremely large levels of wind power are seen on the system. At these levels of installed wind, while the system can operate without storage, it is less costly to do so with storage. The capacity credit of the storage unit is also examined, using a simplified approach, and shown to decrease as larger amounts of intermittent wind power are added to the system.

Market Designs for the Primary Frequency Response Ancillary Service—Part I: Motivation and Design

The first part of this two-paper series discusses the motivation of implementing a primary frequency response (PFR) market in restructured pool-based power markets, as well as the market design that would create the right incentives to provide the response reliably. PFR is the immediate, autonomous response of generation and demand to system frequency deviations. It is the critical response required to avoid triggering under- and over- frequency relays or instability that could lead to machine damage, load-shedding, and in the extreme case, blackouts. Currently, in many restructured power systems throughout the world, ancillary services markets have been developed to incent technologies to provide the services to support power system reliability. However, few ancillary services markets include a market explicitly incentivizing the provision of PFR. Historically, PFR was an inherent feature available in conventional generating technologies, and in most systems, more was available than needed. Yet, recent trends in declining frequency response, the introduction of emerging technologies, and market behavior may soon require innovative market designs to incent resources to provide this valuable service.

Rolling Unit Commitment for Systems with Significant Installed Wind Capacity

As wind power penetration grows, the amount of reserve needed on the system also grows, due to the increases in the uncertainty of wind power, which grows larger as forecast horizon increases. By scheduling the system more often the amount of extra reserve to be carried to cater for wind uncertainty decreases, depending on the flexibility of plant on the system. This reduces the costs of operating the system. There is a trade off between reduced costs due to more frequent commitment, the ability of wind forecasts to be made more accurately, and the increased costs of more flexible plant. This paper examines the benefits of committing the system more frequently, and how different factors such as reliability of the system, accuracy of the forecasts and plant mix impact on this.

Short-Term Energy Balancing With Increasing Levels of Wind Energy

Increasing levels of wind energy are adding to the uncertainty and variability inherent in electricity grids and are consequently driving changes. Here, some of the possible evolutions in optimal short-term energy balancing to better deal with wind energy uncertainty are investigated. The focus is mainly on managing reserves through changes in scheduling, in particular market structure (more regular and higher resolution scheduling), reserve procurement (dynamic as opposed to static), and improved operational planning (stochastic as opposed to deterministic). Infrastructure changes including flexible plant, increased demand side participation, more interconnection, transmission, larger balancing areas, and critically improved forecasting can also be significant and are dealt with in the discussion. The evolutions are tightly coupled, their impact is system-dependent and so no “best” set is identifiable but experience of system operators will be critical to future developments.

Solar Forecasting: Methods, Challenges, and Performance

The deployment of solar-based electricity generation, especially in the form of photovoltaics (PVs), has increased markedly in recent years due to a wide range of factors including concerns over greenhouse gas emissions, supportive government policies, and lower equipment costs. Still, a number of challenges remain for reliable, efficient integration of solar energy. Chief among them will be developing new tools and practices that manage the variability and uncertainty of solar power.

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.

Market Designs for the Primary Frequency Response Ancillary Service—Part II: Case Studies

The second part of this two-paper series analyzes the primary frequency response (PFR) market design developed in its companion paper with several case studies. The simulations will show how the scheduling and pricing change depending on whether requirements for PFR are included as well as how the requirements are defined. We first perform simulations on the base case IEEE RTS and show differences in production costs, prices, and amount of PFR when incorporating the PFR constraints. We show how new market designs can affect other linked markets when performing co-optimization. We then test a system with a significant amount of wind power, which does not provide PFR or synchronous inertia, to see how the incorporation of PFR constraints may become more critical on future systems. We then show how pricing can reduce make-whole payments and ensure resources needed for reliability reasons are incentivized. Lastly, we show how resources that improve their capabilities can earn additional profit if the improvement is needed ensuring the incentives can work for innovation in PFR capabilities.

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.