Increasing Wind Penetration Research Articles

Effect of increased wind penetration on system prices in Korea's electricity markets

ABSTRACTIn this paper, we examine the effect of increased wind penetration on system marginal prices (SMPs) in South Korea's electricity market. Korea's renewable portfolio standard (RPS) went into effect in 2012, with a goal of increasing the share of renewable generation to 10% of the total load by 2022. We examine the output of wind installations across the Korean peninsula and simulate an increase in wind penetration consistent with Korea's RPS targets. Under a variety of assumptions on demand elasticity, we find that higher shares of wind generation in total supply reduce both the average SMP and its variation. In particular, we find that wind energy output on the Korean peninsula is more correlated with peak electricity demand than has been reported for other regions. The per‐unit value of wind energy to owners of wind assets is thus higher for South Korea than would be the case for European or North American locations with a similar mix of fuels other than wind. Copyright © 2013 John Wiley & Sons, Ltd.

Wind Power Uncertainty and Power System Performance

The penetration of wind power into global electric power systems is steadily increasing, with the possibility of 30% to 80% of electrical energy coming from wind within the coming decades. At penetrations below 10% of electricity from wind, the impact of this variable resource on power system operations is manageable with historical operating strategies. As this penetration increases, new methods for operating the power system and electricity markets need to be developed. As part of this process, the expected impact of increased wind penetration needs to be better understood and quantified. This paper presents a comprehensive modeling framework, combining optimal power flow with Monte Carlo simulations used to quantify the impact of high levels of wind power generation in the power system. The impact on power system performance is analyzed in terms of generator dispatch patterns, electricity price and its standard deviation, CO2 emissions and amount of wind power spilled. Simulations with 10%, 20% and 30% wind penetration are analyzed for the IEEE 39 bus test system, with input data representing the New England region. Results show that wind power predominantly displaces natural gas fired generation across all scenarios. The inclusion of increasing amounts of wind can result in price spike events, as the system is required to dispatch down expensive demand in order to maintain the energy balance. These events are shown to be mitigated by the inclusion of demand response resources. Benefits include significant reductions in CO2 emissions, up to 75% reductions at 30% wind penetration, as compared to emissions with no wind integration.

Assessing the value of wind generation in future carbon constrained electricity industries

This paper employs a novel Monte-Carlo based generation portfolio assessment tool to explore the implications of increasing wind penetration and carbon prices within future electricity generation portfolios under considerable uncertainty. This tool combines optimal generation mix techniques with Monte Carlo simulation and portfolio analysis methods to determine expected overall generation costs, associated cost uncertainty and expected CO2 emissions for different possible generation portfolios. A case study of an electricity industry with coal, Combined Cycle Gas Turbines (CCGT), Open Cycle Gas Turbines (OCGT) and wind generation options that faces uncertain future fossil-fuel prices, carbon pricing, electricity demand and plant construction costs is presented to illustrate some of the key issues associated with growing wind penetrations. The case study uses half-hourly demand and wind generation data from South Eastern Australia, and regional estimates of new-build plant costs and characteristics. Results suggest that although wind generation generally increases overall industry costs, it reduces associated cost uncertainties and CO2 emissions. However, there are some cases in which wind generation can reduce the overall costs of generation portfolios. The extent to which wind penetration affects industry expected costs and uncertainties depends on the level of carbon price and the conventional technology mix in the portfolios.

Commitment and Dispatch With Uncertain Wind Generation by Dynamic Programming

Fluctuating wind production over short time periods is balanced by adjusting generation from thermal plants to meet demand. Thermal ramp rates are limited, so increased variation in wind output as wind penetration increases can add to system operating costs because of the need for more thermal operating reserves. Traditional deterministic modeling techniques fail to fully capture these extra costs. We propose a stochastic dynamic programming (SDP) approach to unit commitment and dispatch, minimizing operating costs by making optimal unit commitment, dispatch, and storage decisions in the face of uncertain wind generation. The SDP solution is compared with two other solutions: 1) that of a deterministic dynamic program with perfect wind predictions to find the cost of imperfect information, and 2) that of a simulation model run under a decision rule, derived from Monte Carlo simulations of the deterministic model, to assess the cost of suboptimal stochastic decision making. An example Netherlands application shows that these costs can amount to several percent of total production costs, depending on installed wind capacity. These are the conclusions of a single simplified case study. Nonetheless, the results indicate that efforts to improve wind forecasting and to develop stochastic commitment models may be highly beneficial.

Effective Wind Farm Sizing Method for Weak Power Systems Using Critical Modes of Voltage Instability

Current methods for determining wind farm maximum sizes which do not consider voltage stability margins (VSMs) may result in reducing the overall levels of wind generation in a system. In this paper, new methods have been developed to increase wind penetration level by placing new wind generation at voltage stability strong wind injection buses. Placing new generation at these buses has the least impact on VSMs not only in the vicinity of new wind generation, but also throughout the power system. The new methods provide a comprehensive methodology for the identification of system weaknesses for each wind penetration level. The new methods incorporate modal analysis as well as traditional voltage stability methods (Q-V curves) in sizing and placing new wind farms. The study shows that the location of SVCs is also key to increasing wind penetration. Wind penetration can be increased when placing SVCs at the weakest buses in the system instead of only locating them at the wind generation buses.

Agent-based modeling for trading wind power with uncertainty in the day-ahead wholesale electricity markets of single-sided auctions

This paper, for the first time, adopts agent-based simulation approach to investigate the bidding optimization of a wind generation company in the deregulated day-ahead electricity wholesale markets, by considering the effect of short-term forecasting accuracy of wind power generation. Two different wind penetration levels (12% and 24%) are investigated and compared. Based on MATPOWER 4.0 software package and the 9-bus 3-generator power system defined by Western System Coordinating Council, the agent-based models are built and run under the uniform price auction rule and locational marginal pricing mechanism. Each generation company could learn from its past experience and improves its day-ahead strategic offers by using Variant Roth–Erev reinforcement learning algorithm. The results clearly demonstrate that improving wind forecasting accuracy helps increase the net earnings of the wind generation company. Also, the wind generation company can further increase its net earnings with the adoption of learning algorithm. Besides, it is verified that increasing wind penetration level within the investigation range can help reduce the market clearing price. Furthermore, it is also demonstrated that agent-based simulation is a viable modeling tool which can provide realistic insights for the complex interactions among different market participants and various market factors.

Safety in Numbers: Online Security Analysis of Power Grids with High Wind Pentration

This article presents an application example of online DSA technology in performing near-real-time security assessment of the power system that covers Ireland and Northern Ireland. It is a single synchronous system that has limited HVDC interconnection to Scotland. The combined maximum and minimum demand of these two systems is approximately 6,800 and 2,500 MW, respectively. Tripping of the largest generator (440 MW) can result in a frequency fall of more than 0.6 Hz even with a primary fast-acting operating reserve of 75% of the maximum in-feed. The relatively small size of the system also dictates frequency variations wider than those in continental Europe under normal conditions. Generation plant (installed capacity) is mostly thermal, with some 6% of hydro and hydro pumped storage and a 16% wind share that is increasing rapidly. An additional 500-MW HVDC link to the U.K. grid based on voltage source converter (VSC) technology (due for commissioning in 2012) is expected to improve the power system's ability to accommodate wind generation. Increased wind penetration changes the operational characteristics of the power system, primarily due to the unique nature of the wind generation technology described earlier. Increased levels of wind generation introduce new risks and challenges for the transmission system operator.

Multi-Mode Operation of Combined-Cycle Gas Turbines With Increasing Wind Penetration

As power systems evolve to incorporate greater penetrations of variable renewables, the demand for flexibility within the system is increased. Combined-cycle gas turbines are traditionally considered as relatively inflexible units, but those which incorporate a steam bypass stack are capable of open-cycle operation. Facilitating these units to also operate in open-cycle mode can benefit the power system via improved system reliability, while reducing the production needed from dedicated peaking units. The utilization of the multi-mode functionality is shown to be dependent on the flexibility inherent in the system and the manner in which the system is operated.

Optimal Wind Clustering Methodology for Adequacy Evaluation in System Generation Studies Using Nonsequential Monte Carlo Simulation

In this paper, several clustering algorithms are investigated in order to group together wind parks with close statistical behavior. Here, the proposed approach is practically founded on a fast incremental algorithm validated by a normalized principal component analysis combined with a k-means process. Both methods are practically based on the definition of a Pearson correlation coefficient. The advantage of such a clustering methodology is mainly perceptible in large-scale electrical systems with increased wind penetration. Indeed, it allows to group together highly correlated wind parks into the same cluster and to integrate them in a realistic way into a nonsequential Monte Carlo adequacy evaluation process. Here, the implemented clustering methodology is applied to 94 wind sites located in Occidental Europe. Then, in order to point out the efficiency of this clustering methodology that is afterwards combined with an original wind speed sampling process, an adequacy study is applied to the Roy Billinton Test System in the particular case of two wind clusters.

Pumped storage in systems with very high wind penetration

This paper examines the operation of the Irish power system with very high levels of wind energy, with and without pumped storage. A unit commitment model which accounts for the uncertainty in wind power is used. It is shown that as wind penetration increases, the optimal operation of storage depends on wind output as well as load. The main benefit from storage is shown to be a decrease in wind curtailment. The economics of the system are examined to find the level at which storage justifies its capital costs and inefficiencies. It is shown that the uncertainty of wind makes the option of storage more attractive. The size of the energy store has an impact on results. At lower levels of installed wind (up to approximately 50% of energy from wind in Ireland), the reduction in curtailment is insufficient to justify building storage. At greater levels of wind, storage reduces curtailment sufficiently to justify the additional capital costs. It can be seen that if storage replaces OCGTs in the plant mix instead of CCGTs, then the level at which it justifies itself is lower. Storage increases the level of carbon emissions at wind penetration below 60%.

Base-Load Cycling on a System With Significant Wind Penetration

Certain developments in the electricity sector may result in suboptimal operation of base-load generating units in countries worldwide. Despite the fact they were not designed to operate in a flexible manner, increasing penetration of variable power sources coupled with the deregulation of the electricity sector could lead to these base-load units being shut down or operated at part-load levels more often. This cycling operation would have onerous effects on the components of these units and potentially lead to increased outages and significant costs. This paper shows the serious impact increasing levels of wind power will have on the operation of base-load units. Those base-load units which are not large contributors of primary reserve to the system and have relatively shorter start-up times were found to be the most impacted as wind penetration increases. A sensitivity analysis shows the presence of storage or interconnection on a power system actually exacerbates base-load cycling until very high levels of wind power are reached. Finally, it is shown that if the total cycling costs of the individual base-load units are taken into consideration in the scheduling model, subsequent cycling operation can be reduced.

Impact of wind power on the power system imbalances in Finland

A study on the imbalance costs or payments that wind power producers pay on the one hand and the cost incurred for the power system on the other hand is presented. Both the producer side and the system side will be examined with case data on prediction errors, system net imbalances and the balancing costs. The up-scaled forecast errors of wind power that result in imbalances have been combined with the system real net imbalance. Comparisons and discussion about the balancing costs of wind power depending on the wind penetration are provided. The results for Finland show that a two-price system for imbalances results in higher imbalance costs than a one-price system. At low wind power penetration levels, the difference in imbalance payments is high for one- and two-price system. When wind penetration increases, there is not so much difference in the different balance settlement rules used. According to the comparison between imbalance payments and system costs, the increase in system costs because of wind power is lower than imbalance payments for wind power producers when using either average prices for up- and down-regulation or the regulation prices that increase linearly with regulation demand.

Forecasting Wind Generation, Uncertainty and Reserve Requirement on the Irish Power System Using an Ensemble Prediction System

The ability to quantify forecast uncertainty is critical to safe, efficient and economical operation of the power system, given the rapidly increasing wind penetration into the relatively small synchronous Irish system (over 1.5 GW of wind in an all-island system with a peak demand of less than only 7 GW). An ensemble prediction system has been employed for the forecasting of generation for wind farms in the Republic of Ireland, as well as for the quantification of the forecast uncertainty at each farm. Results indicate the forecast (mean absolute) error for the total wind generation capacity (over the 51 wind farms studied) was less than 7% (normalised to installed capacity). Single-site forecast errors are typically almost twice as much as this, which highlights the benefits of regional, aggregated wind generation forecasting for safe and efficient power system operations.

Operating policies for wind-pumped storage hybrid power stations in island grids

Pumped storage is today viewed as the most suitable storage technology for achieving high wind penetration levels in multi-megawatt-sized autonomous island grids, where the technical constraints introduced by the conventional generating units impose limitations on the output of wind farms. In this study, an operating policy is proposed for hybrid wind-hydro power stations (HPSs) in island grids, to increase wind penetration levels, while at the same time minimising the impact on the conventional generation system and ensuring the viability of the HPS investment. The proposed operating strategy is applied to three different autonomous island systems using a dedicated logistic model, to evaluate the effect of the HPS on the overall operation and economics of the island systems and to assess the feasibility of HPS investments.

Dynamic Reserve Allocation for System Contingency by DFIG Wind Farms

With the increasing wind penetration into the power system, guidelines of the operating reserve need to be revised to ensure system security. Due to the uncertain characteristics of the wind production, the general way of the reserve management for wind integration is to provide additional reserve margin by conventional plants. Such a strategy could not only increase the operating cost but also impose additional unit stress during the frequency event. This paper presents a strategy that incorporates doubly-fed induction generator (DFIG) wind farms to actively provide primary reserve for frequency control. The wind reserve allocation according to available wind speed is proposed. An integrated system that consists of the traditional units and DFIG wind farms has been developed to assess the frequency response and generating interactions. Simulation results are discussed to illustrate the superiority of the presented strategy in reserve operation.

Provision of a synchronising power characteristic on DFIG-based wind farms

The significant increase in wind penetration expected in the near future imposes the requirement that the bulk addition of wind farms to the network should not be detrimental to the overall network-operating characteristics. One way of ensuring this is to aim to provide a wind farm with a dynamic characteristic that is similar to that of a conventional synchronous-generator-based power station. A control strategy is presented that provides a DFIG-based wind farm with a power-response characteristic to network disturbances that dynamically resembles that of a synchronous generator. The DFIG controller is aimed at minimising the effect on network operation that the replacement of a conventional generator by a DFIG-based wind farm will have. A simple but realistic test network that combines synchronous and wind-farm generation has been modelled and used to assess dynamic performance. Simulation results are presented and discussed that demonstrate the capabilities of the new DFIG controller, although these are gained at the expense of losing some of the damping provided by conventional DFIG operation.

Challenges of Increased Wind Energy Penetration in Ireland

Ireland is a facing a critical time in the formation of a robust renewable energy (RE) policy, due to its size, relative isolation, grid infrastructure, and fuel import dependency. The inherent intermittency and unpredictability of wind power make its increased penetration into the electricity network an area requiring significant further analysis. This paper details the state of the Irish electricity system at the end of 2003, describes the status of the electricity market and puts into perspective the technical issues which need to be resolved to increase wind penetration on the island of Ireland.

Effects of tool/workpiece temperature on tool wear when cutting hard steels : R. Dewes et al. (Universty of Birmingham, Birmingham, UK.)

This paper presents a generic bulk energy storage dispatch model for production costing simulation, and assesses the performance and economics of storage under various system scenarios. The storage model presented captures the dynamic relationship between the reservoir energy status and the storage commitments in energy and ancillary co-optimization market, thereby enabling the dispatch of storage for both energy and cross-market arbitrage opportunities. The paper also presents a methodology to quantify the cycling costs incurred by conventional generating units due to frequent start–shut cycles and ancillary services. The bulk storage technology modeled is compressed air energy storage (CAES), and it is represented within the IEEE 24 bus reliability test system. Simulations are performed to quantify the impacts of bulk energy storage in terms of reduction in market prices, system production and cycling costs, and also to investigate the economic viability of storage projects in terms of payback periods under increasing wind penetration levels.

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The maturity of wind technology combined with availability of suitable sites means Ireland is on course to generate 40% of its electricity from the wind by 2020.This work sets out to quantify, to what degree, if any, increased wind penetration translates into reduced wholesale and retail prices for electricity. The consensus from the literature is that increasing wind penetration reduces wholesale electricity prices, but views vary as to what degree this translates into reduced retail prices for the consumer.This work demonstrates the effect of wind energy penetration on the price of electricity in Ireland using quantitative data from the market and grid operators. An analysis of the data reveals that increasing wind penetration is having little impact on average prices.This work concludes that, due to the fact that imported UK gas powered generation is the main (48%) form of electricity generation in Ireland, the changes in Irish wholesale electricity prices are primarily determined by UK gas prices and that increases in wind penetration in recent years have not affected this relationship. This, and the presence of a minimum tariff received by producers, enables wind energy providers to compete on price, representing a sound commercial basis for investment in renewables, while continuing the trend of reduced, imported fossil fuel, dependence in Ireland.