Increased Wind Generation Research Articles

Development of an Equivalent Wind Farm Model for Frequency Regulation

The operational security of power systems for wind farm (WF) integration becomes more important as the penetration of wind generation increases. A WF may contain hundreds of wind turbines (WT) and thus the power system simulations based on the complex model of a WT consume much time. This article proposes an equivalent WF model with the frequency-regulation function. The main research works include the establishment of the generic model of a WT, the development of single- and multimachine equivalent models for a large WF, the clustering of WTs based on the developed nonlinear wake model and the fuzzy C-means (FCM) clustering algorithm, the integration of the frequency-regulation function into the equivalent WF model, and the validation of the developed equivalent WF model by various operating scenarios. The results demonstrate that the proposed multimachine equivalent method based on the FCM clustering provides a more accurate model than a single-WT equivalent model. Consequently, the research results provide a solution for simulating a large-scale wind power integration, providing efficient, accurate, and fast steady-state and dynamic analyses.

Transmission costs and the value of wind generation for the CREZ project

This paper analyzes the recent expansion of transmission lines in Texas, essentially completed in 2013 at a cost of approximately $7 billion. This project was intended to improve access to areas with high wind generation potential and the resulting increase in wind generation reduced fuel costs and emissions from the displaced fossil fuel generators. I find that the value of the resulting emissions reduction from additional wind generation is approximately twice that of the fuel savings. Additionally, when incorporating the value of reduced emissions, increased generation from already existing wind turbines alone could offset about half of the annualized cost of this transmission expansion while using only 2% of the new transmission capacity. Incorporating the value of emissions reductions could make extending transmission lines to access high quality wind resources more viable, especially if production from already-existing wind turbines in the area are being non-trivially curtailed, as was true in this case.

Marginal Bottleneck Identification in Power System Considering Correlated Wind Power Prediction Errors

This letter investigates how to identify the marginal bottleneck, which is defined as the constraint most likely to be violated with the increasing wind generation uncertainty of power system in real-time dispatch. The presented method takes the correlation of wind power prediction error (WPPE) into account, leading to an ellipsoidal formulation of wind power generation region (WGR). Based on constructed WGR, the identification procedure is formulated as a max-max-min problem, which is solved by the algorithm based on iteration linear program with the proposed method to select appropriate initial points of WPPE. Finally, two cases are tested, demonstrating the efficacy and efficiency of the procedure to identify marginal bottleneck.

Impact of Wind Generation on Power Swing Protection

Large-scale integration of wind generation changes the power swing characteristics of a power system and may result in the misoperation of legacy power swing protection schemes. This paper presents a qualitative study on the impact of wind generation on power swing protection. The objective is to provide an understanding of the problem through case studies and present possible solutions and adjustments in protection schemes to ensure the efficiency of protection under large-scale integration of wind generation. The misoperation of power swing protection functions, namely power swing blocking and out-of-step tripping (OST), as a result of increased wind generation levels, are shown through case studies. It is also shown that the electrical center of a power system may move due to wind generation. In this case, it would be necessary to revise the optimal location of the OST protection. Finally, the impact of various factors, such as wind generator type, control scheme and fault-ride-through function, and wind generation level and capacity are investigated to determine the key features that need to be accounted for in practical protection studies.

Financial support vis-à-vis share of wind generation: Is there an inflection point?

Wind power is one of the leading source of renewable energy in terms of installed capacity, power generation and technology maturity in the world today. It is promoted through financial support such as Feed-In Tariffs (FIT), renewable certificates, investment grants and tax incentives almost everywhere in the world. Attractive power pricing and a general global thrust for renewables have resulted in increasing the wind power capacity from 17 GW in 2000 to 514 GW in 2017. This paper analyses the relationship between financial mechanisms and wind capacity and wind power generation across 15 countries and 10 US states over 2006–2017. These countries/states contribute to 88% of total wind generation capacity in 2017, and contribution of their individual wind capacities to overall electricity generation rose from 0.15 to 24.2% (2006) to 1.2–38.5% (2017). Our analysis indicates that the trend of financial support reverses beyond an inflection point vis-à-vis the share of wind power in total power generated. The inflection point exists for all countries but the value varies across countries. The relationships are statistically significant. This has important policy implications with regard to the governments’ approach towards promoting wind power as share of wind generation increases.

The impacts of demand response participation in capacity markets

Demand Response is capable of reducing the total amount of generation capacity investment required to ensure electricity system security. We utilise this fact to devise a novel methodology to estimate the contribution of a load-shifting demand response resource to system adequacy. We then simulate an electricity market using mixed complementarity models to determine how the participation of demand response in capacity markets impacts on market outcomes. Demand response primarily affects the equilibrium outcome through the energy market, however demand response also reduces both equilibrium prices and consumer costs through its capacity market contribution. The effect is particularly pronounced when there is a high level of variable renewable generation and initial undercapacity. In the absence of demand response, increased wind generation leads to higher capacity prices as generators seek to offset depressed energy prices. However, we find that demand response’s participation in the capacity market can combat these increased capacity prices. These results suggest that demand response participation in capacity markets can mitigate some of the market challenges of renewable integration, particularly that of the “missing money” problem.

Operating Reserve Demand Curve, Scarcity Pricing and Intermittent Generation: Lessons from the Texas ERCOT Experience

Resolving the resource adequacy problem has been usually entrusted to the imposition of some kind of long-term capacity requirements or to forward markets. The Operating Reserve Demand Curve (ORDC), which is linked to short-term market conditions and does not require central planning, has been presented as an alternative system with which to ensure resource adequacy. Using hourly data from the Texas ERCOT market, we empirically show that ORDC prices are significantly negatively affected by wind generation. We find that, if wind generation is relatively low, a 1% increase in wind generation decreases the ORDC price by around 0.2-0.1%. Moreover, if wind generation is greater than 8,000-9,000 MW, the ORDC price is expected to be zero. This may preclude investors from obtaining clearly perceivable long-term price signals, such as capacity requirements intent.

Effects on power system operations of potential changes in wind and solar generation potential under climate change

Climate change will likely impact wind and solar resources. As power systems increasingly shift towards wind and solar power, these resource changes will increasingly impact power system operations. We assess how power system operations will be affected by climate change impacts on wind and solar resources by generating wind and solar generation profiles for a reference period and five climate change projections. We then run a unit commitment and economic dispatch model to dispatch a high-renewable generator fleet with these profiles. For climate change projections, we use 2041–2050 output from five global climate models (GCMs) for Representative Concentration Pathway 8.5 for Texas, our study system. All five GCMs indicate increased wind generation potential by 1%–4% under climate change in Texas, while three and two GCMs indicate increased and decreased solar generation potential, respectively, by up to 1%. Uneven generation potential changes across time result in greater changes in dispatched generation by fuel type. Notably, nuclear generation decreases across GCMs by up to 7%, largely in low-demand (winter) months when nuclear plants, which have a high minimum stable load, must reduce their generation to avoid overgeneration. Increased wind and/or solar generation result in reduced system CO2 emissions and electricity production costs across four of the five GCMs by 8–16 million tons and $216–516 million, or by 2% and 1%, respectively. Future research should assess the atmospheric and climate dynamics that underlie such changes in power system operations.

Electricity market prices for day-ahead ancillary services and energy: Texas

Applying a regression-based approach to a large sample of hourly observations for the seven-year period of January 1, 2011 to December 30, 2017, we explore determinants of day-ahead market (DAM) prices for ancillary services (ASs) and energy in the Electric Reliability Council of Texas (ERCOT). For each GW increase in responsive reserve (RRS) or nonspinning reserve (NSRS) procurement quantities, we estimate price increases of about US$3.47 per MW per hour and US$5.63 per MW per hour, respectively; while the cost of an additional 1 GW of regulation up (REGUP) and regulation down (REGDN) is a much higher US$17 per MW per hour and US$31 per MW per hour, respectively. A US$1/MWh increase in the DAM energy price tends to increase RRS and REGUP prices by nearly US$1 per MW per hour, about twice the estimated impact for NSRS that is not necessarily online when selected. The participation of interruptible loads to provide RRSs reduces the RRS price, and this effect increased nearly six-fold from the first to the second half of our sample time period. An increase in wind generation tends to decrease AS prices because it reduces the DAM energy price via the merit-order effect. Hence, Texas’s wind generation expansion has not raised ERCOT’s AS prices in our sample period, which is characterized by a stable AS requirement and declining natural gas prices. Going forward, however, Texas could face AS cost escalation due to the high REGUP and REGDN prices, should ERCOT’s requirement and procurement of those services increase due to rising renewable production.

Estimating lower probability bound of power system's capability to fully accommodate variable wind generation

As the penetration of wind generation increases, the uncertainty it brings has imposed great challenges to power system operation. To cope with the challenges, tremendous research work has been conducted, among which two aspects are of most importance, that is, making immune operation strategies and accessing the power system's capability to accommodate the variable energy. Driven and inspired by the latter problem, this paper will discuss the power system's capability to accommodate variable wind generation in a probability sense. Wind generation, along with its uncertainty is illustrated by a polyhedron, which contains prediction, risk, and uncertainty information. Then, a three-level optimisation problem is presented to estimate the lower probability bound of power system's capability to fully accommodate wind generation. After reformulating the inner max-min problem, or feasibility check problem, into its equivalent mixed-integer linear program (MILP) form, the bisection algorithm is presented to solve this challenging problem. Modified IEEE systems are adopted to show the effectiveness of the proposed method.

The impact of wind generation on wholesale electricity market prices in the midcontinent independent system operator energy market: An empirical investigation

The Midcontinent Independent System Operator (MISO) is the second largest organized competitive wholesale electricity market in the U.S. Wholesale electricity prices in MISO have decreased over the past several years, as both natural gas prices have fallen, and large amounts of wind generation capacity have been added. Using an empirical econometric approach studying historical hourly real-time electricity prices, load, natural gas prices, and other MISO market data, a series of econometric models are estimated using historical data from 2008 to 2016, to identify the impact of increased wind generation on wholesale electricity prices in MISO. This is the first such empiric study for MISO, the largest wholesale electricity market by geography in the world. Furthermore, this is the first empiric study estimating impacts of wind generation on electricity price that utilizes a comprehensive set of predictor variables to control for many sources of potential bias. The results show a statistically significant impact of wind generation on real-time hourly MISO system prices, ranging from an estimated decrease of $0.14 to $0.34 per mega-watt hour, for each 100 mega-watt hours of additional wind generation. It is observed that the estimated marginal impacts of additional wind generation have declined over time. This is likely attributable to the long-term shifts in the supply and demand dynamics experienced in the MISO energy market, as well as to changes made to the MISO market structure to better accommodate variable generation.

Wide Area Hierarchical Voltage Control to Improve Security Margin for Systems With High Wind Penetration

Due to growing environmental concerns, wind power has taken a larger share of the generation market. While the increase in wind generation provides diversification of the supply, it also undermines system reliability by introducing uncertainty in power supply and decreasing the maneuverability of the grid in terms of VAR absorbance and provision. To restore the reliability of high wind penetrated systems, this paper proposes hierarchical voltage control (HVC). The proposed pattern generalization methodology is based on principle component analysis and a three-layer feedback architecture utilizing online state estimation. The proposed control includes both steady-state and dynamic constraints. Governed by an optimization trained with cases representing operating snapshots and solved via an active-set algorithm adopting stepwise linearization, the proposed HVC provides efficiency and adaptability. As a result, the proposed control provides adequate system support under a wide range of contingencies and operating conditions to enhance grid reliability. Its capability to regulate yearly round operations in real time is validated using a reduced Western Electricity Coordinating Council power system model.

Does The Increase in Wind Generation in ERCOT Justify An Arbitrary Increase to its ORDC LOLP Calculation

A suggestion of multiplying the standard deviation () used in the Electric Reliability Council of Texas’ (ERCOT) Operating Reserve Demand Curve (ORDC) loss of load probability (LOLP) by a factor greater than 1.0 has been posited to solve the “missing money argument.” After the fact justification for this position has been given by the rational assumption that the increase in intermittent generation in ERCOT (mostly wind) has increased the LOLP but has not resulted in a corresponding increase in the standard deviation used in the equation. No supporting data has been provided for this rational hypothesis. This paper provides some supporting data of increased intermittency and provides an analysis (with assumptions) of the data to estimate the factor (calculated to be 1.02 to no more than 1.08) to be applied to the standard deviation to account for the increase in intermittent generation in ERCOT. Other less controversial methods of eliminating this perceived shortcoming of the ERCOT LOLP are also discussed.

Observation-based solar and wind power capacity factors and power densities

Power density is the rate of energy generation per unit of land surface area occupied by an energy system. The power density of low-carbon energy sources will play an important role in mediating the environmental consequences of energy system decarbonization as the world transitions away from high power-density fossil fuels. All else equal, lower power densities mean larger land and environmental footprints. The power density of solar and wind power remain surprisingly uncertain: estimates of realizable generation rates per unit area for wind and solar power span 0.3–47 We m−2 and 10–120 We m−2 respectively. We refine this range using US data from 1990–2016. We estimate wind power density from primary data, and solar power density from primary plant-level data and prior datasets on capacity density. The mean power density of 411 onshore wind power plants in 2016 was 0.50 We m−2. Wind plants with the largest areas have the lowest power densities. Wind power capacity factors are increasing, but that increase is associated with a decrease in capacity densities, so power densities are stable or declining. If wind power expands away from the best locations and the areas of wind power plants keep increasing, it seems likely that wind’s power density will decrease as total wind generation increases. The mean 2016 power density of 1150 solar power plants was 5.4 We m−2. Solar capacity factors and (likely) power densities are increasing with time driven, in part, by improved panel efficiencies. Wind power has a 10-fold lower power density than solar, but wind power installations directly occupy much less of the land within their boundaries. The environmental and social consequences of these divergent land occupancy patterns need further study.

Effects of wholesale electricity markets on wind generation in the midwestern United States

This paper estimates the effect of starting the Midcontinent ISO electricity market in 2005 on wind generation. An average increase in wind plant capacity factors of 1.7–2.8 percentage points associated with the start of the market is estimated, relative to neighboring wind plants not in the market. These results are robust to potentially confounding variation associated with wind speed differences determined by weather. Policy makers in regions of increasing wind generation should consider expanding the wholesale market region as a tool to deal with variability of renewable generation. Many technical experts and market participants provide anecdotes that competitive wholesale markets are beneficial for wind energy, this analysis provides the first statistical evidence to support that claim.

Issues and mitigations of\xa0wind energy penetrated network: Australian network case study

Longest geographically connected Australian power system is undergoing an unprecedented transition, under the effect of increased integration of renewable energy systems. This change in generation mix has implications for the whole interconnected system designs, its operational strategies and the regulatory framework. Frequency control policies about real-time balancing of demand and supply is one of the prominent and priority operational challenge requiring urgent attention. This paper reviews the Australian electricity market structure in presence of wind energy and its governance. Various issues related to increased wind generation systems integration are discussed in detail. Currently applied mitigations along with prospective mitigation methods requiring new or improved policies are also discussed. It is concluded that developing prospective frequency regulation ancillary services market desires further encouraging policies from governing authority to keep pace with current grid transition and maintain its security.

Distributional costs of wind energy production in Portugal under the liberalized Iberian market regime

Wind generation in Portugal and Spain has grown due to a decrease in technology cost and the availability of renewables electricity generation incentives. There is a strong interconnection between Spain's and Portugal's transmission systems, resulting in common prices in both countries. However, Portuguese and Spanish producers receive the incentives for producing wind-based electricity that are specified in their own national policies, resulting in different costs to rate-payers. In this paper, we estimate the costs to Portuguese rate-payers associated with the current market design and policy incentives. To do so, we regress hourly spot electricity market prices as a function of hourly wind generation, and estimate the resulting feed-in-tariff costs distributional effects over the various rate-payer categories. Total costs for rate payer are at the minimum level if joint wind generation in Portugal and Spain increases by 5.5% from what it is today. If wind generation increases much further, then the costs increase due to the FiT overcost increase. If wind generation decreases from current levels, then costs also increase due to the merit-order effect. Furthermore, we find that rate-payer categories will endure different portions of the costs, with an increase in wind generation penalizing predominantly ≤ 20.7kVA rate-payers.

Wind, storage, interconnection and the cost of electricity generation

We evaluate how increasing wind generation affects wholesale electricity prices, balancing payments and the cost of subsidies using the Irish Single Electricity Market (SEM) as a test system, with hourly data from 1 January 2008 to 28 August 2012.We model the spot market using a system of seemingly unrelated regressions (SUR) where the regressions are the 24hours of the day. Wind has a negative impact on the system marginal price, with every MWh increase in wind generation (equal to about 0.2% of the average wind generation in our sample) leading to a decrease of the system marginal price of €0.018MWh, or about 0.3% of its average value.We use time series models to analyse the balancing market and show that wind generation increases balancing payments, as do the forecast errors of demand and wind.Every MWh of additional wind generation is associated with an increase in constraint payments of €3.2, or about 0.01%.Lack of storage increases the impact of wind on balancing payments whereas the lack of interconnection has no effect. Overall, wind decreases costs through its effect on the electricity price more than it increases constraint payments, even when storage is on outage. The effect of wind remains positive after including the cost of subsidies given to wind generation.

Dynamics of ionospheric disturbances during the 17–19 March 2015 geomagnetic storm over East Asia

Based on vertical sounding data from nine ionosondes located at 19–66°N, 100–130°E we investigated the latitude-temporal dynamics of ionospheric disturbances during the 17–19 March 2015 severe two-step geomagnetic storm, and compared it with temporal dynamics of total electron content (TEC) profiles along 120°E. The phenomena that accompanied the main and early recovery storm phases were in particular focused on in this study. The distinct storm-related ionospheric disturbances began 2.5, 4 and 5h after onset of the storm main phase at subauroral, middle and low latitudes, respectively. To clarify the main mechanisms causing the disturbances at different latitudes we compared the changes in ionospheric parameters and TEC profiles with changes in the northern polar cap index and geomagnetic field in the vicinity of 120°E. The equatorward shift of the main ionospheric trough (MIT) and diffuse precipitations zone accompanied by an increase in precipitating particle flux was found to have a substantial influence on the subauroral ionosphere during the main and early recovery phases. The thermosphere Joule heating due to westward and polarized jets led to an increase in neutral wind velocity and generation of disturbed dynamo electric field. The strengthened wind was the main reason of the positive ionospheric disturbance observed at middle latitudes in the evening on 17 March. The further enhancement of magnetospheric convection caused the displacement of MIT and its associated negative ionospheric disturbance to middle latitudes. At low latitudes superposition of prompt penetration and disturbed dynamo electric fields play the decisive role in the ionosphere behavior till the end of the early recovery phase.

Impact of Wind Electricity Forecasts on Bidding Strategies

The change in the generation mix from conventional electricity sources to renewables has important implications for bidding behaviour and may have an impact on prices. The main goal of this work is to discover the role played by expected wind production, together with other relevant factors, in explaining the day-ahead market price through a data panel model. The Spanish market, given the huge increase in wind generation observed in the last decade, has been chosen for this study as a paradigmatic example. The results obtained suggest that wind power forecasts are a new key determinant for supply market participants when bidding in the day-ahead market. We also provide a conservative quantification of the effect of such trading strategies on marginal prices at an hourly level for a specific year in the sample. The consequence has been an increase in marginal price to levels higher than what could be expected in a context with notable wind penetration. Therefore, the findings of this work are of interest to practitioners and regulators and support the existence of a wind risk premium embedded in electricity prices to compensate for the uncertainty of wind production.