Investigation of wind shear coefficients and their effect on electrical energy generation

Wind measurements are generally performed below wind turbine hub heights due to higher measurement and tower costs. In order to obtain the wind speed at the hub height of the turbine, the measurements are extrapolated, assuming that the wind shear is constant. This assumption may result in some critical errors between the estimated and actual energy outputs. In this paper wind data collected in Bal?kesir from October 2008 to September 2009, has been used to show the effects of wind shear coefficient on energy production. Results of the study showed that, the difference between wind energy production using extrapolated wind data and energy production using measured wind data at hub height may be up to 49.6%.     

Economics of compressed air energy storage to integrate wind power: A case study in ERCOT

Compressed air energy storage (CAES) could be paired with a wind farm to provide firm, dispatchable baseload power, or serve as a peaking plant and capture upswings in electricity prices. We present a firm-level engineering-economic analysis of a wind/CAES system with a wind farm in central Texas, load in either Dallas or Houston, and a CAES plant whose location is profit-optimized. With 2008 hourly prices and load in Houston, the economically optimal CAES expander capacity is unrealistically large – 24 GW – and dispatches for only a few hours per week when prices are highest; a price cap and capacity payment likewise results in a large (17 GW) profit-maximizing CAES expander. Under all other scenarios considered the CAES plant is unprofitable. Using 2008 data, a baseload wind/CAES system is less profitable than a natural gas combined cycle (NGCC) plant at carbon prices less than $56/tCO₂ ($15/MMBTU gas) to $230/tCO₂ ($5/MMBTU gas). Entering regulation markets raises profit only slightly. Social benefits of CAES paired with wind include avoided construction of new generation capacity, improved air quality during peak times, and increased economic surplus, but may not outweigh the private cost of the CAES system nor justify a subsidy.     

Adequacy evaluation of wind power generation systems

This paper attempts to assess the adequacy of wind power generation systems using the data collected from seven wind farms in Muppandal, Tamilnadu (India) with a total capacity of 37 MW. A Monte Carlo model simulation is incorporated in the algorithm to obtain the hourly power output of wind farms, which also takes into account the unavailability of wind turbines. A typical load demand profile is used to examine the chronological hourly wind power generation for each month. The reliability index of LOLE (loss of load expectation) is used to estimate the reliable contribution of wind farm power generation.     

Uncertainty in wind climate parameters and their influence on wind turbine fatigue loads

According to the wind turbine standard IEC 61400-1, structural integrity of wind turbines is determined either by direct reference to wind data or by load calculation. In both cases, deterministic values are applied and uncertainties neglected for the wind climate parameters and the structural resistance.The uncertainty related to the wind climate parameters depends highly on the presence, duration and quality of on-site wind measurements, and the perturbations introduced by flow modelling. For the wind speed distribution, the uncertainty is considered in assessment of the annual energy production. For other wind climate parameters which potentially have a large influence on the wind turbine loads, the uncertainty is often not well investigated.This paper presents a probabilistic framework for assessment of the structural reliability level of wind turbines in fatigue loading. Uncertainty of the site specific wind climate parameters at each turbine position is estimated based on the local wind measurements, speed-up factors and the distance between the wind turbine and the measuring position. The framework is demonstrated for a wind turbine project in flat terrain. The results show that the uncertainty in the site specific wind climate parameters normally accounts for 10–30% of the total uncertainty in the structural reliability analyses.     

The interaction of wind power generation with electricity demand in the context of a small grid

An investigation into the integration of the intermittent electricity output of a hypothetical wind farm in Malta with the actual electricity demand for one particular year is reported. Available hourly wind data from three sites for 2001 were analysed. The probability density of the load resulting from the reduction of the renewable output from the electricity demand on an hourly basis was determined by a convolution method. The calculated shift in the load duration extends over the whole spectrum of power demand. The equivalent power at the most favourable site was considerably higher than the nominal value commonly in use. In view of the limited availability of sites for wind farms in Malta rotor designs better suited to the lower wind speed régime inland should be considered.     

A review on reliability assessment for wind power

The application of wind energy in electric power systems is growing rapidly due to enhanced public concerns to adverse environmental impacts and escalation in energy costs associated with the use of conventional energy sources. Electric power from wind energy is quite different from that of conventional resources. The fundamental difference is that the wind power is intermittent and uncertain. Therefore, it affects the reliability of power system in a different manner from that of the conventional generators. This paper, from available literatures, presents the model of wind farms and the methods of wind speed parameters assessment. Two main categories of methods for evaluating the wind power reliability contribution, i.e., the analytical method and the Monte Carlo simulation method have been reviewed. This paper also summarizes factors affecting the reliability of wind power system, such as wake effect, correlation of output power for different windturbines, effect of windturbine parameters, penetration and environment. An example has been used to illustrate how these factors affect the reliability of wind power system. Finally, mainstream reliability indices for evaluating reliability are introduced. Among these reliability indices, some are recently developed, such as wind generation interrupted energy benefit (WGIEB), wind generation interruption cost benefit (WGICB), Equivalent Capacity Rate (ECR), load carrying capacity benefit ratio (LCCBR).     

High penetration wind generation impacts on spot prices in the Australian national electricity market

This paper explores wind power integration issues for the South Australian (SA) region of the Australian National Electricity Market (NEM) by assessing the interaction of regional wind generation, electricity demand and spot prices over 2 recent years of market operation. SA's wind energy penetration has recently surpassed 20% and it has only a limited interconnection with other regions of the NEM. As such, it represents an interesting example of high wind penetration in a gross wholesale pool market electricity industry. Our findings suggest that while electricity demand continues to have the greatest influence on spot prices in SA, wind generation levels have become a significant secondary influence, and there is an inverse relationship between wind generation and price. No clear relationship between wind generation and demand has been identified although some periods of extremely high demand may coincide with lower wind generation. Periods of high wind output are associated with generally lower market prices, and also appear to contribute to extreme negative price events. The results highlight the importance of electricity market and renewable policy design in facilitating economically efficient high wind penetrations.     

Assessment of imbalance settlement exemptions for offshore wind power generation in Belgium

This article deals with a specific support mechanism exempting offshore wind power generators partially from their balancing responsibilities by means of a tolerance margin. This specific support mechanism was enforced in Belgium as from 2009 and is defended by its proponents in view of the lower power output predictability at offshore locations. Although policies accommodating offshore developments may be seen as important to tap better wind resources, this contribution stresses the importance of full balancing responsibility for variable renewables. After a detailed evaluation of the support mechanism and its impact on the balancing costs for wind power generators, the use of current applied production support mechanisms is recommended. These can be used to acquire the same financial effect without increasing market complexity and harming the operation of the balancing market. The first part of the study deals with the specific implementation of the tolerance margin in the Belgian context. Secondly, its underlying motivation is quantitatively assessed, namely the relatively higher offshore prediction errors. Finally, the total offshore subsidy resulting from the measure is determined. Expressed in €/MWh, this subsidy is currently determined at €1.4–1.7/MWh, which represents the required increase of production support in order to replace the regulation.     

The large-scale integration of wind generation: Impacts on price,reliability and dispatchable conventional suppliers

This work examines the effects of large-scale integration of wind powered electricity generation in a deregulated energy-only market on loads (in terms of electricity prices and supply reliability) and dispatchable conventional power suppliers. Hourly models of wind generation time series, load and resultant residual demand are created. From these a non-chronological residual demand duration curve is developed that is combined with a probabilistic model of dispatchable conventional generator availability, a model of an energy-only market with a price cap, and a model of generator costs and dispatch behavior. A number of simulations are performed to evaluate the effect on electricity prices, overall reliability of supply, the ability of a dominant supplier acting strategically to profitably withhold supplies, and the fixed cost recovery of dispatchable conventional power suppliers at different levels of wind generation penetration. Medium and long term responses of the market and/or regulator in the long term are discussed.     

Electricity market design for facilitating the integration of wind energy: Experience and prospects with the Australian National Electricity Market

Australia has been an early and enthusiastic adopter of both electricity industry restructuring and market-based environmental regulation. The Australian National Electricity Market (NEM) was established in 1999 and Australia also implemented one of the world's first renewable energy target schemes in 2001. With significant recent growth in wind generation, Australia provides an interesting case for assessing different approaches to facilitating wind integration into the electricity industry. Wind project developers in Australia must assess both potential energy market and Tradeable Green Certificate income streams when making investments. Wind-farm energy income depends on the match of its uncertain time varying output with the regional half hourly market price; a price that exhibits daily, weekly and seasonal patterns and considerable uncertainty. Such price signals assist in driving investments that maximize project value to the electricity industry as a whole, including integration costs and benefits for other participants. Recent NEM rule changes will formally integrate wind generation in the market's scheduling processes while a centralized wind forecasting system has also been introduced. This paper outlines experience to date with wind integration in the NEM, describes the evolution of market rules in response and assesses their possible implications for facilitating high future wind penetrations.     

Coordinated generation and transmission expansion planning in deregulated electricity market considering wind farms

This paper deals with a coordinated generation expansion planning (GEP)–transmission expansion planning (TEP) in competitive electricity market. In the proposed method, GEP and TEP are performed at the same time, with consideration of wind farm uncertainty. The uncertainty is modeled by normal probability distribution function (PDF) and Monte-Carlo simulation (MCS) is used to include the uncertainty into the problem. The planning is managed for two master and slave levels. At slave level, all generation company (GENCO) and transmission company (TRANSCO) maximize their profit and then at master level, the system constraints are checked by independent system operator (ISO). In other words, the proposed planning aims at maximizing the expected profit of all GENCOs and TRANSCOs, while considering security and reliability constraints such as reserve margin and loss of load expectation (LOLE). The proposed problem is a constrained, nonlinear, mixed-integer optimization programming and solved by using particle swarm optimization (PSO) method. Simulation results verify the effectiveness and validity of the proposed planning for maximizing GENCOs and TRANSCOs profit in the presence of wind farm uncertainty under electricity market.     

Public attitudes of wind energy in Texas: Local communities in close proximity to wind farms and their effect on decision-making

Wind energy is now recognized as an important energy resource throughout the world. Within the United States, the state of Texas currently has the largest wind energy capacity with 8797 total megawatts and an additional 660 MW under construction. With this rapid growth, it is important to achieve a better understanding of how wind energy is being perceived by the public.     

The influence of generation mix on the wind integrating capability of North China power grids: A modeling interpretation and potential solutions

The large-scale wind power development in China has reached a bottleneck of grid integrating capability. As a result, excess wind electricity has to be rejected in the nighttime low demand hours, when the wind power is ramping up. To compensate for the fluctuation of wind power, new coal-fired power plants are being constructed along with the big wind projects in the North China grids. This study analyzed why adding coal-fired generation cannot remove the bottleneck of wind integration by modeling the operating problem of the wind integration. The peak-load adjusting factor of the regional grid is defined. Building more coal-fired power plants will not increase the adjusting factor of the current grid. Although it does help to increase the total integrated wind power in the short term, it will add difficulties to the long-term wind integration. Alternatively, the coordinated resource utilization is then suggested with the discussion of both the effective pumped hydro storage and the potential electric vehicle storage.     

Potential wind power generation in the State of Kuwait

The wind characteristics of six locations in the State of Kuwait have been assessed. The annual average wind speed for the considered sites ranged from 3.7 to 5.5 m/s and a mean wind power density from 80 to 167 W/m² at standard height of 10 m. The Weibull parameters and power density of each station have been determined using Weibull distribution. The wind data at heights 15, 20, 25 and 30 m were obtained by extrapolation of the 10 m data using the Power-Law. The potential wind energy at different heights was estimated using Weibull parameters. Maximum power density is found at 30 m height which varies between 130 and 275 W/m² with 70% increase from the standard height indicating fairly potential wind energy especially in the northern part of the country. The highest potential wind power was found during the summer season which is the peak demand season of electricity in Kuwait.     

The impact of increased interconnection on electricity systems with large penetrations of wind generation: A case study of Ireland and Great Britain

Increased interconnection has been highlighted as potentially facilitating the integration of wind generation in power systems by increasing the flexibility to balance the variable wind output. This paper utilizes a stochastic unit commitment model to simulate the impacts of increased interconnection for the island of Ireland with large penetrations of wind generation. The results suggest that increased interconnection should reduce average prices in Ireland, and the variability of those prices. The simulations also suggest that while increased interconnection may reduce carbon dioxide emissions in Ireland, Great Britain would experience an increase in emissions, resulting in total emissions remaining almost unchanged. The studies suggest that increased interconnection would not reduce excess wind generation. This is because under unit commitment techniques which incorporate wind power forecasts in the scheduling decisions, wind curtailment is minimal even with low levels of interconnection. As would be expected an increase in interconnection should improve system adequacy considerably with a significant reduction in the number of hours when the load and reserve constraints are not met.     

The value of compressed air energy storage with wind in transmission-constrained electric power systems

In this work, we examine the potential advantages of co-locating wind and energy storage to increase transmission utilization and decrease transmission costs. Co-location of wind and storage decreases transmission requirements, but also decreases the economic value of energy storage compared to locating energy storage at the load. This represents a tradeoff which we examine to estimate the transmission costs required to justify moving storage from load-sited to wind-sited in three different locations in the United States. We examined compressed air energy storage (CAES) in three “wind by wire” scenarios with a variety of transmission and CAES sizes relative to a given amount of wind. In the sites and years evaluated, the optimal amount of transmission ranges from 60% to 100% of the wind farm rating, with the optimal amount of CAES equal to 0–35% of the wind farm rating, depending heavily on wind resource, value of electricity in the local market, and the cost of natural gas.     

Evaluation of wind energy potential and electricity generation at six locations in Turkey

In this study, wind characteristics were analyzed using the wind speed data collected of the six meteorological stations in Turkey during the period 2000–2006. The annual mean wind speed of the six stations (Erzurum, Elaz??, Bingöl, Kars, Manisa and Ni?de) is obtained as 8.7, 8.5, 5.9, 6.9, 7.4 and 8.0 m/s at 10 m height, respectively. The mean annual value of Weibull shape parameter k is between 1.71 and 1.96 while the annual value of scale parameter c is between 6.81 and 9.71 m/s. A technical assessment has been made of electricity generation from four wind turbines having capacity of (600 kW, 1000 kW, 1500 kW and 2000 kW). The yearly energy output and capacity factor for the four different turbines were calculated.     

The role of energy storage in accessing remote wind resources in the Midwest

Replacing current generation with wind energy would help reduce the emissions associated with fossil fuel electricity generation. However, integrating wind into the electricity grid is not without cost. Wind power output is highly variable and average capacity factors from wind farms are often much lower than conventional generators. Further, the best wind resources with highest capacity factors are often located far away from load centers and accessing them therefore requires transmission investments. Energy storage capacity could be an alternative to some of the required transmission investment, thereby reducing capital costs for accessing remote wind farms. This work focuses on the trade-offs between energy storage and transmission. In a case study of a 200 MW wind farm in North Dakota to deliver power to Illinois, we estimate the size of transmission and energy storage capacity that yields the lowest average cost of generating and delivering electricity ($/MW h) from this farm. We find that transmission costs must be at least $600/MW-km and energy storage must cost at most $100/kW h in order for this application of energy storage to be economical.     

Estimating global hydrogen production from wind

It is likely that intermittent renewable sources such as wind and solar will provide the greatest opportunity for future large-scale hydrogen production. Here, on-shore wind is examined. Global wind energy is estimated by placing one 2 MW turbine/km² over the surface of the earth. Wind energy production is based on monthly mean wind speed data. Wind turbines are grouped to form arrays that are linked to local hydrogen generation and transmission networks. Hydrogen generation is done via low-pressure electrolysis and transmission via high-pressure gas pipelines. The wind/hydrogen system is considered within a global energy system that must not only provide hydrogen, but also energy for electricity consumption at the local generation site. The technical potential of the hydrogen produced is estimated to be 116 EJ. Uneven distribution of the hydrogen-rich sites results in the need to export much of the hydrogen produced to energy-poor regions. To overcome system losses, a combined wind/HVDC/hydrogen system is considered.     

Overview of worldwide wind generation

An summary of the growth in wind energy generation worldwide.