Analyzing major challenges of wind and solar variability in power systems

Ambitious policy targets together with current and projected high growth rates indicate that future power systems will likely show substantially increased generation from renewable energy sources. A large share will come from the variable renewable energy (VRE) sources wind and solar photovoltaics (PV); however, integrating wind and solar causes challenges for existing power systems. In this paper we analyze three major integration challenges related to the structural matching of demand with the supply of wind and solar power: low capacity credit, reduced utilization of dispatchable plants, and over-produced generation. Based on residual load duration curves we define corresponding challenge variables and estimate their dependence on region (US Indiana and Germany), penetration and mix of wind and solar generation. Results show that the impacts of increasing wind and solar shares can become substantial, and increase with penetration, independently of mix and region. Solar PV at low penetrations is much easier to integrate in many areas of the US than in Germany; however, some impacts (e.g. over-production) increase significantly with higher shares. For wind power, the impacts increase rather moderately and are fairly similar in US Indiana and Germany.     

Boosting UK renewables: The market way

Why, after all these years of grants, subsidies and central government planning does Britain still have only 3% of electricity from renewable sources? Could it be that government policy is not working? Are there better market driven ways to do it? Dan Lewis provides his perspective on the current UK situation.     

Area price and demand response in a market with 25% wind power

Denmark, east and west of the Great Belt are bidding areas with separate hourly area prices for the Nord Pool power exchange, covering four Nordic countries and parts of Germany. The share of wind power has now increased to 25% on an annual basis in western Denmark. This has a significant impact not only on the electricity wholesale prices, but also on the development of the market. Hourly market data are available from the website of Danish TSO from 1999. In this paper these data are analysed for the period 2004–2010. Electricity generators and customers may respond to hourly price variations, which can improve market efficiency, and a welfare gain is obtained. An important limitation for demand response is events of several consecutive hours with extreme values. The analysis in this paper is a summary and update of some of the issues covered by the EU RESPOND project. It shows that extreme events were few, and the current infrastructure and market organisation have been able to handle the amount of wind power installed so far. This recommends that geographical bidding area for the wholesale electricity market reflects external transmission constraints caused by wind power.     

The dark side of the sun: How solar power production affects the market value of solar and gas sources

Using daily data for the Italian wholesale day-ahead power market over the period 2008–2013, we assess the impact of solar production on the market value of solar and gas sources, defined using the concepts of value factor and unit revenues. We find that, on average, solar generation negatively affects the solar source market value, causing a departure from the grid parity condition and mining their competitiveness once public incentives are removed. This negative relation is not constant over time and becomes stronger for increasing solar penetration in the energy mix. Interestingly, the opposite is found when looking at gas. While the relation between solar production and the gas market value is negative or not significant when the former is low, it turns positive for higher levels of solar production. This is the result of a change in gas producers' bidding strategies. Indeed, in the Italian power market the highest hourly price has shifted from the peak daytime, when solar production is concentrated, to the off-peak nighttime, when solar is absent from the market and gas can exploit temporary market power.     

Supporting solar power in renewables portfolio standards: Experience from the United States

Renewables portfolio standards (RPS) have become an increasingly popular option for encouraging the deployment of renewable electricity. It is a relatively new policy mechanism, however, and experience with its use is only beginning to emerge. One key concern is whether RPS policies offer adequate support to a wide range of renewable energy technologies and applications or whether, alternatively, they will favor a small number of the currently least-cost forms of renewable energy. This article documents the design of and early experience with state-level RPS programs in the United States that have been specifically tailored to encourage a wider diversity of renewable energy technologies, and solar energy in particular. As shown here, state-level RPS programs specifically designed to support solar have already proven to be an important driver for solar energy deployment, and those impacts are projected to build in the coming years. State experience in supporting solar energy with RPS programs is mixed, however, and full compliance with existing requirements has not been achieved. The comparative experiences described herein highlight the opportunities and challenges of applying an RPS to specifically support solar energy, as well as the importance of policy design details to ensuring that program goals are achieved.     

风力发电的环境价值

风能资源是无污染的清洁能源.文章对风电的环境影响进行了评价;相对于煤电评估了风电的减排污染物的环境价值;通过风电环境价值评价,认为风力发电具有减排污染物0.28元/kWh的环境价值.发展风电有显著的环境效益和经济效益.     

我国风电项目的投资与电价初探

一引言我国的并网型风电经过了科研、示范、小规模商业运营三个阶段,近二十年发展历程,目前正进入一个大规模开发时期。为鼓励和规范可再生能源的开发利用,国家发     

Understanding the variability of wind power costs

Wind power has a significant contribution to make in efforts to abate CO₂ emissions from global energy systems. Currently, wind power generation costs are approaching parity with costs attributed to conventional, carbon-based sources of energy but the economic advantage still rests decidedly with conventional sources. Therefore, there is an imperative to ensure that wind power projects are developed in the most economically optimal fashion. For wind power project developers, shaving a few tenths of a cent off of the kilowatts per hour cost of wind power can mean the difference between a commercially viable project and a non-starter. For civic authorities who are responsible for managing municipally supported wind power projects, optimizing the economics of such projects can attenuate stakeholder opposition. This paper attempts to contribute to a better understanding of how to economically optimise wind power projects by conflating research from the fields of energy economics, wind power engineering, aerodynamics, geography and climate science to identify critical factors that influence the economic optimization of wind power projects.     

Production price of hydrogen from grid connected electrolysis in a power market with high wind penetration.

In liberalized power markets, there are significant power price fluctuations due to independently varying changes in demand and supply, the latter being substantial in systems with high wind power penetration. In such systems, hydrogen production by grid connected electrolysis can be cost optimized by operating an electrolyzer part time. This paper presents a study on the minimization of the hydrogen production price and its dependence on estimated power price fluctuations. The calculation of power price fluctuations is based on a parameterization of existing data on wind power production, power consumption and power price evolution in the West Danish power market area. The price for hydrogen is derived as a function of the optimal electrolyzer operation hours per year for four different wind penetration scenarios. It is found to amount to 0.41–0.45 €/Nm³. The study further discusses the hydrogen price sensitivity towards investment costs and the contribution from non-wind power sources.     

The advantages of using continuously variable transmissions in wind power systems

When connected to appropriate electric power generators, wind turbines may be used to produce electric energy. This may become complicated because wind speed tends to change. Traditionally, electric power was produced by electric generators connected to mechanical devices whose movement could be perfectly controlled and adapted to user's needs by special governors. This paper explores the feasibility of incorporating a continuously variable mechanical transmission between a wind turbine and an electric generator. Such a system would allow the turbine to operate at maximum efficiency levels and the generator to produce electric power at a desired frequency without using other devices. A mathematical model has been used to simulate a system formed by a wind turbine connected to an induction generator by means of a continuously variable transmission. The simulation was aimed at assessing whether the system was stable and attempted to adjust the transmission in order to ensure the required power supply.     

风压对太阳能热风发电系统的影响分析

根据太阳能热风发电系统的工作特征,以内蒙古乌海金沙沙漠太阳能热风发电系统为模型,模拟计算了不同形式的太阳能热风发电系统;对比不同系统内的气流分布,研究讨论了风压对气流流动和气流速度大小的影响。模拟结果表明:半圆形集热棚系统更具优势,其利用率较高,塔囱底部的平均气流速度可达24.38 m/s。该研究分析为乌海金沙沙漠太阳能热风发电站的建设提供了技术指导。     

Persistence of low wind speed conditions and implications for wind power variability

As the penetration of wind generation increases on power systems throughout the world, the effects of wind variability on power systems are of increasing concern. This study focuses on sustained occurrences of low wind speeds over durations ranging from 1 h to 20 days. Such events have major implications for the variability of energy yields from wind farms. This, in turn, influences the accuracy of wind resource assessment. The frequency analysis techniques commonly used to study wind variability cannot represent the autocorrelation properties of wind speeds and thus provide no information on the probabilities of occurrence of such sustained, low wind events. We present two complementary methods for assessing wind variability, runs analysis and intensity–duration–frequency analysis, both with emphasis on characterising the occurrence of continuous, extended periods (up to several days) of low wind speeds. Multi‐annual time series of hourly wind speeds from meteorological stations in Ireland are analysed with both techniques. Sustained 20‐day periods corresponding to extremely low levels of wind generation are found to have return periods of around 10 years in coastal areas. Persistent, widespread low wind speed conditions across the entire country are found to occur only rarely. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of spatial dispersion of wind power plants on the curtailment of wind power in the Greek power supply system

To meet the national target of 29% for electricity production from renewable energy sources by 2020 in Greece, effective implementation of massive wind power installed capacity into the power supply system is required. In such a situation, the effective absorption of wind energy production is an important issue in a relatively small and weak power system such as that of Greece, which has limited existing interconnections with neighboring countries. The curtailment of wind power is sometimes necessary in autonomous systems with large wind energy penetration. The absorption or curtailment of wind power is strongly affected by the spatial dispersion of wind power installations. In the present paper, a methodology for estimating this effect is presented and applied for the power supply system of Greece. The method is based on probability theory, and makes use of wind forecasting models to represent the wind energy potential over any candidate area for future wind farm installations in the country. Moreover, technical constraints imposed by the power supply system management, the commitment of power plants and the load dispatch strategies are taken into account to maximize the wind energy penetration levels while ensuring reliable operation of the system. Representative wind power development scenarios are studied and evaluated. Results show that the spatial dispersion of wind power plants contributes beneficially to the wind energy penetration levels that can be accepted by the power system. Copyright © 2009 John Wiley & Sons, Ltd.     

Simulation of a combined wind and solar power plant

The combined generation of electricity by wind and solar energy is a very attractive solution for isolated regions with high levels of yearly wind energy and insolation. A computer model is developed for the simulation of the electricity system of a Mediterranean island, including a wind power plant, a photovoltaic power plant and a storage system. In order to obtain an overall view of the system performance and economic aspects, the model also incorporates a number of diesel generators. Daily simulations for the Greek island Kythnos show that such a combined system of moderate size can provide a large fraction of the electrical energy requirements. Various parameters calculated in the simulation can be used to improve the configuration of the system and to estimate the cost of the electrical energy unit.     

Optimization of a combined wind and solar power plant

The paper is concerned with determining the optimized active areas of a photovoltaic conversion system, of a group of electricity generating wind machines and the optimal capacity of a battery storage system for a combined power plant. Minimization of the total life-cycle cost of the system is the criterion to obtaining the optimized parameters of the system. The algorithm consists of generating the system costs corresponding to various values of the parameters and to use these costs in a search procedure to determine the minimum. Each point is generated by a simulation program describing the system behaviour.     

Stochastic reactive power market with volatility of wind power considering voltage security

While wind power generation is growing rapidly around the globe; its stochastic nature affects the system operation in many different aspects. In this paper, the impact of wind power volatility on the reactive power market is taken into account. The paper presents a novel stochastic method for optimal reactive power market clearing considering voltage security and volatile nature of the wind. The proposed optimization algorithm uses a multiobjective nonlinear programming technique to minimize market payment and simultaneously maximize voltage security margin. Considering a set of probable wind speeds, in the first stage, the proposed algorithm seeks to minimize expected system payment which is summation of reactive power payment and transmission loss cost. The object of the second stage is maximization of expected voltage security margin to increase the system loadability and security. Finally, in the last stage, a multiobjective function is presented to schedule the stochastic reactive power market using results of two previous stages. The proposed algorithm is applied to IEEE 14-bus test system. As a benchmark, Monte Carlo Simulation method is utilized to simulate the actual market of given period of time to evaluate results of the proposed algorithm, and satisfactory results are achieved.     

基于协整分析法的我国风电电价形成机制有效性检验

由于可再生能源发电技术要求和并网发电成本较高,导致其与传统的煤电相比竞争力较弱。我国通过一系列政策措施的推动,特别是补贴政策的扶持,使可再生能源发电在技术、应用等方面取得了一些成绩。可再生能源电价形成机制中不仅包含上网电价部分,电价补贴也是相当重要的一部分。文章选取风电作为研究对象,从风电电价补贴的角度,对风电电价与所选变量之间进行协整关系检验,利用Eviews建立长期均衡模型,得出各变量之间影响作用的机理和程度。结果表明,基于补贴而形成的风电电价对增加风电发电量、提高风电发电量在总电量中的份额是有效的。     

Probabilistic modelling of hybrid solar/wind power system with solar tracking system

This paper presents a probabilistic model applied to a hybrid solar-wind power system (HSWPS), which is equipped with either a one-axis or a two-axis solar tracking system.Within the framework of a case study, the potential of the developed probabilistic approach is presented, and the effect of the solar tracking systems on the annual energy gain is discussed.Specifically, the impact of a tracking system on the probability density function (PDF) of the power produced by a photovoltaic system (PVS) is evaluated through the first four moments (mean, variance, skewness and kurtosis) of a PDF.Finally, to estimate the impact of a tracking system on HSWPS energy performance, a reliability analysis is performed using the energy index of reliability (EIR), which is directly related to energy expected not supplied (EENS), given different annual load scenarios.