Market and regulatory aspects of trans‐national offshore electricity networks for wind power interconnection

Subsea cable connections are an essential part of offshore wind power projects. Apart from direct connections between an offshore wind park to the national grid, several alternatives can be envisaged, including the connection to interconnectors between countries or direct connection to a country outside the jurisdiction where the wind park is based. Besides the technical‐economical constraints of these new types of grid connection, market and regulatory aspects need to be assessed. The paper gives an overview of these trans‐national connection schemes for wind power and considers integration into electricity markets and discusses regulatory implications. The scope of the research is Western Europe. Copyright © 2009 John Wiley & Sons, Ltd.     

Nordic hydropower flexibility and transmission expansion to support integration of North European wind power

The expected increase of wind power production in the North and Baltic Seas will substantially increase the variability of the generation portfolio in Northern Europe. Access to available resources of flexible power production will be necessary to support the power system against this variability. Since the Nordic hydro‐based power system can provide such resources, a stronger interconnection between continental Europe and the Nordic region seems to be beneficial. This paper assesses the challenges related to wind power production variability, especially offshore, in the North and Baltic Seas. Assessment on the transmission grid needed for both harvesting the available wind production located far away from load centres and to enable the optimal use of hydropower flexibility is studied in a long‐term cost‐benefit analysis. Special focus is devoted to the role of an offshore grid structure and the impact of onshore grid constraints. The analysis includes two interrelated simulation steps. The first step focuses on the strategic use of hydro energy in the day‐ahead market, where detailed modelling of water courses and hydro production in the Nordic region is considered. Then, in a second step, flow‐based simulations are conducted on a detailed grid model for the whole European system. The results show that long‐term strategies for the expansion of offshore and onshore grids must be defined in a coordinated way to ensure optimal developments. Copyright © 2014 John Wiley & Sons, Ltd.     

Well-functioning balancing markets: A prerequisite for wind power integration

This article focuses on the design of balancing markets in Europe taking into account an increasing wind power penetration. In several European countries, wind generation is so far not burdened with full balancing responsibility. However, the more wind power penetration, the less bearable for the system not to allocate balancing costs to the responsible parties. Given the variability and limited predictability of wind generation, full balancing exposure is however only feasible conditionally to well-functioning balancing markets. On that account, recommendations ensuring an optimal balancing market design are formulated and their impact on wind generation is assessed. Taking market-based or cost-reflective imbalance prices as the main objective, it is advised that: (1) the imbalance settlement should not contain penalties or power exchange prices, (2) capacity payments should be allocated to imbalanced BRPs via an additive component in the imbalance price and (3) a cap should be imposed on the amount of reserves. Efficient implementation of the proposed market design may require balancing markets being integrated across borders.     

Statistical analysis of negative prices in European balancing markets

The presence of renewable power generation technologies increases the need for system flexibility due to their variable nature. The increasing share of variable renewables in European power systems create a downward adequacy problem, which deals with the ability of power systems to cope with periods of excess generation. The occurrence of negative prices on Central Western European electricity markets confirms the relevance of this issue, which is referred to as “incompressibility of power systems” and is assessed as a barrier for further renewable power integration. The objective of this article is to identify the main drivers of negative price periods in European balancing markets, by means of both an empirical and regression analysis. Results confirm a positive relation with the scheduled generation of renewables and inflexible base load, as well as a negative relation with the scheduled system load. Furthermore, the occurrence of negative prices is related to the positive and negative forecast error of renewable generation and demand, respectively. It is concluded that negative balancing market prices provide a market signal for investments in flexibility sources such as flexible generation, demand response, electricity storage, and interconnector capacity.     

Review of recent offshore wind power developments in china

Rapid wind power development in China has attracted worldwide attention. The huge market potential and fast development of wind turbine manufacturing capacity are making China a world leader in wind power development. In 2010, with the newly installed wind power capacity and the cumulative installed capacity, China was ranked first in the world. In 2009, China also constructed and commissioned its first large offshore wind farm near Shanghai. Following earlier papers reviewing the state of China's onshore wind industry, this paper presents a broader perspective and up‐to‐date survey of China's offshore wind power development, making comparisons between the developments in the rest of the world and China, to draw out similarities and differences and lessons for the China offshore wind industry. The paper highlights six important aspects for China's offshore wind development: economics, location, Grid connection, technological development, environmental adaptation and national policies. The authors make recommendations for mitigating some outstanding issues in these six aspects for the future development of China's offshore wind resource. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic model for market-based capacity investment decision considering stochastic characteristic of wind power

This paper proposes a decentralized market-based model for long-term capacity investment decisions in a liberalized electricity market with significant wind power generation. In such an environment, investment and construction decisions are based on price signal feedbacks and imperfect foresight of future conditions in electricity market. System dynamics concepts are used to model structural characteristics of power market such as, long-term firms’ behavior and relationships between variables, feedbacks and time delays. For conventional generation units, short-term price feedback for generation dispatching of forward market is implemented as well as long-term price expectation for profitability assessment in capacity investment. For wind power generation, a special framework is proposed in which generation firms are committed depending on the statistical nature of wind power. The method is based on the time series stochastic simulation process for prediction of wind speed using historical and probabilistic data. The auto-correlation nature of wind speed and the correlation with demand fluctuations are modeled appropriately. The Monte Carlo simulation technique is employed to assess the effect of demand growth rate and wind power uncertainties. Such a decision model enables the companies to find out the possible consequences of their different investment decisions. Different regulatory policies and market conditions can also be assessed by ISOs and regulators to check the performance of market rules. A case study is presented exhibiting the effectiveness of the proposed model for capacity expansion of electricity markets in which the market prices and the generation capacities are fluctuating due to uncertainty of wind power generation.     

Optimal offering and allocation policies for wind power in energy and reserve markets

Proliferation of wind power generation is increasingly making this power source an important asset in designs of energy and reserve markets. Intuitively, wind power producers will require the development of new offering strategies that maximize the expected profit in both energy and reserve markets while fulfilling the market rules and its operational limits. In this paper, we implement and exploit the controllability of the proportional control strategy. This strategy allows the splitting of potentially available wind power generation in energy and reserve markets. In addition, we take advantage of better forecast information from the different day‐ahead and balancing stages, allowing different shares of energy and reserve in both stages. Under these assumptions, different mathematical methods able to deal with the uncertain nature of wind power generation, namely, stochastic programming, with McCormick relaxation and piecewise linear decision rules are adapted and tested aiming to maximize the expected revenue for participating in both energy and reserve markets, while accounting for estimated balancing costs for failing to provide energy and reserve. A set of numerical examples, as well as a case study based on real data, allow the analysis and evaluation of the performance and behavior of such techniques. An important conclusion is that the use of the proposed approaches offers a degree of freedom in terms of minimizing balancing costs for the wind power producer strategically to participate in both energy and reserve markets. Copyright © 2017 John Wiley & Sons, Ltd.     

Impacts of large amounts of wind power on design and operation of power systems,results of IEA collaboration

There are dozens of studies made and ongoing related to wind integration. However, the results are not easy to compare. IEA WIND R&D Task 25 on ‘Design and Operation of Power Systems with Large Amounts of Wind Power’ collects and shares information on wind generation impacts on power systems, with analyses and guidelines on methodologies. In the state‐of‐the‐art report (October, 2007), and the final report of the 3 years period (July, 2009) the most relevant wind power grid integration studies have been analysed especially regarding methodologies and input data. Several issues that impact on the amount of wind power that can be integrated have been identified. Large balancing areas and aggregation benefits of wide areas help in reducing the variability and forecast errors of wind power as well as help in pooling more cost effective balancing resources. System operation and functioning electricity markets at less than day‐ahead time scales help reduce forecast errors of wind power. Transmission is the key to aggregation benefits, electricity markets and larger balancing areas. Best practices in wind integration studies are described. There is also benefit when adding wind power to power systems: it reduces the total operating costs and emissions as wind replaces fossil fuels and this should be highlighted more in future studies. Copyright © 2010 John Wiley & Sons, Ltd.     

A framework to determine optimal offshore grid structures for wind power integration and power exchange

This paper presents a framework to find optimal offshore grid expansions using a transportation model of the power grid. The method extends the standard mixed‐integer linear programming approach to the solution of the transmission expansion planning problem to account for fluctuations in wind power generation and load; this makes the method especially suited to identify optimal transnational offshore high‐voltage direct current grid structures for the integration of large amounts of offshore wind power. The applicability of the method is demonstrated by a case study of the North Sea region. Copyright © 2011 John Wiley & Sons, Ltd.     

海上石油平台风燃互补发电孤立小电网稳定性研究及应用

"渤海海上风力发电示范工程"于2007年初批准正式立项,建设国内第一台海上风力发电机组,容量为1.5MW。由于风能具有间歇性和随机性的特点,为了实现绥中36-1CEP平台孤立电网与风电机组互补发电,并且保证该电网的平稳运行,进行了海上平台孤立小电网的稳定性研究。海上石油平台电网允许的正常频率波动范围为±0.25Hz,频率偏差报警为±0.5Hz,电网频率将随着透平发电机组输出有功功率的变化而波动。当风力发电机组在额定输出有功功率跳闸退出电网时,对电网频率的影响最大;当风力发电机组在额定风速启动并网时,对电网频率的影响较大。在特定的风燃互补孤立小电网中,采用电网负荷频率调节方程,可以计算风力发电机组容量与电网总负荷之比和频率波动的关系。海上平台风燃互补发电孤立小电网稳定运行的条件为风力发电机组的容量与平台电网总容量的比值小于10%。在满足风力发电机组引起平台电网最大频率波动范围为±0.25Hz的条件下,额定有功功率为1.5MW的风力发电机组,可并入最低总有功功率为15MW的电网。将稳定性研究结论应用于渤海风力发电示范项目,保证了示范工程的顺利进行,实现了国内第一台海上风力发电机组与生产平台并网发电的稳定运行。     

Integration of wind power in the liberalized Dutch electricity market

Wind power is becoming a large‐scale electricity generation technology in a number of European countries, including the Netherlands. Owing to the variability and unpredictability of wind power production, large‐scale wind power can be foreseen to have large consequences for balancing generation and demand in power systems. As an essential aspect of the Dutch market design, participants are encouraged to act according to their energy programs, as submitted day‐ahead to the system operator. This program responsibility shifts the burden of balancing wind power away from the system operator to the market. However, the system operator remains the responsible party for balancing any generation/load imbalances that may still be arising in real time. In this article, features that are unique for the Dutch market design are presented and their implications on the system integration of wind power are investigated. It is shown that the Dutch market design penalizes the intermittent nature of wind power. A discussion of opportunities and threats of balancing wind power by use of market forces is provided. Last, an outline is given of future work. Copyright © 2006 John Wiley &Sons, Ltd.     

Optimizing hybrid offshore wind farms for cost-competitive hydrogen production in Germany

Nearly 96% of the world's current hydrogen production comes from fossil-fuel-based sources, contributing to global greenhouse gas emissions. Hydrogen is often discussed as a critical lever in decarbonizing future power systems. Producing hydrogen using unsold offshore wind electricity may offer a low-carbon production pathway and emerging business model. This study investigates whether participating in an ancillary service market is cost competitive for offshore wind-based hydrogen production. It also determines the optimal size of a hydrogen electrolyser relative to an offshore wind farm. Two flexibility strategies for offshore wind farms are developed in this study: an optimal bidding strategy into ancillary service markets for offshore wind farms that build hydrogen production facilities and optimal sizing of Power-to-Hydrogen (PtH) facilities at wind farms. Using empirical European power market and wind generation data, the study finds that offshore-wind based hydrogen must participate in ancillary service markets to generate net positive revenues at current levels of wind generation to become cost competitive in Germany. The estimated carbon abatement cost of “green” hydrogen ranges between 187 EUR/tonCO₂e and 265 EUR/tonCO₂e. Allowing hydrogen producers to receive similar subsidies as offshore wind farms that produce only electricity could facilitate further cost reduction. Utilizing excess and intermittent offshore wind highlights one possible pathway that could achieve increasing returns on greenhouse gas emission reductions due to technological learning in hydrogen production, even under conditions where low power prices make offshore wind less competitive in the European electricity market.     

A simple analytical wind park model considering atmospheric stability

The analytical top‐down wind park model by Emeis and Frandsen 1 is enhanced by consistently making both the downward momentum flux and the momentum loss at the rough surface dependent on atmospheric stability. Specifying the surface roughness underneath the turbines in a wind farm in the model gives the opportunity to investigate principal differences between onshore and offshore wind parks, because the roughness length of the sea surface is two to three orders of magnitude lower than the roughness length of land surfaces. Implications for the necessary distance between single turbines in offshore wind farms and the distance between neighbouring wind parks are computed. It turns out from the model simulations that over smooth surfaces offshore the wind speed reduction at hub height in a wind farm is larger than over rough onshore surfaces given the same density of turbines within the park. Mean wind profiles within the park are also calculated from this model. Offshore wind farms must have a larger distance between each other in order to avoid shadowing effects of the upstream farm. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison of potential power production at on‐ and offshore sites

This article presents analyses of the potential power production from turbines located in the near‐shore and offshore environment relative to an onshore location, using half‐hourly average wind speed data from four sites in the Danish wind monitoring network. These measurement sites are located in a relatively high wind speed environment, and data from these sites indicate a high degree of spatial coherence. For these sites and representative turbine specifications (rated power 1·3–2 W) the fraction of time with power output in excess of 500 kW is twice as high for the offshore location as for the land site. Also, the fraction of time with negligible power production (defined as <100 kW output from the turbines described herein) is less than 20% for the offshore site and twice as high at the land‐based location. Capacity factors are higher for coastal sites than for the land site, and the annual capacity factor for the offshore location is twice that of the land site. Potential power output at the offshore site exhibits approximately the same seasonal variation as at the land site but little diurnal variation. Copyright © 2001 John Wiley & Sons, Ltd.     

中欧海上风电产业发展比较

相对于陆地风能,海上风能资源丰富,发电产能大,海上风电将是最有可能大规模发展的能源资源之一。欧洲是世界发展海上风力发电的先驱,从1991年至2009年,欧洲建设完成并投入运营的共有38个海上风电场,装机容量达到2056MW,其中一半以上的海上风电场是近5年建成的。欧洲海上风电产业拥有先进的核心技术,海上风电场正朝着大规模、深水化、离岸化方向发展,目前正处于示范阶段向商业扩展阶段的过渡时期。而我国虽然拥有丰富的海上风能资源,但海上风电产业的发展却比较缓慢,目前还处于研发阶段和示范阶段的过渡期,海上风电技术仍然面临着核心技术缺失、行业标准混乱、研发能力不足等问题。我国海上风电产业发展面临的主要问题包括:缺乏统筹;产能过剩、质量不高;难以盈利;缺少标准、无法推广等。为促进我国海上风电产业的发展,政府应进一步细化海上风能开发的有关规定,完善政策体系,统筹产业发展,采取多种措施推进政策具体落实;充分发挥市场作用,构建海上风电产品认证检测体系;提升核心技术含量,提高产品技术水平和工艺水平;加快培养专业人才。     

世界风力发电现状与前景预测

全球可再生能源发电装机容量中风电占有压倒性优势,今后可望成为欧洲、亚洲、北美的主要电力来源.2011年中国以62GW的累计装机容量蝉联世界第一,按照我国“十二五”规划目标,预计到2015年风电装机容量将达到1×108kW,年发电量1900×108kW·h.GWEC和Greenpeace预测,今后20年风力发电将成为世界主力电源,2030年装机容量有可能达到23×108kW,可供应世界电力需求的22％.欧美正大力开发海上风电产业.欧洲是世界海上风电发展的先驱和产业中心,欧洲企业不仅拥有自己的核心技术,而且还向世界各地输出技术,今后欧洲海上风力发电将急速增长.美国采取与英国、德国等欧洲厂家相同的战略,大力发展海上风力发电.我国海上风电产业刚刚起步,预计2015年海上风电装机500×104kW.日本学者大岛教授推算了不同电源的发电成本:包括政府财政补贴,运行年限30年的核电站发电成本为12.06日元/(kW·h);按标准设备利用率,风力发电成本11.30日元/(kW·h),与核电相比已经有竞争力.假设风况好时设备利用率达到35％,发电成本为7.95日元/(kW·h),比核电低得多.     

A data‐driven approach to study the role of interconnectors in a future low‐carbon electricity supply system

This paper investigates the potential role of the electricity interconnectors in improving the security of supply in Great Britain (GB) in 2030. Real electricity demand and price data for GB and France in 2016 were used to understand the relationship between power exchange between the two countries and their wholesale electricity prices. A linear programming optimisation model was developed to find the economic power dispatch. Two interconnection links were considered; two‐way trade interconnector with a capacity of 5.4 GW and a 12.3 GW import‐only interconnector between GB and other states. The GB–France link transmits electricity from cheaper system to the more expensive one. The total electricity demand in 2030 will be 406 TWh. Gas‐fired power plants w/wo CCS will provide 83 TWh of the total electricity demand, whereas nuclear power plants will produce 74 TWh. In addition, wind farms and solar PVs are expected to deliver ~120 TWh electricity. CHP units will provide 88 TWh electricity in 2030. The electricity traded between GB and France in 2030 was found to be 33 TWh, which is 160% larger compared with 2016. The power import from France is about 27 TWh and occurs in 59% of the time. For 64% of the time, the interconnector with France is fully loaded. The electricity imported via the 12.3 GW interconnector in 2030 is 1 TWh and mainly occurs during winter‐time when the demand in GB is high. De‐rated capacity margin was calculated based on instantaneous electricity demand and varies between ?2% and 139%. The impact of the price of the imported electricity via the 12.3 GW link was investigated. Increasing the price of the imported electricity via the 12.3 GW link results in a higher capacity factor for all the generation options except the 12.3 GW interconnector link.     

Coordinated control of series‐connected offshore wind park based on matrix converters

Optimization and reliability are two important aspects in design and operation of wind parks either for offshore as for onland emplacements. However, offshore locations demand conscientious effort in optimizing the size and the weight of each component in the energy conversion system because of the high investment and maintenance costs related with the supporting structures and transportation respectively. Achieving these two objectives requires the combination of different optimization stages, which consider a suitable design of the entire conversion system with innovative and more e?cient power electronic devices, optimized topology of the offshore grid and customized control strategies for optimizing the operation of the park. This paper presents an energy conversion concept for wind turbines on the basis of a reduced matrix converter (RMC) that will enable series direct current architecture in offshore wind parks thus preventing the need for offshore platforms. The RMC is built with bidirectional semiconductors that give reduced losses because of both superior topology and more e?cient semiconductors. The proposed conversion topology is tested in stationary state and transient operation. In addition to operational features of the concept, control and operation of a wind park with several turbines are presented. Dynamic operation of the turbine as well as the high‐voltage direct current transmission line effects are considered. Three types of models are therefore developed. First, an accurate and detailed model for analyzing one single turbine with the converter operated at high‐frequency switching is presented. This model considers a new modulation for the RMC. A second and simpli?ed model is used for small signal analysis. This model permits to simulate several series‐connected cluster during transient. Finally, an optimal direct current load ?ow model is used for evaluating stationary state operation. Results show the technical feasibility of the proposed concept and their advantages over conventional topologies. The paper also discusses the technological challenges that this type of offshore grid architecture will bring. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimal selection of time windows for preventive maintenance of offshore wind farms subject to wake losses

The maintenance of wind farms is one of the major factors affecting their profitability. During preventive maintenance, the shutdown of wind turbines causes downtime energy losses. The selection of when and which turbines to maintain can significantly impact the overall downtime energy loss. This paper leverages a wind farm power generation model to calculate downtime energy losses during preventive maintenance for an offshore wind farm. Wake effects are considered to accurately evaluate power output under specific wind conditions. In addition to wind speed and direction, the influence of wake effects is an important factor in selecting time windows for maintenance. To minimize the overall downtime energy loss of an offshore wind farm caused by preventive maintenance, a mixed-integer nonlinear optimization problem is formulated and solved by the genetic algorithm, which can select the optimal maintenance time windows of each turbine. Weather conditions are imposed as constraints to ensure the safety of maintenance personnel and transportation. Using the climatic data of Cape Cod, Massachusetts, the schedule of preventive maintenance is optimized for a simulated utility-scale offshore wind farm. The optimized schedule not only reduces the annual downtime energy loss by selecting the maintenance dates when wind speed is low but also decreases the overall influence of wake effects within the farm. The portion of downtime energy loss reduced due to consideration of wake effects each year is up to approximately 0.2% of the annual wind farm energy generation across the case studies—with other stated opportunities for further profitability improvements.     

The impact of European balancing rules on wind power economics and on short-term bidding strategies

Wind power represents a significant percentage of the European generation mix and this will increase to fulfill the renewable energy targets. Different balancing rules are applied to wind power among the countries; for instance, to what extent wind power producers (WPPs) are responsible for the energy imbalances and how those imbalances are penalized. This paper discusses those different rules and evaluates their effects on WPP bidding strategies. To do so, a quantitative analysis is presented for an offshore wind farm, considering the differences in the balancing rules and prices of Belgium, Denmark, Germany and the Netherlands. The quantitative approach consists of a stochastic optimization model that maximizes the profits of a WPP by trading in different markets (day-ahead and intraday) and computes the final energy delivered. The model considers uncertainties of most important parameters such as wind energy forecasts and prices at different time frames. The results show that the imbalance pricing design and the allocation of balance responsibility significantly affect WPP’ revenues. Additionally, WPPs deviate differently from the expected energy depending on the balancing rules, which can impact the system. Furthermore, these balancing rules should be considered with other market regulations, such as the design of support schemes.