Role of the GB-France electricity interconnectors in integration of variable renewable generation

The integration of large capacities of wind and solar generation into the France and Great Britain (GB) power systems is expected to pose significant operational challenges. Electricity interconnectors can play a role in facilitating the integration of renewable generation in neighbouring countries by allowing power to flow freely between power systems and therefore smooth the net electricity demand. In this paper, role of the electricity interconnectors in efficient balancing of supply and demand in the France and GB power systems was evaluated in terms of overall reduction in the operational costs and curtailment of renewable generation, and also its impact on operation of gas-fired plants. The value of the France-GB interconnectors was studied for two generation mix scenarios in 2030 using PLEXOS. The outputs of the modelling showed the interconnectors will result in larger amount of wind and solar to be absorbed by both power systems which consequently will reduce overall operational costs and CO₂ emissions. In addition, the interconnectors will reduce burden on gas-fired plants compensating for variation in wind and solar generation. This can have a significant value in operation and required investment of gas networks in both countries.     

Private and social benefits of a pumped hydro energy storage with increasing amount of wind power

In this paper, we calculate the long-term profitability of a pumped hydro energy storage (PHES) plant that is planned to be built in an old mine. We model the optimal PHES operation for several scenarios with different wind power penetration levels. Our modelling approach first involves estimating wholesale electricity prices for the day-ahead, intraday and balancing market as a function of wind power penetration. The estimated price profiles are implemented in a dynamic programming model, where the PHES plant maximises its balancing market revenue given the optimal commitment in the day-ahead market. We show that increasing the wind penetration changes the optimal PHES operation and increases the PHES profits. Additionally, we quantify how the costs of wind power balancing are affected by the PHES investment. Policy implications are drawn based on the estimated private and social benefits from the investment.     

The Spanish intraday market design: A successful solution to balance renewable generation?

The increasing penetration of renewable energy sources in Europe requires market mechanisms which allow an efficient balancing of these sources. This paper analyzes the participation of renewable generators in the Spanish intraday market. First, the organization of the intraday market and the short-term market mechanisms influencing intraday trading are described. After that, day-ahead and intraday market prices, as well as intraday trading volumes, are used to study the behavior of market agents in the Spanish intraday market. Regarding renewable generators, the influence of support schemes on the behavior of these agents in the intraday market is also analyzed. This paper shows that the Spanish intraday market has effectively contributed to renewable generation balancing. Despite this, market distortions have incentivized some renewable generators to arbitrate between the day-ahead and intraday markets, giving rise to higher system costs. Based on the presented analysis, it is argued that these distortions need to be removed from short-term markets to incentivize market parties, especially intermittent generators, to reduce forecast errors over time, improving economic efficiency and avoiding the use of costly balancing actions performed by the System Operator.     

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.     

连接体结构对固体氧化物燃料电池性能影响的数值分析

固体氧化物燃料电池（SOFC）中连接体结构对电池性能有重要影响。为探究连接体结构对固体氧化物燃料电池性能的影响，建立了传统直通、圆柱形、矩形和凹形4种不同连接体结构SOFC的三维数值模型，并对其流体流动、组分传递、电化学反应和固体流体传热的多物理场耦合过程进行了数值模拟。结果表明，在一定条件下，圆柱形、矩形和凹形连接体结构有利于电池中气体的传输，使电池的电流密度和输出功率均有所提升，其中凹形连接体结构的提升效果最明显，圆柱形、矩形连接体结构的次之。不同孔隙率下圆柱形、矩形和凹形连接体结构均优于传统直通连接体结构，在阴极孔隙率较小时其优势更加明显。     

Transmission needs across a fully renewable European power system

The residual load and excess power generation of 30 European countries with a 100% penetration of variable renewable energy sources are explored in order to quantify the benefit of power transmission between countries. Estimates are based on extensive weather data, which allows for modelling of hourly mismatches between the demand and renewable generation from wind and solar photovoltaics. For separated countries, balancing is required to cover around 24% of the total annual electricity consumption. This number can be reduced down to 15% once all countries are networked together with unconstrained interconnectors. The reduction represents the maximum possible benefit of transmission for the countries. The total Net Transfer Capacity of the unconstrained interconnectors is roughly 11.5 times larger than current values. However, constrained interconnector capacities 5.7 times larger than the current values are found to provide 98% of the maximum possible benefit of transmission. This motivates a detailed investigation of several constrained transmission capacity layouts to determine the export and import capabilities of countries participating in a fully renewable European electricity system.     

Balancing energy strategies in electricity portfolio management

Traditional management of electricity portfolios is focused on the day-ahead market and futures of longer maturity. Within limits, market participants can however also resort to the balancing energy market to close their positions. In this paper, we determine strategic positions in the balancing energy market and identify corresponding economic incentives in an analysis of the German balancing energy demand. We find that those strategies allow an economically optimal starting point for real-time balancing and create a marketplace for flexible capacity that is more open than alternative marketplaces. The strategies we proffer in this paper we believe will contribute to an effective functioning of the electricity market.     

Economic analysis of the electricity market in England and Wales

The electricity supply industry in England and Wales (E&W) was restructured and privatized on Vesting Day, 31 March 1990. Eight years on, the UK government has reviewed the trading arrangements of the E&W electricity market and accepted the regulator's proposal of replacing the day-ahead market (the pool) by several forward markets, a short-term bilateral market, and a balancing market. This letter looks at what some economists had examined of the present E&W electricity market under the day-ahead arrangement. Such economic analysis may serve as a reference to power engineers elsewhere participating in the restructuring of their electricity supply industries     

Interconnector economics

This paper explains why the utilization of some interconnectors is sub-optimal. The nature of the benefits that interconnectors can provide and the complexity of estimating them ex ante is first described. Then the two major problems of securing efficient use are examined for a single interconnector linking two separate control areas. One is matching user nominations accepted by both system operators; the other is organising a system of transmission rights which will manage congestion efficiently. Finally, there is a discussion of some proposed methods for dealing with the much more complex problems which arise when several interconnectors provide meshed links between several control areas.     

Transactive energy management for optimal scheduling of interconnected microgrids with hydrogen energy storage

In recent years, renewable energy sources (RESs) have attracted substantial attention due to carbon-free and cost-effective advantages that have made them one of the main sources of energy generation in the modern structure of the power grid. This paper proposes the stochastic day-ahead scheduling model for optimal energy management of renewable-based microgrids. In this paper, each microgrid is equipped with 100% RESs including the PV system and wind turbine for full pollutant-free energy generation while the hydrogen energy storage (HES) system is used for alleviating the intermittences of the RESs aiming to dynamically balance the energy during a day. To model the fluctuations such as day-ahead market price in the microgrids, the autoregressive integrated moving average and fast forward selection methods are exerted for scenario production and reduction, respectively. Transactive energy as a sustainable and reliable technique is considered for controlling and coordinating energy sharing among the microgrids and the energy network for dynamic energy balancing in the deregulated environment. For energy management in the demand-side, the price and load response schemes are presented, aiming to revise the consumers' patterns in energy consumption in line with balancing energy and minimizing the microgrids’ energy cost. The effectiveness of the suggested model is validated using the modified IEEE 24-bus case study. The realistic modeling of the system based on the proposed model has led to an 8.51% increment in energy cost.     

Cost-profit analysis for Japan-Russia and Japan-South Korea interconnectors

This paper describes the results of cost-profit analysis related to interconnectors for Japan-Russia and Japan- South Korea based on the Asia International Grid Connection Study Group 2^nd report. The Group has been established in 2016 for conducting research on international electric power networks in Asia from the viewpoint of technology, investment and legal framework. 2^nd report of the Group was published in June 2018, examining the profitability of an interconnectors between Japan and neighboring countries. The Group has calculated expected profit from operation of these interconnectors.The Group has categorized interconnector business into four models from the survey of preceding and current business on grids and interconnectors. To clarify profitability, expected internal rate of return (IRR) was calculated for each business model based on estimated investment cost for each route. When interconnector is dedicated to specific power plants or suppliers and electricity can be sold at Japan wholesale market at 2016-2017 price level, positive IRR levels are expected in case that Free on Board (FOB) price lower than 7 JPY /kWh. When the investment will be covered by electricity tariff by final consumers, tariff for consumers will just slightly increase by approximately 0.1JPY/ kWh.     

Design and fabrication of novel interconnectors for solid oxide fuel cells via rubber pad forming

Rubber pad forming is studied numerically and experimentally to fabricate interconnectors for solid oxide fuel cells (SOFCs) from thin Crofer sheets instead of classical thick ones with machined flow channels. In the theoretical program, the effects of the rib angle, rib width and channel depth on the formability are numerically investigated and optimized as 120°, 0.5 mm and 0.5 mm, respectively. In addition, flow simulations are performed to analyze the flow uniformity in the flow-field for the final geometry and homogenous reactant distributions are observed. In the experimental program, the interconnector with numerically optimized geometry is successfully manufactured by rubber pad forming, trimming, piercing and spot welding processes. This interconnector is used to build a two-cell stack. A similar stack is also constructed with a conventional interconnector for comparison. The performances of these stacks are measured at different operating temperatures. According to the simulation and experimental results, rubber pad forming is found to be a highly effective manufacturing route to fabricate SOFC interconnectors from thin Crofer sheets, providing higher specific and volumetric power density values for SOFC stacks compared to those of conventional stacks with interconnectors having machined flow channels.     

Interconnector capacity allocation in offshore grids with variable wind generation

Different capacity allocation regimes have a strong impact on the economics of offshore wind farms and on interconnectors in offshore grids. Integrating offshore generation in offshore grids is currently a subject of discussion for different regions, e.g. the North Sea. A novel question is how the interconnector capacity should be allocated for wind generation and for international power trading. The main difficulty arises from the stochastic nature of wind generation: in a case with radial connections to the national coast, the wind park owner has the possibility of aggregating the offshore wind park with onshore installations to reduce balancing demand. This is not necessarily the case if the interconnector capacity is sold through implicit or explicit auctions. Different design options are discussed and quantified for a number of examples based on Danish, Dutch, German and Norwegian power markets. It is concluded that treating offshore generation as a single price zone within the interconnector reduces the wind operator's ability to pool it with other generation. Furthermore, a single offshore price zone between two markets will always receive the lower spot market price of the neighbouring zones, although its generation flows only to the high‐price market. Granting the high‐price market income for wind generation as the opposite design option reduces congestion rents. Otherwise, compensation measures through support schemes or different balancing responsibilities may be discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Elecxit: The cost of bilaterally uncoupling British-EU electricity trade

The UK's withdrawal from the European Union could mean that it leaves the EU's Internal Energy Market for electricity (Elecxit). This paper develops methods to study the longer-term consequences of this electricity market disintegration, especially the end of market coupling. Before European electricity markets were coupled, different market closing times forced traders to commit to cross-border trading volumes based on anticipated market prices. Interconnector capacity was often under-used, and power sometimes flowed from high- to low-price areas. A model of these market frictions is developed, empirically verified on 2009 data (before French and British market coupling) and applied to estimate the costs of market uncoupling in 2030. A less efficient market and the abandonment of some planned interconnectors would raise generation costs by €700 m a year (2%) compared to remaining in the Internal Energy Market. This result is sensitive to how the British and French electricity systems develop over the coming decades. Economic losses are four times greater (€2700 m a year) if France retains substantial nuclear capacity due to its low marginal costs. Conversely, losses are reduced by two-thirds if UK weakens its decarbonisation ambitions, as lower carbon prices subsidise British fossil fuel generation, allowing electricity prices to converge with those in France. A Hard Elecxit would make British prices rise and French prices fall in three of our four scenarios, with the opposite movements in the fourth scenario.     

Price volatility in commodity markets with restricted participation

In commodity markets, price volatility may rise significantly if the product granularity increases. To gain insights into the underlying drivers, we analyze price volatility based on the example of German electricity markets. We develop a theoretical model to reproduce the price formation in the day-ahead and intraday auction which are sequential short-term electricity markets with 60-minute and 15-minute products. As cross-border trade is allowed in the day-ahead but not in the intraday auction, the model accounts for the impact of restricted market participation. The theoretical model is then transferred into an empirical analysis to first validate the modeling approach and second to comparatively assess the impact of increasing product granularity and restricted market participation. The empirical results indicate that the disproportional rise in quarter-hourly price volatility is mainly triggered by limited market participation and not only by the high volatility of renewable supply and demand. Since restricted market participation refers to a lack of market coupling, we derive a proxy for efficiency losses ranging from EUR 55 million to EUR 108 million that may be reduced if markets are coupled.     

Transmission capacities and competition in Western European electricity market

The integration of national electricity markets into a single European one is expected to reduce the ability of dominant players to exercise market power. This paper investigates whether or not existing transmission capacities of cross-border interconnectors are sufficient to achieve this result and create vigorous competition in the market. A model with two decision levels is used. On the first level profit maximizing generators play Cournot game against each other. On the last level the system operator clears the market and determines flows in the network to maximize social welfare subject to a set of physical constraints. As each strategic generator anticipates her impact on equilibrium prices and congestion in the system, her optimization problem is subject to equilibrium constraints from the system operator's problem.The analysis demonstrates that interconnector capacities in Western Europe are insufficient for integration alone to reduce the exercise of market power. I compare several possible competition-enhancing policies: expansion of interconnectors and different scenarios of national markets’ restructuring. I show that although increase of line capacity is a useful tool to stimulate competition in an integrated market, it is not a substitute for the restructuring of large players.     

Experimental Investigation of the Effect of Tube-to-Tube Porous Medium Interconnectors on the Thermohydraulics of Confined Tube Banks

This experimental study investigates the effect of tube-to-tube copper porous interconnectors on the thermohydraulic performance of an in-line and staggered confined tube bank. The porous medium, having a transverse thickness equal to that of the diameter of the tube (9 mm), connects longitudinally six successive tubes kept as in-line and staggered arrangements with a square pitch of 2.0. The tubes are subjected to a constant and uniform heat flux and are cooled by forced convection under laminar-transition flow range (200 < Reynolds number < 1500) using air with a Prandtl number of 0.71 as cooling fluid. Experimental data presented here establish that by introducing tube-to-tube porous medium interconnectors for the maximum Reynolds number tested here, a reduction in the pressure drop by 18% is observed in the in-line configuration while the heat transfer is enhanced by 100% in the staggered configuration, when compared to their respective configurations without the porous medium. Defining an overall energy gain as the ratio of the heat transfer enhancement due to the presence of the porous inserts to the pressure drop incurred, it is seen that fixing the porous inserts in the in-line configuration is advantageous.     

国产600MW汽轮发电机组轴系动平衡研究

针对国产600MW汽轮发电机组运行中普遍存在的轴系异常振动问题,分析了振动现象、振动特征、振动机理及其原因,并对现场动平衡问题的处理方法进行了总结.结果表明：国产600MW高中压转子由于结构不对称存在较大的振型干扰,现场对转子进行动平衡时应考虑各阶振型的干扰系数,尤其是一阶配重对二阶振型的影响;部分机组低压转子轴承座振动超标的原因为采用坐缸式轴承座的支承刚度不足,现场可以通过精细动平衡来消除;发电机转子振动主要呈现三阶振型,现场校正三阶不平衡的方法就是在低-发对轮或发-励对轮上加重,且在动平衡分析时应注意区分振型畸变;集电小轴的振动受发-励对轮的安装工况影响较大,现场对其进行动平衡分析时应考虑发-励对轮下张口对加重响应的影响.     

A novel two‐part interconnector for solid oxide fuel cells

A two‐part interconnector is developed for solid oxide fuel cell stacks to reduce cost and to improve sealing. The novel interconnector involves a metallic core for current collection and gas distribution and a ceramic support to house the metallic core and to separate two short stacks. The new interconnector reduces usage of expensive metallic alloys and substantially reduce mismatch between stack components due to higher expansion coefficient of metals. The new interconnectors also improve sealing with glass–ceramics eliminating chromium evaporation which is a major reason for sealing failure in fully metallic interconnectors. A proof of concept short stack is manufactured and tested in this study. A comparable performance with a convectional interconnector is obtained with new interconnector, while substantially improving the sealing quality. Copyright © 2014 John Wiley & Sons, Ltd.