Integrating distributed generation: Regulation and trends in three leading countries

This paper explores the trends in the deployment and integration of distributed generation in Germany, Denmark and Sweden. The study concentrates on the regulation of renewable energy generation with a focus on grid access and connection mechanisms. The high rate of distributed generation penetration is mainly based on the early support that these countries gave to the expansion of renewable energy generation – mainly wind and solar – within their respective national policies. Germany and Denmark are the ones with the most sophisticated support schemes, which have shown a dynamic design over time. In terms of connections, Germany has the most favorable connection regime which provides not only priority connection but also priority grid access for generation units that produce electricity from renewable energy sources. Sweden guarantees equal treatment among different technologies (i.e. a non-discrimination principle). High connection costs have been observed specially in Germany and Denmark. The costs of network upgrades are usually socialised across demand customers. However, integration issues should be taken into consideration in order to avoid expansion of distributed generation in a way which unnecessarily raises total system costs, via high connection costs.     

Increasing penetration of renewable and distributed electricity generation and the need for different network regulation

The amount of decentralised electricity generation (DG) connected to distribution networks increases across EU member states. This increasing penetration of DG units poses potential costs and benefits for distribution system operators (DSOs). These DSOs are regulated since the business of electricity distribution is considered to be a natural monopoly. This paper identifies the impact of increasing DG penetration on the DSO business under varying parameters (network characteristics, DG technologies, network management type) and argues that current distribution network regulation needs to be improved in order for DSOs to continue to facilitate the integration of DG in the network. Several possible adaptations are analysed.     

基于多群体自学习群搜索算法的分布式发电优化

为减少分布式发电(DG)对配电网电压和网络损耗的影响,在考虑DG的接入位置、接入容量及接入方法等因素对配电网影响的基础上,建立了以潮流方程及DG接入容量为约束、以配电网中电压偏差和网络损耗同时最小、以DG接入容量最大为优化目标的多目标优化模型。在此基础上,提出了一种多群体自学习群搜索算法(MSLGSO),并将其应用于求解DG优化问题。通过对IEEE33节点的标准配电网算例仿真分析,表明DG的合理配置可使配电网电压水平提升和减少有功网损,且所提算法具有良好的实用性和适应性。     

基于蚁群算法的多类型分布式电源优化配置

鉴于不同类型分布式电源接入配电网的位置及注入容量对系统潮流分布的影响,主要体现在能源的梯级利用率、电网规划成本、供电可靠性和电能质量等方面,在配电网规划建设期间建立各种分布式电源(DG)的出力模型,综合考虑需求侧的经济利益,建立以用户侧的投资运行成本和网络损耗费用最小为优化目标的函数,采用蚁群算法对函数进行求解得到优化的位置和容量。算例分析表明,该方法可以得到较为合理的方案,并可有效降低系统网损、节点电压偏差,提高需求侧的经济效益和电能质量。     

基于故障模式分析法对含DG的配电网供电可靠性评估

分析DG的接入对小型配电网供电可靠性的影响,利用故障模式后果分析法对含有DG的配电网进行供电可靠性计算和分析,得出接人DG后供电可靠性较接人DG之前有提高,故采用正确的方式将DG接入配电网,有利于提高用户的供电可靠性。     

Towards a higher share of distributed generation in Turkey

In 2006, there is 8.5% distributed generation (DG) in Turkey which are generation units connected to the low and medium voltage distribution network. Out of this, 56% is industrial combined heat and power production (CHP) and 20% are renewables (RES-E), mainly runoff small scale hydro. Various technical and economical barriers have kept the DG share relatively low. This paper assesses how Turkey could increase the DG share. The methodology employed in this paper consist of a survey of the literature and legislation, combined with interviews with regulators, transmission and distribution system operators. Scenarios for DG are developed, barriers to increase the DG share are identified, DG and central generation (CG) are compared economically and regulatory measures are identified. The addition of long-run marginal transmission costs to the investment cost of new power generation units could close the long-run marginal cost difference between DG and CG. However, the share of DG is likely to stay low unless regulatory measures are taken. Moreover, a specific policy and regulation on DG is needed, the distribution grid needs strengthening, local dispatch centres need to become active and RES-E limits are needed for Turkey.     

Efficient investment signals for distributed generation

Distributed generation units are desirable from an environmental point of view but also have an impact on the costs of electricity grids at the distribution and transmission level. Therefore, investment planning has to consider all benefits and costs of DG to build DG sources at sites where they are economically efficient. Unfortunately, this is not an easy task in an unbundled industry where distribution and generation of electricity are not planned by one single institution. For this reason, this article analyses possible policy options for giving incentives to distributed generation and focuses on the long-term investment signals related to DG.     

Optimal planning of distributed generation systems in distribution system: A review

This paper attempts to present the state of art of research work carried out on the optimal planning of distributed generation (DG) systems under different aspects. There are number of important issues to be considered while carrying out studies related to the planning and operational aspects of DG. The planning of the electric system with the presence of DG requires the definition of several factors, such as: the best technology to be used, the number and the capacity of the units, the best location, the type of network connection, etc. The impact of DG in system operating characteristics, such as electric losses, voltage profile, stability and reliability needs to be appropriately evaluated. For that reason, the use of an optimization method capable of indicating the best solution for a given distribution network can be very useful for the system planning engineer, when dealing with the increase of DG penetration that is happening nowadays. The selection of the best places for installation and the preferable size of the DG units in large distribution systems is a complex combinatorial optimization problem.This paper aims at providing a review of the relevant aspects related to DG and its impact that DG might have on the operation of distributed networks. This paper covers the review of basics of DG, DG definition, current status of DG technologies, potential advantages and disadvantages, review for optimal placement of DG systems, optimizations techniques/methodologies used in optimal planning of DG in distribution systems. An attempt has been made to judge that which methodologies/techniques are suitable for optimal placement of DG systems based on the available literature and detail comparison(s) of each one.     

Assessing the performance and benefits of customer distributed generation developers under uncertainties

In this paper, the performance of customer-owned distributed generation (DG) units is quantified from different perspectives through an uncertainty study. A Monte Carlo-based method is applied to assess the stochastic operation of the customer-owned DG units in the power distribution system. Several cases are studied to analyze the impact on system performance of using such generators, with the emphasis on benefits. The results of the studied cases show that proper operation of customer-owned DG units placed close to significant consumption centers offers several benefits which lead to significant energy savings and improvement in the performance indices while maintaining the cost-effectiveness. Furthermore, based on the energy demand, different electricity price scenarios considering a cost sensitivity analysis are performed to indicate how the variations in electricity price influence each scenario’s feasibility. It is concluded that implementation of a proper energy purchase policy, and allocating the benefits of DG units to the owners, improves the economic performance of their investments and encourages customer DG developers to connect DG to the distribution network.     

Offshore transmission for wind: Comparing the economic benefits of different offshore network configurations

It has been argued that increasing transmission network capacity is vital to ensuring the full utilisation of renewables in Europe. The significant wind generation capacity proposed for the North Sea combined with high penetrations of other intermittent renewables across Europe has raised interest in different approaches to connecting offshore wind that might also increase interconnectivity between regions in a cost effective way. These analyses to assess a number of putative North Sea networks confirm that greater interconnection capacity between regions increases the utilisation of offshore wind energy, reducing curtailed wind energy by up to 9 TWh in 2030 based on 61 GW of installed capacity, and facilitating a reduction in annual generation costs of more than €0.5bn. However, at 2013 fuel and carbon prices, such additional network capacity allows cheaper high carbon generation to displace more expensive lower carbon plant, increasing coal generation by as much as 24 TWh and thereby increasing CO₂ emissions. The results are sensitive to the generation “merit order” and a sufficiently high carbon price would yield up to a 28% decrease in emissions depending on the network case. It is inferred that carbon pricing may impact not only generation investment but also the benefits associated with network development.     

配电网对电动汽车可接纳能力分析

随着新能源汽车保有量持续上涨,大规模电动汽车接入对城市配电网的安全稳定运行带来了一定影响,研究配电网对电动汽车可接纳能力十分迫切。该研究基于不同类型电动汽车性能参数和驾驶者行为特性建立了电动汽车充电功率需求模型,分析了一定规模电动汽车接入对配电网日负荷曲线的影响。设置了含电动汽车V2G和DG并网发电4种不同场景,从电压偏差和静态电压稳定极限两个方面定量分析了配电网对电动汽车的接纳能力,以IEEE33节点配电系统为例,对比了4种不同场景下配电网对电动汽车的接纳能力。     

Towards a future with large penetration of distributed generation: Is the current regulation of electricity distribution ready? Regulatory recommendations under a European perspective

The European Energy Policy promotes renewable energy sources and energy efficiency as means to mitigate environmental impact, increase security of supply and ensure economic competitiveness. As a result, the penetration levels of distributed generation (DG) in electricity networks are bound to increase. Distribution networks and distribution system operators (DSOs) will be especially affected by growing levels of DG. This paper reviews the current regulation of distribution in the European Union Member States, focusing on those aspects that might hinder the future integration of DG. Several regulatory issues that may hinder a successful integration of DG have been identified. Recommendations to improve the current situation are proposed. Regarding economic signals sent to DG, connection charges and cost-reflective use-of-system charges together with incentives to provide ancillary services are the key aspects. Concerning DSOs regulation, unbundling from generation and supply according to the European Electricity Directive, incentives for optimal planning and network operation considering DG, including energy losses and quality of service, and innovation schemes to migrate to active networks are the most relevant topics.     

Planning and operating non-firm distributed generation

The penetration of distributed generation (DG) is increasing on distribution networks across the world. Non-firm access to the network is now being proposed as a cost effective way to facilitate DG. However, concerns remain about the operational details of non-firm access and also with regard to the financing of DG projects, which, by their nature, are not guaranteed permission to export power at all times. Here, the pertinent planning and operational issues that arise with non-firm access are analysed. The index of coincidence is used to assess the probability of constraint breaches, through analysis of historical generation and load profiles. Further to this, a novel method is proposed, which minimises the cost to the generators of non-firm access through coordinated operation.     

Conditions and costs for renewables electricity grid connection: Examples in Europe

This paper compares conditions and costs for RES-E grid connection in selected European countries. These are Germany, the Netherlands, the United Kingdom, Sweden, Austria, Lithuania and Slovenia. Country specific case studies are presented for wind onshore and offshore, biomass and photovoltaic power systems, as based on literature reviews and stakeholder interviews. It is shown that, especially for wind offshore, the allocation of grid connection costs can form a significant barrier for the installation of new RES-E generation if the developer has to bear all such costs. If energy policy makers want to reduce the barriers for new large-scale RES-E deployment, then it is concluded that the grid connection costs should be covered by the respective grid operator. These costs may then be recouped by increasing consumer tariffs for the use of the grid.     

Optimization of hybrid solar energy sources/wind turbine systems integrated to utility grids as microgrid (MG) under pool/bilateral/hybrid electricity market using PSO

This study presents an optimized design of microgrid (MG) in distribution systems with multiple distributed generation (DG) units under different market policies such as pool/hybrid electricity market.Proposed microgrid includes various energy sources such as photovoltaic array and wind turbine with energy storage devices such as battery bank.In this study, microgrid is considered as independent power producer company (IPP) in power system. Price of selling/buying power in on-peak or off-peak for MG, DG and upstream power system (DISCO) under pool/bilateral/hybrid electricity market are different. In this study, particle swarm optimization (PSO) algorithm has been implemented for the optimization of the microgrid cost. The costs include capital cost, replacement cost, operation and maintenance costs and production cost for microgrid and DGs. Then, an objective function to maximize total net present worth (NPW) is presented. PSO approach is employed to obtain the minimum cost of microgrid, during interconnected operation by optimizing the production of local DGs and power exchanges with the main distribution grid. The optimization algorithm is applied to a typical LV network operating under different market policies.     

State of the art of the virtual utility: the smart distributed generation network

The world of energy has lately experienced a revolution, and new rules are being defined. The climate change produced by the greenhouse gases, the inefficiency of the energy system or the lack of power supply infrastructure in most of the poor countries, the liberalization of the energy market and the development of new technologies in the field of distributed generation (DG) are the key factors of this revolution. It seems clear that the solution at the moment is the DG. The advantage of DG is the energy generation close to the demand point. It means that DG can lower costs, reduce emissions, or expand the energy options of the consumers. DG may add redundancy that increases grid security even while powering emergency lighting or other critical systems and reduces power losses in the electricity distribution. After the development of the different DG and high efficiency technologies, such as co‐generation and tri‐generation, the next step in the DG world is the interconnection of different small distributed generation facilities which act together in a DG network as a large power plant controlled by a centralized energy management system (EMS). The main aim of the EMS is to reach the targets of low emissions and high efficiency. The EMS gives priority to renewable energy sources instead of the use of fossil fuels. This new concept of energy infrastructure is referred to as virtual utility (VU). The VU can be defined as a new model of energy infrastructure which consists of integrating different kind of distributed generation utilities in an energy (electricity and heat) generation network controlled by a central energy management system (EMS). The electricity production in the network is subordinated to the heat necessity of every user. The thermal energy is consumed on site; the electricity is generated and distributed in the entire network. The network is composed of one centralized control with the EMS and different clusters of distributed generation utilities and heat storage tanks. Each of these clusters is controlled by a local management station (LMS). Every LMS has information about the requirements (heat, cold and electricity) of the users connected to its cluster and the state of the utilities and water level of the storage tanks in its cluster. The EMS receives the information from the LMSs and sets the electricity input or output of every cluster in the network. With the information ordered by the EMS, the LMS set the run or stand‐by of the utilities of its cluster. The benefits of the VU are the optimization of the utilization yield of the whole network, the high reliability of the electricity production, the complete control of the network for achieving the main aim of the EMS, the high velocity for assuming quick changes in the demand of the system and high integration of renewable energy sources, plus the advantages of the DG. This paper indicates the state of the art of the VU concept, analyses the projects that are being developed in this field and considers the future of the VU concept. Copyright © 2004 John Wiley & Sons, Ltd.     

分布式发电对电力系统继电保护的影响

传统配电网一般都是单一电源的辐射状网络,继电保护按照辐射型网络进行设计和整定。随着分布式发电（DG）的接入,辐射式的网络将变为一种遍布电源和用户互联的网络,使得配电网中的潮流分布发生根本变化。详细分析了分布式发电对原有配电网中的电流保护,距离保护以及对重合闸等传统继电保护所带来的影响;最后根据DG接入电网位置的不同以及容量不同提出了相应的解决方案。     

Distributed Generation in an isolated grid: Methodology of case study for Lesvos – Greece

The purpose of this article is to evaluate the economic effects of Distributed Generation (DG) in isolated grids and in particular Lesvos island in Greece. DG penetration is expected to rise in the following years since the island’s wind potential is still not exploited at a satisfying level. The necessity to replace the existing oil-fired power plant together with the need to cut down on greenhouse gases makes DG, and in particular wind turbines quite a promising technology. The present study with the use of specific software simulates the current electricity production for a whole year looking at its technical and economic performance. The sensitivity analysis that is carried out shows the effects of a potential increase in renewable energy sources (RES) capacity. Different sensitivity factors are investigated such as diesel price and hub height. The results show the environmental benefits of increased RES capacity and the variation of the cost of electricity production which remains high compared to other interconnected areas in Greece.     

Small distributed generation versus centralised supply: a social cost–benefit analysis in the residential and service sectors

This paper aims at measuring the social benefits of small CHP distributed generation (DG) in the residential and service sectors. We do this by comparing the social costs of decentralised and centralised supplies, simulating “ideal” situations in which any source of allocative inefficiencies is eliminated. This comparison focuses on assessing internal and external costs. The internal costs are calculated by simulating the optimal prices of the electricity and gas inputs. The external costs are estimated by using and elaborating the results of the dissemination process of the ExternE project, one of the most recent and accurate methodologies in this field. The analysis takes into account the main sources of uncertainty about the parameter values, including uncertainty about external cost estimations. Despite these sources of uncertainty, the paper concludes that centralised supply is still preferable to small DG. In fact, the overall range of DG social competitiveness is restricted, even considering further remarkable improvements in DG electrical efficiency and investment costs. The results are particularly unfavourable for the residential sector, whereas, in the service sector, the performance of DG technologies is slightly better.     

Large-Scale Integration of Wind Generation Including Network Temporal Security Analysis

This paper presents a methodology to assess large-scale wind generation projects that considers their effect on network security. The proposed method is based on contingency analysis, including temporal study. Inputs to the simulation are grid model, forecasted load, conventional generation profiles, and wind variability of proposed projects. A time-step simulation is run for the time horizon to produce benefit indices for every location (bus) in the system. The congested transmission elements that require expansion are identified and ranked as part of the simulation. Each wind project in the proposed portfolio can result in benefits or costs for grid security. Policy makers can then use the method to design policies that ensure preservation of long-term system security. Developers could use the tool to identify security effects and assess their wind portfolios. Measuring network security and determining benefits of large-scale wind projects is a complex planning task that involves several aspects: temporal wind variability, spatial distribution of flows, multiple load and generation profiles, and numerous possible contingencies. All these wind project development aspects must be isolated to identify and correctly assign security costs and benefits