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.     

The relative impacts of distributed and centralized generation of electricity on local air quality in the South Coast Air Basin of California

This paper examines the air quality impact of using distributed generation (DG) to satisfy future growth in power demand in the South Coast Air Basin of Los Angeles, relative to the impact when the demand is met by expanding current central generation (CG) capacity. The impact of decreasing boiler emissions by capturing the waste heat from DGs is not examined. The air quality impacts of these two alternate scenarios are quantified in terms of hourly maximum ground-level and annually averaged primary NO_x concentrations, which are estimated using AERMOD. This study focuses on the impact of primary emissions at source–receptor distances of tens of kilometers. We find that the shift to DGs has the potential for decreasing maximum hourly impacts of power generation in the vicinity of the DGs. The maximum hourly concentration is reduced from 25 to 6 ppb if DGs rather than CGs are used to generate power. However, the annually averaged concentrations are likely to be higher than for the scenario in which existing CGs are used to satisfy power demand growth. Future DG penetration will add an annual average of 0.1 ppb to the current basin average, 20 ppb, while expanding existing CGs will add 0.05 ppb.     

Large-scale integration of renewable and distributed generation of electricity in Spain: Current situation and future needs

Similar to other European countries, mechanisms for the promotion of electricity generation from renewable energy sources (RESs) and combined heat and power (CHP) production have caused a significant growth in distributed generation (DG) in Spain. Low DG/RES penetration levels do not have a major impact on electricity systems. However, several problems arise as DG shares increase. Smarter distribution grids are deemed necessary to facilitate DG/RES integration. This involves modifying the way distribution networks are currently planned and operated. Furthermore, DG and demand should also adopt a more active role. This paper reviews the current situation of DG/RES in Spain including penetration rates, support payments for DG/RES, level of market integration, economic regulation of Distribution System Operators (DSOs), smart metering implementation, grid operation and planning, and incentives for DSO innovation. This paper identifies several improvements that could be made to the treatment of DG/RES. Key aspects of an efficient DG/RES integration are identified and several regulatory changes specific to the Spanish situation are recommended.     

Economic and environmental impacts from the implementation of an intelligent demand side management system at the European level

This paper presents the results of an analysis on the economic and environmental impacts of the application of an intelligent demand side management system, called the Energy Consumption Management System (ECMS), in the European countries. The ECMS can be applied for the control of individual, widely distributed electric loads, using the power distribution network as the command communication channel. The system can be applied in public lighting, in the tertiary and residential sectors, as well as in the industry. A top-down analysis investigates the possible penetration levels in each application area. The long-term impacts following the application of system are evaluated using the LEAP2006 platform. The WASP IV model is also used for the optimization of the power generation expansion and the corresponding calibration of LEAP2006. Several operational strategies combining variable market penetration of the ECMS and expected energy savings are examined. Results show that, under a logical market penetration, a reduction of 1–4% in primary energy, of 1.5–5% in CO₂ emissions and a 2–8% saving in investment costs for power generation expansion is to be expected for the EU-15. The results also justify that innovative devices may be attractive to end users and also help in the implementation of global energy-saving policies.     

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.     

Effective active power control of a high penetration wind diesel system with a Ni–Cd battery energy storage

High penetration (HP) Wind Diesel Hybrid Systems (WDHS) have three modes of operation: Diesel Only (DO), Wind Diesel (WD) and Wind Only (WO). The HP-WDHS presented in this article consists of a Wind Turbine Generator (WTG), a Diesel Generator (DG), the consumer Load, a Ni–Cd Battery based Energy Storage System (BESS), a discrete Dump Load (DL) and a Distributed Control System (DCS). The DG includes a friction clutch which allows the Diesel Engine (DE) to be engaged (DO and WD modes)/disengaged (WO mode) to the Synchronous Machine (SM). The DCS consists of a sensor node which measures the SM speed and active power, calculates the reference active power P_REF necessary to balance the active power in the WDHS and communicates this P_REF value through a message to the BESS and DL actuator nodes. In the WD mode both the DG and WTG supply active power to the system and the DE speed governor regulates the system frequency. However in an HP-WDHS the power produced by the WTG (P_T) can be greater than the one consumed by the load (P_L). This situation means a negative power in the DG (power inversion) with its speed governor unable to regulate frequency. To avoid this situation, the DCS must order coordinated power consumption to the BESS and DL in order to keep the DG produced power positive. In this article it is shown by simulation how the DCS manages both a temporary power inversion and a permanent one with the mandatory transition from WD to WO mode. The presented graphs for frequency, voltage, active powers of the system elements and battery voltage/current show the effectiveness of the designed control.     

Power generation of microbial fuel cells (MFCs) with low cathodic platinum loading

This study aims at investigating the effects of platinum (Pt) loadings on the cathodic reactions in Single Chamber Microbial Fuel Cells (SCMFCs) and developing cost-effective MFC operational protocols. The power generation of SCMFCs was examined with different Pt loadings (0.005–1 mgPt/cm²) on cathodes. The results showed that the power generation of the SCMFCs with 0.5–1 mgPt/cm² were the highest in the tests, decreased 10–15% at 0.01–0.25 mgPt/cm², and decreased further 10–15% at 0.005 mgPt/cm². The SCMFCs with Pt-free cathode (graphite) had the lowest power generation. In addition, the power generation of SCMFCs with different Pt loadings were compared in raw wastewater (Chemical oxygen demand (COD): 0.36 g/L) and wastewater enriched with sodium acetate (COD: 2.95 g/L). The solution conductivity in SCMFCs decreased with the degradation of organic substrates. Daily polarization curves (V–I) showed a decrease in current generation and an increase in ohmic losses over the operational period (8 days). The SCMFCs (with 0.5–1 mgPt/cm² at cathode) fed with wastewater and sodium acetate (NaOAc) reached the highest power generation (786 mW/m²), while the SCMFCs (with 0.5–1 mgPt/cm² at cathode) fed only with wastewater obtained the lower power generation (81 mW/m²). The study demonstrated that lowering the Pt loadings in two magnitude orders (1 to 0.01, 0.5 to 0.005 mgPt/cm²) only reduced the power generation of 15–30%, and this reduction of the power generation become less substantial with the decrease in the solution conductivity of SCMFCs.     

The perspectives of energy production from coal‐fired power plants in an enlarged EU

The aim of this paper is to present the current status of the coal‐fired power sector in an enlarged EU (EU‐15 plus EU member candidate states) in relation with the main topics of the European Strategy for the energy production and supply. It is estimated that 731 thermoelectric units, larger than 100 MW_e, are operating nowadays, and their total installed capacity equals to 200.7 GW_e. Coal contribution to the total electricity generation with reference to other fuel sources, is by far more intensive in the non‐EU part (EU member candidate states), compared to the EU member states. It is expected that even after the enlargement, the European Union will strongly being related to coal. Enlargement will bring additional factors into play in order to meet the requirements of rising consumption, growing demand for conventional fuels and increasing dependence on imports. Besides the technology, boiler size, efficiency, age and environmental performance will determine the necessities of the coal‐fired power sector in each country. Depending on the case, lifetime extension measures in operating coal‐fired power plants or clean coal technologies can play an important role towards the energy sector restructuring. Low efficiency values in the non‐EU coal‐fired units and heavily aged power plants in EU countries will certainly affect decisions in favour of upgrading or reconstruction. The overall increase of efficiency, the reduction of harmful emissions from generating processes and the co‐combustion of coal with biomass and wastes for generating purposes indicate that coal can be cleaner and more efficient. Additionally, plenty of rehabilitation projects based on CCT applications, have already been carried out or are under progress in the EU energy sector. The proclamations of the countries' energy policies in the coming decades, includes integrated renovation concepts of the coal‐fired power sector. Further to the natural gas penetration in the electricity generation and CO₂ sequestration and underground storage, the implementation of CCT projects will strongly contribute to the reduction of CO₂ emissions in the European Union, according to the targets set in the Kyoto protocol. In consequence, clean coal technologies can open up new markets not only in the EU member candidate states, but also in other parts of the world. Copyright © 2004 John Wiley & Sons, Ltd.     

The European power plant infrastructure—Presentation of the Chalmers energy infrastructure database with applications

This paper presents a newly established database of the European power plant infrastructure (power plants, fuel infrastructure, fuel resources and CO₂ storage options) for the EU25 member states (MS) and applies the database in a general discussion of the European power plant and natural gas infrastructure as well as in a simple simulation analysis of British and German power generation up to the year 2050 with respect to phase-out of existing generation capacity, fuel mix and fuel dependency. The results are discussed with respect to age structure of the current production plants, CO₂ emissions, natural gas dependency and CO₂ capture and storage (CCS) under stringent CO₂ emission constraints.     

Evaluation on the electro-electrodialysis stacks for hydrogen iodide concentrating in iodine–sulphur cycle

In thermochemical water-splitting iodine–sulfur cycle, concentrating hydrogen iodine in the HI–H₂O–I₂ solution is crucial for the efficient hydrogen production. Electro-electrodialysis (EED) is a very promising HI concentrating method. In this paper, EED experiments were carried out using stacked cells, aiming at the scale up of EED equipment. Compared with the single-unit EED cell, the multi-cell EED stacks could concentrate HI in catholyte much more rapidly. During the EED process, the cell voltages increased gradually with the expansion of the concentration difference between catholyte and anolyte. For the stacks with more EED cells, the voltage increased much more steeply. High operating temperature ensured EED process carried out under low cell voltages and avoided voltage swelling. The apparent transport number (t₊) of all the experiments were very close to 1, while the ratio of permeated quantities of water to H⁺ (β) changed in a range of 1.79–3.05, influenced by temperature, I₂ content and current density.     

Grid integrated renewable DG systems: A review of power quality challenges and state-of-the-art mitigation techniques

Increased energy demands due to rapid industrialization, environmental concerns with fossil fuel–based generation, diminishing fossil energy resources, transmission network congestion, and technical performance deterioration are the motivations behind the integration of small renewable distributed generation (DG) units and turning the existing power systems into a restructured one. Optimizing the technical benefits offered by DG placement is a well-known challenge for distribution network operators (DNOs) for both fossil and renewable energy resource–based DGs, but renewable DG systems have several power quality (PQ) challenges associated additionally. Power quality is a very significant characteristic of renewable DG systems because today's loads are more sensitive to PQ disturbances and penetration of renewable energy as well as nonlinear loads is proliferating in distribution power networks. So the need for innovative power quality improvement (PQI) techniques becomes inevitable due to ongoing reformation in traditional distribution networks by the integration of renewable energy. This article presents a comprehensive analysis of power quality challenges with grid integration of renewable DG systems and current research status of associated mitigation techniques. Firstly, this paper puts emphasis on theoretically illustrating all the crucial power quality challenges associated with grid integration of renewable energy, and secondly, a thorough survey, of all PQI techniques introduced till date, is elaborated along with highlighting the opportunities for future research. Furthermore, all the crucial power quality issues, the impact of high penetration of renewable energy and mitigation techniques on power quality, are demonstrated also by simulating a grid integrated PV-based DG system in MATLAB/Simulink. This article is believed to be very beneficial for academics as well as industry professionals to understand existing PQ challenges, PQI techniques, and future research directions for renewable energy technologies.     

Reactive power control strategy for a wind farm with DFIG

Reactive power control strategy for a wind farm with a doubly fed induction generator (DFIG) is investigated. Under stator flux-oriented (SFO) vector control, the real power of the DFIG is controlled by the q-axis rotor current I_qr and the reactive power is mainly affected by the d-axis rotor current I_dr. To examine the effect of I_dr on stator reactive power Q_s and rotor reactive power Q_r, the DFIG is operated under five different operating modes, i.e, the maximum Q_s absorption mode, the rotor unity power factor mode, the minimum DFIG loss mode, the stator unity power factor mode, and the maximum Q_s generation mode. In pervious works, stator resistance R_s was usually neglected in deriving the d-axis rotor currents I_dr for different DFIG reactive power operating modes. In the present work, an iterative algorithm is presented to compute the d-axis rotor currents I_dr for the five reactive power control modes. To demonstrate the effectiveness of the proposed iterative algorithm, the rotor current, rotor voltage, stator current, real power and reactive power of a 2.5 MW DFIG operated under the five different operating modes are computed.     

Rents in the European power sector due to carbon trading

The European Union Emissions Trading Scheme (EU ETS) has imposed a price on the allowances for CO₂ emissions of electricity companies. Integrating this allowance price into the price of electricity earns a rent for companies who have received these allowances for free. During Phase I, 2005–2007, rents corresponding to the aggregate value of allocated allowances amounted to roughly € 13 billion per year. However, due to the specific price-setting mechanism in electricity markets true rents were considerably higher. This is due to the fact that companies also that have not received any allowances gain additional infra-marginal rents to the extent that their variable costs are below the new market price after inclusion of the allowance price. Producers with low carbon emissions and low marginal costs thus also benefit substantially from carbon pricing. This paper develops a methodology to determine the specific interaction of the imposition of such a CO₂ constraint and the price-setting mechanism in the electricity sector under the assumption of marginal cost pricing in a liberalized European electricity market. The article thus provides an empirical estimate of the true total rents of power producers during Phase I of the EU-ETS (2005–2007). The EU ETS generated in Phase I additional rents in excess of € 19 billion per year for electricity producers. These transfers are distributed very unevenly between different electricity producers. In a second step, the paper assesses the impact of switching from free allocation to an auctioning of allowances in 2013. We show that such a switch to auctioning will continue to create additional infra-marginal rents for certain producers and will leave the electricity sector as a whole better off than before the introduction of the EU ETS.     

分布式发电对配电网继电保护的影响

分布式发电是一种新兴的高效、环保的发电技术,近年来获得飞速发展。然而,大量分布式发电系统的接入改变了配电网的故障电流大小和分布以及原有继电保护装置的基础条件,对配电网的继电保护造成影响。分析了分布式发电接入对馈线的两段式保护和自动重合闸以及分支线的熔断器保护产生的各种可能影响,对分布式发电的广泛推广具有一定的意义。     

HIx concentration by electro-electrodialysis using stacked cells for thermochemical water-splitting IS process

In the thermochemical water-splitting iodine–sulfur process for hydrogen production, efficient concentration/separation of HI from HIx solution, a mixture of HI–H₂O–I₂, is very important. In this paper, an experimental study on concentrating HI in HIx using stacked electro-electrodialysis (EED) cells was carried out under the conditions of 1atm, 80 °C and the current density of 0.10 A/cm². The performance of EED stacks including 1, 2 and 4 EED units was evaluated. The results showed that multi-unit EED cells could concentrate HI in catholyte much faster than single-unit cells. The apparent transport number (t₊) of all the experiments were very close to 1, while the ratio of permeated quantities of water to H⁺ (β) changed in a relatively larger range of 1.98–2.89. Although the current efficiency will degrade faster when using a multi-unit stack than a single-unit cell at the late stage of EED process, at high iodine content multi-unit stack could maintain quite high current efficiency.     

Contribution of Nafion loading to the activity of catalysts and the performance of PEMFC

Different amounts of Nafion loadings (in the range of 0–2.0 mg cm⁻²) were added to a catalyst containing 0.5 mg cm⁻² of Pt; these were prepared by spraying a Nafion solution on an electrode surface. The effect of Nafion loading on the activity of the catalyst and the performance of a proton exchange membrane fuel cell (PEMFC) was investigated by using electrochemical methods such as direct current polarization (using an I–V curve), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear scan voltammetry (LSV). The results of the I–V and EIS were compared in order to resolve the ohmic resistance (R_Ω, calculated from the I–V curve) into interfacial and internal resistances (R_if and R_s, simulated from the EIS). The analysis of the electrochemical data revealed that the interfacial resistance (R_if) is closely related to the reactive region of three-phase zones (interfaces among the reactants, electrolyte and catalyst), and it provides a major parameter for diagnosing the activity of the catalysts and the performance of the PEMFC.     

The future developments of the electricity prices in view of the implementation of the Paris Agreements: Will the current trends prevail,or a reversal is ahead?

We assess the impact on the European electricity market of the European Union “Clean energy for all Europeans” package, which implements the EU Nationally Determined Contribution in Paris COP 21. We focus on the year 2030, which is the year with defined climate targets. For the assessment, we employ a game-theoretic framework of the wholesale electricity market, with high technical detail. The model is applied to two core scenarios, a Base scenario and a Low Carbon scenario to provide insights regarding the future electricity capacity, generation mix, cross-border trade and electricity prices. We also assess three additional variants of the core scenarios concerning different levels of: a) fossil and CO₂ prices; b) additional flexibility provided by batteries; c) market integration. We find that the electricity prices in 2030 substantially increase from today's level, driven by the increase in fuel and CO₂ prices. The flexibility from batteries helps in mitigating the price peaks and the price volatility. The increased low marginal cost electricity generation, the expansion of non-dispatchable and distributed capacities, and the higher market integration further reduce the market power from producers in the electricity markets from today's level.     

A multi-objective control strategy for grid connection of DG (distributed generation) resources

This paper presents a flexible control technique for connection of DG (distributed generation) resources to distribution networks, especially during ride-through on faulty grid. This strategy is derived from the abc/αβ and αβ/dq transformations of the ac system variables. The active and reactive currents injected by the DG source are controlled in the synchronously rotating orthogonal dq reference frame. The transformed variables are used to control the VSI (voltage source inverter) which connects the DG to the distribution network. Using a P.L.L. (phase locked loop) in circuit of proposed control technique, the angle of positive sequence has been detected, in order to synchronize the currents to the distribution network. The proposed control technique has the capability of providing active and reactive powers and harmonic currents to nonlinear loads with a fast dynamic response. Simulation results and mathematical analysis have been completed in order to achieve a reduced THD (total harmonic distortion), increased power factor and compensated load’s active and reactive powers. The analyses show the high performance of this control strategy in DG applications in comparison with other existing strategies.     

Cycle life improvement of alkaline batteries via optimization of pulse current deposition of manganese dioxide under low bath temperatures

Pulse current electrodeposition (PCD) method has been applied to the preparation of novel electrolytic manganese dioxide (EMD) in order to enhance the cycle life of rechargeable alkaline MnO₂–Zn batteries (RAM). The investigation was carried out under atmospheric pressure through a systematic variation of pulse current parameters using additive free sulfuric acid–MnSO₄ electrolyte solutions. On time (t_on) was varied from 0.1 to 98.5 ms, off time (t_off) from 0.25 to 19.5 ms, pulse frequencies (f) from 10 to 1000 Hz and duty cycles (θ) from 0.02 to 0.985. A constant pulse current density (I_p) of 0.8 A dm⁻² and average current densities (I_a) in the range of 0.08–0.8 A dm⁻² were applied in all experiments. Resultant materials were characterized by analyzing their chemical compositions, X-ray diffractions (XRD) and scanning electron microscopy (SEM). Electrochemical characterizations carried out by charge/discharge cycling of samples in laboratory designed RAM batteries and cyclic voltammetric experiments (CV). It has been proved that specific selection of duty cycle, in the order of 0.25, and a pulse frequency of 500 Hz, results in the production of pulse deposited samples (pcMDs) with more uniform distribution of particles and more compact structure than those obtained by direct current techniques (dcMDs). Results of the test batteries demonstrated that, in spite of reduction of bath temperature in the order of 40 °C, the cycle life of batteries made of pcMDs (bath temperature: 60 °C) was rather higher than those made of conventional dcMDs (boiling electrolyte solution). Under the same conditions of EMD synthesis temperature of 80 °C and battery testing, the maximum obtainable cycle life of optimized pcMD was nearly 230 cycles with approximately 30 mAh g⁻¹ MnO₂, compared to that of dcMD, which did not exceed 20 cycles. In accordance to these results, CV has confirmed that the pulse duty cycle is the most influential parameter on the cycle life than the pulse frequency. Because of operating at lower bath temperatures, the presented synthetic mode could improve its competitiveness in economical aspects.     

Diffusion coefficient of hydrogen in the Pd3Mn compound as deduced from absorption measurements at high temperature

The hydrogen absorption rate has been investigated by the gas–solid reaction method in the disordered and ordered (L1₂) Pd₃Mn compound. With the disordered material the measurements were carried out from 825 K up to 1038 K, with the ordered one from 485 K to 666 K. The H absorption data, analyzed according to the second Fick's equation, provided the H chemical diffusion coefficient D_c which exhibited an exponential temperature dependence. In the disordered state D_c was higher than in the ordered one in agreement with previous lower temperature data from Gorsky relaxation. This finding could be accounted for in terms of the different kinds of jumps between adjacent interstitial (I) octahedral sites that H is able to make in the two different states of order. In the disordered state H diffusion takes place through sequences of I₆–I₆, I₆ ↔ I₅ and I₅–I₅ jumps (sub-index indicates the number of Pd atoms in the first atomic shell of an octahedral interstitial site), while in the state of order L1₂ the involved jumps are I₆ ↔ I₄ and I₄–I₄.