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In this paper, a combinational AC/DC power flow approach is proposed for the solution of the combined AC/DC network. The unified power flow approach is extended to include DC voltage droop control. In the VSC based MTDC grids, DC droop control is regarded as more advantageous in terms of operational flexibility, as more than one VSC station controls the DC link voltage of the MTDC system. This model enables the study of the effects of DC droop control on the power flows of the combined AC/DC system for steady state studies after VSC station outages or transient conditions without needing to use its complete dynamic model. Further, the proposed approach can be extended to include multiple AC and DC grids for combined AC/DC power flow analysis. The algorithm is implemented by modifying the MATPOWER based MATACDC program and the results shows that the algorithm works efficiently.

This paper investigates the operating regimes of CCS power plants in future generation portfolios with large amounts of variable- output wind generation. An advanced electricity system dispatch model is developed and coupled with a Monte Carlo based energy storage optimization model to simulate the least-cost dispatch of an assumed thermal-energy storage generation portfolio with CCS. A historic high-resolution wind speed reanalysis dataset is employed and the proposed locations of future wind farms are used to produce plausible and internally consistent wind capacity deployment scenarios. The fundamental and structural changes that occur to CCS operating profiles and start-up/shut-down schedules are investigated for increasing levels of wind capacity, which creates seasonal and diurnal variations and potential flexibility implications. Non-linear interactions between flexible CCS power plants and other energy vectors are demonstrated for an illustrative case study example in Great Britain. This temporally explicit analysis of the short-term scheduling decisions of thermal plants with CCS highlights the asymmetric displacement of mid-merit thermal plants and the importance of using time-dependent start-up costs in wind-based unit commitment studies.

The total supply capability (TSC) is an important index for assessing the reliability of a distribution power system. In this paper, two models to evaluate the TSC are established. In the first, the TSC is acquired with the conditions that all load outages can be restored via network reconfiguration with transformers' N-1 contingencies, i.e., that all constraints related to branch thermal ratings and bus-voltage limits can be satisfied following restoration for each N-1 contingency. The second model, which is revision of the first, considers the daily load curves for different classes of customers, e.g., residential, commercial and industrial. Both models can be formulated as mixed integer problems with second-order cone programming (MISOCP), which can be solved using commercially available optimization software. Two test systems are used to demonstrate the applicability of the presented models. Numerical results show that the presented model is more accurate than the previously published models. This proposed analytical approach can be applied in a range of network planning studies, e.g., for selecting appropriate ratings of transformers, or for optimal locating of circuit breakers and distributed energy resources.

Marine energy has a significant role to play in lowering carbon emissions within the energy sector. Paradoxically, it may be susceptible to changes in climate that will result from rising carbon emissions. Wind patterns are expected to change and this will alter wave regimes. Despite a lack of definite proof of a link to global warming, wind and wave conditions have been changing over the past few decades. Changes in the wind and wave climate will affect offshore wind and wave energy conversion: where the resource is constrained, production and economic performance may suffer; alternatively, stormier climates may create survival issues. Here, a relatively simple sensitivity study is used to quantify how changes in mean wind speed—as a proxy for wider climate change—influence wind and wave energy production and economics.

The aim of this paper is to present a new method for the allocation of new generation capacity, which takes into account fault level constraints imposed by protection equipment such as switchgear. It simulates new generation capacities and connections to other networks using generators with quadratic cost functions. The coefficients of the cost functions express allocation preferences over connection points. The relation between capacity and subtransient reactance of generators is used during the estimation of fault currents. An iterative process allocates new capacity using optimal power flow mechanisms and readjusts capacity to bring fault currents within the specifications of switchgear. The method was tested on a 12-bus LV meshed network with three connection points for new capacity and one connection to an HV network. It resulted in significantly higher new generation capacity than existing first-come-first-served policies.

Limiting the emissions of greenhouse gases from power generation will depend, among other things, on the continuing and increased use of hydroelectric power. However, climate change itself may alter rainfall patterns, adversely affecting the financial viability of existing and potential hydro schemes. Previous work developed a methodology for quantifying the potential impact of climate change on the economics of hydropower schemes. Here, the analysis is extended to examine the potential for changes in project risk. A case study is presented that indicates that the applied climate change scenarios alter not only the mean financial performance of the scheme but also the financial risk facing it. Given that investors must balance project risk and reward, this finding has implications for the future provision of hydropower.

Grid connected electrical energy storage could enable large numbers of intermittent renewable generators to be deployed in the UK. Many studies investigate the revenue which could be achieved through arbitrage assuming perfect foresight of electricity prices. In practice, storage operators will not have perfect foresight and will have to devise operational strategies using price forecasts. This paper investigates the impact of forecast accuracy on the optimality of storage revenue. The optimal revenue available is determined using linear programming and historic electricity prices. The results are compared to those found using dynamic programming and electricity price forecasts with increasing percentage error. A small scale lithium ion battery and a large pumped hydro energy storage (PHES) device are compared. The results show that revenue reduces at an increasing rate with increasing forecast error. The PHES device is more sensitive to forecast accuracy than the lithium ion battery. For both technologies, with a maximum error of 30%, 80% of the optimal revenue can be achieved. With increased capacity and significantly increased power rating, the lithium ion battery becomes more sensitive to price forecast accuracy.

The paper presents a detailed study of the potential impact on the cost and greenhouse gas emissions (GHG) through low voltage (LV) residential demand-side management (DSM). The proposed optimisation algorithm is used to shift non-critical residential loads, with the wet load category used as a case study, in order to minimise the total daily cost and emissions of GHG due to generation. This study shows that it is possible to reshape the total power demand and reduce the cost and emissions of demand to some extent. It is also shown that further optimisation of the cost leads to an increase in GHG emissions because of their conflicting nature.

This paper presents a secondary control for MTDC systems to update the DC voltage and converter power references of the VSC stations operating under droop control, in order to eliminate the large power deviation from their desired reference power. The rated values of the VSC station used as reference does not take into account the power losses in the converter, DC line and the voltage drops in the DC transmission lines. This creates a constant difference between rated DC voltage reference and actual DC voltage value of the VSC station. This difference is multiplied by the droop gain of the VSC station, hence causing power deviations in the MTDC grid system. In this paper a secondary control is implemented for a four-terminal HVDC system modelled in EMTDC/PSCAD, to demonstrate the reduction in power deviation by the proposed secondary control.

Tidal energy has the potential to play a key role in meeting renewable energy targets set out by the United Kingdom (UK) government and devolved administrations. Attention has been drawn to this resource as a number of locations with high tidal current velocity have recently been leased by the Crown Estate for commercial development. Although tides are periodic and predictable, there are times when the current velocity is too low for any power generation. However, it has been proposed that a portfolio of diverse sites located around the UK will deliver a firm aggregate output due to the relative phasing of the tidal signal around the coast. This paper analyses whether firm tidal power is feasible with 'first generation' tidal current generators suitable for relatively shallow water, high velocity sites. This is achieved through development of realistic scenarios of tidal current energy industry development. These scenarios incorporate constraints relating to assessment of the economically harvestable resource, tidal technology potential and the practical limits to energy extraction dictated by environmental response and spatial availability of resource. The final scenario is capable of generating 17 TWh/year with an effective installed capacity of 7.8 GW, at an average capacity factor of 29.9% from 7 major locations. However, it is concluded that there is insufficient diversity between sites suitable for first generation tidal current energy schemes for a portfolio approach to deliver firm power generation. (C) 2012 Elsevier Ltd. All rights reserved.

It is difficult to estimate how much distributed generation (DG) capacity will be connected to distribution systems in the coming years; however, it is certain that increasing penetration levels require robust tools that help assess the capabilities and requirements of the networks in order to produce the best planning and control strategies. The work of this Task Force is focused on the numerous strategies and methods that have been developed in recent years to address DG integration and planning. This paper contains a critical review of the work in this field. Although there have been numerous publications in this area, widespread implementation of the methods has not taken place. The barriers to implementation of the advanced techniques are outlined, highlighting why network operators have been slow to pick up on the research to date. Furthermore, key challenges ahead which remain to be tackled are also described, many of which have come into clear focus with the current drive towards smarter distribution networks. Science Foundation Ireland Deposited by bulk import

Increasing penetration of distributed generation in distribution networks requires active constraint management to provide greater flexibility and use ofexisting network assets. Curtailing DG output under worse case scenarios to keep the network operating below voltage and thermal limits will play a major role in active network management. While a number of curtailment priority schemes are established there is a need to demonstrate the benefit of different priority schemes for curtailing multiple DGs. Comparing with ‘first in last out’ and other priority methods, this paper proposes and demonstrates that optimalsetting of DG curtailment priority using multi-period OPF is not just technically appropriate but also economically beneficial. By extending this idea into the planning arena, the impact of curtailment management schemes on networkhosting capacity is evaluated.

To be able to integrate significant levels of dispersed renewable energy generation (DG) into rural distribution networks, the conventional ‘fit-and-forget’ approach will have to be evolved into a ‘connect-and-actively-manage’system using Active Network Management techniques. Coordinated scheduling and control of DG and network assets can avoid having to constrain renewable capacity and significantly increase energy production and economicperformance of DG in weak or congested networks. This paper proposes a time-dependent receding-horizon OPF technique for the ‘pseudo-real time’ scheduling of network control set-points to better integrate DG into previouslypassive areas of distribution networks. The methodology demonstrates the potential for real time reconfigurable autonomous network control over windows of previously problematic network power flows. Modelling of the real time controller application is performed through a purpose built pseudo-real time distribution network simulator.

Harmonic emissions from converter-interfaced distributed generation connection can potentially lead to voltage distortion levels that are above applicable standards. The risk increases as greater connection volumes are facilitated by Active Network Management schemes. By incorporating harmonic limits into assessment of the hosting capacity of active networks, this paper demonstrates that by incorporating harmonic levels at the planning stage can prevent inadvertent restrictions on the integration of renewables. Other aspects considered include: the impact of active network controls on harmonic propagation and hosting capacity and the role of active harmonic mitigation methods.

The capacity of distributed generation (DG) connected in distribution networks is increasing as part of the drive to connect renewable energy sources. Due to widespread application of power electronic inverter interfaces, DG can inject harmonic current through the point of common connection into the upstream network. Harmonic current emission may cause voltage distortion problems when harmonic resonance exists in the network. Harmonic distortion is one area of concern for electric utilities in determining whether DG could be connected, although there are differences in utility practices in applying limits. To explore the impact of harmonic regulations on the ability of distribution networks to host DG, this work incorporates harmonic voltage constraints into an established optimal power flow (OPF) planning method. The case study shows that harmonic distortion limits have substantial impacts on the allowable penetration of DG. Furthermore, the complex interconnectivity between DG locations means that voltage, thermal and harmonic constraints have a large influence on the location preference for DG capacity.

The Pelamis wave energy converter is emerging as one of the most promising devices to harness the available power in the waves. This study examines the environmental impacts of the device, presenting the results as a set of impact potentials, and demonstrating that it performs well in comparison to other renewable energy converters and fossil-fuelled generators. (6 pages)

This paper describes a pseudo-real time distribution network simulator developed to investigate the use of real time distribution system control presets to better integrate high levels of distributed energy resources into active distribution networks. A combination of historical and modelled generation profiles, along with varying demand patterns, are used to demonstrate the real time application and improved system response from active network management control strategies. (4 pages)

The connection of renewable distributed generation (DG) is expected to increase significantly in the UK. A large volume of this capacity will continue to connect to rural areas where voltage and thermal constraints are the main issues. It is in this context that Distribution Network Operators (DNOs) need to provide cost-effective connection arrangements, avoiding expensive reinforcements, and looking at innovative ways of actively managing the network. Herein, a decentralized, local control of (renewable) DG is proposed to manage voltage and thermal constraints by regulating the DG reactive power capacity and applying generation curtailment. Given that DG developers will require the highest possible returns of energy exports and DNOs might tolerate short-term, low-impact voltage and thermal breaches, the settings of the actual control mechanism (e.g., thresholds, target values and holding time) require special attention. Consequently, this work focuses on fine tuning of the corresponding control settings of the decentralized control scheme to assess technical and economic trade-offs. A concept based on operational windows (related to time and severity) to capture the constraint situations is introduced. Results using a radial test feeder will be presented in highlighting the performance of different tuned settings.

Renewable distributed generation (DG), primarily wind power, will represent the lion’s share of the new generation capacity that will be connected to distribution systems. However, while both firm and variable generation present our traditionally passive distribution networks with well-established technical challenges, the requirements and practices related to the power factor operation of these generation plants might lead to undesirable effects at the transmission level with the reactive power support needed by high penetrations of DG capacity potentially impacting on weak areas of the transmission grid. In this work, this problem is formulated as the minimization of the reactive support for DG and is investigated using two different operational perspectives: adopting passive but enhanced power factor and substation settings, and implementing Smart Grid control schemes. These two approaches are modeled using a tailored multi-period AC optimal power flow technique that caters for the variability of demand and generation, and considers N-1 contingencies. The results demonstrate that the enhanced passive approach is able to achieve a performance almost as good as Smart Grid control without the need for any additional investment.

Background Surgical site infection (SSI) is a common complication following abdominal surgery. It is associated with considerable morbidity and mortality, and its management results in significant cost to health services within both primary and secondary care. Some surgeons believe that the use of a wound-edge protection device may reduce the incidence of SSI. Whilst there is some encouraging evidence showing that such devices may lead to a reduction in SSI, there are no controlled trials of sufficient size or quality to support their routine use. Methods/Design 750 patients will be recruited from around 20 surgical units within the United Kingdom. Patients undergoing laparotomy through any major abdominal incision for any indication, elective or emergency, are eligible. Patients under the age of 18, those undergoing a laparoscopic assisted procedure or who have undergone laparotomy within the previous 3 months, and those who are unable to give informed consent will be excluded. Patients will be randomised (1:1 ratio) to the use of a wound-edge protection device or no wound-edge protection device during surgery. Follow up will consist of blinded clinical wound reviews at 5-7 days and 30-33 days postoperatively with a self-completed questionnaire covering the intervening period. Quality of life questionnaires will be completed prior to surgery and at the subsequent wound review points and information on resource usage will also be captured. The primary outcome measure is SSI within 30 days of surgery. Secondary outcomes include the impact of the degree of wound contamination, patient comorbidity, and operative characteristics on the efficacy of a wound-edge protection device in reducing SSI and whether the use of a wound-edge protection device has an effect on health-related quality of life or length of hospital stay and is cost-effective. Discussion Rossini is the first multicentre observer-blinded randomised controlled trial of sufficient size and quality to establish whether the use of a wound-edge protection device in adult patients undergoing abdominal surgery leads to a lower rate of SSI. The results of this study will be used to inform current surgical practice and may potentially benefit patients undergoing surgery in the future. Trial registration number Current Controlled Trials ISRCTN: ISRCTN40402832

Efficient power generators have been of increasing interest recently due to growing environmental concerns. Micro Combined Heat and Power (micro-CHP) generators combine the benefits of the high-efficiency cogeneration technology and microgeneration, that is being promoted as a means of lowering greenhouse gas emissions by decentralizing the power network. Additionally, Life Cycle Assessment of energy systems is becoming a substantial part of decision making in the energy industry, helping manufacturers promote their low carbon devices, and consumers choose the most environmentally friendly options. This report summarizes a study on life-cycle energy and carbon auditing of a typical wall-hung gas-powered domestic micro-CHP device that is commercially available across Europe. Combining a very efficient condensing boiler to a Stirling engine,the device can deliver enough heat to cover the needs of a typical household (up to 24kW) while generating power (up to 6kW) that can be used locally or sold to the grid. Assuming an annual heat production of 20 MWh the study has calculated the total energy consumption and carbon emissions over an operational lifetime of 15 years at 1606 GJ and 90 tonnes of CO2 respectively.Assuming that such a micro CHP device replaces the most efficient gas-powered condensing boiler for domestic heat production, and the power generated substitutes electricity from the grid, the potential energy and carbon savings are 4922 - 5118 MJ/year and 522 - 543 kg CO2/year respectively, implying apayback period of the embodied energy and carbon at 1.32 - 2.32 and 0.75 - 1.35 years respectively. Apart from the embodied energy and carbon and the respective savings, additional key outcomes of the study are the evaluationof the energy intensive phases of the device’s life cycle and the exploration of potential improvements.

An approach is proposed to solve multistage distribution network expansion planning problems considering future uncertainties, guiding the planner from production of expansion plans, evaluation of the plans under various future uncertain scenarios, to the selection of the best strategy. A new balanced genetic algorithm (BGA) is introduced that improves the intensification of the solution search procedure by trading-off diversification ability. This facilitates searching for the optimal solution, but also the efficient production of suboptimal solutions for the planner to take into consideration. The features of the BGA allow a multistage planning problem to be solved more efficiently; the BGA can consider a set of expansion plans in an early planning stage in a single run and produce planning strategies required to solve network problems in a later stage along the planning horizon. The overall performance of each plan under different uncertain scenarios is evaluated using a modified data envelopment analysis to assist decisions on which solution to adopt. The approach is applied to a multistage greenfield distribution network expansion problem considering scenarios for the location of future loads. The results clearly show the advantages of the approach over more conventional methods. © 2010 IEEE.

Distributed Generation (DG) is increasing in penetration on power systems across the world. In rural areas, voltage rise limits the permissible penetration levels of DG. Another increasingly important issue is the impact on transmission system voltages of DG reactive power demand. Here, a passive solution is proposed to reduce the impact on the transmission system voltages and overcome the distribution voltage rise barrier such that more DG can connect. The fixed power factors of the generators and the tap setting of the transmission transformer are determined by a linear programming formulation. The method is tested on a sample section of radial distribution network and on a model of the all island Irish transmission system illustrating that enhanced passive utilisation of voltage control resources can deliver many of the benefits of active management without any of the expense or perceived risk, while also satisfying the conflicting objectives of the transmission system operator. Science Foundation Ireland Other funder Charles Parsons Energy Research Awards EPSRC Supergen V, UK Energy Infrastructure (AMPerES) au, ti, pe, la, ke, sp, ab - kpw19/10/11

The problem of minimizing losses in distribution networks has traditionally been investigated using a single, deterministic demand level. This has proved to be effective since most approaches are generally able to also result in minimum overall energy losses. However, the increasing penetration of (firm and variable) distributed generation (DG) raises concerns on the actual benefits of loss minimization studies that are limited to a single demand/generation scenario. Here, a multiperiod AC optimal power flow (OPF) is used to determine the optimal accommodation of (renewable) DG in a way that minimizes the system energy losses. In addition, control schemes expected to be part of the future Smart Grid, such as coordinated voltage control and dispatchable DG power factor, are embedded in the OPF formulation to explore the extra loss reduction benefits that can be harnessed with such technologies. The trade-off between energy losses and more generation capacity is also investigated. The methodology is applied to a generic U.K. distribution network and results demonstrate the significant impact that considering time-varying characteristics has on the energy loss minimization problem and highlight the gains that the flexibility provided by innovative control strategies can have on both loss minimization and generation capacity. © 2010 IEEE.

The extent to which large volumes of offshore wind can contribute to a secure and reliable electricity supply is a subject of much debate. Key to providing credible answers requires a detailed understanding of the wind resource and its variability in time and space. Here, a mesoscale atmospheric model was employed to create a ten year hindcast of British onshore and offshore wind speeds. This was used to simulate the output of a British offshore wind fleet and combined with demand data to assess reliability during periods of high demand. Further, capacity value calculations using Effective Load Carrying Capability for the combined onshore and offshore GB wind fleet provides an estimate of the long-term reliability of production. (6 pages)

Voltage rise is a significant limitation when connecting large volumes of distributed generation (DG), particularly in rural distribution networks. One means of allowing further capacity penetration is to control voltage regulation devices such as on-load tap changers in a coordinated manner considering the variability of demand and generation. This approach, however, requires the deployment of communication systems, making it a potentially expensive option. To date, most DG technologies feature capabilities such as provision of reactive power or power factor control. Nonetheless, the “fit and forget” approach for the connection of DG units to distribution networks neglects a more active, decentralised management where those and other capabilities could be used without the need of further infrastructure. This work proposes a decentralised control scheme where wind power-based DG units have a dual operation mode (power factor control and voltage control) in order to maintain the voltage at the connection bus within limits. Generators are also able to curtail their power output as a last resort to regulate the local voltage. Time-series analyses demonstrate the effectiveness of the decentralised methodology in adequately integrating DG capacity.

Analysis of lower carbon power systems has tended to focus on the operational carbon dioxide (CO2) emissions from power stations. However, to achieve the large cuts required it is necessary to understand the whole-life contribution of all sectors of the electricity industry. Here, a preliminary assessment of the life cycle carbon emissions of the transmission network in Great Britain is presented. Using a 40-year period and assuming a static generation mix it shows that the carbon equivalent emissions (or global warming potential) of the transmission network are around 11 gCO(2-eq)/kWh of electricity transmitted and that almost 19 times more energy is transmitted by the network than is used in its construction and operation. Operational emissions account for 96% of this with transmission losses alone totalling 85% and sulphur hexafluoride (SF6) emissions featuring significantly. However, the CO2 embodied within the raw materials of the network infrastructure itself represents a modest 3%. Transmission investment decisions informed by whole-life cycle carbon assessments of network design could balance higher financial and carbon 'capital' costs of larger conductors with lower transmission losses and CO2 emissions over the network lifetime. This will, however, necessitate new regulatory approaches to properly incentivise transmission companies. (C) 2010 Elsevier Ltd. All rights reserved.

While it is difficult to estimate how much distributed generation (DG) capacity will be connected to distribution systems in the coming years, it is certain that increasing penetration levels require robust tools that help assess the capabilities and requirements of the networks in order to produce the best planning strategies. This work presents an overview of some of the uses to which a tailored AC Optimal Power Flow (OPF) can be applied to DG planning and optimisation. Its application to maximising connectable capacity and energy loss minimisation are presented and discussed. The incorporation of a wide range of network constraints, including fault levels, voltage step change and N-1 security are also outlined. The AC OPF technique is extended to a multi-period approach to cater for the variability of demand and renewable generation. Advanced smart grid-like control strategies are also incorporated into this planning tool in order to evaluate the potential benefits. Simple test feeders as well as generic UK distribution systems are adopted to demonstrate the methodology.

This paper presents three case studies of risk-based standards from Great Britain: the pre-liberalisation generation planning standard, the present method for setting operational reserve requirements, and the transmission network planning standard. These illustrate a number of key issues in developing planning and operational standards for wind, including: the benefits of risk-based standards in adapting to new circumstances; the importance of considering model assumptions carefully when interpreting risk calculations; the difficulty in calculating the cost of risk; and the need to account for uncertainty in system background. The transmission network planning standard is studied in particular detail, especially how the present combination of deterministic and probabilistic sections might evolve for use in a future power system with a very high renewable penetration.

This paper presents a novel method for determining the capacity of a network to accommodate new generation under network security constraints. The assessment is performed by maximizing the total generation capacity in an optimal power flow model; this is solved by gradually adding limited numbers of line outage contingencies, until a solution to the complete problem is obtained. The limit on the number of contingencies added is key to the method's efficiency, as it reduces the size of the optimization problems encountered. Moreover, varying this limit on contingencies added provides a simple and highly efficient means of searching for multiple local optima of the nonlinear optimization problem. The method has been tested on a modified version of the highly meshed IEEE Reliability Test System with N-1 security, where a significant reduction in the system's capacity for new generation is seen when security constraints are imposed. The method is generic and may be applied at any voltage level, for other security models and for other similarly structured problems such as the analysis of multiple resource availability scenarios. © 2009 IEEE.

Distribution networks are increasingly required to host medium to large volumes of distributed (renewable) generation capacity. To facilitate high penetration levels of these new network participants it is crucial to adopt new control strategies in which the distribution systems are operated actively. The wide deployment of schemes such as coordinated voltage control (CVC) or non-firm connections will depend on communication and control infrastructure that is likely to be part of future Smart Grid investments. This infrastructure scenario might also make viable the use of advanced real-time measurement devices required to dynamically assess overhead line ratings. Given the inherent correlation of wind power output, wind speeds and temperature, this work is aimed at demonstrating the benefits that the adoption of dynamic ratings might bring to allow the connection of more wind power capacity. A multi-period AC Optimal Power Flow (OPF)-based technique is used to evaluate the maximum capacity of new generation considering control strategies such as dynamic ratings and CVC. The method caters for the variability of demand, wind resource and temperature. Results from a simple test feeder demonstrate the significant generation capacity gains compared to the passive operation of the network.

With funding from the UK’s Royal Academy of Engineering, the University of Edinburgh has developed a set of three truly interdisciplinary group design exercises aimed at improving penultimate-year undergraduate students’ ability to work across disciplines and improve their preparation for transfer into industry. Three exercises on hydropower system design, potable water supply and a micro-system accelerometer are each designed and led by a Visiting Industrial Professor. The group design exercises are both challenging and popular with students and have achieved several very successful outcomes: experience of real system design; enhanced appreciation of other engineering disciplines; experience of team working where participants have different skills and expertise; demonstration of the links between design and economic viability and introduction to non-technical areas essential to fulfilling the UK Standard for Professional Engineering Competence.

Gas-fired power stations currently generate over a third of the electricity demand of the United Kingdom (UK) and will play an increasing role in the future. At the same time the UK is becoming increasingly reliant on external supplies for gas security. The levels of physical and economic interaction between the gas and electricity systems offer a new set of risks for energy security. This paper traces the development of the UK gas industry, its growing links with the electricity sector and sets out some of the important developments in Europe and within the UK that influence UK energy security.

The potential for distributed generation (DG) to act as an alternative distribution planning option is now well-recognised by academia and industry, and could play a significant role in electricity distribution utility operation and design. However, the unbundling requirements of European Directive 2003/54/EC, coupled with traditional network planning approaches adopted by European Distribution Network Operators (DNOs), appear to be hindering development of DG and its deployment for distribution network ancillary services. The incentives - or otherwise - that arise from alternative models of DG ownership by bundled and unbundled distribution utilities are examined here. The preference for the siting and sizing of DG installations by DNOs is simulated using a multi-year multi-period optimal power flow. Broadly based on the recent UK regulatory framework, the DG ownership issue and its potential to influence DG penetration are explored. © 2009 The Institution of Engineering and Technology.

High penetrations of wind power on distribution networks are causing voltage rise on many networks. This voltage rise is limiting the permissible penetration levels of wind. Numerous active control schemes have been proposed to solve this issue, but widespread adoption of active management by network operators has yet to occur. Here, the fixed power factors of the generators' and the tap setting of the transmission transformer are optimally determined such that the voltage rise barrier is overcome and more wind can connect. The impact on the transmission system is becoming increasingly important and is also taken account of in the method. The method is tested on a sample section of radial distribution network illustrating that the optimal selection of voltage control settings can deliver some of the benefits of active management without any of the expense or perceived risk.

In order for governments worldwide to achieve their renewable targets, large amounts of new capacity, mainly wind power, need to be connected to power systems. A significant share is expected to be deployed at distribution levels. This paper is aimed at assessing the maximum wind power capacity a distribution network is able to integrate based on a multi-period AC Optimal Power Flow technique tailored to cater for Active Network Management schemes such as coordinated voltage control, adaptive power factor control and energy curtailment. The methodology is applied to an Irish 38kV circuit, considering the time-varying characteristics of demand and multiple wind generation profiles based on the coincident hours of different loading levels and wind power outputs over a year.

Wind power is currently the fastest growing renewable technology and will play a significant role in constraining the extent of climate change. However, the very fact that its ‘fuel source’ is driven by the climate may leave it exposed as climate changes over the coming decades. In this preliminary assessment, the potential for changes in climate to affect the significant onshore wind resource in the United Kingdom (UK) is explored using the regional climate change scenarios published by the UK Climate Impacts Programme in 2002. The scenarios indicate seasonal changes in potential wind production with winter production generally increasing while summer decreases.

The capacity of distributed generation (DG) connected in distribution networks is increasing, largely as part of the drive to connect renewable energy sources. The voltage step change that occurs on the sudden disconnection of a distributed generator is one of the areas of concern for distribution network operators in determining whether DG can be connected, although there are differences in utility practice in applying limits. To explore how voltage step limits influence the amount of DG that can be connected within a distribution network, voltage step constraints have been incorporated within an established optimal power flow (OPF) based method for determining the capacity of the network to accommodate DG. The analysis shows that strict voltage step constraints have a more significant impact on ability of the network to accommodate DG than placing the same bound on voltage rise. Further, it demonstrates that progressively wider step change limits deliver a significant benefit in enabling greater amounts of DG to connect. © 2009 IEEE.

In the last decade, distributed generation, with its various technologies, has increased its presence in the energy mix presenting distribution networks with challenges in terms of evaluating the technical impacts that require a wide range of network operational effects to be qualified and quantified. The inherent time-varying behavior of demand and distributed generation (particularly when renewable sources are used), need to be taken into account since considering critical scenarios of loading and generation may mask the impacts. One means of dealing with such complexity is through the use of indices that indicate the benefit or otherwise of connections at a given location and for a given horizon. This paper presents a multiobjective performance index for distribution networks with time-varying distributed generation which consider a number of technical issues. The approach has been applied to a medium voltage distribution network considering hourly demand and wind speeds. Results show that this proposal has a better response to the natural behavior of loads and generation than solely considering a single operation scenario. © 2008 IEEE.

Worldwide interest in renewable energy combined with technology advances has increased the connection of intermittent distributed generation to distribution networks. To allow maximum penetration of such developments without compromising the normal operation of the network requires several technical issues to be assessed. In this context, active management of the network, i.e., the integration of assets and network participants through the real-time use of control and communication systems, will play a major role. This paper proposes a multi-period steady-state analysis for maximising the connection of intermittent distributed generation through an optimal power flow-based technique adapted for active network management. A medium voltage distribution network is analysed considering different loading levels and discretised wind power outputs over a year. Results are presented and discussed.

While independently conducted polls suggest significant public support for wind energy, there are often objections to particular wind farm developments from the local population which can result in planning permission being declined and a restriction in the ability to meet renewable energy and greenhouse gas reduction targets. The aim of the study was to determine whether the pre-construction opinions held by communities local to a wind farm change after an extended period following commissioning. Residents of St. Newlyn East, Cornwall, England, were asked to recall their opinions of Carland Cross wind farm in 1991 and 2006. Statistically significant changes in opinion were observed for attitudes regarding the wind farm's visual attractiveness and the importance of the energy security it provides. This study continues by exploring potential reasons for this in the context of recent literature on public attitudes towards renewable energy. The findings of this study support the proposals in the 2007 UK White Paper, Planning for a Sustainable Future, for community engagement early in the project process and for the requirement of infrastructure to be debated at the national level.

Many methods have been applied to examine the capacity of existing distribution networks to accept distributed generation (DG). One aspect missing from existing approaches is the capability to efficiently site and size a predefined number of DGs. Here, a hybrid method employing genetic algorithms and optimal power flow aims to overcome this shortcoming. It could be applied by distribution network operators to search a network for the best sites and capacities available to strategically connect a defined number of DGs among a large number of potential combinations. Some applications of the proposed methodology in the UK under current Ofgem financial incentives for DNOs confirmed its effectiveness in siting and sizing an assigned number of DG units.

The world's first commercial‐scale grid‐connected tidal current energy installation will feature the Seagen marine current turbine developed by Marine Current Turbines Ltd. With potential for the manufacture of significant numbers of such devices there is a need to assess their environmental impact and, in particular, their life cycle energy and carbon dioxide (CO2) performance. This paper presents an analysis of the life cycle energy use and CO2 emissions associated with the first generation of Seagen turbines. The detailed assessment covers the embodied energy and CO2 in the materials and manufacturing of components, device installation, and operation along with those for decommissioning. With relatively conservative assumptions, and despite the early stage of development, the study shows that at 214 kJ/kWh and 15 g CO2/kWh, the respective energy and carbon intensities are comparable with large wind turbines and very low relative to the 400 to 1000 g CO2/kWh typical of fossil‐fuelled generation. The energy payback period is approximately 14 months and the CO2 payback is around 8 months. The embodied energy and carbon show limited sensitivity to assumptions with environmental performance remains excellent even under the most adverse scenarios considered. Materials use is identified as the primary contributors to embodied energy and carbon with shipping also significant. Improvements in the environmental impact of the Seagen can be achieved primarily by increased structural efficiency and the use of alternative installation methods to increase recovery of steel at decommissioning.

A range of techniques has been proposed to define the optimal locations and capacities of distributed generation (DG) as a means of ensuring that the maximum amount of DG can be connected to existing and future networks. However, there are limitations inherent in these methods, not least in finding the best combination of sites for connecting a predefined number of DGs. Here, a method combining optimal power flow and genetic algorithms aims to meet this requirement. Its use would be in enabling Distribution Network Operators to search a network for the best sites and capacities available to strategically connect a defined number of DGs among a large number of potential combinations. Some applications of the proposed methodology confirmed its effectiveness in sitting and sizing an assigned number of DG units.

Regulators are aiming to incentivize developers and Distribution Network Operators to connect distributed generation (DG) to improve network environmental perform-ance and efficiency. A key question is whether these incentives will encourage both parties to connect DG. Here, multi-objective optimal power flow is used to simulate how the par-ties’ incentives affect their choice of DG capacity within the limits of the existing network. Using current UK incentives as a basis, this paper explores the costs, benefits and trade-offs associated with DG in terms of connection, losses and, in a simple fashion, network deferral.

With high levels of variable renewable generation in distribution or transmission systems, the application of demand and generation time series to power flow analysis can be advantageous. Demand data are often available from historic measurements, while renewable generation such as wind turbine output may be recorded or can be derived from resource measurements over the corresponding period of time. Power flow solutions with hourly time steps over a year or more can then be used to produce load duration curves for system components. This paper shows, by example, how utilities can use the method to determine overload conditions or to specify non-firm connection agreements for new generators.

With the rapid increase in distributed generation (DG), the issue of voltage regulation in the distribution network becomes more significant and centralized voltage control (or active network management) is one of the proposed methods.Alternative work on intelligent distributed voltage and reactive power control of DG has also demonstrated benefits in terms of the minimization of voltage variation and violations as well as the ability to connect larger generators to the distribution network. This paper uses optimal power flow to compare the two methods and shows that intelligent distributed voltage and reactive powercontrol of the DG gives similar results to those obtained by centralized management in terms of the potential for connecting increased capacities within existing networks.

Incentives for using wind power and the increasing price of energy might generate in a relatively short time a scenario where low voltage customers opt to install roof-top wind turbines. This paper focuses on evaluating the effects of such situation in terms of energy consumption, loss reduction, reverse power flow and voltage profiles. Various commercially-available roof-top wind turbines are installed in two secondary distribution circuits considering real-life wind speed data and seasonal load demand. Results are presented and discussed.

Evaluating the technical impacts associated with connecting distributed generation to distribution networks is a complex activity requiring a wide range of network operational and security effects to be qualified and quantified. One means of dealing with such complexity is through the use of indices that indicate the benefit or otherwise of connections at a given location and which could be used to shape the nature of the contract between the utility and distributed generator. This paper presents a multiobjective performance index for distribution networks with distributed generation which considers a wide range of technical issues. Distributed generation is extensively located and sized within the IEEE-34 test feeder, wherein the multiobjective performance index is computed for each configuration. The results are presented and discussed. © 2006 IEEE.

One solution to reduce the extent of climate change is to replace fossil-fuelled electricity generation with renewable sources including hydropower. However, simultaneous changes in climate may alter the available hydropower resource, threatening the financial viability of schemes. To illustrate the potential problem, a sensitivity analysis is presented that considers the impact of altered precipitation and temperature on river flows, energy production and financial performance measures of a planned hydro scheme in Sub-Saharan Africa. The behaviour of the river basin was found to amplify changes in precipitation and, while the design and planned operational strategy of the station tended to moderate the impact, the overall financial impact remained significant. Comparison with (non-climate) project parameters indicated that financial performance, not surprisingly, depends strongly on discount rate and electricity sales price and that, importantly, it showed a similar sensitivity to precipitationchange and rising temperature. Critical changes in climate were identified in order to indicate the severity of climate change that could be tolerated before the project becomes financially non-viable.