Post-peak ICT: graceful degradation for communication networks in an energy constrained future

In recent years, rising energy prices and increasing environmental concerns have boosted research in the so called green ICT and green networking research tracks, aimed at improving the energy efficiency of communications while still offering maximal functionality. In this article we explore a future scenario in which low power networking is no longer optional, but instead becomes a necessity due to fluctuating energy availability. The contribution of this work is twofold. First, we argue why a so called post-peak future scenario, in which we can no longer rely on fossil fuels as our main resource for electricity production, is not unlikely, and what it might entail. Second, we explore the consequences of such a scenario for ICT: How well can current and future infrastructures cope with temporary energy limitations? As an illustration, we present a case study showing the impact of reduced energy availability on a wireless access network

On the feasibility of collaborative green data center ecosystems

The increasing awareness of the impact of the IT sector on the environment, together with economic factors, have fueled many research efforts to reduce the energy expenditure of data centers. Recent work proposes to achieve additional energy savings by exploiting, in concert with customers, service workloads and to reduce data centers’ carbon footprints by adopting demand-response mechanisms between data centers and their energy providers. In this paper, we debate about the incentives that customers and data centers can have to adopt such measures and propose a new service type and pricing scheme that is economically attractive and technically realizable. Simulation results based on real measurements confirm that our scheme can achieve additional energy savings while preserving service performance and the interests of data centers and customers.Peer ReviewedPostprint (author's final draft

Creep monitoring using permanently installed potential drop sensors

Creep is the primary life limiting mechanism of static high temperature, high pressure power station components. Creep state evaluation is currently achieved by surface inspection of microstructure during infrequent outages; a methodology which is laborious, time consuming and considered inadequate. The objective of this work is to develop a monitoring technique that is capable of on-load creep damage monitoring. A continuous update of component integrity will enable better informed, targeted inspections and outage maintenance providing increased power generation availability. A low-frequency, permanently installed potential drop system has been previously developed and will be the focus of this thesis. The use of a quasi-DC inspection frequency suppresses the influence of the electromagnetic skin effect that would otherwise undermine the stability of the measurement in the ferromagnetic materials of interest; the use of even low frequency measurements allows phase sensitive detection and greatly enhanced noise performance. By permanently installing the electrodes to the surface of the component the resistance measurement is sensitive to strain. A resistance - strain inversion is derived and validated experimentally; the use of the potential drop sensor as a robust, high temperature strain gauge is therefore demonstrated. The strain rate of a component is known to be an expression of the creep state of the component. This concept was adopted to develop an interpretive framework for inferring the creep state of a component. It is possible to monitor the accumulation of creep damage through the symptomatic relative increase in strain rate. By taking the ratio of two orthogonal strain measurements, instability and drift common to both measurements can be effectively eliminated; an important attribute considering the necessity to monitor very low strain rates over decades in time in a harsh environment. A preliminary study of using the potential drop technique for monitoring creep damage at a weld has been conducted. Welds provide a site for preferential creep damage accumulation and therefore will frequently be the life limiting feature of power station components. The potential drop technique will be sensitive to both the localised strain that is understood to act as precursor to creep damage at a weld and also the initiation and growth of a crack. Through the course of this project, two site trials have been conducted in power stations. A measurement system and high temperature hardware that is suitable for the power station environment has been developed. The focus of this thesis is the effective transfer of the technique to industry; the realisation of this is detailed in the final chapter.Open Acces

Definition of a Balancing Point for Electricity Transmission Contracts

Electricity transmission contracts allocate scarce resources, allow hedging against locational price differences and provide information to guide investment. Liquidity is increased if all transmission contracts are defined relative to one balancing point, then a set of two contracts can replicate any point to point contract. We propose an algorithm and apply it to the European electricity network to identify a well connected balancing point that exhibits minimal relative cross-price responses and hence reduces market power exercised by generation companies. Market level data which is difficult to obtain or model such as price levels in different regions or that is dependent on the time scale of interaction, as demand elasticity, is not required. The only critical input quantities are assumptions on future transmission constraint patterns

Investigation of FACTS devices to improve power quality in distribution networks

Flexible AC transmission system (FACTS) technologies are power electronic solutions that improve power transmission through enhanced power transfer volume and stability, and resolve quality and reliability issues in distribution networks carrying sensitive equipment and non-linear loads. The use of FACTS in distribution systems is still in its infancy. Voltages and power ratings in distribution networks are at a level where realistic FACTS devices can be deployed. Efficient power converters and therefore loss minimisation are crucial prerequisites for deployment of FACTS devices. This thesis investigates high power semiconductor device losses in detail. Analytical closed form equations are developed for conduction loss in power devices as a function of device ratings and operating conditions. These formulae have been shown to predict losses very accurately, in line with manufacturer data. The developed formulae enable circuit designers to quickly estimate circuit losses and determine the sensitivity of those losses to device voltage and current ratings, and thus select the optimal semiconductor device for a specific application. It is shown that in the case of majority carrier devices (such as power MOSFETs), the conduction power loss (at rated current) increases linearly in relation to the varying rated current (at constant blocking voltage), but is a square root of the variable blocking voltage when rated current is fixed. For minority carrier devices (such as a pin diode or IGBT), a similar relationship is observed for varying current, however where the blocking voltage is altered, power losses are derived as a square root with an offset (from the origin). Finally, this thesis conducts a power loss-oriented evaluation of cascade type multilevel converters suited to reactive power compensation in 11kV and 33kV systems. The cascade cell converter is constructed from a series arrangement of cell modules. Two prospective structures of cascade type converters were compared as a case study: the traditional type which uses equal-sized cells in its chain, and a second with a ternary relationship between its dc-link voltages. Modelling (at 81 and 27 levels) was carried out under steady state conditions, with simplified models based on the switching function and using standard circuit simulators. A detailed survey of non punch through (NPT) and punch through (PT) IGBTs was completed for the purpose of designing the two cascaded converters. Results show that conduction losses are dominant in both types of converters in NPT and PT IGBTs for 11kV and 33kV systems. The equal-sized converter is only likely to be useful in one case (27-levels in the 33kV system). The ternary-sequence converter produces lower losses in all other cases, and this is especially noticeable for the 81-level converter operating in an 11kV network

Recent blackouts in US and continental Europe: is liberalisation to blame?

The paper starts with a detailed technical overview of recent blackouts in the US, Sweden/Denmark and Italy in order to analyse common threads and lessons to be learnt. The blackouts have exposed a number of challenges facing utilities worldwide. Increased liberalisation of electricity supply industry has resulted in a significant increase in inter-area (or cross-border) trades which often are not properly accounted for when assessing system security. The traditional decentralised way of operating systems by TSOs, with each TSO looking after its own control area and little information exchange, resulted in inadequate and slow response to contingencies. A new mode of coordinated operation for real-time security assessment and control is needed in order to maintain system security. This new mode of operation requires overcoming a number of organisational, psychological, legal and technical challenges but the alternative is either to risk another blackout or run the interconnected system very conservatively, maintaining large security margin at a high cost to everyone. The paper also includes technical appendices explaining engineering power system concepts to non-engineering audience

Take-or-Pay Contracts for Renewables Deployment

Renewables require support policies to deliver the European 20% target. We discuss the requirements for least cost development and efficient operation and quantify how different schemes (i) allow for the development of a renewable energy technology portfolio; (ii) reduce rent transfers to infra-marginal technologies or better than marginal resource bases; and (iii) minimise regulatory risk and thus capital costs for new projects. Long-term take or pay contracts minimise regulatory uncertainty, create appropriate incentives for location and operation, allow for efficient system operation and seem compatible with European state aid. We discuss how property rights legislation protects existing renewables investors, and thus can ensure ongoing investment during a transition towards the new scheme