Showing papers on "Efficient energy use published in 2007"

Power provisioning for a warehouse-sized computer

Abstract: Large-scale Internet services require a computing infrastructure that can beappropriately described as a warehouse-sized computing system. The cost ofbuilding datacenter facilities capable of delivering a given power capacity tosuch a computer can rival the recurring energy consumption costs themselves.Therefore, there are strong economic incentives to operate facilities as closeas possible to maximum capacity, so that the non-recurring facility costs canbe best amortized. That is difficult to achieve in practice because ofuncertainties in equipment power ratings and because power consumption tends tovary significantly with the actual computing activity. Effective powerprovisioning strategies are needed to determine how much computing equipmentcan be safely and efficiently hosted within a given power budget.In this paper we present the aggregate power usage characteristics of largecollections of servers (up to 15 thousand) for different classes ofapplications over a period of approximately six months. Those observationsallow us to evaluate opportunities for maximizing the use of the deployed powercapacity of datacenters, and assess the risks of over-subscribing it. We findthat even in well-tuned applications there is a noticeable gap (7 - 16%)between achieved and theoretical aggregate peak power usage at the clusterlevel (thousands of servers). The gap grows to almost 40% in wholedatacenters. This headroom can be used to deploy additional compute equipmentwithin the same power budget with minimal risk of exceeding it. We use ourmodeling framework to estimate the potential of power management schemes toreduce peak power and energy usage. We find that the opportunities for powerand energy savings are significant, but greater at the cluster-level (thousandsof servers) than at the rack-level (tens). Finally we argue that systems needto be power efficient across the activity range, and not only at peakperformance levels.

Virtual power plant and system integration of distributed energy resources

Abstract: A concept is presented along with the overarching structure of the virtual power plant (VPP), the primary vehicle for delivering cost efficient integration of distributed energy resources (DER) into the existing power systems. The growing pressure, primarily driven by environmental concerns, for generating more electricity from renewables and improving energy efficiency have promoted the application of DER into electricity systems. So far, DER have been used to displace energy from conventional generating plants but not to displace their capacity as they are not visible to system operators. If this continues, this will lead to problematic over-capacity issues and under-utilisation of the assets, reduce overall system efficiency and eventually increase the electricity cost that needs to be paid by society. The concept of VPP was developed to enhance the visibility and control of DER to system operators and other market actors by providing an appropriate interface between these system components. The technical and commercial functionality facilitated through the VPP are described and concludes with case studies demonstrating the benefit of aggregation (VPP concept) and the use of the optimal power flow algorithm to characterise VPP

Fuel efficiency and motor vehicle travel: the declining rebound effect

Abstract: It has long been realized that improving energy efficiency releases an economic reaction that partially offsets the original energy saving. As the energy efficiency of some process improves, the process becomes cheaper, thereby providing an incentive to increase its use. Thus total energy consumption changes less than proportionally to changes in physical energy efficiency. For motor vehicles, the process under consideration is use of fuel in producing vehicle-miles traveled (VMT). Our empirical specification is based on a simple aggregate model that simultaneously determines VMT, vehicles, and fuel efficiency. The coefficient on the lagged dependent variable implies considerable inertia in behavior, with people adjusting their travel in a given year by just 21 percent of the ultimate response to a permanent change. The equation exhibits only mild autocorrelation, giving people confidence that their specification accounts for most influences that move sluggishly over time.

The rebound effect: an assessment of the evidence for economy-wide energy savings from improved energy efficiency

Abstract: The UK Energy Research Centre (UKERC) has launched a major new report on how 'Rebound Effects' can result in energy savings falling short of expectations, thereby threatening the success of UK climate policy. An example of a rebound effect would be the driver who replaces a car with a fuel-efficient model, only to take advantage of its cheaper running costs to drive further and more often. Or a family that insulates their loft and puts the money saved on their heating bill towards an overseas holiday.

Tracking Industrial Energy Efficiency and CO2 Emissions

Abstract: Tracking Industrial Energy Efficiency and CO2 Emissions responds to a G8 request. This major new analysis shows how industrial energy efficiency has improved dramatically over the last 25 years. Yet important opportunities for additional gains remain, which is evident when the efficiencies of different countries are compared. This analysis identifies the leaders and the laggards. It explains clearly a complex issue for non-experts. With new statistics, groundbreaking methodologies, thorough analysis and advice, and substantial industry consultation, this publication equips decision makers in the public and private sectors with the essential information that is needed to reshape energy use in manufacturing in a more sustainable manner.

Software-based on-line energy estimation for sensor nodes

Abstract: Energy is of primary importance in wireless sensor networks. By being able to estimate the energy consumption of the sensor nodes, applications and routing protocols are able to make informed decisions that increase the lifetime of the sensor network. However, it is in general not possible to measure the energy consumption on popular sensor node platforms. In this paper, we present and evaluate a software-based on-line energy estimation mechanism that estimates the energy consumption of a sensor node. We evaluate the mechanism by comparing the estimated energy consumption with the lifetime of capacitor-powered sensor nodes. By implementing and evaluating the X-MAC protocol, we show how software-based on-line energy estimation can be used to empirically evaluate the energy efficiency of sensor network protocols.

Handbook of energy efficiency and renewable energy

Abstract: Global energy system / D. Yogi Goswami, Frank Kreith -- Energy policy -- Economics methods / Rosalie Ruegg, Walter Short -- Environmental impacts and costs of energy / Ari Rabl, Joseph V. Spadaro -- Distributed generation and demand-side management -- Generation technologies through the year 2025 -- Outlook for U.S. energy consumption and prices in the midterm / Andy S. Kydes -- Transportation systems / Beth Isler -- Infrastructure risk analysis and security -- Electrical energy management in buildings / Craig B. Smith, Kelly E. Parmenter -- Heating, ventilating, and air conditioning control systems / Jan F. Kreider, David E. Claridge, Charles H. Culp -- Energy efficient technologies -- Compact heat exchangers : recuperators and regenerators / Ramesh K. Shah -- Industrial energy efficiency and energy management / Craig B. Smith, Barney L. Capehart, Wesley M. Rohrer Jr. -- Process energy efficiency : pinch technology -- Energy audits for buildings / Moncef Krarti -- Cogeneration / W. Dan Turner -- Energy storage, transmission, and distribution -- Availability of renewable resources -- Solar thermal energy conversion -- Concentrating solar thermal power / Manuel Romero-Alvarez, Eduardo Zarza -- Wind energy conversion / Dale E. Berg -- Photovoltaics fundamentals, technology, and application -- Waste-to-energy combustion / Charles O. Velzy, Leonard M. Grillo -- Biomass conversion processes for energy recovery -- Geothermal power generation / Kevin Kitz -- Hydrogen energy technologies / S.A. Sherif, F. Barbir, T.N. Veziroglu, M. Mahishi, S.S. Srinivasan -- Fuel cells / Xianguo Li -- Appendices / Nitin Goel.

Evaluation of 400V DC distribution in telco and data centers to improve energy efficiency

Abstract: In a typical data center, less than half the energy consumed is delivered to the compute load, with the rest lost in power conversion, distribution and cooling. Traditionally power distribution is at 400/480 V AC in data centers and at -48 V DC in telco facilities. Higher voltage DC has been proposed as an energy efficient distribution option for both types of facilities, and this paper presents an analytical evaluation of several data center power delivery architectures over a range of loads, showing that a 400 V facility-level DC distribution option is the most efficient. The equipment required to support such an architecture is discussed and results from a small scale demonstration are included.

Dozer: ultra-low power data gathering in sensor networks

Abstract: Environmental monitoring is one of the driving applications in the domain of sensor networks. The lifetime of such systems is envisioned to exceed several years. To achieve this longevity in unattended operation it is crucial to minimize energy consumption of the battery-powered sensor nodes. This paper proposes Dozer, a data gathering protocol meeting the requirements of periodic data collection and ultra-low power consumption. The protocol comprises MAC-layer, topology control, and routing all coordinated to reduce energy wastage of the communication subsystem. Using a tree-based network structure, packets are reliably routed towards the data sink. Parents thereby schedule precise rendezvous times for all communication with their children. In a deployed network consisting of 40 TinyOS- enabled sensor nodes, Dozer achieves radio duty cycles in the magnitude of 0.2%.

Context-for-wireless: context-sensitive energy-efficient wireless data transfer

Abstract: Ubiquitous connectivity on mobile devices will enable numerous new applications in healthcare and multimedia. We set out to check how close we are towards ubiquitous connectivity in our daily life. The findings from our recent field-collected data from an urban university population show that while network availability is decent, the energy cost of network interfaces poses a great challenge. Based on our findings, we propose to leverage the complementary strength of Wi-Fi and cellular networks by choosing wireless interfaces for data transfers based on network condition estimation. We show that an ideal selection policy can more than double the battery lifetime of a commercial mobile phone, and the improvement varies with data transfer patterns and Wi-Fi availability.We formulate the selection of wireless interfaces as a statistical decision problem. The key to attaining the potential battery improvement is to accurately estimate Wi-Fi network conditions without powering up its network interface. We explore the use of different context information, including time, history, cellular network conditions, and device motion, for this purpose. We consequently devise algorithms that can effectively learn from context information and estimate the probability distribution of Wi-Fi network conditions. Simulations based on field-collected traces show that our algorithms can improve the average battery lifetime of a commercial mobile phone for a three-channel electrocardiogram (ECG) reporting application by 39%, very close to the theoretical upper bound of 42%. Finally, our field validation of our most simple algorithm demonstrates a 35% improvement in battery lifetime.

Energy-Aware Clustering for Wireless Sensor Networks using Particle Swarm Optimization

Abstract: Wireless sensor networks (WSNs) are mainly characterized by their limited and non-replenishable energy supply. Hence, the need for energy efficient infrastructure is becoming increasingly more important since it impacts upon the network operational lifetime. Sensor node clustering is one of the techniques that can expand the lifespan of the whole network through data aggregation at the cluster head. In this paper, we present an energy-aware clustering for wireless sensor networks using particle swarm optimization (PSO) algorithm which is implemented at the base station. We define a new cost function, with the objective of simultaneously minimizing the intra-cluster distance and optimizing the energy consumption of the network. The performance of our protocol is compared with the well known cluster-based protocol developed for WSNs, LEACH (low-energy adaptive clustering hierarchy) and LEACH-C, the later being an improved version of LEACH. Simulation results demonstrate that our proposed protocol can achieve better network lifetime and data delivery at the base station over its comparatives.

An Energy-Efficient Data Collection Framework for Wireless Sensor Networks by Exploiting Spatiotemporal Correlation

Abstract: Limited energy supply is one of the major constraints in wireless sensor networks. A feasible strategy is to aggressively reduce the spatial sampling rate of sensors, that is, the density of the measure points in a field. By properly scheduling, we want to retain the high fidelity of data collection. In this paper, we propose a data collection method that is based on a careful analysis of the surveillance data reported by the sensors. By exploring the spatial correlation of sensing data, we dynamically partition the sensor nodes into clusters so that the sensors in the same cluster have similar surveillance time series. They can share the workload of data collection in the future since their future readings may likely be similar. Furthermore, during a short-time period, a sensor may report similar readings. Such a correlation in the data reported from the same sensor is called temporal correlation, which can be explored to further save energy. We develop a generic framework to address several important technical challenges, including how to partition the sensors into clusters, how to dynamically maintain the clusters in response to environmental changes, how to schedule the sensors in a cluster, how to explore temporal correlation, and how to restore the data in the sink with high fidelity. We conduct an extensive empirical study to test our method using both a real test bed system and a large-scale synthetic data set.

JouleSort: a balanced energy-efficiency benchmark

Abstract: The energy efficiency of computer systems is an important concern in a variety of contexts. In data centers, reducing energy use improves operating cost, scalability, reliability, and other factors. For mobile devices, energy consumption directly affects functionality and usability. We propose and motivate JouleSort, an external sort benchmark, for evaluating the energy efficiency of a wide range of computer systems from clusters to handhelds. We list the criteria, challenges, and pitfalls from our experience in creating a fair energy-efficiency benchmark. Using a commercial sort, we demonstrate a JouleSort system that is over 3.5x as energy-efficient as last year's estimated winner. This system is quite different from those currently used in data centers. It consists of a commodity mobile CPU and 13 laptop drives connected by server-style I/O interfaces.

Integrating Adaptive Components: An Emerging Challenge in Performance-Adaptive Systems and a Server Farm Case-Study

Abstract: The increased complexity of performance-sensitive software systems leads to increased use of automated adaptation policies in lieu of manual performance tuning. Composition of adaptive components into larger adaptive systems, however, presents challenges that arise from potential incompatibilities among the respective adaptation policies. Consequently, unstable or poorly-tuned feedback loops may result that cause performance deterioration. This paper (i) presents a mechanism, called adaptation graph analysis, for identifying potential incompatibilities between composed adaptation policies and (ii) illustrates a general design methodology for co-adaptation that resolves such incompatibilities. Our results are demonstrated by a case study on energy minimization in multi-tier Web server farms subject to soft real-time constraints. Two independently efficient energy saving policies (an on/off policy that switches machines off when not needed and a dynamic voltage scaling policy) are shown to conflict leading to increased energy consumption when combined. Our adaptation graph analysis predicts the problem, and our co-adaptation design methodology finds a solution that improves performance. Experimental results from a 17-server farm running the industry standard TPC-W e-commerce benchmark show that co-adaptation renders a cut-down in energy consumption by more than 50%, when workload is not high, while maintaining latency within acceptable bounds. The paper serves as a proof of concept of the proposed conflict-identification and resolution methodology and an invitation to further investigate a science for composing adaptive systems.

Wireless sensor networks with energy harvesting technologies: a game-theoretic approach to optimal energy management

Abstract: Energy harvesting technologies are required for autonomous sensor networks for which using a power source from a fixed utility or manual battery recharging is infeasible An energy harvesting device (eg, a solar cell) converts different forms of environmental energy into electricity to be supplied to a sensor node However, since it can produce energy only at a limited rate, energy saving mechanisms play an important role to reduce energy consumption in a sensor node In this article we present an overview of the different energy harvesting technologies and the energy saving mechanisms for wireless sensor networks The related research issues on energy efficiency for sensor networks using energy harvesting technology are then discussed To this end, we present an optimal energy management policy for a solar-powered sensor node that uses a sleep and wakeup strategy for energy conservation The problem of determining the sleep and wakeup probabilities is formulated as a bargaining game The Nash equilibrium is used as the solution of this game

Cooperative Routing in Static Wireless Networks

Abstract: We study the problem of transmission-side diversity and routing in a static wireless network. It is assumed that each node in the network is equipped with a single omnidirectional antenna and that multiple nodes are allowed to coordinate their transmissions in order to obtain energy savings. We derive analytical results for achievable energy savings for both line and grid network topologies. It is shown that the energy savings of and are achievable in line and grid networks with a large number of nodes, respectively. We then develop a dynamic-programming-based algorithm for finding the optimal route in an arbitrary network, as well as suboptimal algorithms with polynomial complexity. We show through simulations that these algorithms can achieve average energy savings of about in random networks, as compared to the noncooperative schemes.

Architecture Complexity and Energy Efficiency of Small Wind Turbines

Abstract: The power characteristics of wind turbines are nonlinear. It is particularly true for vertical-axis turbines whose provided power is very sensitive to the load. Thus, controlling the operating point is essential to optimize the energetic behavior. Several control strategies (maximum power point tracking) can be used for the energy conversion. If the wind-turbine characteristic Cp(lambda) is supposed to be a priori known, it can be used for optimal control of the torque, speed, or system output power. On the contrary, if this characteristic is unknown, an operational seeking algorithm such as fuzzy logic has to be implemented. Several structures with different associated complexity degrees can be used, in particular, the structure of the ac-dc conversion, which can be either a pulsewidth-modulation voltage-source rectifier or a simple diode bridge. A comparative study of the corresponding control strategies and architectures is proposed in this paper regarding the tradeoffs between structure complexity and energy efficiency. The analysis is based on simulations and experiments

TMMAC: An Energy Efficient Multi-Channel MAC Protocol for Ad Hoc Networks

Abstract: This paper presents a TDMA based multi-channel MAC protocol called TMMAC for Ad Hoc Networks. TMMAC requires only a single half-duplex radio transceiver on each node. In addition to explicit frequency negotiation which is adopted by conventional multi-channel MAC protocols, TMMAC introduces lightweight explicit time negotiation. This two-dimensional negotiation enables TMMAC to exploit the advantage of both multiple channels and TDMA, and achieve aggressive power savings by allowing nodes that are not involved in communication to go into doze mode. Moreover, TMMAC dynamically adjusts its negotiation window size based on different traffic patterns, which further improves communication throughput and energy savings. In this paper, the performance of TMMAC is analyzed and evaluated. The evaluations show that TMMAC achieves up to 113% higher communication throughput while consuming 74% less per packet energy over the state-of-the-art multi-channel MAC protocols for single-transceiver wireless devices.

Performance of Fountain Codes in Collaborative Relay Networks

Abstract: Cooperative communications, where parallel relays forward information to a destination node, can greatly improve the energy efficiency and latency in ad-hoc networks. However, current networks do not fully exploit its potential as they only use traditional energy-accumulation, which is often used in conjunction with repetition coding or cooperative space-time codes. In this paper, we show that the concept of mutual- information-accumulation can be realized with the help of fountain codes, and leads to a lower energy expenditure and a lower transmission time than energy accumulation. We then provide an analysis of the performance of mutual information accumulation in relay networks with N relay nodes. We first analyze the quasi-synchronuous scenario where the source stops transmitting and the relay nodes start transmitting after L relay nodes have successfully decoded the source data. We show that an optimum L exists, and is typically on the order of 3 or 4. We also give closed-form equations for the energy savings that can be achieved by the use of mutual-information-accumulation at the receiver. We then analyze and provide bounds for an alternate scenario where each relay node starts its transmission to the destination as soon as it has decoded the source data, independent of the state of the other relay nodes. This approach further reduces the transmission time, because the transmission by the relay nodes helps the other relay nodes that are still receiving.

Energy-Efficient Resource Allocation in Wireless Networks: An Overview of Game-Theoretic Approaches

Abstract: An overview of game-theoretic approaches to energy-efficient resource allocation in wireless networks is presented. Focusing on multiple-access networks, it is demonstrated that game theory can be used as an effective tool to study resource allocation in wireless networks with quality-of-service (QoS) constraints. A family of non-cooperative (distributed) games is presented in which each user seeks to choose a strategy that maximizes its own utility while satisfying its QoS requirements. The utility function considered here measures the number of reliable bits that are transmitted per joule of energy consumed and, hence, is particulary suitable for energy-constrained networks. The actions available to each user in trying to maximize its own utility are at least the choice of the transmit power and, depending on the situation, the user may also be able to choose its transmission rate, modulation, packet size, multiuser receiver, multi-antenna processing algorithm, or carrier allocation strategy. The best-response strategy and Nash equilibrium for each game is presented. Using this game-theoretic framework, the effects of power control, rate control, modulation, temporal and spatial signal processing, carrier allocation strategy and delay QoS constraints on energy efficiency and network capacity are quantified.

Energy and Sustainability

Abstract: ![Figure][1] The theme for the 2007 annual meeting of the AAAS, to be held in San Francisco on 15 to 19 February, is “Science and Technology for Sustainable Well-Being.” The problem of energy, which is the focus of this special issue of Science linked to the meeting, looms as a central element in the web of intertwined challenges that this theme embodies. Well-being has environmental, sociopolitical, and cultural dimensions as well as economic ones, and the goal of sustainable well-being entails improving all of these dimensions in ways and to end points that are consistent with maintaining the improvements indefinitely. This challenge includes not only improving sustainably the standard of living in developing countries, but also converting to a sustainable basis the currently unsustainable practices supporting the standard of living in industrialized ones. Civilization's ability to meet this immense challenge clearly depends on our strengths in natural science and engineering. But it also depends on our strengths in the social sciences and in “social technology” in the form of business, government, and law, as well as on the societal wit and will to integrate all of these elements in pursuit of the sustainable-well-being goal. ![Figure][1] CREDIT: JUPITER IMAGES No part of this challenge is more complex or more demanding than its energy dimension. This is so in part because energy supply is tightly intertwined with national and international security and with many of the most damaging and dangerous environmental problems—from indoor air quality to global climate change—as well as with the capacity to meet basic human needs and fuel economic growth. The multiplicity and importance of these linkages would make energy a vexing issue even in a world where energy demand was constant. But that is not the world we live in. Continuing population growth and rapidly rising affluence in many parts of the globe are driving a rate of increase in energy use that has staggering implications. Even if the energy efficiency of the world economy—gross world product per unit of energy—were to continue to increase at the long-term historical rate of about 1% per year, the realization of middle-of-the-road population and economic projections would entail quadrupling world energy use in this century. In a world where today one-third of primary energy comes from oil (two-thirds of the remaining high-quality supplies of which probably lie under the volatile Middle East) and 80% comes from oil, coal, and natural gas combined (virtually all of the carbon dioxide from the combustion of which continues to go straight into the atmosphere), that middle-of-the-road energy trajectory cannot be managed simply by expanding what we are already doing. Such a path is not merely unsustainable; it is a prescription for disaster. The perils of oil dependence and climate change, coupled with the demand for large increases in the per-capita availability of energy services, compel an early transition to a different path. Its requirements include a reduction in global population growth (achievable, fortunately, by means that are desirable in their own right) and a sharply increased emphasis on improving the efficiency of energy conversion and end use (aiming to improve the energy efficiency of the world economy not by 1% per year but by 2% per year or more). Also required is a several fold increase in public and private investments to improve the technologies of energy supply. We need to know whether and how the carbon dioxide from fossil-fuel use can be affordably and reliably sequestered away from the atmosphere; whether and how nuclear energy can be made safe enough and proliferation-resistant enough to be substantially expanded worldwide; and to what extent biofuel production can be increased without intolerable impacts on food supply or ecosystem services. And we need to improve the affordability of the direct harnessing of sunlight for society's energy needs. Much insight about the current prospects in these and other dimensions of the energy problem is available in this special issue of Science. Still more about energy is on the agenda for the San Francisco meeting, along with much else germane to “Science and Technology for Sustainable Well-Being.” I commend it all to your attention. Nothing is more important to the human condition in the 21st century than rising to this set of challenges. [1]: pending:yes