Showing papers on "Electricity generation published in 2001"

Wind Energy Handbook

Abstract: As environmental concerns have focused attention on the generation of electricity from clean and renewable sources wind energy has become the world's fastest growing energy source. The Wind Energy Handbook draws on the authors' collective industrial and academic experience to highlight the interdisciplinary nature of wind energy research and provide a comprehensive treatment of wind energy for electricity generation. Features include: * An authoritative overview of wind turbine technology and wind farm design and development * In-depth examination of the aerodynamics and performance of land-based horizontal axis wind turbines * A survey of alternative machine architectures and an introduction to the design of the key components * Description of the wind resource in terms of wind speed frequency distribution and the structure of turbulence * Coverage of site wind speed prediction techniques * Discussions of wind farm siting constraints and the assessment of environmental impact * The integration of wind farms into the electrical power system, including power quality and system stability * Functions of wind turbine controllers and design and analysis techniques With coverage ranging from practical concerns about component design to the economic importance of sustainable power sources, the Wind Energy Handbook will be an asset to engineers, turbine designers, wind energy consultants and graduate engineering students.

Fuel Cells - Fundamentals and Applications

Abstract: Fuel cells will make a valuable contribution to future power generation facilities. They improve the flexibility and increase the options for many applications, such as distributed power, vehicle propulsion, and portable devices. Their main property is the high electrical efficiency compared to other energy conversion devices. Both the low-temperature and the high-temperature fuel cells have their advantages and disadvantages depending on the application. Sometimes, they can both be implemented in similar applications. The modularity of fuel cells makes them quite flexible as the power needed can easily be attained by changing the number of modules. Twenty years ago, mainly universities and research institutions but only a few companies conducted fuel cell research working on the fundamentals of fuel cells. Nowadays due to the commercial interest innumerable research groups and companies have fuel cell activities ranging from the investigation of catalysts (both improving existing catalyst systems as searching for new catalysts), the development of novel membranes for PEMFCs and DMFCs, to the development of other components for fuel cells. Optimisation of flow field structures, backing layers, and other components of the single cells have intensified. (orig.)

Novel maximum-power-point-tracking controller for photovoltaic energy conversion system

Abstract: A novel maximum-power-point-tracking (MPPT) controller for a photovoltaic (PV) energy conversion system is presented. Using the slope of power versus voltage of a PV array, the proposed MPPT controller allows the conversion system to track the maximum power point very rapidly. As opposed to conventional two-stage designs, a single-stage configuration is implemented, resulting in size and weight reduction and increased efficiency. The proposed system acts as a solar generator on sunny days, in addition to working as an active power line conditioner on rainy days. Finally, computer simulations and experimental results demonstrate the superior performance of the proposed technique.

The Energy Harvesting Eel: a small subsurface ocean/river power generator

Abstract: The Energy Harvesting Eel (Eel) is a new device that uses piezoelectric polymers to convert the mechanical flow energy, available in oceans and rivers, to electrical power. Eel generators make use of the regular trail of traveling vortices behind a bluff body to strain the piezoelectric elements; the resulting undulating motion resembles that of a natural eel swimming. Internal batteries are used to store the surplus energy generated by the Eel for later use by a small, unattended sensor or robot. Because of the properties of commercially available piezoelectric polymers, Eels will be relatively inexpensive and are easily scaleable in size and have the capacity to generate from milli-watts to many watts depending on system size and flow velocity of the local environment. A practical Eel structure has been developed that uses the commercially available piezoelectric polymer, PVDF. Future Eels may use more efficient electrostrictive polymer. Every aspect of the system from the interactions between the hydrodynamics of the water flow and structural elements of the Eel, through the mechanical energy input to the piezoelectric material, and finally the electric power output delivered through an optimized resonant circuit has been modeled and tested. The complete Eel system, complete with a generation and storage system, has been demonstrated in a wave tank. Future work on the Eel will focus on developing and then deploying a small, lightweight, one-watt power generation unit, initially in an estuary and then subsequently in the ocean. Such Eels will have the ability to recharge batteries or capacitors of a distributed robotic group, or remote sensor array, thus extending the mission life indefinitely in regions containing flowing water.

Hydrogen Production. Green Algae as a Source of Energy

Abstract: Hydrogen gas is thought to be the ideal fuel for a world in which air pollution has been alleviated, global warming has been arrested, and the environment has been protected in an economically sustainable manner. Hydrogen and electricity could team to provide attractive options in transportation and power generation. Interconversion between these two forms of energy suggests on-site utilization of hydrogen to generate electricity, with the electrical power grid serving in energy transportation, distribution utilization, and hydrogen regeneration as needed. A challenging problem in establishing H2 as a source of energy for the future is the renewable and environmentally friendly generation of large quantities of H2 gas. Thus, processes that are presently conceptual in nature, or at a developmental stage in the laboratory, need to be encouraged,

Dielectric elastomers: generator mode fundamentals and applications

Abstract: Dielectric elastomers have shown great promise as actuator materials. Their advantages in converting mechanical to electrical energy in a generator mode are less well known. If a low voltage charge is placed on a stretched elastomer prior to contraction, the contraction works against the electrostatic field pressure and raises the voltage of the charge, thus generating electrical energy. This paper discusses the fundamentals of dielectric elastomer generators, experimental verification of the phenomenon, practical issues, and potential applications. Acrylic elastomers have demonstrated an estimated 0.4 J/g specific energy density, greater than that of piezoelectric materials. Much higher energy densities, over 1 J/g, are predicted. Conversion efficiency can also be high, theoretically up to 80-90%; the paper discusses the operating conditions and materials required for high efficiency. Practical considerations may limit the specific outputs and efficiencies of dielectric elastomeric generators, tradeoffs between electronics and generator material performance are discussed. Lastly, the paper describes work on potential applications such as an ongoing effort to develop a boot generator based on dielectric elastomers, as well as other applications such as conventional power generators, backpack generators, and wave power applications.

Design and fabrication of a new vibration-based electromechanical power generator

Abstract: A device is described for generating electrical power from mechanical energy in a vibrating environment. The design utilises an electromagnetic transducer and its operating principle is based on the relative movement of a magnet pole with respect to a coil. The approach is suitable for embedded remote microsystems structures with no physical links to the outside world. Simulation, modelling and test results following fabrication of a first prototype have demonstrated that generation of practical amounts of power within a reasonable space is possible. Power generation of more than 1 mW within a volume of 240 mm3 at a vibration frequency of 320 Hz has been obtained.

Geothermal energy for the benefit of the people

Abstract: Geothermal energy for electricity generation has been produced commercially since 1913, and for four decades on the scale of hundreds of MW both for electricity generation and direct use. The utilization has increased rapidly during the last three decades. In 2000, geothermal resources have been identified in over 80 countries and there are quantified records of geothermal utilization in 58 countries in the world. The worldwide use of geothermal energy amounts to 49 TWh/a of electricity and 53 TWh/a for direct use. Electricity is produced with geothermal steam in 21 countries spread over all continents. Five countries obtain 10–22% of their electricity from geothermal energy. Only a small fraction of the geothermal potential has been developed so far, and there is ample space for an accelerated use of geothermal energy both for electricity generation and direct applications. A comparison of the renewable energy sources (data from the UN World Energy Assessment Report) shows the current electrical energy cost to be 2–10 US¢/kWh for geothermal and hydro, 5–13 US¢/kWh for wind, 5–15 US¢/kWh for biomass, 25–125 US¢/kWh for solar photovoltaic and 12–18 US¢/kWh for solar thermal electricity. Of the total electricity production from renewables of 2826 TWh in 1998, 92% came from hydropower, 5.5% from biomass, 1.6% from geothermal and 0.6% from wind. Solar electricity contributed 0.05% and tidal 0.02%. Comparing four “new” renewable energy sources (geothermal, wind, solar and tidal), shows 70% of the electricity generated by the four to come from geothermal with only 42% of the total installed capacity. Wind energy contributes 27% of the electricity, but has 52% of the installed capacity. Solar energy produces 2% of the electricity and tidal energy 1%. Biomass constitutes 93% of the total direct heat production from renewables, geothermal 5%, and solar heating 2%. Heat production from renewables is commercially competitive with conventional energy sources. The current cost of direct heat from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh, and solar heating 3–20 US¢/kWh. Geothermal energy, with its proven technology and abundant resources, can make a significant contribution towards reducing the emission of greenhouse gases.

Dynamic modelling of a wind turbine with doubly fed induction generator

Abstract: As a result of increasing environmental concern, more and more electricity is generated from renewable sources. One way of generating electricity from renewable sources is to use wind turbines. A tendency to erect more and more wind turbines can be observed. As a result of this, in the near future wind turbines may start to influence the behaviour of electrical power systems. Therefore, adequate models to study the impact of wind turbines on electrical power system behaviour are needed. In this paper, a dynamic model of an important contemporary wind turbine concept is presented, namely a doubly fed (wound rotor) induction generator with a voltage source converter feeding the rotor. This wind turbine concept is equipped with rotor speed, pitch angle and terminal voltage controllers. After derivation of the model, the wind turbine response to two measured wind sequences is simulated.

Microgrids [distributed power generation]

Abstract: Environmentally friendly renewable energy technologies such as photovoltaics and clean, efficient, fossil-fuels technologies such as micro-turbines and fuel cells are among new generating systems driving the demand for distributed generation of electricity. If combined heat and power at residential industrial plants or commercial buildings can be achieved the efficiencies can be higher than conventional central generation plants. The smallness of these new distributed generation along with the low voltages at the interface create a new class of problems which requires innovative approaches to managing and operating the distributed resources. One such concept is the microgrid.

Reactive Power as an Ancillary Service

Abstract: This paper addresses the problem of reactive power procurement by an independent system operator (ISO) in deregulated electricity markets. A reactive bid structure is proposed in the context of a reactive power market. Based on the reactive power price offers and technical constraints involved in reactive power planning, a two-tier approach is developed to determine the most beneficial reactive power contracts for the ISO. The reactive capability of a generator and, therefore, the opportunity costs in providing reactive power is also included in the model. Uncertainty in reactive demand and in reactive bids of participating parties is incorporated through Monte Carlo simulations and the expected reactive power procurement plan for the ISO is hence determined. The CIGRE 32-bus network, approximately representing the Swedish system, is used for the studies.

Steady-State Performance of a Grid-Connected Rooftop Hybrid Wind-Photovoltaic Power System with Battery Storage

Abstract: This paper reports the performance of a 4 kW grid-connected residential wind-photovoltaic system (WPS) with battery storage located In Lowell, MA. The system was originally designed to meet a typical New England (TNE) load demand with a loss of power supply probability (LPSP) of one day in ten years, as recommended by the Utility Company. The data used in the calculation were wind speed and irradiance of Logan Airport Boston (LAB), obtained from the National Climate Center in North Carolina. The present performance study is based on two-year operation (May 1996 to April 1998) of the WPS. Unlike conventional generation, the wind and the sunrays are available at no cost and generate pollution-free electricity. At around noon the WPS satisfies its load and provides additional energy to the storage or to the grid. On-site energy production is undoubtedly accompanied with minimization of environmental pollution, reduction of losses in power systems transmission and distribution equipment, and supports the utility in demand side management (DSM). This paper includes discussions on system reliability, power quality, loss of supply, and effects of the randomness of the wind and the solar radiation on system design.

Using neural networks to estimate wind turbine power generation

Abstract: This paper uses data collected at Central and South West Services Fort Davis wind farm (USA) to develop a neural network based prediction of power produced by each turbine. The power generated by electric wind turbines changes rapidly because of the continuous fluctuation of wind speed and direction. It is important for the power industry to have the capability to perform this prediction for diagnostic purposes-lower-than-expected wind power may be an early indicator of a need for maintenance. In this paper, characteristics of wind power generation are first evaluated in order to establish the relative importance for the neural network. A four input neural network is developed and its performance is shown to be superior to the single parameter traditional model approach.

Control system for hybrid vehicle

Abstract: A control system for a hybrid vehicle has a consumed electric power calculator (20), which calculates electric power consumption, and a battery state calculator (21), which calculates battery state SOC of a battery (5). Based on this battery state, a physical quantity per effective electric power calculator (25) calculates a physical quantity per effective power when electric power equal to or greater than consumed electric power is generated for various electric power consumption and electric power generation, and a threshold value calculator (22) obtains a threshold value having the same unit as that of the physical quantity per effective power using predetermined calculation for selecting operating modes of a generator and the battery. An operating mode selector (23) selects operating modes for an engine (1) and the battery (5) based on comparison between the above threshold value and the physical quantity per effective power corresponding to the consumed electric power, and a target generated electric power calculator (24) calculates target electric power generation. An electric power distribution controller (6) controls the engine (1) and the motor (3).

Efficiency and economy of wood-fired biomass energy systems in relation to scale regarding heat and power generation using combustion and gasification technologies

Abstract: Policy objectives to increase biomass’ contribution to the energy supply in industrialised countries are quite ambitious, but biomass resources are rather limited and expensive in many situations. Therefore, an optimal utilisation of resources producing a maximum of energy at minimal costs is desirable. A wide variety of biomass conversion options with different performance characteristics exists. Also, the economic and energetic performance depends on many variables, such as costs of logistics, scaling effects and degree of heat utilisation to name a few. Therefore, system analysis is needed to identify optimal systems. In this study, different biomass energy systems are analysed regarding their energetic and economic performance related to fossil primary energy savings. The systems studied contain residual woody biomass, logistics, heat distribution and combustion or gasification units producing heat, power or CHP. The performance of systems is expressed as a function of scale. This is done by applying generic functions to describe plants’ efficiencies and specific investment costs and by expressing costs and energy use of logistic and heat distribution as a function of conversion unit capacities. Scale effects within biomass energy systems are significant. Up-scaling increases the relative primary energy savings of the studied systems within the scale range of 0– 300 MW th−input regarded, while costs per unit of primary energy savings decrease or have an optimum at medium scales. The relative primary energy savings lay between 0.53 and 1.13 GJ fossil−saved GJ biomass −1 . With costs of 4– 20 GJ fossil−saved −1 systems are not profitable under Dutch conditions with residual wood prices of 3.8 GJ LHV −1 while firing waste wood with zero costs at the plant gate renders profitable operation possible. Favourable in both economic and energy terms are BIG/CC plants.

Reliability/Cost Implications of PV and Wind Energy Utilization in Small Isolated Power Systems

Abstract: The application of renewable energy in electric power systems is growing rapidly due to enhanced public concerns for adverse environmental impacts and escalation in energy costs associated with the use of conventional energy sources. Photovoltaics and wind energy sources are being increasingly recognized as cost-effective generation sources in small isolated power systems primarily supplied by costly diesel fuel. The utilization of these energy sources can significantly reduce the system fuel costs but can also have considerable impact on the system reliability. A realistic cost/reliability analysis requires evaluation models that can recognize the highly erratic nature of these energy sources while maintaining the chronology and interdependence of the random variables inherent in them. This paper presents a simulation method that provides objective indicators to help system planners decide on appropriate installation sites, operating policies, and selection of energy types, sizes, and mixes in capacity expansion when utilizing PV and wind energy in small isolated systems.

Loss balancing in three-level voltage source inverters applying active NPC switches

Abstract: This paper investigates the use of active neutral point clamp switches in a three-level NPC voltage source inverter to balance the losses among the semiconductors. Both a control structure and algorithm are proposed which enable a substantially increased output power of the inverter and an improved performance at zero speed.

Exergy analysis of the United Kingdom energy system

Abstract: The exergy method has been used to analyse changes in the structure of the UK energy system over a period of more than 30 years from 1965. A sectoral approach was employed, with the supply side examined in terms of themain energy sources, while final demand was separated into four energy end-use groups: the domestic, service, industrial and transport sectors. Estimates of sector-weighted or ‘lumped’ parameters, such as exergy efficiencies, were obtained from the particular characteristics of each sector. These were employed to determine the exergetic ‘improvement potential’ for critical elements of the energy system. Electricity generation together with final energy demand in the domestic sector and in transport are shown to account for nearly 80 per cent of the Second Law improvement potential. This poor thermodynamic performance is principally due to exergy losses in combustion and heat transfer processes associated with power generation, space heating and main transport modes. The results of th...

Integrated control system and method for controlling mode, synchronization, power factor, and utility outage ride-through for micropower generation systems

Abstract: An integrated system for comprehensive control of an electric power generation system utilizes state machine control having particularly defined control states and permitted control state transitions. In this way, accurate, dependable and safe control of the electric power generation system is provided. Several of these control states may be utilized in conjunction with a utility outage ride-through technique that compensates for a utility outage by predictably controlling the system to bring the system off-line and to bring the system back on-line when the utility returns. Furthermore, a line synchronization technique synchronizes the generated power with the power on the grid when coming back on-line. The line synchronization technique limits the rate of synchronization to permit undesired transient voltages. The line synchronization technique operates in either a stand-alone mode wherein the line frequency is synthesized or in a connected mode which sensed the grid frequency and synchronizes the generated power to this senses grid frequency. The system also includes power factor control via the line synchronization technique or via an alternative power factor control technique. The result is an integrated system providing a high degree of control for an electric power generation system.

System and method for enabling the real time buying and selling of electricity generated by fuel cell powered vehicles

Abstract: The present invention relates to a network communication system and method to enable the real time buying and selling of electricity generated by fuel cell powered vehicles between a fuel cell powered vehicle and a consumer. The method comprises: providing connections to the vehicle for the supply of a fuel and for transfer of electricity; determining the current cost of fuel and price paid for generating electricity; based at least on the cost of fuel and price paid for generating electricity, determining whether to make the fuel cell powered vehicle available for generation of electricity; when fuel is consumed by the vehicle and electricity generated by the vehicle, collecting data on the quantity of fuel consumed and amount of electricity generated, calculating the cost of the fuel and the value of the electricity generated, providing a debit charge for the cost of fuel consumed and a credit charge for the value of electricity generated. A method to enable the real time buying and selling of electricity generated by fuel cell powered vehicles between an energy service provider and a consumer of electricity is also disclosed.

A life cycle assessment of biomass cofiring in a coal-fired power plant

Abstract: The generation of electricity, and the consumption of energy in general, often result in adverse effects on the environment. Coal-fired power plants generate over half of the electricity used in the U.S., and therefore play a significant role in any discussion of energy and the environment. By cofiring biomass, currently operating coal plants have an opportunity to reduce the impact they have, but to what degree, and with what trade-offs? A life cycle assessment has been conducted on a coal-fired power system that cofires wood residue. The assessment was conducted in a cradle-to-grave manner to cover all processes necessary for the operation of the power plant, including raw material extraction, feed preparation, transportation, and waste disposal and recycling. Cofiring was found to significantly reduce the environmental footprint of the average coal-fired power plant. At rates of 5% and 15% by heat input, cofiring reduces greenhouse gas emissions on a CO2-equivalent basis by 5.4% and 18.2%, respectively. Emissions of SO2, NOx, non-methane hydrocarbons, particulates, and carbon monoxide are also reduced with cofiring. Additionally, total system energy consumption is lowered by 3.5% and 12.4% for the 5% and 15% cofiring cases, respectively. Finally, resource consumption and solid waste generation were found to be much less for systems that cofire.

Electromagnetic linear generator and shock absorber

Abstract: An electromagnetic linear generator and regenerative electromagnetic shock absorber is disclosed which converts variable frequency, repetitive intermittent linear displacement motion to useful electrical power. The innovative device provides for superposition of radial components of the magnetic flux density from a plurality of adjacent magnets to produce a maximum average radial magnetic flux density within a coil winding array. Due to the vector superposition of the magnetic fields and magnetic flux from a plurality of magnets, a nearly four-fold increase in magnetic flux density is achieved over conventional electromagnetic generator designs with a potential sixteen-fold increase in power generating capacity. As a regenerative shock absorber, the disclosed device is capable of converting parasitic displacement motion and vibrations encountered under normal urban driving conditions to a useful electrical energy for powering vehicles and accessories or charging batteries in electric and fossil fuel powered vehicles. The disclosed device is capable of high power generation capacity and energy conversion efficiency with minimal weight penalty for improved fuel efficiency.

Hybrid vehicle and method of controlling hybrid vehicle

Abstract: In a hybrid vehicle of the present invention, an engine EG is subjected to feedback control to attain a target revolving speed NE*. In the case of malfunction of an inverter P 1 for a generator GN, operation of the inverter P 1 is stopped. When the generator GN is driven to rotate at a predetermined rotational speed, a counter electromotive force arises in a multiphase phase coil of the generator GN. When a motor MG is connected to the generator GN as a loading, electric current runs via a protection diode of the inverter P 1 to implement power generation by the generator GN. The electric power generated by the generator GN is directly consumed by the motor MG. This arrangement enables the quantity of power generation to balance the quantity of consumption. Here the revolving speed of the engine EG is varied according to the loading applied to the vehicle. The arrangement of the present invention thus enables the amount of electric power generated by one of the generator GN and the motor MG to balance the amount of electric power consumed by the other of the generator GN and the motor MG, thus attaining a drive of the hybrid vehicle without using a secondary battery.

Power quality issues in a hybrid power system

Abstract: We analyzed a power system network, which consisted of two types of power generation: wind turbine generation and diesel generation. The power quality and the interaction of diesel generation, the wind turbine, and the local load were the subjects of investigation. From an energy-production point of view, it is desirable to have as much wind energy production as possible in order to save fuel consumption of the diesel engines and to reduce the level of pollution. From the customer point of view, it is desirable to have good power quality at the receiving end. The purpose of this paper is to show the impact of wind power plant in the entire system. Also, we discuss how the startup of the wind turbine and the transient condition during load changes affects the voltage and frequency in the system.

A series active power filter adopting hybrid control approach

Abstract: The series active power filter (APF) is suitable for compensating a voltage type harmonics-producing load, whereas the control approach it adopts may directly influence its compensation characteristics. This paper first discusses the control approach of detecting source current in terms of the basic operation principle of a series APF, then developing a control approach of detecting load voltage. On the basis of these, a hybrid control approach is proposed. In this approach, the reference signal of the compensation voltage needed by the series APF is obtained by detecting both source current and load voltage. Thus, this approach has the advantages of the first and the second control approaches and, at the same time, it can overcome their respective drawbacks. For practical realization, the control methods of the PWM inverter in the series APF and for regulating its DC side voltage are discussed in detail. A prototype of the series APF is manufactured and corresponding experimental investigation is done. The results show that when the series APF, if adopting the hybrid control approach instead of the other two, compensates for the voltage type harmonics-producing load, its performance can be improved greatly.