Showing papers on "Stand-alone power system published in 2002"

A techno-economic comparison of power production by biomass fast pyrolysis with gasification and combustion

Abstract: This paper presents an assessment of the technical and economic performance of thermal processes to generate electricity from a wood chip feedstock by combustion, gasification and fast pyrolysis. The scope of the work begins with the delivery of a wood chip feedstock at a conversion plant and ends with the supply of electricity to the grid, incorporating wood chip preparation, thermal conversion, and electricity generation in dual fuel diesel engines. Net generating capacities of 1–20 MWe are evaluated. The techno-economic assessment is achieved through the development of a suite of models that are combined to give cost and performance data for the integrated system. The models include feed pretreatment, combustion, atmospheric and pressure gasification, fast pyrolysis with pyrolysis liquid storage and transport (an optional step in de-coupled systems) and diesel engine or turbine power generation. The models calculate system efficiencies, capital costs and production costs. An identical methodology is applied in the development of all the models so that all of the results are directly comparable. The electricity production costs have been calculated for 10th plant systems, indicating the costs that are achievable in the medium term after the high initial costs associated with novel technologies have reduced. The costs converge at the larger scale with the mean electricity price paid in the EU by a large consumer, and there is therefore potential for fast pyrolysis and diesel engine systems to sell electricity directly to large consumers or for on-site generation. However, competition will be fierce at all capacities since electricity production costs vary only slightly between the four biomass to electricity systems that are evaluated. Systems de-coupling is one way that the fast pyrolysis and diesel engine system can distinguish itself from the other conversion technologies. Evaluations in this work show that situations requiring several remote generators are much better served by a large fast pyrolysis plant that supplies fuel to de-coupled diesel engines than by constructing an entire close-coupled system at each generating site. Another advantage of de-coupling is that the fast pyrolysis conversion step and the diesel engine generation step can operate independently, with intermediate storage of the fast pyrolysis liquid fuel, increasing overall reliability. Peak load or seasonal power requirements would also benefit from de-coupling since a small fast pyrolysis plant could operate continuously to produce fuel that is stored for use in the engine on demand. Current electricity production costs for a fast pyrolysis and diesel engine system are 0.091/kWh at 1 MWe when learning effects are included. These systems are handicapped by the typical characteristics of a novel technology: high capital cost, high labour, and low reliability. As such the more established combustion and steam cycle produces lower cost electricity under current conditions. The fast pyrolysis and diesel engine system is a low capital cost option but it also suffers from relatively low system efficiency particularly at high capacities. This low efficiency is the result of a low conversion efficiency of feed energy into the pyrolysis liquid, because of the energy in the char by-product. A sensitivity analysis has highlighted the high impact on electricity production costs of the fast pyrolysis liquids yield. The liquids yield should be set realistically during design, and it should be maintained in practice by careful attention to plant operation and feed quality. Another problem is the high power consumption during feedstock grinding. Efficiencies may be enhanced in ablative fast pyrolysis which can tolerate a chipped feedstock. This has yet to be demonstrated at commercial scale. In summary, the fast pyrolysis and diesel engine system has great potential to generate electricity at a profit in the long term, and at a lower cost than any other biomass to electricity system at small scale. This future viability can only be achieved through the construction of early plant that could, in the short term, be more expensive than the combustion alternative. Profitability in the short term can best be achieved by exploiting niches in the market place and specific features of fast pyrolysis. These include: •countries or regions with fiscal incentives for renewable energy such as premium electricity prices or capital grants; •locations with high electricity prices so that electricity can be sold direct to large consumers or generated on-site by companies who wish to reduce their consumption from the grid; •waste disposal opportunities where feedstocks can attract a gate fee rather than incur a cost; •the ability to store fast pyrolysis liquids as a buffer against shutdowns or as a fuel for peak-load generating plant; •de-coupling opportunities where a large, single pyrolysis plant supplies fuel to several small and remote generators; •small-scale combined heat and power opportunities; •sales of the excess char, although a market has yet to be established for this by-product; and •potential co-production of speciality chemicals and fuel for power generation in fast pyrolysis systems.

Feasibility of a DC network for commercial facilities

Abstract: This paper analyzes the feasibility of direct current for the supply of offices and commercial facilities. This is done by analyzing a case study, i.e. the supply to the Department of Electric Power Engineering, Chalmers University of Technology, Gothenburg, Sweden. Voltage drop calculations have been carried out for different voltage levels. A backup system for reliable power supply is designed based on commercially available batteries. Finally, an economic evaluation of AC versus DC is performed and protection of the proposed system is briefly addressed.

Photovoltaic power generation system with storage batteries

Abstract: An object of the present invention is to provide a system capable of reducing optimally peak demand for power by using small capacity storage batteries. The present invention was made to provide a photovoltaic power generation system which links with a utility power system, feeds electric power generated by a solar cell device to an inverter in order to convert the electric power into alternating current, and supplies the alternating current to a power consumption section. The photovoltaic power generation system comprises storage batteries for storing electric power and a switch control device for switching to output electric power from the solar cell device to the storage batteries or the inverter. Also the photovoltaic power generation system controls discharge of the electric power stored in the storage batteries with reference to a specific period of high power demand represented by a fluctuation curve of power demand, and supplies the electric power from the storage batteries along with generation power from the solar cell device to the inverter.

Aggregation of distributed generation resources

Abstract: A method and system are associated with distributed generation of electric power. Power demand data of at least one electric power consumer is monitored over time. Power supply data of a regional power distribution system is also monitored over time. The power demand data and the power supply data are analyzed to coordinate control of at least one distributed generation system associated with the electric power consumer.

Energy storage device for loads having variable power rates

Abstract: An electrical energy storage device for storing electrical energy and supplying the electrical energy to a driving motor at different power levels is disclosed. The electrical storage device has an energy battery connected to a power battery. The energy battery has a higher energy density than the power battery. However, the power battery can provide electrical power to the electrical motor at different power rates, thereby ensuring that the motor has sufficient power and current when needed. The power battery is continuously recharged by the energy storage battery. In this way, the power battery temporarily stores electrical energy received from the energy battery and provides the electrical energy at the different power rates as required by the motor. The energy storage device can be releasably connected to an external power source in order to recharge both batteries. Both batteries can be recharged independently to optimize the recharging and lifetime characteristics of the batteries.

Wind powered hydroelectric power plant and method of operation thereof

Abstract: A hydroelectric power plant uses a plurality of windmills connected to compressed air generators to produce pressurized air. Pressurized air is used to drive water through a turbine to produce electrical power. The water is recycled and the power plant includes reserve pressurized air tanks to allow the plant to continue to operate when the wind levels are not sufficient to produce high pressure air. The power plant is designed to be operated on a continuous basis based on wind power. When the wind subsides and the reserve capacity has been exhausted, electricity can be drawn from the local utility supplier. When excess power is generated by the power plant, electricity from the power plant can be added to the grid of the local electricity supplier.

Modelling and Analysing Impacts of Wind Power on Transient Stability of Power Systems

Abstract: This paper considers the impact of increasingly large numbers of wind turbine generators on the stability of power grid networks. Most modern wind turbines do not have conventional grid coupled synchronous generators, as is the case with most other technologies for electrical power generation. Instead, squirrel cage induction generators are used, or generators that are grid coupled with power electronic converters. Consequently, wind turbines interact with the power system in a way that differs from conventional generators. In the paper, the interaction between wind turbines and the power system is investigated using simulations of a widely used representative dynamics test system in which a high wind power penetration is assumed. It is concluded that the impact of wind power on power system transient stability varies much when either constant or variable speed wind turbines are used.

Online-monitoring and prediction of wind power in german transmission system operation centres

Abstract: Normally, electrical systems are able to absorb a certain amount of unregulated and fluctuating production from renewable energy sources (RES), especially wind power. The electrical systems must be designed and operated in order to accommodate the changes in the consumption, a trip of a conventional production unit or a fault on a transmission line. For systems with a high penetration of wind power, the most significant difference is that in addition to forecasts of the consumption, predictions are also to be prepared of the unregulated wind power production. Such predictions are necessary both for the TSO and for the players on the power market that owns significant wind power production sites as well. At the end of 2002, more than 13,500 Wind Turbines (WTs) with an installed capacity of 11,850 MW generated approx. 17,300 GWh and supplied about 3.6 % of the German electricity consumption in 2002 [1]. Wind-generated power now provides a noticeable percentage of the total electrical power consumed, and also exceeds the base load on the network in some utility areas. This indicates that wind is becoming a significant factor in electricity supply, and in balancing consumer demand with power production. Not least in the grid areas of the German TSO’s E.ON Netz and Vattenfall Europe Transmission GmbH more than 100 % of the electricity consumption at times has been covered by wind power. A well-established and scientific analysis of the time response of wind power as well as the accurate determination of the current and expected wind power will lead to an improved integration of wind generation into the electrical power system and reduce CO2 emissions sustainable. In frame of governmental and EC funded projects and in co-operation with the German TSO’s E.ON Netz, RWE Net and Vattenfall Europe Transmission, ISET developed a new planning tool to support large scale wind power integration into the electrical energy supply system – the Wind Power Management System WPMS. WPMS provides the current level of wind power generation (onlinemonitoring) as well as the short-term prediction from 1 hour up to 72 hours.

Integration of wind power in the power system

Abstract: Wind power is going through a very rapid development. It is the fastest growing power source in the world, the technology is being developed rapidly and wind power is supplying significant shares of the energy in large regions. The integration of wind power in the power system is therefore now an issue in order to optimise the utilisation of the resource and in order to continue the high rate of installation of generating capacity, which is necessary in order to achieve the goals of sustainability and security of supply. This development of the wind power from just being a negative load to have power plant like features of course also bring with it large challenges. These challenges include connection of wind farms to weak grids, securing power quality, reduction or elimination of power fluctuations, prediction of power output and changes in operating strategies of conventional power plants. Many of these challenges can be faced by the application of power electronics in wind turbines or in wind farms, but many of them will also require other technologies to be developed such as fuel cells and energy storage. The key issues for success is the utilisation of power electronics and information technology. The paper highlights, through examples (from Denmark and from finalised and current research work), the challenges and present the current research direction.

Energy storage device and loads having variable power rates

Abstract: An electrical energy storage device for storing electrical energy and supplying the electrical energy to a driving motor at different power levels is disclosed. The electrical storage device has an energy battery connected to a power battery. The energy battery has a higher energy density than the power battery. However, the power battery can provide electrical power to the electrical motor at different power rates, thereby ensuring that the motor has sufficient power and current when needed. The power battery is continuously recharged by the energy storage battery. In this way, the power battery temporarily stores electrical energy received from the energy battery and provides the electrical energy at the different power rates as required by the motor. The energy storage device can be releasably connected to an external power source in order to recharge both batteries. Both batteries can be recharged independently to optimize the recharging and lifetime characteristics of the batteries.

Flyback type inverter for small scale photovoltaic power system

Abstract: This paper presents a newly developed flyback type inverter for a small scale (low power) photovoltaic power system and a maximum power point tracking (MPPT) controller without a current sensor for this system. As the small scale photovoltaic power systems are used in parallel, cost reduction with high reliability is strongly required. In the proposed inverter, the current is controlled with open loop, and then the generated power of photovoltaic array is calculated by an equation using the voltage of the photovoltaic array. Therefore, the system can obtain the power by detecting only the voltage of the photovoltaic array. As a result, we may obtain the performance of the MPPT without a current sensor as well as with a current sensor.

Coordinating Overcurrent Protection and Voltage Sag in Distributed Generation Systems

Abstract: S ensitive equipment protection against voltage sags can be given for overcurrent protective devices, provided that careful coordination has been carried out. The inclusion of distributed resources (DR) in a distribution system creates the possibility of an important change in the coordination procedure. Overcurrent protection and voltage sag coordination studies are based on the upstream impedance of the point of common coupling (PCC) or system impedance (Z1). Voltage sag magnitude is obtained taking into account the voltage drop across (ZI). Sag duration depends on the operating time of the overcurrent protective device. The normal coordination procedure is obtained by comparing the sensitive equipment (SE) dropout curve with the time-voltage characteristic (TVC) of the protective device. TVC is obtained from the time-current characteristic using (ZI) as the the conversion factor. Under normal system conditions, (Zi) is approximately constant, but, in the case of distributed generation (DG), this impedance can change from a low value (utility plus distributed generators) to a high value when the nonutility generators are the only supply (emergency). The new scenario implies that the protective device TVC is changed into a zone that modifies previous methodologies and increases the SE dropout susceptibility. The new situation should be considered, since SE will be kept operating under emergency conditions. An example using fuses as protective device is illustrated in this article.

System and method for electric power network management

Abstract: PROBLEM TO BE SOLVED: To implement an electric power network management system wherein an electric power network which is supplied with generated output from a plurality of natural energy generating sets (e.g. photovoltaic power generator, wind turbine generator) is stabilized. SOLUTION: The controller 15 for each natural energy generator system 1 predicts the electricity generated for an expected date of power generation based on weather information for the expected date of power generation according to weather forecasting or the present season and predetermined electricity generated information. In addition, the controller 15 predicts the power consumption of a load 14 for the expected date of power generation based on the weather information, present season, or the expected data of power generation or its day of the week and predetermined power consumption information. An electric power network management apparatus 3 determines the amount of power supply of each natural energy generator system 1 based on the predicted electricity generated and power consumption, so that the sum of the amounts of power supply to the electric power network 2 becomes constant in the expected date of power generation. COPYRIGHT: (C)2004,JPO

Multi-agent based automatic generation control of isolated stand alone power system

Abstract: This paper presents a new automatic generation control (AGC) scheme based on a multi-agent system through computer networks for a small sized stand alone power system with dispersed power sources such as photo-voltaic unit, wind turbine unit, and diesel unit together with a small sized energy capacitor system (ECS) for the energy storage. The AGC performance is highly improved through the proposed AGC scheme even in the existence of communication delay time.

Fuel cell apparatus and method of controlling fuel cell apparatus

Abstract: A fuel cell apparatus includes a fuel cell connected directly to a load. An electricity accumulation circuit including an electricity accumulator is connected in parallel to the fuel cell. The electricity accumulator supplies electric power to the load when electric power supplied by the fuel cell is less than electric power that the load requires. The electricity accumulator is charged by regenerative power generated at the load and electric power output from the fuel cell. The fuel cell outputs electric power within a predetermined range.

Development of a measurement system for power quantities in electrical energy distribution systems

Abstract: The design of an experimental flexible energy measurement system consisting of a DSP, sensor and communication units is treated. This system is intended to be used in modern electricity distribution networks, characterized by multiple suppliers in a deregulated market, bi-directional energy flows due to distributed generation and a diversified demand for the quality of electricity delivery. Various system aspects concerning signal processing, communication and dependability are discussed Examples of the use of such devices are included.

Evaluation and effective management of nontechnical losses in electrical power networks

Abstract: Market-driven power economies and deregulated electricity industry environments have stimulated the minimisation of technical and nontechnical losses (NTL) even though they do not constitute major operational or quality of supply problems. Their negative impact on the economics of utility operations is often passed down as costs to consumers. NTL need to be addressed to determine the overall performance of power networks, as these losses are expected to be more dominant at the sub-transmission (132 kV-33 kV) and reticulation (22 kV and 11 kV) levels of the electricity supply industry value chain. In some national grid operations, NTL are estimated to account for up to 30% in revenue losses to electric utilities, and overhead expenditure in added maintenance costs. This paper discusses a method for NTL evaluation and an effective management approach to loss minimisation and revenue collection.

Method for operating power source system and power source system comprising secondary battery

Abstract: A method for operating a power source system and a power source system which enable the efficient operation of a power generation facility and for cutting down the operation time. A method for operating a power source system wherein a secondary battery is connected between a power generation facility and a load comprises the step of operating the power generation facility at a constant output. A diesel generator or the like is used for the power generation facility. The continuance of operating the power generation facility at a rated output enhances its operation efficiency. A power is supplied according to demands by charging the secondary battery when an extra power occurs by the operation of the power generation facility, and by discharging the Redox flow battery when a shortage occurs.

The control strategies for photovoltaic regulators applied to stand-alone systems

Abstract: This paper presents the study of the control strategies enclosed in photovoltaic charge control, including maximum power point trackers (MPPTs) It was simulated and evaluated using simulating tool Simulink/spl reg/ It is supposed to be integrated on a photovoltaic stand-alone systems where it is very important to maximize the efficiency of its power source: the array of photovoltaics panels

Controlling energy supply of mobile device with electric drive motor(s) and hybrid energy supply system involves deriving difference between fuel cell system and storage battery power components

Abstract: The method involves processing power demand, mode selection, fuel cell current and voltage sensor and mobile device speed signals to determine power components from the fuel cell and dynamic energy systems and deriving the difference between the fuel cell system power component and the desired power from storage batteries of the dynamic energy system by subjecting a direct current to direct current converter to suitable demand values. The method involves processing a power demand signal, a mode selection signal, fuel cell current and voltage sensor signals and mobile device speed signals to determine the power components from the fuel cell system (7) and dynamic energy system and deriving the difference between the power component generated by the fuel cell system with a delay according to the transfer function and the desired power from storage batteries of the dynamic energy system obtained by subjecting a direct current to direct current converter (9) to suitable demand values. An Independent claim is also included for an arrangement for controlling the energy supply of a mobile device with at least one electric drive motor and a hybrid energy supply system with a fuel cell system and a dynamic energy supply system.

CO2 emissions related to the electricity consumption in the european primary aluminium production a comparison of electricity supply approaches

Abstract: The objective of this study is to estimate the specific CO2 emissions related to the electricity consumption in the European primary aluminium production and to compare different choices of system boundaries of its electricity supply. The study covers all European aluminium smelters, except Russia and the Ukraine. The concepts of single power plant supply, contract mix, national mix and European grid mix are compared as alternative choices of system boundaries of the electricity supply. The calculations of the electricity consumption in the electrolysis are based on plant-specific information on technology, production and electricity supply. Detailed fuel and country-specific data on CO2 emissions of the relevant types of electricity generation are used with a ‘from cradle to grave’ perspective. The specific emissions calculated for Europe fall into the range of 6-7 kg CO2/kg Al depending on the choice of system boundaries.

Communication-based power management

Abstract: Communication-based power management (CBPM) is a new battery-driven system-level power management methodology. It aims at improving battery life beyond what is achievable using state-of-the-art low-power design techniques. CBPM uses the system-level communication architecture to regulate the execution of system components. Regulating execution provides the desirable system-level power profiles and improved battery efficiency.

Utilization method and receiving system for secondary battery

Abstract: PROBLEM TO BE SOLVED: To provide a secondary battery, capable of enhancing advantage of electric power charge reduction, when liberalization of power retail is real ized. SOLUTION: In the using method of a secondary battery, electric power can be selectively received from a plurality of power supply companies. A secondary battery is charged (S16) by electric power received for the selected power supply company (S2). By using electric power (S10) discharged from the secondary battery, the charge of the received electric power is paid to the selected power supply company. By using the data of respective electric power charges obtained from the plurality of power supply companies (S2), the power supply company offering the lowest electric power rate is selected to receive electricity (S4). When the electric power charge of the selected power supply company is larger than the prescribed first electric power rate (S6), the secondary battery is discharged (S10). When the electric power charge is not larger than the second electric power rate, which is lower than the first electric power rate (S12), the secondary battery is charged by the received electric power (S16). COPYRIGHT: (C)2004,JPO

Power compensation system for partially shaded PV array using electric double layer capacitors

Abstract: In this paper, the power compensation and control system for the partially shaded photovoltaic (PV) array is presented. The proposed system utilizes electric double layer capacitors (EDLCs), which has some advantages, e.g. the high density of output power, the long lifetime, compared with other energy storage devices. This system is constructed by the simple combination of EDLCs-bank and a relay. Comparing with the prevalent measures, the proposed system can realize more efficient usage of generation power from PV array. The feasibility of the system is investigated and verified from some simulation results.

Application of the extension pq theory to a mains-coupled photovoltaic system

Abstract: A mains-coupled photovoltaic system is economical because of having no storage battery. In the coupled photovoltaic system, the currents flowing from or into the power system must have no distortion. This system,must have the function supplying the appropriate reactive power at the coupling point. In other words, a coupled photovoltaic system must have the function of an active power filter. Even if the three phase voltage is unsymmetrical, these two functions must be given to the coupled photovoltaic system. In that case, the extension pq theory which the authors had previously published for the active power filter control may be used. In this paper, the authors develop the effectiveness of applying the extension pq theory to the coupled photovoltaic system.