Showing papers on "Grid-connected photovoltaic power system published in 1997"

Low-cost industrial technologies of crystalline silicon solar cells

Abstract: Approximately 2 billion people, mainly in Third World countries, are not connected to an electric grid. The standard, centralized grid development is too expensive and time consuming to solve the energy demand problem. Therefore, there is a need for decentralized renewable energy sources. The main attractiveness of solar cells is that they generate electricity directly from sunlight and can be mounted in modular, stand-alone photovoltaic (PV) systems. Particular attention is paid in this paper to crystalline silicon solar cells, since bulk silicon solar-cell (mono and multi) modules comprise approximately 85% of all worldwide PV module shipments. Energy conversion efficiency as high as 24% has been achieved on laboratory, small-area monocrystalline silicon cells, whereas the typical efficiency of industrial crystalline silicon solar cells is in the range of 13-16%. The market price of PV modules remains for the last few years in the range of $3.5-4.5/watt peak (Wp). For the photovoltaic industry, the biggest concern is to improve the efficiency and decrease the price of the commercial PV modules. Efficiency-enhancement techniques of commercial cells are described in detail. Adaptation of many high-efficiency features to industrially fabricated solar cells. The latest study shows that increasing the PV market size toward 500 MWp/y and accounting for realistic industrial improvements can lead to a drastic PV module price reduction down to $1/Wp.

Power control apparatus for solar power generation system

Abstract: In a power control apparatus of a solar power generation system for converting power generated by a solar panel and supplying the converted power to a load, the output voltage and output current of the solar panel are sensed, and, under ordinary conditions, MPPT control is performed so that the solar cells will operate at a maximum output point. If the output power of the solar panel exceeds a predetermined power, a power conversion unit is controlled so as to raise the output voltage of the solar panel, thereby limiting the output power of the solar panel. As a result, excessive power is prevented from being output by the power control apparatus.

Apparatus for controlling a solar array power system

Abstract: A system for controlling power supplied by a solar array panel to one of either a load or a battery for optimal power consumption is disclosed. The solar array power control system of the present invention includes a power stage for directing the solar array to discharge an appropriate amount of current, a signal conditioner for receiving and conditioning voltage and current signals from the solar array and determining the signs of the time derivatives of solar array voltage and power, a processor for evaluating the signs of the time derivatives of solar array power voltage and for directing operation of either a battery current control mode or a peak power tracking mode and a high gain amplifier for directing an appropriate voltage to the power stage according to the operating mode. The signal conditioner, processor and high gain amplifier cooperate to determine whether the solar array is capable of supplying the power demanded by at least one of the battery and the load. When it has been determined that the required power level to be supplied from the solar array is within the capability of the solar array, the system commands the solar array to discharge the exact power demanded. In times when the solar array is not capable of completely satisfying the required power level, the system commands the solar array to discharge the maximum power available under the present conditions.

Control of DC/DC converters for solar energy system with maximum power tracking

Abstract: Solar power converters were used to convert the electrical energy from solar arrays to a stable and reliable power source. The object of this paper is to analyze and design DC/DC power converters of different types in a PV power system to investigate the performance of such converters. A simple method which combines discrete time control and a PI compensator is used to track the maximum power points (MPPs) of the solar array. The system is kept to operate close to the MPPs, thus the maximum possible power transfer from the solar array is achieved. The implementation of the proposed power converter system was based on a digital signal processor. Experimental tests were carried out for buck, boost and buck-boost power converters using a simple maximum power point tracking algorithm. The efficiencies for the system with different power converters are compared and presented.

Apparatus and method for providing supplemental alternating current from a solar cell array

Abstract: A novel solar inverter circuit is used to connect a solar photovoltaic (PV) array with an alternating current (AC) voltage source to convert direct current (DC) power from the PV array to AC power. The solar inverter circuit employs the current-voltage (I-V) characteristic of the PV or solar cell, and an H-Bridge circuit with gate controller. The gate controller synchronizes the H-bridge with the AC voltage source. The PV array and the solar inverter circuit can plug directly into a residential AC plug and provides electrical power as a supplementary AC supply. Electrical energy required by the home appliances is supplied by the municipal AC line and solar energy concurrently. Advantages of the solar inverter circuit of the present invention include the flexibility of using the solar inverter circuit with any number of solar cell panels through the implementation of an impedance transformer, and the implementation of an additional, optional output for DC battery charging.

Power flow of photovoltaic system using buck-boost PWM power inverter

Abstract: This paper presents a buck-boost PWM power inverter and its application for residential photovoltaic power systems. The PWM power inverter is realized by combining two sets of high frequency buck-boost choppers and by making them operate in the discontinuous conduction mode. A PV power system with the power inverter has the following advantages: (1) the power generated by the photovoltaic array can be transferred to the load and the utility line under any array voltage; (2) isolation between the photovoltaic array and the utility line is performed by a small high frequency reactor operating as energy storage element; (3) unity power factor operation is provided; (4) there is no need of a reactor for interconnection with the utility line; and (5) so the system configuration is very simple. The input-output characteristics of the system are analyzed. As a result, the ripple component of the array current and the power flow between the interface and the utility line are derived and verified experimentally.

Photovoltaic system reliability

Abstract: This paper discusses the reliability of photovoltaic projects including SMUD's PV Pioneer project, various projects monitored by Ascension Technology, and the Colorado Parks project. System times-to-failure range from 1 to 16 years, and maintenance costs range from 1 to 16 cents per kilowatt-hour. Factors contributing to the reliability of these systems are discussed, and practices are recommended that can be applied to future projects. This paper also discusses the methodology used to collect and analyze PV system reliability data.

SunSine300, utility interactive AC module anti-islanding test results

Abstract: Test results are presented for the SunSine300 AC photovoltaic module's anti-islanding protection. These tests were conducted on a single SunSine300 AC module inverter under controlled laboratory conditions. The various passive and active anti-islanding methods used in the SunSine300 are discussed. Other forms of anti-islanding protection are also discussed. Data is presented to show how tightly matched the PV and load must be for special islanding detection methods to be needed. The data also shows how effectively our proprietary Zebra method of anti-islanding performs. In all of the trip tests conducted, the SunSine300 never exhibited run-on. In this paper, run-on is defined as operation into an islanded load longer than 2 seconds.

Development and testing of a 20-kW grid interactive photovoltaic power conditioning system in Western Australia

Abstract: A prototype current-controlled power conditioning system has been developed and tested on a weak rural feeder line at Kalbarri, about 600 km northwest of Perth in Western Australia. This system sources 20 kW of power from a photovoltaic array with maximum power point tracking control. In addition, it provides voltage support for the power grid at Kalbarri by varying its reactive power in response to the measured voltage at the point of connection. This paper describes the development and testing of the power conditioning system.

Advanced photovoltaic inverter with additional active power line conditioning capability

Abstract: This paper presents an advanced photovoltaic inverter which can deliver the maximum power from photovoltaic arrays to the utility grid for all sunlight conditions, as well as simultaneously providing power conditioning to suppress power line distortions. A new control strategy is developed to maximize the inverter output from the photovoltaic array and to suppress current harmonics in the power line using a single inverter configuration. A new control strategy and experimental results are given.

Solar thermal power

Abstract: Solar thermal power is produced by three types of concentrating systems, which utilize parabolic troughs, dishes, and heliostats as the solar concentrators. These systems are at various levels of development and commercialization in the United States and in Europe. The U.S. Industry is currently developing these systems for export at the end of this century and at the beginning of the next one for remote power, village electrification, and grid-connected power. U.S. utilities are not forecasting to need power generation capacity until the middle of the first decade of the 21{sup st} century. At that time, solar thermal electric power systems should be cost competitive with conventional power generation in some unique U.S. markets. In this paper, the authors describe the current status of the development of trough electric, dish/engine, and power tower solar generation systems. 46 refs., 20 figs., 8 tabs.

A hybrid wind-photovoltaic power supply for a telecommunication system

Abstract: This paper describes a stand-alone hybrid wind-photovoltaic power plant for a remote telecommunication system located on the Black Sea Coast. First, the wind and solar potential of the site and also the load profile were assessed. It is shown that the two energy sources are complementary, so it is possible to have a better energy utilization factor. As a consequence, the storage unit resulting is smaller than in the case of individual wind or PV systems. The power system consists of a 1500 W wind turbine and a 900 W photovoltaic array. Since solar and wind energy converters are finite sources of power, the energy capture efficiency is improved by using a power conditioner (which includes a peak-power tracker and a battery charger). A 220 V/50 Hz inverter was used. The power system was tested and monitored for one year under real conditions in the authors' test facility, also located on the Black Sea Coast.

Performance of a grid connected residential photovoltaic system with energy storage

Abstract: In 1995, Salt River Project (SRP), a public power utility located in Phoenix, Arizona, USA, collaborated with the Electric Power Research Institute (EPRI) and Sandia National Laboratories (Sandia) to initiate a research project to evaluate the feasibility of using a photovoltaic (PV) power system with battery energy storage to match PV output with residential customer peak energy demand periods. The PV power system, a 2.4 kW PV array with 25.2 kWh of energy storage, was designed and installed by the Southwest Technology Development Institute (SWTDI) at an SRP-owned facility, known as the Chandler Research House during August 1995. This paper presents an overview of the system design, operation and performance.

Solar generator for generating direct current power by sunlight and outputting generated power to commercial AC power source

Abstract: An air conditioner equipped with a solar generator is disclosed. The solar generator is capable of converting the DC power generated by a solar cell into the AC power whose voltage and frequency correspond to that of the commercial power source. The electrical power generated by the solar cell and the electrical power consumed by the air conditioner are monitored and may be displayed. The DC power generated by the solar cell is used directly by the air conditioner or used indirectly as the commercial power source by merging the converted AC power to the commercial power source. Further, the converted AC power may be selectively merged to the commercial power source depending on the various states of the air conditioner, and the air conditioning operations may be regulated depending on the electrical power generated by the solar cell.

Modelling and optimal controllers design for a stand-alone photovoltaic-diesel generating unit

Abstract: This papr presents a dynamic model and optiml controllers design for a stand-alone photovoltaicdiesel generating unit. The controller objectives are to limit the continual wariations on load bus voltage and frequency as vel1 as extracting the nmximma photovoltaic generator power. The dynamic behaviour of the closed-loop system folloving connnon disturbances such as load changes, solar insolation mriations and three-phase short circuit is investigated. The use of Photovoltaic (PV) generators in remote areas can pose a problem because solar electricity is generated only during sunny day time hours, while most applications need electricity to be available during cloudy periods and at night. The resolution of this problem Is to use of another back up sources such as a battery enerqy storage and diesel generators t11. The PV/diesel generating unit considered in this paper consists of a PV generator connected to a synchronous generator driven by a diesel engine through a 3-phase line commutated inverter. The tvo generators supply an isolated lmd. Figure 1 shovs the schematic diagram of the PV/diesel generating unit. The PV generator and the 3-phase line commutated inverter vere simulated by nonlinear equatjons !2, 31. These equatiors veze combined vith the nonlinear differential equations of the diesel generator to form the complete 7th order model of PV/diesel unit [41. To simplify the controller design, the reduced 3rd-order linearized model was derived from the complete model by neglecting the transfent of the fast mode state variables. The reduced order mdel form is k=Ax+Bu+rd where

System-interconnected generator for converting solar energy to AC power

Abstract: A system-interconnected generator permits effective use of surplus power generated by a solar battery for operating electric equipment such as an air conditioner. The system-interconnected generator having a power converter for converting solar energy to AC power and supplying the AC power to a system on a commercial AC power supply so as to make it possible to sell the power to the system is equipped with: a storing section for storing an integrated value of the AC power which has been converted from solar energy by the power converter; a correcting section for subtracting a value of power, which is consumed by particular electric equipment receiving power supplied from the system, from the integrated value stored in the storing section; and a demanding section for enabling a demanding function of the electric equipment when the integrated value stored in the storing section becomes smaller than a predetermined value.

Grid-independent power supply for repeaters in mobile radio networks using photovoltaic/thermoelectric hybrid systems

Abstract: At Fraunhofer ISE, a photovoltaic/thermoelectric hybrid system has been developed as a power supply for repeaters (e.g. mobile telephone repeaters) and integrated into a newly constructed repeater station. A modified thermoelectric generator from the Canadian Global Thermoelectric company has been used as the auxiliary generator. A microprocessor-controlled energy management system (EMS) allows fully automatic operation with minimal use of fossil fuels and appropriate battery operation management. As the auxiliary power supply can support the PV generator in supplying power to the load during periods with little sunlight, a very reliable power supply is achieved. Further, the dimensions of the PV generator and the battery capacity can be reduced without affecting the supply reliability. In Central Europe, for instance, the size of the PV generator can be reduced to a third of that needed for an exclusively PV system, if only 10% of the annual demand is met by the auxiliary generator. This allows a compact construction of the photovoltaic hybrid system and helps the numerous requirements on isolated telecommunications facilities to be fulfilled.

Electric tree, leaf-shaped solar battery panel generation and solar tracking device

Abstract: PROBLEM TO BE SOLVED: To fix leaf-shaped solar battery panels on the edge parts of the branches and twigs of an electric tree, which is an artificial tree, and moreover, to mount movable type leaf-shaped solar battery panels provided in a solar tracking device at required places, where a large number of the leave-shaped solar battery panels are fixed, around the electric tree and to provide clean energy generated by central generation of the sunlight. SOLUTION: A large number of leaves of leave-shaped solar battery panels are fixed on an electric tree. The sizes of the solar battery panels 2 are also changed according to the kinds of the sizes of the various leaf shapes of the leaf-shaped solar battery panels 2 and the kinds of the sizes of the various leaf shapes of movable type leaf-shaped solar battery panels of a solar tracking device and a generation output also comes to change. Moreover, the solar battery panels are integrally constituted with the leaf-shaped surface, which are made of synthetic resin or a light metal, to be fixed. COPYRIGHT: (C)1999,JPO

Photovoltaics as a long-term solution to power outages. Case study: The great 1996 WSCC power outage

Abstract: The Western System Coordinating Council (WSCC) experienced two major power outages during the summer of 1996. Both outages occurred during extreme heat waves and virtually cloud-free conditions. Focusing on the August 10 outage, the authors present evidence that dispersed photovoltaic power generation has the potential to mitigate the effects of massive power outages. The authors have previously shown that PV output is highly correlated with heat-wave-driven loads (A/C driven loads). The following analysis indicates that the circumstances of the August 10 event are no exception. PV availability was at a maximum and the high loads on the system were directly attributed to the heat wave. The paper presents PV deployment strategies that would serve to mitigate the effects of the outage, initially from the perspective of direct consumer relief. However, as dispersed PV generation saturates the electrical system over the long term, the high load demand match relief could prevent the cascading trips of large generating plants, thereby providing system relief.

Solar power generation and charging system

Abstract: PROBLEM TO BE SOLVED: To provide a system, in which a secondary battery is charged stably in a mass-production manner by a method wherein sunlight is used to the full when it can be used and a commercial power supply is used, when the sunlight cannot be used. SOLUTION: A system is provided with a solar cell 8, with a DC-DC converter 33, by which a voltage generated by the solar cell 8 is converted into a prescribed voltage, with an AC-DC converter 22 through which the AC voltage of a commercial power supply 1 is converted into a DC voltage, with a secondary battery 9 for power failure, with a secondary-battery charger 23 by which the secondary battery 9 is charged, with a changeover control circuit 21 through which the solar cell 8 is connected to the secondary-battery charger 23 when the solar cell 8 generates power and by which the AC-DC converter 22 is connected to the secondary-battery charger 23, when the solar cell 8 does not generate power and with an inverter 10 with which the DC power of the secondary battery 9 for power failure is converted into the AC voltage of the commercial power supply 1 in the power failure of the commercial power supply 1.

Advanced space photovoltaic technology: applications to telecommunication systems

Abstract: For nearly two decades, most NASA and commercial space power systems were typically in the 1 to 2 kilowatt range. Now, however, the demand for more power per unit mass and area of satellite solar arrays is rising dramatically, driven entirely by the telecommunications industry and some US Military applications. Commercial satellites with power system capabilities exceeding 10 kilowatts have already been launched, and hundreds more are in the planning stages. At the same time, however, NASA mission programs are striving for smaller, more specialized spacecraft which can still achieve complex mission objectives, but at lower total mission cost. These apparently divergent sets of requirements are surprisingly synergistic: both place a high priority on developing power systems with high efficiency, low mass and long life in the space environment. Key elements of the near term NASA advanced technology program include (1) development and eventual commercial production of multibandgap (MBG) solar cells with air mass zero (AM0) efficiencies approaching 30%; and (2) commercial availability of a night qualified concentrator solar array with superior lifetime and lower cost than conventional planar solar arrays. For the far term, the program is focussed on development of ultra lightweight, thin film solar arrays. The potential impact of all these technologies on telecommunication satellites is discussed.

Building load analysis of dispatchable peak-shaving photovoltaic systems: A regional analysis of technical and economic potential

Abstract: Roof-mounted photovoltaic (PV) systems, including a modest amount of battery storage, can provide firm peak-demand reductions for commercial buildings. The cost-effectiveness of a dispatchable peak-shaving PV system is determined by the demand reduction, which is a function of the solar resource and the building`s load profile, and electric utility rates. The analysis presented in this paper identifies building types and regions, from a database of eleven electric utility service territories distributed throughout the country, for which the economics of dispatchable peak-shaving PV are most favorable.

Maximum power point tracking charge controllers for telecom applications-analysis and economics

Abstract: Simple charge controllers connect photovoltaic modules directly to the battery bank resulting in a significant power loss if the battery bank voltage differs greatly from the PV Maximum Power Point (MPP) voltage. Modeling work at AES has shown that DC-DC converter type MPP tracking charge controllers can deliver more than 30% more energy from PV modules to the battery when the PV modules are cool and the battery state of charge is low-this is typically both the worst case condition (i.e., winter) and also the design condition that determines the PV array size. Economic modeling, based on typical telecom system installed costs shows benefits of more than $3/Wp for MPPT over conventional charge controllers in this application-a value that greatly exceeds the additional cost of the DC-DC converter.

Evaluation of PV module designs at irregular operation conditions

Abstract: Building integrated PV systems are interesting due to a double use of PV modules as facade or roof elements though PV facades suffer often from the effect of partial shading. Usual strategies apply bypass diodes for solar cell protection. This however requires unwelcome and costly centre taps of the strings to a junction box at large area PV facade modules. The choice of a suitable protection scheme demands information regarding the effects of irregular operating conditions like shading. This contribution shows the influence of PV module design regarding thermal effects at partial shading without bypass diodes. Current module designs in glass/glass technique do not allow renunciation of bypass diodes. Modified designs regarding cell connectors or rear back covers could make it possible to work without bypass diodes and with that to simplify electrical module layout with such "Hot Spot resistant" facade modules.