Showing papers on "Photovoltaic system published in 1995"

Maximum photovoltaic power tracking: an algorithm for rapidly changing atmospheric conditions

Abstract: As the maximum power operating point (MPOP) of photovoltaic (PV) power generation systems changes with changing atmospheric conditions (e.g. solar radiation and temperature), an important consideration in the design of efficient PV systems is to track the MPOP correctly. Many maximum power tracking (MPT) techniques have been considered in the past but techniques using microprocessors with appropriate MPT algorithms are favoured because of their flexibility and compatibility with different PV arrays. Although the efficiency of these MPT algorithms is usually high, it drops noticeably in cases of rapidly changing atmospheric conditions. The authors have developed a new MPT algorithm based on the fact that the MPOP of a PV generator can be tracked accurately by comparing the incremental and instantaneous conductances of the PV array. The work was carried out by both simulation and experiment, with results showing that the developed incremental conductance (IncCond) algorithm has successfully tracked the MPOP, even in cases of rapidly changing atmospheric conditions, and has higher efficiency than ordinary algorithms in terms of total PV energy transferred to the load.

A multilevel voltage-source inverter with separate DC sources for static VAr generation

Abstract: A new multilevel voltage-source inverter with separate DC sources is proposed for high-voltage, high-power applications, such as flexible AC transmission systems (FACTS) including static VAr generation (SVG), power-line conditioning, series compensation, phase shifting, voltage balancing, fuel cell, and photovoltaic utility systems interfacing, etc. The new M-level inverter consists of (M-1)/2 single-phase full bridges in which each bridge has its own separate DC source. This inverter can generate almost sinusoidal waveform voltage with only one time switching per cycle as the number of levels increases. It can solve the size-and-weight problems of conventional transformer-based multipulse inverters and the component-counts problems of multilevel diode-clamp and flying-capacitor inverters. To demonstrate the superiority of the new inverter, an SVG system using the new inverter topology is discussed through analysis, simulation, and experiment.

Multilevel cascade voltage source inverter with seperate DC sources

Abstract: A multilevel cascade voltage source inverter having separate DC sources is described herein. This inverter is applicable to high voltage, high power applications such as flexible AC transmission systems (FACTS) including static VAR generation (SVG), power line conditioning, series compensation, phase shifting and voltage balancing and fuel cell and photovoltaic utility interface systems. The M-level inverter consists of at least one phase wherein each phase has a plurality of full bridge inverters equipped with an independent DC source. This inverter develops a near sinusoidal approximation voltage waveform with only one switching per cycle as the number of levels, M, is increased. The inverter may have either single-phase or multi-phase embodiments connected in either wye or delta configurations.

Identification of optimal operating point of PV modules using neural network for real time maximum power tracking control

Abstract: This paper presents an application of a neural network for the identification of the optimal operating point of PV modules for the real time maximum power tracking control. The output power from the modules depends on the environmental factors such as insolation, cell temperature, and so on. Therefore, accurate identification of optimal operating point and real time continuous control are required to achieve the maximum output efficiency. The proposed neural network has a quite simple structure and provides a highly accurate identification of the optimal operating point and also a highly accurate estimation of the maximum power from the PV modules. >

Photovoltaic module-site matching based on the capacity factors

Abstract: In this paper, a methodology for the selection of the optimum photovoltaic module for a specific power plant site is developed. The selection is based on the capacity factors (CF) of the available PV modules. Long term irradiance data recorded for every hour of the day for 30 years are used. These data are used to calculate the probability density function of the irradiance for different hours of a typical day in a month. The irradiance probability density function and the manufacturer's specifications on PV modules are used to calculate the capacity factors for the PV modules. The PV module with the highest average capacity factor for the specific site is the optimal and recommended PV module. In this paper, the price per installed maximum peak watt is approximately the same for different modules and hence the cost is not an issue. >

Solar concentrator for heat and electricity

Abstract: A solar concentrator for producing usable power as heat and/or electricity uses a self-steering heliostat 1502 to concentrate solar radiation 1509 onto an absorbing surface such as, or including, a solar cell array 1511 capable of absorbing power from the radiation, meanwhile removing heat (such as from long-wave infra-red radiation or resistive losses) from the surface with fluid heat transfer means 1503, 1504, then making effective use of that low-grade heat. Thus the solar cell array is kept relatively cool and a larger proportion of the solar energy incident on the reflector unit is used. The invention uses electricity 1506 from the solar cells to move a transporting fluid through a heat exchanger 1504. Excess electricity may be available for local storage or use 1510, or feeding 1512 to the power distribution grid. Applications include warming swimming pools 1501, heating hot-water supplies using excess electricity, or warming, lighting and ventilating open spaces.

Power conditioning system for a four quadrant photovoltaic array with an inverter for each array quadrant

Abstract: A photovoltaic (PV) power system having distributed square wave current DC to AC inverters integral with strings of PV cells in a PV array. The PV array is arranged into four quadrants and phase-shifted and summed AC voltages from each quadrant are further summed in a 12-phase to 3-phase transformer to produce a sinusoidal 3-phase AC voltage with a total harmonic distortion of less than 5 percent.

The value of grid-support photovoltaics in reducing distribution system losses

Abstract: Strategically sited grid-support photovoltaic (PV) power applications have been proposed to provide value (cost savings) to electric utilities experiencing transmission and distribution system overloads. These applications can potentially defer transformer and transmission line upgrades, extend equipment maintenance intervals, reduce electrical line losses, and improve distribution system reliability. This research presents and tests a method to calculate the reduction in distribution system electrical line losses. It also describes how to optimize plant size, plant location along a distribution feeder, and load transfer from an adjacent feeder. Results at Pacific Gas and Electric Company indicate that a 0.50 MW PV power plant at Kerman, California, has $37,000 in energy loss savings value over the plant's life with additional value due to capacity loss savings. These results are site specific. >

Solar energy concentrator apparatus for bifacial photovoltaic cells

Abstract: A solar energy concentrator apparatus which simultaneously focuses incident solar radiation upon both sides of a bifacial photovoltaic cell. The concentrator apparatus includes a corrugated-shaped reflector sheet and an open-grid support structure. Bifacial photovoltaic cells are held in place by the open-grid support structure and are mounted either horizontally or vertically with respect to the plane of the reflector sheet. The cells are specifically positioned so as to receive solar radiation--either directly or by reflection--at 90° angles to their surfaces. The system is designed to operate in conjunction with any one of the tracking systems currently available in the industry whereby the apparatus is maintained at a 90° angle with respect to the angle of incidence of the sun.

Fiber optic power-generation system

Abstract: A fiber optical solar power generating system provides a tower outside a structure to be supplied with solar energy and on which a multiplicity of collectors is provided. An optical fiber trunk carries the collected optical energy to the structure in which a photovoltaic and/or a light/heat transducing stack can be provided and to which light is distributed from the optical fiber trunk so that the transducers need not occupy large areas of the property.

Solar roofing system

Abstract: A photovoltaic module that serves as a shingle, tile or other building material that may be placed onto the exterior of a structure. The photovoltaic module generates a voltage when exposed to light and this voltage may be directed onto transmission lines of a power utility and/or into an external battery that may serve as a source of power for the building on which the photovoltaic shingles are laid. The practice of the present invention provides for a variety of mechanical and electrical connectors for securing together the photovoltaic modules and/or for connecting the photovoltaic modules to the exterior structure. Furthermore, the structure of the modules is such that the modules are automatically electrically connected together when laid on the building.

A novel grid interface, optimized for utility-scale applications of photovoltaic, wind-electric, and fuel-cell systems

Abstract: Utility-interactive photovoltaic, wind-electric and fuel-cell systems are being planned at sufficiently large power levels. The technical and economic feasibility of such systems partially depends on the reliability, cost, and the efficiency of their grid interface. Here, a novel interface, which takes advantage of the system conditions in a utility-scale application is presented. The paper describes the basic principle of operation and characteristics. It is shown that the Total Harmonic Distortion in the line currents meets the 5 percent limit recommended by the IEEE. 519-1992, with one-third the high frequency switch kVA ratings as compared to other topologies. Various options are discussed for utility-scale applications. Simulation results for a 25 kW unit are presented. The new conceptual circuit is validated by a prototype hardware design at the 2.2 kW power level. >

Multi-purpose solar energy conversion system

Abstract: Apparatus for converting solar energy to thermal and electrical energy including a substantially unsealed enclosure, an array of photovoltaic cells for converting solar energy to electrical energy located within the enclosure, and a plurality of interconnected heat collecting tubes located within the enclosure and disposed on the same plane as the array of photovoltaic cells for converting solar energy to thermal energy in a fluid disposed within the heat collecting tubes.

Development of an Axial Flux Permanent Magnet Brushless DC Motor for Wheel Drive in a Solar Powered Vehicle

Abstract: Fig. 1. The “Desert Rose” on the road. presented here is based on a high-performance solar vehicle, many of the issues addressed are applicable to conventional, battery powered vehicles. The paper presents a review of electric propulsion characteristics and wheeled vehicle physics with an emphasis on the solar application. A weight-power tradeoff forms the basis for the in-wheel drive design which is discussed in detail. Experimental results for a 1-kW machine verify the design concepts introduced.

Solar energy system

Abstract: The object of the prevent invention is to provide a solar energy system of simple construction capable of utilizing the photovoltaic source always at a high efficiency without being affected by environmental changes or yearly declination of photovoltaic cell, etc. A solar energy system S provided, between photovoltaic array P constructed by connecting at least two photovoltaic arrays PL, PR of identical characteristics in parallel and a lead L to which the electric energy of the photovoltaic array P is supplied, with a detecting circuit NC for detecting the operating point of the photovoltaic array P, characterized in that the detecting circuit MC is provided with current limiting elements DL, DR with different voltage drops in forward direction connected in series to each of the two photovoltaic arrays PL, PR and that the system calculates the power of the two photovoltaic arrays PL, PR by detecting the terminal voltages of the two photovoltaic arrays PL, PR by means of those current limiting elements DL, DR and detects the operating point of the photovoltaic array P from the difference of power (or differential current) between the two photovoltaic arrays PL, PR.

200 W low cost module integrated utility interface for modular photovoltaic energy systems

Abstract: This paper describes the design of a utility interface for a 200 W solar cell array. The interface comprises high frequency soft switching PWM power conversion, analog and logic control and protection circuits and an analog maximum power point tracker (MPPT). All circuits are implemented with standard components (no microcontroller) and thus facilitates integration into ASIC components at a later development stage. The design emphasis is on module integration, low cost production and compliance with standards on utility interfacing. The special requirements of utility interfacing and solar cell array utilization are described and the design of the components of the utility interface is described. The theory and design are verified with the implemented laboratory prototype, which shows excellent performance and verifies the operation of the interface.

Photovoltaic inverter with a novel cycloconverter for interconnection to a utility line

Abstract: A PV (photovoltaic) inverter is the power conversion equipment that converts DC power generated by PV cells into isolated AC power and interconnects it to a utility line. This paper describes a PV inverter with a novel cycloconverter for interconnection to a utility line. The authors developed this novel cycloconverter as a way of frequency conversion so that a small, high-frequency transformer can be used to minimize the size of the PV inverter. They manufactured a 3 kW PV inverter as an experimental model with this novel cycloconverter for interconnection to a utility line. This equipment is 25% the size in volume and 17% the weight compared to previous commercial-frequency isolation type inverters. In rated operations, excellent results were obtained; the output current distortion factor was less than 5.0% and conversion efficiency was as high as 92.1%.

Energy Analysis of Solar Photovoltaic Module Production in India

Abstract: The objective of this article is to evaluate the energy consumption in solar photovoltaic (SPV) module production in India and examine its implications for large-scale introduction of SPV plants in the country. Data on energy used in SPV production were collected from existing manufacturing facilities in the country. The energy payback period turns out to be approximately 4 years. This is comparable to energy payback periods of similar modules produced internationally. However, if an ambitious program of introducing SPV power production is undertaken to contribute substantially to the power scenario in the country, an annual growth rate beyond 21% will render the program an energy sink rather than an energy source, as borne out by dynamic energy analysis. Policy implications are also discussed in light of this analysis.

Optimization of a-SiGe:H Alloy Composition for Stable Solar Cells

Abstract: The film properties and solar cell performance of amorphous SiGe:H (a-SiGe:H) samples have been systematically investigated, using constant optical gap and various compositions of hydrogen and germanium. It was found that the hydrogen content and bonding configurations play important roles in determining both the initial properties and stability. The optimum compositions were clarified for the minimum Urbach tail characteristic energy and defect density in the as-deposited film, and for the maximum conversion efficiency of the solar cells. The stability of a-SiGe single and a-Si/a-SiGe tandem solar cells becomes higher as the hydrogen content of the photovoltaic layer becomes lower. As a result, the optimum composition after light soaking shifts to the region of lower hydrogen content. Applying the above findings to the design of devices, the highest stabilized conversion efficiencies of 3.3% (initial 3.7%) under red light (λ>650 nm) for an a-SiGe single-junction solar cell and 10.6% (initial 11.6%) for an a-Si/a-SiGe tandem solar cell have been achieved (area: 1 cm2).