Showing papers on "Photovoltaic system published in 1988"

Coupling network for improving conversion efficiency of photovoltaic power source

Abstract: A switching network for improving the conversion efficiency of a photovoltaic power supply comprises a variable coupling circuit for coupling an array of photovoltaic cells to a load resistance. The combined effective impedance of the network and load is varied to match the value required for maximum output power. A switching transistor (22) which connects the source module (20) to the load (30) is pulse-width modulated with a variable duty cycle determined by the control signal from the sensor circuit. A photovoltaic cell (32) similar to those comprising the photovoltaic power module (20) is used to track variations in the ambient light intensity. The open-circuit voltage of a sensor cell (32) is used to determine the proper value of duty cycle required for maximum power transfer. The output voltage of the module (20) is sampled and compared with the proper value to produce a control signal.

A feasibility study of photovoltaic-fuel cell hybrid energy system

Abstract: The concept and feasibility study results of applying fuel cells to provide operational support to photovoltaic (PV) arrays are presented. Through simulation using actual data, it is shown that it is feasible to use fuel cells in coordination with PV to meet variable loads to either utility or stand-alone applications. The dynamic response required of the fuel cell to support the hybrid operation is found to be well within the capabilities of the prototype designs that have been tested in the United States and Japan. The hybrid operation overcomes the intermittency problem inherent with PV and makes possible novel applications for the fuel cell technology. >

Solar cell arrangement

Abstract: In a solar cell arrangement comprising a plurality of solar cell elements having a photovoltaic layer around an elongate center electrode, each solar cell element as a whole forms an individual separate voltage cell with a counterelectrode. The construction may comprise different photovoltaically operative inorganic and organic materials and may assume various configurations. An electrode assembly for such a cell arrangement provides that center electrodes in wire or thread form which are disposed in parallel juxtaposed or superposed relationship are electrically connected together by way of photoactive layers encasing same. The solar cell arrangement may be produced by a continuous process of passing center electrode material through a plurality of working stations to provide the finished construction with photoactive layer structure thereon.

Photoelectrochemical solar energy conversion

Abstract: In the present paper the progress in the field of solar energy conversion for the production of electricity and storable chemical fuels during the last decade is reviewed. The current-potential behavior of regenerative photovoltaic cells are derived and related to charge transfer processes at the solid/liquid interface. Various cells are critically analyzed in view of their stability and conversion efficiency. A number of factors limiting the photovoltage are discussed in terms of a stabilization mechanism, trapping of minority carriers at the interface and the forward dark current. Concerning the production of chemical fuels the photocleavage of water and hydrogen sulfide, the reduction of carbon dioxide and the formation of ammonia is evaluated. The main emphasis is laid here on catalytic processes at semiconductor electrodes and particles. The principle function of catalysts being deposited on extended electrodes and particles are discussed in detail.

Metallization of solar cells with ink jet printing and silver metallo-organic inks

Abstract: A computer-controlled ink-jet printing system for photovoltaic metallization is proposed. Ink-jet printable MOD (metalorganic decomposition) inks of Ag, Bi, Nb, and Ti were synthesized for the photovoltaic study. Computer-controlled ink-jet-assisted metallization for photovoltaics in the low processing temperature range was studied. With a titanium/palladium thin-film underlayer and the multilayer printing method, satisfactory cells for 8.08% average without AR coating were obtained. The effects of thermal processes on the solar cells were investigated. It was observed that appropriate thermal processes could improve the contact resistance and the efficiency of the solar cells, but excess thermal processes would destroy the solar cells. >

Photovoltaic array with two-axis power maximization tracking

Abstract: A control system for maximizing the power supplied by an array of solar cells senses the current and voltage produced and multiplies these to determine the instantaneous power. The array is tilted slightly in a first direction and the effect on the instantaneous power is noted. If an increase in power was produced, a further movement in the same direction is executed; but if the first movement produced a reduction in power, a movement in the opposite direction is executed. The process continues until no increase in power is obtained in either direction. Thereafter, the same process is carried out with respect to a second axis of the solar array.

Solar electric conversion unit and system

Abstract: A solar electric conversion unit and system includes substantially increased efficiency with reduced losses and increased acceptance angles. The system employs a short focal length fresnel lens extruded to further include depending side walls. The free edges of the sides carry a heat sink supporting a photovoltaic cell. The extruded side walls function as light pipes for carrying light directly to the photovoltaic cell. The walls are reflective inwardly of the unit to further avoid loss of stray light.

Short term generation scheduling in a small autonomous system with unconventional energy sources

Abstract: The authors present a method for problem solving the short-term generation-scheduling problem in a small autonomous system with both conventional and unconventional energy sources and a storage battery. The system generation consists of diesel generators, wind turbine generators, and photovoltaic panels. This is the generation mix of the power system of the Greek island of Kythons, and may be applied to other Greek islands. A dynamic programming algorithm together with a standard unit commitment, is used to determine the optimal short-term scheduling, which minimizes the fuel consumption for a certain scheduling horizon, e.g., for the next 24 h. >

Matching of DC motors to photovoltaic generators for maximum daily gross mechanical energy

Abstract: The matching to solar-cell generators of both separately excited and series DC motors driving pumping loads is addressed. It is shown that the maximum gross mechanical power can be obtained at slightly higher voltages and slightly lower currents compared to the maximum electrical-power points on the solar-cell generator characteristics at different insolation levels. Guidelines for constructing the loci of the motor voltage-current points for maximum mechanical power and for determining the optimal motor parameters to match the solar generator are derived in terms of the mechanical load characteristics and the solar array parameters. Results of applying these design criteria to practical case studies enabled the assessment and comparison of both kinds of motors, especially as far as the daily utilizable output mechanical energy is concerned. The superiority of the separately excited motors in such systems is quantitatively indicated. The results are also compared to corresponding information available in the literature. >

A study of dispersed photovoltaic generation on the PSO system

Abstract: Results of a study on dispersed photovoltaic (PV) generation on the Public Service Company of Oklahoma (PSO) system with simulated dispersed PV generation are presented. It is found that, with high penetrations of PV, as insolation changes, significant variations in power flows occur on transmission and subtransmission lines that may require changes in system protection and voltage control practices. >

Application of ink jet technology on photovoltaic metallization

Abstract: Computer-controlled ink-jet assisted metallization of the grid pattern of solar cells with metallo-organic decomposition (MOD) silver inks offers a maskless alternative method to conventional photolithographic thin-film technology and screen-printing technology. This method can provide low-cost, fine-resolution reduction in process complexity by direct ink-jet patterning, avoidance of degradation of p-n junctions by firing at low temperature (350 degrees C), and uniform line film on rough-surface solar cells (unpolished solar cells for low-cost purposes). The metallization process involves jet-printed metallo-organic inks, belt furnace firing, and thermal spiking. With titanium thin-film underlayer as an adhesion promoter and multilayer ink jet printing, solar cells of 8.08% average efficiency without AR coating can be obtained. This efficiency value is approximately equal to that of thin-film metallized solar cells of the same lot. >

Sun-powered vest

Abstract: A vest garment to be worn by persons working out of doors and which has an array of photovoltaic cells mounted on the back panel thereof. The individual cells are connected in series relationship with one another across a pair of output terminals which are brought out through a belt attached along the waistband of the vest to an output jack. The voltage developed across the photocell array may then be used to charge rechargeable batteries suspended from the belt or, alternatively, they be coupled to an input jack of a power tool having a self-contained rechargeable battery whereby charging current is generated when the vest is being worn out of doors.

Modeling and simulation of spacecraft power systems

Abstract: Modeling of a complete spacecraft power processing system is presented, using the Boeing EASYS software. Component models are developed, and several system models including a solar array switching system, a partially shunted solar system, and cosmic background explorer (COBE) system are simulated. The modes of operation of the power system, such as shunt mode, battery-charge mode, and battery-discharge mode, are simulated for a complete orbit cycle. >

Solar powered construction light

Abstract: A recharging network for a solar powered construction light, including a solar powered battery, that recharges a storage battery at a constant rate and can be selectively operated to burn the light continuously to produce a continuous light or to burn intermittently to provide a flashing light. The network allows a solar cell to recharge the storage battery when sunlight is impinging upon the solar cell to provide virtually maintenance free and long term operation of the construction light during the dark or twilight hours when construction lights are commonly employed to warn motorists of road hazards.

Is central station photovoltaic power dispatchable

Abstract: An operational tool for integrating a photovoltaic system into the utility's generation mix is introduced The development and implementation of a new approach-a dynamic rule-based (RB) dispatch algorithm-is presented A Box-Jenkins time-series method is used to model the subhourly solar irradiance The model is extended to yield forecast parameters which are then used to predict the photovoltaic output expected to occur at certain lead times coinciding with the economic dispatch intervals The RB dispatch algorithm is introduced to operate as either a substitute for or an aid to the dispatch operator It is concluded that results depend on the time of the year and the specific utility The utility generating-capacity mix significantly influences the results >

System performance improvement provided by a power conditioning subsystem for central station photovoltaic-fuel cell power plant

Abstract: An augmented power conditioning subsystem (APCS), which can improve the power system performance besides performing DC/AC power conversion, is proposed. With the benefits provided by the APCS, connecting photovoltaic cells, fuel cells, or their combination to a power system would provide not only additional sources and control of real power, but also additional economic reactive power control as well. The basic principle of the APCS, its operation and control, economic considerations, and the results of a preliminary study are presented. >

Hybrid method for depositing semi-conductive materials

Abstract: The invention provides a method and apparatus for depositing alloy films useful in manufacturing photovoltaic solar cells. In the preferred embodiment an alloy comprising copper, indium, and selenium is deposited on a substrate. Sputtering is utilized to provide the copper and indium, with the selenium being provided by evaporization. Other alloys may also be formed using the disclosed apparatus and techniques.

Analysis of interrelationships between photovoltaic power and battery storage for electric utility load management

Abstract: The impact of photovoltaic power generation on an electric utility's load shape under supply-side peak load management conditions is explored. Results show that some utilities utilizing battery storage for peak load shaving might benefit from use of photovoltaic (PV) power, the extent of its usefulness being dependent on the specific load shapes as well as the photovoltaic array orientations. Typical utility load shapes both in the eastern (at Rayleigh, NC) and in the western (at Hesperia, CA) parts of the USA are examined for this purpose. It is concluded that while photovoltaic power generation seems to present a bigger impact on the load of the western utility, both utilities will experience considerable savings on the size of the battery system required to shave the peak loads as well as in the night-time base capacity required to charge the battery. >

Electrical fault protection for a large photovoltaic power plant inverter

Abstract: The authors analyze the original protection design and describe changes made to improve fault protection after electrical faults caused fires in the DC wiring of a photovoltaic (PV) power plant. The zone-of-protection was extended, and fault detection and response were improved. The results suggest a need for better coordination between DC and AC fault protection philosophies that are commonly applied independently by designers. Design lessons for PV array fault protection are described to assist electrical designers in eliminating fault vulnerabilities from future PV systems. These take into account the unique electrical characteristics of PV generators, including the dispersed-rather than point-source and the current- rather than voltage-source nature of the PV array. >

A discussion on the diversity in the applications of photovoltaic systems

Abstract: References on the diverse applications of photovoltaic (PV) systems around the world are classified. The classes presented are (i) stand-alone, (ii) grid-connected, (iii) PV-thermal, (iv) PV-wind, and (v) dedicated applications. 73 papers are cited and classified into these five categories including a brief summary of each paper. Out of these, 42 papers relate to grid-connected applications in many industrialized countries of the world. These papers reflect the importance given to such applications. Due to the rapidly changing nature of PV and related industries, only papers published during the last ten years are considered. >

Simulation of photovoltaic power systems and their performance prediction

Abstract: A number of photovoltaic (PV) performance-analysis models are tested for their ability to estimate the AC power output and validated against historical observations from a PV test facility. A method to estimate meteorological parameters is developed for use in PV performance models for predicting future AC power output from a PV test site. Twelve such PV performance models are examined, and the PVFORM system analysis program and lifetime cost and performance models are extensively tested. These two models are tested using the typical meteorological year and the VPI model-generated estimates of long-term data. Performance prediction results are compared against actual observations at a 4 kW PV test facility. Results show that the VPI model-generated data, when used with the PVFORM model, provide the best predictions for AC power output from this 4 kW PV test facility. >

A novel utility interfaced high-frequency link photovoltaic power conditioning system

Abstract: Utility-line-interfaced photovoltaic power conditioning (PVPC) systems are gaining popularity in augmenting energy. PVPC systems utilizing a high-frequency (HF) isolation link have the well-known advantages of small size, light weight, etc. Here, a utility interfaced HF-link PVPC system is presented. The system discussed consists of a resonant (load commutated asymmetrical silicon-controlled rectifier) (ASCR) HF inverter, a rectifier, and a line-commutated inverter working with a power factor near unity. An HF transformer provides the isolation between the photovoltaic array and the utility line. The HF resonant inverter uses an LCC type commutation circuit and has inherent fault-protection capability under a number of fault conditions. The working details of the scheme are presented together with logic circuit schematics. Experimental results obtained with a prototype unit are also given. >

Resonant inverters for photovoltaic array to utility interface

Abstract: A number of high-frequency link power converter schemes suitable for interconnecting a photovoltaic (PV) array to the utility line using resonant inverters are presented. Use of high-frequency resonant inverters (HFRI) results in reduced size, weight and cost. Scheme 1 uses the HFRI-cycloconverter, scheme 2 uses the HFRI-rectifier pulsewidth-modulated voltage source inverter, scheme 3 uses the HFRI-rectifier line commutated inverter working with a fixed maximum possible inverting fringe angle, and scheme 4 uses the HFRI-rectifier line-connected inverter (with line current modulation). These schemes are compared. Based on the comparison, scheme 3 was selected for an initial study. To overcome various problems associated with scheme 3, the line current is modulated sinusoidally in scheme 4. In this scheme, the HFRI is controlled appropriately to obtain a rectified sine wave of 120 Hz in the DC link and the function of the line-connected inverter is to unfold this waveform on alternate half cycles to obtain a sinusoidal line current with the line voltage. Methods of commutation of the line connected inverter are explained. Experimental results obtained with scheme 4 are presented. >