Showing papers on "Photovoltaic system published in 1993"

Renewable energy : sources for fuels and electricity

Abstract: This book assesses the technical and economic prospects for making fuels and electricity from renewable energy sources. Twenty-three chapters discuss the following renewable technologies: hydropower; wind energy; solar thermal electric technology; photovoltaic technology (6 chapters); ocean energy systems; geothermal energy; biomass conversion technology (8 chapters); solar hydrogen; and utility strategies for using renewables. All chapters have been processed for inclusion on the data base.

A high-efficiency maximum power point tracker for photovoltaic arrays in a solar-powered race vehicle

Abstract: A maximum power point tracker for photovoltaic arrays is presented. Components are optimized for weight/power-loss tradeoff in a solar-powered vehicle, resulting in over 97% efficiency. The control circuit uses a robust auto-oscillation method. Measurement and multiplication of array voltage and current is shown to be unnecessary, and the control is based only on output current measurement. Multiple local maxima arising from partial shading of the solar array are discussed. >

A general battery model for PV system simulation

Abstract: A battery model is proposed as a tool to simulate and optimize photovoltaic (PV) / storage systems. the normalized form of the equations with respect to the battery capacity allows us to generalize its use for any type and size of lead-acid batteries. The validity of this model to represent the battery voltage evolution during charge, overcharge and discharge processes and to predict the performance of solar systems under different operational conditions is analysed. Moreover, the battery efficiency losses are presented as a function of the upper regulation thresholds of the charge controllers and the size of the array and storage systems in a domestic application in the climate of Madrid.

Thermally induced bending vibrations of a flexible rolled-up solar array

Abstract: An analytical approach for determining the thermal-structural response of a flexible rolled-up solar array due to a sudden increase in external heating is developed. Two analyses are presented: 1) an uncoupled thermal-structural analysis that assumes the heating and temperature gradients are not affected by thermally induced motions, and 2) a coupled thermal-structural analysis that includes the effects of structural deformations on heating and temperature gradients. The analytical methods identify key parameters for understanding the static and dynamic response. A stability criterion given in nondimensional parameters establishes the conditions for thermal flutter. Key parameters for thermal flutter include the ratio of thermal and structural response times, the solar inclination angle, and the system damping. Numerical calculations are presented for the solar arrays on the Hubble Space Telescope. Unstable oscillations are possible but are unlikely to have practical importance.

Microprocessor control of multiple peak power tracking DC/DC converters for use with solar cell arrays

Abstract: A method and an apparatus for efficiently controlling the power output of a solar cell array string or a plurality of solar cell array strings to achieve a maximum amount of output power from the strings under varying conditions of use. Maximum power output from a solar array string is achieved through control of a pulse width modulated DC/DC buck converter which transfers power from a solar array to a load or battery bus. The input voltage from the solar array to the converter is controlled by a pulse width modulation duty cycle, which in turn is controlled by a differential signal comparing the array voltage with a control voltage from a controller. By periodically adjusting the control voltage up or down by a small amount and comparing the power on the load or bus with that generated at different voltage values a maximum power output voltage may be obtained. The system is totally modular and additional solar array strings may be added to the system simply be adding converter boards to the system and changing some constants in the controller's control routines.

Recent progress in thin‐film cadmium telluride solar cells

Abstract: Cadmium telluride (CdTe) with a room-temperature bandgap energy of 1.45 eV has been shown to be the most promising low-cost, thin-film photovoltaic material for terrestrial applications. Significant progress has been made during the past several years, and thin-film CdTe solar cells of > 1 cm2 area with conversion efficiencies higher than 12% have been prepared by several techniques. Thin-film CdTe photovoltaic modules with 10% efficiency have also been produced. They are of the heterojuntion configuration using a transparent conducting semiconductor (TCS) as the window and p-CdTe as the absorber. In this paper, the potential window materials for thin-film CdTe solar cells are discussed. Thus far, cadmium sulphide (CdS) with a bandgap energy of 2.42 eV at room temperature has been found to be best suited for efficient CdTe solar cells. the deposition techniques for p-CdTe films capable of producing efficient solar cells, including close-spaced sublimation (CSS), electrodeposition, screen printing and spraying, are briefly reviewed, and the characteristics of the resulting solar cells are discussed. It is concluded that the efficiency of thin-film CdTe solar cells can be increased to 18-19% in the near-term, leading to 15-16.5% efficient modules.

A new maximum power point tracking system

Abstract: In power systems involving a load, a battery and a solar array, MPPT (maximum power point tracking) is a promising principle to extract the maximum amount of energy from the solar array and distribute it to the battery and loads. A digital hill-climbing control strategy combined with a bidirectional current mode power cell is presented that makes it possible to get a regulated bus voltage topology, suitable for space applications, by means of two converters. Theory, simulation, and breadboard validation are successively detailed. >

Multiple reflector concentrator solar electric power system

Abstract: Disclosed is a solar electric power system that utilizes multiple reflectors to concentrate sun light onto a panel of photovoltaic (PV) cells. The power system, consisting of multiple reflectors, mounted PV cells, and a heat dissipation component, is mounted on a tracker that keeps the system directed to the sun. A noteworthy feature of this system is its designed-in capability of being retrofitted with advanced reflectors, PV components, and heat dissipation components during the system's multi-year operating life. The common axes design feature of the system allows for low cost materials and manufacturing concepts. The system can operate on either a single or a dual axis tracker with active or passive cooling.

Starting characteristics of direct current motors powered by solar cells

Abstract: The authors deal with the calculation of the starting to rated current ratio and starting to rated torque ratio of the permanent magnet, separately, series and shunt excited motors when powered by solar cells for the two cases where the system includes a maximum-power-point-tracker (MPPT), and without an MPPT. Comparing these two cases, one gets a torque magnification of about three for the permanent magnet motor and about seven for other motor types at rated design insolation. The calculation of the torques may assist the photovoltaic system designer to determine the advantage of including an MPPT in the system as far as the starting characteristics of the DC motors are concerned. >

Use of PV circuit simulation for fault detection in PV array fields

Abstract: Faults in PV array fields do not only affect the performance and services of the plant but may also lead to critical and detrimental situations. Although such faults change the electrical characteristics of the PV system, usually, they are not easily observed. Causes are the uncertainty of overall efficiency values, the limited number of measured operation data, and the lack of precise reference values, especially. A procedure for the detection of solar cell array faults is proposed, comparing actual to expected electrical parameters; accurate reference data being computed by a detailed PV circuit simulation program. Since the program delivers the whole IV curve, not only the maximum power point values can be checked but actual voltage and current under any operating conditions. An analysis of all faults, which may occur in PV fields, has been carried out for the development of comparison rules. >

The charge equalizer-a new system to extend battery lifetime in photovoltaic systems, UPS and electric vehicles

Abstract: Investigations of battery banks in photovoltaic systems, UPS and electric vehicles show that individualization of single cells due to different properties leads to premature failures of the whole battery. Single cell monitoring is no way to overcome this problem. The new "charge equalizer" (CHEQ) introduced in this paper keeps all cells in the same state of charge at all times by transferring energy between the cells. For different applications, specially suited implementations of this fundamental principle are shown. The main advantages of the CHEQ will be: protection against overcharging and deep discharging of individual cells, extension of lifetime, decrease of maintenance costs, availability of the full nominal capacity. >

Battery power supply system

Abstract: A battery power supply system permits inexpensive introduction of a transfer break system to a solar cell generation system and quick release of reverse charge phenomenon. The battery power supply system comprises a solar cell array (1), a DC-AC inverter (2), a break device (3) for a commercial power system, and wireless communication device (4) as control device for controlling the conduction and break of the break device based on the information derived through wireless communication.

Photovoltaic power generating equipment capable of jointly using battery

Abstract: PURPOSE:To make the power generation capacity of a solar battery maximum, and to effectively utilize solar radiation energy by operating a DC/DC converter and controlling the output voltage of the solar battery so that the generated power of the solar battery becomes maximum. CONSTITUTION:At the time of supplying electric power from a solar battery 1 to an inverter 3, a DC/DC converter 5 controls an output voltage of the solar battery 1 so that the generated electric power of the solar battery 1 becomes maximum. When the generatable maximum electric power PPVL of the solar battery 1 is smaller than the consumption electric power PINV of the inverter 3, insufficient electric power obtained by subtracting the generated electric power PPVI of the solar battery from the consumption electric power PINV of the inverter 3 is supplied by electric power supply caused by discharge of a battery 4. On the other hand, when the generatable maximum electric power PPVI of the solar battery 1 is larger than the consumption electric power PINV of the inverter 3, surplus electric power obtained by subtracting the consumption electric power PINV of the inverter 3 from the generated electric power PPVI of the solar battery 1 is used for the charging of the battery 4.

Value analysis of intermittent generation sources from the system operations perspective

Abstract: The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels. >

Economical, PV maximum power point tracking regulator with simplistic controller

Abstract: A 30% cost reduction of photovoltaic generation can be brought about by the investment in a novel, highly efficient maximum power point tracker (MPPT). Such a power converter is currently under development, implementing a feedforward output current controller as tracking algorithm. The DC-DC power converter, typical of a MPPT, exploits the efficient high-frequency operation, associated with zero-transition switching. Thus the output filter only consists of the combination of a storage battery and its cabling. The resulting power converter is suitable for integration into standard PV panels during manufacturing. The efficiency of the MPPT is 96% for a range of output powers at a low battery voltage of 12.5 V and a component cost of US$21.00. >

Method and apparatus for mowing lawns

Abstract: The present invention discloses an unattended lawn mowing system in which multiple solar powered self propelled, random motion lawn mowers are used singly or in combination to mow a pre-defined lawn area. The mowing zone is defined as a region of grass bounded by naturally occurring or man made obstacles of infinite variation including, but not limited to, high grass, flowers, trees, fences and lawn edging. Each mowing unit is a solar powered, self-propelled, random motion lawn mower which comprises a frame with a set of drive and coaster wheels on the frame. A set of batteries and battery powered electric motors are mounted on said frame with output means from the motors to power drive wheels and a cutting mechanism on the frame. Photovoltaic panels are mounted on said frame to receive solar rays and convert them into electrical power to charge the batteries with means for controlling the orientation of the solar panels so as to face the direction of greatest solar intensity. The actuation of the mower is controlled by monitoring means that detects the battery charge level and the solar energy output of the panels. Such actuation modes include starting the mower, stopping the mower, altering the direction of travel of the mower and re-charging the batteries of the mower. Random motion of the mowers is accommodated by providing contact switches on the outer periphery of the frame of the mower so that direction of the mowers is changed by more than 90 degrees when the contact switches impact a physical barrier surrounding or within the area to be cut. The mower further includes switch means so constructed that the solar cells are connected to said batteries in a manner that allows for automatic switching between batteries for optimum use and re-charging.

Computer particle simulation of high-voltage solar array arcing onset

Abstract: The operation of a high-voltage solar array in low Earth orbit may cause arcing on the negatively biased parts of a solar array. This sets a practical limit on the operational voltage of solar arrays.This paper is the extension of three earlier works" regarding high-voltage solar array arcing. The onset of arcing is reproduced by self-consistent computer simulations to verify the arcing onset model developed in the earlier work. It is shown that neutral gas is desorbed from the dielectric surface forming a localized neutral cloud over the surface, and the arcing onset occurs as the gas breakdown at a parameter pd (pressure times distance) much smaller than the Paschen minimum. Analytical expressions for the prebreakdown electron currents and the neutral densities are also derived and used to obtain a parametric formula of the breakdown condition. Arcing rates are calculated including the breakdown condition of the desorbed neutral gas. The theory is compared to the Japanese Space Flyer Unit High-Voltage Solar Array ground experiment and shown to give a reasonable explanation for data relating the arcing rate to the solar array temperature.

Solar Pumping: An Introduction and Update on the Technology, Performance, Costs, and Economics

Abstract: Although the number of units in the field is still small, solar photovoltaic powered pumping systems offer many advantages over the more traditional technologies. Because there are few moving parts, maintenance is reduced to a minimum, and reliability is very high. Also, because the time of greatest water demand usually coincides with the maximum daily solar energy, the available pumping power is well matched to the demand. Solar pumping was first introduced into the field in the late nineteen-seventies, and since manufacturers have refined their products to give considerable increases in performance and reliability. The steady fall in prices of solar photovoltaic (PV) panels means that solar pumping is becoming economic for an increasingly wide range of applications. This guide is written for the potential user to give a simple background to PV pumping technology and to help to identify the situations in which solar pumping should be considered. The paper illustrates typical applications and reviews current technology in solar pumping. It also gives information dealing with the range of currently available equipment as well as the practical aspects of choosing a pumping system.

Method for regulating photovoltaic solar systems and circuit arrangements for carrying out the method

Abstract: The invention relates to the use of maximum power point regulation for the optimum operation of photovoltaic solar systems. According to the invention, the MPP is determined by measuring the short circuit current, measuring the idle voltage and comparing the characteristics by means of the computer control, preferably an SPS, and the dynamic load impedance of the load is set by pulse width modulation by means of a control signal output by the SPS and thus the maximum power is taken from the solar module.

Photovoltaics: Unlimited Electrical Energy from the Sun

Abstract: The first practical solar cell was developed at Bell Laboratories in 1954. With the advent of the space program, photovoltaic cells made from semiconductor‐grade silicon quickly became the power source of choice for use on satellites. The systems were very reliable, and cost was of little concern. In the early 1970s, the disruption of oil supplies to the industrialized world led to serious consideration of photovoltaics as a terrestrial power source. This application focused research attention on improving performance, lowering costs and increasing reliability. These three issues remain important today even though researchers have made extraordinary progress over the years. This article details that progress.

Photovoltaic receivers for laser beamed power in space

Abstract: One of the most promising beamed power concepts uses a laser beam to transmit power to a remote photovoltaic array. Large lasers can be located on cloud-free sites at one or more ground locations, and illuminate solar arrays to a level sufficient to provide operating power. Issues involved in providing photovoltaic receivers for such applications are discussed. >

Efficiency improvements of silicon solar cells by the impurity photovoltaic effect

Abstract: This paper presents a theoretical investigation of the impurity photovoltaic (IPV) effect for improving silicon solar cell efficiency. The authors' approach is better than previous analyses because of the improved treatment of generation and recombination via impurities, and because it includes the effects of optical competition and light trapping. The approach is applied to indium as the IPV effect impurity incorporated into an idealised silicon solar cell. The analysis is based on experimentally determined parameters for indium. Improvements of cell current, subgap spectral response and energy conversion efficiency are quantified. Their analysis reveals the importance of light trapping and proper selection of indium and dopant concentrations. For the first time, the IPV effect is shown to lead to improved solar cell efficiency. >

Space Station Freedom electrical performance model

Abstract: The baseline Space Station Freedom electric power system (EPS) employs photovoltaic (PV) arrays and nickel hydrogen (NiH2) batteries to supply power to housekeeping and user electrical loads via a direct current (dc) distribution system. The EPS was originally designed for an operating life of 30 years through orbital replacement of components. As the design and development of the EPS continues, accurate EPS performance predictions are needed to assess design options, operating scenarios, and resource allocations. To meet these needs, NASA Lewis Research Center (LeRC) has, over a 10 year period, developed SPACE (Station Power Analysis for Capability Evaluation), a computer code designed to predict EPS performance. This paper describes SPACE, its functionality, and its capabilities.

Turn-on control method and turn-on control circuit for an invertor coupling a solar generator to the electricity mains

Abstract: Known turn-on control methods and turn-on control circuits provide the monitoring of the solar generator no-load voltage (open-circuit voltage), the invertor being activated when this voltage exceeds a predetermined threshold value. The turn-on accuracy is unsatisfactory because the no-load voltage is strongly dependent on the module temperature. In contrast, the novel method provides the measurement of the short-circuit current of the solar generator (1) and the stipulation of a corresponding short-circuit current threshold value, the invertor being turned on in the event of this threshold value being exceeded. A circuit relating to this contains a short circuit (Ki) with a short-circuit current measuring element (2) as well as an evaluation unit (10, 3, 4) for identifying when the threshold value is exceeded and the invertor is activated. On account of the comparatively low dependence of the short-circuit current on the temperature, very accurately timed turning-on of the invertor is produced for varying solar module temperatures. Use in photovoltaic installations which feed power to the electricity mains.

Study of Solar-Assisted Thermoelectric Technology for Automobile Air Conditioning

Abstract: An analytical study was conducted to determine the feasibility of employing solar energy assisted thermoelectric (TE) cooling technology in automobile air conditioners. The study addressed two key issues -- power requirements and availability of thermoelectric materials. In this paper a mathematical model was developed to predict the performance of TE air conditioners and to analyze power consumption. Results show that the power required to deliver a cooling capacity of 4 kW (13,680 Btu/h) in a 38 C (100 F) environment will be 9.5 kW electric. Current TE modules suitable for air conditioning are made of bismuth telluride. The element tellurium is expected to be in short supply if TE cooling is widely implemented for auto air conditioning; some options available in this regard were studied and presented in this paper. The photovoltaic (PV) cells, assumed to cover the roof area of a compact car can only generate about 225 W. However, this is more than enough to power a fan to provide air ventilation to the car interior which significantly reduces the peak cooling load when the car is parked in bright sunlight.

Solar array module plasma interactions experiment (SAMPIE) - Science and technology objectives

Abstract: The solar array module plasma interactions experiment (SAMPIE) is an approved NASA flight experiment manifested for Shuttle deployment in early 1994. The SAMPIE experiment is designed to investigate the interaction of high voltage space power systems with ionospheric plasma. To study the behavior of solar cells, a number of solar cell coupons (representing design technologies of current interest) will be biased to high voltages to measure both arcing and current collection. Various theories of arc suppression will be tested by including several specially modified cell coupons. Finally, SAMPIE will include experiments to study the basic nature of arcing and current collection. This paper describes the rationale for a space flight experiment, the measurements to be made, and the significance of the expected results. A future paper will present a detailed discussion of the engineering design.