Showing papers on "Solar energy published in 1997"

Increasing the Efficiency of Ideal Solar Cells by Photon Induced Transitions at Intermediate Levels

Abstract: Recent attempts have been made to increase the efficiency of solar cells by introducing an impurity level in the semiconductor band gap. We present an analysis of such a structure under ideal conditions. We prove that its efficiency can exceed not only the Shockley and Queisser efficiency for ideal solar cells but also that for ideal two-terminal tandem cells which use two semiconductors, as well as that predicted for ideal cells with quantum efficiency above one but less than two.

High Light-to-Energy Conversion Efficiencies for Solar Cells Based on Nanostructured ZnO Electrodes

Abstract: Photoelectrochemical properties of nanostructured ZnO thin film electrodes have been investigated in the UV and visible regions. For films consisting of 15 nm large undoped crystallites a maximum monochromatic current conversion efficiency of 58% was obtained in the visible using a ruthenium-based dye as a sensitizer. The overall solar energy conversion efficiency for this film was 2%. In comparison, sensitized films consisting of 150 nm large Al-doped crystallites yield a monochromatic current conversion efficiency of 31% and an overall solar energy conversion efficiency of 0.5%. The study also shows that nanostructured ZnO may give high efficiencies in the UV region, approaching unity for the Al-doped films.

Endogenous Substitution among Energy Resources and Global Warming

Abstract: The theory of resource extraction has focused primarily on extraction when there is a single, homogeneous demand for the resource. In reality, however, we observe the simultaneous extraction of different resources such as oil, coal, and natural gas and multiple demands such as trasportation, residential and commercial heating, and electricity generation. This paper develops a model with multiple resources and grades and multiple demands. The model is simulated with extraction cost, estimated reserves, and energy demand data for the world economy. It is shown that if historical rates of cost reduction in the production of solar energy are maintained, more than 90 percent of the world's coal will never be used. The world will move from oil and natural gas use to solar energy. Global temperatures will rise by only about 1.5–2 degrees centigrade by the middle of the next century and then decline steadily to preindustrial levels, even without carbon taxes. These results are significantly lower than those predi...

Field experience with a new performance characterization procedure for photovoltaic arrays

Abstract: As photovoltaic systems become larger and more numerous, improved methods are needed for testing and modeling their performance. Test methods that successfully separate the interacting, time-of-day dependent influences of solar irradiance, operating temperature, solar spectrum, and solar angle-of-incidence have now been developed. These test methods have resulted in a new array performance model that is reasonably simple, yet accurately predicts performance for all operating conditions. This paper describes the new model, outdoor tests required to implement it, results of field tests for five arrays of different technologies, and the evolution of the model into a numerical tool for designing and sizing photovoltaic arrays based on annual energy production.

Measuring solar spectral and angle-of-incidence effects on photovoltaic modules and solar irradiance sensors

Abstract: Historically, two time-of-day dependent factors have complicated the characterization of photovoltaic module and array performance; namely, changes in the solar spectrum over the day and optical effects in the module that vary with the solar angle-of-incidence. This paper describes straightforward methods for directly measuring the effects of these two factors. Measured results for commercial modules, as well as for typical solar irradiance sensors (pyranometers) are provided. The empirical relationships obtained from the measurements can be used to improve the methods used for system design, verification of performance after installation, and diagnostic monitoring of performance during operation.

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.

Sizing and techno-economical optimization for hybrid solar photovoltaic/wind power systems with battery storage

Abstract: A general methodology is presented for the sizing and optimization of renewable power supply systems, including hybrids such as those with solar photovoltaic and wind power components. The technical and economic optimum configurations are found by reference to periods over which the average resource (e.g. wind/solar) is least or the average load demand is greatest. For stand-alone systems, the annual autonomy is an important further design factor. This is the fraction of time for which the specified load can be met. The optimization seeks the least expensive system configuration which achieves the required autonomy level. It is the autonomy level which largely determines the size of battery storage capacity required. A system performance simulation procedure, with an hourly time-step, is used to obtain the autonomy levels of potentially optimum arrangements as the battery size is varied. Illustrative examples of the use of the method employ annual and monthly averaging periods, although any other period may be used. Data refer to the particular location and load pattern for an existing hybrid system, but the method is quite generally applicable. © 1997 by John Wiley & Sons, Ltd.

Integrated power source layered with all polymer rechargeable batteries, solar cells, rf charger, charge control and indicator

Abstract: A self-contained, small, lightweight, portable, renewable, modular integrated power source (10) The power source consists of solar cells (18, 20) that are laminated onto a solid state polymer battery (12) which in turn is laminated onto a substrate containing circuits (26) which manage the polymer battery charging Charging of the battery can occur via solar energy or, alternatively, via RF coupling using external RF charging equipment (3O) or a hand held generator For added support, the integrated power source is then bonded to an applications housing or structure This integrated power source can independently power the electronic application It can also serve as casing or housing by taking the shape of the application enclosure

The DIAPR: A High-Pressure, High-Temperature Solar Receiver

Abstract: A solar central receiver absorbs concentrated sunlight and transfers its energy to a working medium (gas, liquid or solid particles), either in a thermal or a thermochemical process. Various attractive high-performance applications require the solar receiver to supply the working fluid at high temperature (900--1,500 C) and high pressure (10--35 bar). As the inner receiver temperature may be well over 1,000 C, sunlight concentration at its aperture must be high (4--8 MW/m{sup 2}), to minimize aperture size and reradiation losses. The Directly Irradiated Annular Pressurized Receiver (DIAPR) is a volumetric (directly irradiated), windowed cavity receiver that operates at aperture flux of up to 10 MW/m{sup 2}. It is capable of supplying hot gas at a pressure of 10--30 bar and exit temperature of up to 1,300 C. The three main innovative components of this receiver are: a Porcupine absorber, made of a high-temperature ceramic (e.g., alumina); a Frustum-Like High-Pressure (FLHIP) window, made of fused silica; a two-stage secondary concentrator followed by the KohinOr light extractor. This paper presents the design principles of the DIAPR, its structure and main components, and examples of experimental and computational results.

Laminated photovoltaic modules using back-contact solar cells

Abstract: Photovoltaic modules which comprise back-contact solar cells, such as back-contact crystalline silicon solar cells, positioned atop electrically conductive circuit elements affixed to a planar support so that a circuit capable of generating electric power is created. The modules are encapsulated using encapsulant materials such as EVA which are commonly used in photovoltaic module manufacture. The module designs allow multiple cells to be electrically connected in a single encapsulation step rather than by sequential soldering which characterizes the currently used commercial practices.

Space concentrator for advanced solar cells

Abstract: A solar concentrator is provided that comprises two stages. The first stage comprises either a trough-shaped concentrator cusp unit having two major opposed sides joined by two ends. The inner surfaces of the first stage concentrator are mirrored. Further, the ends have two flat, angled surfaces, while the two sides have a Bezier-generated cylindrical shape that approximate parabolic surfaces followed by a straight section. The second stage comprises a bi-axial gradient refractive index (GRIN) element, in which two gradient refractive index materials, each having a high index surface and a low index surface, are joined together along their high index surfaces. The two ends of the bi-axial element are flat, while the two sides also have a Bezier-generated cylindrical shape that approximate parabolic surfaces followed by a straight section. The top surface of the bi-axial element is provided with a cylindrical surface, while the bottom, or exit, surface is ground flat. The high index boundary is parallel to the side surfaces of the first stage unit. A solar cell is bonded to the flat exit surface of the second stage of the concentrator of the present invention. An array of such concentrators and solar cells, in which the solar cells are electrically interconnected, may then be deployed for converting solar energy into useful electrical energy. The 2-D/3-D concentrator evidences much lower mass than prior art concentrators. Further, as the array, or panel, of solar cells wobbles in space, the concentrator will continue to operate, even at lower efficiencies, due to the larger acceptance angle. Concentration ratios on the order of 50× are realized with the present concentrator. However, design studies allow concentration ratios in excess of 300× when used with 3-D versions of the same concept. The second stage can comprise mirrored surfaces. Or, the first stage can comprise a conical section and the second stage a radial GRIN element.

Integrated power source layered with thin film rechargeable batteries, charger, and charge-control

Abstract: A self-contained, small, lightweight, portable, renewable, modular integrated power source. The power source consists of a recharging means such as solar cells that are laminated onto a rechargeable energy source such as a solid state polymer battery which in turn is laminated onto a substrate containing circuits which manage the polymer battery charging. Charging of the battery can occur via solar energy or, alternatively, via RF coupling using external RF charging equipment or a hand held generator. For added support, the integrated power source is then bonded to an applications housing or structure. This integrated power source can independently power the electronic application. It can also serve as casing or housing by taking the shape of the application enclosure.

Novel cost-effective bifacial silicon solar cells with 19.4% front and 18.1% rear efficiency

Abstract: Bifacial solar cells are a promising possibility to lower the costs of solar electricity compared to conventional monofacial solar cells. These devices utilize the sunlight more efficiently since they are able to convert light incident on both sides of the cell. In this letter, a novel, cost-effective bifacial silicon solar cell structure is presented. On float-zone silicon, the cells exhibit conversion efficiencies of 19.4% and 16.5% under 1-sun front and rear illumination, respectively. Furthermore, a “symmetrical” version of the cells is presented demonstrating front and rear efficiencies of 18.4% and 18.1%. In spite of the simplicity of the cell fabrication process, these are the highest independently confirmed efficiencies ever reported for bifacial silicon solar cells.

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.

Silicon-photodiode pyranometers: operational characteristics, historical experiences, and new calibration procedures

Abstract: Small, low-cost, silicon-photodiode pyranometers are now widely used for solar irradiance measurements associated with solar thermal and photovoltaic power systems, as well as for agricultural applications. Without correction, the irradiance values indicated by these pyranometers may differ from the "true" broadband solar irradiance by over 10%. This paper identifies the time-of-day dependent factors responsible for these systematic errors and describes new procedures that effectively compensate for the systematic influences. Application of the procedures should improve calibration methods and the accuracy of field measurements.

Optical power generating system

Abstract: PROBLEM TO BE SOLVED: To provide an optical power generating system that can prevent decrease of power generating efficiency of the whole system. SOLUTION: An optical power generating system 100 comprises a plurality of solar battery modules 1a to 1n, and a plurality of power converters 2a to 2n respectively connected to the modules 1a to 1n and having maximum solar energy pursuing functions. The converters 2a to 2n are connected in series to one another. The modules 1a to 1n have their output current and output voltage controlled by the maximum solar energy pursuing functions of the converters 2a to 2n, so that the maximum power generating efficiency can be always obtained. Further, a common output current flows through the output terminals of the converters 2a to 2n, and the output voltages are automatically adjusted, so that the ratio of any two voltages becomes equal to the ratio of the maximum powers of the corresponding two of the modules 1a to 1n.