J. Appelbaum

Starting and Steady-State Characteristics of DC Motors Powered by Solar Cell Generators

The performance of dc motors (series, separately-excited, and shunt motors) powered by a solar cell generator and loaded by two different types of loads, one a constant load and one a ventilator load, were analyzed with respect to the transient (starting) and steady state operation. Direct current motors are employed in photovoltaic water pumping systems; therefore, the understanding of the system operation and the matching of the system components (solar cells, dc motor type, and load type) are important factors of the system design. Since the solar cell generator in a nonlinear and time-dependent power supply with an output that varies with the insolation (hourly and daily), the performance characteristics of the dc motor are different when supplied by a solar cell generator than when supplied by a conventional constant voltage source. The transient solution was obtained by using an available computer program - SUPER SCEPTRE. The separately - excited (or permanent magnet) motor with a ventilator load was found to be the most suitable for the solar cell generator. The series motor is quite acceptable, but the shunt motor gives poor performance. In all cases the ventilator load is more compatible with the solar cell generator than with the constant load.The performance of dc motors (series, separately-excited, and shunt motors) powered by a solar cell generator and loaded by two different types of loads, one a constant load and one a ventilator load, were analyzed with respect to the transient (starting) and steady state operation. Direct current motors are employed in photovoltaic water pumping systems; therefore, the understanding of the system components (solar cells, dc motor type, and load type) are important factors of the system design. Since the solar cell generator in a nonlinear and time-dependent power supply with an output that varies with the insolation (hourly and daily), the performance characteristics of the dc motor are different when supplied by a solar cell generator than when supplied by a conventional constant voltage source. The transient solution was obtained by using an available computer program - SUPER SCEPTRE. The separately - excited (or permanent magnet) motor with a ventilator load was found to be the most suitable for the solar cell generator. The series motor is quite acceptable, but the shunt motor gives poor performance. In all cases the ventilator load is more compatible with the solar cell generator than with the constant load.

Optimization of Three-Phase Induction Motor Design Part I: Formulation of the Optimization Technique

This two-part paper deals with the optimization of the induction motor designs with respect to cost and efficiency. Most studies on the design of an induction motor using optimization techniques are concerned with the minimization of the motor cost and describe the optimization technique that was employed, giving the results of a single (or several) optimal design(s). In the present paper, a more comprehensive study on the optimization of a three-phase induction motor design was performed. This includes the relationship between motor cost, efficiency, and power factor; the effect of the properties of the electrical steel; and other effects as they occur in an optimal design. In addition, the optimization procedure that was used in this paper includes a design program, where some of the secondary parameters (which are called here variable constants), are modified according to the optimal results, in contrast to other studies where these parameters remain constant for the entire optimization. In this part, a new mathematical formulation of the optimization problem of the induction motor is presented.

Shadow effect of adjacent solar collectors in large scale systems

Abstract In large scale solar systems and in other cases with limited field area (such as on tops of buildings), shadowing of collectors, (thermal or photovoltaic) by their neighbours might occur during the day. This situation calls for an optimal solution of collector deployment in a given field area for maximum or desired energy. The paper deals firstly with the shadowing analysis of vertical and inclined poles and collectors (the shadow components, height and area). This useful information is used in an example of optimal deployment of collectors in a given area (which includes the tilt angle, collector size, spacing between collectors and the number of collector rows).

Starting characteristics of direct current motors powered by solar cells

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. >

The effect of shading on the design of a field of solar collectors

Abstract General expressions are derived for the shading and insolation of a field of solar thermal or photovoltaic collectors. The shading on a collector may be cast by its neighbour and/or by a fence, and is dependent on the spacing between collectors, and on collector height, row length, tilt angle and latitude location. The equations for the shadow height, length and area are given in dimensionless form and are therefore general relations. The derivations pertain to collectors arranged in rows in a horizontal plane, or raised in a step-like structure. The field may be oriented either towards the equator, or towards any azimuth. The equations for the collector insolation include the direct, diffuse and global insolation for the above collector fields. The variation of the shadow on the collector during the day is most important in solar system design, where the performance is highly affected by the shape of the shadow as found in photovoltaic systems. The results of this study may be used for the design and performance analysis of a field of solar collectors (thermal or photovoltaic).

Solar radiation on Mars—Update 1991

Abstract Detailed information on solar radiation characteristics on Mars are necessary for effective design of future planned solar energy systems operating on the surface of Mars. In this paper we present a procedure and solar radiation related data from which the daily variation of the global, direct beam, and diffuse insolation on Mars are calculated. Given the optical depth of the Mars atmosphere, the global radiation is calculated from the normalized net flux function based on multiple wavelength and multiple scattering of the solar radiation. The direct beam was derived from the optical depth using Beers law, and the diffuse component was obtained from the difference of the global and the direct beam radiation. The optical depths of the Mars atmosphere were derived from images taken of the Sun with a special diode on the cameras used on the two Viking Landers.

Performance analysis of d.c.-motor-photovoltaic converter system—I separately excited motor

Abstract The performance of a solar-electrical system composed of a solar cell array, d.c. separately exicted motor and a mechanical load was analysed. The system operating points in the mechanical plane, (n, T) were transferred to the photovoltaic converter plane (I, U). The relative position of the load line to the maximum power output line of the photovoltaic converter indicates its utilization. The venitlator type load (centrifugal pump) fits very well the converter in contrast to a constant load. The speed variation of the ventilator type load-motor link remains in reasonable limits during the day. For a centrifugal pump, this characteristic corresponds to an almost constant pumping rate during most of the day.

Solar radiation on Mars

Detailed information on solar radiation characteristics on Mars are necessary for effective design of future planned solar energy systems operating on the surface of Mars. Presented here is a procedure and solar radiation related data from which the diurnally, hourly and daily variation of the global, direct beam and diffuse insolation on Mars are calculated. The radiation data are based on measured optical depth of the Martian atmosphere derived from images taken of the sun with a special diode on the Viking cameras; and computation based on multiple wavelength and multiple scattering of the solar radiation.

Optimal Solar Field Design of Stationary Collectors

The optimal design of stationary photovoltaic and thermal collectors in a solar field, taking into account shading and masking effects, may be based on several criteria: maximum incident energy on collector plane from a given field, minimum field area for given incident energy, minimum cost per unit energy, minimum plant cost, maximum energy per unit collector area or other objectives. These design problems may be formulated as optimization problems with objective functions and sets of constraints (equality and inequality) for which mathematical optimization techniques may be applied. This article deals with obtaining the field design parameters (optimal number of rows, distance between collector rows, collector height and collector inclination angle) that produce maximum annual energy from a given field. A second problem is determination of the minimum field area (length and width) and field design parameters that produce a given required annual energy. The third problem is determination of the optimal field design parameters for obtaining maximum energy per unit collector area from a given field. The results of these optimal designs are compared to a recommended approach of the Israeli Institute of Standards (ITS) in which the solar field design result in negligible shading. An increase in energy of about 20% for a fixed field area and a decrease infield area of about 15% for a given annual incident energy, respectively, may be obtained using the approach formulated in the present article compared to the IIS approach.

Advantage of boost vs. buck topology for maximum power point tracker in photovoltaic systems

Electrical systems employing solar cells as the energy source are designed to be operated at the point of maximum power of the solar cells. To track this point as the solar radiation and temperature vary, a maximum-power-point-tracker (MPPT) is used. Most MPPT are based on a DC to DC converter of the buck or boost types. In this article we compare the energy efficiency of these converters and show that an MPPT based on the boost converter configuration results in higher output power, thus better utilizing the solar cells.