E. Sanchez

A new method for experimental determination of the series resistance of a solar cell

A new method for determining the series resistance of a solar cell from illuminated<tex>I-V</tex>measurements is presented. The method, based on the computation of the area<tex>A</tex>, under the<tex>I-V</tex>curve, evaluates R<inf>s</inf>using the equation<tex>R_{s} = 2[V_{oc}/I_{sc} - A/_sc^2 - (mkT/q) (1/I_{sc})]</tex>This technique takes advantage of the special feature of integration as a procedure to smooth data errors. The R<inf>s</inf>obtained represents the resistive effects globally.

Determination of the two-exponential solar cell equation parameters from empirical data

Abstract The determination of the dark current-voltage two-exponential equation parameters of a solar cell from experimental data is presented. The approach used here is based on a least-squares technique for linear functions; this is possible because m 1 , m 2 and R s are considered as constant parameters while the standard deviation σ is calculated. After a matrix of σ values has been evaluated in this way the parameters corresponding to the minimum value of σ are chosen as those of the best fit. The technique is simple enough to be carried out using only a scientific pocket calculator.

A simplified broad-band large-signal nonquasi-static table-based FET model

In this paper, a simplified nonquasi-static table-based approach is developed for high-frequency broad-band large-signal field-effect-transistor modeling. As well as low-frequency dispersion, the quadratic frequency dependency of the /spl gamma/-parameters at high frequencies is taken into account through the use of linear delays. This model is suitable for applications related to nonlinear microwave computer-aided design and can be both easily extracted from dc and S-parameter measurements and implemented in commercially available simulation tools. Model formulation, small-signal, and large-signal validation will be described in this paper. Excellent results are obtained from dc up to the device f/sub T/ frequencies, even when f/sub T/ is as high as 100 GHz.

Analytical expressions for the determination of the maximum power point and the fill factor of a solar cell

Simple approximate analytical expressions for calculating the values of current and voltage at the maximum power point and the fill factor of a solar cell are proposed. The ratios Im/IL and Vm/Voc, and hence the fill factor, are shown to depend on the two normalized parameters νoc = VocmkTe and νR = RSILmkTe which are closely related to the diode quality factor and the series resistance. The accuracy of the approach proposed here is fairly good for νR 15, for relative errors of less than 1%. These ranges for νR and νoc cover the real situations for most silicon and GaAs solar cells. The usefulness of the analytical expressions as indicators of the behavior of the cell is discussed, and the influence of the series resistance and the diode quality factor is emphasized. The application of these expressions to the determination of the series resistance and the diode quality factor is also discussed.

Direct extraction of nonlinear FET Q-V functions from time domain large signal measurements

The authors present a simple and accurate procedure for the direct extraction of the quasi-static FET model nonlinear charge functions from large signal measurements. The method is based on the proper use of a vector nonlinear network analyzer (VNNA) with load-pull facilities. To our knowledge, these results show for the first time a direct procedure to extract the nonlinear charges of a FET using a very reduced number of large signal measurements.

An optimized 25.5-76.5 GHz PHEMT-based coplanar frequency tripler

This letter presents an optimized single-stage MMIC tripler with W-band output frequency (76.5 GHz). The circuit is based on an 0.15 μm gate-length AlGaAs/InGaAs/GaAs PHEMT. By using a class AB transistor bias point and carefully selecting its input and output terminations, a high conversion gain of -4.3 dB for an 8.5 dBm input signal and a saturated output power of 7 dBm have been obtained. To our knowledge, these results represent the best performance reported up to date for an active frequency tripler with W-band output frequency.

Research knowledge and needs for orchard floor management in organic tree fruit systems.

While pest management and tree horticulture dominate the research agenda for temperate tree fruits, organic production requires more attention to weed control and nutrient management because of the limited options growers have. Weed control and tree nutrition are interlinked and can have impacts on other parts of the system such as rodent pests, beneficial insect habitat, water use, and soil quality. Trade-offs commonly occur when trying to solve weed control and nutrient management in organic orchards. This article reviews numerous orchard-floor management studies relevant to finding solutions for organic systems and suggests areas for further research. Alternatives to soil tillage are needed, as it can degrade soil and tree performance. Conversely, mulching frequently leads to improved tree performance and increased soil quality but can be a costly practice relative to other options. Currently effective organic analogues to the herbicide strip-grass alley system are lacking. A plant-based solution would be ideal from a sustainability standpoint, but no satisfactory solution has been developed for widespread use.

Mathematical analysis of the efficiency-concentration characteristic of a solar cell

Abstract A new general method of calculating the efficiency-concentration characteristic (including the direct determination of the maximum efficiency point) of a solar cell is presented. The method is valid for any model which describes the dark current density-voltage characteristic of the cell, including the common single-exponential and double-exponential models. For the single-exponential model, two simpler methods are derived: (a) a parametric method, which is both exact and analytical, and (b) an approximate method which provides a schematic representation of the efficiency-concentration characteristic and which can be extended to a double-exponential model. On the basis of this second method, the influence of the internal parameters of the solar cell on its behaviour under concentrated sunlight is discussed.

38/76 GHz PHEMT MMIC balanced frequency doublers in coplanar technology

Two 38/76 GHz push-push frequency doublers have been realized in a 0.15 μm GaAs PHEMT technology. The circuits are based on different 180/spl deg/ power divider structures: a Lange coupler followed by a 90/spl deg/ transmission line, and a balun. The circuits achieve maximum conversion gains of -4 and -6 dB for 12 and 14 dBm input signals, respectively. The fundamental suppression is approximately 30 dBc in both cases. To our knowledge, these results represent the best performance reported to date for W-band balanced doublers.

On the analytical determination of solar cell fill factor and efficiency

Abstract A comparison of several analytical, approximate expressions proposed by various authors to calculate the fill factor and the efficiency of a sol ar cell is presented. The comparison is referred to the conventional single-exponential solar cell model and it has been made by using a normalized nomenclature. The accuracy of the expressions has been examined as a function of the concentration factor and it is shown that the usefulness of the approximations decreases as the concentration factor increases. However, the loss in accuracy is different for each expression and, consequently, some of them can still be used for high concentration factors.