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Showing papers by "Technical University of Madrid published in 1981"


Journal ArticleDOI
TL;DR: In this article, the effective surface recombination velocity of the high-low junction (Seff) and of the base diffusion length are carried out for Al-alloyed n+pp+ bifacial cells and the results are presented in form of histograms.
Abstract: Experimental estimations of the effective surface recombination velocity of the high-low junction (Seff) and of the base diffusion length are carried out for Al-alloyed n+pp+ bifacial cells and the results are presented in form of histograms. These results agree with calculated values of Seff when the characteristics of the recrystallized Si layer and heavy doping effects are taken into account. It is concluded that thick Al layers and high alloying temperatures (over 800°C) are necessary to obtain low values of Seff. This conclusion agrees with experimental results of other authors. Recomendations to avoid diffusion length degradation are given and the operating limits of the Al alloying technology are discussed.

159 citations


Journal ArticleDOI
TL;DR: In this article, a new theoretical model to calculate the effective surface recombination velocity of a high-low junction with an arbitrary impurity distribution is presented, which is applied to erfc-diffused pp+ junctions using experimental data of bandgap narrowing, lifetime and mobility.
Abstract: A new theoretical model to calculate the effective surface recombination velocity ($a) of a high-low junction with an arbitrary impurity distribution is presented. The model is applied to erfc-diffused pp+ junctions using experimental data of bandgap narrowing, lifetime and mobility. Bandgap narrowing is shown to degrade the minority carrier reflecting properties of the high-low junction. Computer results are applied for the design of BSF solar cells and to study other solar cell structures based on high-low junctions. NOTATION diffusivity of minority carriers diffusivity of electrons in a p+ region minority carrier current electron current in a p+ region

58 citations


Journal ArticleDOI
TL;DR: A study of amino acids, sugars, and mineral elements is carried out with the sweet almond cultivated in Mallorca (Spain). Seventeen amino acids are determined by ion-exchange liquid-liquid chromatography as discussed by the authors.
Abstract: A study of amino acids, sugars, and mineral elements is carried out with the sweet almond cultivated in Mallorca (Spain). Seventeen amino acids are determined by ion-exchange liquid-liquid chromatography. Glutamic acid is the most abundant, and the essential amino acids determined constitute 34% by weight of the total amino acids determined. The absence of reducing sugars is noted by several methods, and the content of sucrose is found to be 5.52%. The elements Fe, Ca, K, Na, Mg, Cu, Zn, Mn, P, Co, and Mo are determined by atomic absorption and colorimetric methods. Cobalt and molybdenum have not been previously cited in this fruit by other authors. © 1981 American Chemical Society.

50 citations


Journal ArticleDOI
TL;DR: An arbitrarily shaped lineal Fresnel lens acting either as sole concentration stage or as the first stage of a two-stage concentration system in which the second stage considers the first as a Lambertian source.
Abstract: In this paper we analyze an arbitrarily shaped lineal Fresnel lens acting either as sole concentration stage or as the first stage of a two-stage concentration system in which the second stage considers the first as a Lambertian source. We determine the gain and position of the lens for all possible configurations, and we demonstrate that a curved lens with a refractive-index approaching infinity and with a given profile turns out to be an ideal concentrator.

46 citations


Journal ArticleDOI
TL;DR: In this article, the first p+n-n+ bifacial solar cells are presented, achieving mean efficiencies of 15.7% and 13.6% under front and back air mass one illumination respectively at 28°C.

36 citations


Journal ArticleDOI
TL;DR: In this paper, the theoretical bases for casting maximum energy on a cell placed in a static concentrator of minimum entry aperture were derived and several concentrators were analysed according to this theory and the gain achievable with each is obtained.

28 citations


Journal ArticleDOI
TL;DR: A new theory is presented that is very useful for the design of feedback transistor amplifiers, including considerations on stability, gain equalization, and matching, based on graphical feedback diagrams whose construction rides and practical circuit design techniques are described.
Abstract: A new theory is presented that is very useful for the design of feedback transistor amplifiers, including considerations on stability, gain equalization, and matching. The theory is based on graphical feedback diagrams whose construction rides and practical circuit design techniques are described. The method provides insight into the effects of the feedback network elements and saves computer time and money. Three applications are presented: a tuned neutralized bipolar transistor amplifier; a broad-band medium power MESFET amplifier in the 3.7-4.2-GHz range; and a ultrawide-band matched MESFET amplifier covering the 0.1- 12-GHz frequency range.

27 citations


Book ChapterDOI
01 Jan 1981
TL;DR: In this article, several problems relevant to the equilibrium and stability of liquid bridges under microgravity conditions are discussed, which are amenable to theoretical analysis while still presenting many of the most intriguing characteristics of several experiments which will be performed onboard Spacelab by use of the ESA Fluid Physics Module.
Abstract: A liquid column, supported by surface tension forces, can bridge the gap between two solid surfaces. When these surfaces are two parallel, coaxial, circular discs, the resulting configuration is often used to model a floating zone in melting, provided that a number of simplifying assumptions is fulfilled. Several problems which are relevant to the equilibrium and stability of liquid bridges under microgravity conditions are discussed in this paper. These problems have been selected because they are amenable to theoretical analysis while still presenting many of the most intriguing characteristics of several experiments which will be performed onboard Spacelab by use of the ESA Fluid Physics Module.

20 citations


Journal ArticleDOI
TL;DR: A parameter is defined that allows one to estimate the degradation of the thermodynamic quality of the concentrator due to the effect of chromatic aberration, which follows a hyperbolic law.
Abstract: In concentration systems using Fresnel lenses the effect of the chromatic aberration can become important. In this paper we propose a method to take this effect into account for designing purposes. Also we define a parameter that allows one to estimate the degradation of the thermodynamic quality of the concentrator due to this effect. This parameter follows a hyperbolic law, with the acceptance angle showing that it is important to consider chromatic aberration when modeling concentrators with a high concentration factor. However, this complexity is unnecessary for moderate or low concentration factors.

20 citations


Book ChapterDOI
01 Jan 1981
TL;DR: In turbulent diffusion flames chemical reaction and mixing occur simultaneously in thin strained and distorted laminar mixing layers separating fuel from the oxidizer as mentioned in this paper, where the Damkohler number is measured by the ratio of the characteristic mixing time tm and the characteristic chemical time tc.
Abstract: In turbulent diffusion flames chemical reaction and mixing occur simultaneously in thin strained and distorted laminar mixing layers separating fuel from the oxidizer. If the reaction can be modelled in terms of an irreversible reaction F + n 02 —> Products the relative importance of chemical production and transportation terms in the conservaron equations is measured by the Damkohler number, or ratio of the character-istic mixing time tm and the characteristic chemical time tc. A typical mixing time is the inverse of the straining rate y, while tc~' is proportional to the frequency factor of the reaction times the Arrhenius exponential exp (-E/RT) involving the ratio of the activation energy of the reaction E to the thermal energy TR. Combustion reactions are exothermic and with large values of the ratio E/RT, and, as a result we find in the flow-field regions of low temperature, where the Damkohler number is very small and, therefore, the chemical reaction is frozen. These regions coexist with regions of high temperature where because the reaction is so fast, one of the reactants is depleted, so that either the local concentration of the fuel or of the oxidizer must be zero.

9 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of edge recombination in silicon solar cells is investigated and the effect is related to the edge area to junction area ratio (E2JR) of the solar cells.
Abstract: This work shows experimentally the decrease in open-circuit voltage produced by edge recombination in silicon solar cells. The effect is related to the edge area to junction area ratio.

Journal ArticleDOI
TL;DR: The maximum power cast on a collector from a source of finite angular extension by a concentrator of fixed position occurs when the collector sees the concentrator as a Lambertian source, and rules for effective cost design are given leading to the conclusion that Lambertian concentrators must be used if the collector cost is high.
Abstract: The maximum power cast on a collector from a source of finite angular extension by a concentrator of fixed position occurs when the collector sees the concentrator as a Lambertian source. Concentrators not fully meeting this requirement are evaluated using a parameter called the shape quality factor. Lambertian concentrators can be obtained with mirrors but not with lenses of finite n. In many cases they are not ideal, and some rays are cast outside the collector leading to an intercept factor below unity. Among those mirrors with the highest intercept factor, shape inaccuracies reduce this parameter and the shape quality factor to the extent which is analyzed. Rules for effective cost design are given leading to the conclusion that Lambertian concentrators must be used if the collector cost is high, while ideal concentrators should be used if the concentrator cost is high.

Book ChapterDOI
01 Jan 1981
TL;DR: In this article, the authors derived the rules for casting maximum energy on a cell placed in a static concentrator of minimum entry aperture and derived a cost estimate of $3.19 W/peak.
Abstract: The rules for casting maximum energy on a cell placed in a static concentrator of minimum entry aperture are derived. A concentration of 9.13 for collecting the direct sunbeam throughout the year and of 4.5 for collecting diffuse light are upper bounds when using practical materials. Practical bifacial solar cells required to achieve those figures are presented. A prototype of concentrator with bifacial cells has been fabricated and its results are also presented. Based on the possible improvements of such a concentrator we arrived at a cost estimate of $3.19 W/peak.

Book ChapterDOI
01 Jan 1981
TL;DR: In this paper, a bifacial Bifacial solar cells were used to experimentally analyse the behavior of Al-alloyed high-low junctions, formation mechanisms of the highlow junction are explained, and used to calculate its effective surface recombination velocity.
Abstract: n+ pp+ bifacial BSF solar cells are used to experimentally analyse the behaviour of Al-alloyed high-low junctions, formation mechanisms of the high-low junction are explained, and used to calculate its effective surface recombination velocity. It is concluded that thick Al layers and high alloying temperatures (over 800°C) are necessary to obtain low values of Seff. These conclusions are checked with experimental results of other workers. Recommendations for BSF solar cell processing are given.

Book ChapterDOI
01 Jan 1981
TL;DR: In this paper, a two-axis photovoltaic tracking array of 20.80 m2 aperture equipped with monocrystalline silicon solar cells and hybrid silicone-glass Fresnel lenses, capable of yielding 1.5 KW peak under AM1 conditions.
Abstract: We have developed a two-axis photovoltaic tracking array of 20.80 m2 aperture equipped with monocrystalline silicon solar cells and hybrid silicone-glass Fresnel lenses, capable of yielding 1.5 KW peak under AM1 conditions. The effective concentration ratio is 55X. We have found that the use of certain two-level metallization grids reduces the series resistance and improves the performances of concentration solar cells. We have made n p silicon solar cells of 5 cm diameter with an efficiency of 16.6% at AM1 and 28°C and we measured series resistance values comprised between 40 and 200 mΩcm. These cells have been encapsulated over metal plates to achieve good thermal and electrical contacts. We measured 6°C thermal drop between the cell and the cooling element for AM1 irradiance. The maximum temperature between the cell and the ambient under the same conditions in a windless day has been 35°C.


Proceedings ArticleDOI
01 Oct 1981
TL;DR: In this paper, the design of a medium power MESFET amplifier stage in the 3.7 - 4.2 GHz communication band using a simple and universal feedback network is presented.
Abstract: A new method is presented which allows the design of a medium power MESFET amplifier stage in the 3.7 - 4.2 GHz communication band using a simple and universal feedback network. Using a commercially avalaible Nippon Electric Co. NE-464194 MESFET, an amplifier stage has been constructed using-thick-film microstrip circuitry. A gain of 8±0.3 dB has been obtained, with input and output VSWR less than 2. Power output at 1 dB compression is 22.5 dBm with an 3er O.I.P. of 33 dBm. Noise figure is 4.7 dB. The method is applicable to other types of MESFET.