盐梯度太阳池有机朗肯循环发电系统热力性能分析

针对盐梯度太阳池具有长期聚热及跨季节蓄热的特性,选取R245fa作为循环工质,以实验用小型盐梯度太阳池下对流层60~90℃储存热量作为供热热源,建立盐梯度太阳池低温有机朗肯循环(ORC)发电系统数学模型,研究了有机工质的蒸发温度对系统性能的影响。分析结果表明:蒸发温度的变化对太阳池下对流层回热温度、系统工质流量、不可逆损失和效率都有着重要影响,另外蒸发温度变化对功率有双重影响,存在一个最佳蒸发温度,使得系统功率达到最大。     

Construction and operation activities at the University of Illinois Salt Gradient Solar Pond

The construction and operational activities at the University of Illinois (U.I.) salt gradient solar pond facility are described. Several discussions are given on major topics related to solar ponds. The discussions also contain cost information where available or relevant.Overall, the U.I. solar pond has demonstrated that solar ponds for low grade heating applications, such as space heating and grain drying, can be designed in a simple manner that requires minimal maintenance duties. More time is needed to refine operation procedures, however, enough information has been collected such that the basic design used for the pond can be replicated without significant modifications.     

Solar desiccant systems for grain drying

The mathematical model for the Kathabar Spray-Cel System developed by the authors in a previous work was used to predict the temperature and humidity ratio of the air at the drying bin inlet. The unsteady grain cooling model developed by Huzayyin (Ph.D. dissertation, Kansas State Univ. at Manhattan (1972); Ref. [1]) is modified and coupled with the liquid desiccant system model to study the feasibility of using the system desiccated air in drying applications. The model shows the infeasibility of using desiccated air for grain drying. The liquid desiccant system was modified to simulate adiabatic operation and coupled to the drying model. The new system gave much better results, but its use for grain drying is still predicted to be economically unfeasible.     

Effect of Temperature Dependent Internal Heat Transfers on the Performance of a Solar Still

In this paper, an effect of the temperature dependence of internal heat transfer coefficients on the performance of a single basin solar still has been studied by incorporating the change of water mass in the basin with time, initial basin water temperature etc. On the basis of numerical calculations based on simple transient analysis, the following conclusions have been drawn:

i) the evaporative heat transfer coefficient is a strong function of brine temperature, and

ii) the change of brine mass with time has insignificant effect on the performance of the still in nocturnal production which is in accordance with the assumption made by Malik and Tran (1973). This is true for other cases also.

These have also been validated by experimental results.     

High Concentration Silicon Solar Cells

The present state-of-the-art of silicon high concentration solar cells is reviewed. Two cell structures, the silicon point contact cell and the microgrooved cell structure, have demonstrated efficiencies of 28% at 150× and 24.7% at 100×, respectively. The problems associated with operation at high concentration are discussed. It is noted that Auger recombination is the limiting factor in the operation of high efficiency solar cells, affecting not only the open circuit voltage, but having a great impact on the short circuit current as well. With additional design improvements, efficiencies over 30% at concentration appear to be within reach.     

太阳能热泵技术研究进展

综述了国内外太阳能热泵的理论与实验研究进展，介绍了太阳能热泵系统的分析与评价方法，列举了一些有关太阳能热泵技术的研究及应用成果，并阐述了太阳能热泵的应用前景。     

Solar still with vapor adsorption basin: Performance analysis

In this work, a vapor adsorption type solar still was designed, fabricated and tested at Thiagarajar College of Engineering, Madurai, India. A vapor adsorbent pipe network comprising activated carbon–methanol pair was integrated with the basin. Losses from the bottom of the still are considerably reduced due to sensible heat absorption by the activated carbon and latent heat of vaporization by methanol. Also water circulated through the inner tube of the adsorbent bed is used as a feed to basin, thus enhancing the evaporation rate during day time. The increase in temperature of the basin due to adsorbent bed and condensation of methanol vapor, augments the evaporation rate during the night time also. Sponges, gravels, sand and black rubbers were used in the vapor adsorption type solar still for improving the yield. Experimental results were compared with ordinary conventional basin type still. The governing energy balance equations for both conventional and vapor adsorption type solar still were solved analytically and compared with experimental results. Theoretical analysis gave very good agreement with experimental results.     

Solar hydrogen production: A comparative performance assessment

Hydrogen is a sustainable fuel option and one of the potential solutions for current energy and environmental problems. Its eco-friendly production is really crucial for better environment and sustainable development. In this paper, various solar hydrogen production methods are discussed. A comparative performance assessment study of solar thermal and photovoltaic (PV) hydrogen production methods is carried out. It is found that the solar thermal hydrogen production via electricity production is an environmentally benign method and possesses higher exergy efficiency than PV hydrogen production. However, the latter is better in a way that it does not involve any moving parts. PV hydrogen production suffers lower exergy efficiency because of low PV efficiency.     

Heat pipes thermoelectric solar collectors for energy applications

This study investigates the load characteristics of heat pipe thermoelectric solar collector (HPTSC) in practice. Heat pipe thermoelectric solar collector converts the heat generated by the Sun directly into electrical energy and produces hot water as well. The maximum power in HPTSC is obtained when the internal resistance of the thermoelectric module is equal to the load resistance. It has been observed to be possible to produce both hot water and electricity by improving available solar collectors or producing new generation HPTSC. While it is possible to generate an electrical power of 160 W from a HPTSC of one square meter using the thermoelectric method, the power produced with an average photovoltaic panel with the same area is only 132 W. Accordingly, HPTSC is a superior alternative not only to available solar collectors, but also to available PV panels. HPTSC, involving three different technologies, is environmentally friendly and certainly a product that allows for more efficient use of solar energy.     

太阳能热水器传热传质和强化传热研究

在低温太阳能光热光伏联合应用试验台的基础上,结合GB/T 17049—2005,利用Gambit、Ansys Fluent和Tecplot软件,对全玻璃真空管太阳能热水器进行传热传质和强化传热分析。结果表明:所建立的二维数值计算模型,能准确反映同一条件下,全玻璃真空管太阳能热水器的变化趋势;在数值模拟基础上,确定了单面受热时的最佳安装角度为51°,加装反光板类似双面受热的最佳安装角度为38°;在粗略估算和细化分析的基础上,确定了不同真空管结构的最佳导流板长度及安装位置;通过实验和数值模拟,确定了58mm×1 800mm为优化的全玻璃真空管结构。     

Theoretical maximal efficiency for a silicon solar cell with a two infrared-photon absorption in an inserted sub-structure

One of the possible optimized device designs far silicon solar cell photocurrent enhancement, consists of a cell having an inserted sub-structure with extrinsic gap levels. A middle-gap impurity and defect level band may actually allow a two infrared photon absorption. The junction near local defect layer design (Li et al., 1992) was assumed to enhance the sub-band-gap light absorption but it also enhances the recombination mechanisms strongly. Kuznicki (1993) has proposed another design with an L-H interface insertion at the edges of a continuous sub-structure to avoid extra recombination. The maximal photocurrent due to an additional infrared absorption calculated in this way is smaller than ΔI_ph = 16.8 mA cm⁻². In the case when the widths of the absorbing sub-structure are negligible compared to the width of the emitter, the simulated maximal efficiency can vary from 30.87 mW cm⁻² to 40.51 mW cm⁻².     

塔式太阳能电站熔盐换热器设计发展概述

熔盐换热器作为塔式太阳能熔盐储热发电系统中的一个重要设备,随着太阳能储热发电技术的发展,产生了各种不同形式的设计。从熔盐物性特点和太阳能储热发电技术特点的角度出发,对熔盐换热器设计要点进行了阐述。并通过归纳总结新型换热器技术在熔盐换热器上的应用,来展望熔盐换热器技术的发展趋势。     

Transient Analysis of a Two-Phase Flat-Plate Solar Collector

A tubeless flat-plate solar collector, assembled in a natural circulation circuit and charged with refrigerant-11 (R-11), was analysed and investigated. It is found that the transient response of this system could be predicted with good accuracy by an exponential function. The deviation between theoretical and experimental values were insignificant.     

Solar cells from carbon

A photovoltaic device, of the Schottky-barrier variety, has been fabricated from pure buckminsterfullerene and silver. The paper presents, as motivation for this work, a number of reasons why fullerenes may turn out to be excellent materials for solar cell fabrication. A summary is given of the experimental techniques employed and the results obtained thus far.     

Modeling and Testing of a Thermosiphon Solar Air-Heater

A flat-plate solar air-heater was analysed and tested. A model was proposed to predict air mass-flow rate and useful energy collection. The model snowed good agreement with the experimental data. The system performance was characterised with wide scatter of data and low efficiency. However, the low efficiency is tolerated for the sake of simplicity and economic considerations.     

Salt diffusion in a temperature field: Application to salinity profiles in solar ponds

In the present investigation, the process of diffusion of salt in a vertical column of liquid, subjected to temperature variations of the types T(x) = constant, linear ( = a + bx) and parabolic ( = a + bx - cx²); with a constant concentration difference between the top and the bottom (0 and 25 per cent, respectively) is studied. It is seen that a linear temperature gradient, T(x) = a + bx, leads to a near convex parabolic salt concentration profile with maximum deviations increasing from 13.5 per cent (at 40°C) to 14.8 per cent (at 70°C) and eventually to 15.7 per cent (at 90°C) with respect to the linear concentration value of 12.5 per cent (by weight) at the midpoint. Conversely, the parabolic temperature profile as well as the modified profile due to the Soret effect leads to near cubic salt profiles which differ only by 2–3 per cent in the upper half of the pond. However, they show a point of inflexion at larger depths near the bottom around which the convex profiles change over and become concave. Subsequently, these studies have been extended to compute the salinity profiles of thermal configurations of the operational solar pond.     

Solar energy conversion with hot electrons from impact ionisation

Impact ionisation in combination with carrier-carrier scattering in the absence of phonon scattering in an illuminated semiconductor leads to an energy distribution of electrons in the conduction band and of holes in the valence band which is best described by a single Fermi-distribution with no splitting of quasi-Fermi-energies, but with a temperature different from the lattice temperature. To make proper use of this distribution in a solar cell, electrons and holes must be withdrawn through membranes, which are composed of narrow band, large bandgap semiconductors and which allow only electrons or holes in a narrow energy range to be transmitted. Current-voltage characteristics and efficiencies are calculated analytically for maximum concentration of the solar radiation. A maximal efficiency of 85% is found for a vanishing bandgap of the solar cell material.     

Solar distillation of water using a V-trough solar concentrator with a wick-type solar still

A V-trough solar concentrator has been combined with an inclined flat-plate wick-type solar still. Outdoor testing was carried out with and without the solar concentrator on clear days in summer and winter. The equipment was used to investigate the enhancement of the outdoor performance of the wick-type solar still by the solar concentrator.It has been concluded that use of the solar concentrator with the inclined wick-type solar still can lead to a greater fractional increase in still efficiency and productivity on clear days in winter than on clear days in summer.     

以空气为携热介质的开式太阳能蓄能热泵循环研究与分析

以空气为携热介质的开式太阳能吸收式热泵系统为研究对象，在原有制冷循环基础上，根据冬季蓄能热泵循环运行特点对系统进行改进；并以西安地区为例对循环进行计算和分析，探讨其蓄能情况和影响系统工作性能的因素。     

Solar angles revisited using a general vector approach

Rather than follow the standard technique using direction cosines or major axes vectors to define the angles of the sun, we develop the necessary formulae from a 3-tuple vector based analysis. The direction of the sun with respect to a Cartesian coordinate system is defined as a unit vector, as is the orthogonal to a surface intended to accept solar radiation. The vector formulation is powerful and universal. More importantly, the diagrams used to describe the relative motion of the sun with respect to the Earth are quite simple, leading to less confusion when translating the geometry to algebra. An interesting result on the change in solar angle with time follows.