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.     

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 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.     

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.     

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。     

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.     

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.     

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 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.     

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.     

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 energy investments in a developing economy

Almost all technical development efforts in both the developed and the developing nations depend on electrical energy. However, the sources of conventional means of electricity generation are fast depleting. Consequently, most industrialised nations have research on solar energy as a way to avert impending energy crisis.This paper presents the investments in energy generation in Nigeria. The efforts made in solar energy research and utilization are highlighted. The financial investments by the Nigerian government to the development of electrical power industry between 1990 and 1994 are presented and discussed. A case is made for a systematic and coordinated financial investments in solar energy research and adaptation to complement power generation from conventional sources.     

Experimental investigation of a solar tower based photocatalytic hydrogen production system

In this paper, production of hydrogen from concentrated solar radiation is examined by a laboratory scale solar tower system that is capable of handling continuous flow photocatalysis. The system is built and studied under a solar simulator with an aiming area of 20 × 20 cm². The fraction of solar spectrum useful for water splitting depends on the energy band gap of the selected photocatalyst. Two types of nano-particulate photocatalysts are used in this work: ZnS (3.6 eV) and CdS (2.4 eV). The effect of light concentration on photocatalysis performance is studied using Alfa Aesar 99.99% pure grade, 325 mesh ZnS nano-particles. An improved quantum efficiency of 73% is obtained as compared to 45% with the same sample under non-concentrated light in a previous study. Only 1.1% of the energy of the solar radiation spectrum can be used by ZnS catalyst. A mixture of CdS and ZnS nano-particulate photocatalysts (both Alfa Aesar 99.99% pure grade, 325 mesh) is used to conduct a parametric study for a wider spectrum capture corresponding to 18% of the incident energy. Hydrogen production increases from 0.1 mmol/h to 0.21 mmol/h when the operating conditions are varied from 25 °C and 101 kPa to 40 °C and 21 kPa absolute pressures. Furthermore, the implementation of a continuous flow process results in an improvement in the energy efficiency by a factor of 5.5 over the batch process.     

Solar thermochemical production of hydrogen––a review

This article reviews the underlying science and describes the technological advances in the field of solar thermochemical production of hydrogen that uses concentrated solar radiation as the energy source of high-temperature process heat.     

Solar passive heating through a thermosyphon air panel

Thermosyphon air panels installed on the south wall of a building are being used for solar space heating in the cold desert climates of North India. This paper presents a simulation model to predict the performance of such panels; a numerical evaluation of the performance has been made, using the meteorological data for January (having maximum and minimum temperatures equal to ?2·°C and ?14·2°C, respectively, and an insolation of 4·58 kWh/m² day on the horizontal surface). For typical weather condition in January a 1·62 m² thermosyphon air panel is seen to collect about 2·3 kWh of energy per day with a rise of temperature of about 2·5°C to 13·5°C (with room air at 18°C as inlet air) and a working efficiency of approximately 32·5 per cent.     

一种多孔介质太阳能吸热器传热研究

为了研究塔式太阳能多孔介质吸热器的传热传质特性,建立吸热器稳态传热模型,选择适合多孔介质太阳能吸热器的体积对流换热系数模型,采用数值方法求解,并分别分析孔隙密度、孔隙率和入口空气速度对温度场的影响。文中技术可以为同类型太阳能吸热器的设计和改造提供参考。