Analysis of terrestrial solar radiation exergy

Based on Candau’s definition of radiative exergy, the exergy of the extraterrestrial and the terrestrial solar radiation are computed and compared by using the solar spectral radiation databank developed by Gueymard. The results show that within the spectrum region from 0.28 to 4.0 μm, the total energy quality factor (i.e., the exergy-to-energy ratio) of extraterrestrial solar radiation is about 0.9292, and that of the global terrestrial solar radiation is about 0.9171 under US standard atmosphere condition and zero solar zenith angle. The terrestrial solar spectral radiation exergy flux is large in the near ultraviolet and the visible light region. The reference radiation exergy spectra are obtained under atmospheric conditions consistent with ASTM standard G173-03. The effect of tilt angle on the terrestrial solar radiative exergy for inclined surface, and the effect of air mass on total energy quality factor of the terrestrial solar radiation for horizontal surface are analyzed. With the increase of tilt angle, the terrestrial solar spectral radiation exergy flux initially increases and then decreases, the total energy quality factor of the diffuse part decreases monotonically, while that of the direct part is invariant. The total energy quality factor of the direct, the diffuse and the global terrestrial solar radiation all decrease with the increase of air mass.     

Direct beam and hemispherical terrestrial solar spectral distributions derived from broadband hourly solar radiation data

Multiple junction and thin film photovoltaic (PV) technologies respond differently to varying terrestrial spectral distributions of solar energy. PV device and system designers are concerned with the impact of spectral variation on PV specific technologies. Spectral distribution data are generally very rare, expensive, and difficult to obtain. We modified an existing empirical spectral conversion model to convert hourly broadband global (total hemispherical) horizontal and direct normal solar radiation to representative spectral distributions. Hourly average total hemispherical and direct normal beam solar radiation, such as provided in Typical Meteorological Year (TMY) data, are spectral model input data. Default or prescribed atmospheric aerosols and water vapor are possible inputs. Individual hourly and monthly and annual average spectral distributions are computed for a specified tilted surface. The spectral range is from 300 nm to 1800 nm. The model is a modified version of the Nann and Riordan SEDES2 model. Measured hemispherical spectral distributions for a wide variety of conditions at the Solar Radiation Research Laboratory at the National Renewable Energy Laboratory, Golden, Co. and Florida Solar Energy Center (Cocoa, FL) show that reasonable spectral accuracy of about ±10% is obtainable with exceptions for weather events such as snow. Differing cloud climatology and variable albedo and aerosol optical depth atmospheric conditions can lead to spectral model differences of 30–40%.     

The solar radiation resource

We discuss the characteristics of solar radiation which are most useful for the assessment of solar technologies. Graphs are presented which show the total annual insolation incident on the principal tracking and non-tracking collectors. Additional graphs are developed for the latitudinal and seasonal variations of solar radiation in the absence of an atmosphere. These are then compared with measurements averaged over the U.S. SOLMET sites to provide an understanding of the role of atmospheric effects on the seasonal variations of solar radiation.     

The solar radiation climate of Thailand

Geographical, seasonal, and diurnal variations of global solar radiation in Thailand are surveyed. Seasonal effects are shown by separate studies for eight 1.5 month periods of the year defined by standard solar declination values. Detailed maps are given of the geographical distribution of solar radiation prepared from data on cloudiness at 44 stations, duration of sunshine at 18 stations, and linear regressions relating radiation to sunshine at Chiang Mai and Bangkok. The highest mean values are above 19.5 MJ m⁻² d⁻¹ and are widespread in spring. The lowest values are below 15.0 MJ m⁻² d⁻¹ in restricted localities with heavy rainfall in autumn.Rough estimates of diffuse solar radiation and atmospheric turbidity are made from the radiation-sunshine regression parameters. Diffuse radiation averages 8.4 MJ m⁻² d⁻¹. Turbidity at Chiang Mai is high in spring and low in summer and autumn; at Bangkok it is high throughout the year.The diurnal variation of global solar radiation determined from hourly measurements at Chiang Mai and Bangkok is analysed. The mean midday radiation fluxes range from 0.80 kW m⁻² in spring to 0.60 kW m⁻² in autumn. On the average the radiation received in the afternoon is slightly less than that received in the morning.     

Sunshape distributions for terrestrial solar simulations

In considering solar concentrating systems, the energy distribution in the focal plane depends, among other things, on the radial distribution (sunshape) of the incident solar energy. Individual sunshapes are created by the small angle forward scattering of sunlight off aerosols in the troposphere, having the effect of transferring some part of the solar energy from within the solar disk to the circumsolar aureole. The ratio of the amount of energy contained in the circumsolar aureole to the total amount of direct energy arriving from the sun, being that from the solar aureole and within the solar disk, is termed the circumsolar ratio (CSR) and is a useful parameter for characterising individual sunshapes. The degree to which the energy distribution in the focal plane of an optical system depends on a characteristic sunshape is usually not well defined, but it is clear that it is non-negligible. Using the Lawrence Berkeley Laboratory’s vast circumsolar database, collected from 11 sites across the United States in the late 1970s and early 1980s, and the recently published sunshapes from the German Aerospace Centre (DLR) correlating three European sites, this paper describes a sunshape model that is independent of geographic location. Further, this paper illustrates that, on average, the circumsolar ratio defines the spatial energy distribution across the solar disk and aureole, and presents an algorithm that can be used to model these distributions for simulating solar concentrating systems.     

A terrestrial solar energy power system

Development of an effective solar energy utilization technique is of prime importance in solving the energy crisis mankind is confronted with today. In recent years advancements have been made in high temperature measurements, high efficiency selective radiation materials, high temperature heat pipes, heat storage medium, semiconductor manufacturing techniques, space technology, etc. In this article the authors outline a solar energy utilization system (a terrestrial solar energy power system) and discuss the feasibility of a solar energy power system.     

Design of solar cells for terrestrial use

The various aspects that must be considered to successfully design solar cells for terrestrial systems are presented. Some of the more recent developments in solar cell technology are mentioned. It is concluded that the most logical approach to the use of silicon solar cells for terrestrial applications is to utilize solar concentrators in conjunction with cells specially designed for such operations. The factors that affect solar-cell performance are discussed, and an experiment is described that optimizes the most important parameters for obtaining the best performance at intensities of between 100 and 400 milliwatts per square centimeter. The characteristics of such optimized cells are compared with the more common cell designs with regard to the various electrical parameters. A discussion of cell-concentrator systems is presented and some cost estimates are given.     

The fluctuation of solar radiation in Thailand

Fluctuations in the daily solar radiation are examined in an unbroken 5-yr sequence of measurements at Bangkok, and are also estimated from daily sunshine measurements at Bangkok and 3 other stations in Thailand. Seasonal effects are shown by separate studies for eight $\text{1}\text{1}\text{2}$ month periods of the year defined by standard solar declination values.During the dry season in winter and spring the frequency distribution of daily totals of global solar radiation at Bangkok has a peak near 20 MJ m^?2 d^?1 and is skewed towards low values. During the wet season in summer and autumn the distribution is more dispersed. Elsewhere the distributions are similar to those at Bangkok.The time series of daily totals of global solar radiation at Bangkok is analysed as a second order random process. The observed annual frequencies of runs of consecutive days with low radiation at Bangkok are given. There are 32.0 isolated days, 9.4 pairs of days, and 3.4 runs of 3 days per year with radiation less than 12.57 MJ m^?2 d^?1. These results are adequately described by the second order theory. The runs are most likely to occur in summer and autumn. Elsewhere in Thailand the annual frequencies of the runs and their seasonal distributions are almost the same as at Bangkok, except that in the south the runs are more likely to occur later in the year.     

The estimation of solar radiation in New Zealand

Measurements of solar radiation which were made during the solar energy projects at DSIR, together with Meteorological Service data have been used to establish New Zealand parameters for the ASHRAE clear sky radiation model. It is shown that these new parameters give good agreement between observed and estimated values for both horizontal and vertical surfaces. There is, however, some complication for east- and south-facing surfaces. The values of sky-diffuse radiation on clear days were appreciably lower than those observed in the US and some other countries. Otherwise the diffuse/global ratios differed by not more than 15% from those of other investigators for most of the range.     

The estimation of solar radiation data in Czechoslovakia

Estimation of radiation data for solar energy utilization in Czechoslovakia is described. The mean monthly sums and average instantaneous values of global and diffuse irradiances were calculated using relationships after Angström, Liu-Yordan and Collares-Pereira tested for Czechoslovak conditions. Characterization of the network of radiation measurements is given.     

紫外线知识讲座——紫外辐射定义及其分类

臭氧洞和全球气候变化是本世纪人类面临的两大环境危机,关系着全人类文明的延续和毁灭。这两大环境危机,也为人类开启全新的环境史观。从侧重环境污染问题的解决到鉴定国际公约禁止氟氯碳化物使用、限制温室气体排放总量等,现实环境问题全球化的趋势没有任何个人、地区或国家可以置身事外。 就国内来说,紫外线问题长久以来并未受到应有的重视。而国外自上个世纪80年代以来,在世界卫生组织、世界气象组织、联合国开发计划署等国际机构的倡议下,通过电视、广播及报纸等媒体和网络上获知当天或次日的紫外线指数,使得紫外线议题走进普通百姓生活。此举不但可使公众到户外工作或活动之前,能获得正确的紫外线辐射量的信息以助其采取相应的防护措施,更提高了一般民众避免过度曝晒紫外线的危机意识,使公众健康咨询的水准向前迈进一大步,也是近年来环保工作的一大突破。作为宣传和利用太阳能的媒体,在宣传利用太阳能技术的同时,也有义务普及紫外线知识,让公众了解紫外线。紫外线知识讲座从本期开始,由中国气象局研究员王炳忠先生主讲。     

Low-cost encapsulation materials for terrestrial solar cell modules

Solar cell modules must undergo dramatic reductions in cost in order to become economically attractive as practical devices for the production of electricity. A federal goal seeks to have, by 1986, an industrial capability of producing solar cell modules at a cost of 50¢ per W (in 1975 dollars) and a service lifetime of 20 yr. Today's modules cost more than $11.00 per W, and they have an undefined lifetime. Part of the cost reductions must be realized by the encapsulation materials which are used to package, protect, and support the solar cells, electrical interconnects, and other ancillary components. It is estimated that to meet a cost goal of 50¢ per W, encapsulation materials, including the structural substrate or superstrate, should cost between $2.70 and $5.00 per m² of module area (in 1975 dollars). This article presents the findings of material surveys intended to identify low cost materials which could be functional as encapsulants. This article further assesses the prognosis for achieving an encapsulation system at the lower cost goal of $2.70 per m², and identifies the technologies which must be advanced or developed to achieve 20-yr life with the lowest costing materials.     

Measurement of solar radiation by silicon solar cell

Investigations into the use of a silicon solar cell to measure solar radiation intensity are described. The effect of optical path length ratio and atmospheric constituents are discussed. A survey is made of other photovoltaic devices. It is concluded that, on presently available data, the silicon cell is the most suitable for the purpose.

Comparisons are made between the signals obtained from a silicon-solar-cell radiometer and a Kipp thermopile type solarimeter used as a standard. One set of comparisons is made for 30-minute intervals on clear days and is analysed so that known effects due to angle of incidence are allowed for and variations in the signals caused by spectral quality of the radiation can be separated. This set of comparisons shows an extreme spread of ±13 percent on a reference constant determined for midday clear sky. This extreme spread includes variations of +6.5 to −3 percent at midday together with variations during the course of any one day.

A second set of comparisons made during whole days or long periods, during which conditions were stable, gave rise to two calibration constants, one for clear-sky and one for overcast-sky conditions.

If an over-all calibration constant is desired for all conditions, then a value of 15.79 mA cm⁻² min/Langley is obtained with a probable error of to percent. The skew effect here is because more readings were taken for clear-sky conditions, thus favoring the lower constant for these conditions.     

Global solar radiation estimation

This paper presents the comparison between the observed and estimated values of global solar radiation on horizontal surfaces obtained from the linear Angstrom type of correlation of Rehman and Halawani [1] for 52 cities spread in 11 countries; viz. India, Egypt, Sri Lanka, Spain, Zimbabwe, Yemen, Sudan, Italy, Zambia, Hong Kong, and Malaysia. The comparisons are also made with the local linear models wherever available. The estimated values are compared with the measured values in terms of percent error, mean bias error (MBE), mean absolute bias error (MABE), root mean square error (RMSE), and mean percent error (MPE). This study finds that the model of Rehman and Halawani [1] is capable of giving estimates within an acceptable mean percent error of 5% and less for 33% of cities and between 5–10% for 50% of cities.     

The oblateness effect on the extraterrestrial solar radiation

Calculations of the daily solar radiation incident at the top of the Earth's atmosphere, with and without the effect of the oblateness, are presented in a figure illustrating the seasonal and latitudinal variation of the ratio of both insolations. It is shown that, in summer, the daily insolation of an oblate Earth is slightly increased in two regions symmetric with respect to the summer solstice. In winter, the flattening effect results in a somewhat more extensive polar region, the solar energy input being always reduced (in some cases by more than 2 per cent) when compared to a spherical one. In addition, we also numerically studied the mean daily solar radiation. It is found that the mean summer daily insolation is scarcely increased between the equator and the subsolar point, but decreased poleward of the above mentioned limit. In winter, however, the mean daily insolation is always reduced, the maximum loss of insolation attaining as much as 1 per cent in the 55–85° latitude interval. The partial gain of the mean summertime insolation being much smaller than the reduction during winter season evidently yields a mean annual daily insolation which is decreased, maximally by about 0.3 per cent, at all latitudes.     

The influence of radiation absorption on solar pond stability

This paper presents a study of the gravitational stability of a salty layer of a fluid subject to an adverse temperature gradient as a result of heat absorption. This is intended to model solar ponds where an artificial gradient of salt concentration in water is used to prevent convective motions induced by the absorption of solar radiation. The stability of the Boussinesq approximation of the Navier-Stokes equations is analysed for perturbations of a certain kind imposed on the stationary solution. The marginal states for the onset of convection are obtained using a Galerkin method based on a weak formulation of the governing equations. The analysis considers solar energy absorption in the layer and assumes prescribed heat flux values as boundary conditions for the temperature equation. Results are compared with those obtained earlier by different authors for a layer of fluid, heated from below, with linear profiles of both salt concentration and temperature.