The Sun’s apparent position and the optimal tilt angle of a solar collector in the northern hemisphere

In this paper, the Julian dating system is adopted to calculate the Sun’s apparent position. Both the sunshine duration and the optimal installation angle of a fixed solar collector are obtained for different time periods and latitudes in the northern hemisphere. To simulate different operating environments, both kinds of radiation flux are considered, i.e. extraterrestrial radiation and the global radiation calculated using an empirical model. The results show that Julian dating system is precise enough to predict the Sun’s locus according to analyses of the solar declination and the azimuth and elevation angles. The orientation that a solar collector must be installed at can be roughly estimated by determining the sunshine duration. The majority of the Sun’s path lies in the southern sky over a year, and hence the sunshine duration in the southern sky is longer, except for locations with latitudes below 1.5°. The yearly optimal angles are positive (approximately 0.91 and 0.76 multiplied by the latitude for extraterrestrial and global radiation, respectively), for latitudes below 65^o. Above this, the curves are flatter, and the differences between the two types of radiation flux become greater. The ratio of the yearly irradiation captured by a collector installed at its yearly optimal angle to that captured by the ground surface increases with latitude, and reaches a maximum of 1.71 and 1.35 near latitudes of 65° for extraterrestrial and global radiation, respectively. The efficiency of a solar collector decreases when operating in a cloudy environment. The amount of global radiation incident on the ground surface is about 0.51-0.66 times that of extraterrestrial radiation throughout the hemisphere.     

Models of solar radiation with hours of bright sunshine: A review

In the design and study of solar energy, information on solar radiation and its components at a given location is very essential. Solar radiation data are required by solar engineers, architects, agriculturists and hydrologists for many applications such as solar heating, cooking, drying and interior illumination of buildings. For this purpose, in the past, several empirical correlations have been developed in order to estimate the solar radiation around the world. The main objective of this study is to review the global solar radiation models available in the literature. There are several formulate which relate global radiation to other climatic parameters such as sunshine hours, relative humidity and maximum temperature. The most commonly used parameter for estimating global solar radiation is sunshine duration. Sunshine duration can be easily and reliably measured and data are widely available.     

Solar constant values for estimating solar radiation

There are many solar constant values given and adopted by researchers, leading to confusion in estimating solar radiation. In this study, some solar constant values collected from literature for estimating solar radiation with the Ångström-Prescott correlation are tested in China using the measured data between 1971 and 2000. According to the ranking method based on the t-statistic, a strategy to select the best solar constant value for estimating the monthly average daily global solar radiation with the Ångström-Prescott correlation is proposed.     

Correction to McCartney et al. (2010).

Reports an error in "Testing a series of causal propositions relating time in child care to children’s externalizing behavior" by Kathleen McCartney, Margaret Burchinal, Aliso Clarke-Stewart, Kristen L. Bub, Margaret T. Owen and Jay Belsky (Developmental Psychology, 2010[Jan], Vol 46[1], 1-17). On the first page of the article “Testing a Series of Causal Propositions Relating Time in Child Care to Children’s Externalizing Behavior,” by Kathleen McCartney, Margaret Burchinal, Alison Clarke- Stewart, Kristen L. Bub, Margaret T. Owen, Jay Belsky, and the NICHD Early Child Care Research Network (Developmental Psychology, 2010, Vol. 46, No. 1, pp. 1–17), author Alison Clarke- Stewart’s name was misspelled as Aliso Clarke-Stewart. In addition, the e-mail address listed for the corresponding author Kathleen McCartney is incorrect. The correct e-mail address is: kathleen_mccartney@gse.harvard.edu. The online versions of this article have been corrected. (The following abstract of the original article appeared in record 2009-24671-001.) Prior research has documented associations between hours in child care and children’s externalizing behavior. A series of longitudinal analyses were conducted to address 5 propositions, each testing the hypothesis that child care hours causes externalizing behavior. Data from the National Institute of Child Health and Human Development Early Child Care Research Network (NICHD) Study of Early Child Care and Youth Development were used in this investigation because they include repeated measures of child care experiences, externalizing behavior, and family characteristics. There were 3 main findings. First, the evidence linking child care hours with externalizing behavior was equivocal in that results varied across model specifications. Second, the association between child care hours and externalizing behavior was not due to a child effect. Third, child care quality and proportion of time spent with a large group of peers moderated the effects of child care hours on externalizing behavior. The number of hours spent in child care was more strongly related to externalizing behavior when children were in low-quality child care and when children spent a greater proportion of time with a large group of peers. The magnitude of associations between child care hours and externalizing behavior was modest. Implications are that parents and policymakers must take into account that externalizing behavior is predicted from a constellation of variables in multiple contexts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

考虑保障收购年利用小时数的光伏发电系统最佳容配比分析

针对目前普遍通过分析度电成本来确定光伏发电系统最佳容配比(光伏组件的标称功率之和与逆变器功率的比值)的现状,本文提出了一种采用净现值法确定已设定保障收购年利用小时数的光伏发电系统最佳容配比的方法.以太阳能资源较好的银川地区为例,通过计算该地区建立的光伏电站在不同保障收购年利用小时数下的净现值,分析了不同交易电价、不同保...     

Quality control and estimation of global solar radiation in China

Measurements of surface radiation in China are too sparse to meet demand for scientific research and engineering applications. Moreover, the radiation data often include erroneous and questionable values though preliminary quality-check has been done before the data release. Therefore, quality control of radiation data is often a prerequisite for using these data. In this study, a set of quality-check procedures were implemented to control the quality of the solar radiation measurements at 97 stations in China. A hybrid model for estimating global solar radiation was then evaluated against the controlled data. The results show that the model can estimate the global radiation with accuracy of MBE less than 1.5 MJ m⁻² and RMSE less than 2.8 MJ m⁻² for daily radiation and RMSE less than 2.0 MJ m⁻² for monthly-mean daily radiation at individual stations over most of China except at a few stations where unsatisfactory estimates were possibly caused by severe air pollution or too dense clouds. The MBE averaged over all stations are about 0.7 MJ m⁻² and RMSE about 2.0 MJ m⁻² for daily radiation and RMSE about 1.3 MJ m⁻² for monthly-mean daily radiation. Finally, this model was used to fill data gaps and to expand solar radiation data set using routine meteorological station data in China. This data set would substantially contribute to some radiation-related scientific studies and engineering applications in China.     

工科院校如何面对课时数“缩水”的有机化学

有机化学是工科院校一门重要的专业基础课,文章针对工科院校有机化学课时数减少的问题,结合笔者有机化学教学经验,阐述了工科院校如何应对这一现状,从课程内容、教学方法、考核方式等方面提出了课程的改革措施。     

基于数字孪生的复杂产品离散装配车间动态调度

面向多品种变批量生产的复杂产品离散装配车间是典型的复杂制造系统,其运行过程呈现高复杂性、强动态性和不确定性因素多等特征,为实现复杂产品离散装配车间的动态调度,提出一种基于数字孪生的复杂产品离散装配车间动态调度方法,通过物理空间和虚拟空间之间的数据交互进行更精确的动态调度.构建了基于数字孪生的复杂产品离散装配车间调度框架...     

地埋管间断工作进出孔平均温度预测方法研究

按不改变每天总换热量的原则,将单位长度地埋管换热孔在制冷季或制热季中每天的实际释热或取热过程简化为一个矩形释热或取热脉冲,脉冲大小为单位长度地埋管换热孔的设计释热量或设计取热量,时间为每天的等效满负荷释热或取热小时数。采用线热源理论和热流叠加原理,推导若干个矩形脉冲负荷作用后地埋管换热器进出口温度平均值的计算公式,并通过长期现场岩土热响应试验对该公式进行了验证。在已知制冷季或制热季天数和地埋管换热器每天等效满负荷工作小时的基础上,通过设定地埋管在制冷季和制热季传热流体的最高或最低温度,可用该公式计算单位长度地埋管换热孔的设计释热量或取热量。