Investigation of the effect of weather conditions on solar radiation in Brunei Darussalam

The amount of solar radiation received on the earth's surface is known to be highly influenced by the weather conditions and the geography of a particular area. This paper presents some results of an investigation that was carried out to find the effects of weather patterns on the solar radiation in Brunei Darussalam, a small country that experiences equatorial climate due to its geographical location. Weather data were collected at a suitable location in the University Brunei Darussalam (UBD) and were compared with the available data provided by the Brunei Darussalam Meteorological Services (BDMS). It has been found that the solar radiation is directly proportional to the atmospheric temperature while it is inversely proportional to the relative humidity. It has also been found that wind speed has little influence on solar radiation. Functional relationships between the solar radiation and the atmospheric temperature, and between the solar radiation and the relative humidity have also been developed from the BDMS weather data. Finally, an artificial neural network (ANN) model has been developed for training and testing the solar radiation data with the inputs of temperature and relative humidity, and a coefficient of determination of around 99% was achieved. This set of data containing all the aforementioned results may serve as a guideline on the solar radiation pattern in the geographical areas around the equator.     

新型遮阳系统对太阳散射辐射的遮阳效果研究

通过搭建室外太阳散射辐射得热量的测量装置,对透过遮阳系统进入室内的太阳散射辐射得热量进行了试验研究,并通过建立理论模型对测试结果进行了验证分析,结果表明:该实验装置对透过遮阳系统的太阳散射辐射得热量的测试是可行的,同时通过试验得到了该遮阳系统对太阳散射辐射的遮阳效果。     

太阳日散射概率密度模型

太阳散射是太阳能系统分析的重要参数。在有太阳总射而没有散射的情况下，散射可通过总射估计出。在北京和成都实测数据基础上，建立了具有2个参数的日散射概率密度模型。该模型的参数通过迭代方法给出。模型基本反映了日散射的分布特征。给出了模型应用的一般方法。讨论了模型的通用性。     

带有平面反射板的全玻璃真空集热管表面能流分析

本文用解析方法对带平面反射板的单根太阳能真空集热管表面辐射流分布进行了分析，并得出了相应的结果。太阳直射辐射和散射辐射直接或通过反光板间接散布在真空管吸热体表面。为能更清楚地理解辐射的物理过程，在文中对不同辐射成分，不同反射方式分别进行了分析计算。     

Optimum tilt angle and orientation for solar collector in Brunei Darussalam

One of the important parameters that affects the performance of a solar collector is its tilt angle with the horizontal. This is due to the fact that the variation of tilt angle changes the amount of solar radiation reaching the collector surface. A mathematical model was used for estimating the total (global) solar radiation on a tilted surface, and to determine the optimum tilt angle and orientation (surface azimuth angle) for the solar collector in Brunei Darussalam on a daily basis, as well as for a specific period. The optimum angle was computed by searching for the values for which the total radiation on the collector surface is a maximum for a particular day or a specific period. The results reveal that changing the tilt angle 12 times in a year (i.e. using the monthly-averaged optimum tilt angle) maintains approximately the total amount of solar radiation near the maximum value that is found by changing the tilt angle daily to its optimum value. This achieves a yearly gain in solar radiation of 5% more than the case of a solar collector fixed on a horizontal surface.     

Estimation of solar radiation from Australian meteorological observations

A carefully prepared set of Australian radiation and meteorological data was used to develop a system for estimating hourly or instantaneous broad band direct, diffuse and global radiation from meteorological observations. For clear sky conditions relationships developed elsewhere were adapted to Australian data. For cloudy conditions the clouds were divided into two groups, high clouds and opaque (middle and low) clouds, and corrections were made to compensate for the bias due to reporting practices for almost clear and almost overcast skies. Careful consideration was given to the decrease of visible sky toward the horizon caused by the vertical extent of opaque clouds. Equations relating cloud and other meteorological observations to the direct and diffuse radiation contained four unknown quatities, functions of cloud amount and of solar elevation, which were estimated from the data. These were the proportions of incident solar radiation passed on as direct and as diffuse radiation by high clouds, and as diffuse radiation by opaque clouds, and a factor to describe the elevation dependance of the fraction of sky not obscured by opaque clouds. When the resulting relationships were used to estimate global, direct and diffuse radiation on a horizontal surface, the results were good, especially for global radiation. Some discrepancies between estimates and measurements of diffuse and direct radiation were probably due to erroneously high measurements of diffuse radiation.     

文莱LNG的生产和出口

文莱在东盟地区天然气市场中占据着重要地位,其天然气储量为13.8×1012ft3,生产的天然气主要以LNG的形式出口至日本和韩国.文莱的天然气主要由文莱壳牌石油公司(BSP)进行生产,道达尔旗下的两个近海油田也提供一小部分天然气.生产的天然气在文莱液化天然气公司(BLNG)所属的液化处理厂进行液化处理,LNG年生产能力720×104t.文莱国内的天然气消费通过文莱石油销售公司(BSM)供应,其余的天然气由文莱壳牌油轮公司(BST)和文莱天然气油轮公司(BGC)运往海外.白1990年以来,文莱就一直将80％左右的天然气都出口到海外市场.从1973年开始,文莱每年向日本输出500×104t的LNG,1999年又签订了增加供货协议,每年增加到601×104t.韩国与文莱在1997年签订了为期16年的合同,保证每年70×104t的LNG供应.面对2013年即将到期的合同,日、韩两国都加紧了确保LNG长期供应的步伐.这使得中国、印度等国从文莱进口大量LNG的机会变小,但是通过日本和韩国在文莱整个LNG供应链建设过程中所付出的努力,其他LNG进口国至少能够借鉴到保障能源供应的一点经验.     

Diffuse solar radiation estimates from sunshine hours and clearness index for Karachi, Pakistan

Correlations for the estimation of monthly average daily diffuse solar radiation as a function of the sunshine hours and clearness index have been obtained from Karachi. Generally, two types of correlations are used: (a) diffuse radiation as a function of relative sunshine hours and extraterrestrial radiation, and (b) diffuse radiation as a function of global and extraterrestrial radiation. These correlations are mostly first- and second-order polynomials in the sunshine hours and clearness index, indicating the presence of the diffuse solar radiation component. The diffuse solar radiation shows a peak value during the monsoon months of July–August. The diffuse to global ratio is found to be 0.32 from the analysis, and the diffuse to extraterrestrial radiation ratio is nearly 0.19 throughout the year. Among the established relations, Iqbal and Stanhill overestimate the radiation value, while Liu and Jordan underestimate it.     

Evaluation of hourly tilted surface radiation models

This study investigates the performance of the isotropic and four anisotropic hourly tilted surface radiation models by using monthly average hourly utilizable energy as a standard of measure. Utilizable energy is the radiation above a specified threshold level. Differences between the utilizable energy measured and the utilizable energy predicted are observed for various surface slope/azimuth orientations and critical radiation levels. Normalized root mean square difference and normalized mean bias difference statistics are formed to quantify the ability of each model to estimate the utilizable energy on a tilted surface. The influence of horizontal diffuse radiation on tilted surface model performance is examined by comparing the predicted utilizable energy on a tilted surface using both measured horizontal diffuse and estimated horizontal diffuse found from diffuse fraction correlations. On an overall basis, the isotropic sky model showed the poorest performance and is not recommended for estimating the hourly radiation on a tilted surface. The anisotropic models have comparable performance to each other. There was no significant degradation of tilted surface model performance when the diffuse radiation is estimated from a diffuse fraction correlation rather than obtained from measurements.     

Study of diffuse and global radiation characteristics in India

Recently, the Indian Meteorological Department has made available, for 13 locations in India, pyranometric data for total and diffuse radiation on an hourly and daily basis. The period of observation is from 1957 to 1975. This data is analysed to reexamine the correlations between monthly-average daily values of diffuse and total insolation and between hourly and daily insolation. The relationship between monthly diffuse/total and total/extraterrestrial ratios is found to be linear. The present correlation implies that the diffuse component is significantly larger than that predicted by other correlations. No noticeable effect of location or seasonal variation was found. Comparison of the present data with earlier studies for India indicates a trend of increasing diffuse radiation with the lapse of time. The ratio of hourly to daily insolation agrees with the Liu and Jordan correlation for total insolation but differs significantly for diffuse radiation. The need for refinement of the Liu and Jordan correlation between hourly and daily diffuse radiation is pointed out.     

垂直面太阳散射辐射计算方法研究

建筑设计必须考虑太阳辐射在建筑立面上的热作用,但气象台站仅观测水平面辐射数据,垂直面上的太阳辐射资料稀缺。为提出一种依据水平面辐射观测数据来计算垂直面散射辐射的方法,该文研究并建立辐射观测站,并进行长期辐射观测,积累了一定量的辐射数据。通过对垂直面上散射辐射主要影响因素的分析,提出基于晴空指数Kt和直射辐射与垂直面法线方向夹角φ的垂直面散射辐射计算方法。利用观测数据确定公式中的计算系数,并将该文研究提出的计算方法与国内外的5种太阳散射辐射计算模型进行比较分析。结果表明:1)该文提出的计算方法所需计算参数仅依据国内常规辐射观测数据即可。2)该方法能够实现对不同朝向垂直面散射辐射的计算。3)与国内外常用计算模型相比,该方法在不同天空晴朗度、不同朝向上整体精度更高。研究认为该文方法与国内气象部门的辐射观测数据相匹配,所需计算参数少、精度高、简单易用,可为建筑能耗计算和热环境分析提供新的垂直面散射辐射计算方法。     

Prediction of hourly diffuse solar radiation from measured hourly global radiation on a horizontal surface

A statistical procedure has been employed to develop correlations between the hourly global horizontal radiation and its diffuse component. Several years', hourly radiation data from three Canadian stations and two French stations have been employed for this purpose. The relationships have been developed in dimensionless form which predict for particular solar altitudes when is given.Under heavily cloudy conditions or when the sky is completely covered ( ), diffuse radiation increases linearly with the global radiation. In this region, solar altitude has no bearing on the fraction of diffuse radiation.As goes beyond 0.35, the effect of solar altitude begins to appear and the region immediately following this may be considered as partly-cloudy-skies conditions. In the beginning of this region, the diffuse component increases briefly with the increase in global radiation and then begins to decrease as the partly cloudy skies become clearer. At particular solar altitudes, a minimum value of the diffuse radiation is reached. The value of where reaches its minimum value varies with solar altitude.The region beyond which a minimum value of is reached may be considered as mainly-clear-sky conditions. In this region, increases again with , lower solar altitudes giving a higher percentage of diffuse radiation.Under partly cloudy skies and under clear skies, solar altitudes lower than 30° had a marked effect on the fraction of diffuse radiation. However, solar altitudes greater than 30° had minimal influence on the fraction of diffuse radiation.     

A modified method of estimating Ångström’s turbidity coefficient for solar radiation models

The method by Pinazo et al. (Pinazo JM, Cañada J, Boscá JV. A new method to determine Ångström’s turbidity coefficient: its application for Valencia. Solar Energy 1995;54(4):219–226) to determine the Ångström turbidity coefficient is modified. Two new correlations are developed that link Pinazo’s method with model ‘C’ by Iqbal (Iqbal M. An introduction to solar radiation. New York: Academic Press, 1983), and are derived using measured horizontal visibility data. The modified model is used to compute Ångström turbidity coefficient for Brunei Darussalam using measured data on solar radiation for a period of 5 years (1990–1994). The data were collected from the Meteorological Department of Civil Aviation, Ministry of Communication, Brunei Darussalam. A comparison of the modified model is made with those by Pinazo and Iqbal. The preliminary calculations reveal that the modified model is capable of computing Ångström turbidity coefficient more accurately than that developed by Pinazo and it can be used to compute Ångström turbidity coefficient for any location irrespective of the climatological zones.     

北京地区的太阳辐射分析

根据北京市1958年-2000年的太阳辐射和日照时间的日值数据资料,对北京市的年太阳辐射历年平均 值进行了计算,分析了北京市太阳辐射量的长期变化;研究了太阳总辐射和日照时间之间的关系以及散射辐射 与总辐射之间的关系,分别得到了估算太阳总辐射和散射辐射的经验公式,研究中对所得到的经验公式进行了 误差统计,结果表明能满足工程应用的要求。     

Investigation of wind energy potentials in Brunei Darussalam

Conventional power generation mainly depends on natural gas and diesel oil in Brunei Darussalam. The power utility company is now thinking of power generation using natural wind. In this paper, wind energy, being one of the most readily available renewable energy sources, was studied. The wind characteristic, velocity and directions were studied using Weibull distribution based on the measurement of wind speed at two different locations in Brunei Darussalam. These wind speed distributions were modeled using the Wind Power program. The wind rose graph was obtained for the wind direction to analyze the wind power density onshore and offshore. Based on this analysis, it has been found that the wind speed of 3 to 5 m/s has a probability of occurrence of 40%. Besides, the annual energy production at a wind speed of 5 m/s has been found to be in the range between 1000 and 1500 kWh for both the locations in Brunei Darussalam.     

Estimating monthly average daily diffuse solar radiation with multiple predictors: A case study

Solar radiation measurements are not easily available, especially for the diffuse solar radiation. In this study, two models for estimating the diffuse solar radiation are proposed based on multiple predictors including the clearness index, relative sunshine duration, ambient temperature and relative humidity. One of them aims to increase the estimation accuracy, and the other aims to estimate the diffuse solar radiation direct from other meteorological elements in the absence of the global solar radiation. For a case study, the performance of the proposed models is validated by comparing with eight existing models selected from literature against the measured data at Guangzhou station in China. Through the analysis based on statistical error tests, results show that the two models can estimate the monthly average daily diffuse solar radiation with good accuracy.     

A comparative study of solar irradiation models on various inclined surfaces for India

This paper presents a statistical approach for the estimation of the diffuse/global irradiation on various inclined surfaces from the measured data of horizontal surface. In fact diffuse solar radiation on an inclined plane consists of two components: sky diffuse radiation and reflected radiation from the ground. For analyzing estimation of the daily tilted sky diffuse component from the daily horizontal diffuse irradiance, we have considered six models Badescu, Circumsolar, Skartveit and Olseth, Hay, Klucher and Liu and Jordan (Isotropic). All these models except Badescu adopted the same methodology for estimating the ground-reflected radiation component, therefore, only sky diffuse component was analyzed at Lucknow (latitude 26.75°, longitude 80.50°), India location. Statistical analysis showed that the Skartveit and Olseth model gives good prediction for the low inclination angle however; Klucher model gave better performance for highly inclined south-facing surfaces. The Root Mean Square Errors (% RMSE) value varies from 3.45% to 24.15% except for Badescu and Circumsolar model which predict worse results. In general, Klucher’s model provides close agreement with the measurements.     

Analysis of monthly average daily global radiation and monthly average sunshine duration at two tropical locations

The diffuse radiation falling on a horizontal surface at Madras, India has been analysed and the results presented. Five years of data have been used for the analysis and a correlation has been established between the daily average diffuse radiation with the monthly average clearness index. It has also been shown that there is an appreciable difference in the ratio of monthly average hourly diffuse to the monthly average daily diffuse radiation with respect to day length.     

Evaluation of models for predicting insolation on slopes within the Colorado alpine tundra

This empirical study evaluates insolation predictions for the Colorado tundra from models based upon isotropic and anisotropic distribution approximations for diffuse sky and reflected solar radiation. The data set of hourly insolation values was obtained from 40 locations on an alpine ridge by simultaneous measurement of direct beam irradiance and total insolation to the horizontal ridge crest and two nearby sloping surfaces. Six models are used to predict insolation, two based on the isotropic distribution of diffuse solar radiation and four on anisotropic diffuse distribution fields. Three models (one isotropic and two anisotropic) employ measurements of normal direct beam irradiance while the other 3 models incorporate the correlation between the “clearness index” and the ratio of diffuse sky to total insolation. The precision of insolation estimates from models using the correlation method is only slightly less than from other models. Accounting for the increase of diffuse radiation in the circumsolar sky improves insolation predictions. However, inclusion of additional regions of diffuse radiation anisotropy decreases model accuracy. Errors of insolation estimates for the alpine tundra from all models vary in a systematic manner as a function of relative azimuth and ground slope angles.     

Diffuse solar radiation—Daily and monthly values as affected by snow cover

It is generally recognized that surface albedo (terrain reflectance) has a significant effect on the diffuse fraction of global radiation. In colder climates, ground snow cover could be expected to alter the terrain reflectance significantly. The objective of this paper was to study the effect of ground snow cover on the diffuse fraction of the daily and the monthly average global radiation and to develop empirical relationships which would permit the calculation of the diffuse solar component.