A model for calculating hourly global solar radiation from satellite data in the tropics

A model for calculating global solar radiation from geostationary satellite data is presented. The model is designed to calculate the monthly average hourly global radiation in the tropics with high aerosol load. This model represents a physical relation between the earth-atmospheric albedo derived from GMS5 satellite data and the absorption and scattering coefficients of various atmospheric constituents. The absorption of solar radiation by water vapour which is important for the tropics, was calculated from ambient temperature and relative humidity. The relationship between the visibility and solar radiation depletion due to aerosols was developed for a high aerosol load environment. This relationship was used to calculate solar radiation depletion by aerosols in the model. The total column ozone from TOMS/EP satellite was employed for the determination of solar radiation absorbed by ozone. Solar radiation from four pyranometer stations was used to formulate the relationship between the satellite band earth-atmospheric albedo and broadband earth-atmospheric albedo required by the model. To test its performance, the model was used to compute the monthly average hourly global radiation at 25 solar radiation monitoring stations in tropical areas in Thailand. It was found that the values of monthly average of hourly global radiations calculated from the model were in good agreement with those obtained from the measurements, with the root mean square difference of 10%. After the validation the model was employed to generate hourly solar radiation maps of Thailand. These maps reveal the diurnal and season variation of solar radiation over the country.     

Satellite-derived solar resource maps for Myanmar

Solar resource maps for use in solar energy applications have been produced for Myanmar. A satellite-based solar radiation model, originally developed for the tropics, was improved and applied for the region. A 13-year period (1998–2010) of imagery data from GMS 5, GOES 9 and MTSAT-1R satellites was used as the main input in the model. The absorption and scattering of solar radiation by various atmospheric constituents was also taken into account. The absorption of solar radiation due to water vapour was estimated from precipitable water database obtained from the National Center for Environmental Protection (NCEP), USA. The total column ozone obtained from TOMS/EP and OMI/AURA satellites were used to calculate solar radiation absorption by ozone. The visibility data observed at meteorological stations in Myanmar and neighbouring countries were employed to estimate solar radiation depletion due to aerosols. In order to validate the model, five pyranometer stations were established in different regions of Myanmar and a two-year period of data from these stations were used for the model validation. Additionally, global solar radiation measured at 10 stations in a neighbouring country was also employed for the validation. It was found that monthly average global radiation obtained from the measurements and that estimated from the model was in good agreement, with a root mean square difference of 9.6% at monthly scale. After the validation, the model was used to estimate monthly average global radiation over Myanmar and the results were presented as solar resource maps. The maps revealed that geographical distribution of solar radiation was strongly influenced by the topography of the country and the tropical monsoons.     

基于系统辨识的地表太阳辐射Box-Jenkins模型的建立

利用天文辐射作为输入数据,采用系统辨识的方法得到地表太阳辐射的BJ(Box-Jenkins)模型,并通过残差分析和零极点检验。该方法可用于预测5～15min时间间隔的地表太阳辐射,为太阳能电站的功率输出预测提供太阳能辐射数据。     

高空飞艇薄膜太阳电池内辐射量计算研究

修正了任一方向的平面内太阳辐射计算模型,使之适用于编程计算各种倾角和方位角平面上的太阳辐射。在曲面上进行网格划分,生成若干个小平面,推导出平面法向量与倾角和方位角之间的关系式,逐个计算每个小平面上太阳辐射量,叠加后近似代替整个曲面上的太阳辐射量。运用此方法计算了高空飞艇的薄膜太阳电池上辐射量,并与此薄膜太阳电池在水平投影面内辐射量计算结果进行比较。结果表明,用水平投影面内辐射量代替薄膜太阳电池内辐射量有很大的偏差。因此,在高空飞艇能源系统性能详细分析阶段需要使用曲面内太阳辐射量计算模型,为随后的光电转换与能源系统计算提供准确的太阳辐射数据。     

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。     

Estimation of solar radiation over Cambodia from long-term satellite data

In this work, monthly average daily global solar irradiation over Cambodia was estimated from a long-term satellite data. A 14-year period (1995–2008) of visible channel data from GMS5, GOES9 and MTSAT-1R satellites were used to provide earth-atmospheric reflectivity. A satellite-based solar radiation model developed for a tropical environment was used to estimate surface solar radiation. The model relates the satellite-derived earth-atmospheric reflectivity to absorption and scattering coefficients of various atmospheric constituents. The absorption of solar radiation due to water vapour was calculated from precipitable water derived from ambient relative humidity and temperature. Ozone data from the TOMS and OMI satellite data were employed to compute the solar radiation absorption by ozone. The depletion of radiation due to aerosols was estimated from the visibility data. Five new solar radiation measuring stations were established at Cambodian cities, namely Siem Reap (13.87°N, 103.85°E), Kompong Thom (12.68°N, 104.88°E), Phnom Penh (11.55°N, 104.83°E), Sihanouke Ville (10.67°N, 103.63°E) and Kampot (10.70°N, 104.28°E). Global solar radiation measured at these stations was used to validate the model. The validation was also carried out by using solar radiation measured at four Thai meteorological stations. These stations are situated near the Cambodian border. Monthly average daily global irradiation from these stations was compared with that calculated from the model. The measured and calculated irradiation is in good agreement, with the root mean square difference of 6.3%, with respect to the mean values. After the validation, the model was used to calculate monthly average daily global solar irradiation over Cambodia. Based on this satellite-derived irradiation, solar radiation maps for Cambodia were generated. These maps show that solar radiation climate of this country is strongly influenced by the monsoons. A solar radiation database was also generated for solar energy applications in Cambodia.     

Performance of Sayigh''s universal formula for the estimation of global solar radiation in Ghana

The performance of Sayigh's universal formula for the estimation of global solar radiation is tested against that of Angstrom-Black model for 13 stations in Ghana, using monthly mean daily global solar radiation averaged over the years 1957–1981.Sayigh's model is found not to perform as creditably as the Angstrom-Black model in the estimation of monthly global solar radiation in Ghana. Of the 156 values of monthly global solar radiation estimated by Sayigh's model, 123 (or 78.8%) had discrepancies of more than 10% with the measured values. The corresponding value for the Angstrom-Black model was 7 (or 4.5%).     

Simulation and modeling of solar radiation in Saudi Arabia

A mathematical model is used to generate the hourly data for the total solar radiation on a horizontal surface. The generated data are based on the hourly recorded visibility data for 20 years (1970–1989). The model year technique was then applied to model the 20 years of hourly data of solar radiation into one statistically representative year. A model year of hourly data was then generated for the beam and diffuse components of solar radiation on a horizontal surface. Similarly, a model year of hourly data was also generated for the total solar radiation on tilted surfaces with different orientations with its beam, diffuse and reflected components. A simple methodology is proposed for calculating the solar radiation on vertical surfaces, based on a solar impact factor (SIF). Monthly means and daily totals of hourly sums for each month of the year are discussed. The hourly data of solar radiation for a typical day for each month of the year are presented. The data were generated for the four climatic zones of Saudi Arabia, the hot-dry (Riyadh), the warm-humid (Jeddah), the maritime inland desert climate (Dhahran) and the upland climate zone (Taif). The accuracy of the results is discussed and found to be above 90% representative.     

POTSOL: Model to predict extraterrestrial and clear sky solar radiation

A model was developed to predict potential and clear sky solar radiation for any latitude. The model (POTSOL) uses the fundamental geometric relationships between the earth and sun to predict the theoretical solar radiation outside the earth's atmosphere, clear sky solar radiation received at the earth's surface after accounting for atmospheric interference, and clear sky solar radiation on a panel with any tilt angle between 0° and 90° from the horizontal. The only model input parameters are latitude (PHI), clearness number (CN), and panel tilt angle (PT). The model was verified using weather data obtained from the National Climatic Center, Asheville, North Carolina for Ely, Nevada.     

Modelling of solar energy potential in Nigeria using an artificial neural network model

In this study, an artificial neural network (ANN) based model for prediction of solar energy potential in Nigeria (lat. 4–14°N, log. 2–15°E) was developed. Standard multilayered, feed-forward, back-propagation neural networks with different architecture were designed using neural toolbox for MATLAB. Geographical and meteorological data of 195 cities in Nigeria for period of 10 years (1983–1993) from the NASA geo-satellite database were used for the training and testing the network. Meteorological and geographical data (latitude, longitude, altitude, month, mean sunshine duration, mean temperature, and relative humidity) were used as inputs to the network, while the solar radiation intensity was used as the output of the network. The results show that the correlation coefficients between the ANN predictions and actual mean monthly global solar radiation intensities for training and testing datasets were higher than 90%, thus suggesting a high reliability of the model for evaluation of solar radiation in locations where solar radiation data are not available. The predicted solar radiation values from the model were given in form of monthly maps. The monthly mean solar radiation potential in northern and southern regions ranged from 7.01–5.62 to 5.43–3.54 kW h/m² day, respectively. A graphical user interface (GUI) was developed for the application of the model. The model can be used easily for estimation of solar radiation for preliminary design of solar applications.     

基于DEM的坡地太阳总辐射估算

借鉴国内外计算坡地太阳辐射的方法,利用数字高程模型(DEM)生成了计算山地太阳辐射的地形因子(坡度、坡向、遮蔽度、各向同性可见因子),比现有的模型更准确地计算了晴空下山地太阳总辐射、直接辐射、散射辐射和周围地形的反射辐射,在此基础上分析了坡度、坡向对太阳辐射的影响。     

利用神经网络估算太阳辐射

太阳辐射是一项对太阳能利用，建筑能耗分析和农业等十分重要的气象数据，本文建立了日总太阳辐射月均值的神经网络估算模型，在此基础上利用北京市1971年至1995年的气象数据资料对神经网络进行了训练，用1996至2000年的数据对神经网络的估算进行了检验，并与其它经验模型的估算结果进行了对比，结果表明神经网络的估算结果与实测值吻合的较好，并且精度高于其它经验模型。因此利用神经网络来估算太阳辐射具有很好的应用前景。     

Solar radiation modeling and measurements for renewable energy applications: data and model quality

Measurement and modeling of broadband and spectral terrestrial solar radiation is important for the evaluation and deployment of solar renewable energy systems. We discuss recent developments in the calibration of broadband solar radiometric instrumentation and improving broadband solar radiation measurement accuracy. An improved diffuse sky reference and radiometer calibration and characterization software for outdoor pyranometer calibrations are outlined. Several broadband solar radiation model approaches, including some developed at the National Renewable Energy Laboratory, for estimating direct beam, total hemispherical and diffuse sky radiation are briefly reviewed. The latter include the Bird clear sky model for global, direct beam, and diffuse terrestrial solar radiation; the Direct Insolation Simulation Code (DISC) for estimating direct beam radiation from global measurements; and the METSTAT (Meteorological and Statistical) and Climatological Solar Radiation (CSR) models that estimate solar radiation from meteorological data. We conclude that currently the best model uncertainties are representative of the uncertainty in measured data.     

Measurements and predictions of solar radiation incident on horizontal surfaces at Santa Fe, Argentina (31° 39′S, 60° 43′W)

Measurements and predictions of solar radiation during a period of 10 years on horizontal surfaces at Santa Fe (31° 39′ S, 60° 43′ W), Argentina, reported as average daily global radiation for each month, are presented. Data are compared to those obtained with a previously published and verified model for computing solar radiation on horizontal planes at the earth's surface for cloudless sky days. Measurements show an important reduction of global radiation with respect to the cloudless sky model predictions for all months of the year. Conversely, averaged daily diffuse solar radiation calculated with Page's formula shows a small increment with respect to the predicted diffuse solar radiation for cloudless sky conditions. When direct solar radiation data, calculated from global and diffuse solar radiation values, are compared to theoretical prediction, a significant decrease is observed. This trend is similar to that obtained for global solar radiation.     

倾斜面太阳辐射量计算方法研究

倾斜面辐射数据是保证准确设计太阳能利用系统的基础数据,一般由水平面数据计算得出。针对现有计算模型误差较大的现状考虑,试验测试了水平面及不同倾角斜面上的太阳辐射数据,提出了针对直接辐射转换系数的修正方法;通过倾斜面散射辐射数据的计算和分析,在散射辐射模型的基础上,建立耦合计算模型。试验与模型计算结果表明,散射辐射的各向同性受天气工况的影响,耦合模型具有较高的准确性,计算值与实测值的偏差可控制在5.3%以内。     

DSG太阳能槽式集热器动态特性

采用数值模拟方法,分析了以水,水蒸气为工质的DSG槽式集热器的动态流动与传热特性.首先建立了管内流体的一维多相流动与传热模型,并利用差分法对该模型进行求解,计算结果与现有文献数据吻合较好.分析了稳态条件下,集热器出口流体工质参数受太阳辐射强度、流体质量流量、人口温度和入口压力的影响规律.在动态分析中,研究了辐射强度变化所导致的出口参数变化特性.从阶跃响应和脉冲响应的分析中得出,虽然热惯性存在,但短期的辐射强度波动对出口温度仍有较大影响,但对出口压力的影响较小.辐射波动将对一次直通DSG系统出口温度产生很大波动.     

Evaluation and comparison of hourly solar radiation models

In this paper, an attempt has been made to develop a new model to evaluate the hourly solar radiation for composite climate of New Delhi. The comparison of new model for hourly solar radiation has been carried out by using various model proposed by others. The root mean square error (RMSE) and mean bias error (MBE) have been used to compare the accuracy of new and others model. The results show that the ASHRAE and new proposed model estimate hourly solar radiation better for composite climate of New Delhi in comparison to other models. Hourly solar radiation estimated by constants obtained by new model (modified ASHRAE model) for composite climate of India is fairly comparable with measured data. The percentage mean bias error with new constants for New Delhi was found as low as 0.15 and 0% for hourly beam and diffuse radiation, respectively. There is a 1.9–8.5% RMSE between observed and predicted values of beam radiation using new constants for clear days. The statistical analysis has been used for the present study. Copyright © 2008 John Wiley & Sons, Ltd.     

Relationship between the total solar radiation on tilted surfaces and the sunshine hours in Hong Kong

Solar energy technologies can play an important role in meeting the ultimate goal of replacing fossil fuels to generate inexhaustible, clean and safe energy. The availability of more comprehensive solar radiation data is invaluable for the design and evaluation of solar-based conversion systems. In many places of the world, particularly the developing countries, the basic solar radiation data for the surfaces of interests are not readily obtainable. This paper presents an approach to estimate the annual global solar radiation on various inclined planes facing different orientations based on measured sunshine hours. Solar radiation and sunshine hours data recorded in 2004 were used for the model development. The performance of the proposed model was assessed against data measured in 2005. It is shown that the solar radiations estimated by the proposed method are in good agreements with the measured data and the peak difference was found less than 5.2%. The predictive ability and the simplicity nature of the model provide a reliable and convenient alternative for estimating inclined solar radiation.     

A comparison of daily solar radiation estimates for the Northeastern United States using the Northeast Regional Climate Center and National Renewable Energy Laboratory models

Observed solar radiation data at three sites in the northeastern United States are compared with values estimated for nearby airport locations using the National Renewable Energy Laboratory (NREL) and Northeast Regional Climate Center (NRCC) models. A tendency toward considerable overestimation of relatively low values of observed solar radiation is evident in the NREL model. This bias is apparently regardless of season. A similar bias is not detected in the NRCC model. For moderate to high values of solar radiation both models produce estimates with similar accuracy for most practical applications. However, these models both tend to underestimate observed solar radiation on days when near maximum possible radiation levels are received. The tendency for the NREL model to overestimate low solar radiation values appears to be linked to the use of total sky cover, rather than the combination of cloud coverage and cloud base height information. Although total sky coverage data may be superior for estimates of moderate to high daily solar radiation values, it appears that information regarding the height of low overcast layers and the presence of obstructions to visibility, such as fog or haze, is required to accurately estimate low daily solar radiation totals.     

Effects of air pollution for estimating global solar radiation in India

Solar energy is the primary resource for all biological, chemical and physical processes. The amount of global solar radiation is an important parameter for solar energy applications. It is common to estimate a monthly average of daily global solar radiation using different regression models. These models in turn exploit the correlation between solar radiation and various atmospheric factors. These factors are commonly derived from meteorological, geographical and climatological data that are readily available for majority of weather stations across the world. In this paper, a novel regression model that can predict location-independent daily global solar radiation is presented. The proposed exponential quadratic model captures the correlation between measured global solar radiation values, sunshine hour and Air Pollution Index for Indian cities. In addition to this, an extended study of several other regression models (e.g. linear, quadratic, exp.-linear and exp.-quadratic) is also presented. This analysis with real data from Indian cities suggests that air pollution is a more significant factor than location when predicting solar radiation. Finally, the model parameters (regression coefficients) for each model are listed out. Additionally, the generalised model equation for the best performing model is also presented.