EVALUATION OF SYMMETRIC AND ASYMMETRIC CORRELATIONS TO PREDICT MONTHLY AVERAGE HOURLY GLOBAL SOLAR RADIATION

The present article deals with evaluating the relative performance of the correlations to predict symmetric and asymmetric monthly average hourly values of global solar radiation from corresponding daily values. It has been found that the symmetric correlation due to CoUares-Pereira and Rabl [7] and asymmetric form due to Satyamurty and Lahiri [9] perform satisfactorily over a wide range of locations tested.     

A model to predict expected mean and stochastic hourly global solar radiation I(h;nj) values

This paper describes an improved approach for (a) the estimation of the mean expected hourly global solar radiation I(h;n_j), for any hour h of a day n_j of the year, at any site, and (b) the estimation of stochastically fluctuating I(h;n_j) values, based on only one morning measurement of a day. Predicted mean expected values are compared, on one hand with recorded data for the period of 1995–2000 and, on the other, with results obtained by the METEONORM package, for the region of Patra, Greece. The stochastically predicted values for the 17th January and 17th July are compared with the recorded data and the corresponding values predicted by the METEONORM package. The proposed model provides I(h;n_j) predictions very close to the measurements and offers itself as a promising tool both for the on-line daily management of solar power sources and loads, and for a cost effective PV sizing approach.     

Stochastic prediction of hourly global solar radiation for Patra,Greece

This paper describes the stochastic prediction of the hourly profile of the intensity of the global solar radiation, I(h; n_j) for any day n_j at a site. The prediction model requires one, two, or three morning measurements of the global solar radiation in a day n_j, makes use of a rich data bank of past years recorded data, and provides I(h; n_j) values for the rest hours of the day. The model is validated by comparing the I(h; n_j) profiles generated for Patra, Greece, with the solar radiation measurements recorded for Winter, Autumn and Spring days, when solar radiation fluctuations often appear to be strong, while also comparing with the predicted by the METEONORM package I(h; n_j) profile. Conclusions are deducted for the predictive power of the model. The proposed model, which is developed in MATLAB for the purpose of this research, provides I(h; n_j) profile predictions very close to the measured values and offers itself as a promising tool for a predictive on-line daily load management.     

Correlation between hourly diffuse and global radiation for New Delhi

Estimation of hourly insolation on tilted surfaces is required in simulation of solar energy systems. This necessitates splitting of hourly global horizontal insolation into diffuse and direct components. Many models have been developed for this purpose, and the aim of this study is to develop a correlation between hourly diffuse ratio and clearness index for New Delhi. The correlation is developed on the basis of measured data for two years. The performance of this correlation was checked by calculating the difference between computed and measured diffuse radiation. The correlation proved to perform quite well. A comparison of the present correlation with those for other locations showed that such correlations are location dependent.     

Prediction of global daily solar radiation using higher order statistics

The main concern of the present paper is to present and to analyse two procedures for modelling daily global solar radiation. The first one uses the clearness index techniques and the second one uses a totally different type of approach for taking in consideration important properties of such data, including non-Gaussian shape and non-stationarity. This procedure uses the difference between the extraterrestrial and the observed daily global radiation denoted “lost solar component”. Both procedures are based on higher order statistics for generating the global solar radiation using mainly a random process. The prediction results show that the sequences of values generated have the same statistical characteristics as those of sequences observed. The comparison between the two methods used indicates that the developed model based on the “lost solar component” is better than the model obtained using the conventional procedure based on the clearness index.     

Computing global and diffuse solar hourly irradiation on clear sky. Review and testing of 54 models

Fifty-four broad band models for computation of global and diffuse irradiance on horizontal surface are shortly presented and tested. The input data for these models consist of surface meteorological data, atmospheric column integrated data and data derived from satellite measurements. The testing procedure is performed for two meteorological stations in Romania (South-Eastern Europe). The testing procedure consists of forty-two stages intended to provide information about the sensitivity of the models to various sets of input data. There is no model to be ranked “the best” for all sets of input data. Very simple models as well as more complex models may belong to the category of “good models”. The best models for solar global radiation computation are, on equal-footing, ESRA3, Ineichen, METSTAT and REST2 (version 81). The second best models are, on equal-footing, Bird, CEM and Paulescu & Schlett. The best models for solar diffuse radiation computation are, on equal-footing, ASHRAE2005 and King. The second best model is MAC model. The best models for computation of both global and diffuse radiation are, on equal-footing, ASHRAE 1972, Biga, Ineichen and REST2 (version 81). The second best is Paulescu & Schlett model.     

Assessment of diffuse solar energy under general sky condition using artificial neural network

In this paper, artificial neural network (ANN) models are developed for estimating monthly mean hourly and daily diffuse solar radiation. Solar radiation data from 10 Indian stations, having different climatic conditions, all over India have been used for training and testing the ANN model. The coefficient of determination (R²) for all the stations are higher than 0.85, indicating strong correlation between diffuse solar radiation and selected input parameters. The feedforward back-propagation algorithm is used in this analysis. Results of ANN models have been compared with the measured data on the basis of percentage root-mean-square error (RMSE) and mean bias error (MBE). It is found that maximum value of RMSE in ANN model is 8.8% (Vishakhapatnam, September) in the prediction of hourly diffuse solar radiation. However, for other stations same error is less than 5.1%. The computation of monthly mean daily diffuse solar radiation is also carried out and the results so obtained have been compared with those of other empirical models. The ANN model shows the maximum RMSE of 4.5% for daily diffuse radiation, while for other empirical models the same error is 37.4%. This shows that ANN model is more accurate and versatile as compared to other models to predict hourly and daily diffuse solar radiation.     

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.     

福州城市发展对太阳辐射的影响

利用福州市日射站１９６０年至１９９４年的观测资料，分析了福州城市发展对太阳直接辐射，散射辐射和总辐射的影响，建立了福州市太阳直接辐射和散射辐的１０年滑动平均值的年，月趋势方程和年总辐射及其分量与市区人口的相关方程。     

Study of hourly and daily solar irradiation forecast using diagonal recurrent wavelet neural networks

An accurate forecast of solar irradiation is required for various solar energy applications and environmental impact analyses in recent years. Comparatively, various irradiation forecast models based on artificial neural networks (ANN) perform much better in accuracy than many conventional prediction models. However, the forecast precision of most existing ANN based forecast models has not been satisfactory to researchers and engineers so far, and the generalization capability of these networks needs further improving. Combining the prominent dynamic properties of a recurrent neural network (RNN) with the enhanced ability of a wavelet neural network (WNN) in mapping nonlinear functions, a diagonal recurrent wavelet neural network (DRWNN) is newly established in this paper to perform fine forecasting of hourly and daily global solar irradiance. Some additional steps, e.g. applying historical information of cloud cover to sample data sets and the cloud cover from the weather forecast to network input, are adopted to help enhance the forecast precision. Besides, a specially scheduled two phase training algorithm is adopted. As examples, both hourly and daily irradiance forecasts are completed using sample data sets in Shanghai and Macau, and comparisons between irradiation models show that the DRWNN models are definitely more accurate.     

On a universal model for the prediction of the daily global solar radiation

A model to predict the mean expected daily global solar radiation, H(n) on a day n, at a site with latitude φ is proposed. The model is based on two cosine functions. A regression analysis taking into account the mean measured values H_m.meas(n) obtained from SoDa database for 42 sites in the Northern Hemisphere resulted in a set of mathematical expressions of split form to predict H(n). The parameters of the two cosine model for 0°<φ < 23° are obtained by regression analysis using a sum of 3–8 Gaussian functions, while for 23°<φ < 71° the two cosine model parameters are expressed by a sum of exponential functions or the product of an exponential and a cosine function. The main equation of the model and the set of parametric expressions provide H(n) for any φ on Earth. Validation results of this model are provided along with the statistical estimators NMBE, NRMSE and t-statistic in comparison to the corresponding values from three databases of NASA, SoDa and the measured values from ground stations provided in Meteonorm.     

A Method of Estimating Monthly Global Radiation for Singapore

The design of solar systems and the determination of cooling and heating load of buildings require information on global radiation in addition to other meteorological data. In this study, equations have been developed for the clearness index K_T , which is the ratio of monthly average daily values of global radiation to that of extraterrestrial radiation on a horizontal surface, as a function of the ratio of monthly average daily values of sunshine hours and day length. The extraterrestrial radiation and the day length can be calculated from Eqs. (5) and (3) respectively. The sunshine hours can be obtained from the meteorological station of Singapore. A reasonable estimate of monthly average daily global radiation can be obtained from these equations.     

用Lowtran7进行分光辐射的计算研究（Ⅰ）—不同波段分光总日射比较份额的计算研究

利用Lowtran7所能提供的计算参数，分别计算了小于400nm(紫外辐射），400－700nm(光合有效辐射）和大于700nm（红外辐射）3个波段的总日射占全波段总日射的比例，并研究了不同太阳高度角、不同气溶胶、不同海拔高度以及大气中不同水汽和气溶胶含量对上述比例的影响。以前实测中发现的光合有效辐射所占比例有随地理纬度减少而略有增长的趋势得到了合理的论证；而理论模式的计算结果与我们的实测季节过完全一致，则证明所用方法是合理和可行的。     

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。     

1992年夏季珠穆朗玛峰地区的太阳直接辐射和总辐射

用１９９２年夏季珠穆朗玛峰地区考察的多通道有线遥测辐射观测资料,对珠峰地区的太阳直接辐射和总辐射特征进行了研究。结果表明。１９９２年珠峰地区夏季中午前后的大气透明度状况与１９５９年没有明显差异。夏季在珠峰绒布寺地区最大总辐射大于太阳常数现象的出现十分频繁。本次考察时,在有完整资料的１６天中,１４天观测到了瞬时总辐射大于太阳常数的现象;这种现象从地方时９时到１４时都可出现,有时竟连续出现５个时欢。瞬时总辐射的最大值为１６８８Ｗｍ－２,超出了太阳常数２３％。考察期间记录到的总辐射时累计值的最大值为４．７１ＭＪｍ－２,平均强度１３０８Ｗｍ－２,达太阳常数的９５．７％。青藏高原地区持续出现总辐射大于太阳常数的现象对近地面辐射平衡及生态环境的影响尚有待进一步研究。     

Survey on the P.V. Generator of Castellina in Chianti (Italy)

The aim of this study was the definition of low-cost solutions to optimise and maintain a satisfactory cost balance in the medium-long term between the different sub-systems and components of P.V. power generators.

In particular, the long-term objective is to keep the cost of support structures below about 20% of the total system cost.

A unit of about 200 modules was investigated in the Chianti Region of Castellina and in this paper results will be presented on the following topics

-the feasibility study of the most appropriate solution of a low-cost, simple, light-weight (0.3 kg/Wp), flexible and continuous array support structure (made of timber and steel wires).

-The study of the soil and of the site including site preparation by simple machines.

-The design of the solution retained valid after the imposed limitations for the plant approval.

-The construction and assembling of the entire P.V. plant.

-The measurements' campaigns carried out on the main structural components and the discussion of these results compared with design assumptions.

-The extrapolation of the real costs to larger P.V. units.

-The conclusive remarks on the experience acquired during the implementation of the project, its realization, its testing and operation over more than 18 months of life-time.     

关于利用卫星数据计算西藏地区太阳能资源的研究

利用１９９２－１９９４年从日本静止气象卫星提取的云量资料，借助云量与日照百分率之间的非线性关系以及后者与总日射间的线性关系，对西藏地区的太阳能资源分布进行了计算研究，并绘制了１９９２－１９９４年的太阳能资源图。     

建筑外窗对采暖热负荷的影响分析

以天津市某三层办公楼一层办公室南向外窗为研究对象,通过计算整个采暖季南向外窗的逐时累计得热量及失热量,分析不同类型窗对于整个采暖季累积采暖热负荷的影响.     

Estimation of global solar radiation using artificial neural networks

This paper introduces a neural network technique for the estimation of global solar radiation. There are 41 radiation data collection stations spread all over the kingdom of Saudi Arabia where the radiation data and sunshine duration information are being collected since 1971. The available data from 31 locations is used for training the neural networks and the data from the other 10 locations is used for testing. The testing data was not used in the modeling to give an indication of the performance of the system in unknown locations. Results indicate the viability of this approach for spatial modeling of solar radiation.