Daily Global Radiation Research Articles

Comparison of some existing models for estimating global solar radiation for Antalya (Turkey)

Solar radiation data for Antalya (36°53′ N, 30°42′ E) in Turkey were used to test the applicability of twenty six models available for computing the monthly average daily global radiation on a horizontal surface. The models were compared on the basis of statistical error tests using the mean percentage error (MPE), root mean square error (RMSE) and the mean bias error (MBE). According to our results, the Samuel model below (Samuel T.D.M.A. Estimation of global radiation for Srilanka. Solar Energy 1991;47(5):333) showed the best estimation of global solar radiation on a horizontal surface for Antalya by means of the MPE (1.5%), RMSE (0.27 MJ/m 2) and MBE (−0.02 MJ/m 2) statistical tests: H H 0 =−2.4275+11.946 S S 0 −16.745 S S 0 2+7.9575 S S 0 3

A general multivariate qualitative model for sizing stand-alone photovoltaic systems

We considered a general model for sizing a stand-alone photovoltatic system, using as energy input data the information available in any irradiation atlas. The parameters of the model are estimated by multivariate linear regression. The results obtained from the numerical loss of load probability size method (LOLP) were used as initial input data to fit the mode. For this fit we have used daily global irradiation data taken from 222 US meteorological stations for the period 1961–1990. The expression proposed allows us to determine the photovoltatic array size, with a coefficient of determination to 0.96. This coefficient is independent of the used LOLP value. System parameters and mean monthly values for daily global irradiation on the modules surface are taken as independent variables in the model. It also shows that the proposed model can be used with the same accuracy for other locations not considered in the estimation of the model. We also propose a model which would allow us to calculate optimum tilts for the array surface taking the latitude into account as well as the variability of the incident irradiation.

UV-B radiation at Penang

A new series of measurements including global and UV radiation was initiated in 1994 at Penang. These high quality data were used to study diurnal and seasonal variations. The mean daily total UV-B and global radiation is about 1.43×10 4 J and 1.77×10 7 J, respectively. Maximum radiation values for both the UV-B and global radiation are received in March and September. The daily total global radiation shows a bigger seasonal variation than UV-B radiation. On clear days, the erythemal UV radiation flux is in the high or extreme range for about 5 h beginning at around 1030 hours throughout the year. Penang (5.3°N) and Natal (6°S) are found to exhibit similar daily maximum erythemal UV irradiance values. A simple empirical relationship for the noontime UV-B flux and global irradiance in the equatorial/tropical regions has been established.

Estimation of monthly average daily global radiation on horizontal surface for Antalya (Turkey)

In this study, multiple linear regression models were used to estimate the monthly average daily global radiation using nine different variables for Antalya, Turkey; the extraterrestrial radiation, solar declination, mean relative humidity, ratio of sunshine duration, mean temperature, mean soil temperature, mean cloudiness, mean precipitation and mean evaporation. The results showed that the models can estimate global radiation within relative error (|e|) of −5.7 and 3.9%, a mean error (MPE) of 2.0% and root-mean square error (RMSE) of 2.5% for Antalya.

CLIMATE CHANGE PROJECTIONS BASED ON GCM-SIMULATED DAILY DATA

Three-dimensional general circulation models (GCMs) are 'state-of-the-art' tools for projecting possible changes in climate. Scenarios constructed for the Czech Republic are based on daily outputs of the ECHAM-GCM in the central European region. Essential findings, derived from validating, procedures are summarized and changes in variables between the control and perturbed experiments are examined. The resulting findings have been used in selecting the most proper methods of generating climate change projections for assessing possible hydrological and agricultural impacts of climate change in selected exposure units. The following weather variables have been studied: Daily extreme temperatures, daily mean temperature, daily sum of global solar radiation, and daily precipitation amounts. Due to some discrepancies revealed, the temperature series for changed climate conditions (2×CO 2 ) have been created with the help of temperature differences between the control and perturbed runs, and the precipitation series have been derived from an incremental scenario based on an intercomparison of the GCMs' precipitation performance in the region. Solar radiation simulated by the ECHAM was not available and, therefore, it was generated using regression techniques relating monthly means of daily extreme temperatures and global radiation sums. The scenarios published in the paper consist of monthly means of all temperatures, their standard deviations, and monthly means of solar radiation and precipitation amounts. Daily weather series, the necessary input to impact models, are created (i) by the additive or multiplicative modification of observed weather daily series or (ii) by generating synthetic time series with the help of a weather generator whose parameters have been modified in accord with the suggested climate change scenarios.

Multiplicative ARMA models to generate hourly series of global irradiation

A methodology to generate hourly series of global irradiation is proposed. The only input parameter which is required is the monthly mean value of daily global irradiation, which is available for most locations. The procedure to obtain new series is based on the use of a multiplicative autoregressive moving-average statistical model for time series with regular and seasonal components. The multiplicative nature of this models enables us to capture the two types of relationships observed in recorded hourly series of global irradiation: on the one hand, the relationship between the value at one hour and the value at the previous hour; and on the other hand, the relationship between the value at one hour in one day and the value at the same hour in the previous day. In this paper the main drawback which arises when using these models to generate new series is solved: namely, the need for available recorded series in order to obtain the three parameters contained in the statistical ARMA model which is proposed (autoregressive coefficient, moving-average coefficient and variance of the error term). Specifically, expressions which enable estimatation of these parameters using only monthly mean values of daily global irradiation are proposed in this paper.

The diffuse component of the global solar radiation at Qena / Egypt

Diffuse solar radiation on horizontal surfaces is estimated at Qena / Egypt. The basic procedure is to develop relationships of the widespread use Liu & Jordan types between the daily global horizontal radiation (G) and its diffuse component (D) using measured values of these two quantities. An error analysis has been done for the results of diffuse radiation calculated using the regression models obtained in this paper and those estimated from other known ones of the Liu & Jordan type, According to statistical evaluation of the various relationships, it is seen that our models provide the best estimation of the diffuse radiation, Effect of climatic conditions was considered in the discussion.

A simple method to estimate global radiation

The objective of this study was to develop a method to provide estimates of daily global radiation as input for the Crop Growth Monitoring System of the European Union, from meteorological observations transmitted via the Global Telecommunication System for locations where sunshine duration observations are not available and hence the Ångström, or any other sunshine duration based method, cannot be applied. A simple method to estimate global radiation from mean daytime cloud cover and maximum and minimum temperature has been tested. The test was executed for various locations in Europe, ranging from Finland to Italy. Average RMSE and MBE for the comparison between observed and estimated global radiation for the tested locations using the proposed method is 2.48 and −0.25 MJ m −2 d −1, respectively.

Modeling clear weather day solar irradiance in Baghdad, Iraq

A clear day model for the beam transmittance of the atmosphere is presented. The clear sky is modeled because this condition generally produces the maximum energy available. This maximum established the criteria from which engineers can design solar cells, space and process water heating equipment and estimate the thermal loading on buildings, etc. The model is based on five-years of daily global radiation data assembled from measurements at the Solar Energy Research Center at Baghdad, Iraq. The model offers the prediction of clear day hourly values of direct normal and global solar radiation for any day of the year at a given location with no required meteorological inputs. Modeled data are compared with observations, demonstrating good agreement for several days from different seasons. This model provides a baseline for solar energy researchers and is utilized for quality control of solar radiation parameters.

A simple model for sizing stand alone photovoltaic systems

We consider a general model for sizing a stand-alone photovoltaic system, using as energy input data the information available in any radiation atlas. The parameters of the model are estimated by multivariate linear regression. The results obtained from a numerical sizing method were used as initial input data to fit the model. The expression proposed allows us to determine the photovoltaic array size, with a coefficient of determination ranging from 0.94 to 0.98. System parameters and mean monthly values for daily global radiation on the solar modules surface are taken as independent variables in the model. It is also shown that the proposed model can be used with the same accuracy for other locations not considered in the estimation of the model.

Estimation of atmospheric transmittance from upper-air humidity

A very simple model of atmospheric transmittance uses as its input regularly observed and archived measures of upper air humidity. The five model parameters were determined empirically to optimize the agreement with radiation measured at six sites in the northwestern contiguous U.S. in summer and winter 1990. The model uses the relative humidity at 500 hPa, the relative humidity at either 950 hPa or 800 hPa depending on the altitude of the station, and the precipitable water. Although the model does not use cloud observations explicitly, it is partitioned into a low-humidity stage and a high-humidity stage with markedly different dependences on relative humidity. In the low-humidity stage the transmittance is approximated as the product of factors for dry air and for water vapor. In the high-humidity stage the transmittance is the product of the transmittances of each of the two layers used; the product is a strongly decreasing function of relative humidity, as a representation of the effect of cloud. A split-sample test using measurements for spring and autumn indicated that the model parameters were not badly distorted by conditions unique to the summer and winter seasons. In terms of the average daily global shortwave radiation received at the surface, the rms errors are 31 W m −2 in spring, 33 in summer, 30 in autumn, and 18 in winter. The corresponding relative errors are 0.25, 0.17, 0.20, and 0.31. Because of high-frequency temporal variation in the model residuals, the error declines to about half of the daily error for 7-day averages and to about a quarter of the daily error for 30-day averages.

Some comments on time variation in solar radiation over Baghdad, Iraq

In the present work an attempt was made to study and examine some aspects of radiation climatology which are important in solar energy utilization. The yearly cumulative global radiation for Baghdad is 216 MJ/m 2 per year, while the annual total of daily diffuse radiation at Baghdad is about 70.82 MJ/m 2. The mean monthly values of clearness index K T present a maximum of 65.9% in August and a minimum value of 48.4% in January. The annual mean of daily global radiation and its spectral OG1, RG2 and RG8 at Baghdad is about, 18.03, 13.53, 10.86 and 9.36 MJ/m 2, respectively. Over the year, the highest UV radiation were received during June and July (243 Wh/m 2) and the lowest in December (79 Wh/m 2). Furthermore, UV radiation constituted on average 3.25% of global radiation.

Comparison between three years of daily global radiation measurements in three Tunisian sites against assessments from METEOSAT Wefax images

GISTEL is a satellitary methodology based on a simple physical model with two components. It is used to estimate global solar irradiance from METEOSAT data. The treated images in the present sequel are of Wefax type of the ‘visible channel’ of METEOSAT. Our method has been applied in Tunisia. The estimated daily solar global radiation is compared to the measured values performed in three meteorological stations in the North of Tunisia during three successive years. The obtained results have shown that the accuracy level of our method is acceptable for energy applications. Our results show the convenience of GISTEL method to METEOSAT-Wefax images. In general, the relative error does not exceed 20% of the global irradiation. The recorded errors between estimated and measured values are, in some cases, linked to the model's parameters. They may also arise from the geographical situation of the site, the satellitary data or from the earth-based solar irradiation.

Temperature Behavior of a Natural Shallow Water Body during a Summer Period

For many biological processes, the daily and seasonal behavior of the temperature of the water layer close to the water surface is very important. An example is the development of larvas of mosquito species which develop in small still water bodies. An outdoor experiment during a summer period of four months has been executed in a small water body situated within a bog area, in order to obtain insight into the daily and seasonal temperature behavior of this water body. The measurements show that during daytime a strong thermal stratification occurs in the water body and that during nighttime a well mixed layer develops growing from the water surface. In the upper water layer a well developed daily temperature cycle is present. This cycle is strongly reduced by depth. On average, the daily maximum water temperature excursion from the mean agree with the daily maximum air temperature excursion from the mean. The range between maximum and minimum water temperature correlate well with the daily global irradiation.

Open‐top designs for manipulating field temperature in high‐latitude ecosystems

Passive open‐top devices have been proposed as a method to experimentally increase temperature in high‐latitude ecosystems. There is, however, little documentation on the efficacy of these devices. This paper examines the performance of four open‐top chambers for altering temperature at six sites in the Arctic and Antarctica. Most of the heating effect was due to daytime warming above ambient; occasional night‐time cooling below ambient, especially of air temperatures, depressed mean daily temperature. The mean daily temperatures at four arctic sites were generally increased by 1.2–1.8 °C; but occasionally, temperature depressions also occurred. Under optimal conditions at the antarctic site (dry soils, no vegetation, high radiation) mean daily soil temperatures were increased by +2.2 °C (–10 cm) to +5.2 °C (0 cm). Protection from wind may play a more important role than temperature per se in providing a favourable environment for plant growth within open‐top devices. Wind speed had a generally negative impact on mean daily temperature. Daily global radiation was both positively and negatively related to chamber temperature response. The effect of chambers on snow accumulation was variable with the Alexandra Fjord site showing an increased accumulation in chambers but no difference in the date of snowmelt, while at Latnjajaure in a deep snowfall site, snowmelt occurred 1–2 weeks earlier in chambers, potentially increasing the growing season. Selection of a passive temperature‐enhancing system requires balancing the temperature enhancement desired against potential unwanted ecological effects such as chamber overheating and altered light, moisture, and wind. In general, the more closed the temperature‐enhancing system, the higher is the temperature enhancement, but the larger are the unwanted ecological effects. Open‐top chambers alter temperature significantly and minimize most unwanted ecological effects; as a consequence, these chambers are a useful tool for studying the response of high‐latitude ecosystems to warming.

Investigation of solar radiation in Botswana and some anomalous phenomena observed

Daily global insolation on a horizontal surface in Botswana is recorded continuously at several synoptic stations and at the University of Botswana's Physics Department. Over a number of years, daily total insolation on a tilted surface (β = −30°) was recorded at the Botswana Technology Centre. Hourly, and instantaneous direct normal, global, diffuse and UV-components are continuously recorded at the University of Botswana. All these measurements are done with standard EPLAB equipment. It is found out that the instantaneous direct normal radiation at Solar noon can be as high as 1150 W·m −2; and that at 30 min before sunset it can be above 600 W·m −2; and it can also be as high as 100 W·m −2 at sunset or sunrise moments (i.e. with half of the solar disk under the horizon). Daily direct normal solar radiation can exceed 45 MJ·m −2. Mean daily global radiation varies from 31 MJ·m −2 in December to 16 MJ·m −2 in June. Such big values of daily direct normal and global radiation are explained by low humidity and low turbidity. Cases of an anomalous phenomenon which lead to an abnormally big phase shift when direct normal radiation is increasing greatly after Solar noon are observed, and discussed. It is also found that when humidity is low and visibility is high, hourly I g values recorded with a pyranometer can be less than I bn (cos θ z) + I d-values. This discrepancy could be quite common for regions where humidity and turbidity are low. The trend in the behaviour of the UV-component during the last five years is also analyzed and discussed. The conclusion is made that the ozone layer over Botswana is continuously being depleted.

Compilation and evaluation of solar and wind energy resources in Sudan

A number of years worth of data concerning the solar radiation on a horizontal surface, sunshine duration and wind speed in Sudan have been compiled, evaluated and presented in this article. Measurements of global solar radiation on a horizontal surface at 16 stations for several years are compared with predictions made by several independent methods. In the first method the Angstrom formula was used to correlate relative global solar irradiance to the corresponding relative duration of bright sunshine. Regression coefficients are obtained and used for prediction of global solar irradiance. The predicted values were consistent with measured values (± 8.01% variation). In the second method, by Barbaro et al. [ Solar Energy, 1978, 20, 431] sunshine duration and minimum air mass were used to drive an empirical correlation for the global radiation. The predicted values compared well with measured values (± 12% variation). The diffuse solar irradiance is estimated. The results of two formulas have close agreement. A radiation map of Sudan was prepared from the estimated radiation values. The annual daily mean global radiation ranges from 3.05 to 7.62 kW h m −2 per day. Routine wind data from 70 stations were analyzed. Monthly averaged wind speed and average powers were determined for each station. The derived annual average speeds range from 1.53 to 5.07 m s −1. Maximum extractable average wind powers were found to vary between 1.35 and 49.5 W m −2. A wind map of Sudan was also prepared. Sudan possessed a relatively high abundance of sunshine and moderate wind speed. It is concluded that Sudan is blessed with abundant solar and wind energy.

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.

Comparison between measurements and models for daily solar irradiation on tilted surfaces in Athens, Greece

This paper presents a comparison of several models against measurements of daily total solar radiation on surfaces of various tilts and azimuths in Athens. Such measurements are carried out at the Institute of Meteorology and Physics of the Atmospheric Environment, National Observatory of Athens and are the first of this kind in Greece. The models encounter a constant surface albedo of 0.2 and are of two categories. Category I includes models estimating hourly diffuse radiation on tilted planes (Bugler, Gueymard, Reindl and Temps-Coulson), which obtain the necessary global and diffuse horizontal radiations from either measurements or estimations from the Meterological Radiation Model (MRM) developed at the National Observatory of Athens. Category II includes Isotropic and Klein models for daily estimations; the models obtain their input from available measurements. Three types of diffuse radiation estimation in the second category are encountered. The purpose of the present paper is two-fold. First, it aims at showing the difference in estimating daily global irradiation between hourly models (category I) and daily models (category II). Second, it intends to give an alternative way to estimating daily irradiations on tilted surfaces using just MRM for engineering purposes.

Numerical optimization of nitrogen application to rice. Part I. Description of MANAGE-N

A tool (MANAGE-N) to identify optimal nitrogen (N) management in irrigated rice is presented. It combines a dynamic crop growth model (ORYZA-0) with a numerical optimization procedure and a user interface reading local weather and soil and crop characteristics as inputs to generate site-tailored recommendations for N-fertilizer management. These have the form of generalized logistic curves expressing the ideal temporal pattern to apply any user-defined total N dose. ORYZA-0 simulates crop N uptake, N allocation, growth and yield with only seven equations and a number of empirical constraint parameters. A single exponential relation describes crop growth rate as a function of daily incident global radiation ( R, MJ m 2 d 1), bulk leaf nitrogen ( N L, g N per m 2 ground area) and a site calibration factor ƒ v. Leaf area and light interception are not explicitly distinguished. Harvest index is calculated from biomass at flowering and cumulative incident radiation after flowering. Values of model parameters are provided based on 16 data sets from China, India, The Philippines and Australia covering 94 nitrogen management treatments (doses, timing). The corresponding 94 growth curves are used to evaluate three aspects of the growth equation, using observed time series of R and L as boundary conditions: (i) goodness of fit of growth curves after calibration of ƒ v (ii) variation in ƒ v w within and across locations; and (iii) errors in predicted crop biomass at flowering and harvest, using cross-validation between treatments within each site. All curves were fitted with correlation coefficients from 0.97 to 0.99. Parameter ƒ v varied more between sets (experiments) than within sets ( p < 0.001), with preflowering values between 0.68 and 0.97 and postflowering values 0.38 to 0.96. Root mean squared errors of biomass prediction were 230 to 1600 kg/ha at flowering and 280 to 3000 kg/ha at harvest, or 5 to 15% of observed values in most cases. Further tests of the model are presented in Part II (Ten Berge et al., Field Crops Research, this issue).