Fourier analysis of meteorological data to obtain a typical annual time function

A method of calculation has been developed for obtaining a typical annual time function, by means of Fourier analysis, that is applicable to meteorological parameters which show significant frequencies and have sufficient climatological series. Applied with excellent results to annual series of daily data on global solar irradiation (9 yr) and average, maximum and minimum air temperatures (10 yr) of Barcelona city, with the observation that only the annual harmonic contributes in any significant way.     

Empirical relations for the determination of solar radiation in Ibadan, Nigeria

Variations in the average monthly, seasonal and daily patterns of total radiation, relative humidity, temperature and sunshine duration in Ibadan have been presented. Various empirical models relating solar radiation to the basic climatological parameters such as relative humidity, sunshine hours, temperature as well as geographical declination, latitude and altitude factors were investigated from the viewpoint of obtaining appropriate empirical formulae to determine solar radiation from such common parameters. The average monthly total radiation is shown to be predicted with reasonable accuracy by a couple of empirical formulae with the best result obtained from a newly proposed formula. The new formula is shown to give also good agreement when applied to the analysis of annual daily insolation data on a seasonal basis. Finally, the proposed formula predicts a linear relationship between the daily diffuse radiation and the daily total radiation in line with the Liu and Jordan model but with the fiffuse component generally higher in qualitative agreement with observations in the tropics.     

Solar ponds—Corrections

Variations in the average monthly, seasonal and daily patterns of total radiation, relative humidity, temperature and sunshine duration in Ibadan have been presented. Various empirical models relating solar radiation to the basic climatological parameters such as relative humidity, sunshine hours, temperature as well as geographical declination, latitude and altitude factors were investigated from the viewpoint of obtaining appropriate empirical formulae to determine solar radiation from such common parameters. The average monthly total radiation is shown to be predicted with reasonable accuracy by a couple of empirical formulae with the best result obtained from a newly proposed formula. The new formula is shown to give also good agreement when applied to the analysis of annual daily insolation data on a seasonal basis. Finally, the proposed formula predicts a linear relationship between the daily diffuse radiation and the daily total radiation in line with the Liu and Jordan model but with the fiffuse component generally higher in qualitative agreement with observations in the tropics.     

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.     

Test reference year generation from meteorological and simulated solar radiation data

In this paper, a new method for generating test reference year (TRY) from the measured meteorological variables is proposed. Hourly recorded data of air temperature, relative humidity and wind velocity for two stations, Valladolid and Madrid (Spain) were selected to develop the method and a TRY was obtained. Monthly average solar radiation values were calculated taking into account the temperature and solar radiation correlations. Four different methodologies were used to evaluate hourly global solar radiation from hourly weather data of temperature and, as a consequence, four different TRYs with common data sets of temperature, relative humidity and wind velocity were generated for Valladolid and Madrid (Spain) stations. In order to evaluate the four different methodologies, TRYs data were compared with long-term measured data series using statistical estimators such as average, standard deviation, root mean square error (rmse) and mean bias error (mbe). Festa and Ratto and the TAG model, from Aguiar and Collares-Pereira, respectively, turned out to be the best methods for generating hourly solar irradiation data. The best performance was shown by the TRY0 year which was based on the solar radiation models mentioned above. The results show that the best reference year for each site varies with the season and the characteristics of the station.     

The influence of climate and location on collector performance

The influence of annual climate variations on the performance of solar thermal collectors in the northern part of Europe has been investigated. The annual solar collector energy output has been calculated with the MINSUN simulation program using hourly, measured climatic data for the years 1983–98 for three cities situated in the south (Lund), central (Stockholm) and north (Luleå) of Sweden. A synthetic year created with the Meteonorm weather simulation program was also used in the simulations. Two solar thermal collectors were modelled: a flat plate solar collector and a tubular vacuum collector, both of commercial standard.The thermal energy output is strongly correlated to the annual global irradiation at a horizontal surface. The annual average energy delivered from the flat plate collector was 337 kWh/m² for Stockholm (337 for Lund and 298 for Luleå), and from the vacuum tube collector 668 kWh/m² for Stockholm (675 for Lund and 631 for Luleå) at an operating temperature of T=50°C. Maximum deviations from the average value for this 16-year period are around 20% for the flat plate and 15% for the vacuum tube collector, at T=50°C.The relation between global irradiation on a horizontal surface and the annually collected thermal energy at a constant operating temperature could be fitted to a linear equation: q_u=aG(0°)+bT, where q_u is the energy output from the collector, G(0°) the global irradiation at a horizontal surface, T the average temperature of the collector fluid, and a and b fitting parameters in a double linear regression analysis.     

SOLAR INDUSTRIAL PROCESS HEAT POTENTIAL IN ALEXANDRIA,EGYPT

The present paper investigates the economic viability of the solar domestic hot water systems for industrial processes in Alexandria, Egypt. Also, the optimum parameters of such systems in Alexandria, Egypt have been determined.

The industries covered in the present study are soft drinks, and vegetable oil. The weather data for Alexandria, Egypt (latitude 31.2°) was used. The data file of Alexandria contains monthly average values of daily radiation on a horizontal surface, clearness index, ambient temperature, wind speed, and relative humidity.

The economic calculations for this study are based on life-cycle savings calculations. The f-chart design method is used to estimate the long-term annual thermal performance of solar domestic hot water systems.

The main results obtained can be summarized in the following: 1) solar domestic hot water systems are preferable alternatives to the conventional heating systems currently used in food industries in Egypt. 2) significant life-cycle savings can be achieved with solar heating systems.     

Experimental and theoretical investigation of global and diffuse solar radiation in the United Arab Emirates

In the present study, the global, direct and diffuse components of solar radiation as well as temperature, relative humidity and wind speed have been continuously monitored and analysed on an hourly, daily and monthly basis. The monthly average daily total solar radiation varies from 2700 W h/m² in December to 8000 W h/m² in June with an average clearness index of 0.65. Experimental data are compared to the predictions of different theoretical models as functions of declination and hour angles. Correlations are obtained describing the variation of hourly, daily and monthly averages of total and diffuse solar radiation using polynomial expressions. Empirical correlations describing the dependence of the daily average diffuse to total radiation ratio on the clearness index are also obtained. Data for the daily diffuse to total radiation ratio are compared to correlations obtained by other investigators. The comparison shows a reasonable agreement with some scatter due to the seasonal dependence of the correlation. Comparison of calculations with experimental measurements under clear sky conditions show excellent agreement with a maximum error of 8%.     

Thermal management of solar photovoltaics modules for enhanced power generation

Industry and government interest in solar energy has increased in recent years in the Middle East. However, despite high levels of solar irradiance in the Arabian Gulf, harsh climatic conditions adversely affect the electrical performance of solar photovoltaics (PV). The objective of this study is to compare the annual performance characteristics of solar PV modules that utilize either sun-tracking or water cooling to increase electrical power generation relative to that of stationary, passively cooled modules in the Middle East climatic conditions. This is achieved using an electro-thermal model developed and validated against experimental data acquired in this study. The model is used to predict the annual electrical power output of a 140 W PV module in Abu Dhabi (24.43°N, 54.45°E) under four operating conditions: (i) stationary geographical south facing orientation with passive air cooling, (ii) sun-tracked orientation with passive air cooling, (iii) stationary geographical south facing orientation with water cooling at ambient air temperature, and (iv) stationary geographical south facing orientation with water refrigerated at either 10 °C or 20 °C below ambient air temperature. For water cooled modules, annual electrical power output increases by 22% for water at ambient air temperature, and by 28% and 31% for water refrigerated at 10 °C and 20 °C below ambient air temperature, respectively. 80% of the annual output enhancement obtained using water cooling occurs between the months of May and October. Finally, whereas the annual yield enhancement obtained with water cooling at ambient air temperature from May to October is of 18% relative to stationary passive cooling conditions, sun-tracking over the complete year produces an enhancement of only 15% relative to stationary passive cooling conditions.     

Estimation of global solar radiation over the city of La Serena (Chile) using a neural network

An artificial neural network for the estimation of hourly global solar radiation in La Serena (Chile), was developed using data measured from a meteorological station. La Serena city (29°54′ S, 71°15′ W) is located in the bay area at south of the hyper-arid Atacama Desert. In this study, 25123 data points of global solar radiation of 5 years (2001–2005) were used to train the network and then 7618 data points of global solar radiation not used in the training process were predicted (years 2006 and 2007). The meteorological data used in the model were: wind speed, relative humidity, air temperature, and soil temperature. The results were compared with the real data and other models available in the literature, and shows that the neural network obtained can be properly trained and can estimate the hourly global radiation with acceptable accuracy.     

Global solar radiation in Northeastern Saudi Arabia

This paper presents the actual global solar radiation on a horizontal surface along with the prevailing meteorological conditions encountered during the measurement period from 1 January–31 December, for one complete year, in the Arabian Gulf Coast near the city of Dhahran. High resolution, real time solar radiation and meteorological data were collected, and processed. Hourly, daily, and monthly statistics of solar radiation was made from the one-minute averaged recorded values. The highest measured daily, and monthly mean solar radiation were found to be 351 and 328 W/m⁻², respectively. The highest one-minute averaged solar radiation values up to 1183 W/m⁻² were observed in the summer season, from May–September. The highest hourly solar radiation value was recorded as 1053 W/m⁻² in the middle of June. Beside the global solar radiation measurements, the main observed meteorological parameters were temperature, pressure, wind speed, precipitation, and relative humidity. On the other hand, the estimation of daily and monthly mean global solar radiation was performed based upon two empirical formulas which relate the solar radiation to the sunshine duration, relative humidity, maximum temperature, the latitude of the monitoring location, sunset hour and declination angles. The agreement between the measured and estimated solar radiation values was found to be satisfactory. Nevertheless, the empirical formula under-estimates the solar radiation values during summer, and over-estimates during winter.     

Estimation of global solar radiation on horizontal surfaces in Jeddah, Saudi Arabia

The measured data of global solar radiation on a horizontal surface, as well as the number of sunshine hours, mean daily ambient temperature, maximum and minimum ambient temperatures, relative humidity and amount of cloud cover, for Jeddah (latitude 21° 42′37″N, longitude 39° 11′12″E), Saudi Arabia for the period 1996–2006 are analyzed. The data are divided into two sets. The sub-data set 1 (1996–2004) are employed to develop empirical correlations between the monthly average of daily global solar radiation fraction (H/H₀) and various meteorological parameters. The nonlinear Angström type model developed by Sen and the trigonometric function model proposed by Bulut and Büyükalaca are also evaluated. New empirical constants for these two models have been obtained for Jeddah. The sub-data set 2 (2005, 2006) are then used to evaluate the derived correlations. Comparisons between measured and calculated values of H have been performed. It is indicated that, the Sen and Bulut and Büyükalaca models satisfactorily describe the horizontal global solar radiation for Jeddah. All the proposed correlations are found to be able to predict the annual average of daily global solar radiation with excellent accuracy. Therefore, the long term performance of solar energy devices can be estimated.     

Harmonic analysis of monthly insolation levels in the United States

The purpose of this paper is to analyze independent temporal variance structures in long-term mean monthly insolation data for the conterminous United States. Harmonic analysis is applied to the annual march of insolation levels at 221 stations, and nearly all variance in the data is explained by one harmonic fit. The statistics from the harmonic analysis display coherent spatial patterns that reveal the extent to which radiation levels are affected by synoptic climatological phenomena. The results suggest a method for accurately interpolating insolation estimates using as few as three parameters.     

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.     

UV solar radiation on a tilted and horizontal plane: Analysis and comparison of 4 years of measurements

In the global wavelength range (300–3000 nm), it is known that a plane with a slope equal to the latitude of the location, receives more annual energy than the horizontal plane, mainly due to the increase in direct irradiation on the interest plane. The UV (280–400 nm) spectra at the earth surface, has a larger component of diffuse and a minor component of direct solar radiation compared to the global wavelength range, therefore the increase in annual energy due to plane inclination should also be different. This work, analyzes 4 years of solar UV radiation measurements performed on tilted and horizontal planes located at the Plataforma Solar de Almería, Spain. The monthly mean ratio of tilted/horizontal solar UV irradiation varies with the time of the year, reaching values of 1.25 and 0.95 for winter and summer, respectively. The same ratio in the solar global spectra rises up to 1.70 and 0.85 for the same months. The annual UV solar energy increase on a plane tilted 37° and oriented towards the equator is around 3–4%, whereas is around 10% in the global spectra. In this way UV annual energy increase due to inclination and orientation of the plane is much lower than that for global radiation. Determination of a unique method to assess all possible inclinations and orientations, require simultaneous measurement of diffuse and direct UV radiation performed with radiometers of identical spectral response. Given the worldwide scarcity of these type of data, an empirical correlation that relates horizontal UV irradiation to that on a 37° inclined plane was determined. Monthly and annual tendencies of solar UV irradiation have been analyzed and compared with the solar global irradiation.     

Experimental analysis of evacuated tube solar air heater (ETSAH) with inbuilt sensible thermal energy storage

In the present work, an evacuated tube solar air heater (ETSAH) with inbuilt sensible heat storage material (SHSM) is experimentally evaluated. The system comprises two sets each having 50 evacuated tubes with an H-type arrangement and a total collector area of 16.92 m². For the purpose of hot air generation, ETSAH is simultaneously connected in series and in parallel with and without the use of reflectors. Three different mass flow rates of 122.90, 164.87, and 212.83 kg/h were fixed to get 12 diverse cases of ETSAH operation. The highest hot air temperature reported by the system is 121.7°C when it was connected in series with conventional reflectors at 212.83 kg/h of flow rate and 469 W/m² average solar intensity. The system reported an overall average energy efficiency of 49.76% and an exergy efficiency of 17.97% with the highest average hot air temperature difference of 56.12°C from 09:00 to 20:00 h. Without the incorporation of any additional SHSM, the average hot air temperature delivered by ETSAH (when under the neighbor building shadow) is 49.73°C logged from 17:00 to 20:00 h. The economic analysis is also carried out to ensure its practical application and feasibility. For the best system performance, the annual cost of hot air generation is 0.0194 Rs./kg (0.0002433 $/kg).     

Optimum fixed orientations and benefits of tracking for capturing solar radiation in the continental United States

Optimum tilt and azimuth angles for solar panels were calculated for a grid of 0.1° by 0.1° National Solar Radiation Database (NSRDB-SUNY) cells covering the continental United States. Optimum tilt and azimuth angles varied by up to 10° from the rule of thumb of latitude tilt and due south azimuth, especially in coastal areas, Florida, Texas, New Mexico, and Colorado. The yearly global irradiation incident on a panel at this optimum orientation was compared to the solar radiation received by a flat horizontal panel and a 2-axis tracking panel. Compared to global horizontal irradiation, irradiation at optimum fixed tilt increased with increasing latitude and by 10%–25% per year. Irradiation incident on a 2-axis tracking panel in one year was 25%–45% higher than irradiation received by a panel at optimum fixed orientation. The highest increases in tracking irradiation were seen in the southwestern states, where irradiation was already large, leading to annual irradiation of over 3.4 MWh m^?2.     

An assessment of the solar radiation climate of the Cyprus environment

The solar radiation climate of Athalassa, Cyprus, is reported upon in detail. The database utilized in this analysis consisted of daily global and diffuse radiation on a horizontal surface, and global radiation on tilted surfaces, together with the calculated daily values of horizontal beam radiation. In addition, the data reported here include maximum and minimum temperature, relative humidity and percentage of possible sunshine. Monthly average hourly global and diffuse radiation for the time interval 5 a.m.–7 p.m. are reported and analyzed. The annual means of the daily global, diffuse and beam solar radiation on a horizontal surface are about 17.26, 5.75 and 12.35 MJ m⁻², respectively. The average monthly fraction of daily horizontal global radiation that is beam radiation varies from 0.61 in February to 0.77 in September. The average monthly clearness index varies from 0.636 in July to 0.491 in December, whereas the ratio of diffuse to global radiation varies from 0.494 in February to 0.257 in July. The solar radiation climate of the Cyprus environs has also been compared to those reported for two neighbouring countries. We conclude, based upon the above analysis, that Athalassa and its environs are characterized on average, by relatively high daily irradiation rates, both global and beam, and a relatively high percentage of clear days.     

Thermal performance of a parallel earth air-pipes system

In the present analysis the thermal performance of a parallel earth air-pipe system has been evaluated in terms of annual heating and cooling potential. The influence of the pipes on each other's thermal performance has been considered. The effect of seasonal variation of environmental parameters (ambient temperature, solar radiation, relative humidity, earth temperature etc.) has been considered. The results are obtained for the hot-dry climate of Jodhpur and the composite climate of Delhi. From the various possible earth surface treatments to increase the effectiveness of earth storage systems for air conditioning purposes, the results are presented for wet-shaded earth surface conditions, the most effective earth surface treatment for the climate considered. Thermal performance of the parallel air-pipe system is evaluated for the two cases. In the first case, inlet air temperature to the pipes is taken to be the hourly mean of the ambient air temperature of the average day of each month, and, in the second case, the inlet air temperature is taken to be equal to that of a conditioned room whose set-point temperature varies from month to month.     

Climatological study of the adrano site of the eurelios solar mirror power plant

This article concerns the climatological characterization of the Adrano site, where is operating the EURELIOS solar mirror power plant. Meteorological characteristics such as climatic trend of air temperature, wind roses, average monthly values of global radiation, and insolation are presented. In particular, the percentage of solar radiation received at the site has been evaluated with respect to the extraterrestrial radiation and the average daily insolation at Adrano has been compared with that of a nearby station (Catania) for which statistical, long-term estimates exist.