Monthly Average Daily Values Research Articles

Parametric study of hybrid (wind + solar + diesel) power generating systems

The combined utilization of renewables such as solar and wind energy is becoming increasingly attractive and is being widely used for substitution of oil-produced energy, and eventually to reduce air pollution. In the present investigation, hourly wind-speed and solar radiation measurements made at the solar radiation and meteorological monitoring station, Dhahran (26°32′N, 50°13′E), Saudi Arabia, have been analyzed to study the impact of key parameters such as photovoltaic (PV) array area, number of wind machines, and battery storage capacity on the operation of hybrid (wind + solar + diesel) energy conversion systems, while satisfying a specific annual load of 41,500 kWh. The monthly average wind speeds for Dhahran range from 4.1 to 6.4 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.6 to 7.96 kWh/m2. Parametric analysis indicates that with two 10 kW wind machines together with three days of battery storage and photovoltaic deployment of 30 m2, the diesel back-up system has to provide about 23% of the load demand. However, with elimination of battery storage, about 48% of the load needs to be provided by diesel system.

Feasibility of hybrid (wind + solar) power systems for Dhahran, Saudi Arabia

Hourly mean wind-speed and solar radiation data for the period 1986–1993 [except the years 1989 (some data is missing) and 1991 (Gulf War)] recorded at the solar radiation and meteorological monitoring station, Dhahran (26° 32′ N, 50° 13′ E), Saudi Arabia, have been analyzed to report the monthly variation of wind speed and solar radiation, probability distribution of wind speed and to investigate the feasibility of using hybrid (wind+solar) energy conversion systems at Dhahran. The monthly average wind speeds for Dhahran range from 4.21 to 6.97 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.61 kwh/sq.m to 7.96 kwh/sq.m. The hybrid system considered in the present analysis consists of two 10 kW Wind Energy Conversion Systems (WECS), 120 sq.m of Photovoltaic (PV) panels together with a battery storage system and a diesel back-up. The monthly average daily energy generated from the above hybrid system has been presented. The energy generated from the back-up diesel generator and the no. of operational hours of the diesel system to meet a specific annual electrical energy demand of 41531 kWh have also been presented.

Analysis of daily clearness index, global and beam radiation for Beer Sheva, Israel: Partition according to day type and statistical analysis

The magnitude of the daily clearness index K T has been utilized to classify a day as either clear, partially cloudy or cloudy. The range of values for defining a day type was based upon a previous analysis of the Beer Sheva radiation database. These criteria were employed to partition the days according to type and the corresponding monthly average daily values for the clearness index, global, normal incidence and horizontal beam radiation were calculated. A statistical analysis was performed on each of the monthly average daily value subsets to help convey the shape of their respective distribution curves. The monthly average frequency of days according to type was also determined. Such an analysis of the solar radiation database for a particular site can be utilized to determine the relative merits of different types of solar energy conversion systems, e.g. concentrating vis-à-vis non-concentrating solar collector systems. The results of this analysis for Beer Sheva indicate that this region is very amenable to the utilization of non-concentrating solar energy conversion systems, since the combined frequency of both clear and partially cloudy days exceeds 80% annually. In addition, the Beer Sheva region is a prime candidate for the use of solar energy conversion systems utilizing concentrating collectors due to its relatively high frequency of clear days and the fact that the monthly average daily values of the clearness index, even for partially cloudy days, are relatively high ( K T > 0.50).

Solar radiation incident on tilted surfaces in Burgos, Spain: Isotropic models

A number of hourly measurements of global solar radiation on a horizontal surface, taken during the period 1981–1986 in Burgos, Spain, have been analyzed into diffuse and beam components. The components of global solar radiation were used to calculate the monthly average hourly and daily values on an inclined surface. The results obtained using isotropic models have been compared, tabulated and plotted against the angle of tilt for summer, winter and all year. The optimum tilt angle and the solar radiation on a south facing tilted surface have been calculated for different periods of time and by three different models. The optimum tilt angle values range from 7° in June to 70° in December and January.

Estimation of the diffuse solar irradiation from global solar irradiation. Daily and monthly average daily values

Data sets of total and direct solar irradiation at Valencia (Spain) measured during the years 1990–1991 have been used to analyze diverse methods of estimating the daily values and monthly average daily values of the diffuse fraction of solar radiation from the ratio of the total to the extraterrestrial radiation (clearness index k t). In the case of daily values, all the methods described in the bibliography have led to significant deviations concerning the experimental values, with a MAD (mean absolute deviation) close to 20%. For the monthly average daily values, the methods based on the PDF (probability density function) of daily values of k t provide more accurate results than the deterministic methods based on the correlation of monthly average daily values of k t.

Correlation Between Ultraviolet Radiation and Global Radiation in Riyadh, Saudi Arabia

The global ultraviolet and global radiation were measured and recorded on an hourly basis in Riyadh, Saudi Arabia (lat. 24.6°N, long. 46.7°) during the period 1984–1989. Global radiation, G, was measured by an Eppley PSP pyranometer (0.285≤λ≤2.8 μm) and an Eppley TUVR radiometer (0.29≤λ≤0.385 μm) was used for the measurement of the ultraviolet radiation, UV. Both instruments were mounted on a horizontal surface. The results showed that the monthly average daily ultraviolet radiation was 197.6 Whm−2. The ratio of the monthly average daily ultraviolet radiation to the monthly average daily global radiation (Ku) varied between 0.031 to 0.037, with a mean value of 0.034. Comparison with results obtained in Kuwait, Dhahran, and Makkah showed that the data of Riyadh are in good agreement with those of Makkah and Dhahran; however, it underestimates Kuwait data. A regression correlation between Ku and KT (the ratio of the monthly average daily values of global radiation to extraterrestrial radiation) is developed. Another regression correlation between ultraviolet and global radiation on an hourly basis is also developed.

Dependence on latitude of the relation between the diffuse fraction of solar radiation and the ratio of global-to-extraterrestrial radiation for monthly average daily values

An approach for the prediction of the monthly average daily diffuse radiation, H d , was proposed by Page in 1961. The Page method is based on the use of the linear correlation H d H = c + d H H o , where H and H o are, respectively, the monthly average daily values of global and extraterrestrial radiation, both on a horizontal surface. The values of c and d are a function of atmospheric conditions. cloud cover conditions/types, as well as latitude. In the present work we study the dependence on latitude of c and d for European locations with 36°N < (γ) < 61°N (longitudes between 29°E and 11°W). The dependence is first studied using 28 values of c and d obtained using experimental values of H and H d . Next the dependence on γ is studied using experimental values of H for 64 European locations, obtained for the period 1966–1975, and corresponding values of H d estimated using the European Community Solar Radiation Model (E.C.S.R.M.). In both cases a minimum for c vs. γ and a maximum for d vs. γ are obtained for similar values of γ. Using the E.C.S.R.M. it is shown that both, the minimum and the maximum can be explained by the way H d H and H H o vary with γ.

Accurate computations of monthly average daily extraterrestrial irradiation and the maximum possible sunshine duration

Abstract The monthly average daily values of the extraterrestrial irradiation on a horizontal plane ( H 0 ) and the maximum possible sunshine duration ( S 0 ) are two important parameters that are frequently needed in various solar energy applications. These are generally calculated by solar scientists and engineers each time they are needed and often by using the approximate short-cut methods. Using the accurate analytical expressions developed by J.W. Spencer [Fourier series representation of the position of the sun, Search 2, 172 (1971)] for the declination and the eccentricity correction factor, computations for these parameters have been made for all the latitude values from 90°N to 90°S at intervals of 1° and are presented in a convenient tabular form. Monthly average daily values of the maximum possible sunshine duration as recorded on a Campbell-Stokes sunshine recorded S ′ 0 are also computed and presented. These tables would avoid the need for repetitive and approximate calculations and serve as a useful ready reference for providing the accurate values of H 0 , S 0 and S ′ 0 to the energy scientists and engineers.