Stochastic modeling and generation of synthetic sequences of hourly global solar irradiation at Quetta, Pakistan

Using hourly global radiation data at Quetta, Pakistan for 10 yr, an Autoregressive Moving Average (ARMA) process is fitted. Markov Transition Matrices have also been developed. These models are used for generating synthetic sequences for hourly radiations in MJ/m² and that the generated sequences are compared with the observed data. We found the MTM approach relatively better as a simulator compared to ARMA modeling.     

The frequency distribution of instantaneous insolation values

The frequency distribution of instantaneous terrestrial insolation values based on measurements carried out over a one-year period has been evaluated. The resulting fractional time distribution curves for instantaneous radiation are found to differ from that obtained previously for daily values. The instantaneous fractional time curves exhibit a distinct step associated with the predominance of two radiation states, clear and cloudy. A model derived from the concept of Boltzmann statistics is shown to be in good agreement with the experimental measurements over a wide range of air masses and average clearness indices.     

The frequency distribution of daily insolation values

Frequency distributions of insolation values are needed in order to derive simple correlations for predicting the performance of solar energy systems. In this paper the frequency distribution of daily total hemispherical solar irradiation values on the horizontal surface is derived from measured data for 90 locations in the U.S. The results can be approximated by generalized distribution curves which depend only on the clearness index, defined as ratio of terrestrial over extraterrestrial insolation. The results agree well with the curves originally derived by Liu and Jordan, except for a correction at high insolation values. The deviation of individual locations from the generalized curves is examined. A breakdown according to time of year reveals some seasonal variation. The theoretical distribution corresponding to random insolation sequences is also derived; it agrees very well with the generalized frequency distribution curves.     

Distribution of global insolation over Pakistan

There are only five observatories measuring global insolation in Pakistan, which cannot represent the solar climate of the country. However, 37 observatories, distributed fairly well over the entire country, record sunshine. Therefore, insolation-sunshine empirical equations are developed to estimate global insolation over Pakistan. Three neighbouring observatories for which the insolation/sunshine records are available are also included in the study. Monthly and yearly maps are constructed, for daily global insolation, based on data for 40 locations. The isolines are compared with results obtained in India and with world solar insolation maps.     

On the estimation of global solar insolation

A curve suitable for estimation of global solar energy insolation in equatorial regions has been generated from humidity considerations using an empirical “universal” formula and experimental solar insolation data recorded for over 20 yr at specific locations in Kenya, East Africa. The curve has then been used to estimate global insolation in other locations in Kenya and the neighbouring countries with longstanding experimental data. The agreement between the experimental and theoretical insolation values is found to be satisfactory. This curve, we believe, can serve a useful purpose in estimating global solar insolation in other tropical locations with similar climatic conditions as those in Kenya which lack proper global solar insolation acquisition equipment.     

Time series models to simulate and forecast hourly averaged wind speed in Quetta, Pakistan

Stochastic simulation and forecast models of hourly average wind speeds are presented. Time series models take into account several basic features of wind speed data including autocorrelation, non-Gaussian distribution and diurnal nonstationarity. The positive correlation between consecutive wind speed observations is taken into account by flitting an ARMA (p,q) process to wind speed data transformed to make their distribution approximately Gaussian and standardized to remove scattering of transformed data. Diurnal variations have been taken into account to observe forecasts and its dependence on lead times. We find the ARMA (p,q) model suitable for prediction intervals and probability forecasts.     

Diurnal variation of global insolation over five locations in Pakistan

The diurnal variation of global insolation at five locations in Pakistan is presented in terms of monthly averages of hourly sums. Isopleth diagrams for each station are prepared. These are nearly symmetric about the midday point. On the average, about 70% of the day's total insolation is received between 10 a.m. and 3 p.m. local apparent time. The midday intensity, maximum during summer, exceeds 3 MJ m⁻² h⁻¹ at Quetta, which receives the highest values.     

Control of solar insolation via thermochromic light-switching gels

The investigated thermochromic gels show a phase separation when a characteristic temperature is surpassed. Particles are formed within a polymer network, which are responsible for a drastically increased light scattering efficiency. Accordingly, a reduction in the directional-hemispherical transmission in the solar spectral range from 81 ± 2 to (10₋₁⁺⁵)% for a 1 mm thick foil-gel-foil system was observed. With the help of differential light scattering measurements and Debye's two-phase media model correlation lengths of a_c = (100 ± 20) nm and a_c = (400 ± 50) nm were derived for the scattering entities in the clouded case. From the optical thickness of the specimens the switching temperatures are derived. Additionally performed multiflux calculations for a purely scattering switching system allow to predict the radiation transport under variation of the optical thickness and the correlation length.     

Effects of changes in the atmosphere on solar insolation

A review of the nature of solar radiation and the spectral distribution of its energy is presented. The attenuation of solar radiation by scattering and absorption and the effects of atmospheric pollutants on radiation attenuation with an estimate of the long-term effects of pollutants is discussed.     

Hydrogen production characteristics of a bioethanol solar reforming system with solar insolation fluctuations

The development of a bioethanol steam reforming system (FBSR) is considered as a means of distributing energy using PEM fuel cells. Small-scale solar collectors (collection areas on the order of several m²) are installed in a house as a method for applying the FBSR. However, the temperature distribution of a reforming catalyst fluctuates under conditions of unstable solar insolation. Therefore, heat transfer analysis applied in reforming the catalyst layer of the reactor and the temperature distribution and transient response characteristics of the gas composition of the process were investigated. As a case study, meteorological data for representative days in March and August in Sapporo, Japan were recorded, and the hydrogen production speed, power generation output and amount of electricity purchased were analyzed. The results showed that although fluctuations in solar insolation affected the efficiency of the FBSR, the average efficiency of each representative day exceeded 40%. By installing two solar collectors, each with a collection area of 1 m², 21–25% of the average power demand of an individual house can be supplied.     

A model for the calculation of solar global insolation

A theoretical model is described that is designed to give the total global insolation falling on the earth's surface and the transmission of the atmosphere. It is compared to a model by Braslau and Dave[1] and found to agree to within a few percent in all cases. Climatogical values of total pricipitable water, turbidity, and surface albedo are required as the model inputs, and the sources of these data are described. The model has been applied to 26 stations in the National Weather Service (NWS) pyranometer network, where measured true solar noon atmospheric transmission values are available, as part of the NOAA program to rehabilitate the old pyranometer observations. For three of these stations where reliable true solar noon irradiance and transmission values are available, the model calculations and observations are compared. At 18 locations the calculated and measured daily mean insolation values are compared for clear days. At one location (Boulder, Colorado) calculated and measured radiation climatologies for all weather conditions are compared. In all comparisons the model and observations differ by no more than 2.7 per cent, which is within the experimental accuracy (±5 per cent) of the pyranometers. Possible sources of errors are discussed.     

Use of compact-source iodide (CSI) lamps to simulate solar insolation

Simulating, within a laboratory under accurately controlled conditions, the solar insolation which would be received at ground level—in the open air—for a particular location and preselected time of day is difficult. Nevertheless, it is essential if the performance testing of solar-energy collectors is not to be excessively delayed by the vagaries of the weather. This paper examines the problems of achieving a reasonable simulation and concludes that the use of a CSI lamp provides a viable, acceptable compromise. The limitations of employing this system and other commonly available lamps are discussed.     

Temperature variation in upper earth crust due to periodic nature of solar insolation

An explicit analytical expression for the temperature variation in the upper earth crust has been presented which accounts for inhomogeneity in thermal conductivity of soil due to moisture, porosity, etc. Numerical results show that incorporation of inhomogeneous thermal conductivity leads to significantly modified values of ground temperature over the constant thermal conductivity ground temperature values.     

Characteristics of clear sky normal incidence solar insolation measured with the RG2 filter

The fraction of the normal incidence isolation above the 630 mμ wavelength is measured with the RG2 filter. This fraction is about 60 per cent at 60° solar altitude, slowly increases to about 67 per cent at 20° altitude and then increases rapidly to about 80 per cent as the altitude decreases to 5°. Expressing the fraction as a function of optical air mass produced a linear type of relationship. The apparent attenuation coefficient had a range of 0.17–0.28 for the energy below 630 mμ, a range of 0.06–0.12 for the energy above 630 mμ and for the total spectrum the range was 0.07–0.17. Average monthly values of attenuation coefficient, apparent irradiance at air mass zero and energy are reported.     

Simulation of thermal regime of room,heated by passive insolation solar heating systems with three-layer ventilated translucent barriers

The problem of mathematical modeling of the thermal regime of a room that is heated by passive insolation solar heating systems (IPSSH) with three-layer ventilated translucent barrier (TLVTB) is examined. The dependence of the temperature regime of the room on the TLVTB parameters is studied.     

Transient multidimensional second law analysis of solar collectors subjected to time-varying insolation with diffuse components

This paper presents an unsteady two-dimensional analysis of a flat-plate solar collector subjected to time varying insolation with considerable diffuse components as a better characterization of practical solar collectors. The analysis considers the thermal masses of the absorber, tube, glazing, and the working fluid in the system, as well as the different optical and thermodynamic properties of beam and diffuse radiation. Using two sets of insolation data, one for a near clear day and the other for an overcast day, an exergetic optimization of the system was carried out and flow rates which maximize the total exergy output (extracted and accumulated) were determined for flow update periods of once every 30 min, 1 h, and the entire daylight period. The instantaneous optimum flow rates were found to follow the insolation pattern. On a daily basis, the optimum exergetic efficiencies and optimum flow rates were almost independent of the choice of the interval of fluid update, but were about 30% and 10% respectively, higher for the clear day than for the overcast day.