Spectral Solar Radiation Research Articles

Output variation of photovoltaic modules with environmental factors. I. The effect of spectral solar radiation on photovoltaic module output

Abstract In this study, it was investigated how changes in spectral solar radiation effects the output of photovoltaic modules. First, there was a precise examination of the seasonal changes in spectral solar radiation. Consequently, it was found that the ratio of spectral solar radiation available for solar cell utilization, to global solar radiation, changes from season to season. It varied, from 5% for polycrystalline silicon cells, to 14% for amorphous silicon cells, throughout one year. Obviously a cell made from amorphous silicon is more severely effected by seasonal variations. Next, the seasonal changes of photovoltaic module output were examined. The output was calculated by the conventional output evaluation method using irradiance and cell temperature. This calculated value and the subsequently measured value were accumulated and the two values compared. As a result, the accumulated output of photovoltaic modules was confirmed as changing seasonally in the same way as spectral solar radiation. The output ratio of polycrystalline silicon was found to change by 4%, while that of amorphous silicon varied by 20%. Hence the seasonal variations in spectral solar radiation should be taken into account for optimum photovoltaic power system design.

Hourly to decadal time scale variations of the spectral and total ?solar constant?

The most significant solar spectral radiation bursts that occurred during more than twelve-years observation period at an high altitude station are analyzed. It is shown that the number and amplitudes of solar spectral bursts increase when the solar activity (SA) maximum is approaching. A plausible mechanism of short-term variations of extra-atmospheric solar spectral irradiance (ETSSI) is discussed. It appears that a burst of ETSSI arises when the Earth is sporadically irradiated by a strong flux of induced violet-blue high coming out of magnetic flux tubes in the active region (AR) of the Sun. We confirm earlier conclusions that on the time-scale of decades there is a close relationship between variations in the areas of faculae, the solar constant, and surface air temperature. On the basis of these results we suggest that at the end of the 1930s, when the Sun was very active, its effective output was about 0.4%, and the surface temperature in the Northern hemisphere about 0.4°C, higher than in the first decade of the 20th century.

Estimates of effective aerosol optical depths from spectral solar radiation measurements

This study reports a 37-year long record of direct beam spectral irradiance measurements made in Athens, Greece. An analysis of aerosol effects on the spectral distribution of solar radiation through effective optical depths, are presented. Thus, spectrally resolved aerosol optical depths were calculated and analyzed for the period 1954–1990. Summertime aerosol optical depths were found to be larger than winter values, while their seasonal variations were related to varying weather conditions throughout the year. The interrelationships between effective optical depths were found to be linear and were related strongly to microphysics of aerosol loading in the atmosphere. For the period 1962–1983 as wavelength exponentα0 values ranged between 0.76–1.14 the spectrally resolved optical depths were found to increase markedly with respect to remaining periods 1954–1961 and 1984–1990 in whichα0 values ranged between 1.16–1.39. A minimum in aerosol optical depths, believed to be near background levels, was reached during period 1954–1957, while there was some indication that both optical depths continued to decrease reaching background levels at the end of the study period. From the long-term variation of aerosol effective optical depths some interesting information on the time evolution of air quality in Athens was gained. In addition, their frequency distribution, temporal daily variations and some remarks on photosynthetically active radiation for plant development, are presented and discussed.

On the relationship between total ozone and solar ultraviolet radiation at St. Petersburg, Russia

Daily total ozone observations made with the Total Ozone Mapping Spectrometer (TOMS) flown on the satellite Nimbus‐7 during 1978–1992, have been used in order to investigate the increase in the daily broad‐band and spectral solar ultraviolet radiation reaching the ground through a recently developed parametric model. Total ozone reductions of 3.0% during summer time and 11% during winter time per decade, at St. Petersburg (60°N, 30°E), Russia, cause an increase in erythematically active ultraviolet irradiance of at least 7% and 22%, respectively.

Output variation of photovoltaic modules with environmental factors—I. The effect of spectral solar radiation on photovoltaic module output

In this study, it was investigated how changes in spectral solar radiation effects the output of photovoltaic modules. First, there was a precise examination of the seasonal changes in spectral solar radiation. Consequently, it was found that the ratio of spectral solar radiation available for solar cell utilization, to global solar radiation, changes from season to season. It varied, from 5% for polycrystalline silicon cells, to 14% for amorphous silicon cells, throughout one year. Obviously a cell made from amorphous silicon is more severely effected by seasonal variations. Next, the seasonal changes of photovoltaic module output were examined. The output was calculated by the conventional output evaluation method using irradiance and cell temperature. This calculated value and the subsequently measured value were accumulated and the two values compared. As a result, the accumulated output of photovoltaic modules was confirmed as changing seasonally in the same way as spectral solar radiation. The output ratio of polycrystalline silicon was found to change by 4%, while that of amorphous silicon varied by 20%. Hence the seasonal variations in spectral solar radiation should be taken into account for optimum photovoltaic power system design.

Spectral solar irradiance under Harmattan conditions

Results of spectral solar radiation measurements at Ile-Ife (7°-30′N, 4°31′E; South Western Nigeria) for two non-consecutive months between December 1991 and February 1992 are presented. The Ångström atmospheric turbidity coefficients β, β 0.5 (0.5 referring to 0.5 μm) and α for the wavelength interval 350–1038 nm were derived from a series of spectroradiometric measurements at Ile-Ife. The values of the turbidity parameters, β and β 0.5 are high with averages of 1.06 and 1.38, respectively. The average value of α was about 0.5. Classifying the Harmattan season into periods with “moderate” characteristics (background Harmattan) and periods with intensive spells, the mean background conditions had values ranging from 0.99 (at 350 nm) to 0.53 (at 862 nm) while Harmattan spell conditions had higher turbidities varying from 1.95 at 350 nm to 1.51 at 862 nm. There were severe reductions in the direct solar irradiance at Ile-Ife during this period due to the strong attenuating effects of the Harmattan dust. On the other hand, a significant increase in the diffuse irradiance was observed which, in all the cases examined during the period, exceeded the direct irradiance. The parameters β and β 0.5 were found to decrease when the intertropical discontinuity (ITD) moved North of a station during the Harmattan period and to increase when it migrates South of it. The coefficient α, on the other hand, increased with the Northward movement of the ITD and decreased when it moved southwards.

On the association between the column ozone and the spectral solar ultraviolet radiation

An estimation of the increase in the daily spectral solar ultraviolet radiation reaching the ground is attempted, by using the daily total ozone observations made by the Total Ozone Mapping Spectrometer (TOMS) flown on the satellite Nimbus‐7 during 1978–1992. This investigation has been performed for the high latitudes by employing a recently proposed parametric model for the estimation of the spectral solar ultraviolet radiation at the earth's surface considering the total ozone content and various meteorological parameters.

Detailed analysis of solar ultraviolet radiation: a preliminary investigation on data collected at Rome (‘La Sapienza’ University)

The importance of solar ultraviolet radiation and its impact on human health is well known by the scientific community. Variations of the ozone layer can influence the UV radiation reaching the Earth's surface, especially at short wavelengths. Thus, it is important to study any possible ozone fluctuations. At the Physics Department, University of Rome, a Brewer spectrophotometer MKIV is located and is used to measure total ozone and UV flux in the 290–325 nm region with a resolution of 0.5 nm. Measurements of damaging ultraviolet radiation (DUV), defined as the incident radiation weighted against an action spectrum which relates the sensitivity of the human body to UV radiation, are also processed. This work is a preliminary investigation on the spectral solar UV radiation measurements performed at Rome during the years 1992/1993.

The role of clouds on the solar ultraviolet radiation

The interaction of the various cloud types with the radiation field is examined through a simple parametric model. Furthermore a statistical analysis of the coverage of the Greek region by various cloud types for various seasons is presented in order to be taken into account for the application of the spectral solar ultraviolet radiation reaching the ground.

SIMULATION OF BROAD-BAND AND SPECTRAL SOLAR ULTRAVIOLET RADIATION

Daily broad-band and spectral measurements of solar ultraviolet radiation reaching the ground at Athens, Greece (38°N, 24°E) during 1989-1993 in conjunction with daily total ozone measurements deduced from satellite and ground-based instrumentation were used to investigate their association. Furthermore, employing a new parametric model, the spectral and broad-band solar ultraviolet radiation for die period 1979-1993 were calculated considering the total ozone values, derived from both the satellite Nimbus-7, and the ground-based Dobson spectrophotometer.

Solar cells efficiency variations with varying atmospheric conditions

The resuls of model simulations and analyses of operating solar cell efficiencies are reported. Defined as the ratio (%) between the electrical output power of the device and the total incident radiant power, this efficiency is somewhat ambiguous as it ignores the effects of temperature, total irradiance, and the spectral distribution of the light source. Since the total intensity and spectral distribution of sunlight varies with atmospheric conditions such as cloudiness, total column ozone, turbidity, and precipitable water, the efficiency of a cell operating in a field installation may also be a function of the above factors. This paper examines variation of modeled and observed cell efficiencies with atmospheric variations. Variations in turbidity and water vapor content drive the SPCTRAL2 solar spectral radiation model of Bird and Riordan (1986). Model output, coupled with prescribed spectral response functions representing monocrystalline and amorphous solar cells, is used to model the efficiency of these cell types. The modeled efficiency rises with increasing humidity, especially for the simulated amorphous cell. Simulated efficiency decreases with increasing turbidity for both modeled cell types. The amount of increase or decrease dependents on the spectral response specified. The measured performance of different solar cells operating at the PVUSA site in Davis, California is also analyzed. The major factors found to cause variations in operational efficiency are ambient temperature and total irradiance intensity. The authors also observed increases of the apparent efficiency of amorphous cells with decreasing energy in the red portion of the solar spectrum which are consistent with model predictions.

A study of the link between synoptic air mass type and atmospheric optical parameters

The paper deals with air mass influence on atmospheric spectral transmittance in a rural, pollution‐free area (Sherbrooke, Québec, in eastern Canada). A statistical analysis of aerosol optical depths (0.04 ≤ τa≤0.60) and Angstrom parameters (0.20 ≤ α ≤ 2.1) derived from measurements of direct spectral solar radiation in the period from January 1989 up to August 1991 is presented. The analysis incorporates investigations into correlations with air mass type (obtained from synoptic maps) and source type (deduced from back trajectory analysis). Mean monthly values of aerosol optical depth and corresponding information about frequency of air mass occurrence are also presented. The temporal comparison of these two ensembles of data helps to explain the similarities and differences observed in the month to month variations of aerosol optical depth during the 3‐year measurement period. The data arrays are then partitioned in such a way as to facilitate the interpretation in terms of determining the optical mechanisms which influence the aerosol optical depths. For air masses of arctic origin the discrimination of seasonal variations of aerosol optical depth is consistent with independent measurements of turbidity made in Alaska. The role of air mass source in defining aerosol optical depth is evaluated in terms of its being potentially a more fundamental influence than air mass type.

Relation between the structure of particles of the dispersion layer and its spectral optical thickness in an optically thin environment

The paper focuses on the applicability of simple optimizing methods to determining the aerosol structure based on the measured values of the spectral optical thickness of aerosol δ(λ). The necessary conditions leading to a stable solution are assessed. By applying the particle distribution function in the form of summations of modified gamma functions we obtain the simple form of δ(λ). It is not suitable for proving Gaussian functions. The application of approximate methods to determine the aerosol structure from spectral optical thickness of atmospheric aerosol is based on measurements of the direct spectral solar radiation flux density which formed a part of the radiation experiment conducted in Zingst (Germany) on the coast of the Baltic Sea in 1987.

Evaluation of photovoltaic modules considering spectral solar radiation

AbstractFor the optimum design of photovoltaic power systems, it is very important to estimate their annual maximum amount of output. In general, the annual maximum amount of output has been calculated by using photovoltaic module efficiency under irradiance of 1 kW/m2 at AM 1.5 with solar cell temperature of 25°C. Since the spectral distribution of solar radiation changes with weather, season and time, the efficiency of solar cells is not always constant.This paper describes a method evaluating the maximum amount of output in photovoltaic modules, ‘the spectral method,’ by using the measured annual spectral solar radiation and the spectral response of various photovoltaic modules.The calculated values using the spectral method agreed well with the measured values for amorphous silicon photovoltaic modules from March 1991 to February 1992. The spectral method proved most effective for optimum design of amorphous silicon photovoltaic power systems.

Simple algorithm for the atmospheric correction of reflectance images

Abstract A simple algorithm for the atmospheric correction was developed for the calculation of reflectance images. The proposed method, for a clear atmosphere, is based on a simplification of the radiative transfer equation for multiple scattering in order to calculate the spectral reflectance, including single scattering. Furthermore, the lowest pixel value of each spectral band is related to the backscattered solar spectral radiation towards the satellite. Ground truth data of an experimental area were used to evaluate the spectral reflectance calculations. A visual example of the use of the proposed method is also included.

Spectral measurements of solar UVB radiation and its relations to total ozone, SO2, and clouds

Spectral solar UV radiation measurements performed at Thessaloniki, Greece (40°N), are presented, and the influence of various atmospheric constituents such as total ozone, cloud cover, and columnar SO2 on these measurements is examined. By comparing UV radiation measurements at days with different total ozone amounts the magnification factor was calculated. Its values range from 1 to 20, depending on the wavelength and the total ozone. A relationship between the UV radiation and the cloud cover was established, being representative only for measurements at 50° solar zenith angle. In addition, the influence of columnar SO2 variations on UV irradiances was also studied. Finally, an attempt was made to compare the relative influence of these parameters on UV radiation, which proved that total ozone is the major factor controlling the solar UVB radiation received at the ground.

Evaluation of Photovoltaic Modules Considered Spectral Solar Radiation.

For optimum design of photovoltaic power systems, it is very important to estimate their annual maximum amount of output. In general, the annual maximum amount of output has been calculated by using photovoltaic module efficiency under irradiance of 1kW/m2 at AM 1.5 with solar cell temperature of 25°C. Since the spectral distribution of solar radiation changes with weather, season and time, the efficiency of solar cells is not always constant. This paper describs a method evaluating the maximum amount of output in photovoltaic modules, “the spectral method”, by using the measured annual spectral solar radiation and the spectral response of various photovoltaic modules.The calculated values using the spectral method agreed well with the measured values for amorphous silicon photovoltaic modules from March, 1991 to February, 1992. The spectral method proved most effective for optimum design of amorphous silicon photovoltaic power systems.

Vertical profile calculation of the attenuation coefficient of atmospheric aerosol based on the spectral radiance measurements of day-sky

The vertical profile of the aerosol attenuation coefficient can be calculated from the measurements of the spectral flux density of direct solar radiation and spectral radiance in a clear sky in a certain sun aureola by using the theory applied in this article. The process of solar radiation scattering is solved up to third order.

Relationship between spectral solar radiation extinction and dust pollution in the air of industrial and urban areas in Poland

This work is based on simultaneous measurements of spectral direct solar radiation (using Eppley's pyrheliometer) and total mass particulate concentration (using a high-volume sampler) carried out in Katowice, Upper Silesian Industrial Region (USIR), Poland, in the period 1982–1987. Relationships between spectral aerosol optical depth values ( τ a λ ) expressing the solar radiation extinction and total suspended particulates concentration at near ground-level air are, in general, weak (correlation coefficient r=0.0−0.40) except after rainy (or snowy) periods in cold months [October–March (X-III)] with correlation coefficient r=0.67−0.68. In conclusion, the fundamental effect of relative humidity on variability as well as on the magnitude and range of τ a values in existing anthropogenic emission structure over USIR area was confirmed.

Antarctic radiation exposure doubles

New data reveal that the Antarctic Peninsula received twice its normal maximum dose of hazardous solar ultraviolet radiation in December 1990. The prolonged persistence of the ozone hole over Antarctica caused an increased exposure of radiation, according to a paper published in the October issue of Geophysical Research Letters.John Frederick and Amy D. Alberts of the University of Chicago calculated the amount of ultraviolet solar spectral radiation from data collected at Palmer Station, Antarctica. During the spring of 1990 the largest observed values for ultraviolet radiation were approximately double the values expected, based on previous years. “The measurements from Palmer Station are consistent with similar data from McMurdo Sound, where a factor of three [ultraviolet radiation] enhancement was recorded, according to work by Knut Stamnes and colleagues at the University of Alaska,” Frederick said. “The radiation levels observed over Palmer Station in December 1990 may be the largest experienced in this region of the world since the development of the Earth's ozone layer,” he added.