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Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 32798

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Special Issue Editors

Dr. Harry D. Kambezidis

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Guest Editor

1. Atmospheric Research Team, Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Nymphon, GR-11810 Athens, Greece
2. Soft Energy Systems and Environmental Protection Laboratory, Department of Mechanical Engineering, University of West Attica, P. Ralli & Thivon 250, GR-12244 Egaleo, Greece
Interests: solar radiation; atmospheric aerosols; atmospheric turbidity; daylighting; climatology; meteorology; climate change
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Dr. Basil Psiloglou

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Guest Editor

Institute for Environmental Research & Sustainable Development, National Observatory of Athens, 15236 Athens, Greece
Interests: solar radiation modelling and applications; solar energy; atmospheric physics; meteorology; atmospheric pollution; investigation of climatic parameters' evolution-change; analysis of electricity demand characteristics; air quality, solar radiation, meteorological and hydrological instrumentation and measurements
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The second Special Issue on “Solar Radiation: Measurements and Modelling, Effects and Applications” was a success, with a total of 21 papers accepted for publication. Therefore, we have decided to extend the opportunity to other researchers who were not able to submit their work to this Special Issue. It is with this in mind that we are extending this invitation to the solar radiation scientific community to submit your papers to this Special Issue on “Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III”, which is devoted to some of the topics of Volume II, as well as new ones.

Solar radiation is recognised as the primary source of life on Earth as it controls various fields, such as atmospheric environment, terrestrial ecosystems, and terrestrial climate. Due to its important role, solar radiation has been the subject of numerous studies mostly focusing on solar measurements and models. No work to our knowledge, such as the present volume, volume I and volume II of the Special Issue, has had a holistic approach to solar radiation, i.e., by examining not only issues directly related to solar radiation/energy but also to applications and effects.

This Special Issue will therefore aim to cover advances in (i) the contemporary use of solar radiation/energy, (ii) modelling of solar radiation with advanced now-casting techniques, (iii) the relation of solar radiation with climate, (iv) and the effects of solar radiation on human health, hydrologic cycles, and weather modification.

Dr. Harry D. Kambezidis
Dr. Basil Psiloglou
Guest Editors

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Published Papers (14 papers)

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31 pages, 10429 KiB

Open AccessArticle

Comparison of Sunshine Duration Measurements between the Campbell–Stokes Sunshine Recorder and Three Automatic Sensors at Three Locations in Cyprus

by Stelios Pashiardis, Alexandros Pelengaris and Soteris A. Kalogirou

Appl. Sci. 2023, 13(22), 12393; https://doi.org/10.3390/app132212393 - 16 Nov 2023

Cited by 1 | Viewed by 2223

Abstract

This paper compares the daily sunshine duration (SD) measured by the Campbell–Stokes sunshine recorder (CS) with three automatic instruments (Kipp & Zonen pyranometers (CM6 B), pyrheliometer (CHP1) and CSD3 sunshine recorders). The comparisons are essential, since recently, automatic sunshine duration sensors have been replacing the manual measurements, affecting, therefore, the continuity of the CS time series. The comparisons were applied to the daily SD data of three synoptic stations (Larnaca A/P, Pafos A/P and Athalassa) where parallel measurements of manual and automatic instruments are carried out during the periods 2009–2012 and 2012–2015. The CSD3 measurements were obtained from two automatic weather stations (AWSs) which are close to the synoptic station of Larnaca A/P. The comparisons referred to the daily and monthly sums of sunshine duration, as well as to their statistical distributions and their relationships. The daily differences in the pairs of sunshine recorders installed at the same location are mostly within the range of −1.0 to +1.0 h. At Larnaca, in the period 2009–2012, the pyranometric method’s (Gl) values were higher than the CS in the summer months. Pafos and Athalassa showed higher values of CS compared to Gl and the pyrheliometric method (Pr), respectively, almost throughout the year. Generally, the annual average daily differences between the different pairs range between 0.3 and 0.5 h. Regression equations were determined allowing the estimation of daily SD under different sky conditions. The coefficient of determination (R²) reached the values of 0.91 and 0.96 under ‘all sky’ conditions, and between 0.80 and 0.91 under ‘clear’ sky conditions at the three locations. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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16 pages, 3401 KiB

Open AccessArticle

Ultraviolet Erythemal Irradiance (UVER) under Different Sky Conditions in Burgos, Spain: Multilinear Regression and Artificial Neural Network Models

by S. García-Rodríguez, A. García-Rodríguez, D. Granados-López, I. García and C. Alonso-Tristán

Appl. Sci. 2023, 13(19), 10979; https://doi.org/10.3390/app131910979 - 5 Oct 2023

Cited by 1 | Viewed by 1381

Abstract

Different strategies for modeling Global Horizontal UltraViolet Erythemal irradiance (

G H U V E

) based on meteorological parameters measured in Burgos (Spain) have been developed. The experimental campaign ran from September 2020 to June 2022. The selection of relevant variables for [...] Read more.

Different strategies for modeling Global Horizontal UltraViolet Erythemal irradiance (

G H U V E

(M L R)

and artificial neural network

(A N N)

techniques were employed to model

G H U V E

under different sky conditions (all skies, overcast, intermediate, and clear skies), classified according to the

C I E

standard on a 10 min basis.

A N N

models of

G H U V E

outperform those based on MLR according to the traditional statistical indices used in this study (

R^{2}

M B E

, and

n R M S E

). Moreover, the work proposes a simple all-sky

A N N

model of

G H U V E

based on usually recorded variables at ground meteorological stations. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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30 pages, 13117 KiB

Open AccessArticle

Three-Dimensional Distributions of the Direct Effect of anExtended and Intense Dust Aerosol Episode (16–18 June 2016) over the Mediterranean Basin on Regional Shortwave Radiation, Atmospheric Thermal Structure, and Dynamics

by Maria Gavrouzou, Nikos Hatzianastassiou, Marios-Bruno Korras-Carraca, Michalis Stamatis, Christos Lolis, Christos Matsoukas, Nikos Michalopoulos and Ilias Vardavas

Appl. Sci. 2023, 13(12), 6878; https://doi.org/10.3390/app13126878 - 6 Jun 2023

Cited by 1 | Viewed by 1738

Abstract

In the present study, we used the FORTH deterministic spectral Radiation Transfer Model (RTM) to estimate detailed three-dimensional distributions of the Direct Radiative Effects (DREs) and their consequent modification of the thermal structure of the regional atmosphere during an intense dust episode that took place from 16 to 18 June 2016 over the Mediterranean Basin (MB). The RTM operated on a 3-hourly temporal and 0.5 × 0.625° spatial resolution, using 3-D aerosol optical properties (i.e., aerosol optical depth, single scattering albedo, and asymmetry parameter) and other surface and atmospheric properties from the MERRA-2 reanalysis and cloud properties (i.e., cloud amount, cloud optical depth, and cloud top height) from the ISCCP-H dataset. The model ran with and without dust aerosols, yielding the upwelling and downwelling solar fluxes at the top of the atmosphere, in the atmosphere, and at the Earth’s surface as well as at 50 levels in the atmosphere. The dust direct radiative effect (DDRE) was estimated as the difference between the two (one taking into account all aerosol types and one taking into account all except for dust aerosols) flux outputs. The atmospheric heating rates and subsequent convection induced by dust radiative absorption were calculated at 50 levels to determine how the DDRE affects the thermal structure and dynamics of the atmosphere. The results showed that such a great and intense dust transport event significantly reduces the net surface solar radiation over the MB (by up to 62 W/m² on a daily mean basis, and up to 200 W/m² on an hourly basis, at 12:00 UTC) while increasing the atmospheric solar absorption (by up to 72 W/m² daily and 187 W/m² hourly, at 12:00 UTC). At the top of the atmosphere, both heating (over desert areas) and cooling (over oceanic and other continental areas) are observed due to the significantly different surface albedos. Transported dust causes considerable heating of the region’s atmosphere, which becomes maximum at altitudes where the dust loadings are highest (0.14 K/3 h on 17 June 2016, 12:00 UTC, at 3–5 km above sea level). The dust solar absorption and heating induce a buoyancy as strong as 0.014 m/s², resulting in considerable changes in vertical air motions and possibly contributing to the formation of middle- and high-level clouds over the Mediterranean Basin. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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14 pages, 1524 KiB

Open AccessArticle

Minute-Scale Models for the Diffuse Fraction of Global Solar Radiation Balanced between Accuracy and Accessibility

by Eugenia Paulescu and Marius Paulescu

Appl. Sci. 2023, 13(11), 6558; https://doi.org/10.3390/app13116558 - 28 May 2023

Cited by 3 | Viewed by 2166

Abstract

The separation models are tools used in solar engineering to estimate direct normal (DNI) and diffuse horizontal (DHI) solar irradiances from measurements of global solar irradiance (GHI). This paper proposes two empirical separation models that stand out owing to their simple mathematical formulation: a rational polynomial equation. Validation of the new models was carried out against data from 36 locations, covering the four major climatic zones. Five current top minute-scale separation models were considered references. The tests were performed on the final products of the estimation: DNI and DHI. The first model (M1) operates with eight predictors (evaluated from GHI post-processed measurements and clear-sky counterpart estimates) and constantly outperforms the already established models. The second model (M2) operates with three predictors based only on GHI measurements, which gives it a high degree of accessibility. Based on a statistical linear ranking method according to the models’ performance at every station, M1 leads the hierarchy, ranking first in both DNI and DHI estimation. The high accessibility of the M2 does not compromise accuracy; it is proving to be a real competitor in the race with the best-performing current models. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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42 pages, 14101 KiB

Open AccessArticle

Geographical Distribution of Global Radiation and Sunshine Duration over the Island of Cyprus

by Stelios Pashiardis, Alexandros Pelengaris and Soteris A. Kalogirou

Appl. Sci. 2023, 13(9), 5422; https://doi.org/10.3390/app13095422 - 26 Apr 2023

Cited by 6 | Viewed by 2372

Abstract

In this work, hourly measurements of global solar irradiances obtained from pyranometers and sunshine duration data using either Kipp & Zonen CSD3 automatic sensors or Campbell–Stokes sunshine recorders were assessed through an extensive quality control procedure and statistical analysis on the measured and derived solar parameters for all the actinometric stations installed in various locations over the island of Cyprus, covering mainly the period 2019–2021. This information is useful for engineers concerning the solar energy capture systems and energy efficiency who can therefore take knowledge of the local radiation levels. Monthly mean hourly values of global radiation and sunshine duration are calculated and shown through isoline diagrams. During June or July, daily global irradiations ranged between 25 MJ/m² and 30 MJ/m², with the lowest occurring in the mountainous locations. On the other hand, in January or December, they ranged between 6.5 MJ/m² and 10.5 MJ/m². The total annual number of hours of sunshine duration ranged between 2500 and 3500, with the lowest values recorded at the mountainous sites. The clearness index and relative sunshine duration were used for the classification of the weather conditions over the island. Furthermore, the interrelationships between the said indices were used for the estimation of global radiation. This work has specifically contributed to the characterization and analysis of hourly and daily solar global radiation. Furthermore, the measurements on the ground level could be compared with satellite observations in order to improve the geographical distribution of global radiation, especially in areas where no measurements exist. The analysis could be also extended for the other shortwave radiation components (Direct, Diffuse and Photosynthetic Active Radiation (PAR)) in order to assess the solar radiation regime over the island. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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14 pages, 22906 KiB

Open AccessArticle

Modeling Horizontal Ultraviolet Irradiance for All Sky Conditions by Using Artificial Neural Networks and Regression Models

by M. I. Dieste-Velasco, S. García-Rodríguez, A. García-Rodríguez, M. Díez-Mediavilla and C. Alonso-Tristán

Appl. Sci. 2023, 13(3), 1473; https://doi.org/10.3390/app13031473 - 22 Jan 2023

Cited by 2 | Viewed by 1837

Abstract

In the present study, different models constructed with meteorological variables are proposed for the determination of horizontal ultraviolet irradiance (

I_{UV}

), on the basis of data collected at Burgos (Spain) during an experimental campaign between March 2020 and May 2022. The [...] Read more.

In the present study, different models constructed with meteorological variables are proposed for the determination of horizontal ultraviolet irradiance (

I_{UV}

), on the basis of data collected at Burgos (Spain) during an experimental campaign between March 2020 and May 2022. The aim is to explore the effectiveness of a range of variables for modelling horizontal ultraviolet irradiance through a comparison of supervised artificial neural network (ANN) and regression model results. A preliminary feature selection process using the Pearson correlation coefficient was sufficient to determine the variables for use in the models. The following variables and their influence on horizontal ultraviolet irradiance were analyzed: horizontal global irradiance

(I_{GH}

), clearness index

(k_{t}

), solar altitude angle

(α)

, horizontal beam irradiance

(I_{BH})

, diffuse fraction (

D

), temperature

(T)

, sky clearness

(ε)

, cloud cover

(Cc

), horizontal diffuse irradiance

(I_{DH})

, and sky brightness (Δ). The ANN models yielded results of greater accuracy than the regression models. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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24 pages, 2615 KiB

Open AccessArticle

Calibration and Validation of Global Horizontal Irradiance Clear Sky Models against McClear Clear Sky Model in Morocco

by Abderrahmane Mendyl, Brighton Mabasa, Houria Bouzghiba and Tamás Weidinger

Appl. Sci. 2023, 13(1), 320; https://doi.org/10.3390/app13010320 - 27 Dec 2022

Cited by 8 | Viewed by 3743

Abstract

This study calibrated and compared the capabilities of hourly global horizontal irradiance (GHI) clear sky models for six Moroccan locations, using the McClear clear sky model as a reference. Complex clear sky models, namely Bird, Simplified Solis, Ineichen and Perez, and simple clear sky models, namely Adnot–Bourges–Campana–Gicquel (ABCG), Berger–Duffie, and Haurwitz were tested. The SOLCAST satellite-based dataset estimates were validated against the McClear clear sky model. pvlib python was used to configure the models, and ERA5 hourly fractional cloud cover was used to identify clear-sky days. The study period was from 2014 to 2021, and the study sites were in different climatic regions in Morocco. Bar graphs, tables, and quantitative statistical metrics, namely relative mean bias error (rMBE), relative root mean square error (rRMSE), relative mean absolute error (rMAE), and the coefficient of determination (R²), were used to quantify the skill of the clear sky model at different sites. The overall rMBE was negative in 5/6 sites, indicating consistent overestimation of GHI, and positive in Tantan (14.4%), indicating frequent underestimation of GHI. The overall rRMSE varied from 6 to 22%, suggesting strong agreement between clear sky models and the McClear clear sky model. The overall correlation was greater than 0.96, indicating a very strong relationship. Overall, the Bird clear sky model proved to be the most feasible. Complex clear sky models outperformed simple clear sky models. The SOLCAST satellite-based dataset and ERA5 cloud fraction information could well be used with quantifiable certainty as an accurate clear sky model in the study region and in other areas where complex clear sky models’ inputs are not available. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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12 pages, 1631 KiB

Open AccessArticle

A Semi-Analytical Model for Separating Diffuse and Direct Solar Radiation Components

by Eugenia Paulescu and Marius Paulescu

Appl. Sci. 2022, 12(24), 12759; https://doi.org/10.3390/app122412759 - 12 Dec 2022

Cited by 2 | Viewed by 1990

Abstract

The knowledge of the solar irradiation components is required by most solar applications. When only the global horizontal irradiance is measured, this one is typically broken down into its fundamental components, beam and diffuse, by applying an empirical separation model. This study proposes a semi-analytical model for diffuse fraction, defined as the ratio of diffuse to global solar irradiance. Starting from basic knowledge, a general equation for diffuse fraction is derived. Clearness index, relative sunshine, and the clear-sky atmospheric transmittance are highlighted as robust predictors. Thus, the model equation implicitly provides hints for developing accurate empirical separation models. The proposed equation is quasi-universal, allowing for temporal (from 1-min to 1-day) and spatial (site specificity) customization. As a proof of theory, the separation quality is discussed in detail on the basis of radiometric data retrieved from Baseline Surface Radiation Network (BSRN), station Magurele, Romania. For temperate continental climate, overall results show for the diffuse fraction estimation a maximum possible accuracy around 7%, measured in terms of normalized root mean square error. One of the many options of implementing the semi-analytical model is illustrated in a case study. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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48 pages, 8425 KiB

Open AccessArticle

Shortwave Radiation on Horizontal and Incline Surfaces—One Year of Solar Radiation Measurements at Athalassa, an Inland Location in Cyprus

by Stelios Pashiardis, Soteris A. Kalogirou and Alekos Pelengaris

Appl. Sci. 2022, 12(21), 11035; https://doi.org/10.3390/app122111035 - 31 Oct 2022

Cited by 4 | Viewed by 2460

Abstract

Athalassa is the main actinometric station of Cyprus and is located in the center of the island at a height of about 160 m. The station is equipped with shortwave and longwave radiation instruments. The time step of the measurements is 10 min, and hourly and daily values were derived for the period of June 2020–May 2021. The solar data underwent an extensive quality control process based mainly on the suggested tests of Baseline Surface Radiation Network (BSRN) for both the hourly and daily datasets. More than 98% of the data were within the limits recommended by the BSRN and other radiation networks. A statistical analysis of the shortwave solar radiation components was then performed. Linear and quadratic relationships were established between various radiation components, and their diurnal and monthly variability was assessed. The annual average daily global radiation amount was approximately 19 MJ/m², whereas the amounts of horizontal beam and diffuse radiation were 12.9 MJ/m² and 4.7 MJ/m², respectively. Regarding the modeling of diffuse irradiance, the BRL diffuse fraction model (Boland-Ridley-Lauret) was applied. The results showed that the BRL model can satisfactorily estimate both the diffuse solar irradiance as well as the direct normal irradiance. Furthermore, the levels of the shortwave components were estimated based on the classification of four categories of the clearness index. The annual average of the direct normal beam radiation on clear days was 27.3 MJ/m², and the direct horizontal radiation was 17.7 MJ/m². Finally, the total energy received by an inclined surface was estimated based on measurements on the horizontal surfaces. In practice, photovoltaics were installed with an annual permanent slope of 26° with respect to the horizontal surface, and in a southern direction. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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17 pages, 3890 KiB

Open AccessArticle

Solar Ultraviolet Irradiance Characterization under All Sky Conditions in Burgos, Spain

by Sol García-Rodríguez, Ignacio García, Ana García-Rodríguez, Montserrat Díez-Mediavilla and Cristina Alonso-Tristán

Appl. Sci. 2022, 12(20), 10407; https://doi.org/10.3390/app122010407 - 15 Oct 2022

Cited by 2 | Viewed by 2176

Abstract

Solar Ultraviolet Radiation (UVR), which is identified as a major environmental health hazard, is responsible for a variety of photochemical reactions with direct effects on urban and aquatic ecosystems, human health, plant growth, and the deterioration of industrial systems. Ground measurements of total solar UVR are scarce, with low spatial and temporal coverage around the world, which is mainly due to measurement equipment maintenance costs and the complexities of equipment calibration routines; however, models designed to estimate ultraviolet rays from global radiation measurements are frequently used alternatives. In an experimental campaign in Burgos, Spain, between September 2020 and June 2022, average values of the ratio between horizontal global ultraviolet irradiance (GHUV) and global horizontal irradiance (GHI) were determined, based on measurements at ten-minute intervals. Sky cloudiness was the most influential factor in the ratio, more so than any daily, monthly, or seasonal pattern. Both the CIE standard sky classification and the clearness index were used to characterize the cloudiness conditions of homogeneous skies. Overcast sky types presented the highest values of the ratio, whereas the clear sky categories presented the lowest and most dispersed values, regardless of the criteria used for sky classification. The main conclusion, for practical purposes, was that the ratio between GHUV and GHI can be used to model GHUV. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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36 pages, 9516 KiB

Open AccessArticle

Interdecadal Changes of the MERRA-2 Incoming Surface Solar Radiation (SSR) and Evaluation against GEBA & BSRN Stations

by Michael Stamatis, Nikolaos Hatzianastassiou, Marios Bruno Korras-Carraca, Christos Matsoukas, Martin Wild and Ilias Vardavas

Appl. Sci. 2022, 12(19), 10176; https://doi.org/10.3390/app121910176 - 10 Oct 2022

Cited by 10 | Viewed by 3049

Abstract

This study assesses and evaluates the 40-year (1980–2019) Modern-Era Retrospective Analysis for Research and Applications v.2 (MERRA-2) surface solar radiation (SSR) as well as its interdecadal changes (Δ(SSR)) against high quality reference surface measurements from 1397 Global Energy Balance Archive (GEBA) and 73 Baseline Surface Radiation Network (BSRN) stations. The study is innovative since MERRA-2 (Δ(SSR)) has never been evaluated in the past, while the MERRA-2 SSR fluxes themselves have not been evaluated in such large spatial scale, which is global here, and temporal basis, which counts 40-years. Other novelties of the study are the use of the highest quality BSRN stations, done for the first time in such an evaluation, as well as the use of a greater number of reference-GEBA stations than in other studies. Moreover, the assessment and evaluation in this study are largely based on SSR anomalies, while being done in depth, at spatial scales ranging from the local to global/hemispherical, and separately for land and ocean areas, and at temporal scales spanning intervals from decadal sub-periods to 40 years. Overall, the MERRA-2 deseasonalized SSR anomalies correlate well with either GEBA (R equal to 0.61) and BSRN (R equal to 0.62). The percentage of agreement between the sign of computed GEBA and MERRA-2 Δ(SSR) is equal to 63.4% and the corresponding percentage for MERRA-2 and BSRN is 50%. According to MERRA-2, strong and statistically significant positive Δ(SSR) (Brightening) is found over Europe, Central Africa, Mongolia, Mexico, Brazil, Argentina and some parts of the tropical oceans. In contrast, large and statistically significant negative Δ(SSR) (Dimming) occurs over the western Tropical Warm Pool, India, Southern East China, Amazonia, stratocumulus covered areas and some parts of oceans. MERRA-2 yields a dimming equal to −0.158 ± 0.005 W/m²/year over the globe from 1980 to 2019. This 40-year dimming, which occurred in both hemispheres, more over ocean than continental areas (−0.195 ± 0.006 and −0.064 ± 0.006 W/m²/year, respectively), underwent decadal scale variations. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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28 pages, 8073 KiB

Open AccessArticle

The Sky-Status Climatology of Greece: Emphasis on Sunshine Duration and Atmospheric Scattering

by Harry D. Kambezidis

Appl. Sci. 2022, 12(16), 7969; https://doi.org/10.3390/app12167969 - 9 Aug 2022

Cited by 3 | Viewed by 1977

Abstract

The aim of this work is the study of the sky conditions climatology over Greece based on the diffuse-fraction (k_d) limits, for clear, k_d ∈ [0, 0.26]; intermediate, k_d ∈ (0.26, 0.78); and overcast, k_d ∈ (0.78, 1) skies. k_d is, therefore, used here to characterise the sky conditions over a site. Its values are estimated from diffuse and global horizontal solar irradiances the typical meteorological years of 43 selected Greek sites. The k_d values in each specific range are equivalent to sunshine durations (SSDs) under the particular sky conditions. Annual, seasonal, and intra-annual variations in SSDs are estimated with regression equations to fit their means. Clear skies comprise 33%, intermediate 40%, and overcast 27% of the time in a year. k_d, as an atmospheric scattering index (ASI), shows dependence on the sites’ geographical latitude: best-fit lines mean ASIs are derived showing no trend, while overcast skies show a slight negative trend. A comparison of the clear-sky SSDs for four Greek sites from the Global Climate Data and one site from the Academy of Sciences of Moldova with those derived from k_d shows a remarkable difference. A new methodology is developed that results in much smaller differences. Finally, maps of the annual SSDs and ASIs are derived for Greece. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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20 pages, 5698 KiB

Open AccessArticle

Solar Energy Potential on Surfaces with Various Inclination Modes in Saudi Arabia: Performance of an Isotropic and an Anisotropic Model

by Ashraf Farahat, Harry D. Kambezidis, Mansour Almazroui and Emad Ramadan

Appl. Sci. 2022, 12(11), 5356; https://doi.org/10.3390/app12115356 - 25 May 2022

Cited by 12 | Viewed by 2335

Abstract

The present work investigated the performance of an isotropic (Liu–Jordan, L–J) and an anisotropic (Hay) model in assessing the solar energy potential of Saudi Arabia. Three types of solar collectors were considered: with southward fixed-tilt (mode (i)), with fixed-tilt tracking the Sun (mode (ii)), and with varying-tilt tracking the Sun (mode (iii)). This was the first time such a study was conducted for Saudi Arabia. The average annual difference between anisotropic (Hay) and isotropic (L–J) estimates is least ≈38 kWhm⁻² year⁻¹ over Saudi Arabia for mode (i), and therefore, the L–J model can be used effectively. In modes (ii) and (iii), the difference is greater (≈197 and ≈226 kWhm⁻² year⁻¹, respectively). It is, then, up to the solar energy engineer to decide which model is to be used, but it is recommended that the Hay model be utilised for mode-(iii) solar collectors. These results fill a research gap about the suitability of models in practice. An interesting feature for the ratio of the annual mean solar energy yield of Hay over L–J as function of the latitude, φ, and the ground albedo, ρ_r, is the formation of a “well” for 29° ≤ φ ≤ 31° and 1.15 ≤ ρ_r ≤ 1. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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14 pages, 3842 KiB

Open AccessArticle

Extension of PAR Models under Local All-Sky Conditions to Different Climatic Zones

by Ana García-Rodríguez, Sol García-Rodríguez, Diego Granados-López, Montserrat Díez-Mediavilla and Cristina Alonso-Tristán

Appl. Sci. 2022, 12(5), 2372; https://doi.org/10.3390/app12052372 - 24 Feb 2022

Cited by 7 | Viewed by 1859

Abstract

Four models for predicting Photosynthetically Active Radiation (PAR) were obtained through MultiLinear Regression (MLR) and an Artificial Neural Network (ANN) based on 10 meteorological indices previously selected from a feature selection algorithm. One model was developed for all sky conditions and the other three for clear, partial, and overcast skies, using a sky classification based on the clearness index (k_t). The experimental data were recorded in Burgos (Spain) at ten-minute intervals over 23 months between 2019 and 2021. Fits above 0.97 and Root Mean Square Error (RMSE) values below 7.5% were observed. The models developed for clear and overcast sky conditions yielded better results. Application of the models to the seven experimental ground stations that constitute the Surface Radiation Budget Network (SURFRAD) located in different Köppen climatic zones of the USA yielded fitted values higher than 0.98 and RMSE values less than 11% in all cases regardless of the sky type. Full article

(This article belongs to the Special Issue Solar Radiation: Measurements and Modelling, Effects and Applications—Volume III)

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