Ground-reflected Radiation Research Articles

Skyglow from ground-reflected radiation: model improvements

ABSTRACT Light from ground-based sources directed into the upper hemisphere can be partially controlled, for example, through suitable lamp shades or by reducing the number of luminaires and their lumen output. However, ground-reflected radiation is pervasive in artificially lit urban environments and cannot be entirely avoided. This component of upward-directed light is typically modelled using Lambertian diffuse reflection. Here, we demonstrate that the current analytical models for ground-reflected radiation can be improved by incorporating additional components, such as reflections from vertically oriented surfaces and vegetation. Our findings indicate that near edges of cities, the contribution of the reflected radiation to the overall skyglow is slightly higher than recent models predict. However, at medium-to-long distances the skyglow increases by 50–200 per cent compared to what these models suggest. This is because non-horizontal surfaces reflect more light towards small angles above the horizontal, contrasting with the outcomes predicted by the basic Lambertian framework. Consequently, light escaping from ground-based sources can propagate more effectively over longer distances, even when there is a complete cutoff of light emitted from luminaires in the upper half-space. These findings have significant implications for skyglow modelling. Furthermore, it also limits the available options for implementing measures to reduce skyglow levels at astronomical observatories located well beyond city boundaries.

Modelling global solar radiation to optimise agricultural production

Aim of study: To present a complete global radiation model that includes direct, diffuse sky and ground-reflected radiation, and compare the values with those obtained by the pyranometers.Area of study: The data were analyzed at the meteorological station network in Extremadura, Spain, to validate the results calculated by the model.Material and methods: The method uses the maps from meteorological station data are based on a single piece of daily solar radiation data for an area of 8,000 to 9,000 ha, whereas the maps created by the models are obtained using the spatial resolution of the digital elevation model, in this case 25 × 25m.Main results: The analytical model used in the study obtained global radiation values with a difference of 1.44% relative to the values captured by the meteorological stations in Extremadura. Analysis of the data indicates that on days with a specific type of fog or very diffuse cloud, the global radiation captured by sensors is greater than it would be on clear-sky days in the same area. The method was suitable for calculating global solar radiation on any type of terrain with its corresponding diversity of crop types.Research highlights: The research highlights the importance of understanding and modelling solar radiation for efficient use of water resources in agriculture. Adding these global radiation models to a GIS would provide a very valuable tool for developing regions.

Analytical model for solar radiation transmitting the curved transparent surface of solar greenhouse

This study introduces and examines an improved mathematical model to calculate the total transmitted solar radiation captured by the curved surface of a solar greenhouse. The MATLAB platform is used to calculate the total solar radiation and takes reflected radiation from the outdoor ground into account, and the results were verified in a field test. First, mathematical expression to calculate the equivalent reflected transmissivity of the greenhouse curved surface is developed. The variation for different solar greenhouse aspect ratios on the equivalent transmissivities of beam radiation, scattered radiation, and ground-reflected radiation is simulated for four typical sunny days. Besides, the optimal solar greenhouse aspect ratio is determined for the different latitudes in six cities. Then, the equivalent beam transmissivity is compared between traditional simplified inclined planes and the actual curved surfaces of a specific solar greenhouse, which implies that the calculation results of curved surfaces are more accurate. Additionally, the transmitted solar radiation is calculated for both sunny and snowy days. The results indicate that the intensity of the radiation reflected from outdoor ground is in the same order of magnitude as the scattered radiation. This means reflected sunlight should not be neglected, especially for cities located at high altitudes.

Efficient Routines for Obtaining Radiation View-Factor for Non-Uniform Horizons

There are a large number of engineering applications wherein estimation of radiation exchange between surfaces is required. One important part of the latter procedure is to obtain the so-called ‘view factor’ of the emitter–receiver combination. The principal aim of this article is to present finite-element based procedures to obtain view factor with good time efficiency. As such routines presented here compute the view factor between a non-uniform emitter field and the receiving surface. An example of this is ground-reflected solar radiation to thermal or photovoltaic collectors, the foreground itself being composed of surfaces that have wide-ranging reflectivities. Four routines have been presented here: one based on a uniform grid for emitting and receiving surfaces using a brute force approach (Uniform Populous Grid (UPG)), and another that used non-uniform grid for the receiving surface, where cells’ sizes increased in arithmetic progression as one withdraws from the common edge (Non Uniform Grid Populous (NUGP)). The last two routines used combinations of the first two approaches with Monte-Carlo approach (Uniform Grid Monte-Carlo (UGMC) and Non Uniform Grid Monte-Carlo (NUGMC)). It was found that the NUGP algorithm was the most efficient to reduce the calculation error for the same number of computations, it was about 450 times (430 for non-uniform reflectivity) more accurate than UPG, 160 (125) times more than UGMC and 70 (60) times more than NUGMC. Finally a comparison of advantages and disadvantages of all four considered routines was added, using the following criteria: ease of programming, computational execution time, accuracy of results obtained, and predictability of the errors.

Dynamic energy balance model of a glass greenhouse: An experimental validation and solar energy analysis

Taking only the mean value of cover transmittance and cover absorbance would lead to a large error in estimating the thermal performance of a greenhouse. This paper discusses an innovative dynamic energy balance model of a glass greenhouse, incorporating dynamic cover absorbance and transmittance. Different cover absorbances and transmittances for diffuse, beam, and ground-reflected radiation are used. The model primarily comprises nine differential energy conservation equations for indoor air, seven layers of soil, and the greenhouse’s cover. Greenhouse temperature trends are acquired by solving the unsteady-state equations with MATLAB. The model was verified using experimental data recorded during three non-continuous periods of 15 days each in northern China (36.08°N, 116.95°E), during which the daily maximum outdoor solar radiation flux intensity fell between 191 and 894 Wm-2, the outdoor air temperature fell between −12.3 °C and 24.5 °C, the ground surface temperature fell between 0.6°C and 44.3 °C, and the indoor air temperature fell between −9.0 °C and 51.8 °C. The estimates agree well with the measurements, suggesting that the dynamic model is valid. Meanwhile, the dynamic cover absorbance and transmittance, the solar radiation absorbed by the cover, the solar radiation transmitted into the glass greenhouse and the proportion of solar radiation from each surface are discussed.

A model for predicting the solar reflectivity of the ground that considers the effects of accumulating and melting snow

ABSTRACTSimulation tools for predicting building thermal performance and solar system performance must accurately calculate solar irradiance to surfaces of arbitrary orientation. This is imperative to correctly predict passive solar gains to buildings and to accurately estimate thermal and electrical production of solar collectors. In cold climates, where snow covers the ground for long periods of time, ground reflected radiation can represent a substantial fraction of the total incident irradiance to highly tilted and vertical surfaces (e.g. windows). A new model has been developed to improve the calculation of ground-reflected radiation in simulation tools. The model is based upon empirical observations taken at a measurement site in Ottawa (Canada), and has been validated using disjunct data from the measurement site, and with published data from two other sites in the USA. The model was found to increase the accuracy of ground reflectivity predictions for cold and humid climates.

The bright side of PV production in snow-covered mountains

Our work explores the prospect of bringing the temporal production profile of solar photovoltaics (PV) into better correlation with typical electricity consumption patterns in the midlatitudes. To do so, we quantify the potential of three choices for PV installations that increase production during the winter months when electricity is most needed. These are placements that favor (i) high winter irradiance, (ii) high ground-reflected radiation, and (iii) steeper-than-usual panel tilt angles. In addition to spatial estimates of the production potential, we compare the performance of different PV placement scenarios in urban and mountain environments for the country of Switzerland. The results show that the energy deficit in a future fully renewable production from wind power, hydropower, and geothermal power could be significantly reduced when solar PV is installed at high elevations. Because the temporal production patterns match the typical demand more closely than the production in urban environments, electricity production could be shifted from summer to winter without reducing the annual total production. Such mountain installations require significantly less surface area and, combined with steeper panel tilt angles, up to 50% of the winter deficit in electricity production can be mediated.

Payback calculation system of introduction network solar power plants in private households

The article describes the payback calculation system of introduction a network solar power plants in private households that are locating in Ukraine. The system takes into account such parameters as beam, ground-reflected and diffuse solar radiation with atmospheric attenuation, the angle and the orientation roof, the daily average temperature of photovoltaic cells and the temperature coefficient of solar panels, when calculating the generation of a network solar power plant. The flux of solar radiation that falls on the surface of the photovoltaic cells is determined of the Hay-Davis model. When calculating the payback solar power plant takes into account such parameters as annual electricity consumption, current electricity price, feed-in tariff and annual electricity price increase. The average market price of a network solar power plant is taken at the rate of 1 dollar per 1 watt of installed capacity. Based on these parameters, the system calculates a monthly, daily average and annual generation of a network solar power plant, calculates the relative cost of a network solar power plant, calculates of electricity costs forecast over twenty years and calculates a payback period of a network solar power plant. The monthly and daily average generation of a network solar power plant, electricity costs forecast over twenty years and payback period of a network solar power plant displayed in the system in the form of corresponding graphs and diagrams. In the case if investments necessary for the construction and commissioning of a network solar power plant don’t pay off within twenty years, the system will display this information in the corresponding field.

The Definition of the Optimal Energy-Efficient form of the Building

We consider the problem of finding a geometrical form of a body in a thermal radiation field, for which the thermal balance between the body and the surrounding air is minimal. The case of a point source of heat is investigated. To consider an analogous problem for buildings, one must know the value of incoming thermal energy to a unit square in relation to its orientation. We develop an application package in MATLAB that represents this relation in table form and takes into consideration the direct, diffuse, ground-reflected solar radiation and the thermal radiation of atmosphere.

Theoretical and experimental investigation into incident radiation on solar conical collector

The geometry of a collector is one of the important factors that can increase the incident radiation on the collector surface. In the present study, the incident radiation for a stationary collector with cone geometry, i.e. a conical collector, is theoretically and experimentally investigated. This type of collector is always stable and does not need a fixture to install. Moreover, it has a symmetric geometry, with all its sides facing the sun. The main advantage of this collector is its ability to receive beam, diffuse, and ground-reflected radiation throughout the day. The variation of the incident radiation is theoretically estimated by using an isotropic sky model based on the available data. The theoretical data are validated by an experimental test of a conical collector of a specific size. The results show that the conical solar collector is more operative in receiving total solar radiations than a horizontal plate such as a flat-plate collector and can be a suitable option for solar water heating. A calculation of the incident radiation shows that the incident radiation is maximized when the cone angle of the conical collector is equal to the latitude of the site test.

Mathematical modelling of solar radiation incident on tilted surface for photovoltaic application at Bhopal, M.P., India

In general, solar radiations are the combination of beam plus diffuse and ground-reflected radiation. The availability of recorded data on a tilted surface is very rare due to lack of measuring equipment and techniques involved. In this study, a standard procedure is adopted for estimation of solar radiation on a tilted surface for a location in Central region of India. Solar radiation is estimated for three tilted positions: First, solar collector tilt equal to latitude angle, second, solar collector tilt equal to latitude angle +15° and third, solar collector tilt at latitude −15°. Total global solar radiation estimated on the inclined surface for various photovoltaic (PV) modules was used to obtain the annual energy yield based on the estimated value. It was found that on an average, 14 kWh/m2 of annual energy output can be obtained for monocrystalline solar PV module corresponding to the inclination of 23.26° latitude at Bhopal.

Ant mound as an optimal shape in constructal design: Solar irradiation and circadian brood/fungi-warming sorties

Sizes, shapes, ambient and in-dome temperature, incoming solar radiation and illumination are measured on a Formica rufa anthill in a mixed forest of the Volga-Kama National Reserve in Russia. These data are used in a conceptual model of insolation of a right conical surface by direct-beam, descending atmospheric and ascending ground-reflected radiation. Unlike a standard calculation of the energy flux intercepted by a solar panel, the anthill is a 3-D structure and double-integration of the cosine of the angle between the solar beams and normal to the surface is carried out for a “cozy trapezium”, where the insects expose themselves and the brood to “morning” sunbathing pulses (Jones and Oldroyd, 2007). Several constructal design problems are formulated with the criteria involving either a pure solar energy gained by the dome or this energy, as a mathematical criterion, penalized by additive terms of mechanical energy (potential and friction) lost by the ants in their diurnal forays from a “heartland” of the nest to the sun-basking zone on the surface. The unique and global optima are analytically found, with the optimal tilt angle of the cone explicitly expressed through the zenith angle of the Sun and meteorological constants for the isotropic sky model.

Analytical model for solar irradiance near a planar vertical diffuse reflector – Formulation, validation, and simulations

An analytical model is formulated for the irradiance on a surface (collector) with a rear (opposite the sun) planar vertical diffuse reflector, as is common for a lower roof on a multi-story building. The vast majority of research on solar reflectors has been for specular, or mirror, reflectors, with any diffuse reflections modeled about the specular reflection angle. This model is capable of calculating incident and reflected direct, diffuse, and ground-reflected radiation using components borrowed from the Hay, Davies, Klucher, Reindl (HDKR) irradiance model, and is easily implemented in any computation programming software capable of numeric integration. The model accounts for reflector edge effects and shading of diffuse and ground-reflected radiation by the reflector, but it does not account for shading of beam radiation by the reflector.The model shows good overall agreement with experimental tests, and is three percentage points more accurate than a standard radiation model for tilted surfaces. The model indicates that a planar vertical diffuse reflector increases the irradiance at high clearness indices and low reflector incidence angles, and decreases the irradiance otherwise. Increasing the reflector height and decreasing the collector pitch and distance between the collector and reflector increases the irradiance during clear periods, but decreases the irradiance, to a lesser absolute extent, during cloudy periods. Annual simulations show a gain in winter insolation and a loss in summer insolation for an average collector/reflector, with an increase in annual insolation for collectors near high albedo reflectors.

Electromechanical Coupling Analysis of Ground Reflector Antennas Under Solar Radiation

The surface-accuracy design criterion for the next-generation reflector antennas for the deep-space instrumentation project in China was 0.1 mm rms. However, these antennas have no radome or air-conditioned ventilation to protect against solar radiation. Therefore, the effect on the antenna's electromagnetic performance of thermal deformation due to solar radiation must be carefully evaluated. For this engineering problem, a 40-m reflector antenna was selected as the research object. First, the heat fluxes from direct solar radiation, sky-scattering radiation, and ground-reflected radiation on the antenna's surface were calculated, based on the antenna's location, date, and time. Second, the temperature distribution of the whole antenna was obtained with the Finite-Element Method (FEM), considering three methods of heat transfer: conduction, convection, and radiation. A temperature experiment was then designed via a 7.3-m Cassegrain antenna. The results indicated the validity of the previous heat flux and temperature analyses. Engineering knowledge of the thermal impact on the antenna's radiation was essential to improve the overall design and construction of the antenna. Third, a thermal-structural analysis was carried out with ANSYS. Finally, the electromagnetic parameters of the antenna were calculated using a far-field pattern formula, and three main electromagnetic parameters - the gain loss, the sidelobe level, and the pointing error - were considered in detail. The results of the analysis showed that the degradation of the electromagnetic performance was not only dependent on the rms amount of structural deformation, but also on the distribution of the deformation, especially for the sidelobe level and pointing error. The analysis method and results can be referenced for the design of next-generation reflector antennas.

A comparative study of solar irradiation models on various inclined surfaces for India

This paper presents a statistical approach for the estimation of the diffuse/global irradiation on various inclined surfaces from the measured data of horizontal surface. In fact diffuse solar radiation on an inclined plane consists of two components: sky diffuse radiation and reflected radiation from the ground. For analyzing estimation of the daily tilted sky diffuse component from the daily horizontal diffuse irradiance, we have considered six models Badescu, Circumsolar, Skartveit and Olseth, Hay, Klucher and Liu and Jordan (Isotropic). All these models except Badescu adopted the same methodology for estimating the ground-reflected radiation component, therefore, only sky diffuse component was analyzed at Lucknow (latitude 26.75°, longitude 80.50°), India location. Statistical analysis showed that the Skartveit and Olseth model gives good prediction for the low inclination angle however; Klucher model gave better performance for highly inclined south-facing surfaces. The Root Mean Square Errors (% RMSE) value varies from 3.45% to 24.15% except for Badescu and Circumsolar model which predict worse results. In general, Klucher’s model provides close agreement with the measurements.

Estimation of the ground albedo for the Athens area, Greece

Ground albedo can severely influence the estimation of solar radiation incident on tilted surfaces. Depending on the model used to calculate the reflected radiation, a significant error in the estimation of total radiation on an inclined surface is likely to be introduced. In the present work, several models for calculating the ground albedo are evaluated; the derived values are further used for estimating the ground-reflected radiation on a tilted surface. Four of these models are taken from the international literature and four new correlations are developed for the purpose of this study. All eight models are evaluated against measurements of ground-reflected radiation performed at the National Observatory of Athens in the period 1999–2008. The evaluation shows that the existing models, including that with a constant albedo value (0.2), perform relatively well. Nevertheless, if more accuracy is needed for scientific applications, site-specific models must be developed. Due to this demand new albedo models are derived for the Athens area that can perform efficiently all year round. The results of the work show that: (a) The use of the constant albedo value of 0.2, which is widely accepted and used in most applications when ground-albedo measurements are lacking, is unrealistic for the case of Athens; it is too high. (b) Satisfactory results can be obtained when applying a new constant albedo value estimated or measured at the specific site. (c) Nevertheless, more complicated albedo models adapted to the site characteristics can give better results than any of those using a constant albedo value, if ground-albedo estimations are to be made for a short period of say 5–10 min.

Comparison of the Olmo model with global irradiance measurements on vertical surfaces at Madrid

The recently published Olmo model estimates global irradiance on inclined planes. It only requires the horizontal global irradiance and the sun’s azimuth and elevation as input parameters. As a consequence, it does not contain empirical coefficients that need determination for each location. Olmo and co-authors found a good agreement between predicted and experimental values obtained at their measuring site when a factor accounting for ground-reflected radiation was introduced in the model. In the present paper, the Olmo model is assessed in Madrid for vertical planes facing north, south, east and west. The model gives a root mean square error of ≅27%, when all data are used. With the data for the north-facing plane it becomes worse, i.e. ≅52%. In general, the model performs badly when the surface receives only diffuse radiation. This is the case when the vertical plane does not “see” the sun’s disk, or when for intermediate or overcast skies no direct radiation is incident on both, vertical and horizontal surfaces. A distinctive feature, observed when the model is used with the data for the south, east or west-facing planes, is that many points in the plot of the calculated versus measured global irradiance clearly follow an undulating pattern.

Improved ashrae model to predict hourly and daily solar radiation components in Botswana, Namibia, and Zimbabwe

ASHRAE model empirical coefficients A, B and C are obtained for clear days in Botswana from analysis of different solar radiation components recorded at the University of Botswana, Botswana Technology Centre and some synoptic stations. Investigations show that the direct normal radiation in Botswana usually reveals a specific diurnal profile. For example 30 minutes before sunset, I bn-radiation could be above 600 W m −2 while at sunset and sunrise (half of the solar disc is under the horizon) it can be as high as 100 Wm −2. Such big values of direct normal solar radiation at sunset and sunrise are not only due to low humidity and turbidity but also due to small values of the relative air mass, m, which can be obtained with the help of a new formula developed by Nijegorodov et al. (1995). By using the ASHRAE empirical coefficients obtained, isotropic and anisotropic sky models and the new formula for the relative air mass a computer program to predict hourly and daily beam, diffuse and ground-reflected radiation on tilted, variously oriented surfaces is developed. This computer program can be used in Botswana, Namibia and Zimbabwe.

Evaluation of Different Radiation and Albedo Models for the Prediction of Solar Radiation Incident on Tilted Surfaces, for Four European Locations

The diffuse radiation incident on an inclined surface is composed of both the sky diffuse radiation and the ground-reflected radiation. Depending on the model used to calculate the sky diffuse radiation and the estimated albedo value, it is possible to introduce a significant error in the prediction of the total radiation incident on a tilted surface. Twelve sky diffuse submodels associated with four different albedo submodels are used to estimate the total radiation on the tilted surface from data on the horizontal plane. The predicted total solar radiation values are compared with measured data on a south facing vertical surface, from four representative south and north European locations. Root mean square error, mean bias error, and a t-test are used to determine the intrinsic performance of each combination of diffuse tilt and albedo submodel. Accordingly, the various model combinations do not exhibit a statistically significant difference between measured and calculated values.

Wide-Area Determination of Cloud Microphysical Properties from NOAA AVHRR Measurements for FIRE and ASTEX Regions

A method for satellite remote sensing of cloud optical thickness and effective particle radius has been developed to apply to NOAA AVHRR multispectral radiance data. Undesirable radiation components such as ground-reflected solar radiation and thermal radiation are guessed from satellite-received radiances in channels 1, 3, and 4 of AVHRR and subtracted from radiances in channels 1 and 3 to derive the reflected solar radiation of a cloud layer that includes information about cloud microphysical properties. This method can be applied to a broad range of water clouds from semitransparent to thick clouds. This method was applied to AVHRR data acquired over oceans during the First ISCCP Regional Experiment and the Atlantic Stratocumulus Transition Experiment. The authors found good agreement between satellite-derived and in situ microphysical quantities. The presence of drizzle droplets in optically thin clouds was also confirmed from the satellite observation. Furthermore, the results show that marine stratocumulus clouds were drastically modified by ship track effluents and dust-contaminated aifflow from the continent.