In multiple rows of photovoltaic fields, the rows may be installed with several modules placed along the row width. The verification of the sky view factor model pertains to the second and subsequent rows. Photovoltaic (PV) modules along the row width experience uneven incident diffuse radiation caused by differences in the sky view factor of the modules. The present experimental study verifies first the sky view factor model, and second shows the differences in output power of the PV modules (affected by the sky view factors) placed in different locations along the width of the second row. This work complements the theoretical previous work and emphasizes the importance of the incident diffuse radiation, associated with the sky view factor, on the energy loss of the PV field. Two rows deployed with PV modules were tested on the laboratory roof for several days for different inclination angles and distances between rows. The results show that a top module on a row may generate 8% more power than a bottom module at noontime. The findings of this experimental study have technical significance in designing PV systems.

Missions to Mars need a power source, while, one of the most compatible sources for such a purpose is the photovoltaic system. Photovoltaic systems generate power based on the available energy from the Sun, and thus, solar radiation intensity at Mars should be known for design purposes. In this research, the feed-forward back-propagation artificial neural network is developed to predict solar radiation in terms of longitude, latitude, time of the day, temperature, altitude, pressure, amount of dust, and volume mixing ratio of water ice clouds. Data which are used to develop this model are obtained from the Mars Climate Database. The results of the developed method are accurate as compared with other methods whereas the correlation (R 2 ) coefficient for the developed model is 0.97. The developed model then is used to predict mean solar radiation and mean temperature for every location on Mars and then the data are presented on Mars maps in order to determine the best location for harvesting energy from the Sun by photovoltaic systems. According to results, the solar radiation-temperature belt on Mars is found to be between latitudes 20 deg south and 15 deg north.

Thin-film grating coatings are proposed for smart windows to angular selective filtering of solar radiation. The gratings are formed by absorptive, reflective, or scattering parallel strips (made of chromogenic or other materials) alternating with directionally transmissive strips (untreated surface of pure glass) on two surfaces of the window pane(s). The smart window with grating optical filter has angular selective light transmission and partially or completely blocks the direct solar radiation in a preset angular range and transmits the scattered and reflected radiation without using the daylight redistribution devices. The results of numerical simulation and experimental confirmation of optimum slope angle of the strips on the pane(s), their widths, and relative position on two surfaces to minimize the directional light transmission of the window at the preset date and time of day taking into account orientation of the window to the cardinal, the latitude of the building, and the seasonal and daily distribution of the solar radiation intensity are demonstrated.

This paper develops an advanced methodology to determine the real contribution of the incidence solar radiation components, direct, diffuse, and reflected, onto a semispherical solar collector with spirally rolled up cylindrical absorber, as a function of the intercepted area of the solar radiation components by the collector’s receiver. Based on a previous work (2012, Study and Characterization of New Generation Semispherical Thermal Collectors, Ana Sofía Morillo Candás, Applied Physics Master, Master Thesis, UCM) in which the effective intercepted area for direct radiation was modeled, the present paper develops new algorithms for diffuse and reflected solar radiation and improves the existing one, with the aim at characterizing geometrical parameters of these types of collectors. The determination of the effective area intercepted by the receiver for the different components of the solar radiation is essential for the characterization of the collector’s thermal performance, as the energy received by the absorber depends on the type of radiation and on the effective area covered by each type.

The importance of statistical analysis in the field of energy for environmental engineering is shown in this research paper, in which the adequacy of the data sets of clarity index with the model of “best” probability (based on the criteria used) was studied. In Campo Grande which is the capital of the Brazilian state of Mato Grosso do Sul, located in the Center-West region of the country, there is a predominance of the atmospheric conditions of low cloudiness, with a high frequency of days with a clear sky and in consequence a low-frequency of days with cloudy sky. The aerosols resulting from the burning of sugarcane influence the sky conditions in Campo Grande thus reducing the frequency of the clear sky.

This study evaluated the building cooling capacity of sky radiation, which was previously identified to have the greatest cooling potential among common ambient sources for climates across the U.S. A heat pipe augmented sky radiator system was simulated by a thermal network with nine nodes, including a thin polyethylene cover with and without condensation, white (zinc oxide) painted radiator plate, condenser and evaporator ends of the heat pipe, thermal storage fluid (water), tank wall, room, sky and ambient air. Heat transfer between nodes included solar flux and sky radiation to cover and plate, wind convection and radiation from cover to ambient, radiation from plate to ambient, natural convection and radiation from plate to cover, conduction from plate to condenser, two-phase heat transfer from evaporator to condenser, natural convection from evaporator to water and from water to tank wall, natural convection and radiation from tank wall to room, and overall heat loss from room to ambient. A thin layer of water was applied to simulate condensation on the cover. Nodal temperatures were simultaneously solved as functions of time using typical meteorological year (TMY3) weather data. Auxiliary cooling was added as needed to limit room temperature to a maximum of 23.9 °C. For this initial investigation, a moderate climate (Louisville, KY) was used to evaluate the effects of radiator orientation, thermal storage capacity, and cooling load to radiator area ratio (LRR). Results were compared to a Louisville baseline with LRR = 10 W/m 2 K, horizontal radiator and one cover, which provided an annual sky fraction (fraction of cooling load provided by sky radiation) of 0.855. A decrease to 0.852 was found for an increase in radiator slope to 20 deg, and a drop to 0.832 for 53 deg slope (latitude + 15 deg, a typical slope for solar heating). These drops were associated with increases in average radiator temperature by 0.73 °C for 20 deg and 1.99 °C for 53 deg. A 30% decrease in storage capacity caused a decrease in sky fraction to 0.843. Sky fractions were 0.720 and 0.959 for LRR of 20 and 5, respectively. LRR and thermal storage capacity had strong effects on performance. Radiator slope had a surprisingly small impact, considering that the view factor to the sky at 53 deg tilt is less than 0.5.

The potential of sky radiation (SR) to serve the latent space cooling loads was evaluated. Using ASHRAE standard 55 comfort limits (room temperature 22 °C, relative humidity 60%, and dew-point temperature 13.9 °C), condensation was the chosen mechanism for humidity reduction. Typical meteorological year (TMY3) weather data were used for eleven ASHRAE climate zones. Three values of load-to-radiator ratio (LRR) (infiltration/ventilation volume flow rate times the ratio of building floor area to radiator area) were evaluated: 0.35, 3.5, and 35 m/h. Three thermal storage cases were considered: 1. Annual cooling potential, 2. Diurnal storage, and 3. Minimum storage capacity to serve the entire annual load. Six SR temperatures T rad = 13.9 to −26.1 °C were tested. Even in the most challenging climates, annual SR potential exceeded the total sensible and latent cooling load, at least for the lowest LRR and the highest T rad . For diurnal storage, SR served less than 20% of the load in the hot and humid southeast, but the entire load in the mountain west. The minimum storage capacity to meet the entire annual load decreased with decreasing LRR and decreasing T rad . For the southeast, large capacity was required, but for Louisville, for instance, sufficient capacity was provided by 0.05 m 3 of water per m 2 of floor area for LRR = 0.35 m/h. These results demonstrate that for much of the U.S., sky radiation has the potential to serve the entire annual sensible and latent cooling load.

This paper presents characterization of a new high flux solar simulator consisting of a 10 kW Xenon arc via indirect heat flux mapping technique for solar thermochemical applications. The method incorporates the use of a heat flux gauge (HFG), single Lambertian target, complementary metal oxide semiconductor (CMOS) camera, and three-axis optical alignment assembly. The grayscale values are correlated to heat flux values for faster optimization and characterization of the radiation source. Unlike previous work in heat flux characterization that rely on two Lambertian targets, this study implements the use of a single target to eliminate possible errors due to interchanging the targets. The current supplied to the simulator was varied within the range of 120–200 A to change the total power and to mimic the fluctuation in sun's irradiance. Several characteristic parameters of the simulator were studied, including the temporal instability and radial nonuniformity (RNU). In addition, a sensitivity analysis was performed on the number of images captured, which showed a threshold value of at least 30 images for essentially accurate results. The results showed that the flux distribution obtained on a 10 × 10 cm 2 target had a peak flux of 6990 kWm −2 , total power of 3.49 kW, and half width of 6.25 mm. The study concludes with the illustration and use of a new technique, the merging method, that allows characterization of heat flux distributions on larger areas, which is a promising addition to the present heat flux characterization techniques.

A solar radiation model is applied to a low temperature water-in-glass evacuated tubes solar collector to predict its performance via computational fluid dynamics (CFD) numerical simulations. This approach allows obtaining the transmitted, reflected, and absorbed solar radiation flux and the solar heat flux on the surface of the evacuated tubes according to the geographical location, the date, and the hour of a day. Different environmental and operational conditions were used to obtain the outlet temperature of the solar collector; these results were validated against four experimental tests based on an Official Mexican Standard resulting in relative errors between 0.8% and 2.6%. Once the model is validated, two cases for the solar collector were studied: (i) different mass flow rates under a constant solar radiation and (ii) different solar radiation (due to the hour of the day) under a constant mass flow rate to predict its performance and efficiency. For the first case, it was found that the outlet temperature decreases as the mass flow rate increases reaching a steady value for a mass flow rate of 0.1 kg/s (6 l/min), while for the second case, the results showed a corresponding outlet temperature behavior to the solar radiation intensity reaching to a maximum temperature of 36.5 °C at 14:00 h. The CFD numerical study using a solar radiation model is more realistic than the previous reported works leading to overcome a gap in the knowledge of the low temperature evacuated tube solar collectors.

An accurate assessment of the amount solar radiation incident at specific locations is highly complex due to the dependence of available solar radiation on many meteorological and topographic parameters. Reunion Island, a small tropical French territory, intends to deploy solar energy technologies rapidly. In this context, the variability and intermittency of solar irradiance in different regions of the island is of immediate interest if the generated energy will be integrated in the existing energy network. This paper identifies different features of spatial and temporal variability of daily global horizontal irradiance (GHI) observed on Reunion Island. For this purpose, trends in the mean daily as well as seasonal variability of GHI were investigated. Furthermore, the intermittency and multifractal behaviors of the spatial daily GHI change were examined. Analyzing this daily variability is crucial to day-ahead forecasting of solar resource for better managing solar integration in the power grid, particularly in small island states with isolated power systems. Results revealed that the difference in cumulative GHI for two successive days ranges between −10 and 10 kW/m 2 /day while the highest and lowest variability of daily change occurs during summer and winter, respectively. The decorrelation distance, which gives a measure of the distance over which the variability at distinct geographic locations become independent of one another at a given timescale, was also calculated. It was found that the average decorrelation distance for day-to-day GHI change is about 22 km, a smaller value than that calculated by the previous studies using much sparser radiometric networks. The Hurst exponent, fractal co-dimension, and Lévy parameter, which describe solar radiation intermittency, were also evaluated for Reunion Island.

The accuracy of radiometric temperature measurement in radiatively heated environments is severely limited by the combined effects of intense reflected radiation and unknown, dynamically changing emissivity, which induces two correlated and variable error terms. While the recently demonstrated double modulation pyrometry (DMP) eliminates the contribution of reflected radiation, it still suffers from the shortcomings of single-waveband pyrometry: it requires knowledge of the emissivity to retrieve the true temperature from the thermal signal. Here, we demonstrate an improvement of DMP incorporating the in situ measurement of reflectance. The method is implemented at Paul Scherrer Institute (PSI) in its 50 kW high-flux solar simulator and used to measure the temperature of ceramic foams (SiSiC, ZrO 2 , and Al 2 O 3 ) during fast heat-up. The enhancement allows DMP to determine the true temperature despite a dynamically changing emissivity and to identify well-documented signature changes in ZrO 2 and Al 2 O 3 . The method also allows us to study the two dominant error sources by separately tracking the evolution of two error components during heat-up. Furthermore, we obtain measurements from a solar receiver, where the cavity reflection error limits measurement accuracy. DMP can be used as an accurate radiometric thermometer in the adverse conditions of concentrated radiation, and as a diagnostic tool to characterize materials with dynamic optical properties. Its simple design and ability to correct for both errors makes it a useful tool not only in solar simulators but also in concentrated solar facilities.

The accurate prediction of the direct and diffuse solar radiation is of foremost importance for deployment of photovoltaic (PV) systems. A number of solar radiation forecasting techniques have been developed for longer and shorter forecasting times. Numerical weather prediction (NWP) models provide the best results for the longer forecasting times (4–6 h), required by utility companies. However, NWP methods are usually developed for clear-sky and open areas. These methods cannot be directly applied to urban areas with shading, trees, multisurface reflection, and other sources of solar radiation losses. To overcome these issues, improvement to the existing prediction tools are required. In this study, we develop an automated radiation forecasting tool for urban areas. This tool combines a NWP model (Weather Research and Forecasting (WRF) model) and a solar calculator (developed in the numerical toolbox O pen FOAM ) to compute shading, reflection, and other losses in the urban canopy. An algorithm for extraction of building outlines and heights (if they are publicly available) is also developed as a part of the tool. Finally, the coupled solar power estimator can be applied to past, present, or future solar power predictions. Initial results obtained using the developed tool are demonstrated for an urban neighborhood in Singapore.

The present indoor experimental study is focused on performance enhancement of a parabolic trough collector (PTC) with twisted tape insert by incorporating an innovative Soltrace ® —mathematical model—differential heating combination. This simulation-based methodology is very useful in analyzing the system behavior under defined environmental conditions. By the use of insert, the circumferential temperature difference has been dropped considerably in all cases compared to plain receiver. Hence, this gain is reflected in both instantaneous and thermo-hydraulic efficiency. As the role of inserts is justified in different thermal parameters, the system evaluation factors have been defined as H-W-B constants. Further, to take into account the influence of enhanced heat transfer on geometry, receiver length optimization has been performed which gave a maximum of 26% short in length of the receiver with best twist ratio under the transition flow regime. Hence, for moderate flow and medium temperature applications, inserts are useful. The range of Reynolds number considered in the experimental study is 2600–24,000 to analyze the flow regime based effect.

Conjugate laminar natural convection heat transfer and air flow with radiation of tube solar receiver with glass window were numerically investigated. The discrete ordinate method was used to solve the radiative transfer equation. And the three-dimensional steady-state continuity, Navier–Stokes, and energy equations were solved. The temperature difference based on environment and high temperature surface of receiver is varied from 100 K to 1000 K. The influence of the surface emissivity, heating temperature, convective coefficient, and convective temperature of environment on the heat transfer from the receiver with glass window has also been investigated. The numerical results indicated that the highest temperature of glass window increases and the high temperature area becomes wide, with the temperature of heating wall and surface emissivity increasing. Adopting higher convective coefficient of glass window can reduce the peak magnitude of temperature distribution on glass window of tube receiver up to 45%.

Radiation absorption is investigated in a particle curtain formed in a solar free-falling particle receiver. An Eulerian–Eulerian granular two-phase model is used to solve the two-dimensional mass and momentum equations by employing computational fluid dynamics (CFD) to find particle distribution in the curtain. The radiative transfer equation (RTE) is subsequently solved by the Monte Carlo (MC) ray-tracing technique to obtain the radiation intensity distribution in the particle curtain. The predicted opacity is validated with the experimental results reported in the literature for 280 and 697 μ m sintered bauxite particles. The particle curtain is found to absorb the solar radiation most efficiently at flowrates upper-bounded at approximately 20 kg s −1 m −1 . In comparison, 280 μ m particles have higher average absorptance than 697 μ m particles (due to higher radiation extinction characteristics) at similar particle flowrates. However, as the absorption of solar radiation becomes more efficient, nonuniform radiation absorption across the particle curtain and hydrodynamic instability in the receiver are more probable.

A solar heating compound parabolic collector (CPC) using air and palm oil as heat carrier fluid is proposed and analyzed within this study via heat transfer and ray tracing simulations. The system is a linear focusing solar system intended to be used for applications across a broad range of industrial sectors for generating medium temperature heat up to 250 °C. The Monte Carlo ray tracing method was used to predict the optical performances of the receiver. We have developed a simplified thermal model to investigate and analyze the thermal performances of the receiver under different conditions. It has been demonstrated that the investigated receiver satisfactorily matches the heat demand by producing low and medium temperature heat with an annual system efficiency of 45%.

Radiative properties of transparent insulations made of a layer of parallel, small-diameter, thin-walled, visible light transparent pipes placed perpendicularly to the surface of a flat solar absorber are investigated theoretically. A formula for the radiation heat losses through the insulation is derived based on two main assumptions: the system is in steady-state and the fourth power of the temperature along each pipe is linear. Arguments in favor of the assumptions are given. The formula, combined with standard formulas for the conductive heat flux, enables prediction that a 10 cm thick transparent insulation under insolation of 1000 W/m 2 , at ambient temperature 20 °C, could theoretically raise the absorber temperature to 429 °C and produce 410 W mechanical power under the ideal Carnot cycle. In order to reach that high energy conversion efficiency, the insulation pipes should have diameter less than 0.5 mm and walls about 5 μm thick, which may be technologically challenging.

Photovoltaic (PV) hybrid systems and their optimal energy management are still being actively studied. PV systems must be positioned at optimal tilt and azimuth angles to obtain maximum system performance. This paper presents the effect of energy management of a grid-connected PV-battery-load system on optimal PV placement using a linear programing (LP) method. The optimal placement of PV arrays aims to minimize the electricity cost of a fixed PV system for investors by considering monthly average daily global radiation, ambient temperature, wind speed, demand management constraints, and electricity tariffs in Turkey. The analysis is extended to consider 68 locations across Turkey. The analysis reveals that the optimal placement (optimal tilt and azimuth angle) can be different from that of previous studies because of multiple objective considerations. The optimal tilt angle results are lower than the local latitude in the range of 0 deg–8 deg in all regions. Furthermore, the optimal azimuth angle results are in the range of 6 deg–24 deg westbound throughout Turkey. These results can play a significant role for investments in the design of grid-connected PV-battery-load systems.

Variation in direct solar radiation is one of the main disturbances that any solar system must handle to maintain efficiency at acceptable levels. As known, solar radiation profiles change due to earth's movements. Even though this change is not manipulable, its behavior is predictable. However, at ground level, direct solar radiation mainly varies due to the effect of clouds, which is a complex phenomenon not easily predictable. In this paper, dynamic solar radiation time series in a two-dimensional (2D) spatial domain are obtained using a biomimetic cloud-shading model. The model is tuned and compared against available measurement time series. The procedure uses an objective function based on statistical indexes that allow extracting the most important characteristics of an actual set of curves. Then, a multi-objective optimization algorithm finds the tuning parameters of the model that better fit data. The results showed that it is possible to obtain responses similar to real direct solar radiation transients using the biomimetic model, which is useful for other studies such as testing control strategies in solar thermal plants.

Optimization based on reconstruction of the velocity, temperature, and radiation fields in a porous absorber with continuous linear porosity or pore diameter distribution is carried out in this work. This study analyzes three typical linear pore structure distributions: increasing (“I”), decreasing (“D”), and constant (“C”) types, respectively. In general, the D type porosity ( ϕ ) layout combined with the I type pore diameter (d p ) distribution would be an excellent pore structure layout for a porous absorber. The poor performance range, which should be avoided in the absorber design, is found to be within a wide range of porosity layouts ( ϕ i = ∼0.7 and ϕ o > 0.6) and pore diameter layouts (d i = 1.5–2.5 mm), respectively. With a large inlet porosity ( ϕ i > 0.8), the D type layout with larger porosity gradient (G p ) has a better thermal performance; however, the I type d p layout with a smaller inlet pore diameter (d i < 1.5 mm) and a larger pore diameter gradient (G dp ) is recommended when considering the lower pressure drop. Different pore structure layouts (D type or I type) have a significant effect on the pressure drop, even with the same average ϕ a and d a , the maximum deviation can be up to 70.1%. The comprehensive performance evaluation criteria (PEC) value shows that the D type ϕ layout with a larger ϕ a has an excellent thermopressure drop performance, and a part of PEC values for the I type d p layout are greater than unity.